- 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.
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Search Results
- 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/A+A/575/L6
- Title:
- Optical observations of LS I +61 303
- Short Name:
- J/A+A/575/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The gamma-ray binary LS I +61 303 is composed of a Be star and a compact companion orbiting in an eccentric orbit. Variable flux modulated with the orbital period of ~26.5d has been detected from radio to very high-energy gamma-rays. In addition, the system presents a superorbital variability of the phase and amplitude of the radio outbursts with a period of ~4.6yr. We present optical photometric observations of LS I +61 303 spanning ~1.5yr (table 1) and contemporaneous H-alpha equivalent width (EW) data (table 2). The optical photometry shows, for the first time, that the known orbital modulation suffers a positive orbital phase shift and an increase in flux for data obtained 1-yr apart. The orbital modulation of the EW presents, for the first time, a positive orbital phase shift. These orbital phase shifts of the thermal indicators are in line with the observed behavior for nonthermal indicators, such as X-ray or radio emission. This shows that there is a strong coupling between the thermal and nonthermal emission processes in the gamma-ray binary LS I +61 303.
- 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/PAZh/32/662
- Title:
- Photometric Variability of HD 51585
- Short Name:
- J/PAZh/32/662
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric observations of HD 51585 (OY Gem), a B[e] star with an infrared excess and a candidate for protoplanetary nebulae, obtained with a 60-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in 1992-2005 are presented. The star exhibited rapid irregular brightness variations with amplitudes from 0.1mag in the V band to 0.2mag in the U band within the observing season as well as slow systematic variations with amplitudes from 0.3mag in the V band to 0.65mag in the U band and with a quasi-period of ~2800days. The B-V color index varied within 0.1mag and did not follow the slow systematic brightness variations, while U-B correlated with the U brightness and varied between 0.7mag at maximum light and 0.35mag at minimum light. Our low-resolution spectroscopy performed in 1994-2005 has revealed significant variability of the Balmer and Paschen hydrogen emission lines as well as the He I and OI lines. Equivalent widths are given for the HI, He I, OI, and Fe II lines; a correlation has been found between the star's photometric variability and the hydrogen line intensities. Our joint analysis of the photometric and spectroscopic data suggests that variations in a strong stellar wind are responsible for the variability of the star.
- ID:
- ivo://CDS.VizieR/J/AJ/151/104
- Title:
- Photometry and spectroscopy of LS V+44 17
- Short Name:
- J/AJ/151/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the spectroscopic and photometric observations on the Be/X-ray binary RX J0440.9+4431 from 2001 to 2014. The short-term and long-term variability of the H{alpha} line profile indicates that one-armed global oscillations existed in the circumstellar disk. Several positive and negative correlations between the V-band brightness and the H{alpha} intensity were found from the long-term photometric and spectroscopic observations. We suggest that the monotonic increase of the V-band brightness and the H{alpha} brightness between our 2005 and 2007 observations might be the result of a continuous mass ejection from the central Be star, while the negative correlation in 2007-2010 should be caused by the cessation of mass loss from the Be star just before the decline in V-band brightness began (around our 2007 observations). With the extension of the ejection material, the largest circumstellar disk during the last two decades has been observed in our 2010 observations with an equivalent width of approximately -12.88{AA}, which corresponds to a circumstellar disk with a size of 12.9 times the radius of the central Be star. Three consecutive X-ray outbursts peaking around MJD 55293, 55444, and 55591 might be connected with the largest circumstellar disk around the Be star. We also use the orbital motion of the neutron star as a probe to constrain the structure of the circumstellar disk and estimate the eccentricity of the binary system to be >=0.4. After three years of the H{alpha} intensity decline after the X-ray outbursts, a new circumstellar disk was being formed around the Be star after our 2013 observations.
- ID:
- ivo://CDS.VizieR/J/A+A/639/A23
- Title:
- Photometry & spectroscopy of EE Cep: 2014-15
- Short Name:
- J/A+A/639/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- EE Cep is one of few eclipsing binary systems with a dark, dusty disk around an invisible object similar to epsilon Aur. The system is characterized by grey and asymmetric eclipses every 5.6yr, with a significant variation in their photometric depth, ranging from ~0.5mag to ~2.0mag. The main aim of the observational campaign of the EE Cep eclipse in 2014 was to test the model of disk precession (Galan et al. 2012). We expected that this eclipse would be one of the deepest with a depth of ~2m.mag. We collected multicolor observations from almost 30 instruments located in Europe and North America. This photometric data covers 243 nights during and around the eclipse. We also analyse the low- and high- resolution spectra from several instruments. The eclipse was shallow with a depth of 0m.71 in V-band. The multicolor photometry illustrates small color changes during the eclipse with a total amplitude of order ~+0.15mag in B-I color index. The linear ephemeris for this system is updated by including new times of minima, measured from the three most recent eclipses at epochs E=9, 10 and 11. New spectroscopic observations were acquired, covering orbital phases around the eclipse, which were not observed in the past and increased the data sample, filling some gaps and giving a better insight into the evolution of the H{alpha} and NaI spectral line profiles during the primary eclipse. The eclipse of EE Cep in 2014 was shallower than expected 0.71mag instead of ~2.0mag. This means that our model of disk precession needs revision.
- 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.