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17871. X-Shooter Spectral Library (XSL). DR2
ID:
ivo://CDS.VizieR/J/A+A/634/A133
Title:
X-Shooter Spectral Library (XSL). DR2
Short Name:
J/A+A/634/A133
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the second data release (DR2) of the X-Shooter Spectral Library (XSL), which contains all the spectra obtained over the six semesters of that program. This release supersedes our first data release from 2014, with a larger number of spectra (813 observations of 666 stars) and with a more extended wavelength coverage as the data from the near-infrared arm of the X-Shooter spectrograph are now included. The DR2 spectra then consist of three segments that were observed simultaneously and, if combined, cover the range between 300nm and 2.45um at a spectral resolving power close to R=10000. The spectra were corrected for instrument transmission and telluric absorption, and they were also corrected for wavelength-dependent flux-losses in 85% of the cases. On average, synthesized broad-band colors agree with those of the MILES library and of the combined IRTF and Extended IRTF libraries to within 1%. The scatter in these comparisons indicates typical errors on individual colors in the XSL of 2-4%. The comparison with 2MASS point source photometry shows systematics of up to 5% in some colors, which we attribute mostly to zero-point or transmission curve errors and a scatter that is consistent with the above uncertainty estimates. The final spectra were corrected for radial velocity and are provided in the rest-frame (with wavelengths in air). The spectra cover a large range of spectral types and chemical compositions (with an emphasis on the red giant branch), which makes this library an asset when creating stellar population synthesis models or for the validation of near-ultraviolet to near-infrared theoretical stellar spectra across the Hertzsprung-Russell diagram.
17872. X-shooter spectra of AGN and inactive galaxies
ID:
ivo://CDS.VizieR/J/A+A/654/A132
Title:
X-shooter spectra of AGN and inactive galaxies
Short Name:
J/A+A/654/A132
Date:
22 Feb 2022
Publisher:
CDS
Description:
The relation between nuclear (<~50pc) star formation and nuclear galactic activity is still elusive; theoretical models predict a link between the two, but it is unclear whether active galactic nuclei (AGNs) should appear at the same time, before, or after nuclear star formation activity. We present a study of this relation in a complete, volume-limited sample of nine of the most luminous (log_L14-195keV_>10^42.5^erg/s) local AGNs (the LLAMA sample), including a sample of 18 inactive control galaxies (six star-forming; 12 passive) that are matched by Hubble type, stellar mass (9.5<~logM*/M_{sun}_<~10.5), inclination, and distance. This allows us to calibrate our methods on the control sample and perform a differential analysis between the AGN and control samples. We performed stellar population synthesis on VLT/X-shooter spectra in an aperture corresponding to a physical radius of ~150pc. We find young (<~30Myr) stellar populations in seven out of nine AGNs and in four out of six star-forming control galaxies. In the non-star-forming control population, in contrast, only two out of 12 galaxies show such a population. We further show that these young populations are not indicative of ongoing star formation, providing evidence for models that see AGN activity as a consequence of nuclear star formation. Based on the similar nuclear star formation histories of AGNs and star-forming control galaxies, we speculate that the latter may turn into the former for some fraction of their time. Under this assumption, and making use of the volume completeness of our sample, we infer that the AGN phase lasts for about 5% of the nuclear starburst phase.
17873. X-shooter spectra of 43 metal-poor M dwarfs
ID:
ivo://CDS.VizieR/J/A+A/628/A61
Title:
X-shooter spectra of 43 metal-poor M dwarfs
Short Name:
J/A+A/628/A61
Date:
21 Oct 2021
Publisher:
CDS
Description:
The aim of the project is to define metallicity/gravity/temperature scales for different spectral types of metal-poor M dwarfs. We obtained intermediate-resolution ultraviolet (UVB), optical (VIS), and near-infrared (NIR) spectra of 43 metal-poor M dwarfs (16 sdMs, 16 esdMs, and 12 usdMs with the ESO VLT X-shooter spectrograph. We compared our atlas of spectra to the BT-Settl synthetic spectral energy distribution over a wide range of metallicities, gravities, and effective temperatures to infer the physical properties for the whole M dwarf sequence at sub-solar metallicities and constrain the latest atmospheric models. The BT-Settl models accurately reproduce the observed spectra across the 450--2500 nm wavelength range except for a few regions. We find that the best fits for gravities of log(g)=5.0-5.5 for the three metal classes. We infer metallicities of [Fe/H]=-0.5, -1.5, and -2.0+/-0.5dex and effective temperatures of 3700-2600K, 3800-2900K, and 3700-2900K for sdMs, esdMs, and usdMs, respectively.
