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27 results for “X-ray:stars”
S254-S258 Star-Forming Region Chandra X-Ray Point Source Catalog
The aim of this study was to find an explanation for the remarkable morphology of the central part of the S254-S258 star forming complex. The authors performed a deep Chandra X-ray observation of the S254-S258 region in order to efficiently discriminate young stars (with and without circumstellar matter) from the numerous older field stars in the area. They detected 364 X-ray point sources in a 17' x 17' (~ 8 x 8 pc) field. This X-ray catalog provides, for the first time, a complete sample of all young stars in the region down to about 0.5 M_{sun}_. A clustering analysis identifies three significant clusters: the central embedded cluster S255-IR and two smaller clusterings in S256 and S258. Sixty-four X-ray sources can be classified as members in one of these clusters. After accounting for X-ray background contaminants, this implies that about 250 X-ray sources constitute a widely scattered population of young stars, distributed over the full field-of-view of the X-ray image. This distributed young stellar population is considerably larger than the previously known number of non-clustered young stars selected by infrared excesses. Comparison of the X-ray luminosity function with that of the Orion Nebula Cluster suggests a total population of ~ 2000 young stars in the observed part of the S254-S258 region. The S254-S258 complex was observed (PI: Preibisch) in November 2009 with the Imaging Array of the Chandra Advanced CCD Imaging Spectrometer (ACIS-I). ACIS-I provides a field of view of 17' x 17' on the sky. At the 1.6 kpc distance of S254-S258 this corresponds to 7.9 x 7.9 pc. The aimpoint of the observation was RA(J2000) = 06h12m54.0s, Dec(J2000) = +17d 59' 24". The observation was performed in the standard 'Timed Event, Faint' mode (with 3 x 3 pixel event islands). The total net exposure time of 74725 s (20.76 h) was split into two parts, separated by about 4 days. The details of these two observation parts are given in Table 1 of the reference paper. The authors first employed the wavdetect algorithm (Freeman et al. 2002, ApJS, 138, 185, a CIAO mexican-hat wavelet source detection tool) for locating X-ray sources in the merged image, and used a rather low detection threshold of 10<sup>-5</sup>. This step was performed in three different energy bands, the total band (0.5 - 8.0 keV), the soft band (0.5 - 2.0 keV), and the hard band (2.0 - 8.0) keV, and with wavelet scales between 1 and 16 pixels. They also performed a visual inspection of the images and added some 30 additional candidates to the merged catalog from the wavelet analysis, resulting in a final catalog of 511 potential X-ray sources. To clean this catalog from spurious sources, they then performed a detailed analysis of each individual candidate source with the ACIS Extract (AE hereafter) software package (Broos et al. 2010, ApJ, 714, 1582). The Poisson probability (P<sub>B</sub>) associated with the "null hypothesis", i.e. that no source exists and the extracted events are solely due to Poisson fluctuations in the local background, was computed for each source using AE. All candidate sources with P<sub>B</sub> > 0.01 were rejected as background fluctuations. After 8 iterations of this pruning procedure the final catalog consisted of 364 sources. It contains 344 primary sources with P<sub>B</sub> < 0.003, and 20 tentative sources with 0.003 < P<sub>B</sub> < 0.01. To obtain an estimate of the intrinsic, i.e. extinction-corrected, X-ray luminosity for sources that are too weak for a detailed spectral analysis, the authors used the XPHOT software, developed by Getman et al. (2010, ApJ, 708, 1760). XPHOT is based on a non-parametric method for the calculation of fluxes and absorbing X-ray column densities of weak X-ray sources. X-ray extinction and intrinsic flux are estimated from the comparison of the apparent median energy of the source photons and apparent source flux with those of high signal-to-noise spectra that were simulated using spectral models characteristic of much brighter sources of similar class previously studied in detail. This method requires at least 4 net counts per source (in order to determine a meaningful value for the median energy) and can thus be applied to 255 of the 364 sources in this table. To calculate luminosities, a distance of 1.6 kpc was assumed. The resulting intrinsic X-ray lumonosities range from 10<sup>29.4</sup> to 10<sup>32.3</sup> erg s<sup>-1</sup>. This table was created by the HEASARC in October 2011 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/533/A121">CDS Catalog J/A+A/533/A121</a> files table2.dat, table3.dat and table5.dat. This is a service provided by NASA HEASARC .
