- ID:
- ivo://CDS.VizieR/J/AJ/159/233
- Title:
- Observations of binary stars with the DSSI. IX.
- Short Name:
- J/AJ/159/233
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report 370 measures of 170 components of binary and multiple-star systems, obtained from speckle imaging observations made with the Differential Speckle Survey Instrument (DSSI) at Lowell Observatory's Discovery Channel Telescope in 2015 through 2017. Of the systems studied, 147 are binary stars, 10 are seen as triple systems, and 1 quadruple system is measured. Seventy-six high-quality nondetections and 15 newly resolved components are presented in our observations. The uncertainty in relative astrometry appears to be similar to our previous work at Lowell, namely, linear measurement uncertainties of approximately 2mas, and the relative photometry appears to be uncertain at the 0.1-0.15mag level. Using these measures and those in the literature, we calculate six new visual orbits, including one for the Be star 66Oph and two combined spectroscopic-visual orbits. The latter two orbits, which are for HD22451 (YSC127) and HD185501 (YSC135), yield individual masses of the components at the level of 2% or better, and independent distance measures that in one case agrees with the value found in the Gaia DR2 and in the other disagrees at the 2{sigma} level. We find that HD22451 consists of an F6V+F7V pair with orbital period of 2401.1{+/-}3.2days and masses of 1.342{+/-}0.029 and 1.236{+/-}0.026M_{sun}_. For HD185501, both stars are G5 dwarfs that orbit one another with a period of 433.94{+/-}0.15days, and the masses are 0.898{+/-}0.012 and 0.876{+/-}0.012M_{sun}_. We discuss the details of both the new discoveries and the orbit objects.
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- ID:
- ivo://CDS.VizieR/J/A+A/657/A62
- Title:
- OB stars spectral classification automated tool
- Short Name:
- J/A+A/657/A62
- Date:
- 17 Mar 2022 14:50:02
- Publisher:
- CDS
- Description:
- As an increasing number of spectroscopic surveys become available, an automated approach to spectral classification becomes necessary. Due to the significance of the massive stars, it is of great importance to identify the phenomenological parameters of these stars (e.g., the spectral type), which can be used as proxies to their physical parameters (e.g., mass and temperature). In this work, we aim to use the random forest (RF) algorithm to develop a tool for the automated spectral classification of OB-type stars according to their sub-types. We used the regular RF algorithm, the probabilistic RF (PRF), which is an extension of RF that incorporates uncertainties, and we introduced the KDE-RF method which is a combination of the kernel-density estimation and the RF algorithm. We trained the algorithms on the equivalent width (EW) of characteristic absorption lines measured in high-quality spectra (Signal-to-Noise (S/N)>50) from large Galactic (LAMOST, GOSSS) and extragalactic surveys (2dF, VFTS) with available spectral types and luminosity classes. By following an adaptive binning approach, we grouped the labels of these data in 11 spectral classes within the O2-B9 range. We examined which of the characteristic spectral lines (features) are more important for the classification based on a number of feature selection methods, and we searched for the optimal hyperparameters of the classifiers to achieve the best performance. From the feature-screening process, we find that the full set of 17 spectral lines is needed to reach the maximum performance per spectral class. We find that the overall accuracy score is ~70%, with similar results across all approaches. We apply our model in other observational data sets providing examples of the potential application of our classifier to real science cases. We find that it performs well for both single massive stars and for the companion massive stars in Be X-ray binaries, especially for data of similar quality to the training sample. In addition, we propose a reduced ten-features scheme that can be applied to large data sets with lower S/N~20-50. The similarity in the performances of our models indicates the robustness and the reliability of the RF algorithm when it is used for the spectral classification of early-type stars. The score of ~70% is high if we consider (a) the complexity of such multiclass classification problems (i.e., 11 classes), (b) the intrinsic scatter of the EW distributions within the examined spectral classes, and (c) the diversity of the training set since we use data obtained from different surveys with different observing strategies. In addition, the approach presented in this work is applicable to products from different surveys in terms of quality (e.g., different resolution) and different formats (e.g., absolute or normalized flux), while our classifier is agnostic to the luminosity class of a star, and, as much as possible, it is metallicity independent.
