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- ID:
- ivo://CDS.VizieR/J/ApJS/211/9
- Title:
- Variability in UV line emission of F-M stars
- Short Name:
- J/ApJS/211/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Variations in stellar flux can potentially overwhelm the photometric signal of a transiting planet. Such variability has not previously been well-characterized in the ultraviolet lines used to probe the inflated atmospheres surrounding hot Jupiters. Therefore, we surveyed 38 F-M stars for intensity variations in four narrow spectroscopic bands: two enclosing strong lines from species known to inhabit hot Jupiter atmospheres, C.II {lambda}{lambda}1334, 1335 and SiIII{lambda}1206; one enclosing SiIV {lambda}{lambda}1393, 1402; and 36.5{AA} of interspersed continuum. For each star/band combination, we generated 60s cadence lightcurves from archival Hubble Space Telescope Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph time-tagged photon data. Within these lightcurves, we characterized flares and stochastic fluctuations as separate forms of variability. Flares: we used a cross-correlation approach to detect 116 flares. These events occur in the time-series an average of once per 2.5hr, over 50% last 4 minutes or less, and most produce the strongest response in SiIV. If the flare occurred during a transit measurement integrated for 60 minutes, 90/116 would destroy the signal of an Earth, 27/116 Neptune, and 7/116 Jupiter, with the upward bias in flux ranging from 1% to 109% of quiescent levels. Fluctuations: photon noise and underlying stellar fluctuations produce scatter in the quiescent data. We model the stellar fluctuations as Gaussian white noise with standard deviation {sigma}_x_. Maximum likelihood values of {sigma}_x_ range from 1% to 41% for 60s measurements. These values suggest that many cool stars will only permit a transit detection to high confidence in ultraviolet resonance lines if the radius of the occulting disk is >~1R_J_. However, for some M dwarfs this limit can be as low as several R_{oplus}_.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/1411
- Title:
- Variability of broad emission lines in QSOs
- Short Name:
- J/MNRAS/434/1411
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the variability of the high-ionization Ly{alpha} {lambda}1216 broad emission line (BEL) in a sample of 61 high-luminosity, high-redshift quasars observed at two epochs by the Sloan Digital Sky Survey. These bright objects lie in the redshift interval z=[2.5, 4.3] and have luminosities 3.4x10^45^<~{lambda}*L_{lambda}_<~3.4x10^46^erg/s at 1450{AA}. Utilizing improved spectrophotometric flux calibrations relative to nearby compact stars observed simultaneously, we are able to measure the flux changes in Ly{alpha} and the nearby continuum at two epochs. We find 20 objects that exhibit Ly{alpha} BEL flux variability at a significance level greater than 5{sigma} on time-scales ranging from days to years in the quasar rest frame.
3034. Variability of OB stars
- ID:
- ivo://CDS.VizieR/J/A+A/639/A81
- Title:
- Variability of OB stars
- Short Name:
- J/A+A/639/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The lack of high-precision long-term continuous photometric data for large samples of stars has impeded the large-scale exploration of pulsational variability in the OB star regime. As a result, the candidates for in-depth asteroseismic modelling have remained limited to a few dozen dwarfs. The TESS nominal space mission has surveyed the southern sky, including parts of the galactic plane, yielding continuous data across at least 27d for hundreds of OB stars. We aim to couple TESS data in the southern sky with ground-based spectroscopy to study the variability in two dimensions, mass and evolution. We focus mainly on the presence of coherent pulsation modes that may or may not be present in the predicted theoretical instability domains and unravel all frequency behaviour in the amplitude spectra of the TESS data. We compose a sample of 98 OB-type stars observed by TESS in Sectors 1-13 and with available multi-epoch, high-resolution spectroscopy gathered by the IACOB and OWN surveys. We present the short-cadence 2 min light curves of dozens of OB-type stars, which have one or more spectra in the IACOB or OWN database. Based on these light curves and their Lomb-Scargle periodograms, we performed variability classification and frequency analysis. We placed the stars in the spectroscopic Hertzsprung-Russell diagram to interpret the variability in an evolutionary context. We deduce the diverse origins of the mmag-level variability found in all of the 98 OB stars in the TESS data. We find among the sample several new variable stars, including three hybrid pulsators, three eclipsing binaries, high frequency modes in a Be star, and potential heat-driven pulsations in two Oe stars. We identify stars for which future asteroseismic modelling is possible, provided mode identification is achieved. By comparing the position of the variables to theoretical instability strips, we discuss the current shortcomings in non-adiabatic pulsation theory and the distribution of pulsators in the upper Hertzsprung-Russell diagram.
