- 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.
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- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/368/912
- Title:
- Polarization and rotational velocities of Be stars
- Short Name:
- J/A+A/368/912
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of statistical analyses of a sample of 628 Be stars. The parameters of intrinsic polarization p_*_, projected rotational velocity (vsini), and near IR excesses have been investigated. The values of p_*_ have been estimated for a much larger and more representative sample of Be stars (~490 objects) than previously.