17874. X-shooter spectra of 12 young stellar objects
ID:
ivo://CDS.VizieR/J/A+A/548/A56
Title:
X-shooter spectra of 12 young stellar objects
Short Name:
J/A+A/548/A56
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present high-quality, medium-resolution X-shooter/VLT spectra in the range 300-2500nm for a sample of 12 very low mass stars in the {sigma} Orionis cluster. The sample includes eight stars with evidence of disks from Spitzer and four without disks, with masses ranging from 0.08 to 0.3M_{sun}_. The aim of this first paper is to investigate the reliability of the many accretion tracers currently used to measure the mass accretion rate in low-mass young stars and the accuracy of the correlations between these secondary tracers (mainly accretion line luminosities) found in the literature. We use our spectra to measure the accretion luminosity from the continuum excess emission in the UV and visual; the derived mass accretion rates range from 10^-9^M_{sun}_/yr down to 5x10^-11^M_{sun}_/yr, allowing us to investigate the behavior of the accretion-driven emission lines in very low mass accretion rate regimes. We compute the luminosity of ten accretion-driven emission lines from the UV to the near-IR, which are all obtained simultaneously. In general, most of the secondary tracers correlate well with the accretion luminosity derived from the continuum excess emission. We recompute the relationships between the accretion luminosities and the line luminosities, and we confirm the validity of the correlations given in the literature, with the possible exception of H{alpha}. Metallic lines, such as the CaII IR triplet or the NaI line at 589.3nm, show a larger dispersion. When looking at individual objects, we find that the hydrogen recombination lines, from the UV to the near-IR, give good and consistent measurements of L_acc_ that often better agree than the uncertainties introduced by the adopted correlations. The average L_acc_ derived from several hydrogen lines, measured simultaneously, have a much reduced error. This suggests that some of the spread in the literature correlations may be due to the use of nonsimultaneous observations of lines and continuum. Three stars in our sample deviate from this behavior, and we discuss them individually.
17875. X-shooter spectra of 24 young stellar objects
ID:
ivo://CDS.VizieR/J/A+A/551/A107
Title:
X-shooter spectra of 24 young stellar objects
Short Name:
J/A+A/551/A107
Date:
21 Oct 2021
Publisher:
CDS
Description:
The lack of knowledge of photospheric parameters and the level of chromospheric activity in young low-mass pre-main sequence stars introduces uncertainties when measuring mass accretion rates in accreting (Class II) young stellar objects. A detailed investigation of the effect of chromospheric emission on the estimates of mass accretion rate in young low-mass stars is still missing. This can be undertaken using samples of young diskless (Class III) K and M-type stars. Our is to measure the chromospheric activity of Class III pre main sequence stars to determine its effect on the estimates of the accretion luminosity (Lacc) and mass accretion rate (dMacc/dt) in young stellar objects with disks. Using VLT/X-shooter spectra, we analyzed a sample of 24 nonaccreting young stellar objects of spectral type between K5 and M9.5. We identified the main emission lines normally used as tracers of accretion in Class II objects, and we determined their fluxes in order to estimate the contribution of the chromospheric activity to the line luminosity. We have used the relationships between line luminosity and accretion luminosity derived in the literature for Class II objects to evaluate the impact of chromospheric activity on the accretion rate measurements. We find that the typical chromospheric activity would bias the derived accretion luminosity by L_acc,noise_<10^-3^L_{sun}_, with a strong dependence on the Teff of the objects. The noise on Macc depends on stellar mass and age, and the typical values of log(M_acc,noise_) range between ~-9.2 to -11.6M_{sun}_/yr. Values of L_acc_<10^-3^L_{sun}_ obtained in accreting low-mass pre main sequence stars through line luminosity should be treated with caution because the line emission may be dominated by the contribution of chromospheric activity.
