publicationDate stringlengths 1 2.79k | title stringlengths 1 36.5k ⌀ | abstract stringlengths 1 37.3k ⌀ | id stringlengths 9 47 |
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1999-05-05 | Gamma Doradus Stars: Defining a New Class of Pulsating Variables | In this paper we describe a new class of pulsating stars, the prototype of
which is the bright, early, F-type dwarf, Gamma Doradus. These stars typically
have between 1 and 5 periods ranging from 0.4 to 3 days with photometric
amplitudes up to 0.1 in Johnson V. The mechanism for these observed variations
is high-order,... | 9905042v1 |
1999-05-20 | The rp Process Ashes from Stable Nuclear Burning on an Accreting Neutron Star | We calculate the nucleosynthesis during stable nuclear burning on an
accreting neutron star. This is appropriate for weakly magnetic neutron stars
accreting at near-Eddington rates in low mass X-ray binaries, and for most
accreting X-ray pulsars. We show that the nuclear burning proceeds via the
rapid proton capture pr... | 9905274v1 |
1999-05-26 | X-ray and radio observations of RX J1826.2-1450/LS 5039 | RX J1826.2-1450/LS 5039 has been recently proposed to be a radio emitting
high mass X-ray binary. In this paper, we present an analysis of its X-ray
timing and spectroscopic properties using different instruments on board the
RXTE satellite. The timing analysis indicates the absence of pulsed or periodic
emission on ti... | 9905344v1 |
1999-06-09 | A Method of Mass Measurement in Black Hole Binaries Using Timing and High Resolution X-ray Spectroscopy | In X-ray binaries, several percent of the compact object luminosity is
intercepted by the surface of the normal companion and re-radiated through
Compton reflection and the K-fluorescence. This reflected emission follows the
variability of the compact object with a delay approximately equal to the
orbital radius divide... | 9906170v1 |
1999-07-08 | An Ultraviolet Fe II Image of SN 1885 in M31 | Ultraviolet imaging of the remnant of Supernova 1885 in M31 with the Hubble
Space Telescope using the F255W filter on the WFPC2 reveals a dark spot of Fe
II absorption at the remnant's known position in the bulge of M31. The diameter
of the absorbing spot is 0"55 +- 0"15, slightly smaller than, but consistent
with, the... | 9907102v1 |
1999-07-14 | X-ray dependencies on luminosity in AGN | Several X-ray properties of active galactic nuclei depend, or appear to
depend, on their luminosity. It has long been suggested that alpha o-x, the
X-ray ``loudness'' decreases with luminosity. There never has been a
satisfactory explanation of this observational claim, and the statistical
soundness of the result has b... | 9907192v1 |
1999-07-15 | Stroemgren photometry of globular clusters: M55 & M22 | We present Stroemgren CCD photometry for the two galactic globular clusters
M55 (NGC 6809) and M22 (NGC 6656). We find average Stroemgren metallicities of
-1.71 dex for M55 and -1.62 dex for M22. The determination of metal abundances
in cluster giants with the Stroemgren m1 index in comparison with spectroscopic
data f... | 9907200v1 |
1999-07-15 | Fitting the spectrum of the X-ray background: the effects of high metallicity absorption | Recent work by Risaliti et al.(1999) suggests that more than half of all
Seyfert 2 galaxies in the local universe are Compton-thick (N_H > 10^24 cm^-2).
This has implications for AGN synthesis models for the X-ray background (XRB),
the flexibility of which for the inclusion of large numbers of high-z type 2
sources we ... | 9907204v1 |
1999-07-27 | Testing Narrow-line Seyfert 1 scenarios with photoionization models | Narrow Line Seyfert 1 (NLSy1) galaxies have recently received a lot of
attention due to their unusual optical--X-ray properties which are not yet well
understood. Photoionization models of the circum-nuclear emission/absorption
regions allow to investigate scenarios to explain the main characteristics of
NLSy1s, i.e., ... | 9907373v1 |
1999-08-06 | Iron K-alpha line profiles driven by non-axisymmetric illumination | Previous calculations of Fe K-alpha line profiles are based on axisymmetric
emissivity laws. In this paper, we show line profiles driven by non-axial
symmetric illumination which results from an off-axis X-ray point source. We
find that source location and motion have significant effects on the red wing
and blue horn o... | 9908079v1 |
1999-08-24 | GRB: A Signature of Phase Transition to QGP? | It is suggested that the inner energetic engine of Gamma ray burst (GRB) may
be the result of the transition of normal hadron to quark-gluon plasma (QGP) in
rapidly-rotating and spin-down newborn neutron star. When such a nascent
neutron star slows down through dipole electromagnetic and quadruple
gravitational radiati... | 9908262v1 |
1999-09-27 | Blue Horizontal--Branch Stars: The "Jump" in Stromgren u, Low Gravities, and Radiative Levitation of Metals | We study the ``jump'' in the blue horizontal--branch (BHB) distribution first
detected by Grundahl et al. (1998) in the Galactic globular cluster (GC) M13.
On the basis of Stromgren photometry for a sample of fourteen GC's we show
that: 1) The jump is best characterized as a systematic shift, on a (u, u-y)
color-magnit... | 9909448v1 |
1999-09-30 | NLTE Model Atmospheres for Central Stars of Planetary Nebulae | Present observational techniques provide stellar spectra with high resolution
at a high signal-to-noise ratio over the complete wavelength range -- from the
far infrared to the X-ray.
