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2002-03-10 | Mass Composition of Cosmic Rays in the Range 2 x 10^17 - 3 x 10^18 Measured with Haverah Park Array | At the Haverah Park Array a number of air shower observables were measured
that are relevant to the determination of the mass composition of cosmic rays.
In this paper we discuss measurements of the risetime of signals in large area
water-Cherenkov detectors and of the lateral distribution function of the
water-Cherenkov signal. The former are used to demonstrate that the CORSIKA
code, using the QGSJET98 model, gives an adequate description of the data with
a low sensitivity, in this energy range, to assumptions about primary mass. By
contrast the lateral distribution is sufficiently well measured that there is
mass sensitivity. We argue that in the range 0.2-1.0 EeV the data are well
represented with a bi-modal composition of 34+-2 % protons and the rest iron.
We also discuss the systematic errors induced by the choice of hadronic model. | 0203150v1 |
2002-03-13 | Reprocessing of X-rays in AGN. I. Plane parallel geometry -- test of pressure equilibrium | We present a model of the vertical stratification and the spectra of an
irradiated medium under the assumption of constant pressure. Such a solution
has properties intermediate between constant density models and hydrostatic
equilibrium models, and it may represent a flattened configuration of gas
clumps accreting onto the central black hole. Such a medium develops a hot
skin, thicker than hydrostatic models, but thinner than constant density
models, under comparable irradiation. The range of theoretical values of the
alpha_ox index is comparable to those from hydrostatic models and both are
close to the observed values for Seyfert galaxies but lower than in quasars.
The amount of X-ray Compton reflection is consistent with the observed range.
The characteristic property of the model is a frequently multicomponent iron K
alpha line. | 0203202v1 |
2002-03-15 | Chandra Observations of the Gravitational Potential Structure in Abell 1060 | We present results from a Chandra observation of Abell 1060, the nearby
cluster of galaxies. The ACIS-I image shows that the central cusp-like
structure, previously seen from PSPC, is caused mainly by an emission from the
central elliptical galaxy NGC 3311. We confirmed that the central region is
remarkably isothermal with a temperature of 3.2 keV, based on the spectral fits
for fine pixels. An extended region in the northeast of NGC 3311 indicates high
iron abundance. The surface brightness profile excluding the central galaxy,
NGC 3311, can be fitted only by a double beta model, with core radii about 40
and 140 kpc, out to a radius of about 200 kpc. This suggests that the
gravitational potential in Abell 1060 consists of 2 components. | 0203244v1 |
2002-03-18 | X-Ray Spectroscopy of Gamma-Ray Bursts | Observational evidence of iron absorption and emission lines in X-ray spectra
of Gamma-Ray Bursts is quite compelling. I will briefly review the results,
summarize different models and describe the connection with massive progenitors
in star-forming regions implied by these results. This link is also supported
by measurements of the X-ray absorbing gas in several GRB's, with column
density consistent with that of Giant Molecular Clouds harbouring
star-formation in our Galaxy, as well as by evidences gathered in other
wavelengths. However, the volume density inferred by the fireball-jet model is
much lower than typical of a GMC, and I will confront this with the alternative
explanation of fireball expansion in a high dense medium, outlining the
problems that both models have at present. Finally I will briefly summarize
some results on dark GRB's, and describe the prospects of high resolution X-ray
spectroscopy in getting closer to the central environment of GRB, and far in
the Early Universe by using GRB as beacons to probe star and galaxy formation. | 0203275v1 |
2002-03-20 | Lyman-break galaxies: are they young spheroids? | We have compared the results from a model for the chemical evolution of an
elliptical galaxy with initial luminous mass of 2x10^10 M_sun and effective
radius of 2 kpc with the recent abundance determinations for the Lyman-break
galaxy MS 1512-cB58 at a redshift z=2.7276. After correcting the iron abundance
determination for the presence of dust we concluded that the observed [Si/Fe],
[Mg/Fe], [N/Fe] are consistent with our model when a galactic age between 20
and 35 Myr is assumed. Moreover, the [N/O] ratio also suggests the same age.
This age is in very good agreement with other independent studies based on the
analysis of the spectral energy distribution suggesting that this object is
younger than 35 Myr. Therefore, we suggest that MS 1512-cB58 is a truly young
normal elliptical galaxy experiencing its main episode of star formation and
galactic wind. | 0203329v1 |
2002-03-22 | Iron abundance in HII regions | Optical CCD spectra are used to determine the Fe abundances at several
positions inside seven bright Galactic HII regions. The observed [FeIII] line
ratios are compared with the predictions of different sets of collision
strengths and transition probabilities for this ion to select the atomic data
providing the best fit to the observations. The values found for the Fe++ and
Fe+ abundances, along with ionization correction factors for the contribution
of Fe3+, obtained from available grids of photoionized models, imply that the
Fe/O ratio in the ionized gas is between 2% and 30% of solar. The Fe abundances
derived for each area are correlated both with the degree of ionization and the
colour excess. A possible explanation is suggested, namely the presence of a
population of small grains, probably originating from the fragmentation of
larger grains. These small grains would release Fe atoms into the gas after the
absorption of energetic photons; the small grains surviving this destruction
process would be swept out of the ionized region by the action of radiation
pressure or stellar winds. An indication of a further and more efficient
destruction agent is given by the high Fe abundance derived for a position
sampling the optical jet H399 in M20, where dust destruction due to shock waves
has presumably taken place. | 0203394v1 |
2002-03-26 | New Members of the Cluster Family in Nearby Lenticulars | Using spectra obtained with the Keck I telescope we have demonstrated
conclusively that the faint (23<V<24 mag.) and unusually extended objects we
discovered in HST images of the lenticular galaxies, NGC 1023 and NGC 3384, are
star clusters associated with their respective galaxies. In the case of NGC
1023 we were further able to establish that these objects are old (>7--8 Gyr),
moderately metal-rich ([Fe/H]=-0.58+/-0.24) and, having a system rotation curve
which is very similar to that of the host galaxy, are associated with the
lenticular disk. Alpha-element to iron abundance ratios are highly supersolar
with [alpha/Fe] between +0.3 and +0.6. With moderately high metallicities and
luminosities, and effective radii in the range 7--15 pc (compared to the 2--3
pc sizes typical of normal globular and open clusters), this population of
clusters has no known analog in the Milky Way or elsewhere in the Local Group. | 0203454v2 |
2002-04-10 | The broad band X-ray spectrum of the black hole candidate GRS1758-258 | We present the results of a BeppoSAX observation of the black hole candidate
GRS1758-258 carried out in 1997, while the source was in its low/hard state.
The X-ray spectrum, simultaneously observed over the broad energy range from
0.1 to 200 keV, can be well described by a Comptonized emission model with
electron temperature kT_e = 31.4 keV and optical depth of 4.0 (spherical
geometry), although a cut-off power-law and a reflection model cannot be
excluded. Additionally, a broad iron line at 6.4 keV with equivalent width EW =
67 eV has been marginally detected. The 0.1-200 keV luminosity is 1.4x10^37
erg/s for an assumed distance of 8 kpc. The soft and hard luminosities are such
that the source falls inside the so-called "burster box". No evidence for a
soft excess is present. | 0204176v1 |
2002-05-02 | An unusual iron Lo-BAL quasar detected by ISOCAM | We report the discovery of an unusual low--ionization broad absorption line
quasar at z=1.776 which exhibits absorption lines from many excited states of
Feii. This member of the rare class of 'FeLoBAL' quasars was serendipitously
found in a mid-infrared (MIR) survey of distant clusters carried out with the
ISOCAM camera. ISO J005645.1-273816 has a high MIR to UV luminosity ratio,
suggesting a strong dust obscuration plus emission from very hot dust. This
characteristic makes MIR surveys particularly efficient at detecting LoBAL
quasars. | 0205022v1 |
2002-05-17 | Rotation and activity in the solar-metallicity open cluster NGC2516 | We report new measures of radial velocities and rotation rates (v sin i) for
51 F and early-G stars in the open cluster NGC2516, and combine these with
previously published data. From high signal-to-noise spectra of two stars, we
show that NGC2516 has a relative iron abundance with respect to the Pleiades of
delta([Fe/H])= +0.04 +/- 0.07 at the canonical reddening of E(B - V) = 0.12, in
contrast to previous photometric studies that placed the cluster 0.2 to 0.4 dex
below solar. We construct a color-magnitude diagram based on radial velocity
members, and explore the sensitivity of photometric determinations of the
metallicity and distance to assumed values of the reddening. For a metal
abundance near solar, the Hipparcos distance to NGC2516 is probably
underestimated. Finally, we show that the distribution of rotation rates and
X-ray emission does not differ greatly from that of the Pleiades, when
allowance is made for the somewhat older age of NGC2516. | 0205300v1 |
2002-06-10 | On the formation of inner vacuum gaps in radio pulsars | The problem of formation of the Ruderman-Sutherland type inner vacuum gap in
neutron stars with ${\bf\Omega}\cdot{\bf B}<0$ is considered. It is argued by
means of the condition $T_i/T_s>1$ (where $T_i$ is the critical temperature
above which $^{56}_{26}$Fe ions will not be bound at the surface and $T_s$ is
the actual temperature of the polar cap surface heated by the back-flow of
relativistic electrons) that the inner vacuum gap can form, provided that the
actual surface magnetic field is extremaly strong ($B_s\gtrsim 10^{13}$ G) and
curved (${\cal R}<10^6$ cm), irrespective of the value of dipolar component
measured from the pulsar spin down rate. Calculations are carried out for
pulsars with drifting subpulses and/or periodic intensity modulations, in which
the existence of the quasi steady vacuum gap discharging via ${\bf E}\times{\bf
B}$ drifting sparks is almost unavoidable. Using different pair-production
mechanisms and different estimates of the cohesive energies of surface iron
ions, we show that it is easier to form the vacuum gap controlled by the
resonant inverse Compton scaterring seed photons than by the curvature
radiation seed photons. | 0206141v1 |
2002-06-11 | Multiple X-ray reflection from ionized slabs | Multiple reflection of X-rays may be important when an accretion disc and its
hot corona have a complicated geometry, or if returning radiation due to
gravitational light bending is important, or in emission from a funnel such as
proposed in some gamma-ray burst models. We simulate the effects of multiple
reflection by modifying the boundary condition for an X-ray illuminated slab.
