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ii regions based on the [MATH] ii [MATH] vs. [MATH] ii [MATH] diagnostic diagram. Recently, Rosolowsky & Simon ( 2008 reported oxygen abundances of 61 ii regions in the southwest region of M33 derived from the temperature sensitive emission line iii [MATH] Å. They found a shallow gradient which we show as the solid lin... |
Our results are more consistent with an overall shallow gradient or a flattening in the gradient at large radii (Magrini et al., 2007 |
than they are with a constant gradient over M33’s entire disc. However, even if the gradient was flat beyond [MATH] our results would be several tenths of a dex higher than expected from the data in Fig. 10 The magnitude of this discrepancy is comparable to the random and systematic uncertainties in our results, so it ... |
have their own systematic uncertainties. For example, the abundances of ii regions tend to be lower than supergiants and PNe by [MATH] dex. This offset could indicate a problem in how the temperature and ionization structures of ii regions are treated |
(e.g., García-Rojas & Esteban, 2007 ; Esteban et al., 2004 ; Kennicutt et al., 2003 , and references therein) but larger samples need to be compared before the nature of this discrepancy can be fully understood. |
Discussion 7.1 Comparison to Models of the Solar Vicinity and Magellanic Clouds In Fig. 11 , we compare the [ [MATH] /Fe] vs. [Fe/H] relation in this region of M33 to that of the SV, LMC, and SMC derived in PT95 and PT98 The models for these other three systems have been cited often in the literature because of their s... |
Fig. 11 reveals that M33’s [ [MATH] /Fe] vs. [Fe/H] relation is generally similar to the other systems. Because we have used almost identical chemical evolution equations and identical stellar yields as PT95 and |
PT98 , our models show a similar overall behavior in response to gas flows. The discontinuities in the relation for each system can be traced back to the interplay between the SFR, IFR, and the delayed injection of iron into the ISM from SNe Ia. Therefore, the differences between the relations arise primarily from diff... |
In the IRA, the abundance ratio of any two elements is a constant determined by the ratio of their nucleosynthetic yields. Thus, the initial [MATH] ratio is |
[MATH] After 1.3 Gyr have elapsed, the DPA begins operating as the first SN Ia inject iron into the ISM and produce the first downturn, or “knee”, in the relation. The [Fe/H] location of this knee is dependent on the SFR, which, in turn, depends on the IFR and outflow rate. The SFR was on average higher in the SV than ... |
The large loop in the Padova model results from three successive steps: a sudden large increase in the IFR at an age [MATH] Gyr which dilutes metals in the ISM (see the IFH in Fig. a), a corresponding increase in the SFR which raises [ [MATH] /Fe], and the subsequent drop in [ [MATH] /Fe] 1.3 Gyr later due to SN Ia. Th... |
7.2 Implications for the Formation of the MW’s Halo The [MATH] CDM hierarchical picture of galaxy formation predicts that dark matter haloes are built up from the accretion/merging of smaller subhaloes similar to the protogalactic fragments proposed by Searle & Zinn ( 1978 This picture can be tested by comparing the ch... |
It is interesting to compare our results for M33’s outer disc to the spectroscopic measurements in other LG systems. Such an exercise places our results into the context of the LG as a whole and could have some implications for the formation of the MW’s halo. To that end, in Fig. 12 , we summarize the high-resolution s... |
The green line represents the halo’s dissipative collapse component while the green open stars represent the halo’s accretion component, as defined by Gratton et al. ( 2003 based on orbital kinematics. These authors postulated the dissipative component formed during the collapse of the MW’s gaseous halo, as earlier out... |
The green open diamonds at [Fe/H] [MATH] represent extremely metal-poor halo giants analysed by Cayrel et al. ( 2004 , for which no separation into kinematic components has been made. All other green open points represent samples of MW halo stars selected for their unusual orbital properties and which therefore are add... |