NLTE effects are particularly important for hot stars, hence the use of
reliable NLTE stellar model atmosphere fluxes is required for ... | 9909507v1 |
1999-10-04 | X-ray spectral components from a broad band BeppoSAX observation of the Seyfert galaxy IC 4329A | From the spectral analysis of a broadband (0.1-200 keV) BeppoSAX observation
of the Seyfert 1 galaxy IC 4329A, the main results obtained are: a) the amount
of reflection, together with the intensity of the iron K line, indicate a
geometry with a solid angle substantially less than 2pi; b) the power law is
affected by a... | 9910054v1 |
1999-10-14 | The nature of the hard X-ray power-law tail in M87 | Spatially-resolved spectroscopy of the elliptical galaxy M87 with the MECS
instrument on board BeppoSAX demonstrates that the hard X-ray power-law tail,
originally discovered by ASCA (Matsumoto et al 1996; Allen et al. 1999),
originates in the innermost 2'. Our results are consistent with it being
produced in an Accret... | 9910271v1 |
1999-10-20 | The r-Process Enriched Low Metallicity Giant HD 115444 | New high resolution, very high signal-to-noise spectra of ultra-metal-poor
(UMP) giant stars HD 115444 and HD 122563 have been gathered with the
High-Resolution Echelle Spectrometer of the McDonald Observatory 2.7m
Telescope. With these spectra, line identification and model atmosphere
analyses have been conducted, emp... | 9910376v1 |
1999-10-27 | Metallicity distribution of bulge planetary nebulae and the [O/Fe] x [Fe/H] relation | The O/H metallicity distribution of different samples of planetary nebulae in
the bulge of the Milky Way and M31 are compared. O/H abundances are converted
into [Fe/H] metallicity by the use of theoretical [O/Fe] x [Fe/H] relationships
both for the bulge and the solar neighbourhood. It is found that these
relationships... | 9910496v1 |
1999-11-01 | Effects of Kerr Spacetime on Spectral Features from X-Ray Illuminated Accretion Discs | We performed detailed calculations of the relativistic effects acting on both
the reflection continuum and the iron line from accretion discs around rotating
black holes. Fully relativistic transfer of both illuminating and reprocessed
photons has been considered in Kerr spacetime. We calculated overall spectra,
line p... | 9910562v1 |
1999-11-05 | Pulsar Kick and Asymmetric Iron Velocity Distribution in SN 1987A | We have investigated the relation of the direction of the momentum among the
matter, neutrino, and proto-neutron star in a collapse-driven supernova in
order to discuss the pulsar kick. In particular, we have investigated the
effects of the pulsar motion on the explosion, which are neglected in the
previous study. As a... | 9911077v2 |
1999-12-03 | The Type Ib/c Supernova, Gamma-Ray Burst, Soft Gamma-Ray Repeater, Magnetar Connection | The polarization of core-collapse supernovae shows that many if not all of
these explosions must be strongly bi-polar. The most obvious way to produce
this axial symmetry is by the imposition of a jet as an intrinsic part of the
explosion process. These jets could arise by MHD processes in the formation of
pulsars and ... | 9912080v2 |
1999-12-07 | Spectral analysis of four multi mode pulsating sdB stars | Four members of the new class of pulsating sdB stars are analysed from Keck
HIRES spectra using NLTE and LTE model atmospheres. Atmospheric parameters
(Teff, log g, log(He/H)), metal abundances and rotational velocities are
determined. Balmer line fitting is found to be consistent with the helium
ionization equilibrium... | 9912133v1 |
2000-01-18 | Implications of Abundance Gradients in Intracluster Gas | Analysis of spatially resolved ASCA spectra of the intracluster gas in Abell
496 confirms that metal abundances increase toward the center. We also find
spatial gradients in several abundance ratios, indicating that the fraction of
iron from SN Ia increases toward the cluster center. The dominant metal
enrichment mecha... | 0001304v1 |
2000-01-25 | X-Ray Afterglows of Gamma-Ray Bursts | The afterglow emission has become the main stream of Gamma-Ray burst research
since its discovery three years ago. With the distance-scale enigma solved, the
study of the late-time GRB emission is now the most promising approach to
disclose the origin of these explosions and their relationship with the
environment of t... | 0001436v1 |
2000-01-27 | LiBeB Production and Associated Astrophysical Sites | The various modes of spallative LiBeB production are summarized, and
classified according to their dependence or independence on the abundance of
medium heavy elements (CNO) illustrated by that of oxygen in the interstellar
medium.