Star Formation in Nearby Clouds (SFiNCs) X-Ray Source Catalog
The Star Formation in Nearby Clouds (SFiNCs) project is aimed at providing a detailed study of the young stellar populations and of star cluster formation in the nearby 22 star-forming regions (SFRs) for comparison with our earlier MYStIX survey of richer, more distant clusters. As a foundation for the SFiNCs science studies, in the reference paper homogeneous data analyses of the Chandra X-ray and Spitzer mid-infrared archival SFiNCs data are described, and the resulting catalogs of over 15,300 X-ray and over 1,630,000 mid-infrared point sources are presented. On the basis of their X-ray/infrared properties and spatial distributions, nearly 8500 point sources have been identified as probable young stellar members of the SFiNCs regions. Compared to the existing X-ray/mid-infrared publications, the SFiNCs member list increases the census of YSO members by 6%-200% for individual SFRs and by 40% for the merged sample of all 22 SFiNCs SFRs. Sixty-five X-ray observations of the 22 SFiNCs SFRs made with the imaging array on the Advanced CCD Imaging Spectrometer (ACIS) were extracted from the Chandra archive (spanning from 2000 January to 2015 April). See Tables 1 and 2 of the reference paper for the list of SFRs and the log of Chandra ACIS observations, respectively. The final Chandra-ACIS catalog for the 22 SFiNCs SFRs comprises 15,364 X-ray sources (presented in Tables 3 and 4 and section 3.2 of the reference paper, and the contents of this HEASARC table, SFINCSXRAY). To obtain MIR photometry for X-ray objects and to identify and measure MIR photometry for additional non-Chandra disky stars that were missed in previous studies of the SFiNCs regions (typically faint YSOs), the authors have reduced the archived Spitzer-IRAC data by homogeneously applying the MYStIX-based Spitzer-IRAC data reduction methods of Kuhn et al. (2013, ApJS, 209, 29) to the 423 Astronomical Object Request (AORs) data sets for the 22 SFiNCs SFRs (Table 5 of the reference paper). As in MYStIX, the SFiNCs IRAC source catalog retains all point sources with the photometric signal-to-noise ratio > 5 in both [3.6] and [4.5] um channels. This catalog covers the 22 SFiNCs SFRs and their vicinities on the sky and comprises 1,638,654 IRAC sources with available photometric measurements for 100%, 100%, 29%, and 23% of these sources in the 3.6, 4.5, 5.8, and 8.0um bands, respectively (see table 6 and section 3.4 of the reference paper). Source position cross-correlations between the SFiNCs Chandra X-ray source catalog and an IR catalog, either the "cut-out" IRAC or 2MASS, were made using the steps described in section 3.5 of the reference paper. Tables 7 and 8 of the reference paper provide the list of 8,492 SFiNCs probable cluster members (SPCMs) and their main IR and X-ray properties (see section 4 of the reference paper): this list as available at the HEASARC as the SFINCSPCM table (q.v.). This table was created by the HEASARC in September 2017 based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/229/28">CDS Catalog J/ApJS/229/28</a> files table3.dat (the list of SFiNCs X-ray sources and their basic properties) and table4.dat (the list of SFiNCs X-ray source fluxes). This is a service provided by NASA HEASARC .
RCW 108 Star Formation Region Chandra X-Ray Point Source Catalog
This table contains some of the results of an approximately 90 ks Chandra observation of a complex region that hosts multiple sites of recent and active star formation in ARA OB1a. The field is centered on the embedded cluster RCW 108-IR and includes a large portion of the open cluster NGC 6193. The authors detected over 420 X-ray sources in the field and combined these data with deep near-IR, Spitzer/IRAC and Midcourse Space Experiment (MSX) mid-IR data. They find that about 360 of the X-ray sources have near-IR counterparts. They divide the region into five parts based on the X-ray point source characteristics and extended 8 micron emission. The most clearly defined regions are the central region, identified by embedded sources with high luminosities in the both the near-IR and X-ray as well as high X-ray temperatures (~3 keV), and the eastern region, identified by low extinction and ~1 keV X-ray temperatures. Other regions, identified by their directional relationship to RCW 108-IR, are less uniform, representing combinations of the first two regions, independent star formation epochs, or both. The cluster members range in X-ray luminosity from 10<sup>29</sup> to 10<sup>33</sup> erg s<sup>-1</sup>. Over 18% of the cluster members with over 100 counts exhibit flares. All sources with over 350 counts are variable. Overall about 10% (16% in RCW 108-IR) appear to have optically thick disks as derived from their position in the (J - H), (H - K) diagram. The disk fraction becomes much higher when IRAC data are employed. The largest fraction of X-ray sources is best described as possessing some disk material via a more detailed extinction fitting. The authors fit the bulk of the X-ray spectra as absorbed Raymond-Smith-type plasmas, and find that the column to the RCW 108-IR members varies from 10<sup>21</sup> to 10<sup>23</sup> cm<sup>-2</sup>. They find that the field contains 41 candidate O or B stars, and estimate that the total number of pre-main-sequence stars in the field is about 1600 +/- 200. Approximately 800 are confined to the 3' (~1.1 pc) central region. The field was observed by Chandra on 2004 October 25 starting at 02:37 UT for 92.2 ks of total time and 88.8 ks of so-called "good-time" (ObsId 4503). The ACIS was used in the nominal imaging array (chips I0-I3) which provides a field of view of approximately 17' by 17' (~6.5 pc on a side). The aimpoint was at RA, Dec = 16:39:58.7, -48:51:54.4 (J2000.0). In addition, the S2 and S3 chips were on and located over IRAS 16379-4856. About 20 point sources were detected associated with this object; however, the analysis of these data is not presented here because they are far off-axis. This table was created by the HEASARC in June 2008 based on electronic versions of Tables 1, 2, 5, 7, 10 and 11 from the reference paper which were obtained from the Astronomical Journal web site. This is a service provided by NASA HEASARC .
