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8261. X-ray flares in Orion young stars. I.
ID:
ivo://CDS.VizieR/J/ApJ/688/418
Title:
X-ray flares in Orion young stars. I.
Short Name:
J/ApJ/688/418
Date:
21 Oct 2021
Publisher:
CDS
Description:
Pre-main-sequence (PMS) stars are known to produce powerful X-ray flares, which resemble magnetic reconnection solar flares scaled by factors up to 104. However, there are numerous puzzles, including the structure of X-ray-emitting coronae and magnetospheres, the effects of protoplanetary disks, and the effects of stellar rotation. To investigate these issues in detail, we examine 216 of the brightest flares from 161 PMS stars observed in the Chandra Orion Ultradeep Project (COUP, Getman et al. Cat. J/ApJS/160/319). The current study (Paper I) examines the flare morphologies, and provides a general comparison of COUP flare characteristics with those of other active X-ray stars and the Sun.
8262. X-ray imaging of RCW 49
ID:
ivo://CDS.VizieR/J/ApJ/665/719
Title:
X-ray imaging of RCW 49
Short Name:
J/ApJ/665/719
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW 49 and its central OB association Westerlund 2. We obtained a ~40ks X-ray image of a ~17'x17' field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ~8.3'x8.3' region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer MIR counterparts for 379 of them.
8263. X-ray-luminous galaxy cluster RX J0142.0+2131
ID:
ivo://CDS.VizieR/J/AJ/130/445
Title:
X-ray-luminous galaxy cluster RX J0142.0+2131
Short Name:
J/AJ/130/445
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a photometric and spectroscopic study of stellar populations in the X-ray-luminous cluster of galaxies RX J0142.0+2131 at z=0.280. This paper analyzes the results of high signal-to-noise ratio spectroscopy, as well as g'-, r'-, and i'-band imaging, using the Gemini Multi-Object Spectrograph on Gemini North.
8264. X-ray & MIR AGNs in Stripe 82 with eBOSS spectra
ID:
ivo://CDS.VizieR/J/ApJ/876/50
Title:
X-ray & MIR AGNs in Stripe 82 with eBOSS spectra
Short Name:
J/ApJ/876/50
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of a Sloan Digital Sky Survey IV eBOSS program to target X-ray sources and mid-infrared-selected Wide-field Infrared Survey Explorer (WISE) active galactic nucleus (AGN) candidates in a 36.8deg^2^ region of Stripe 82. About half this survey (15.6deg^2^) covers the largest contiguous portion of the Stripe 82 X-ray survey. This program represents the largest spectroscopic survey of AGN candidates selected solely by their WISE colors. We combine this sample with X-ray and WISE AGNs in the field identified via other sources of spectroscopy, producing a catalog of 4847 sources that is 82% complete to r~22. Based on X-ray luminosities or WISE colors, 4730 of these sources are AGNs, with a median sample redshift of z~1. About 30% of the AGNs are optically obscured (i.e., lack broad lines in their optical spectra). BPT analysis, however, indicates that 50% of the WISE AGNs at z<0.5 have emission line ratios consistent with star-forming galaxies, so whether they are buried AGNs or star-forming galaxy contaminants is currently unclear. We find that 61% of X-ray AGNs are not selected as mid-infrared AGNs, with 22% of X-ray AGNs undetected by WISE. Most of these latter AGNs have high X-ray luminosities (Lx>10^44^erg/s), indicating that mid-infrared selection misses a sizable fraction of the highest luminosity AGNs, as well as lower luminosity sources where AGN-heated dust is not dominating the mid-infrared emission. Conversely, ~58% of WISE AGNs are undetected by X-rays, though we do not find that they are preferentially redder than the X-ray-detected WISE AGNs.
8265. X-ray/NIR correlation for early-type galaxies
ID:
ivo://CDS.VizieR/J/MNRAS/367/627
Title:
X-ray/NIR correlation for early-type galaxies
Short Name:
J/MNRAS/367/627
Date:
21 Oct 2021
Publisher:
CDS
Description:
The relation between X-ray luminosity and near-infrared (NIR) luminosity for early-type galaxies has been examined. NIR luminosities should provide a superior measure of stellar mass compared to optical luminosities used in previous studies, especially if there is significant star formation or dust present in the galaxies. However, we show that the X-ray-NIR relations are remarkably consistent with the X-ray-optical relations. This indicates that the large scatter of the relations is dominated by scatter in the X-ray properties of early-type galaxies, and is consistent with early-types consisting of old, quiescent stellar populations. We have investigated scatter in terms of environment, surface brightness profile, Mg2, H{beta}, H{gamma} line strength indices, spectroscopic age and nuclear H{alpha} emission.