The predictions of the models are confronted to the available observational
correlatio... | 0001474v1 |
2000-02-08 | The hard X-ray properties of the Seyfert nucleus in NGC 1365 | We present BeppoSAX observations of the Seyfert 1.8 galaxy NGC1365 in the
0.1--100 keV range. The source was 6 times brighter than during an ASCA
observation 3 years earlier. The 4--10 keV flux is highly variable during the
BeppoSAX observation, while the soft (0.1-4 keV) emission is constant within
the errors. Both a ... | 0002169v1 |
2000-03-02 | Gamma-loud quasars: a view with BeppoSAX | We present $Beppo$SAX observations of the $\gamma $-ray emitting quasars
0836+710, 1510-089 and 2230+114. All the objects have been detected in the PDS
up to 100 keV and have extremely flat power-law spectra above 2 keV ($\alpha
_x$=0.3--0.5). 0836+710 shows absorption higher than the galactic value and
marginal eviden... | 0003019v1 |
2000-03-13 | Grain Survival in Supernova Remnants and Herbig-Haro Objects | By using the flux ratio [FeII]8617/[OI]6300, we demonstrate that most of the
interstellar dust grains survive in shocks associated with supernova remnants
and Herbig-Haro objects. The [FeII]/[OI] flux ratio is sensitive to the
gas-phase Fe/O abundance ratio, but is insensitive to the ionization state,
temperature, and ... | 0003170v1 |
2000-03-27 | Massive Stars in the Range $\rm 13-25 M_\odot$: Evolution and Nucleosynthesis. II. the Solar Metallicity Models | We present the evolutionary properties of a set of massive stellar models
(namely 13, 15, 20 and 25 $\rm M_\odot$) from the main sequence phase up to the
onset of the iron core collapse. All these models have initial solar chemical
composition, i.e. Y=0.285 and Z=0.02. A 179 isotope network, extending from
neutron up t... | 0003401v1 |
2000-04-03 | The Absolute Abundance of Iron in the Solar Corona | We present a measurement of the abundance of Fe relative to H in the solar
corona using a technique which differs from previous spectroscopic and solar
wind measurements. Our method combines EUV line data from the CDS spectrometer
on SOHO with thermal bremsstrahlung radio data from the VLA. The coronal Fe
abundance is ... | 0004007v1 |
2000-04-25 | Non-LTE Abundances and Consequences for the Evolution of the alpha elements in the Galaxy | Abundances of alpha-elements such as Ca and Mg in disk and halo stars are
usually derived from equivalent widths lines measured on high resolution
spectra, and assuming Local Thermodynamic Equilibrium (LTE) . In this paper, we
present non-LTE differential abundances derived by computing the statistical
equilibrium of C... | 0004337v1 |
2000-05-04 | Oscillating structure of γ-bursts and their possible origin | As it is well-known that the hydrodinamic collapse of the massive star iron
core should lead to the production of a hot neutron star. The assumption is
made that the thermonuclear burning of the envelope matter, accreting onto the
hot neutron star, can proceed in the oscillatoric regime (analogously to that
happens dur... | 0005078v1 |
2000-05-04 | Composition of UHE Cosmic Ray Primaries | Project GRAND presents results on the atomic composition of primary cosmic
rays. This is accomplished by determining the average height of primary
particles that cause extensive air showers detected by Project GRAND. Particles
with a larger cross sectional area, such as iron nuclei, are likely to start an
extensive air... | 0005089v1 |
2000-05-08 | X-ray Continuum Slope and X-ray Spectral Features in NLS1 Galaxies | The idea that some of the unusual features in the X-ray spectra of
Narrow-Line Seyfert 1 galaxies (NLS1s) are due to the steep X-ray continuum is
tested by comparing photoionization model calculations with various observed
properties of Seyfert 1 galaxies. A meaningful comparison must involve the
careful use of the rig... | 0005142v1 |
2000-05-08 | The Fe II problem in NLS1s | For more than twenty years, strong Fe II emission lines have been observed in
Active Galactic Nuclei and in particular in Narrow Line Seyfert 1 galaxies. A
quick overview of the observations and of the models proposed to interpret the
Fe II spectrum is given. The influence of atomic data and of physical
parameters are ... | 0005153v1 |
2000-05-08 | X-ray reprocessing in Narrow-Line Seyfert 1 Galaxies: Ton S180 and Ark 564 | We present the results of spectral analysis of the ASCA data for the
Narrow-Line Seyfert 1 galaxy (NLS1) Ton S180 and simultaneous ASCA and RXTE
data modelling for the NLS1 Ark 564. We model both the primary and reflected
continuum as well as the iron K alpha line, the energy of which depends on the
ionization state of... | 0005156v1 |
2000-05-08 | Modelling of the X-ray broad absorption features in Narrow-Line Seyfert 1s | We investigate the origin of the broad absorption features detected near
1-1.4 keV in several Narrow Line Seyfert 1 galaxies, by modelling the absorbing
medium with various physical parameters, using the ionization code PEGAS. The
observed properties of the X-ray absorption features can be reproduced by
taking into acc... | 0005169v1 |
2000-05-08 | Studies of the high luminosity quasar, PDS 456 | X-ray and multi-wavelength observations of the most luminous known local
(z<0.3) AGN, the recently discovered radio-quiet quasar PDS 456, are presented.