Star-Forming Galaxies High-Mass X-Ray Binaries Catalog
Based on a homogeneous set of X-ray, infrared and ultraviolet observations from Chandra, Spitzer, GALEX and 2MASS archives, the authors studied populations of high-mass X-ray binaries (HMXBs) in a sample of 29 nearby star-forming galaxies and their relation with the star formation rate (SFR). In agreement with previous results, the authors find that HMXBs are a good tracer of the recent star formation activity in the host galaxy and their collective luminosity and number scale with the SFR, in particular, L<sub>X</sub> ~ 2.6 x 10<sup>39</sup> x SFR. However, the scaling relations still bear a rather large dispersion of rms ~ 0.4 dex, which the authors believe is of a physical origin. This table contains the catalog of 1055 compact X-ray sources detected within the D25 ellipse for galaxies of this sample which the authors used to construct the average X-ray luminosity function (XLF) of HMXBs with substantially improved statistical accuracy and better control of systematic effects than achieved in previous studies. The XLF follows a power law with slope of 1.6 in the log(L<sub>X</sub>) ~ 35 - 40 luminosity range with a moderately significant evidence for a break or cut-off at L<sub>X</sub> ~ 10<sup>40</sup> erg/s. As before, the authors did not find any features at the Eddington limit for a neutron star or a stellar mass black hole. In their paper, the authors discuss the implications of their results for the theory of binary evolution. In particular, they estimate the fraction of compact objects that once during their lifetime experienced an X-ray active phase powered by accretion from a high mass companion and obtain a rather large number, f<sub>X</sub> ~ 0.2 x (0.1 Myr/tau<sub>x</sub>), where tau<sub>x</sub> is the life time of the X-ray active phase. This is about 4 orders of magnitude more frequent than in low-mass X-ray binaries (LMXBs). The authors also derive constrains on the mass distribution of the secondary star in HMXBs. Note that, in their paper, the authors estimate that ~ 300 of the 1055 sources are likely to be background AGNs (cosmic X-ray background or CXB sources) and that the majority (<~ 700) of the remaining ~ 750 sources are young HMXB systems associated with star formation in their host galaxies. This table was created by the HEASARC in March 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/419/2095">CDS Catalog J/MNRAS/419/2095</a> file hmxb.dat. This is a service provided by NASA HEASARC .
ROSAT All-Sky Survey and SDSS Sample of X-Ray Emitting Stars
The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the entire sky. Combining the RASS Bright and Faint Source Catalogs yields an average of about three X-ray sources per square degree. However, while X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine the nature of an X-ray source. As a result, large-scale follow-up programs are required to construct samples of known X-ray emitters. The authors use optical data produced by the Sloan Digital Sky Survey (SDSS) to identify 709 stellar X-ray emitters cataloged in the RASS and falling within the SDSS Data Release 1 footprint. Most of these are bright stars with coronal X-ray emission unsuitable for SDSS spectroscopy, which is designed for fainter objects (g > 15<sup>mag</sup>). Instead, the authors use SDSS photometry, correlations with the Two Micron All Sky Survey (2MASS) and other catalogs, and spectroscopy from the Apache Point Observatory 3.5 m telescope to identify these stellar X-ray counterparts. Their sample of 707 X-ray-emitting F, G, K, and M stars is one of the largest X-ray-selected samples of such stars. The authors derive distances to these stars using photometric parallax relations appropriate for dwarfs on the main sequence, and use these distances to calculate their X-ray luminosities L<sub>X</sub>. They also identify a previously unknown cataclysmic variable (CV) as a RASS counterpart. Much more information on the SDSS is available at the project's web site at <a href="http://www.sdss.org/">http://www.sdss.org/</a>. This table was created by the HEASARC in April 2009 based on the the machine-readable version of Table 4 from the reference paper which was obtained from the ApJ web site. This is a service provided by NASA HEASARC .