- ID:
- ivo://CDS.VizieR/J/ApJ/814/150
- Title:
- Variability of SDSS broad absorption line QSOs
- Short Name:
- J/ApJ/814/150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a qualitative analysis of the variability of quasar broad absorption lines using the large multi-epoch spectroscopic data set of the Sloan Digital Sky Survey Data Release 10. We confirm that variations of absorption lines are highly coordinated among different components of the same ion or the same absorption component of different ions for CIV, SiIV, and NV. Furthermore, we show that the equivalent widths (EWs) of the lines decrease or increase statistically when the continuum brightens or dims. This is further supported by the synchronized variations of emission and absorption-line EWs when the well-established intrinsic Baldwin effect for emission lines is taken into account. We find that the emergence of an absorption component is usually accompanied by the dimming of the continuum while the disappearance of an absorption-line component is accompanied by the brightening of the continuum. This suggests that the emergence or disappearance of a CIV absorption component is only the extreme case, when the ionic column density is very sensitive to continuum variations or the continuum variability the amplitude is larger. These results support the idea that absorption-line variability is driven mainly by changes in the gas ionization in response to continuum variations, that the line-absorbing gas is highly ionized, and in some extreme cases, too highly ionized to be detected in UV absorption lines. Due to uncertainties in the spectroscopic flux calibration, we cannot quantify the fraction of quasars with asynchronized continuum and absorption-line variations.
3036. Variability of WR 86
- ID:
- ivo://CDS.VizieR/J/A+A/384/1012
- Title:
- Variability of WR 86
- Short Name:
- J/A+A/384/1012
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The tables present photometric monitoring of WR 86 in the Walraven VBLUW system during two nights in July 1989, three nights in May/June 1990 and six nights in June 1990, together with UBV photometry during one night in 1995. Radial velocity measurements of WR86 for six emission lines in 1989, three emission lines in 1995 and two absorption lines in 1995. Equivalent width measurements of WR86 for five emission lines in 1989 and three emission lines in 1995.
- ID:
- ivo://CDS.VizieR/J/ApJS/250/3
- Title:
- Variable MgII NALs in SDSS DR14
- Short Name:
- J/ApJS/250/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Compared to high ionization CIV absorption lines, variable MgII absorption lines are rare. Using spectra from the Sloan Digital Sky Survey, we investigate the variations in MgII narrow absorption lines (NALs) for quasars with multi-epoch observations. We have compiled 8958 MgII NALs in the spectral regions from the red wings of CIV emission lines to the red wings of MgII emission lines. Among these 8958 MgII NALs, 22 variable NALs are detected with |{Delta}W_r_^{lambda}2796^|>=3{sigma}_W_ and with velocity offsets ranging from {upsilon}_r_=522 to 145513km/s. We find that: (1) the detected frequency of MgII NALs with {upsilon}_r_<=10000km/s is significantly larger than the uniformly random value expected for the MgII NALs with {upsilon}_r_>10000km/s, (2) the incidence rates of the variable MgII NALs with {upsilon}_r_<=10000km/s are much larger than those with {upsilon}_r_>10000km/s, (3) the velocity offsets of variable MgII NALs with {upsilon}_r_<=10000km/s are much smaller than the maximum velocities expected from radiation-driven outflows, and (4) the variations of variable MgII NALs with {upsilon}_r_<=10000km/s are obviously correlated with the changes in the quasar radiative output. Therefore, the 16 variable MgII NALs, whose velocities are smaller than the maximum velocities expected from radiation-driven outflows, are likely related to quasar outflows, while the 6 variable MgII NALs, whose velocities are much larger than the maximum velocities expected from radiation-driven outflows, possibly originated in intervening gas. We also find that both the variations and fractional variations in absorption strengths are not related to the velocity offsets of MgII NALs and the time intervals between the two epochs of observations. Also, the fractional variations in absorption strengths are inversely correlated with absorption strengths. In addition, both the associated and intervening MgII NALs can significantly vary on a timescale of days.