17876. X-Shooter spectroscopy of YSOs in Lupus
ID:
ivo://CDS.VizieR/J/A+A/602/A33
Title:
X-Shooter spectroscopy of YSOs in Lupus
Short Name:
J/A+A/602/A33
Date:
21 Oct 2021
Publisher:
CDS
Description:
A homogeneous determination of basic stellar parameters of young stellar object (YSO) candidates is needed to confirm their pre-main sequence evolutionary stage, membership to star forming regions (SFRs), and to get reliable values of the quantities related to chromospheric activity and accretion. We used the code ROTFIT and synthetic BT-Settl spectra for the determination of the atmospheric parameters (Teff and logg), the veiling (r), the radial (RV) and projected rotational velocity (vsini), from X-Shooter spectra of 102 YSO candidates (95 of infrared Class II and seven Class III) in the Lupus SFR. The spectral subtraction of inactive templates, rotationally broadened to match the vsini of the targets, enabled us to measure the line fluxes for several diagnostics of both chromospheric activity and accretion, such as H{alpha}, H{beta}, CaII, and NaI lines. We have shown that 13 candidates can be rejected as Lupus members based on their discrepant RV with respect to Lupus and/or the very low logg values. At least 11 of them are background giants, two of which turned out to be lithium-rich giants. Regarding the members, we found that all ClassIII sources have H{alpha} fluxes compatible with a pure chromospheric activity, while objects with disks lie mostly above the boundary between chromospheres and accretion. YSOs with transitional disks displays both high and low H{alpha} fluxes. We found that the line fluxes per unit surface are tightly correlated with the accretion luminosity (L_acc_) derived from the Balmer continuum excess. This rules out that the relationships between L_acc_ and line luminosities found in previous works are simply due to calibration effects. We also found that the CaII-IRT flux ratio is always small, indicating an optically thick emission source. The latter can be identified with the accretion shock near the stellar photosphere. The Balmer decrement reaches instead, for several accretors, high values typical of optically thin emission, suggesting that the Balmer emission originates in different parts of the accretion funnels with a smaller optical depth.
17877. XSL atmospheric parameters
ID:
ivo://CDS.VizieR/J/A+A/627/A138
Title:
XSL atmospheric parameters
Short Name:
J/A+A/627/A138
Date:
21 Oct 2021
Publisher:
CDS
Description:
The X-shooter Spectral Library (XSL) is an empirical stellar library at medium spectral resolution covering the wavelength range from 3000 to 24800 angstrom. This library aims to provide a benchmark for stellar population studies. In this work, we present a uniform set of stellar atmospheric parameters, effective temperatures, surface gravities, and iron abundances for 754 spectra of 616 XSL stars. We used the full-spectrum fitting package ULySS with the empirical MILES library as reference to fit the ultraviolet-blue (UVB) and visible (VIS) spectra. We tested the internal consistency and we compared our results with compilations from the literature. The stars cover a range of effective temperature 2900<Teff<38000K, surface gravity 0<logg<5.7, and iron abundance -2.5<[Fe/H]<+1.0, with a couple of stars extending down to [Fe/H]=-3.9. The precisions of the measurements for the G- and K-type stars are 0.9%, 0.14, and 0.06 in Teff, log g and [Fe/H], respectively. For the cool giants with logg<1, the precisions are 2.1%, 0.21, and 0.22, and for the other cool stars these values are 1%, 0.14, and 0.10. For the hotter stars (Teff>6500K), these values are 2.6%, 0.20, and 0.10 for the three parameters.
17878. XSTPS RR Lyrae in the north Galactic cap
ID:
ivo://CDS.VizieR/J/ApJ/788/105
Title:
XSTPS RR Lyrae in the north Galactic cap
Short Name:
J/ApJ/788/105
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ~376.75 deg^2^ at RA~150{deg} and DE~27{deg} down to a magnitude limit of i~19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more than 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. (2009, J/MNRAS/398/1757) and Sesar et al. (2010, J/ApJ/708/717) RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We consider non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.