are low-mass dSph satellites of the MW (blue filled circles, stars, and asterisks), Sagittarius dSph (red filled circles and stars), LMC (cyan filled squares and upward pointing triangles), and several dIrrs (orange filled downward pointing triangles). Typical random measurement uncertainties are indicated in the botto... |
for a more detailed explanation and for a list of all the references for the data. Based on our results, if we could obtain high resolution spectroscopic abundances for the location we have studied in M33, we would expect most of its stars to lie near [MATH] [MATH] /Fe] [MATH] |
and [MATH] [Fe/H] [MATH] Of all the systems presented in Fig. 12 this region of parameter space is most similar to the LMC. We also note that M33 resembles the MW’s halo more than the low-mass dSphs. The plateau at [Fe/H] [MATH] was built into the models via the chemical yields (see § 7.1 ), but the key fact is that M3... |
Geisler et al. ( 2007 that some of the accreted MW halo stars originated in high mass dwarf systems. Although we have little information on M33’s inner disc evolution, the presence of a metallicity gradient (Magrini et al., 2007 and a wide variety of ages inferred from CMDs (Sarajedini et al., 2000 |
hint at an extended SFH with a faster enrichment taking place there. Therefore, we hypothesize that the knee in the [ [MATH] /Fe] vs. [Fe/H] relation in M33’s inner disc occurs at a higher metallicity than in the outer disc. This brings us to another key point, that candidate accretion halo stars with different [MATH] ... |
How realistic is such a scenario? How much time would have been necessary and available for this hypothetical fragment to attain the range of [Fe/H] and [ [MATH] /Fe] observed today in the MW halo’s accreted stars? Our results indicate M33’s outskirts took |
[MATH] Gyr to reach [Fe/H] [MATH] and [ [MATH] /Fe] [MATH] Zentner & Bullock ( 2003 used a semi-analytic model to examine the survival of orbiting subhaloes in the MW’s potential. They found that for a typical subhalo orbit, the survival time after entering the MW’s halo ranged from 3 to over 8 Gyr, depending on the su... |
Present-day population gradients have been found in most of the dSphs (e.g., Harbeck et al., 2001 ; Winnick, 2003 ; Tolstoy et al., 2004 ; Koch et al., 2006 ; Stetson et al., 1998 ; Bellazzini et al., 2005 ; Battaglia et al., 2006 ; Faria et al., 2007 ; Komiyama et al., 2007 ; McConnachie et al., 2007 in the Sagittariu... |
(Rowe et al., 2005 Paper II Paper III In most cases, the inner regions of the galaxies are more metal rich and/or older than the outer regions. In another recent study, Bernard et al. ( 2008 found that RR Lyrae stars in the central region of Tucana were more metal-rich than in the outer region, suggesting a metallicity... |
The evolution of metallicity gradients in disc galaxies is a matter of some debate, with some studies predicting the gradient to increase with time and others predicting the opposite (Magrini et al., 2007 , and references therein) The evolutionary model of M33 presented in Magrini et al. ( 2007 predicts the metallicity... |
Conclusions In the framework of a simple chemical evolution scenario which adopts instantaneous and delayed recycling for the nucleosynthetic products of Type II and Ia SNe, we have modelled the observed CMD in one location in M33’s outskirts. In this scenario, interstellar gas forms stars at a rate modulated by the KS... |
The precise details of our results depend on which stellar evolutionary tracks are used, Padova or Teramo. Nevertheless, the broad trends appear to be robust. We found that, when the star formation efficiency, |
[MATH] , is constant, the canonical closed box model fails to reproduce the observed distribution of stars in the CMD. Models with an exponentially declining IFR from 14.1 Gyr ago exhibit similar discrepancies, but to a lesser magnitude. Instead, the inflow models which best reproduce the observed CMD have a significan... |
Allowing [MATH] to vary with time, as might be expected if the star formation time-scale depends on local ISM properties, significantly improves the closed box model if the initial metallicity is [Fe/H] [MATH] , but the resulting present-day gas mass surface density is too high compared to the observed value. A model w... |
