- ID:
- ivo://CDS.VizieR/J/ApJS/238/25
- Title:
- UV variability with GALEX gPhoton archive. I.
- Short Name:
- J/ApJS/238/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to develop and test a methodology to search for UV variability over the entire Galaxy Evolution Explorer (GALEX) database down to the shortest timescales, we analyzed time-domain photometry of ~5000 light curves of ~300 bright (mFUV, mNUV<=14) and blue (mFUV-mNUV<0) GALEX sources. Using the gPhoton database tool, we discovered and characterized instrumentally induced variabilities in time-resolved GALEX photometry that may severely impact automated searches for short-period variations. The most notable artifact is a quasi-sinusoidal variation mimicking light curves typical of pulsators, seen occasionally in either one or both detectors, with amplitudes of up to 0.3mag and periods corresponding to the periodicity of the spiral dithering pattern used during the observation (P~120s). Therefore, the artifact may arise from small-scale response variations. Other artifacts include visit-long "sagging" or "hump" in flux, occurring when the dithering pattern is not a spiral, or a one-time change in flux level during the exposure. These instrumentally caused variations were not reported before, and are not due to known (and flagged) artifacts such as hotspots, which can be easily eliminated. To characterize the frequency and causality of such artifacts, we apply Fourier transform analysis to both light curves and dithering patterns, and examine whether artificial brightness variations correlate with visit or instrumental parameters. Artifacts do not correlate with source position on the detector. We suggest methods to identify artifact variations and to correct them when possible.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/140/1137
- Title:
- UV, VIH photometry of NGC 1311
- Short Name:
- J/AJ/140/1137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have extracted point-spread-function-fitted stellar photometry from near-ultraviolet, optical, and near-infrared images, obtained with the Hubble Space Telescope, of the nearby (D~5.5Mpc) SBm galaxy NGC 1311. The ultraviolet and optical data reveal a population of hot main-sequence (MS) stars with ages of 2-10Myr. We also find populations of blue supergiants with ages between 10 and 40Myr and red supergiants with ages between 10 and 100Myr.
- ID:
- ivo://CDS.VizieR/J/MNRAS/431/2063
- Title:
- UV/X-ray activity of M dwarfs within 10pc
- Short Name:
- J/MNRAS/431/2063
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M dwarfs are the most numerous stars in the Galaxy. They are characterized by strong magnetic activity. The ensuing high-energy emission is crucial for the evolution of their planets and the eventual presence of life on them. We systematically study the X-ray and ultraviolet emission of a subsample of M dwarfs from a recent proper-motion survey, selecting all M dwarfs within 10pc to obtain a nearly volume-limited sample (~90 percent completeness). Archival ROSAT, XMM-Newton and GALEX data are combined with published spectroscopic studies of H{alpha} emission and rotation to obtain a broad picture of stellar activity on M dwarfs. We make use of synthetic model spectra to determine the relative contributions of photospheric and chromospheric emission to the ultraviolet flux. We also analyse the same diagnostics for a comparison sample of young M dwarfs in the TW Hya association (~10Myr). We find that generally the emission in the GALEX bands is dominated by the chromosphere but the photospheric component is not negligible in early-M field dwarfs. The surface fluxes for the H{alpha}, near-ultraviolet, far-ultraviolet and X-ray emission are connected via a power-law dependence. We present here for the first time such flux-flux relations involving broad-band ultraviolet emission for M dwarfs. Activity indices are defined as flux ratio between the activity diagnostic and the bolometric flux of the star in analogy to the CaII R'HK index. For given spectral type, these indices display a spread of 2-3dex which is largest for M4 stars. Strikingly, at mid-M spectral types, the spread of rotation rates is also at its highest level. The mean activity index for fast rotators, likely representing the saturation level, decreases from X-rays over the FUV to the NUV band and H{alpha}, i.e. the fractional radiation output increases with atmospheric height. The comparison to the ultraviolet and X-ray properties of TWHya members shows a drop of nearly three orders of magnitude for the luminosity in these bands between ~10Myr and few Gyr age. A few young field dwarfs (<1Gyr) in the 10-pc sample bridge the gap indicating that the drop in magnetic activity with age is a continuous process. The slope of the age decay is steeper for the X-ray than for the UV luminosity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/2586
- Title:
- UWISH2 extended H2 emission line sources
- Short Name:
- J/MNRAS/454/2586
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the extended source catalogue for the UKIRT Wide Field Infrared Survey for H2 (UWISH2). The survey is unbiased along the inner Galactic Plane from l~357{deg} to l~65{deg} and |b|<=1.5{deg} and covers 209deg^2^. A further 42.0 and 35.5deg^2^ of high dust column density regions have been targeted in Cygnus and Auriga. We have identified 33200 individual extended H_2_ features. They have been classified to be associated with about 700 groups of jets and outflows, 284 individual (candidate) planetary nebulae, 30 supernova remnants and about 1300 photodissociation regions. We find a clear decline of star formation activity (traced by H_2_ emission from jets and photodissociation regions) with increasing distance from the Galactic Centre. About 60 percent of the detected candidate planetary nebulae have no known counterpart and 25 percent of all supernova remnants have detectable H_2_ emission associated with them.