The spectral energy distribution shows that PDS 456 has a bolometric luminosity
of 1e47 erg/s, peaking in the UV. The X-ray spectrum obtained by ASCA and RXTE
shows co... | 0005175v1 |
2000-06-02 | Equilibrium configurations of relativistic White Dwarfs | The Feynman-Metropolis-Teller treatment for compressed atoms is here
reconsidered in the framework of the relativistic generalised Fermi-Thomas
model, obtained by Ruffini et al. Physical properties of a zero temperature
plasma is thus investigated and the resulting equation of state, which keeps
into account quantum, r... | 0006036v1 |
2000-06-03 | Analysis of Four A-F Supergiants in M31 from Keck HIRES Spectroscopy | The first stellar abundances in M31 are presented, based on Keck I HIRES
spectroscopy and model atmospheres analyses of three A-F supergiants, 41-2368,
41-3712, and A-207. We also present the preliminary analysis of a fourth star,
41-3654. We find that the stellar oxygen abundances are in good agreement with
those dete... | 0006046v1 |
2000-06-20 | The Effect of Diffusion on Pulsations of Stars on the Upper Main Sequence. delta Scuti and Metallic A Stars | Recent dramatic improvements in the modeling of abundance evolution due to
diffusion in A stars have been achieved with the help of monochromatic opacity
tables from the OPAL group. An important result in the context of stellar
pulsations is the substantial helium abundance shown to be left over in the
driving region o... | 0006272v1 |
2000-06-23 | The Metallicity Distribution Function of Red Giants in the LMC | We report new metallicity determinations for 39 red giants in a 220 square
arcminute region, 1.8 degrees southwest of the bar of the Large Magellanic
Cloud. These abundance measurements are based on spectroscopy of the Ca II
infrared triplet. The metallicity distribution function (MDF) shows a strong
peak at [Fe/H] = -... | 0006327v1 |
2000-07-05 | Face-on galaxies NGC 524 and NGC 6340: chemically decoupled nuclei and inclined circumnuclear disks | Central regions of the early-type disk galaxies NGC 524 and NGC 6340 have
been investigated with the Multi-Pupil Field Spectrograph at the 6m telescope
of the Special Astrophysical Observatory of the Russian Academy of Sciences. I
confirm the existence of chemically distinct stellar nuclei in these galaxies
which have ... | 0007051v1 |
2000-07-06 | Galaxy Mergers: A Search for Chemical Signatures | We have gathered high resolution echelle spectra for more than two dozen
high-velocity metal-poor field stars, including BD+80 245, a star previously
known to have extremely low [alpha/Fe] abundances, as well as G4-36, a new
low-alpha star with unusually large [Ni/ Fe]. In this kinematically selected
sample, other chem... | 0007065v1 |
2000-07-17 | Compton-Thick X-ray Absorption in the Seyfert Galaxies Tololo 0109-383 and ESO 138-G1 | We present analyses of the ASCA X-ray spectra of two Seyfert galaxies, Tololo
0109-383 and ESO 138-G1. In both cases, spectral fitting reveals two
statistically acceptable continuum models: Compton reflection and partial
covering. Both spectra have strong iron K-alpha lines, with equivalent widths
greater than 1.5 keV.... | 0007237v2 |
2000-07-21 | Probing Dense Matter in the cores of AGN: Observations with RXTE and ASCA | Preliminary results from an X-ray spectral study of Seyfert 1 galaxies with
ASCA and RXTE are presented. From an analysis of X-ray reprocessing features of
Compton reflection and Fe K-alpha fluorescence, it is found that iron line
strength is not necessarily a good predictor of the amount of reflection. The
variability... | 0007327v1 |
2000-07-27 | Presupernova collapse models with improved weak-interaction rates | Improved values for stellar weak interaction rates have been recently
calculated based upon a large shell model diagonalization. Using these new
rates (for both beta decay and electron capture), we have examined the
presupernova evolution of massive stars in the range 15-40 Msun. Comparing our
new models with a standar... | 0007412v1 |
2000-08-04 | On the peculiar X-ray properties of the bright nearby radio-quiet quasar PDS456 | BeppoSAX and ASCA observations of the nearby (z=0.184), high-luminosity,
radio-quiet quasar PDS456 are presented. The X-ray spectrum is characterized by
a prominent ionized edge at 8-9 keV (originally discovered by RXTE, Reeves et
al. 2000) and by a soft excess below 1.5 keV. The lack of any significant iron
K alpha em... | 0008090v1 |
2000-08-22 | Interstellar X-ray Absorption Spectroscopy of Oxygen, Neon, and Iron with the Chandra LETGS Spectrum of X0614+091 | We find resolved interstellar O K, Ne K, and Fe L absorption spectra in the
Chandra Low Energy Transmission Grating Spectrometer spectrum of the low mass
X-ray binary X0614+091. We measure the column densities in O and Ne, and find
direct spectroscopic constraints on the chemical state of the interstellar O.
These meas... | 0008349v1 |
2000-08-23 | Strangeness in Neutron Stars | It is generally agreed on that the tremendous densities reached in the
centers of neutron stars provide a high-pressure environment in which numerous
novel particles processes are likely to compete with each other. These
processes range from the generation of hyperons to quark deconfinement to the
formation of kaon con... | 0008376v1 |
2000-09-27 | Unusual Properties of X-Ray Emission near the Galactic Center | The X-ray spectrum in a $1^{\circ}\times1^{\circ}$ region of the Galactic
center observed with the ASCA satellite is examined in detail, following the
first report by Koyama et al. (1996, AAA 65.155.208). The observed spectrum
contains prominent emission lines from helium-like and hydrogen-like ions of
various elements... | 0009445v1 |
2000-09-29 | The beryllium abundance in the very metal-poor halo star G 64-12 from VLT/UVES observations | We report on a new spectroscopic analysis of the very metal deficient star G
64-12 ([Fe/H]=-3.3), aimed at determining, for the first time, its Be content.
