- ID:
- ivo://CDS.VizieR/J/A+AS/31/439
- Title:
- A Survey of HII Regions in M31
- Short Name:
- J/A+AS/31/439
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An H-alpha survey, using a focal reducer and narrow-band interference filters, has resulted in the detection of nearly a thousand HII regions in M31. The catalog gives their positions, dimensions, and surface brightnesses. The surface brightnesses are on an absolute scale; the photographic measures were calibrated by using photoelectric measures from two different sources. The detection limit reached corresponds to an emission measure of 40cm^-6^pc at a temperature of 10000K.
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- ID:
- ivo://CDS.VizieR/J/A+A/653/A134
- Title:
- AT 2018bwo light curves
- Short Name:
- J/A+A/653/A134
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Luminous red novae (LRNe) are astrophysical transients associated with the partial ejection of a binary system's common envelope (CE) shortly before its merger. Here we present the results of our photometric and spectroscopic follow-up campaign of AT 2018bwo (DLT 18x), a LRN discovered in NGC 45, and investigate its progenitor system using binary stellar-evolution models. The transient reached a peak magnitude of M_r_=-10.97+/-0.11 and maintained this brightness during its optical plateau of t_p_=41+/-5d ays. During this phase, it showed a rather stable photospheric temperature of ~3300K and a luminosity of ~10^40^erg/s. Although the luminosity and duration of AT 2018bwo is comparable to the LRNe V838 Mon and M31-2015LRN, its photosphere at early times appears larger and cooler, likely due to an extended mass-loss episode before the merger. Toward the end of the plateau, optical spectra showed a reddened continuum with strong molecular absorption bands. The IR spectrum at +103 days after discovery was comparable to that of an M8.5 II type star, analogous to an extended AGB star. The reprocessed emission by the cooling dust was also detected in the mid-infrared bands ~1.5 years after the outburst. Archival Spitzer and Hubble Space Telescope data taken 10-14yrs before the transient event suggest a progenitor star with T_prog_~6500K, R_prog_~100R_{sun}_, and L_prog_=2x10^4^L_{sun}_, and an upper limit for optically thin warm (1000K) dust mass of M_d_<10^-6^M_{sun}_. Using stellar binary-evolution models, we determined the properties of binary systems consistent with the progenitor parameter space. For AT 2018bwo, we infer a primary mass of 12-16M_{sun}_, which is 9-45% larger than the ~11M_{sun}_ obtained using single-star evolution models. The system, consistent with a yellow-supergiant primary, was likely in a stable mass-transfer regime with -2.4 <= log (M_dot/Msun /yr) <= -1.2 a decade before the main instability occurred. During the dynamical merger, the system would have ejected 0.15-0.5M_{sun}_ with a velocity of ~500km/s.
- ID:
- ivo://CDS.VizieR/J/MNRAS/417/2651
- Title:
- AT20G-optical catalogue
- Short Name:
- J/MNRAS/417/2651
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our current understanding of radio-loud active galactic nuclei (AGN) comes predominantly from studies at frequencies of 5GHz and below. With the recent completion of the Australia Telescope 20GHz (AT20G) survey, we can now gain insight into the high-frequency radio properties of AGN. This paper presents supplementary information on the AT20G sources in the form of optical counterparts and redshifts. Optical counterparts were identified using the SuperCOSMOS data base and redshifts were found from either the 6dF Galaxy Survey or the literature. We also report 144 new redshifts. For AT20G sources outside the Galactic plane, 78.5% have optical identifications and 30.9% have redshift information. The optical identification rate also increases with increasing flux density. Targets which had optical spectra available were examined to obtain a spectral classification.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A93
- Title:
- AT 2020hat and AT 2020kog light curves
- Short Name:
- J/A+A/647/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our monitoring campaigns of the luminous red novae (LRNe) AT 2020hat in NGC 5068 and AT 2020kog in NGC 6106. The two objects were imaged (and detected) before their discovery by routine survey operations. They show a general trend of slow luminosity rise lasting at least a few months. The subsequent major LRN outbursts were extensively followed in photometry and spectroscopy. The light curves present an initial short-duration peak, followed by a redder plateau phase. AT 2020kog is a moderately luminous event peaking at ~7x10^40^erg/s, while AT 2020hat is almost one order of magnitude fainter than AT 2020kog, although it is still more luminous than V838 Mon. In analogy with other LRNe, the spectra of AT 2020kog change significantly with time. They resemble those of type IIn supernovae at early phases, then they become similar to those of K-type stars during the plateau, and to M-type stars at very late phases. In contrast, AT 2020hat already shows a redder continuum at early epochs, and its spectrum shows the late appearance of molecular bands. A moderate-resolution spectrum of AT 2020hat taken at +37d after maximum shows a forest of narrow P Cygni lines of metals with velocities of 180 km/s, along with an Halpha emission with a full-width at half-maximum velocity of 250km/s. For AT 2020hat, a robust constraint on its quiescent progenitor is provided by archival images of the Hubble Space Telescope. The progenitor is clearly detected as a mid-K type star, with an absolute magnitude of M_F606W=-3.33+/-0.09mag and a colour of F606W-F814W=1.14+/-0.05mag, which are inconsistent with the expectations from a massive star that could later produce a core-collapse supernova. Although quite peculiar, the two objects nicely match the progenitor versus light curve absolute magnitude correlations discussed in the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/632/L6