Multiple reflection makes the soft X-ray spectrum steeper (softer) and
strengthens broad emission and absorption features, especially the K-shell
features of iron. This may be important in explaining the spectra of sources
such as the Narrow-Line Seyfert 1 galaxy 1H0707-495. | 0206170v1 |
2002-07-01 | XMM-Newton observations of MR Vel/RX J0925.7-4758 | We report on XMM-Newton observations of the galactic supersoft X-ray source
RX J0925.7-4758. The RGS spectrum exhibits a wealth of spectral features from
iron and oxygen. XMM-Newton data confirm the finding of previous Chandra
HETGS/MEG observations that NLTE models of hot white dwarf atmospheres fail to
represent the complex spectrum. There are clear evidences for P Cygni profiles
with wind velocities of up to 2000 km/s. Small flux variations with time scales
larger than 1000s are present. The strongest power is at ~ 0.21d, a period
close to that seen in V band optical light curves. A detailed analysis of the
associated changes in the RGS and EPIC pn spectra hint at a mostly grey
mechanism suggesting a variation of the visibility of the white dwarf due to
occulting material in the accretion disk. Finally, we detect radial velocity
changes of 173 +/- 47 km/s between two RGS observations obtained half an
orbital cycle apart. The amplitude of the RGS velocity shift is consistent with
that of the optical He II 4686 and thus supports the idea that most of the He
II optical line emission arises from the accretion disk. | 0207004v1 |
2002-06-29 | Discovery of an ionized Fe-K edge in the z=3.91 Broad Absorption Line Quasar APM 08279+5255 with XMM-Newton | Recent XMM-Newton observations of the high-redshift, lensed, broad absorption
line (BAL) quasi-stellar object APM 08279+5255, one of the most luminous
objects in the universe, allowed the detection of a high column density
absorber ($N_H \approx 10^{23}$ cm$^{-2}$) in the form of a K-shell absorption
edge of significantly ionized iron (Fe XV - XVIII) and corresponding ionized
lower-energy absorption. Our findings confirm a basic prediction of
phenomenological geometry models for the BAL outflow and can constrain the size
of the absorbing region. The Fe/O abundance of the absorbing material is
significantly higher than solar (Fe/O = 2-5), giving interesting constraints on
the gas enrichment history in the early Universe. | 0207005v1 |
2002-07-12 | Reflection at large distance from the central engine in Seyfert 1s | We consider the possibility that most of the reflection component, observed
in the hard X-ray spectra of Seyfert galaxies, could be formed on an extended
medium, at large distance from the central source of primary radiation (e.g. on
a torus). Then, the reflector cannot respond to the rapid fluctuations of the
primary source. The observed reflected flux is controlled by the time-averaged
primary spectrum rather than the instantaneous (observed) one. We show that
this effect strongly influences the spectral fit parameters derived under the
assumption of a reflection component consistent with the primary radiation. We
find that a pivoting primary power-law spectrum with a nearly constant
Comptonised luminosity may account for the reported correlation between the
reflection amplitude R and the spectral index Gamma, and simultaneously
produces an iron line EW that is nearly independent of Gamma. We emphasize the
effects of the modelling of the primary component on the determination of the
reflection amplitude, and show that in NGC 5548, when these effects are taken
into account, the RXTE data are consistent with the reflection features being
produced mainly at large distance from the central source. | 0207269v1 |
2002-07-15 | On the Structure of the Iron K-Edge | It is shown that the commonly held view of a sharp Fe K edge must be modified
if the decay pathways of the series of resonances converging to the K
thresholds are adequately taken into account. These resonances display damped
Lorentzian profiles of nearly constant widths that are smeared to impose
continuity across the threshold. By modeling the effects of K damping on
opacities, it is found that the broadening of the K edge grows with the
ionization level of the plasma and that the appearance at high ionization of a
localized absorption feature at 7.2 keV is identified as the K-beta unresolved
transition array. | 0207324v2 |
2002-07-18 | Mrk 1014: An AGN Dominated ULIRG at X-rays | In this paper we report on an XMM-Newton observation of the ultraluminous
infrared QSO Mrk 1014. The X-ray observation reveals a power-law dominated
(photon index of about 2.2) spectrum with a slight excess in the soft energy
range. AGN and starburst emission models fit the soft excess emission equally
well, however, the most plausible explanation is an AGN component as the
starburst model parameter, temperature and luminosity, appear physically
unrealistic. The mean luminosity of Mrk 1014 is about 2 times 10^44 erg s^-1.
We have also observed excess emission at energies greater than 5 keV. This
feature could be attributed to a broadened and redshifted iron complex, but
deeper observations are required to constrain its origin. The light curve shows
small scale variability over the 11 ks observation. There is no evidence of
intrinsic absorption in Mrk 1014. The X-ray observations support the notion of
an AGN dominated central engine. We establish the need for a longer observation
to constrain more precisely the nature of the X-ray components. | 0207378v1 |
2002-08-01 | Chemical Composition of the Carbon-rich, Extremely Metal-Poor Star CS 29498--043: A New Class of Extremely Metal-Poor Stars with Excesses of Magnesium and Silicon | We analyze a high-resolution, high signal-to-noise spectrum of the
carbon-rich, extremely metal-poor star CS29498-043, obtained with the Subaru
Telescope High Dispersion Spectrograph. We find its iron abundance is extremely
low ([Fe/H] = -3.7), placing it among the few stars known with [Fe/H] < -3.5,
while Mg and Si are significantly overabundant ([Mg/Fe] = +1.8, and [Si/Fe] =
+1.1) compared with stars of similar metallicity without carbon excess.
Overabundances of N and Al were also found. These characteristics are similar
to the carbon-rich, extremely metal-poor star CS22949-037. Though the sample is
small, our discovery of CS29498-043 suggests the existence of a class of
extremely metal-poor stars with large excesses of C, N, Mg, and Si. | 0208019v1 |
2002-08-02 | Using Cepheids to determine the galactic abundance gradient. III.First results for the outer disc | As a continuation of our previous work, which concerned the radial abundance
distribution in the galactic disc over the distances 4-10 kpc this paper
presents the first results on the metallicicty in the outer disc (RG > 10 kpc).
Based on high-resolution spectra obtained for 19 distant Cepheids we sampled
galactocentric distances from 10 to 12 kpc. Combined with the results of our
previous work on the inner and middle parts of the galactic disc, the present
data enable one to study the structure of the radial abundance distribution
over a large baseline. In particular, we find indications of a discontinuity in
the radial abundance distribution for iron as well as a number of the other
elements. The discontinuity is seen at a galactocentric distance RG = 10 kpc.
This finding supports the results reported earlier by Twarog et al. (1997). | 0208056v1 |
2002-08-09 | Elemental Abundances and Ionization States within the Local Interstellar Cloud Derived from HST and FUSE Observations of the Capella Line of Sight | We use ultraviolet spectra of Capella from the Hubble Space Telescope (HST)
and Far Ultraviolet Spectroscopic Explorer (FUSE) satellites to study
interstellar absorption lines from the Local Interstellar Cloud (LIC).
Measurements of these lines are used to empirically determine the ionization
states of carbon, nitrogen, and silicon in the LIC, for comparison with the
predictions of theoretical photoionization models. We find that the observed
ionization states are consistent with previously published photoionization
predictions. Total abundances are determined for the elements mentioned above,
and others, for comparison with solar abundances. Magnesium, aluminum, silicon,
and iron are all depleted by at least a factor of 10 toward Capella. The
abundances of carbon, nitrogen, and oxygen are essentially solar, although the
error bars are large enough to also allow depletions of about a factor of 2 for
these elements. | 0208214v1 |
2002-08-25 | A new measurement of zinc metallicity in a DLA at z=3.35 | We present chemical abundance measurements in the z_abs=3.35045 Damped
Lyman-alpha (DLA) system observed in the UVES spectrum of the BAL quasar BR
1117-1329. We measure a neutral hydrogen column density N(HI)=6.9+/-1.7*10^{20}
atoms/cm2 and derive mean abundances relative to solar: [Si/H] = -1.26+/-0.13,
[Fe/H]=-1.51+/-0.13, [Ni/H]=-1.57+/-0.13, [Cr/H]=-1.36+/-0.13,
[Zn/H]=-1.18+/-0.13, [Al/H]>-1.25, [O/H]>-1.25 and [N/H]<-2.24. This is the
third measurement of Zn, an element mildly depleted onto dust grain, at
z_abs>3. The iron to zinc and chromium to zinc ratios, [Fe/Zn]=-0.33+/-0.05 and
[Cr/Zn]=-0.18+/-0.05 demonstrate that the absorber has a low dust content. The
nitrogen ratio [N/Si]<-0.98 suggests that the ``secondary'' N production
process is taking place in this DLA. Finally, this absorber does not seem to
present a convincing alpha-enhancement as shown by the alpha over Fe-peak
element ratios: [Si/Fe]=0.25+/-0.06, [Si/Cr]=0.10+/-0.06 and
[Si/Zn]=-0.08+/-0.06. | 0208450v1 |
2002-09-05 | X-ray spectroscopy of Eta Carinae with XMM-Newton | We present XMM-Newton observations of the luminous star Eta Carinae,
including a high resolution soft X-ray spectrum of the surrounding nebula
obtained with the Reflection Grating Spectrometer. The EPIC image of the field
around Eta Car shows many early-type stars and diffuse emission from hot,
shocked gas. The EPIC spectrum of the star is similar to that observed in
previous X-ray observations, and requires two temperature components. The RGS
spectrum of the surrounding nebula shows K-shell emission lines from hydrogen-
and helium-like nitrogen and neon and L-shell lines from iron, but little or no
emission from oxygen. The observed emission lines are not consistent with a
single temperature, but the range of temperatures observed is not large,
spanning ~0.15-0.6 keV. We obtain upper limits for oxygen line emission and
derive a lower limit of N/O > 9. This is consistent with previous abundance
determinations for the ejecta of Eta Car, and with theoretical models for the
evolution of massive, rotating stars. | 0209087v2 |
2002-09-11 | Ultra-High Energy Heavy Nuclei Propagation in Extragalactic Magnetic Fields | We extend existing work on the propagation of ultra-high energy cosmic rays
in extragalactic magnetic fields to a possible component of heavy nuclei,
taking into account photodisintegration, pion production, and creation of e+e-
pairs. We focus on the influence of the magnetic field on the spectrum and
chemical composition of observed ultra-high energy cosmic rays. We apply our
simulations to the scenarios proposed by Anchordoqui et al, in which Iron
nuclei are accelerated in nearby starburst galaxies, and show that it is in
marginal agreement with the data. We also show that it is highly unlikely to
detect He nuclei from M87 at the highest energies observed $\sim3 10^{20} $eV
as required for the scenario of Ahn et al. in which the highest energy cosmic
rays originate from M87 and are deflected in a Parker spiral Galactic magnetic
field. | 0209192v1 |
2002-09-12 | A Chandra observation of the H2O megamaser IC2560 | A short Chandra ACIS-S observation of the Seyfert 2 galaxy IC 2560, which
hosts a luminous nuclear water megamaser, shows: 1) the X-ray emission is
extended; 2) the X-ray spectrum shows emission features in the soft (E<2 keV)
X-ray band; this is the major component of the extended emission; and 3) a very
strong (EW~3.6 keV) iron K line at 6.4 keV on a flat continuum. This last
feature clearly indicates that the X-ray source is hidden behind Compton-thick
obscuration, so that the intrinsic hard X-ray luminosity must be much higher
than observed, probably close to ~3e42 erg/s. We briefly discuss the
implications for powering of the maser emission and the central source. | 0209245v1 |
2002-10-08 | Spectral Features and Masses in the PeV Region | An analysis is made of the masses and spectral features for cosmic rays in
the PeV region, insofar as they have a bearing on the problem of the
interaction of cosmic ray particles. In our Single Source Model we identified
two 'peaks' seen in a summary of the world's data on primary spectra, and
claimed that they are probably due to oxygen and iron nuclei from a local,
recent supernova. In the present work we examine other possible mass
assignments. We conclude that of the other possibilities only Helium and Oxygen
(instead of O and Fe) has much chance of success; the original suggestion is
still preferred, however. Concerning our location with respect to the SNR
shell, the analysis suggests that we are close to it - probably just inside. | 0210192v1 |
2002-10-18 | The Chemistry of Extragalactic Globular Clusters | We present preliminary results of VLT/FORS spectroscopy of globular clusters
in nearby early-type galaxies. Our project aims at studying the chemistry and
determine the ages of globular cluster (sub-)populations. First results
indicate that the different galaxies host from little to significant
intermediate-age populations, and that the latter have alpha-element over iron
ratios closer to solar than the old population that show an alpha-element
enhancement similar to the diffuse stellar light. | 0210419v1 |
2002-10-21 | Globular Clusters in nearby Galaxy Cluster | The discovery of a large population of intra-cluster star clusters in the
central region of the Hydra I and Centaurus galaxy clusters is presented. Based
on deep VLT photometry (V,I), many star clusters have been identified not only
around the early-type galaxies, but also in the intra-cluster field, as far as
250 kpc from the galaxy centres. These intra-cluster globulars are
predominantly blue, with a siginificant fraction being even bluer than the
metal-poor halo clusters around massive galaxies. When interpreted as a
metallicity effect they would have iron abundances around [Fe/H] = -2 dex.