The spectra were observed during the Science Verification of UVES, the ESO VLT
Ultraviolet and Visible Echelle Spectrograph. The high resolution (~48,000) and
high ... | 0009482v1 |
2000-10-06 | ASCA Observation of an X-Ray-Luminous Active Nucleus in Markarian 231 | We have obtained a moderately long (100 kilosecond) ASCA observation of the
Seyfert 1 galaxy Markarian 231, the most luminous of the local ultraluminous
infrared galaxy (ULIRG) population. In the best-fitting model we do not see the
X-ray source directly; the spectrum consists of a scattered power-law component
and a r... | 0010125v1 |
2000-10-13 | Iron K-alpha Emission from a Decaying Magnetar Model of Gamma-Ray Bursts | The recent report of X-ray Fe features in the afterglow of the gamma-ray
burst GRB 991216 may provide important clues for identifying the nature of its
progenitor and constraining the burst mechanism. We argue that the strong line
emission can be attributed to the interaction of a continuing (but decaying)
post-burst r... | 0010258v1 |
2000-11-09 | Population synthesis of neutron stars, strange (quark) stars and black holes | We compute and present the distribution in mass of single and binary neutron
stars, strange stars, and black holes. The calculations were performed using a
stellar population synthesis code. We follow all phases of single and binary
evolution, starting from a ZAMS binary and ending in the creation of one
compact object... | 0011183v1 |
2000-11-14 | The 2000 outburst of the recurrent nova CI Aquilae: optical spectroscopy | We present low- and medium resolution spectra of the recurrent nova CI
Aquilae taken at 14 epochs in May and June, 2000. The overall appearance is
similar to other U Sco-type recurrent novae (U Sco, V394 CrA). Medium
resolution (R=7000-10000) hydrogen and iron profiles suggest an early expansion
velocity of 2000-2500 k... | 0011270v1 |
2000-11-28 | Chandra detection of reflected X-ray emission from the type 2 QSO in IRAS 09104+4109 | We present X-ray imaging spectroscopy of the extremely luminous infrared
galaxy IRAS 09104+4109 (z=0.442) obtained with the Chandra X-ray Observatory.
With the arcsec resolution of Chandra, an unresolved source at the nucleus is
separated from the surrounding cluster emission. A strong iron K line at 6.4
keV on a very ... | 0011518v1 |
2000-12-01 | The Seyfert-Starburst Connection in X-rays. I. The Data | We analyze X-ray spectra and images of a sample of Seyfert 2 galaxies that
unambiguously contain starbursts, based on their optical and UV
characteristics. Although all sample members contain active galactic nuclei
(AGNs), supermassive black holes or other related processes at the galactic
centers alone cannot account ... | 0012035v1 |
2000-12-05 | Chandra--ASCA--RXTE observations of the micro-quasar GRS 1915+105 | A Chandra AO1 30ks HETGS observation of the X-ray transient micro-quasar GRS
1915+105 reveals absorption edges and faint line emission over the HETG energy
range. We find from a preliminary analysis evidence for prominent neutral K
edges associated with iron, silicon, magnesium, and tentatively sulphur. The
column dens... | 0012111v1 |
2000-12-17 | Stellar spectroscopy far beyond the Local Group | Multi-object spectroscopic observations of blue supergiants in NGC 3621, a
spiral galaxy at a distance of 6.7 Mpc, carried out with the ESO VLT and FORS
are presented. We demonstrate the feasibility of quantitative stellar
spectroscopy at distances approaching a ten-fold increase over previous
investigations by determi... | 0012372v1 |
2001-02-15 | Ionized Iron Lines in X-ray Reflection Spectra | We present results from new calculations of the X-ray reflection spectrum
from ionized accretion discs. These computations improve on our previous models
by including the condition of hydrostatic balance in the vertical direction,
following the work of Nayakshin, Kazanas & Kallman. We find that an ionized Fe
K$\alpha$ ... | 0102268v2 |
2001-03-11 | Contribution of nuclei accelerated by gamma-ray pulsars to cosmic rays in the Galaxy | We consider the galactic population of gamma-ray pulsars as possible sources
of cosmic rays at and just above the ``knee'' in the observed cosmic ray
spectrum at $10^{15}$--$10^{16}$ eV. We suggest that iron nuclei may be
accelerated in the outer gaps of pulsars, and then suffer partial
photo-disintegration in the non-... | 0103160v1 |
2001-03-14 | The Early Formation, Evolution and Age of the Neutron-Capture Elements in the Early Galaxy | Abundance observations indicate the presence of rapid-neutron capture (i.e.,
r-process) elements in old Galactic halo and globular cluster stars. These
observations demonstrate that the earliest generations of stars in the Galaxy,
responsible for neutron-capture synthesis and the progenitors of the halo
stars, were rap... | 0103222v1 |
2001-03-26 | A hard X-ray constraint on the presence of an AGN in the ultra-luminous infrared galaxy Arp220 | We present X-ray results on the ultraluminous infrared galaxy Arp220 obtained
with BeppoSAX. The X-ray emission up to 10 keV is detected. No significant
signal is detected with the PDS detector in the higher energy band. The 2-10
keV emission has a hard spectrum (photon-index of 1.7), similar to M82, and a
luminosity o... | 0103417v1 |