- Title:
- AT 2018hso light curves and spectra
- Short Name:
- J/A+A/632/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The absolute magnitudes of luminous red novae (LRNe) are intermediate between those of novae and supernovae (SNe), and show a relatively homogeneous spectro-photometric evolution. Although they were thought to derive from core instabilities in single stars, there is growing support for the idea that they are triggered by binary interaction that possibly ends with the merging of the two stars. AT 2018hso is a new transient showing transitional properties between those of LRNe and the class of intermediate-luminosity red transients (ILRTs) similar to SN 2008S. Through the detailed analysis of the observed parameters, our study support that it actually belongs to the LRN class and was likely produced by the coalescence of two massive stars. We obtained ten months of optical and near-infrared photometric monitoring, and 11 epochs of low-resolution optical spectroscopy of AT 2018hso. We compared its observed properties with those of other ILRTs and LRNe. We also inspected the archival Hubble Space Telescope (HST) images obtained about 15 years ago to constrain the progenitor properties. The light curves of AT 2018hso show a first sharp peak (reddening-corrected M_r_=13.93mag), followed by a broader and shallower second peak that resembles a plateau in the optical bands. The spectra dramatically change with time. Early-time spectra show prominent Balmer emission lines and a weak [CaII] doublet, which is usually observed in ILRTs. However, the strong decrease in the continuum temperature, the appearance of narrow metal absorption lines, the great change in the H{alpha} strength and profile, and the emergence of molecular bands support an LRN classification. The possible detection of a M_I_~8mag source at the position of AT 2018hso in HST archive images is consistent with expectations for a pre-merger massive binary, similar to the precursor of the 2015 LRN in M101. We provide reasonable arguments to support an LRN classification for AT 2018hso. This study reveals growing heterogeneity in the observables of LRNe than has been thought previously, which is a challenge for distinguishing between LRNe and ILRTs. This suggests that the entire evolution of gap transients needs to be monitored to avoid misclassifications.
- ID:
- ivo://CDS.VizieR/J/ApJ/867/105
- Title:
- ATLAS all-sky stellar ref. catalog, ATLAS-REFCAT2
- Short Name:
- J/ApJ/867/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Asteroid Terrestrial-impact Last Alert System (ATLAS) observes most of the sky every night in search of dangerous asteroids. Its data are also used to search for photometric variability, where sensitivity to variability is limited by photometric accuracy. Since each exposure spans 7.6{deg} corner to corner, variations in atmospheric transparency in excess of 0.01mag are common, and 0.01mag photometry cannot be achieved by using a constant flat-field calibration image. We therefore have assembled an all-sky reference catalog of approximately one billion stars to m~19 from a variety of sources to calibrate each exposure's astrometry and photometry. Gaia DR2 is the source of astrometry for this ATLAS Refcat2. The sources of g, r, i, and z photometry include Pan-STARRS DR1, the ATLAS Pathfinder photometry project, ATLAS reflattened APASS data, SkyMapper DR1, APASS DR9, the Tycho-2 catalog, and the Yale Bright Star Catalog. We have attempted to make this catalog at least 99% complete to m<19, including the brightest stars in the sky. We believe that the systematic errors are no larger than 5mmag rms, although errors are as large as 20mmag in small patches near the Galactic plane.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/13
- Title:
- ATLAS c-o colors and classification of asteroids
- Short Name:
- J/ApJS/247/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here the c-o colors for identified Flora, Vesta, Nysa-Polana, Themis, and Koronis family members within the historic data set (2015-2018) of the Asteroid Terrestrial-impact Last Alert System (ATLAS). The Themis and Koronis families are known to be relatively pure C- and S-type Bus-DeMeo taxonomic families, respectively, and the extracted color data from the ATLAS broadband c- and o-filters of these two families are used to demonstrate that the ATLAS c-o color is a sufficient parameter to distinguish between the C- and S-type taxonomies. The Vesta and Nysa-Polana families are known to display a mixture of taxonomies possibly due to Vesta's differentiated parent body origin and Nysa-Polana actually consisting of two nested families with differing taxonomies. Our data show that the Flora family also displays a large degree of taxonomic mixing and the data reveal a substantial H-magnitude dependence on color. We propose and exclude several interpretations for the observed taxonomic mix. Additionally, we extract rotation periods of all of the targets reported here and find good agreement with targets that have previously reported periods.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A28