However, they might also be relatively young clusters which could have formed
in tidal tails during recent interactions of the central galaxies. | 0210466v1 |
2002-11-11 | Stationary models of relativistic magnetohydrodynamic jets | Highly relativistic jets are most probably driven by strong magnetic fields
and are launched from the accretion disk surrounding a central black hole. In
this paper we review some of our recent results considering the two-dimensional
magnetic field structure and the dynamics of collimating relativistic jets.
Applying the stationarity assumption enables us to calculate global solutions
of the relevant MHD equations. We discuss solutions of the Grad-Shafranov
equation obtained in a general relativistic context applying the 3+1 formalism
for Kerr geometry. These solutions extend from the inner light surface around
the Kerr black hole to the asymptotic regime of a cylindrically collimated jet
with a finite radius. In a further step, we include differential rotation of
the foot points of the field lines. Considering the general relativistic MHD
wind equation, we investigate the dynamics of the collimating jet, in
particular the effects of Kerr metric on the acceleration. Temperature and
density follow a power law. Having at hand a relativistic MHD jet solution, we
calculate the thermal optically thin X-ray spectrum for the innermost hot part
of the jet. Doppler shift and boosting is taken into account. For microquasars
we obtain a jet X-ray luminosity 10^33 erg/s. Iron emission lines are clearly
visible. | 0211233v1 |
2002-11-20 | Quiet Sun magnetic fields at high spatial resolution | We present spectro-polarimetric observations of Inter-Network magnetic fields
at the solar disk center. A Fabry-Perot spectrometer was used to scan the two
Fe I lines at 6301.5 A and 6302.5 A. High spatial resolution (0.5")
magnetograms were obtained after speckle reconstruction. The patches with
magnetic fields above noise cover approximately 45% of the observed area. Such
large coverage renders a mean unsigned magnetic flux density of some 20 G (or
20 Mx/cm^2), which exceeds all previous measurements. Magnetic signals occur
predominantly in intergranular spaces. The systematic difference between the
flux densities measured in the two iron lines leads to the conclusion that,
typically, we detect structures with intrinsic field strengths larger than 1kG
occupying only 2% of the surface. | 0211454v1 |
2002-12-16 | Status of the KASCADE-Grande Experiment | The status and capabilities of the KASCADE-Grande extensive air shower
experiment are presented. The installation is located at Forschungszentrum
Karlsruhe and comprises a large collecting area (0.5 km^2) electromagnetic
array (Grande) operated jointly with the existing KASCADE detectors.
KASCADE-Grande will cover the primary energy range 10^16 eV < E_0 < 10^18 eV
overlapping with KASCADE around 10^16 eV, thus providing continuous information
on the primary energy and mass of cosmic rays from 3x10^14 eV up to 10^18 eV.
The major goal of the measurements is the unambiguous observation of the``iron
knee'' expected in the cosmic ray spectrum at E_k^{Fe} ~ 10^17 eV. | 0212347v1 |
2003-01-09 | An XMM-Newton observation of the Narrow Line Seyfert 1 Galaxy, Markarian 896 | XMM-Newton observations of the NLS1 Markarian 896 are presented. Over the
2-10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is
just resolved and has an equivalent width of ~170 eV. The broad-band spectrum
is well modelled by a power law slope of gamma ~ 2.03, together with two
blackbody components to fit the soft X-ray excess. Using a more physical
two-temperature Comptonisation model, a good fit is obtained for an input
photon distribution of kT ~ 60eV and Comptonising electron temperatures of ~0.3
and 200 keV. The soft excess cannot be explained purely through the
reprocessing of a hard X-ray continuum by an ionised disc reflector. | 0301152v1 |
2003-01-17 | On the Progenitor of Supernova 2001du in NGC 1365 | Hubble Space Telescope (HST) WFPC2 archival images obtained years prior to
the explosion of the Type II-plateau supernova (SN) 2001du in NGC 1365
previously have been analyzed to isolate the progenitor star. The SN site was
located using precise astrometry applied to the HST images, with significant
uncertainty, leaving three possible progenitor candidates. Images of the fading
SN have recently become publicly available in the HST archive, allowing us to
pinpoint the SN's exact location on the pre-explosion images. We show that the
SN occurred in very close proximity to one of the blue candidate stars, but we
argue that this star is not the actual progenitor. Instead, the progenitor was
not detected on the pre-SN images, and we constrain the progenitor's mass to be
less than 13 (+7, -4) Msuns. This is consistent with previous constraints on
the progenitor masses of other Type II-plateau supernovae (SNe), suggesting
that such SNe arise from the iron core collapse of massive stars at the lower
extreme of the possible mass range. | 0301346v2 |
2003-01-17 | Supernovae, Gamma-Ray Bursts, and Stellar Rotation | One of the most dramatic possible consequences of stellar rotation is its
influence on stellar death, particularly of massive stars. If the angular
momentum of the iron core when it collapses is such as to produce a neutron
star with a period of 5 ms or less, rotation will have important consequences
for the supernova explosion mechanism. Still shorter periods, corresponding to
a neutron star rotating at break up, are required for the progenitors of
gamma-ray bursts (GRBs). Current stellar models, while providing an excess of
angular momentum to pulsars, still fall short of what is needed to make GRBs.
The possibility of slowing young neutron stars in ordinary supernovae by a
combination of neutrino-powered winds and the propeller mechanism is discussed.
The fall back of slowly moving ejecta during the first day of the supernova may
be critical. GRBs, on the other hand, probably require stellar mergers for
their production and perhaps less efficient mass loss and magnetic torques than
estimated thus far. | 0301373v1 |
2003-01-27 | The nature of the absorbing torus in compact Radio Galaxies | We present BeppoSAX observations of the two radio galaxies PKS 1934-63 and S5
1946+708. Strong Iron Kalpha lines are detected in both objects indicating that
the two sources are absorbed by column densities higher than 10^24 cm^(-2).
Combining radio continuum, HI absorption and X-ray data we can constrain the
physical state and the dimensions of the absorber. We find that the putative
obscuring torus is molecular and located at a distance higher than 20 pc from
the center in S5 1946+70. In PKS 1934-63 no radio nucleus has been observed. If
this is due to free-free absorption a radius of only a few pc is inferred.
Since the Kalpha lines have been detected only at 90% confidence, we also
discuss the implications if they would be not as strong as found from our data.
From our results it appears that the combination of hard X-ray data and
spatially resolved HI absorption measurements provides a powerful diagnostic
for conditions in the absorbing ``torus''. | 0301522v1 |
2003-02-07 | Parallel Universes | I survey physics theories involving parallel universes, which form a natural
four-level hierarchy of multiverses allowing progressively greater diversity.
Level I: A generic prediction of inflation is an infinite ergodic universe,
which contains Hubble volumes realizing all initial conditions - including an
identical copy of you about 10^{10^29} meters away.
Level II: In chaotic inflation, other thermalized regions may have different
effective physical constants, dimensionality and particle content.
Level III: In unitary quantum mechanics, other branches of the wavefunction
add nothing qualitatively new, which is ironic given that this level has
historically been the most controversial.
Level IV: Other mathematical structures give different fundamental equations
of physics. The key question is not whether parallel universes exist (Level I
is the uncontroversial cosmological concordance model), but how many levels
there are. I discuss how multiverse models can be falsified and argue that
there is a severe "measure problem" that must be solved to make testable
predictions at levels II-IV. | 0302131v1 |
2003-02-11 | A search for X-ray variability in the open cluster NGC 2516 | We present the results of a search for X-ray variability in the galactic open
cluster NGC 2516. This cluster has been observed on 8 occasions using
XMM-Newton making it an excellent target for such a study. We find 4 sources
which show significant variability, implying the detection of one significantly
variable source every 25ksec. All sources exhibit spectra which can be fitted
using an absorbed one or two temperature thermal plasma model. The brightest of
these flares also show a prominent Iron line near ~7.0keV. All 4 sources lie
near the observed main sequence of NGC 2516 suggesting they are cluster
members. We propose that at least 3 of the 4 objects are RS CVn systems. We
compare the properties of the brightest flare with those of solar flares. | 0302200v1 |
2003-02-28 | X-ray spectral evolution of low-mass X-ray binary GX 349+2 | We present the results of a systematic investigation of spectral evolution in
the Z source GX 349+2, using data obtained during 1998 with
Proportional-Counter-Array (PCA) on-board the RXTE satellite. The source traced
a extended normal branch (NB) and flaring branch (FB) in the color-color
diagram (CD) and hardness-intensity diagram (HID) during these observations.
The spectra at different positions of Z-track were best fitted by a model
consisting of a disk blackbody and a comptonized spectrum. A broad (gaussian)
iron line at $\sim 6.7$ keV is also required to improve the fit. The spectral
parameters showed a systematic and significant variation with the position
along the Z-track. The evolution in spectral parameters is discussed in the
view of increasing mass accretion rate scenario, proposed to explain the motion
of Z sources in the CD and HID. | 0302581v2 |
2003-03-18 | Iron Emission in z~6 QSOs | We have obtained low-resolution near infrared spectra of three QSOs at 5.7 <
z < 6.3 using the NICMOS instrument of the Hubble Space Telescope. The spectra
cover the rest-frame ultraviolet emission of the objects between lambda_rest ~
1600A - 2800A. The Fe II emission-line complex at 2500A is clearly detected in
two of the objects, and possibly detected in the third. The strength of this
complex and the ratio of its integrated flux to that of Mg II lambda 2800 are
comparable to values measured for QSOs at lower redshifts, and are consistent
with Fe/Mg abundance ratios near or above the solar value. There thus appears
to be no evolution of QSO metallicity to z~6. Our results suggest that massive,
chemically enriched galaxies formed within 1 Gyr of the Big Bang. If this
chemical enrichment was produced by Type Ia supernovae, then the progenitor
stars formed at z ~ 20 +/- 10, in agreement with recent estimates based on the
cosmic microwave background. These results also support models of an
evolutionary link between star formation, the growth of supermassive black
holes and nuclear activity. | 0303424v1 |
2003-03-19 | Absorption spectra of Fe L-lines in Seyfert 1 galaxies | Absorption L-lines of iron ions are observed, in absorption, in spectra of
Seyfert 1 galaxies by the new generation of X-ray satellites: Chandra (NASA)
and XMM-Newton (ESA). Lines associated to Fe23+ to Fe17+ are well resolved.