8266. X-ray obs. and membership probabilities of M37
ID:
ivo://CDS.VizieR/J/ApJ/809/161
Title:
X-ray obs. and membership probabilities of M37
Short Name:
J/ApJ/809/161
Date:
21 Oct 2021
Publisher:
CDS
Description:
Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods (P_rot_). M37 was observed almost continuously for five days, for a total of 440.5ks, to measure stellar X-ray luminosities (L_X_), a proxy for coronal activity, across a wide range of masses. The cluster's membership catalog was revisited to calculate updated membership probabilities from photometric data and each star's distance to the cluster center. The result is a comprehensive sample of 1699 M37 members: 426 with P_rot_, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, R_0_=P_rot_/{tau}, where {tau} is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, L_X_/L_bol_, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500Myr. We find that fast rotators, for which R_0_<0.09+/-0.01, show saturated levels of activity, with log(L_X_/L_bol_)=-3.06+/-0.04. For R_0_>=0.09+/-0.01, activity is unsaturated and follows a power law of the form R_0_^{beta}^, where {beta}=-2.03^+0.17^_-1.14_. This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4-1.3M_{sun}_, P_rot_ in the range 0.4-12.8 days, and L_X_ in the range 10^28.4-30.5^erg/s. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of ~500Myr.
8267. X-ray observations of NGC 2264
ID:
ivo://CDS.VizieR/J/AJ/134/999
Title:
X-ray observations of NGC 2264
Short Name:
J/AJ/134/999
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from an X-ray imaging survey of the young cluster NGC 2264, carried out with the European Photon Imaging Cameras (EPIC) on board the XMM-Newton spacecraft. The X-ray data are merged with extant optical and near-infrared photometry, spectral classifications, Halpha emission strengths, and rotation periods to examine the interrelationships between coronal and chromospheric activity, rotation, stellar mass, and internal structure for a statistically significant sample of pre-main-sequence stars. A total of 300 distinct X-ray sources can be identified with optical or near-infrared counterparts. The sources are concentrated within three regions of the cluster: in the vicinity of S Mon, within the large emission/reflection nebulosity southwest of S Mon, and along the broad ridge of molecular gas that extends from the Cone Nebula to the NGC 2264 IRS 2 field.
8268. X-ray, optical and radio monitoring of 3C 111
ID:
ivo://CDS.VizieR/J/ApJ/734/43
Title:
X-ray, optical and radio monitoring of 3C 111
Short Name:
J/ApJ/734/43
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of extensive multi-frequency monitoring of the radio galaxy 3C 111 between 2004 and 2010 at X-ray (2.4-10keV), optical (R band), and radio (14.5, 37, and 230GHz) wave bands, as well as multi-epoch imaging with the Very Long Baseline Array (VLBA) at 43GHz. Over the six years of observation, significant dips in the X-ray light curve are followed by ejections of bright superluminal knots in the VLBA images. This shows a clear connection between the radiative state near the black hole, where the X-rays are produced, and events in the jet. The X-ray continuum flux and Fe line intensity are strongly correlated, with a time lag shorter than 90 days and consistent with zero.
8269. X-ray/optical observations of A8-G2V stars
ID:
ivo://CDS.VizieR/J/A+AS/128/29
Title:
X-ray/optical observations of A8-G2V stars
Short Name:
J/A+AS/128/29
Date:
21 Oct 2021
Publisher:
CDS
Description:
Table 1 lists the sample of 173 stars observed for this study. They are selected from the Bright Star Catalogue (Cat. <V/50>), with the following selection criteria: - Spectral type between A8 and G2; no spectral peculiarities noted; not double in spectral type classification (e.g., HR 32 with spectral type F2V+F6V is excluded); - Luminosity class V; - Right ascension between 0h and 2h, or between 14h and 24 h, declination south of +10 degrees (defining the region on the sky visible during the appointed observation times); - Binaries for which both components occurred in the BSC are excluded, if the separation is less than 10". Not listed are five stars for which no (Walraven photometric and ROSAT X-ray) data are available. These are HR 591, HR 5542, HR 6593, HR 8245 and HR 8735. Table 2 lists the Walraven photometric (VBLUW) data for all but four stars from Table 1. Also listed in Table 2 are the effective temperature, surface gravity and the reddening, as derived from comparison with theoretical colours. Table 5 lists the ROSAT All Sky Survey data for all but 11 stars from Table 1. For a description of the Walraven photometric system, see e.g. <GCPD/11>
8270. X-ray properties of Chandra red galaxies
ID:
ivo://CDS.VizieR/J/A+A/501/485
Title:
X-ray properties of Chandra red galaxies
Short Name:
J/A+A/501/485
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the X-ray properties of the extremely red objects (ERO) population observed by Chandra with three partially overlapping pointings (up to ~90ks) over an area of ~500arcmin^2^, down to a 0.5-8keV flux limit of ~10-15erg/cm^2^/s. We selected EROs using a multi-band photometric catalog down to a Ks-band magnitude of ~19.3 (Vega system); 14 EROs were detected in X-rays, corresponding to ~9% of the overall X-ray source population (149 X-ray sources) and to ~5% of the ERO population (288). The X-ray emission of all X-ray detected EROs is consistent with that of an active galactic nucleus (AGN) (>~3.5x10^42^erg/s at photometric redshifts z>1), in agreement with previous X-ray observations, with an indication of increasing absorption between the three X-ray brightest EROs and the 11 X-ray faintest EROs.