We also examined the [ [MATH] /Fe] vs. [Fe/H] relation, a key diagnostic of the evolutionary history of stellar systems. Like the MW’s dwarf satellites, the bulk of stars at this location in M33’s outskirts have [ [MATH] /Fe] ratios lower than the MW’s halo field. Stars formed over 8 Gyr ago have [MATH] [MATH] /Fe] [MA... |
[MATH] and stars forming today have [MATH] [MATH] /Fe] [MATH] [MATH] The mean [ [MATH] /Fe] ratio of all stars ever formed at this location in M33 was found to be [MATH] From the tests we have conducted, we estimate that the systematic errors of these values are [MATH] dex, comparable to that of some high resolution sp... |
(e.g. Monaco et al., 2005 ; Geisler et al., 2007 Our results paint a picture in which M33’s outer disc formed from the protracted inflow of gas over several Gyr with at least half of the total inflow occurring since [MATH] , but relatively little since [MATH] All the acceptable inflow models have a similar IFR [MATH] |
averaged over the lifetime of the Universe. This estimate is uncertain by at least a factor of 2 and the IFR could have intrinsic variations of a factor of [MATH] |
when averaged over 2 [MATH] 3 Gyr time-scales. Nevertheless, it still gives a rough indication of the mean gas IFR that could occur in the outskirts of low mass spiral galaxies. |
A useful baseline for comparison is the lifetime average IFR in the SV, predicted by Colavitti et al. ( 2008 to be [MATH] This estimate comes from several chemical evolution models which adopt different shapes for the IFH and which reproduce many local observables, like the abundances of various elements, MDF of long-l... |
Sommer-Larsen et al. ( 2003 ran an N-body cosmological simulation and selected 12 dark matter haloes for more detailed simulations which included baryons. Two Milky Way-type spirals, S1 and S2, that resulted from the simulations experienced gas accretion at a mean rate of [MATH] at radii of [MATH] disc scale lengths. T... |
[MATH] smaller than those of S1 and S2 at [MATH] Therefore, if the outer disc accretion rate scales with a galaxy’s rotation velocity in the same way as the total disc averaged rate, and if this scaling holds for all redshifts, then our results are consistent with the simulations of Sommer-Larsen et al. ( 2003 |
What is the source and nature of the gas inflow? If it occurs in the disc plane, it could be caused by spiral density waves, viscosity in the disc gas, or gas with lower angular momentum falling onto the disc at larger radii and flowing toward M33’s nucleus |
(Lacey & Fall, 1985 ; Lin & Pringle, 1987 ; Bertin & Lin, 1996 ; Portinari & Chiosi, 2000 ; Roškar et al., 2008 Gas flowing from above the disc plane could come from the condensation of a hot halo corona as described in § However, such a process is expected to be more efficient in a massive spiral like the MW than in a... |
The condensed clouds predicted by numerical simulations to fall onto a disc galaxy have properties similar to the MW’s HVC population (Peek et al., 2008 Recent surveys of HI emission around M31 and M33 have revealed an analogous HVC population around these galaxies |
(Thilker et al., 2004 ; Braun & Thilker, 2004 ; Grossi et al., 2008 Thilker et al. ( 2004 detected 20 clouds within 50 kpc of M31’s disc and the maps presented by Grossi et al. ( 2008 |
show many within [MATH] kpc of M33 with an inferred total mass [MATH] The M31/33 clouds appear to have a mean mass [MATH] and size [MATH] kpc |
(Westmeier et al., 2005 ; Grossi et al., 2008 The lifetime integrated inflow mass of [MATH] in the M33 region we have studied requires the accretion of [MATH] such clouds. Extrapolation to M33’s entire disc is risky given how little we know about its evolution and the population of clouds around M33. In addition to con... |
Acknowledgments We would like to thank the anonymous referee for constructive feedback which helped improve the content and clarity of this paper. We thank Fred Hamann and Stephen Gottesman for stimulating discussions and Annette Ferguson for useful comments on a draft. We gratefully acknowledge Doug Geisler, Samuel Bo... |