- Title:
- ATLAS3D H{alpha} imaging of early-type galaxies
- Short Name:
- J/A+A/611/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The traditional knowledge of the mechanisms that caused the formation and evolution of early-type galaxies (ETG) in a hierarchical universe was challenged by the unexpected finding by ATLAS^3D^ that 86% of the ETGs show signs of a fast-rotating disk at their interior. This implies a common origin of most spiral galaxies, followed by a quenching phase, while only a minority of the most massive systems are slow rotators and were likely to be the products of merger events. Our aim is to improve our knowledge on the content and distribution of ionized hydrogen and their usage to form stars in a representative sample of ETGs for which the kinematics and detailed morphological classification were known from ATLAS^3D^. Methods. Using narrow-band filters centered on the redshifted H{alpha} line along with a broad-band (r-Gunn) filter to recover the stellar continuum, we observed or collected existing imaging observations for 147 ETGs (including members of the Virgo cluster) that are representative of the whole ATLAS3D survey. Fifty-five ETGs (37%) were detected in the H{alpha} line above our detection threshold, (EW(H{alpha})<=-1{AA}), and 21 harbor a strong source (EW(H{alpha})<=-5{AA}). The strong H{alpha} emitters appear associated with mostly low-mass (M*~10^10^M_{sun}_) S0 galaxies that contain conspicuous stellar and gaseous discs. These harbor significant star formation at their interior, including their nuclei. The weak H{alpha} emitters are almost one order of magnitude more massive, contain gas-poor discs and harbor an AGN at their centers. Their emissivity is dominated by [NII] and does not imply star formation. The 92 undetected ETGs constitute the majority in our sample and are gas-free systems that lack a disc and exhibit passive spectra even in their nuclei. These pieces of evidence reinforce the conclusion made previously that the evolution of ETGs followed the secular channel for the less massive systems and the dry merging channel for the most massive galaxies at the center of clusters of galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/146
- Title:
- Atmospheric parameters for nearby B-F stars
- Short Name:
- J/ApJ/804/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Age determination is undertaken for nearby early type (BAF) stars, which constitute attractive targets for high-contrast debris disk and planet imaging surveys. Our analysis sequence consists of acquisition of ubvy{beta} photometry from catalogs, correction for the effects of extinction, interpolation of the photometry onto model atmosphere grids from which atmospheric parameters are determined, and finally, comparison to the theoretical isochrones from pre-main sequence through post-main sequence stellar evolution models, accounting for the effects of stellar rotation. We calibrate and validate our methods at the atmospheric parameter stage by comparing our results to fundamentally determined T_eff_ and log g values. We validate and test our methods at the evolutionary model stage by comparing our results on ages to the accepted ages of several benchmark open clusters (IC2602, {alpha} Persei, Pleiades, Hyades). Finally, we apply our methods to estimate stellar ages for 3493 field stars, including several with directly imaged exoplanet candidates.
- ID:
- ivo://CDS.VizieR/J/AJ/157/153
- Title:
- Atomic lines in spectra of RR Lyrae & RHB stars
- Short Name:
- J/AJ/157/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived relations between FWHMs and equivalent widths of metallic absorption lines in the spectra of RR Lyrae stars to estimate new upper limits on the axial equatorial rotational velocities of RR Lyrae and metal-poor red horizontal branch (RHB) stars. We have also derived the variations of RR Lyrae macroturbulent velocities during the pulsation cycles. In RRab cycles, the line widths are dominated by phase-dependent convolutions of axial rotation and macroturbulence, which we designate as V_macrot_. The behavior of V_macrot_ is remarkably uniform among the RRab stars, but the behavior of V_macrot_ among RRc stars varies strongly from star to star. The RRab stars exhibit an upper limit on V_macrot_ of 5+/-1 km/s with weak evidence of an anticorrelation with T_eff_. The RRc minima range from 2 to 12 km/s. The abrupt decline in large rotations with decreasing T_eff_ at the blue boundary of the instability strip and the apparently smooth continuous variation among the RRab and RHB stars suggests that HB stars gain/lose surface angular momentum on timescales that are short compared to HB lifetimes. The V_macrot_ values for our metal-poor RHB stars agree well with those derived by Fourier analysis of an independent but less metal-poor sample of Carney et al. (2008AJ....135..892C); they conform qualitatively to the expectations of Tanner et al. (2013ApJ...778..117T). A general conclusion of our investigation is that surface angular momentum as measured by V_rot_sin(i) is not a reliable indicator of total stellar angular momentum anywhere along the HB.