Whereas, those corresponding to Fe16+ to Fe6+ are unresolved. Forbidden
transitions of the Fe16+ to Fe6+ ions were previously observed, for the same
objects, in the visible and infra-red regions, showing that the plasma had a
low density. To interpret X-ray, visible and infra-red data, astrophysical
models assume an extended absorbing medium of very low density surrounding an
intense X-ray source. We have calculated atomic data (wavelengths, radiative
and autoionization rates) for n=2 to n'=3-4 transitions and used them to
construct refined synthetic spectra of the unresolved part of the L-line
spectra. | 0303435v1 |
2003-03-20 | A grid of synthetic ionizing spectra for very hot compact stars from NLTE model atmospheres | The precise analysis of properties of planetary nebulae is strongly dependent
on good models for the stellar ionizing spectrum. Observations in the UV -
X-ray wavelength range as well as NLTE model atmosphere calculations of spectra
of their exciting stars have shown that neither blackbody fluxes nor "standard"
NLTE atmosphere models which are composed out of hydrogen and helium only are
good approximations. Strong differences between synthetic spectra from these
compared to observed spectra at energies higher than 54 eV (He II ground state)
can be ascribed to the neglect of metal-line blanketing.
Realistic modeling of the emergent fluxes of hot stars in the UV - X-ray
wavelength range requires metal-line blanketed NLTE model atmospheres which
include all elements from hydrogen up to the iron-group. For this purpose, we
present a grid (solar and halo abundance ratios) of metal-line blanketed NLTE
model atmosphere fluxes which covers the parameter range of central stars of
planetary nebulae. | 0303464v1 |
2003-03-28 | The properties of the absorbing and line emitting material in IGR J16318-4848 | We have performed a detailed analysis of the XMM-Newton observation of IGR
J16318-4848, to study the properties of the matter responsible for the
obscuration and for the emission of Fe and Ni lines. Even if the line of sight
material has a column density of about 2x10^24 cm^-2, from the Fe Kalpha line
EW and Compton Shoulder we argue that the matter should have an average column
density of a few x10^23 cm^-2, along with a covering factor of about 0.1-0.2.
The iron Kalpha line varies on time scales as short as 1000 s, implying a size
of the emitting region smaller than about 3x10^13 cm. The flux of the line
roughly follows the variations of the continuum, but not exactly, suggesting a
variation of the geometrical properties of the emitting region on similar time
scales. | 0303626v1 |
2003-04-02 | Binary Blue Metal-Poor Stars: Evidence for AGB Mass Transfer | We present new abundance analyses of six blue metal-poor (BMP) stars with
very low iron abundances ([Fe/H] < -2), based on new high resolution echelle
spectra. Three are spectroscopic binaries and three have constant radial
velocities. The chemical compositions of these two groups are very different,
as the binary BMP stars have large enhancements of carbon and neutron-capture
elements that are products of s-process nucleosynthesis. One star, CS
29497-030, has an extreme enhancement of lead, [Pb/Fe] = +3.7, the largest
abundance in any star yet discovered. It probably also has an oxygen
overabundance compared to the other BMP stars of our sample. The binary BMP
stars must have attained their status via mass transfer during the asymptotic
giant branch (AGB) evolutions of their companion stars, which are now unseen
and most likely are compact objects. We have not found any examples of AGB mass
transfer among BMP binaries with [Fe/H] > -2. | 0304064v1 |
2003-04-03 | Induced Formation of Primordial Low-Mass Stars | We show that the explosion of the first supernovae can trigger low-mass star
formation via gravitational fragmentation of the supernova-driven gas shell. If
the shell mass does not exceed the host galaxy gas mass, all explosions with
energies E_SN > 10^{51} erg can lead to shell fragmentation. However, the
minimum ambient density required to induce such fragmentation is much larger,
n_0 > 300 cm^{-3}, for Type II supernovae than for pair-instability ones, which
can induce star formation even at lower ambient densities. The typical mass of
the unstable fragments is 10^{4-7} Msun; their density is in the range
110-6x10^7 cm{-3}. Fragments have a metallicity strictly lower than 10^{-2.6}
Zsun and large values of the gravitational-to-pressure force ratio f ~ 8. Based
on these findings, we conclude that the second generation of stars produced by
such self-propagating star formation is predominantly constituted by low-mass,
long-living, extremely metal-poor (or even metal-free, if mixing is suppressed)
stars. We discuss the implications of such results for Pop III star formation
scenarios and for the most iron-poor halo star HE0107-5240. | 0304074v2 |
2003-04-04 | Metastable strange matter and compact quark stars | Strange quark matter in beta equilibrium at high densities is studied in a
quark confinement model. Two equations of state are dynamically generated for
the {\it same} set of model parameters used to describe the nucleon: one
corresponds to a chiral restored phase with almost massless quarks and the
other to a chiral broken phase. The chiral symmetric phase saturates at around
five times the nuclear matter density. Using the equation of state for this
phase, compact bare quark stars are obtained with radii and masses in the
ranges $R\sim 5 - 8$ km and $M\sim M_\odot$. The energy per baryon number
decreases very slowly from the center of the star to the periphery, remaining
above the corresponding values for the iron or the nuclear matter, even at the
edge. Our results point out that strange quark matter at very high densities
may not be absolutely stable and the existence of an energy barrier between the
two phases may prevent the compact quarks stars to decay to hybrid stars. | 0304096v1 |
2003-04-14 | Low-Mass Relics of Early Star Formation | The earliest stars to form in the Universe were the first sources of light,
heat and metals after the Big Bang. The products of their evolution will have
had a profound impact on subsequent generations of stars. Recent studies of
primordial star formation have shown that, in the absence of metals (elements
heavier than helium), the formation of stars with masses 100 times that of the
Sun would have been strongly favoured, and that low-mass stars could not have
formed before a minimum level of metal enrichment had been reached. The value
of this minimum level is very uncertain, but is likely to be between 10^{-6}
and 10^{-4} that of the Sun. Here we show that the recent discovery of the most
iron-poor star known indicates the presence of dust in extremely
low-metallicity gas, and that this dust is crucial for the formation of
lower-mass second-generation stars that could survive until today. The dust
provides a pathway for cooling the gas that leads to fragmentation of the
precursor molecular cloud into smaller clumps, which become the lower-mass
stars. | 0304254v1 |
2003-04-15 | Detailed Analysis of Nearby Bulgelike Dwarf Stars III. Alpha and Heavy-element abundances | The present sample of nearby bulgelike dwarf stars has kinematics and
metallicities characteristic of a probable inner disk or bulge origin. Ages
derived by using isochrones give 10-11 Gyr for these stars and metallicities
are in the range -0.80< [Fe/H]< +0.40. We calculate stellar parameters from
spectroscopic data, and chemical abundances of Mg, Si, Ca, Ti, La, Ba, Y, Zr
and Eu are derived by using spectrum synthesis.
We found that [alpha-elements/Fe] show different patterns depending on the
element. Si, Ca and Ti-to-iron ratios decline smoothly for increasing
metallicities, and follow essentially the disk pattern. O and Mg, products of
massive supernovae, and also the r-process element Eu, are overabundant
relative to disk stars, showing a steeper decline for metallicities [Fe/H] >
-0.3 dex. [s-elements/Fe] roughly track the solar values with no apparent trend
with metallicity for [Fe/H] < 0, showing subsolar values for the metal rich
stars. Both kinematical and chemical properties of the bulgelike stars indicate
a distinct identity of this population when compared to disk stars. | 0304282v2 |
2003-04-23 | How did the metals in a giant star originate? | The chemical composition of stars with extremely low metal contents (taking
``metals'' to mean all elements other than hydrogen and helium) provides us
with information on the masses of the stars that produced the first metals.
Such a direct connection is not possible, however, if the surface of the star
has been polluted by enriched material, either dredged from the star's interior
or transferred from a companion star. Here we argue that, in the case of
HE0107-5240 (ref. 1), the most iron poor star known, the oxygen abundance could
be a discriminant: a ratio of [O/Fe] exceeding +3.5 would favour a pristine
origin of metals, whereas an [O/Fe] ratio of less than +3 would favour the
pollution hypothesis. Using this criterion, we suggest how the required
information on oxygen abundance might be obtained. | 0304415v1 |
2003-05-12 | Stellar Abundances in Dwarf Irregular Galaxies | Dwarf irregular galaxies appear to have undergone very slow chemical
evolution since they have low nebular abundances, but have had ongoing star
formation over the past 15 Gyr. They are too distant for red giant abundance
analyses to examine the details of their chemical evolution, however the
isolated, bright blue supergiants do allow us to determine their present-day
iron abundances to compare with both stellar and nebular alpha-element results.
The [alpha/Fe] ratios in four Local Group dwarf irregular galaxies (NGC6822,
WLM, Sextans A, and GR 8) all appear to have solar ratios regardless of the
differences in their metallicities and star formation histories. Surprisingly,
WLM's stellar metallicity is three times higher than the nebular oxygen
abundance. We compare the [alpha/Fe] ratios in the dwarf irregulars to those
from recent analyses of red giant branch stars in dwarf spheroidal galaxies,
and also to damped Ly-alpha systems, and discuss these in the context of model
predictions. | 0305188v1 |
2003-05-19 | A BeppoSAX observation of MKN6 | We have used the BeppoSAX satellite to study the broad band (0.5-100 keV)
X-ray spectrum of the Seyfert 1.5 galaxy MKN6. The source is characterized by a
power law of Gamma=1.7 [+0.08, -0.07] and there is no strong evidence for
either a reflection bump or a high energy cut-off. We have detected a narrow
iron line at 6.4 keV (rest frame) with an equivalent width of 98 [+33, -35] eV.
MKN6 also exhibits strong and complex absorption. At least two components (NH_1
=1.34 [+0.4,-0.4] x 10^(22) cm^(-2) and NH_2 = 4.18 [+2.2, -1.3] x 10^(22)
cm^(-2)) are present and they both partially cover the source with covering
fractions of ~90% and ~50% respectively. Comparison with a previous ASCA
observation indicates that in both absorbing columns the NH is variable over a
2 year timescale, while the covering fractions are constant over the same
amount of time. The state of each absorber is cold or mildly photoionized. The
Broad Line Region (BLR) is suggested as the possible location for this complex
absorption. | 0305329v1 |
2003-05-20 | An Estimate Of The Primary Mass Of Cosmic Rays At $10^{18}$ eV As Inferred From Volcano Ranch Data | Accurate measurements of the lateral distribution of extensive air showers
produced by cosmic rays of energy greater than $10^{17}$ eV were made in the
1970s by Linsley. At the time, the state of knowledge about the best hadronic
interaction model to use to describe such data prevented conclusions about the
cosmic ray mass from being drawn. We have used a modern model, {\sc qgsjet98},
to infer the primary mass from these data, using the very careful records left
by Linsley. We find that at a median energy of $10^{18}$ eV, the data are well
described by an iron-dominated composition (88 $\pm$ 6(stat) $\pm$ 18 (syst))%.