# Source: arxiv 0808.1968 # Title: LSD and AMAZE: the mass-metallicity relation at z>3 # Sections: all # Downloaded: 2026-03-02T07:58:42.634089+00:00 |
\pagerange 1–5 LSD and AMAZE: the mass-metallicity relation at z [MATH] (2008) Abstract We present the first results on galaxy metallicity evolution at z [MATH] from two projects, LSD (Lyman-break galaxies Stellar populations and Dynamics) and AMAZE (Assessing the Mass Abundance redshift Evolution). These projects use ... |
keywords: Galaxies: abundances; Galaxies: formation; Galaxies: high-redshift; Galaxies: starburst Introduction Metallicity is one the most important property of galaxies, and its study is able to shed light on the detail properties of galaxy formation. It is an integrated property, not related to the present level of s... |
It is well known that local galaxies follow a well-defined mass-metallicity relation, where galaxies with larger stellar mass have higher metallicities Tremonti et al. 2004 Lee et al., 2006 ). The origin of the relation is uncertain because several effects can be, and probably are, active. It is well known that in the ... |
All these effects have a deep impact on galaxy formation, and the knowledge of their relative contributions is of crucial importance. Different models have been built to reproduce the shape of the mass-metallicity relation in the local universe, and different assumptions produce divergent predictions at high redshifts ... |
For several reasons, it is very interesting to explore even higher redshifts. The redshift range at z [MATH] 3–4 is particularly interesting: it is before the peak of the cosmic star formation density (see, for example, |
Mannucci et al. 2007 ), only a small fraction ( 15%, Pozzetti et al. 2007 ) of the total stellar mass have already been created, the number of mergers among the galaxies is much larger than at later times ( Conselice et al. 2007 ). As a consequence, the prediction of the different models tend to diverge above z=3, and ... |
LSD and AMAZE Metallicity at z [MATH] 3 can be obtained by measuring the fluxes of the main optical emission lines ([OII], H [MATH] , [OIII], H [MATH] ), whose ratios have been calibrated against metallicity in the local universe ( Nagao et al. 2006 Kewley & Ellison 2008 ). Of course, this method can be applied only to... |
For the AMAZE project we observed 30 galaxies at z [MATH] 3.3 from various sources (see Maiolino et al. 2008 for details). We only selected galaxies having a good SPITZER/IRAC photometry (3.6–8 [MATH] ), an important piece of information to derive a reliable stellar mass. These galaxies were observed, in seeing-limited... |
For LSD , we extracted 10 galaxies from the UV-selected Lyman Break Galaxies (LBG) sample by Steidel et al. 2004 . The aim of this project is not only to measure metallicities, but also to obtain spatially-resolved spectra to measure dynamics and spectral gradients. For this reason we used adaptive optics to obtain dif... |
Fig. shows the composite spectra of AMAZE (top) and LSD (bottom). For both AMAZE and LSD, the main optical lines are detected in most of the galaxies. A few targets also show the [NeIII]3869 line, and important piece of information to derive a robust measurement of metallicity ( Nagao et al. 2006 ). |
The Mass-metallicity relation and the effective yields Stellar masses are derived by fitting the spectral-energy distributions (SEDs) with spectrophotometric models of galaxy evolutions, as detailed in |
Pozzetti et al. 2007 and Grazian et al. 2007 These fits also provide estimates of the age and dust extinction of the dominant stellar population. The presence, for most of the objects, of good IRAC photometry, allows the determination of reliable stellar masses as the SED is sampled up to the rest-frame J band. |
Metallicities are derived by a simultaneous fit of all the available line ratios, as explained Maiolino et al. 2008 In practice, the derived value is determined by the R23 indicator or, similarly, by the [OIII]5007/H [MATH] ratio, while the [OIII]5007/[OII]3727 ratio is used to discriminate between the two possible bra... |