17879. XTE All-Sky Monitor Long-Term Observed Sources
ID:
ivo://nasa.heasarc/xteasmlong
Title:
XTE All-Sky Monitor Long-Term Observed Sources
Short Name:
XTE/ASM
Date:
11 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
The XTEASMLONG table was created for the purpose of providing a complete listing of RXTE&#39;s All-Sky Monitor (ASM) observations of sources. It is based on information culled from the definitive 1-dwell long-term ASM light curve data products. These data products are available for downloading at &lt;a href="https://heasarc.gsfc.nasa.gov/FTP/xte/data/archive/ASMProducts/definitive_1dwell/lightcurves/"&gt;https://heasarc.gsfc.nasa.gov/FTP/xte/data/archive/ASMProducts/definitive_1dwell/lightcurves/&lt;/a&gt; The XTEASMLONG table is updated usually every week or two whenever new definitive ASM data products are delivered to the RXTE GOF from MIT where the definitive ASM processing is done. This is a service provided by NASA HEASARC .
17880. XTE All-Sky Slew Survey AGN Catalog
ID:
ivo://nasa.heasarc/xteassagn
Title:
XTE All-Sky Slew Survey AGN Catalog
Short Name:
XTEASSAGN
Date:
11 Apr 2025
Publisher:
NASA/GSFC HEASARC
Description:
This table contains the RXTE All-Sky Slew Survey Catalog of AGN and AGN candidates. The catalog authors compiled a sample of 95 AGNs which were serendipitously detected in the 3-20 keV band at Galactic latitude |b| &gt; 10 degrees during the RXTE Slew Survey (XSS, Revnivtsev et al., CDS Cat. &lt;J/A+A/418/927&gt;), and utilized it to study the statistical properties of the local population of AGN, including the X-ray luminosity function and absorption distribution. They find that among low X-ray luminosity (L&lt;sub&gt;X&lt;/sub&gt; &lt; 10&lt;sup&gt;43.5&lt;/sup&gt; erg/s) AGN, the ratio of absorbed (characterized by intrinsic absorption in the range 10&lt;sup&gt;22&lt;/sup&gt; cm&lt;sup&gt;-2&lt;/sup&gt; &lt; N&lt;sub&gt;H&lt;/sub&gt; &lt; 10&lt;sup&gt;24&lt;/sup&gt; cm&lt;sup&gt;-2&lt;/sup&gt;) and unabsorbed (N&lt;sub&gt;H&lt;/sub&gt; &lt; 10&lt;sup&gt;22&lt;/sup&gt; cm&lt;sup&gt;-2&lt;/sup&gt;) objects is 2:1, while this ratio drops to less than 1:5 for higher luminosity AGN. The summed X-ray output of AGN with L&lt;sub&gt;X&lt;/sub&gt; &gt; 10&lt;sup&gt;41&lt;/sup&gt; erg/s estimated here is smaller than the earlier estimated total X-ray volume emissivity in the local Universe, suggesting that a comparable X-ray flux may be produced together by lower luminosity AGN, non-active galaxies and clusters of galaxies. The authors also presented a sample of 35 AGN candidates, composed of unidentified XSS sources. Most of these AGN belong to the local population (z &lt; 0.1). For each confirmed AGN source, the following information is provided: AGN class, the count rate in two energy bands (3-8 keV and 8-20 keV), the observed and intrinsic (absorption-corrected) luminosity in the 3 - 20keV band, and the intrinsic absorption column density. For the AGN candidates, composed of unidentified XSS sources, the following information is provided: the count rate in two energy bands (3-8 keV and 8-20 keV), the estimated intrinsic absorption column density, and information about RASS Bright Source Catalog and HEAO A-1 X-ray source counterparts. This table was created by the HEASARC in December 2004 based on &lt;a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/423/469"&gt;CDS Catalog J/A+A/423/469&lt;/a&gt;, table1.dat and table2.dat (the corrected version of 01-Dec-2004). This is a service provided by NASA HEASARC .

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