- ID:
- ivo://CDS.VizieR/J/A+A/478/659
- Title:
- OGLE Be stars in Galactic Bulge
- Short Name:
- J/A+A/478/659
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first systematic search for Be star candidates in the direction of the Galactic Bulge. We present the full catalogue, give a brief description of the stellar variability seen, and show some light curve examples. We searched for stars matching specific criteria of magnitude, color and variability in the I band. Our search was conducted on the 48 OGLE II fields of the Galactic Bulge.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A125
- Title:
- OGLE-III SMC massive stars VI light curves
- Short Name:
- J/A+A/562/A125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a variability study of 4646 massive stars in the Small Magellanic Cloud (SMC) with known spectral types from the catalog of Bonanos et al. (2010, Cat. J/AJ/140/416) using the light curves from the OGLE-III database. The goal is to exploit the time domain information available through OGLE-III to gain insight into the processes that govern the evolution of massive stars. This variability survey of massive stars with known spectral types is larger than any previous survey by a factor of 7. We find that 60% of our sample (2766 stars) show no significant variability and 40% (1880 stars) exhibit variability distributed as follows: 807 stars display low-amplitude stochastic variability with fluctuations in I-band of up to 0.05mag, 443 stars present irregular variability of higher amplitude (76% of these are reported as variables for the first time), 205 are eclipsing binaries (including 101 newly discovered systems), 50 are candidate rotating variables, 126 are classical Cepheids, 188 stars exhibit short-term sinusoidal periodicity (P<3-days) making them candidate 'slowly pulsating B stars' and non-radial Be pulsators, and 61 periodic stars exhibit longer periods. We demonstrate the wealth of information provided in the time domain, by doubling the number of known massive eclipsing binary systems and identifying 189 new candidate early-type Be and 20 Oe stars in the SMC. In addition, we find that ~80% of Be stars are photometrically variable in the OGLE-III time domain and provide evidence that short-term pulsating stars with additional photometric variability are rotating close to their break-up velocity.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/13
- Title:
- OI equivalent widths in Be stars
- Short Name:
- J/ApJ/753/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The possibility of the Ly{beta} fluorescence mechanism being operational in classical Be (CBe) stars and thereby contributing to the strength of the OI{lambda}8446 line has been recognized for long. However, this supposition needs to be quantified by comparing observed and predicted OI line ratios. In the present work, optical and near-infrared spectra of CBe stars are presented. We analyze the observed strengths of the OI{lambda}7774, {lambda}8446, {lambda}11287, and {lambda}13165 lines, which have been theoretically proposed as diagnostics for identifying the excitation mechanism. We have considered and examined the effects of Ly{beta} fluorescence, collisional excitation, recombination, and continuum fluorescence on these O I line strengths. From our analysis it appears that the Ly{beta} fluorescence process is indeed operative in Be stars.
- ID:
- ivo://CDS.VizieR/J/AJ/155/53
- Title:
- Outbursts and disk variability in Be stars
- Short Name:
- J/AJ/155/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to study the growth and evolution of circumstellar disks around classical Be stars, we analyze optical time-series photometry from the KELT survey with simultaneous infrared and visible spectroscopy from the Apache Point Observatory Galactic Evolution Experiment survey and Be Star Spectra database for a sample of 160 Galactic classical Be stars. The systems studied here show variability including transitions from a diskless to a disk-possessing state (and vice versa), and persistent disks that vary in strength, being replenished at either regularly or irregularly occurring intervals. We detect disk-building events (outbursts) in the light curves of 28% of our sample. Outbursts are more commonly observed in early- (57%), compared to mid- (27%) and late-type (8%) systems. A given system may show anywhere between 0 and 40 individual outbursts in its light curve, with amplitudes ranging up to ~0.5 mag and event durations between ~2 and 1000 days. We study how both the photometry and spectroscopy change together during active episodes of disk growth or dissipation, revealing details about the evolution of the circumstellar environment. We demonstrate that photometric activity is linked to changes in the inner disk, and show that, at least in some cases, the disk growth process is asymmetrical. Observational evidence of Be star disks both growing and clearing from the inside out is presented. The duration of disk buildup and dissipation phases are measured for 70 outbursts, and we find that the average outburst takes about twice as long to dissipate as it does to build up in optical photometry. Our analysis hints that dissipation of the inner disk occurs relatively slowly for late-type Be stars.