Fig. shows the resulting mass-metallicity relation, compared to the same relation as measured at lower redshift. A quantitative interpretation of this result will be given when the whole data sample will be analyzed. Nevertheless, a strong metallicity evolution can be seen, i.e., galaxies at z [MATH] 3.1 have metallici... |
[MATH] 6 times lower than galaxies of similar stellar mass in the local universe. The presence, at z [MATH] 3, of galaxies with relatively high stellar masses (log(M/M [MATH] )=9-11) and low metallicity put strong constraints on the process dominating galaxy formation. Several published models (e.g., de Rossi et al. 20... |
Important hints on the physical processes shaping the mass-metallicity relation can be understood by considering the effective yields, i.e., the amount of metals produced and retained in the galaxy per unit mass of formed stars. If outflows are the main effect in shaping the mass-metallicity relation, then the effectiv... |
(but not by Lee et al., 2006 ). For LSD and AMAZE, preliminary results show that the effective yields tend to decrease, rather than increase, with stellar mass, as in Erb et al. 2006 , Erb et al. (2006)] Such a decrease is partly due to selection effects (see Mannucci et al., in preparation, for a full explanation), bu... |
# Source: arxiv 0808.2179 # Title: Magnetic Reconnection by a Self-Retreating X-Line # Sections: all # Downloaded: 2026-03-02T07:58:43.793711+00:00 |
Magnetic Reconnection by a Self-Retreating X-Line Abstract Particle-in-cell (PIC) simulations of collisionless magnetic reconnection are performed to study asymmetric reconnection in which an outflow is blocked by a hard wall while leaving sufficiently large room for the outflow of the opposite direction. This conditio... |
pacs: 52.35.Vd, 52.65.Rr, 94.30.cp, 96.60.qe Magnetic reconnection triggers many explosive phenomena in laboratory and astrophysical plasma. Importance lies in the diffusion region where the MHD breaks down and the kinetic scale comes in. It is a scientific challenge to understand the structure of the diffusion region ... |
Actual magnetic reconnection, however, occurs in a more complicated situation. During a magnetic reconnection in the Earth’s magneto-tail, an earthward outflow soon collides with the dipole field while the tailward outflow is directed to the interplanetary space. As for the solar flares that take place above the area o... |
In this letter, we investigate the consequences of blocking one side of the outflow. A hard wall is set up just ahead of an outflow while leaving a sufficiently large room for the outflow of the opposite direction. As a result, reconnected magnetic fields are piled-up against the wall. By the time the pile-up region re... |
We utilized the two dimensional, particle-in-cell code (Hoshino, 1987 ; Shinohara et al., 2001 . The initial condition consists of a Harris current sheet. The anti-parallel magnetic field and the density are given by [MATH] and [MATH] , respectively, where [MATH] is the magnetic field at the inflow boundary, [MATH] is ... |
Five simulation runs are performed to study the dependence on the initial distance [MATH] . The values of [MATH] along with the other initial values are compiled in Table . The initial X-line is at the center of the domain for Run 4, and thus, it is a non-retreating case. Run 5 is an additional case intended to study t... |
Upper panels of Figure show snapshots of electron out-of-plane current for Run 1. It is evident that as magnetic reconnection proceeds, a downward flow is blocked by the bottom wall and creates the pile-up region which expands in time and eventually pushes the diffusion region upward. The upward flow, on the other hand... |
The black curve in Figure d shows the X-line position defined by the [MATH] reversal point, [MATH] =0. A distinct retreat process starts at [MATH] 85. The X-line moves away from the wall monotonically. Although a jump appears at [MATH] 145 due to a magnetic island [MATH] 180. |
Figure e shows various flow speeds. While the upward ion flow becomes super-Alfvénic and continues to increase until the time of collision with the wall, the downward ion flow reaches [MATH] 0.3 [MATH] at [MATH] 80 when it is blocked by the bottom wall (marked by the blue arrow). The downward flow speed soon decreases ... |