- ID:
- ivo://CDS.VizieR/J/AJ/124/3061
- Title:
- uz,vz,bz,yz photometry in Coma cluster
- Short Name:
- J/AJ/124/3061
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed three fields of the Coma Cluster of galaxies with a narrowband (modified Stroemgren) filter system. Observed galaxies include 31 in the vicinity of NGC 4889, 48 near NGC 4874, and 60 near NGC 4839, complete to M_5500_=-18 in all three subclusters. Spectrophotometric classification finds all three subclusters of Coma to be dominated by red, E-type (elliptical/S0) galaxies with a mean blue fraction, f_B_, of 0.10.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/128
- Title:
- Validated & new members of NGC 7000/IC 5070 Complex
- Short Name:
- J/ApJ/899/128
- Date:
- 14 Mar 2022 07:05:45
- Publisher:
- CDS
- Description:
- We examine the clustering and kinematics of young stellar objects (YSOs) in the North America/Pelican Nebulae, as revealed by Gaia astrometry, in relation to the structure and motions of the molecular gas, as indicated in molecular-line maps. The Gaia parallaxes and proper motions allow us to significantly refine previously published lists of YSOs, demonstrating that many of the objects previously thought to form a distributed population turn out to be nonmembers. The members are subdivided into at least six spatio-kinematic groups, each of which is associated with its own molecular cloud component or components. Three of the groups are expanding, with velocity gradients of 0.3-0.5km/s/pc, up to maximum velocities of ~8km/s away from the groups' centers. The two known O-type stars associated with the region, 2MASS J20555125+4352246 and HD 199579, are rapidly escaping one of these groups, following the same position-velocity relation as the low-mass stars. We calculate that a combination of gas expulsion and tidal forces from the clumpy distribution of molecular gas could impart the observed velocity gradients within the groups. However, on a global scale, the relative motions of the groups do not appear either divergent or convergent. The velocity dispersion of the whole system is consistent with the kinetic energy gained due to gravitational collapse of the complex. Most of the stellar population has ages similar to the freefall timescales for the natal clouds. Thus, we suggest the nearly freefall collapse of a turbulent molecular cloud as the most likely scenario for star formation in this complex.
- ID:
- ivo://CDS.VizieR/J/A+AS/136/531
- Title:
- Valinhos CCD Meridian Circle radio stars
- Short Name:
- J/A+AS/136/531
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The astrometry of 16 radio stars taken from the list of Wendker (1995, Cat. <II/199>) is presented. The observations were carried out between 1996.3 and 1998.8 at the Valinhos CCD Meridian Circle. The results are given on the Hipparcos/Tycho reference frame. The data obtained relatively to the ACT catalogue is presented here. The ACT reference stars measured on 16 sky strips are listed on the table named tableref. The Table 1 of this paper, is presented, giving the radio star position on each field.
