- 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.
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- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/570/A126
- Title:
- XShooter spectrum of 4 BL Lacs
- Short Name:
- J/A+A/570/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to determine the redshift (or stringent lower limits) of a number of bright BL Lacs objects. We secured optical and near-infrared medium resolution spectra of four bright BL Lac objects of unknown redshift using the spectrograph X-Shooter at the ESO-VLT. In spite of the high quality of the spectra and the extended spectral range of the observations, we have not detected intrisic spectral features for these sources. However, we are able to provide strigent lower limits to their redshift. In particular, for the two TeV sources PG 1553+113 and H 1722+119, we infer z>0.30 and z>0.35 respectively. We also detect an intervening CaII absorption doublet in the spectrum of MH 2136-428 that is ascribed to the the halo of a nearby giant elliptical galaxy at a projected distance of ~100kpc. Under the hypothesis that all BL Lacs are hosted by a luminous bulge dominated galaxies, the presently spectroscopic observations of bright BL Lacs indicate that these objects are likely sources with extremely beamed nuclear emission. We present simulations to show under which circumstances it is possible to probe this hypothesis from the detection of very weak absorptions using the next generation of extremely large optical telescopes.
25274. 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.
- 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.
- ID:
- ivo://nasa.heasarc/xteasmlong
- Title:
- XTE All-Sky Monitor Long-Term Observed Sources
- Short Name:
- XTE/ASM
- Date:
- 25 Oct 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The XTEASMLONG table was created for the purpose of providing a complete listing of RXTE'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 <a href="https://heasarc.gsfc.nasa.gov/FTP/xte/data/archive/ASMProducts/definitive_1dwell/lightcurves/">https://heasarc.gsfc.nasa.gov/FTP/xte/data/archive/ASMProducts/definitive_1dwell/lightcurves/</a> 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 .
- ID:
- ivo://nasa.heasarc/xteassagn
- Title:
- XTE All-Sky Slew Survey AGN Catalog
- Short Name:
- XTEASSAGN
- Date:
- 25 Oct 2024
- 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| > 10 degrees during the RXTE Slew Survey (XSS, Revnivtsev et al., CDS Cat. <J/A+A/418/927>), 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<sub>X</sub> < 10<sup>43.5</sup> erg/s) AGN, the ratio of absorbed (characterized by intrinsic absorption in the range 10<sup>22</sup> cm<sup>-2</sup> < N<sub>H</sub> < 10<sup>24</sup> cm<sup>-2</sup>) and unabsorbed (N<sub>H</sub> < 10<sup>22</sup> cm<sup>-2</sup>) 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<sub>X</sub> > 10<sup>41</sup> 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 < 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 <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/423/469">CDS Catalog J/A+A/423/469</a>, table1.dat and table2.dat (the corrected version of 01-Dec-2004). This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/xteasscat
- Title:
- XTE All-Sky Slew Survey Catalog
- Short Name:
- XTEASSCAT
- Date:
- 25 Oct 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Rossi X-Ray Timing Explorer (RXTE) All-Sky Survey Slew Catalog contains the results of a serendipitous hard X-ray (3 - 20 keV), nearly all-sky (|b|>10 degrees) survey based on observations by RXTE's Proportional Counter Array (PCA) which were performed during satellite reorientations in the period 1996 - 2002. The survey is 80% (90%) complete to a 4-sigma limiting flux of ~1.8 (2.5)x10<sup>-11</sup> erg/s/cm<sup>2</sup> in the 3 - 20 keV band. The achieved sensitivity in the 3 - 8 keV and 8 - 20 keV subbands is similar to and an order of magnitude higher than that of the previously record HEAO-1 A1 and HEAO-1 A4 all-sky surveys, respectively. A combined 7 x 10<sup>3</sup> square degree area of the sky is sampled to flux levels below 10<sup>-11</sup> erg/s/cm<sup>2</sup> (3 - 20 keV). In total 294 sources are detected and localized to better than ~1 degree; 236 (80%) of these can be confidently associated with a known astrophysical object; 22 of these sources have multiple counterparts (17 have 2 counterparts and 5 have 3 counterparts) with which they have been identified, and as these are listed as separate entries, there are 321 entries in this table. 35 detected sources remain unidentified, although for 12 of these we report a likely soft X-ray counterpart from the ROSAT all-sky survey bright source catalog. Of the reliably identified sources, 63 have a local origin (Milky Way, LMC or SMC), 64 are clusters of galaxies and 100 are active galactic nuclei (AGN). The fact that the unidentified X-ray sources have hard spectra suggests that the majority of them are AGN, including highly obscured ones (hydrogen column density > 10<sup>23</sup> cm<sup>-2</sup>). This dataset enabled the authors to present for the first time a log N - log S diagram for extragalactic sources above 4 x 10<sup>-12</sup> erg/s/cm<sup>2</sup> at 8 - 20 keV. This database table was created by the HEASARC in May 2004 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/418/927">CDS Catalog J/A+A/418/927</a>. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/xteslew
- Title:
- XTE Archived Public Slew Data
- Short Name:
- XTESLEW
- Date:
- 25 Oct 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This database table is a catalog of all the RXTE slew observations and is based on information culled from the RXTE Data Archive's latest top-level FMI (FITS Master Index) file that is created when data products are made publicly available each week. ObsIDs listed in this table are available for download from <a href="https://heasarc.gsfc.nasa.gov/FTP/xte/data/archive/">https://heasarc.gsfc.nasa.gov/FTP/xte/data/archive/</a>. See the parameter 'data_loc' for the relative location of specific ObsIDs. The XTESLEW database table is updated automatically, usually on a weekly basis whenever the RXTE GOF updates the top-level FMI for the public data archive and notifies the HEASARC. This is a service provided by NASA HEASARC .
- ID:
- ivo://CDS.VizieR/J/MNRAS/428/1704
- Title:
- XTE J1550-564 quasi-periodic oscillations
- Short Name:
- J/MNRAS/428/1704
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we investigate the energy dependence of the centroid frequency of the low-frequency quasi-periodic oscillations (QPOs; 0.08-20Hz) in XTE J1550-564. We have used the observational data from the Rossi X-ray Timing Explorer during the first half part of the 1998-1999 outburst. We have found that the centroid frequency of the fundamental QPO did not vary with photon energy when its QPO frequency was less than ~0.4-0.8Hz and it did not increase much when its frequency was between ~0.8 and ~3.3Hz. However, it clearly increased with photon energy when it was larger than ~3.3Hz. The most interesting point is that it increased much more quickly with photon energy when its centroid frequency was between ~6 and ~8.5Hz. Subsequently, its rising rate dropped sharply when its frequency was larger than ~8.5Hz.
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