A striking feature can be found around the diffusion region. Figure shows an enlarged view of the diffusion region for Run 1 at [MATH] 115 when the upward electron speed is saturated. In this figure, data are accumulated over one gyro period. Coordinates are shifted so that the X-line comes to the origin. This simulati... |
In contrast to ions, electrons do not show strong deflection and exhibit well developed outflow jets both upward and downward, although the downward jet is limited in length. The typical length of the downward electron jet is [MATH] [MATH] and remains constant throughout the run. The maximum value of the electron flow ... |
We further examined the out-of-plane component of the generalized Ohm’s law along [MATH] =0 as shown in the right panel of Figure |
(Shay et al., 2007 . It is expressed as [EQUATION] where [MATH] is the electron bulk velocity, [MATH] is the flux of [MATH] -directed electron momentum in the reconnection plane (not including convection of momentum) with [MATH] the electron pressure tensor. The observed electric field (solid black curve) is balanced b... |
The above finding leads to the idea that the downward outer diffusion region adjusts itself to buffer the effects of the wall such that the reconnection electric field is determined irrespective of the asymmetric boundary condition. This idea is inspected in Figure which shows the reconnection rate, [MATH] , of all run... |
(Hesse et al., 1999 . Relatively large fluctuations are due to secondary islands whose appearance times are indicated by the horizontal arrows. Also illustrated in Figure are the timings of the jet collision with the wall as well as the X-line retreat. It clearly shows that the rising motion of the diffusion region is ... |
To summarize, the retreat motion of the X-line is constant ( [MATH] 0.1 [MATH] ). This speed does not depend on the initial distance of the X-line from the wall, [MATH] , except of course the non-retreating case. The downward outflow region is largely modulated by the asymmetry. The ion deflection pattern depends on [M... |
In addition to the initial distance from the wall, a dependence on the mass ratio [MATH] should also be addressed. What we have found here is the tendency for more magnetic islands to emerge with smaller [MATH] . These islands may help maintain fast reconnection (Daughton et al., 2006 . In fact, as shown in Figure , th... |
Finally, it should be mentioned that the X-line speed can be faster than the self-retreating speed of 0.1 [MATH] if, say, it is blown by another dominant X-line. Recent two-fluid simulations show that its reconnection rate is reduced and reconnection at the moving X-line is eventually terminated. Particle simulations f... |
Acknowledgements. This work was partially supported by the Grant-in-Aid for Creative Scientific Research (17GS0208) from the MEXT, Japan. MO was supported by the Grant-in-Aid for JSPS Postdoctoral Fellows for Research Abroad. |
# Source: arxiv 0808.2273 # Title: A Possible Icy Kuiper Belt around HD 181327 # Sections: all # Downloaded: 2026-03-02T07:58:44.998242+00:00 |
A Possible Icy Kuiper Belt around HD 181327 Abstract We have obtained a Gemini South T-ReCS -band (18.3 [MATH] m) image and a Spitzer MIPS SED-mode observation of HD 181327, an F5/F6V member of the [MATH] 12 Myr old [MATH] Pictoris moving group. We resolve the disk in thermal-emission for the first time and find that t... |
[MATH] [MATH] with [MATH] consistent with the minimum blow out size and [MATH] = 20 [MATH] m) located at a distance of 86.3 AU from the central star, as observed in previously published scattered-light images. Since the photo-desorption lifetime for the icy particles is [MATH] 1400 yr, significantly less than the estim... |
Subject headings: stars: individual (HD 181327)— stars: circumstellar matter— planetary systems: formation 1. Introduction Debris disks are dusty, gas-poor disks around main sequence stars. The estimated lifetimes for their constituent grains are typically shorter than the ages of their central stars by orders of magni... |
[MATH] 100 K), similar to that expected for dust in the solar system’s Kuiper Belt (Meyer et al. 2007). Broad-band near-infrared photometry and low resolution spectroscopy suggest that KBOs possess ices on their surfaces (Schaller & Brown 2007; Delsanti et al. 2006). The composition of dust in debris disks may be simil... |