- ID:
- ivo://CDS.VizieR/J/ApJ/900/106
- Title:
- Vanadium abundances for 255 metal-poor stars
- Short Name:
- J/ApJ/900/106
- Date:
- 13 Jan 2022 00:15:01
- Publisher:
- CDS
- Description:
- We present vanadium (V) abundances for 255 metal-poor stars derived from high-resolution optical spectra from the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coude Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We use updated VI and VII atomic transition data from recent laboratory studies, and we increase the number of lines examined (from one to four lines of VI, and from two to seven lines of VII). As a result, we reduce the V abundance uncertainties for most stars by more than 20% and expand the number of stars with V detections from 204 to 255. In the metallicity range -4.0<[Fe/H]{<}-1.0, we calculate the mean ratios [VI/FeI]=-0.10+/-0.01 ({sigma}=0.16) from 128 stars with >=2VI lines detected, [VII/FeII]=+0.13+/-0.01 ({sigma}=0.16) from 220 stars with >=2 VII lines detected, and [VII/VI]=+0.25+/-0.01 ({sigma}=0.15) from 119 stars. We suspect that this offset is due to departures from local thermodynamic equilibrium, and we recommend using [VII/FeII], which is enhanced relative to the solar ratio, as a better representation of [V/Fe]. We provide more extensive evidence for abundance correlations detected previously among scandium, titanium, and vanadium, and we identify no systematic effects in the analysis that can explain these correlations.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A118
- Title:
- Vanadium measurements for 135 M dwarfs
- Short Name:
- J/A+A/654/A118
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- M-dwarf spectra are complex and notoriously difficult to model, posing challenges to understanding their photospheric properties and compositions in depth. Vanadium (V) is an iron-group element whose abundance supposedly closely tracks that of iron, but has origins that are not completely understood. Our aim is to characterize a series of neutral vanadium atomic absorption lines in the 800-910nm wavelength region of high signal-to-noise, high-resolution, telluric-corrected M-dwarf spectra from the CARMENES survey. Many of these lines are prominent and exhibit a distinctive broad and flat-bottom shape -- a result of hyperfine splitting (HFS). We investigate the potential and implications of these HFS-split lines for abundance analysis of cool stars. With standard spectral synthesis routines, as provided by the spectroscopy software iSpec and the latest atomic data (including HFS) available from the VALD3 database, we model these striking line profiles. We use them to measure V abundances of cool dwarfs. We determine V abundances for 135 early-M dwarfs (M0.0V to M3.5V) in the CARMENES guaranteed time observations sample. They exhibit a [V/Fe]-[Fe/H] trend consistent with that derived from nearby FG dwarfs. The tight (+/-0.1dex) correlation between [V/H] and [Fe/H] suggests the potential application of V as an alternative metallicity indicator in M dwarfs. We also show hints that a neglect to model HFS could partially explain the temperature correlation in V abundance measurements observed in previous studies of samples involving dwarf stars with Teff<=5300K. Our work suggests that HFS can impact certain absorption lines in cool photospheres more severely than in Sun-like ones. Therefore, we advocate that HFS should be carefully treated in abundance studies in stars cooler than ~5000 K. On the other hand, strong HFS split lines in high-resolution spectra present an opportunity for precision chemical analyses of large samples of cool stars. The V-to-Fe trends exhibited by the local M dwarfs continue to challenge theoretical models of V production in the Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJS/238/19
- Title:
- VANDAM IV. Free-free emission from protostars
- Short Name:
- J/ApJS/238/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Emission from protostars at centimeter radio wavelengths has been shown to trace the free-free emission arising from ionizing shocks as a result of jets and outflows driven by protostars. Therefore, measuring properties of protostars at radio frequencies can provide valuable insights into the nature of their outflows and jets. We present a C-band (4.1 and 6.4cm) survey of all known protostars (Class0 and ClassI) in Perseus as part of the VLA Nascent Disk and Multiplicity (VANDAM) Survey. We examine the known correlations between radio flux density and protostellar parameters, such as bolometric luminosity and outflow force, for our sample. We also investigate the relationship between radio flux density and far-infrared line luminosities from Herschel. We show that free-free emission most likely originates from J-type shocks; however, the large scatter indicates that those two types of emission probe different time and spatial scales. Using C-band fluxes, we removed an estimation of free-free contamination from the corresponding Ka- band (9mm) flux densities that primarily probe dust emission from embedded disks. We find that the compact (<1") dust emission is lower for Class I sources (median dust mass 96M_{Earth}_) relative to Class 0 (248M_{Earth}_), but several times higher than in Class II (5-15M_{Earth}_). If this compact dust emission is tracing primarily the embedded disk, as is likely for many sources, this result provides evidence of decreasing disk masses with protostellar evolution, with sufficient mass for forming giant planet cores primarily at early times.