2001-03-26 | Precipitating Condensation Clouds in Substellar Atmospheres | We present a method to calculate vertical profiles of particle size
distributions in condensation clouds of giant planets and brown dwarfs. The
method assumes a balance between turbulent diffusion and sedimentation in
horizontally uniform cloud decks. Calculations for the Jovian ammonia cloud are
compared with results ... | 0103423v2 |
2001-04-10 | Oxygen Abundances in Metal-Poor Stars (-2.2 < [Fe/H] < -1.2) from Infrared OH lines | Infrared OH lines at 1.55 - 1.56 um in the H-band were obtained with the
Phoenix high-resolution spectrograph at the 2.1m telescope of the Kitt Peak
National Observatory for a sample of 14 metal-poor stars. Detailed analyses of
the sample stars have been carried out, deriving stellar parameters based on
two methods: (a... | 0104184v1 |
2001-04-11 | Evolution of Lithium-Beryllium-Boron and Oxygen in the early Galaxy | Oxygen is a much better evolutionary index than iron to describe the history
of Lithium-Beryllium-Boron (LiBeB) since it is the main producer of these light
elements at least in the early Galaxy. The O-Fe relation is crucial to the
determination of the exact physical process responsible for the LiBeB
production. At low... | 0104194v1 |
2001-04-12 | NLTE Synthetic Spectral Fits to the Type Ia Supernova 1994D in NGC 4526 | We have fit the normal, well observed, Type Ia Supernova (SN Ia) SN 1994D
with non-LTE spectra of the deflagration model W7. We find that well before
maximum luminosity W7 fits the optical spectra of SN 1994D. After maximum
brightness the quality of the fits weakens as the spectrum forms in a core rich
in iron peak ele... | 0104225v1 |
2001-04-17 | A Search for Fine Structure of the Knee in EAS Size Spectra | 28 size spectra of extensive air showers from 7 different experiments are
analysed consistently. They are fitted by adjusting either 4 or 5 parameters:
knee position, power law exponents above and below the knee, overall intensity
and, in addition, a parameter describing the smoothness of the bend. The
residuals are th... | 0104282v1 |
2001-06-04 | Ionisation Structure in Accretion Shocks with a Composite Cooling Function | We have investigated the ionisation structure of the post-shock regions of
magnetic cataclysmic variables using an analytic density and temperature
structure model in which effects due to bremsstrahlung and cyclotron cooling
are considered. We find that in the majority of the shock-heated region where
H- and He-like li... | 0106052v1 |
2001-06-04 | L-dwarf variability: Magnetic star spots or non-uniform clouds? | The recent discovery of photometric variations in L dwarfs has opened a
discussion on the cause of the variations. We argue against the existence of
magnetic spots in these atmospheres and favor the idea that non-uniform
condensate coverage (i.e. clouds) is responsible for the variations. The
magnetic Reynolds number (... | 0106062v1 |
2001-06-06 | The nebular spectra of the hypernova SN 1998bw and evidence for asymmetry | The nebular spectra of the energetic Type Ic supernova SN1998bw (hypernova)
are studied. The transition to the nebular phase occurred at an epoch of about
100 days after outburst, which is assumed to coincide with GRB980425. Early in
the nebular epoch the spectra show the characteristics of a typical SN Ic
spectrum, wi... | 0106095v1 |
2001-06-12 | The Stellar Parameters and Evolutionary State of the Primary in the d'-Symbiotic System StH\alpha190 | We report on a high-resolution, spectroscopic stellar parameter and abundance
analysis of a d' symbiotic star: the yellow component of StH\alpha190. This
star has recently been discovered, and confirmed here, to be a rapidly rotating
(vsini=100 km/s) subgiant, or giant, that exhibits radial-velocity variations
of proba... | 0106215v1 |
2001-06-13 | ASCA observations of massive medium-distant clusters of galaxies. II | We have selected seven medium-distant clusters of galaxies (z ~ 0.1 - 0.3)
for multi-wavelength observations with the goal of investigating their
dynamical state. Following Paper I (Pierre et al. 1999) which reported the ASCA
results about two of them, we present here the analysis of the ASCA
observations of the other ... | 0106248v1 |
2001-06-19 | Bremsstrahlung of Flavor-Degenerate Pairs by Neutrinos in the Nuclear Field | Neutrino Bremsstrahlung of flavor-degenerate pairs in the field of a nucleus
is of potential importance for neutrino astrophysics and is representative of a
class of processes connecting leptonic electroweak sectors to real or virtual
photons. We focus on first generation flavor production by both electron and
muon neu... | 0106317v2 |
2001-06-19 | The K-alpha complex of He-like iron with dielectronic satellites | It is shown that the dielectronic satellites (DES) dominate X-ray spectral
formation in the 6.7 keV K-alpha complex of Fe XXV at temperatures below that
of maximum abundance in collisional ionization equilibrium T_m. Owing to their
extreme temperature sensitivity the DES are excellent spectral diagnostics for
T < T_m i... | 0106330v1 |
2001-07-05 | Spectral Indices of Stars at Super-solar Regime | We derived Lick narrow-band indices for 139 candidate super metal-rich stars
of different luminosity class previously studied in Malagnini et al. (2000).