High resolution scattered-light and thermal-emission imaging and spectroscopy may reveal disk structure and provide insight into grain properties via (1) brightness peaks in scattered-light or thermal-emission images that indicate local dust density enhancements and/or dust temperature asymmetries and (2) spectral feat... |
HD 181327 is an F5/F6V star with a Hipparcos -determined distance of 50.6 pc. It has been identified as a member of the [MATH] Pictoris moving group, with an estimated age of [MATH] 12 Myr (Zuckerman et al. 2001). Mannings & Barlow (1998) first identified HD 181327 as a possible debris disk based on the detection of IR... |
2. Observations 2.1. T-ReCS Observations We used the T-ReCS imager on Gemini-S to observe HD 181327 on the night of 2006 July 21 (GS-2006A-Q-43). These observations were interleaved with exposures of [MATH] Ind, a photometric and point-spread function (PSF) reference. Both targets were imaged in the band ( [MATH] µm) w... |
The data were reduced using custom Python routines. In order to suppress sky and instrumental emission, we used standard addition and subtraction tehcniques for combining the exposures in each AB nod pair. For HD 181327, two of the resulting double-difference images with abnormally high variances (more than twice the m... |
Detailed examination of the resulting image of HD 181327 revealed additional electronic pattern noise, seen as diagonal banding. The power spectrum of the image contained peaks at [MATH] , where [MATH] pix (corresponding to the amplifier channel width), [MATH] pix, and [MATH] After masking a 3″-radius region around the... |
We used aperture photometry of [MATH] Ind for photometric calibration. We computed the flux zero point using an aperture of 3 [MATH] 6 radius, and a flux value of 6.032 Jy. An examination of the enclosed flux as a function of airmass showed no clear trend, suggesting time-variable telluric extinction. The mean airmasse... |
2.2. MIPS SED-mode Observations We obtained follow-up Spitzer (Werner et al. 2004) MIPS (Rieke et al. 2004) SED-mode observations (55.0–90.0 [MATH] m; [MATH] 20) of HD 181327 (AOR key: 16171008) on 15 April 2006, using the 19.6 [MATH] [MATH] 157 [MATH] slit/grating and 10 cycles of 10 s integrations. Each observing cyc... |
We use these newly obtained MIPS SED-mode data in conjunction with previously published Spitzer /IRS observations to model the SED of HD 181327. The observations and data reduction for the IRS data are described in Chen et al. (2006). We estimate the HD 181327 stellar photosphere using a Kurucz stellar atmosphere model... |
[MATH] [MATH] m) in the IRS SL spectrum. We assume a 5% uncertainty in our stellar photosphere model. 3. Thermal Imaging Results |
We plot our -band images of HD 181327 and PSF reference star [MATH] Ind in Figure and their enclosed flux curves in Figure a, with 1- [MATH] uncertainties derived from the background noise. We subtract the PSF star image from our HD 181327 image, assuming that the stellar point source has a flux of 53 mJy (estimated fr... |
HST ACS and NICMOS scattered-light imaging resolve an inclined ring of dust around HD 181327 with (1) a surface brightness that falls off rapidly interior to the 86.3 AU ring and (2) an azimuthal brightness asymmetry that is well-modeled using a Henyey-Greenstein phase function. These observations suggest that the inne... |
The northern-arm of the disk appears brighter than the southern arm, contrary to the equal brightness expected from an azimuthally-symmetric dust ring. We measure the flux in annular wedges, centered on the minor axis, with outer boundaries defined by the outer [MATH] -folding radius measured in scattered light. We mea... |
If the dust grain density is higher in the northern arm, then previous models of the scattering phase function may need to be revised. Schneider et al. (2006) fit the 1.1 [MATH] m NICMOS scattered-light image of the HD 181327 disk using a Henyey-Greenstein-like phase function with an asymmetric scattering parameter, [M... |
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