- ID:
- ivo://CDS.VizieR/J/AJ/153/252
- Title:
- Photometric variability of BeSS-KELT stars
- Short Name:
- J/AJ/153/252
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Be stars have generally been characterized by the emission lines in their spectra, and especially the time variability of those spectroscopic features. They are known to also exhibit photometric variability at multiple timescales, but have not been broadly compared and analyzed by that behavior. We have taken advantage of the advent of wide-field, long-baseline, and high-cadence photometric surveys that search for transiting exoplanets to perform a comprehensive analysis of brightness variations among a large number of known Be stars. The photometric data comes from the KELT transit survey, with a typical cadence of 30 minutes, a baseline of up to 10 years, photometric precision of about 1%, and coverage of about 60% of the sky. We analyze KELT light curves of 610 known Be stars in both the northern and southern hemispheres in an effort to study their variability. Consistent with other studies of Be star variability, we find most of the stars to be photometrically variable. We derive lower limits on the fraction of stars in our sample that exhibit features consistent with non-radial pulsations (25%), outbursts (36%), and long-term trends in the circumstellar disk (37%), and show how these are correlated with spectral sub-types. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectra database allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk.
- ID:
- ivo://CDS.VizieR/J/ApJ/698/2031
- Title:
- Polarimetry of HAeBe stars
- Short Name:
- J/ApJ/698/2031
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the correlation between the direction of the symmetry axis of the circumstellar material around intermediate mass young stellar objects and that of the interstellar magnetic field. We use CCD polarimetric data on 100 Herbig Ae/Be stars. A large number of them show intrinsic polarization, which indicates that their circumstellar envelopes are not spherical. The interstellar magnetic field direction is estimated from the polarization of field stars. There is an alignment between the position angle of the Herbig Ae/Be star polarization and that of the field stars for the most polarized objects. This may be an evidence that the ambient interstellar magnetic field plays a role in shaping the circumstellar material around young stars of intermediate mass and/or in defining their angular momentum axis.
- ID:
- ivo://CDS.VizieR/II/220
- Title:
- Polarisation of Be stars
- Short Name:
- II/220
- Date:
- 20 Dec 2021 15:54:35
- Publisher:
- CDS
- Description:
- The catalogue contains observations of the linear polarization in the UBVRI photometric system of 8 Northern Be stars; the observations are part of a long-term monitoring program begun in 1984.
- ID:
- ivo://CDS.VizieR/J/ApJ/671/2040
- Title:
- Polarisation of candidates Be stars
- Short Name:
- J/ApJ/671/2040
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first detailed imaging polarization observations of six SMC and six LMC clusters, known to have large populations of B-type stars that exhibit excess H{alpha} emission from 2-CD photometric studies, to constrain the evolutionary status of these stars and hence better establish links between the onset of disk formation in classical Be stars and cluster age and/or metallicity. We parameterize and remove the interstellar polarization (ISP) associated with each line of sight, thereby isolating the presence of any intrinsic polarization. We use the wavelength dependence of this intrinsic polarization to discriminate pure gas disk systems, i.e., classical Be stars, from composite gas-plus-dust disk systems, i.e., Herbig Ae/Be or B[e] stars.