- ID:
- ivo://CDS.VizieR/J/ApJ/790/48
- Title:
- Variable stars in M31 & M33. II. LBVs
- Short Name:
- J/ApJ/790/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors and their evolutionary state. A greatly improved census of the likely progenitor class, including the most luminous evolved stars, the luminous blue variables (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-supernova stages of very massive stars. We have begun a survey of the evolved and unstable luminous star populations in several nearby resolved galaxies. In this second paper on M31 and M33, we review the spectral characteristics, spectral energy distributions, circumstellar ejecta, and evidence for mass loss for 82 luminous and variable stars. We show that many of these stars have warm circumstellar dust including several of the Fe II emission line stars, but conclude that the confirmed LBVs in M31 and M33 do not. The confirmed LBVs have relatively low wind speeds even in their hot, quiescent or visual minimum state compared to the B-type supergiants and Of/WN stars which they spectroscopically resemble. The nature of the Fe II emission line stars and their relation to the LBV state remains uncertain, but some have properties in common with the warm hypergiants and the sgB[e] stars. Several individual stars are discussed in detail. We identify three possible candidate LBVs and three additional post-red supergiant candidates. We suggest that M33-013406.63 (UIT301,B416) is not an LBV/S Dor variable, but is a very luminous late O-type supergiant and one of the most luminous stars or pair of stars in M33.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A152
- Title:
- Variation of MgHe line profile with temperature
- Short Name:
- J/A+A/619/A152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Line shapes of the magnesium resonance lines in white dwarf spectra are determined by the properties of magnesium atoms and the structure of the white dwarf atmosphere. Through their blanketing effect, these lines have a dominant influence on the model structure and thus on the determination from the spectra of other physical parameters that describe the stellar atmosphere and elemental abundances. In continuation of previous work on Mg+He lines in the UV, we present theoretical profiles of the resonance line of neutral Mg perturbed by He at the extreme density conditions found in the cool largely transparent atmosphere of DZ white dwarfs. We accurately determined the broadening of Mg by He in a unified theory of collisional line profiles using ab initio calculations of MgHe potential energies and transition matrix elements among the singlet electronic states that are involved for the observable spectral lines. We computed the shapes and line parameters of the Mg lines and studied their dependence on helium densities and temperatures. We present results over the full range of temperatures from 4000 to 12000K needed for input to stellar spectra models. Atmosphere models were constructed for a range of effective temperatures and surface gravities typical for cool DZ white dwarfs. We present synthetic spectra tracing the behavior of the Mg resonance line profiles under the low temperatures and high gas pressures prevalent in these atmospheres. The determination of accurate opacity data of magnesium resonance lines together with an improved atmosphere model code lead to a good fit of cool DZ white dwarf stars. The broadening of spectral lines by helium needs to be understood to accurately determine the H/He and Mg/He abundance ratio in DZ white dwarf atmospheres. We emphasize that no free potential parameters or ad hoc adjustments were used to calculate the line profiles.
- ID:
- ivo://CDS.VizieR/III/256
- Title:
- Vatican Emission-line stars
- Short Name:
- III/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The survey represents a search for H{alpha} emission-line stars, and was conducted with a 12{deg} objective prism on the Vatican Schmidt telescope. The Vatican Emission Stars (VES) survey covers the galactic plane (|b|<=5{deg}) between galactic longitudes 58 and 174{deg}. The catalog was re-examined by B. Skiff (Lowell Observatory), and tne VES stars were cross-identified with modern surveys: GSC (Cat. I/255), Tycho-2 (I/256), 2MASS (II/246), IRAS point source catalog (II/125), MSX6C (V/114), CMC14 (I/304), GSC-2.3 (I/305), UCAC2 (I/289). Cross-identifications are also supplied with HD/BD/GCVS names, and with Dearborn catalog of red stars (II/68). Many of the stars in the first four papers are not early-type emission-line stars, but instead M giants, where the sharp TiO bandhead at 6544{AA} was mistaken for H-{alpha} emission on the objective-prism plates. Based on the revision of paper V and a later list prepared by Jack MacConnell, a column identifies the "non H-alpha" stars explicitly. The links with the Dearborn, IRAS, and MSX catalogues help identify the red stars. These and other identifications and comments are given in the remarks at the end of each line, or in longer notes in a separate file, indicated by an asterisk (*) next to the star number.
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