Indices include Iron Fe50, Fe52, Fe53, and Magnesium Mgb and Mg2 features. By
comparing observations with Kurucz' synthetic model atmospheres, no evidence is
found fo... | 0107105v1 |
2001-07-06 | In-flight performances of SilEye-2 Experiment and cosmic ray abundances inside space station Mir | Cosmic ray measurements performed with the instrument SilEye-2 on Mir space
station are presented. SilEye-2 is a silicon detector telescope for the study
of the causes of Light Flashes perception by astronauts. As a stand-alone
device, it monitors in the short and long term the radiation composition inside
Mir. The cos... | 0107128v1 |
2001-07-13 | BeppoSAX observations of the Narrow-Line Seyfert 1 galaxy RX J1702.5+3247 | We report optical, radio and X-ray observations of the Narrow-Line Seyfert 1
galaxy RX J1702.5+3247. The soft (0.1-2 keV) X-ray flux, measured by BeppoSAX,
is characterized by strong variability on short time scales (< 500 sec). The
most extreme amplitude variations require a radiative efficiency exceeding the
maximum ... | 0107240v1 |
2001-07-18 | A Possible Emission Feature in an X-ray Afterglow of GRB970828 as a Radiative Recombination Edge | A gamma-ray burst of 28 August 1997 was localized by the All-Sky Monitor on
the Rossi XTE satellite and its coordinates were promptly disseminated. An ASCA
followup started 1.17 days after the burst as a Target of Opportunity
Observation and detected an X-ray afterglow. The spectral data displayed a hump
around ~5 keV ... | 0107331v1 |
2001-08-28 | Neutrinos from Early-Phase, Pulsar-Driven Supernovae | Neutron stars, just after their formation, are surrounded by expanding,
dense, and very hot envelopes which radiate thermal photons. Iron nuclei can be
accelerated in the wind zones of such energetic pulsars to very high energies.
These nuclei photo-disintegrate and their products lose energy efficiently in
collisions ... | 0108447v2 |
2001-09-07 | X-ray Spectra and Light Curves of AR Lac: Temperature Structure, Abundances, and Variability | We observed AR Lac, an eclipsing RS CVn binary star, with the Chandra High
Energy Grating Spectrometer for a total of 100 ks divided into six intervals
covering both quadratures and eclipses. We repeated observations at each phase.
At least two flares were seen, in which the flux increased by factors of two
and four. T... | 0109120v1 |
2001-09-10 | A multivariate study of mass composition for simulated showers at the Auger South Observatory | The output parameters from the ground array of the Auger South observatory,
were simulated for the typical instrumental and environmental conditions at its
Malarg\"ue site using the code sample-sim. Extensive air showers started by
photons, protons and iron nuclei at the top of the atmosphere were used as
triggers. The... | 0109140v1 |
2001-09-18 | Inclinations and black hole masses of Seyfert 1 galaxies | A tight correlation of black hole mass and central velocity dispersion has
been found recently for both active and quiescent galaxies. By applying this
correlation, we develop a simple method to derive the inclination angles for a
sample of 11 Seyfert 1 galaxies that have both measured central velocity
dispersions and ... | 0109283v1 |
2001-09-19 | Soft X-Ray Absorption by Fe$^{0+}$ to Fe$^{15+}$ in Active Galactic Nuclei | A full set of calculations is presented for inner-shell n = 2 to 3
photoexcitation of the 16 iron charge states: Fe I through Fe XVI. The blend of
the numerous absorption lines arising from these excitations (mainly 2p - 3d)
forms an unresolved transition array (UTA), which has been recently identified
as a prominent f... | 0109314v1 |
2001-09-21 | The Chandra LETGS high resolution X-ray spectrum of the isolated neutron star RX J1856.5-3754 | We present the Chandra LETGS X-ray spectrum of the nearby (~60 pc) neutron
star RX J1856.5-3754. Detailed spectral analysis of the combined X-ray and
optical data rules out the nonmagnetic neutron star atmosphere models with
hydrogen, helium, iron and solar compositions. We also conclude that strongly
magnetized atmosp... | 0109374v1 |
2001-09-28 | Molybdenum Evidence for Inherited Planetary Scale Isotope Heterogeneity of the Protosolar Nebula | Isotope anomalies provide important information about early solar system
evolution. Here we report molybdenum isotope abundances determined in samples
of various meteorite classes. There is no fractionation of molybdenum isotopes
in our sample set within 0.1 permil and no contribution from the extinct
radionuclide 97Tc... | 0109549v1 |
2001-10-08 | Abundances and Kinematics of Field Stars II: Kinematics and Abundance Relationships | As an investigation of the origin of ``$\alpha$-poor'' halo stars, we analyze
kinematic and abundance data for 73 intermediate metallicity stars ($-1 >$
[Fe/H] $\geq -2$) selected from Paper I of this series. We find evidence for a
connection between the kinematics and the enhancement of certain
element-to-iron ([X/Fe]... | 0110164v1 |
2001-11-01 | Extremely Weak Reflection Features in the X-ray Spectrum of XTE J1118+480: Possible Evidence for X-ray-Emitting Jets? | We have simultaneously fit Chandra and RXTE spectra of the Galactic black
hole XTE J1118+480 with three models for X-ray reflection. We explored a range
of accretion disc ionizations (log(xi)=1-4; xi=L_X/nR^{2}) and iron abundances
(0.10-1.00). Our fits with the constant density ionized disc models of Ross &
Fabian ind... | 0111027v2 |
2001-11-02 | Evidence for Accretion: High-Resolution X-ray Spectroscopy of the Classical T Tauri Star TW Hydrae | We present high resolution X-ray spectra of the X-ray bright classical T
Tauri star, TW Hydrae, covering the wavelength range of 1.5-25 AA. The
differential emission measure derived from fluxes of temperature-sensitive
emission lines shows a plasma with a sharply peaked temperature distribution,
peaking at log T = 6.5.... | 0111049v1 |
2001-11-02 | Disclosing the true nature of the Sy 2 galaxy NGC 3281: one more Compton-thick source | We present the BeppoSAX broad-band X-ray spectrum of the Seyfert 2 galaxy NGC
3281. The source high-energy spectrum is characterized by the nuclear
transmitted component, with an absorbing column density of about 2 10^24 cm^-2,
while the MECS spectrum is reflection-dominated, with a prominent (EW about
0.5-1.2 keV) iro... | 0111056v1 |
2001-11-15 | Millions of Single Cloud Weak MgII Systems | We report on a population of absorption systems selected by the presence of
very weak Mg II doublets. A sub-population of these systems are iron enriched
and have near solar metallicities. This would indicated advanced stages (i.e.