We discuss the systematic errors in this estimate that arise from model
uncertainties and from the range of energies used in the work of Linsley. These
data are used with the permission of the late John Linsley to whom this work is
dedicated. | 0305351v1 |
2003-05-23 | Metal Rich Stars in omega Centauri | I present some preliminary results from a high-resolution spectroscopic
observing campaign conducted with UVES at the ESO VLT, devoted to the study of
the newly discovered, metal-rich red giant branch (RGB-a) in omega Centauri. In
particular, I derive and discuss accurate abundances of iron-peak elements,
alpha-elements and s-process elements. The main results discussed in this
contribution are: (i) the RGB-a is the most metal-rich component of the RGB
stellar mix in omega Cen, with [Fe/H]=-0.62+/-0.06; (ii) the RGB-a has a lower
alpha-enhancement compared to the other red giants, possibly due to SNe type Ia
pollution and (iii) the s-process elements overabundance of the RGB-a is
similar to that of the other red giants in omega Cen, and unusually high for
globular cluster stars, due to pollution by low mass AGB stars. | 0305449v1 |
2003-05-26 | XMM-Newton study of the persistent X-ray source 1E1743.1-2843 located in the Galactic Center direction | We report the results of an XMM-Newton observation of the persistent X-ray
source 1E1743.1-2843, located in the Galactic Center (GC) direction. We
determine the position of the source at alpha_J2000=17h46m21.0s,
delta_J2000=-28deg43'44" (with an uncertainty of 1.5"), which is the most
accurate to date, and will enable cross-identifications at other wavelengths.
The source was bright during this observation (L_2-10keV ~ 2.7 x 10^36
d^2_10kpc erg/s for a power-law continuum), with no significant variability. We
propose that 1E1743.1-2843 may be explained in terms of a black hole candidate
in a low/hard state. There is an indication that the source exhibits different
states from a comparison of our results with previous observations (e.g.,
ART-P, BeppoSAX). However, the present spectral analysis does not rule out the
hypothesis of a neutron star low-mass X-ray binary as suggested previously. If
1E1743.1-2843 is actually located in the GC region, we might expect to observe
significant 6.4keV fluorescent iron line emission from nearby molecular clouds
(e.g., GCM+0.25+0.01). | 0305489v1 |
2003-06-05 | Where was the Iron Synthesized in Cassiopeia A? | We investigate the properties of Fe-rich knots on the east limb of the
Cassiopeia A supernova remnant using observations with Chandra/ACIS and
analysis methods developed in a companion paper. We use the fitted ionization
age and electron temperature of the knots to constrain the ejecta density
profile and the Lagrangian mass coordinates of the knots. Fe-rich knots which
also have strong emission from Si, S, Ar, and Ca are clustered around mass
coordinates q~0.35-0.4 in the shocked ejecta; for ejecta mass 2M_sun, this
places the knots 0.7-0.8 M_sun out from the center (or 2-2.1 M_sun, allowing
for a 1.3 M_sun compact object). We also find an Fe clump that is evidently
devoid of line emission from lower mass elements, as would be expected if it
were the product of alpha-rich freeze out; the mass coordinate of this clump is
similar to those of the other Fe knots. | 0306120v1 |
2003-06-09 | An AGN Sample with High X-ray-to-optical Flux Ratio from RASS II.Optical Emission Line Properties of Seyfert 1 Type AGN | This work studies the optical emission line properties of a sample of 155
low-redshift bright X-ray selected ROSAT Seyfert~1 type AGN for which adequate
signal-to-noise ratio spectroscopic observations are available. We measured
emission line properties by performing multi-component fits to the emission
line profiles, covering the effect of blended iron emission. We also obtained
continuum parameters, including 250eV X-ray luminosities derived from the ROSAT
database. In addition, the measured properties are gathered for a correlation
analysis, which confirms the well-known relations between the strengths of
Fe~II, [O III] emission and the X-ray slope. We also detect striking
correlations between H$\beta$ redshift (or blueshift), flux ratios of Fe `II to
H$\beta$ broad component and [O III] to H$\beta$ narrow component. These trends
are most likely driven by the Eddington ratio. | 0306169v1 |
2003-06-12 | Long Term X-ray Variability in GX13+1: Energy Dependent Periodic Modulation | A search is made for periodic modulation in the X-ray flux from the low mass
X-ray binary GX13+1 using Rossi X-ray Timing Explorer All Sky Monitor data
collected over a period of almost seven years. From a filtered data set, which
excludes measurements with exceptionally large error bars and so maximizes
signal to noise, modulation is found at a period of 24.065 +/- 0.018 days. The
modulation is most clearly detectable at high energies (5 - 12 keV). Spectral
changes are revealed as a modulation in hardness ratio on the 24 day period and
there is a phase shift between the modulation in the 5 - 12 keV energy band
compared to the 1.5 - 5 keV band. The high-energy spectrum of GX13+1 is unusual
in displaying both emission and absorption iron line features and it is
speculated that the peculiar spectral and timing properties may be connected. | 0306262v1 |
2003-06-13 | Delayed soft X-ray emission lines in the afterglow of GRB 030227 | Strong, delayed X-ray line emission is detected in the afterglow of GRB
030227, appearing near the end of the XMM-Newton observation, nearly twenty
hours after the burst. The observed flux in the lines, not simply the
equivalent width, sharply increases from an undetectable level (<1.7e-14
erg/cm^2/s, 3 sigma) to 4.1e-14 erg/cm^2/s in the final 9.7 ks. The line
emission alone has nearly twice as many detected photons as any previous
detection of X-ray lines. The lines correspond well to hydrogen and/or
helium-like emission from Mg, Si, S, Ar and Ca at a redshift z=1.39. There is
no evidence for Fe, Co or Ni--the ultimate iron abundance must be less than a
tenth that of the lighter metals. If the supernova and GRB events are nearly
simultaneous there must be continuing, sporadic power output after the GRB of a
luminosity >~5e46 erg/s, exceeding all but the most powerful quasars. | 0306284v2 |
2003-06-16 | Modeling of iron K lines: radiative and Auger decay data for Fe II-Fe IX | A detailed analysis of the radiative and Auger de-excitation channels of
K-shell vacancy states in Fe II-Fe IX has been carried out. Level energies,
wavelengths, A-values, Auger rates and fluorescence yields have been calculated
for the lowest fine-structure levels populated by photoionization of the ground
state of the parent ion. Different branching ratios, namely
K-alpha_2/K-alpha_1, K-beta/K-alpha, KLM/KLL, KMM/KLL, and the total K-shell
fluorescence yields, omega_K, obtained in the present work have been compared
with other theoretical data and solid-state measurements, finding good general
agreement with the latter. The K-alpha_2/K-alpha_1 ratio is found to be
sensitive to the excitation mechanism. From these comparisons it has been
possible to estimate an accuracy of ~10% for the present transition
probabilities. | 0306321v2 |
2003-06-27 | The Chemical Composition and Gas-to-Dust Mass Ratio of Nearby Interstellar Matter | Recent results on nearby interstellar gas and interstellar byproducts within
the solar system are used to select among the equilibrium radiative transfer
models of the nearest interstellar material of Slavin and Frisch (2002).
Assuming O/H~400 ppm, Models 2 and 8 are found to yield good fits to available
data on local interstellar material, and pickup ions and anomalous cosmic rays
inside of the heliosphere, with the exception of Ne. For these models, the
density of interstellar gas at the entry point to the heliosphere is n(HI)~0.20
/cc and n(e-)~0.1 /cc. These models suggest the chemical composition of the
nearby ISM is ~60--70% subsolar if S is undepleted (where HI and HII must be
included for abundance calculations). Gas-to-dust mass ratios of 178-183 for
solar abundances, or 611-657 for 70% solar abundances are found. The percentage
of the dust mass that is carried by iron is directly correlated with the
gas-to-dust mass ratio implying an Fe-rich grain core remains after grain
destruction. | 0306590v2 |
2003-07-08 | The Chemistry of Galaxy Clusters | From X-ray observations of galaxy clusters one derives the mass of the
intracluster medium along with its chemical composition. Optical/infrared
observations are used to estimate the mass of the stellar components of
galaxies, along with their chemical composition and age. This review shows that
when combining all this information, several interesting inferences can be
drawn, including: (1) galaxies lose more metals than they retain; (2) clusters
and the general field have converted the same fraction of baryons into stars,
hence the metallicity of the $z = 0$ Universe as a whole has to be nearly the
same we see in clusters, $\sim$1/3 solar; (3) for the same reason, the thermal
content of the intergalactic medium is expected to be nearly the same as the
preheating energy of clusters; (4) a strong increase of the Type Ia supernova
(SN) rate with lookback time is predicted if SNe Ia produce a major fraction of
cosmic iron; (5) the global metallicity of the $z\approx 3$ Universe was
already $\sim$1/10 solar; and (6) the Milky Way disk formed out of material
that was pre-enriched to $\sim$1/10 solar by the bulge stellar population. | 0307146v1 |
2003-07-09 | Nitrogen Abundances in High-z DLAs | Determination of chemical abundances for elements produced mainly by Type I
SNae and intermediate mass stars in high redshift DLAs probes the early
chemical build-up on time-scales comparable with their production. Nitrogen
shows a peculiar behaviour never detected before in any other class of objects.
For [N/H] < -3 there is a plateau with [N/Si]= -1.45(\pm 0.05). We interpret
this as empirical evidence for primary N production by massive stars in young
systems where AGB stars have not yet had time to make their contribution. The
plateau provides the observational integrated yields for N production by
massive stars which are theoretically rather uncertain. High N/Si and solar
[alpha/iron-peak] ratios are observed at high redshift and place at an earlier
epoch the onset of star formation. On the other hand, low N/Si, i.e. young
objects, are observed also at relatively low redshifts. These evidences suggest
that DLAs started to be formed at a very early epoch but their formation has
been extended up to later times. | 0307173v1 |
2003-07-30 | On the origin of HE0107-5240, the most iron deficient star presently known | We show that the "puzzling" chemical composition observed in the extremely
metal poor star HE0107-5240 may be naturally explained by the concurrent
pollution of at least two supernovae. In the simplest possible model a
supernova of quite low mass (~15 Msun), underwent a "normal" explosion and
ejected ~0.06 Msun of 56Ni while a second one was massive enough (~35 Msun) to
experience a strong fall back that locked in a compact remnant all the
carbon-oxygen core. In a more general scenario, the pristine gas clouds were
polluted by one or more supernovae of relatively low mass (less than ~25 Msun).
The successive explosion of a quite massive star experiencing an extended fall
back would have largely raised the abundances of the light elements in its
close neighborhood. | 0307527v1 |
2003-08-15 | Stellar pollution and [Fe/H] in the Hyades | The Hyades open cluster presents a unique laboratory for planet formation and
stellar pollution studies because all of the stars have essentially the same
age and were born from the same cloud of gas. Furthermore, with an age of
roughly 650 Myr most of the intermediate and low mass stars are on the main
sequence. Given these assumptions, the accretion of metal rich material onto
the surface of a star during and shortly after the formation of planetary
systems should be evident via the enhanced metallicity of the star. Building on
previous work, stellar evolution models which include the effects of stellar
pollution are applied to the Hyades. The results of several Monte Carlo
simulations, in which the amount of accreted material is drawn at random from a
Gaussian distribution with standard deviation equal to half the mean, are
presented. An effective temperature-[Fe/H] relation is produced and compared to
recent observations. The theoretical predictions presented in this letter will
be useful in future searches for evidence of stellar pollution due to planet
formation. It is concluded that stellar pollution effects at the mean level of
>=2 Earth masses of iron are ruled out by current observational data. | 0308268v1 |
2003-08-20 | The chemical composition of a mild barium star HD202109 | We present the result of chemical abundances of a mild barium star HD202109
(zeta Cyg) determined from the analysis of spectrum obtained by using a 2-m
telescope at the Peak Terskol Observatory and a high-resolution spectrometer
with R=80,000, signal to noise ratio >100. We also present the atmospheric
parameters of the star determined by using various methods including iron-line
abundance analysis. For line identifications, we use whole-range synthetic
spectra computed by using the Kurucz database and the latest lists of spectral
lines. Among the determined abundances of 51 elements, those of P, S, K, Cu,
Zn, Ge, Rb, Sr, Nb, Mo, Ru, Rh, Pd, In, Sm, Gd, Tb, Dy, Er, Tm, Hf, Os, Ir, Pt,
Tl, and Pb have not been previously known. Under the assumption that the
overabundance pattern of Ba stars is due to wind-accretion process, adding
information of more element abundances enables one to show that the heavy
element overabundances of HD202109 can be explained with the wind accretion
scenario model. | 0308337v2 |
2003-08-20 | Rosseland and Planck Mean Opacities for Protoplanetary Discs | In this paper, we present mean gas and dust opacities relevant to the
physical conditions typical of protoplanetary discs. As the principal absorber
for temperatures below ~1,500 K, we consider spherical and aggregate dust
particles of various sizes, chemical structure, and porosity, consisting of
ice, organics, troilite, silicates, and iron. For higher temperatures, ions,
atoms, molecules, and electrons are included as the main opacity sources.