W 40 Star-Forming Region Chandra X-Ray Point Source Catalog
The young stellar cluster illuminating the W40 H II region, one of the nearest massive star-forming regions (SFRs), has been observed with the ACIS detector on board the Chandra X-ray Observatory. Due to its high obscuration, this is a poorly studied stellar cluster with only a handful of bright stars visible in the optical band, including three OB stars identified as primary excitation sources. The authors detect 225 X-ray sources, of which 85% are confidently identified as young stellar members of the region. Two potential distances of the cluster, 260 pc and 600 pc, are used in the paper. Supposing the X-ray luminosity function of SFRs to be universal, it supports a 600 pc distance as a lower limit for W40 and a total population of at least 600 stars down to 0.1 M<sub>sun</sub> under the assumption of a coeval population with a uniform obscuration. In fact, there is strong spatial variation in K<sub>s</sub>-band-excess disk fraction and non-uniform obscuration due to a dust lane that is identified in absorption in optical, infrared, and X-ray. The dust lane is likely part of a ring of material which includes the molecular core within W40. In contrast to the likely ongoing star formation in the dust lane, the molecular core is inactive. The star cluster has a spherical morphology, an isothermal sphere density profile, and mass segregation down to 1.5 M<sub>sun</sub>. However, other cluster properties, including a <= 1 Myr age estimate and ongoing star formation, indicate that the cluster is not dynamically relaxed. X-ray diffuse emission and a powerful flare from a young stellar object are also reported in the reference paper. This table was created by the HEASARC in March 2011 based on electronic versions of Tables, 1, 2 and 4 of the reference paper which were obtained from the ApJ web site. This is a service provided by NASA HEASARC .
Cep B/OB3 Star-Forming Region Chandra X-Ray Point Source Catalog
This table contains the Cepheus B star formation region (the Cep B molecular cloud and the Cep OB3b OB association) Chandra X-Ray point source catalog. The Cepheus B (Cep B) molecular cloud and a portion of the nearby Cep OB3b OB association, one of the most active regions of star formation within 1 kpc, have been observed with the ACIS detector on board the Chandra X-Ray Observatory. 431 X-ray sources have been detected, of which 89% are confidently identified as clustered pre-main-sequence (PMS) stars. Two main results are obtained. First, the best census to date for the stellar population of the region has been made, with many members of two rich stellar clusters, the lightly obscured Cep OB3b association and the deeply embedded cluster in Cep B, whose existence was previously traced only by a handful of radio sources and T Tauri stars, being identified. Second, a discrepancy between the X-ray luminosity functions of the Cep OB3b and the Orion Nebula cluster has been found. This may be due to the different initial mass functions of the two regions (an excess of ~=0.3 M_solar stars) or different age distributions. Several other results are obtained. A diffuse X-ray component seen in the field is attributed to the integrated emission of unresolved low-mass PMS stars. The X-ray emission from HD 217086 (O7n), the principle ionizing source of the region, follows the standard model, involving many small shocks in an unmagnetized radiatively accelerated wind. X-ray source 294 joins a number of similar superflare PMS stars for which long magnetic structures may connect the protoplanetary disk to the stellar surface. The Chandra observation of Cep B and Cep OB3b was obtained on 2003 March 11.51-11.88 with the ACIS camera. Only results from the imaging array (ACIS-I) covering about 17' x 17' on the sky are considered here. The aim point of the array was 22 56 49.4 +62 39 55.6 (J2000.0 RA and Dec), and the satellite roll angle was 7.9 degrees. The total net exposure time was 30 ksec, with no background flaring or data losses. This table was created by the HEASARC in February 2007 based on the merger of electronic versions of tables 1, 2 and 3 from the above reference which were obtained from the ApJS website. This is a service provided by NASA HEASARC .
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