few Gyr) of in situ star formation within the absorbing structures. From
photoionization... | 0111315v1 |
2001-11-21 | Chandra Grating Observations of Seyfert 1 Galaxies | We present new results from a Chandra HETG observation of NGC 5548 and give a
comparison of absorption and emission features found in other Seyfert 1
galaxies using Chandra grating observations. Deep soft X-ray edges are seen in
Mkn 509 and NGC 3783, consistent with ASCA data. In NGC 5548 and NGC 4501 the
edges are wea... | 0111428v1 |
2001-12-17 | Spectral properties of the Narrow-Line Seyfert 1 Quasar PG1211+143 | We propose a theoretical model to explain the spectrum of the quasar
PG1211+143 emitted in the Optical/X-ray bands. In particular, we suggest that
the inner accretion disk may develop a warm, optically thick skin, which
produces a profound emission feature observed in the soft X-ray band. This is
well modelled with the... | 0112387v1 |
2002-01-24 | Inner-shell 1s - 2p Soft X-ray Absorption Lines | The HULLAC atomic code is used to compute wavelengths and oscillator
strengths for the 1s - np inner-shell absorption lines in Li-like to F-like
ions of neon, magnesium, aluminum, silicon, sulfur, argon, calcium, and iron.
Many of these lines are expected to be observed in Chandra and XMM-Newton
high-resolution X-ray s... | 0201416v1 |
2002-01-28 | Theoretical Uncertainties in the Subgiant--Mass Age Relation and the Absolute Age of Omega Cen | The theoretical uncertainties in the calibration of the relationship between
the subgiant mass and age in metal-poor stars are investigated using a Monte
Carlo approach. Assuming that the mass and iron abundance of a subgiant star
are known exactly, uncertainties in the input physics used to construct stellar
evolution... | 0201443v1 |
2002-01-31 | XMM-Newton EPIC observations of Her X-1 | We present spin-resolved X-ray data of the neutron star binary Her X-1. We
find evidence that the Iron line at 6.4 keV originates from the same location
as the blackbody X-ray component. The line width and energy varies over both
the spin period and the 35 day precession period. We also find that the
correlation betwee... | 0201526v1 |
2002-02-04 | The s-process in rotating AGB stars | We discuss the occurrence of the s-process during the radiative interpulse
phase of rotating AGB stars. Due to differential rotation, protons are mixed
into C12-rich layers after thermal pulses, in the course of the so called third
dredge up episode. We follow the time evolution of key isotope abundances in
the relevan... | 0202067v1 |
2002-02-04 | Discovery of complex narrow X-ray absorption features from the low-mass X-ray binary GX13+1 with XMM-Newton | We report the detection of a complex of narrow X-ray absorption features from
the low-mass X-ray binary GX13+1 during 3 XMM-Newton observations in 2000 March
and April. The features are consistent with being due to resonant scattering of
the K_alpha and K_beta lines of He- and H-like iron (Fe xxv and Fe xxvi) and
H-lik... | 0202077v1 |
2002-02-19 | Atomic Processes in Planetary Nebulae | A hot central star illuminating the surrounding ionized H II region usually
produces very rich atomic spectra resulting from basic atomic processes:
photoionization, electron-ion recombination, bound-bound radiative transitions,
and collisional excitation of ions. Precise diagnostics of nebular spectra
depend on accura... | 0202343v1 |
2002-02-27 | Long Term Spectral Variability of Seyfert Galaxies from RXTE Color-Flux Diagrams | We present results from RXTE data obtained during a systematic monitoring
program of four Seyfert galaxies (NGC5548, NGC5506, MCG-6-30-15 and NGC4051).
We studied the variability of three hardness ratios derived from the light
curves in four energy bands. All the objects show similar spectral variations
in all ratios. ... | 0202498v1 |
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