Rosseland and Planck mean opacities are calculated for temperatures between 5 K
and 10,000 K and gas densities ranging from 10^{-18} g/ccm to 10^{-7} g/ccm.
The dependence on the adopted model of dust grains is investigated. We compare
our results with recent opacity tables and show how different opacity models
affect the calculated hydrodynamical structure of accretion discs. | 0308344v1 |
2003-08-21 | Sgr A East and its surroundings observed in X-rays | We report the results of an XMM-Newton observation of Sgr A East and its
surroundings. The X-ray spectrum of Sgr A East is well represented with a
two-temperature plasma model with temperatures of ~1 and ~4 keV. Only the iron
abundance shows clear spatial variation; it concentrates in the core of Sgr A
East. The derived plasma parameters suggest that Sgr A East originated in a
single supernova. Around Sgr A East, there is a broad distribution of hard
X-ray emission with a superimposed soft excess component extending away from
the location of Sgr A East both above and below the plane. We discuss the
nature of these structures as well as the close vicinity of Sgr A*. | 0308373v1 |
2003-08-27 | 3EG J2027+3429 another Blazar behind the Galactic Plane | We report on the association of an X-ray source (WGA J2025.1+3342),
serendipitously found with BeppoSAX in two separate observations, with the
unidentified EGRET source 3EG J2027+3429. The source is detected from 1 keV up
to about 100 keV, has a flat (0.6-1.5) spectrum and is highly variable both in
intensity and shape. The data indicate marginal evidence for an iron line in
the source rest frame. The overall X-ray luminosity is 4 10^{45} erg s^{-1}
typical of a quasar. The X-ray source is coincident in radio with a bright
object characterized by a flat spectrum over the band 0.3-10 GHz while in
optical it is identified with a quasar at redshift 0.22. All available data
indicate a SED compatible with a low frequency peaked or red blazar type
object. This identification is interesting because this is the second blazar
found behind the galactic plane in the direction of the Cygnus region. | 0308473v1 |
2003-08-28 | On the filling factor of emitting material in the upper atmosphere of Epsilon Eri (K2 V) | The emission measure distribution in the upper transition region and corona
of Epsilon Eri is derived from observed emission line fluxes. Theoretical
emission measure distributions are calculated assuming that the radiation
losses are balanced by the net conductive flux. We discuss how the area factor
of the emitting regions as a function of temperature can be derived from a
comparison between these emission measure distributions. It is found that the
filling factor varies from ~0.2 in the mid transition region to ~1.0 in the
inner corona. The sensitivity of these results to the adopted ion fractions,
the iron abundance and other parameters is discussed. The area factors found
are qualitatively similar to the observed structure of the solar atmosphere,
and can be used to constrain two-component models of the chromosphere. Given
further observations, the method could be applied to investigate the trends in
filling factors with indicators of stellar activity. | 0308502v1 |
2003-09-01 | Fe II lifetimes and transition probabilities | Fe II radiative lifetimes were measured applying the time-resolved nonlinear
laser-induced fluoresence technique. We investigated 21 levels of up to 47000
1/cm. The uncertainties are typically 2-3%. The lifetimes provide an improved
absolute scale to our branching fractions which were measured with a Fourier
transform spectrometer and a high-resolution grating spectrometer and which
have been published earlier. We report absolute transition probabilities of 140
Fe II lines in the wavelength range 220-780 nm. The overall uncertainties are
estimated to be 6% for the strong and up to 26% for the weak transitions. The
results are compared with recent experimental data from the literature. Our
large set of accurate data can be used for a reliability check of theoretical
data calculated for iron abundances in astrophysical plasmas. | 0309023v3 |
2003-09-16 | XMM-Newton Observations of the Perseus Cluster II: Evidence for Gas Motions in the Core | The 5-9 keV spectrum of the inner ~100 kpc of the Perseus cluster measured by
XMM-Newton can be well described by an optically thin plasma emission model as
predicted by the APEC code, without any need for invoking a strong Ni
overabundance or the effects of resonant scattering. For the strongest 6.7 keV
line of He-like iron, the optical depth of the cluster, calculated using
observed density, temperature and abundance profiles, is of order 3. The lack
of evidence for resonant scattering effects implies gas motion in the core with
a range in velocities of at least half of the sound velocity. If this motion
has the character of small scale turbulence, then its dissipation would provide
enough energy to compensate for radiative cooling of the gas. The activity of
the supermassive black hole at the center of the cluster may be the driving
force of the gas motion. | 0309427v1 |
2003-09-18 | Inferring the coronal flaring patterns in AGN from reverberation maps | The relativistically broadened iron K-alpha line at 6.4 keV observed in the
Seyfert 1 galaxy MCG-6-30-15 has provided a probe of the strong-gravity
environment near a black hole, in particular suggesting that it is rapidly
spinning. An important variable in such analyses is the geometry of the
illuminating source. We present a new technique which constrains this geometry
based on the spectral line shape, based on a model of discrete, point-like
flaring regions in the X-ray corona. We apply it to simulated reverberation
maps and give examples of successful reconstructions of complex coronal flaring
patterns. For time-averaged spectral lines the problem is highly degenerate,
and so its inversion more challenging. We quantify this degeneracy and give a
measure of the spatial accuracy of the method in this case, before checking
that it is consistent with the existing picture of MCG-6-30-15 by applying it
to recent data from XMM-Newton. | 0309518v2 |
2003-09-29 | A common trend in the chemical evolution of Local Group dwarf spheroidals and Damped Ly-alpha systems | We compare chemical abundances of Local Group dwarf spheroidals, obtained
from recent UVES/VLT observations, and of high redshift Damped Lyman alpha
systems (DLAs), corrected for dust effects. We focus, in particular, on the
abundance ratio between alpha-capture elements and iron, alpha/Fe, a well known
indicator of chemical evolution. Comparison of the data in the plane alpha/Fe
versus Fe/H shows a remarkable similarity between the dwarf spheroidals and the
DLAs, suggestive of a common trend in their chemical evolution. At any given
metallicity these two distinct types of astronomical targets show alpha/Fe
ratios systematically lower than those of Milky Way stars. In terms of chemical
evolution models, this suggests that, on average, dSph galaxies and DLA systems
are characterized by lower, or more episodic, star formation rates than the
Milky Way. | 0309765v1 |
2003-10-06 | A new population of X-ray transients in the Galactic Centre | A comparison of the XMM-Newton and Chandra Galactic Centre (GC) Surveys has
revealed two faint X-ray transients with contrasting properties. The X-ray
spectrum of XMM J174544-2913.0 shows a strong iron line with an equivalent
width of ~2 keV, whereas that of XMM J174457-2850.3 is characterised by a very
hard continuum with photon index ~1.0. The X-ray flux of both sources varied by
more than 2 orders of magnitude over a period of months with a peak X-ray
luminosity of 5 x 10^34 erg/s. We discuss the nature of these peculiar sources. | 0310140v1 |
2003-10-06 | Emission Line Properties of AGN from a post-COSTAR FOS HST Spectral Atlas | This paper joins a series compiling consistent emission line measurements of
large AGN spectral databases, useful for reliable statistical studies of
emission line properties. It is preceded by emission line measurements of 993
spectra from the Large Bright Quasar Survey (Forster et al. 2001) and 174
spectra of AGN obtained from the Faint Object Spectrograph (FOS) on HST prior
to the installation of COSTAR (Kuraszkiewicz et al. 2002). This time we
concentrate on 220 spectra obtained with the FOS after the installation of
COSTAR, completing the emission line analysis of all FOS archival spectra. We
use the same automated technique as in previous papers, which accounts for
Galactic extinction, models blended optical and UV iron emission, includes
Galactic and intrinsic absorption lines and models emission lines using
multiple Gaussians. We present UV and optical emission line parameters
(equivalent widths, fluxes, FWHM, line positions) for a large number (28) of
emission lines including upper limits for undetected lines. Further scientific
analyses will be presented in subsequent papers. | 0310165v1 |
2003-10-08 | Determination of the calorimetric energy in extensive air showers | The contribution of different components of an air shower to the total energy
deposit in the atmosphere, for different angles and primary particles, was
studied using the CORSIKA air shower simulation code. The amount of missing
energy, parameterized in terms of the calorimetric energy, was calculated. The
results show that this parameterization varies less than 1% with angle or
observation level. The dependence with the primary mass is less than 5% and,
with the high energy hadronic interaction model, less than 2%. The systematic
error introduced by the use of just one parameterization of the missing energy
correction function, for an equal mixture of proton and iron at 45deg, was
calculated to be below 3%. We estimate the statistical error due to
shower-to-shower fluctuations to be about 1%. | 0310234v3 |
2003-10-21 | Coronal abundances from high-resolution X-ray data: The case of Algol | We discuss the determination of elemental abundances from high resolution
X-ray data. We emphasize the need for an accurate determination of the
underlying temperature structure and advocate the use of a line ratio method
which allows us to utilize, first, the strongest lines observed in the X-ray
spectra, and second, lines that span a rather wide temperature range. We point
out the need to use continuous emission measure distributions and show via
example that modeling in terms of individual temperature components yields
errors of more than 50%. We stress the need to derive differential emission
measure distributions based on physical assumptions and considerations. We
apply our methods to the Chandra LETGS spectrum of Algol and show that nitrogen
is considerably enhanced compared to cosmic abundances by a factor of 2 while
carbon is depleted by at least a factor of 25. Iron, silicon, and magnesium,
are all depleted compared to cosmic abundances, while the noble gas neon has
the relatively highest abundance. | 0310594v1 |
2003-10-21 | The Formation of the First Low-Mass Stars From Gas With Low Carbon and Oxygen Abundances | The first stars in the Universe are predicted to have been much more massive
than the Sun. Gravitational condensation accompanied by cooling of the
primordial gas due to molecular hydrogen, yields a minimum fragmentation scale
of a few hundred solar masses. Numerical simulations indicate that once a gas
clump acquires this mass, it undergoes a slow, quasi-hydrostatic contraction
without further fragmentation. Here we show that as soon as the primordial gas
- left over from the Big Bang - is enriched by supernovae to a carbon or oxygen
abundance as small as ~0.01-0.1% of that found in the Sun, cooling by
singly-ionized carbon or neutral oxygen can lead to the formation of low-mass
stars. This mechanism naturally accommodates the discovery of solar mass stars
with unusually low (10^{-5.3} of the solar value) iron abundance but with a
high (10^{-1.3} solar) carbon abundance. The minimum stellar mass at early
epochs is partially regulated by the temperature of the cosmic microwave
background. The derived critical abundances can be used to identify those
metal-poor stars in our Milky Way galaxy with elemental patterns imprinted by
the first supernovae. | 0310622v1 |
2003-10-22 | Accretion and Outflow in the AGN and Starburst of NGC 5135 | Observations of the Seyfert 2 and starburst galaxy NGC 5135 with the Chandra
X-ray Observatory demonstrate that both of these phenomena contribute
significantly to its X-ray emission. We spatially isolate the active galactic
nucleus (AGN) and demonstrate that it is entirely obscured by column density
N_H > 10^{24} cm^{-2}, detectable in the Chandra bandpass only as a strongly
reprocessed, weak continuum and a prominent iron K alpha emission line with
equivalent width of 2.4 keV. Most of the soft X-ray emission, both near the AGN
and extending over several-kpc spatial scales, is collisionally-excited plasma.
We attribute this thermal emission to stellar processes. The AGN dominates the
X-ray emission only at energies above 4 keV. In the spectral energy
distribution that extends to far-infrared wavelengths, nearly all of the
emergent luminosity below 10 keV is attributable to star formation, not the
AGN. | 0310669v1 |
2003-10-27 | Oxygen trends in the Galactic thin and thick disks | We present oxygen abundances for 72 F and G dwarf stars in the solar
neighbourhood. Using the kinematics of the stars we divide them into two
sub-samples with space velocities that are typical for the thick and thin
disks, respectively. The metallicities of the stars range from [Fe/H] = -0.9 to
+0.4 and we use the derived oxygen abundances of the stars to: (1) perform a
differential study of the oxygen trends in the thin and the thick disk; (2) to
follow the trend of oxygen in the thin disk to the highest metallicities. We
analyze the forbidden oxygen lines at 6300 {\AA} and 6363 {\AA} as well as the
(NLTE afflicted) triplet lines around 7774 {\AA}. For the forbidden line at
6300 A we have spectra of very high S/N (>400) and resolution (R=215 000). This
has enabled a very accurate modeling of the oxygen line and the blending Ni
lines. The high internal accuracy in our determination of the oxygen abundances
from this line is reflected in the very tight trends we find for oxygen
relative to iron........ | 0310741v1 |
2003-10-29 | Luminosity and Redshift Dependence of Quasar Spectral Properties | Using a large sample of quasar spectra from the SDSS, we examine the
composite spectral trends of quasars as functions of both redshift and
luminosity, independently of one another. Aside from the well known Baldwin
effect (BE) -- the decrease of line equivalent width with luminosity -- the
average spectral properties are remarkably similar. Host galaxy contamination
and the BE are the primary causes for apparent changes in the average spectral
slope of the quasars. The BE is detected for most emission lines, including the
Balmer lines, but with several exceptions including NV1240A. Emission line
shifts of several lines are associated with the BE. The BE is mainly a function
of luminosity, but also partly a function of redshift in that line equivalent
widths become stronger with redshift. Some of the complex iron features change
with redshift, particularly near the small blue bump region. | 0310840v1 |
2003-10-30 | Hints of star fomation at z>6: the chemical abundances of the DLA system in the QSO BRI 1202-0725 (z_abs = 4.383) | The Damped Ly-alpha (DLA) absorber at redshift z_abs=4.383 observed toward
QSO BRI 1202-0725 is studied by means of high resolution (FWHM ~ 7 km/s)
VLT-UVES spectra. We refine a previously determined Si abundance and derive
with confidence abundances for C, N and O which are poorly known in DLAs. The
[O/Fe] ratio is ~0.6, but we cannot establish if iron is partially locked into
dust grains. The [C/Fe]=0.08 \pm 0.13 and [Si/C]=0.31 \pm 0.07. [N/O] and
[N/Si] are about -1, which is consistent with the majority of DLAs. This value
is much larger than the one observed for the DLA toward QSO J0307-4945 at
z_abs= 4.466. The current interpretation of the bimodal distribution of N
abundances in DLAs implies that large [N/alpha] values correspond to relatively
old systems. Adopting a scale time of 500 Myrs for full N production by
intermediate mass stars, the onset of star formation in our DLA took place
already at redshift z> 6. | 0310866v1 |
2003-11-26 | Evolution and nucleosynthesis of primordial low mass stars | We discuss in detail the evolutionary properties of low mass stars M< 1
M(Solar) having metallicity lower than Z=10^(-6) from the pre- main sequence up
to (almost) the end of the Asymptotic Giant Branch phase. We also discuss the
possibility that the large [C,N/Fe] observed on the surface of the most Iron
poor star presently known, HE0107-5240, may be attributed to the autopollution
induced by the penetration of the He convective shell into the H rich mantle
during the He core flash of a low mass, very low metallicity star. On the basis
of a quite detailed analysis, we conclude that the autopollution scenario
cannot be responsible for the observed chemical composition of HE0107-5240. | 0311580v1 |
2003-12-05 | XMM-Newton observations of 3C 273 | A series of nine XMM-Newton observations of the radio-loud quasar 3C 273 are
presented, concentrating mainly on the soft excess. Although most of the
individual observations do not show evidence for iron emission, co-adding them
reveals a weak, broad line (EW ~ 56 eV). The soft excess component is found to
vary, confirming previous work, and can be well fitted with multiple blackbody
components, with temperatures ranging between ~40 and ~330 eV, together with a
power-law. Alternatively, a Comptonisation model also provides a good fit, with
a mean electron temperature of ~350 eV, although this value is higher when the
soft excess is more luminous over the 0.5-10 keV energy band. In the RGS
spectrum of 3C 273, a strong detection of the OVII He-alpha absorption line at
zero redshift is made; this may originate in warm gas in the local
intergalactic medium, consistent with the findings of both Fang et al. (2003)
and Rasmussen et al. (2003). | 0312148v1 |
2003-12-17 | Doppler broadening of the iron line and R-Gamma correlation in black hole binaries | RXTE/PCA observations of several black hole X-ray binaries in the low
spectral state revealed a tight correlation between spectral parameters and
characteristic frequencies of variability of X-ray flux. In particular, the
amplitude of reflection increases and the slope of Comptonized radiation
steepens as the noise frequencies increase. The data also suggest that there is
a correlated increase of the width of the Fe fluorescent line, probably related
to the Doppler broadening of the reflection features. Moreover, the width of
the line seems to follow DeltaE/E ~ nu_qpo^{1/3} law. If confirmed with higher
energy resolution observations, this result will have significant impact on the
models of the accretion flow and on our understanding of the nature of
characteristic frequencies of variability in X-ray binaries. In particular, it
will lend support to the truncated disk picture, confirming that the spectral
variations are indeed related to changes of the position of the inner disk
boundary and that characteristic variability frequencies are proportional to
the Keplerian frequency at the inner boundary of the accretion disk. | 0312445v1 |
2003-12-18 | Atomic and Molecular Data for Stellar Physics: Former Successes and Future Challenges | This review highlights current (and future) hot topics in astrophysics where
atomic or molecular input data are (or will be) essential, with special
emphasis on topics relating to nucleosynthesis and cosmochemistry.
We first discuss issues (like the abundances of oxygen and iron in the Sun,
and that of lithium in post-AGB stars) where the use of poor-quality atomic or
molecular data have led to spurious astrophysical puzzles which sparked fancy
astrophysical models or theories. We then address issues where the advent of
new instruments (like the ultraviolet high-resolution spectrographs--GHRS
onboard HST, Keck-HRS or VLT-UVES--or future infrared satellites) calls for new
and accurate atomic or molecular data. | 0312486v1 |
2003-12-23 | Gamma-Ray Bursts observed by XMM-Newton | Analysis of observations with XMM-Newton have made a significant contribution
to the study of Gamma-ray Burst (GRB) X-ray afterglows. The effective area,
bandpass and resolution of the EPIC instrument permit the study of a wide
variety of spectral features. In particular, strong, time-dependent, soft X-ray
emission lines have been discovered in some bursts. The emission mechanism and
energy source for these lines pose major problems for the current generation of
GRB models. Other GRBs have intrinsic absorption, possibly related to the
environment around the progenitor, or possible iron emission lines similar to
those seen in GRBs observed with BeppoSAX. Further XMM-Newton observations of
GRBs discovered by the Swift satellite should help unlock the origin of the GRB
phenomenon over the next few years. | 0312602v1 |
2004-01-09 | The Evolution of the Accretion Disk around 4U 1820-30 During a Superburst | Accretion from a disk onto a collapsed, relativistic star -- a neutron star
or black hole -- is the mechanism widely believed to be responsible for the
emission from compact X-ray binaries. Because of the extreme spatial resolution
required, it is not yet possible to directly observe the evolution or dynamics
of the inner parts of the accretion disk where general relativistic effects are
dominant. Here, we use the bright X-ray emission from a superburst on the
surface of the neutron star 4U 1820-30 as a spotlight to illuminate the disk
surface. The X-rays cause iron atoms in the disk to fluoresce, allowing a
determination of the ionization state, covering factor and inner radius of the
disk over the course of the burst. The time-resolved spectral fitting shows
that the inner region of the disk is disrupted by the burst, possibly being
heated into a thicker, more tenuous flow, before recovering its previous form
in ~1000 s. This marks the first instance that the evolution of the inner
regions of an accretion disk has been observed in real-time. | 0401154v1 |
2004-01-14 | Abundances of neutron-capture elements in the Hot Extreme-Helium Stars V1920 Cygni and HD 124448 | Analysis of HST STIS ultraviolet spectra of two hot extreme helium stars
(EHes): V1920 Cyg and HD 124448 provide the first measurements of abundances of
neutron-capture elements for EHes. Although the two stars have similar
abundances for elements up through the iron-group, they differ strikingly in
their abundances of heavier elements: V1920 Cyg is enriched by a factor of 30
in light neutron-capture elements (Y/Fe, Zr/Fe) relative to HD 124448. These
differences in abundances of neutron-capture elements among EHes mirrors that
exhibited by the RCrB stars, and is evidence supporting the view that there is
an evolutionary connection between these two groups of hydrogen-deficient
stars. Also, the abundances of Y and Zr in V1920 Cyg provide evidence that at
least one EHe star went through a s-process synthesis episode in its earlier
evolution. | 0401263v1 |
2004-01-15 | INTEGRAL observations of the transient source IGR J19140+098 | IGR J19140+098 was discovered during the early INTEGRAL observations of
GRS1915+105 in March 2003. The following observations by INTEGRAL and RXTE show
significant variability on various time scales from 100s to 1ks, but no
pulsations. The ISGRI spectra show strong spectral variability in the 20-80keV
range. Combined JEMX_2-ISGRI spectra are well fitted by a power-law and a
thermal emission model with a rather high temperature. RXTE data also reveal an
apparently broad ionised iron line not detected in earlier INTEGRAL
observations. These results are compatible with a galactic X-ray binary source. | 0401308v1 |
2004-01-25 | Propagation of electromagnetic waves in space plasma | Coherent Raman Effect on Incoherent Light (CREIL), shifts the frequencies of
normally incoherent light without any blurring of the images or altering the
order of the spectra. CREIL operates in gases having quadrupolar resonances in
the megaherz range, and it is easily confused with Doppler effects. When CREIL
is taken into account, the propagation of light in cosmic low pressure gases
involves a complex combination of absorptions and frequency shifts. Current
star theory predicts very bright accreting neutron stars. These should be
small, very hot objects surrounded by dirty atomic hydrogen. CREIL predicts
spectra for these stars that have exactly the characteristics found in the
spectra of the quasars. The intrinsic redshifting in the extended photosphere
of Quasars as defined by CREIL events drastically reduces both the size and
distance to quasars, and clearly identifies the missing neutron stars as
quasar-like objects. A full interpretation of quasar spectra does not require
jets, dark matter, a variation of the fine structure constant, or an early
synthesis of iron. CREIL is useful in explaining other astrophysical problems,
such as redshifting proportional to the path of light through the corona of the
Sun. CREIL radiation transfers may explain the blueshifting of radio signals
from Pioneer 10 and 11. | 0401529v1 |
2004-02-05 | Timing and spectral studies of the transient X-ray pulsar EXO 053109-6609.2 with ASCA and Beppo-SAX | We report timing and spectral properties of the transient Be X-ray pulsar EXO
053109--6609.2 studied using observations made with the ASCA and BeppoSAX
observatories. Though there must have been at least one spin-down episode of
the pulsar since its discovery, the new pulse period measurements show a
monotonic spin-up trend since 1996. The pulse profile is found to have marginal
energy dependence. There is also evidence for strong luminosity dependence of
the pulse profile, a single peaked profile at low luminosity that changes to a
double peaked profile at high luminosity. This suggests a change in the
accretion pattern at certain luminosity level. The X-ray spectrum is found to
consist of a simple power-law with photon index in the range of 0.4--0.8. At
high intensity level the spectrum also shows presence of weak iron emission
line. | 0402127v1 |
2004-02-10 | Implications of the central metal abundance peak in cooling core clusters of galaxies | Recent XMM-Newton observations of clusters of galaxies have provided detailed
information on the distribution of heavy elements in the central regions of
clusters with cooling cores providing strong evidence that most of these metals
come from recent SN type Ia. In this paper we compile information on the
cumulative mass profiles of iron, the most important metallicity tracer. We
find that long enrichment times (larger than 5 Gyr) are necessary to produce
the central abundance peaks. Classical cooling flows, a strongly convective
intracluster medium, and a complete metal mixing by cluster mergers would
destroy the observed abundance peaks too rapidly. Thus the observations set
strong constraints on cluster evolution models requiring that the cooling cores
in clusters are preserved over very long times. We further conclude from the
observations that the innermost part of the intracluster medium is most
probably dominated by gas originating predominantly from stellar mass loss of
the cD galaxy. | 0402216v1 |
2004-02-13 | Models for extremely metal-poor halo stars | Two alternative scenarios concerning the origin and evolution of extremely
metal-poor halo stars are investigated. The first one assumes that the stars
have been completely metal-free initially and produced observed carbon and
nitrogen overabundances during the peculiar core helium flash typical for
low-mass Population-III stars. The second scenario assumes that the initial
composition resulted from a mixture of primordial material with ejecta from a
single primordial supernovae. Both scenarios are shown to have problems in
reproducing C, N, and O abundances simultaneously, and both disagree with
observed 12C/13C-ratios,though in different directions. We concentrate on the
most iron-poor, carbon-rich object of this class, HE0107-5240, and conclude
that the second scenario presently offers the more promising approach to
understand these objects, in particular because evolutionary tracks match
observations very well. | 0402334v1 |
2004-02-26 | A Far-UV Spectroscopic Analysis of the Central Star of the Planetary Nebula Longmore 1 | We have performed a non-LTE spectroscopic analysis using far-UV and UV data
of the central star of the planetary nebula K1-26 (Longmore 1), and found Teff
= 120+/-10 kK, logg = 6.7 +0.3/-0.7, and y = 0.10. The temperature is
significantly hotter than previous results based on optical line analyses,
highlighting the importance of analyzing the spectra of such hot objects at
shorter wavelengths. The spectra show metal lines (from, e.g, carbon, oxygen,
sulfur, and iron). The signatures of most elements can be fit adequately using
solar abundances, confirming the classification of Longmore 1 as a high gravity
O(H) object. Adopting a distance of 800 pc, we derive R = 0.04 Rsun, L = 250
Lsun, and M = 0.6 Msun. This places the object on the white dwarf cooling
sequence of the evolutionary tracks with an age of ~= 65 kyr. | 0402653v1 |
2004-03-01 | An XMM-Newton study of the RGH 80 galaxy group | We present an X-ray study of the galaxy group RGH 80, observed by XMM-Newton.
The X-ray emission of the gas is detected out to ~ 462h^{-1}_{50} kpc,
corresponding to ~ 0.45 r_{200}. The group is relatively gas rich and luminous
with respect to its temperature of 1.01 +/- 0.01 keV. Using the deprojected
spectral analysis, we find that the temperature peaks at ~ 1.3 keV around
0.11r_{200}, and then decreases inwards to 0.83 keV at the center and outwards
to ~ 70% of the peak value at large radii. Within the central ~ 60 kpc of the
group where the gas cooling time is less than the Hubble time, two-temperature
model with temperatures of 0.82 and 1.51 keV and the Galactic absorption gives
the best fit of the spectra, with ~ 20% volume occupied by the cool component.
We also derive the gas entropy distribution, which is consistent with the
prediction of cooling and/or internal heating models. Furthermore, the
abundances of O, Mg, Si, S, and Fe decrease monotonically with radius. With the
observed abundance ratio pattern, we estimate that ~ 85% or ~ 72% of the iron
mass is contributed by SN Ia, depending on the adopted SN II models. | 0403026v1 |
2004-03-10 | Hydra Observations of Aluminum Abundances in the Red Giants of the Globular Clusters M80 and NGC 6752 | Aluminum and other metal abundances were determined in 21 red giants in the
globular clusters NGC 6752 and M80 as part of a larger study to determine
whether the aluminum distribution on the red giant branch is related to the
second parameter effect that causes clusters of similar metallicity to display
different horizontal branch morphologies. The observations were obtained of the
Al I lines near 6700 Angstroms with the CTIO Blanco 4-m telescope and Hydra
multi-object spectrograph. The spectra have a resolving power of 18000 or 9400,
with typical S/N ratios of 100-200. Mean [Fe/H] values obtained from the
spectra are -1.58 for NGC 6752 and -1.73 for M80; this represents the first
spectroscopic iron abundance determination for M80. Both NGC 6752 and M80
display a spread in aluminum abundance, with mean [Al/Fe] ratios of +0.51 and
+0.37, respectively. No trend in the variation of the mean Al abundance with
position on the giant branch is discernible in either cluster with our small
sample. | 0403263v1 |
2004-03-17 | Chemical Abundances in the Secondary Star in the Black Hole Binary A0620-00 | Using a high resolution spectrum of the secondary star in the black hole
binary A0620-00, we have derived the stellar parameters and veiling caused by
the accretion disk in a consistent way. We have used a chi^2 minimization
procedure to explore a grid of 800 000 LTE synthetic spectra computed for a
plausible range of both stellar and veiling parameters. Adopting the best model
parameters found, we have determined atmospheric abundances of Fe, Ca, Ti, Ni
and Al. The Fe abundance of the star is [Fe/H]=0.14 +- 0.20. Except for Ca, we
found the other elements moderately over-abundant as compared with stars in the
solar neighborhood of similar iron content. Taking into account the small
orbital separation, the mass transfer rate and the mass of the convection zone
of the secondary star, a comparison with element yields in supernova explosion
models suggests a possible explosive event with a mass cut comparable to the
current mass of the compact object. We have also analyzed the Li abundance,
which is unusually high for a star of this spectral type and relatively low
mass. | 0403402v1 |
2004-04-02 | The first broad-band persistent X-ray spectrum of the dipping low mass X-ray binary EXO 0748-676 | We report on the results of a BeppoSAX observation of the dipping LMXRB EXO
0748-676 performed in 2000 November. This is the first simultaneous observation
of this source over the 0.1-100 keV energy range. The persistent spectrum is
complex and shows a soft excess, which requires the inclusion of an ionized
absorber (with a sub-solar abundance of iron). A cutoff power-law is a good fit
to the high energy part of the spectrum, with a photon index of 1.3 and a
cutoff around 50 keV. The 0.1-100 keV luminosity is 8.2E36 erg/s. | 0404038v1 |
2004-04-02 | The complex X-ray spectrum of NGC 4507 | XMM-Newton and Chandra/HETG spectra of the Compton-thin (NH 4x10^{23}
cm^{-2}) Seyfert 2 galaxy, NGC 4507, are analyzed and discussed. The main
results are: a) the soft X-ray emission is rich in emission lines; an (at
least) two--zone photoionization region is required to explain the large range
of ionization states. b) The 6.4 keV iron line is likely emitted from
Compton-thick matter, implying the presence of two circumnuclear cold regions,
one Compton-thick (the emitter), one Compton-thin (the cold absorber). c)
Evidence of an Fe xxv absorption line is found in the Chandra/HETG spectrum.
The column density of the ionized absorber is estimated to be a few x10^{22}
cm^{-2}. | 0404050v1 |
2004-04-16 | Revealing the nature of the highly obscured galactic source IGR J16318-4848 | The X-ray source IGR J16318-4848 was the first source discovered by INTEGRAL
on 2003, January 29. We carried out optical and near-infrared (NIR)
observations at the European Southern Observatory (ESO La Silla) in the course
of a Target of Opportunity (ToO) programme. We discovered the optical
counterpart and confirmed an already proposed NIR candidate. NIR spectroscopy
revealed a large amount of emission lines, including forbidden iron lines and
P-Cygni profiles. The spectral energy distribution of the source points towards
a high luminosity and a high temperature, with an absorption greater than the
interstellar absorption, but two orders of magnitude lower than the X-ray
absorption. We show that the source is an High Mass X-ray binary (HMXB) at a
distance between ~1 and 6 kpc, the mass donor being an early-type star,
probably a sgB[e] star, surrounded by a rich and absorbing circumstellar
material. This would make the second High Mass X-ray Binary (HMXB) with a
sgB[e] star after CI Cam, indicating that a new class of strongly absorbed
X-ray binaries is being unveiled by INTEGRAL. | 0404332v1 |
2004-04-19 | Central Stars of Planetary Nebulae in the Large Magellanic Cloud: A Far-UV Spectroscopic Analysis | We observed seven central stars of planetary nebulae (CSPN) in the Large
Magellanic Cloud (LMC) with the Far Ultraviolet Spectroscopic Explorer (FUSE),
and performed a model-based analysis of these spectra in conjunction with
Hubble Space Telescope (HST) spectra in the UV and optical range to determine
the stellar and nebular parameters. Most of the objects show wind features, and
they have effective temperatures ranging from 38 to 60 kK with mass-loss rates
of ~= 5x10^-8 Msun/yr. Five of the objects have typical LMC abundances. One
object (SMP LMC 61) is a [WC4] star, and we fit its spectra with He/C/O-rich
abundances typical of the [WC] class, and find its atmosphere to be
iron-deficient. Most objects have very hot (T ~> 2000 K) molecular hydrogen in
their nebulae, which may indicate a shocked environment. One of these (SMP LMC
62) also displays OVI 1032-38 nebular emission lines, rarely observed in PN. | 0404367v1 |
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