THE CORRELATION BETWEEN Hα EMISSION AND VISUAL MAGNITUDE DURING LONG-TERM VARIATIONS IN CLASSICAL Be STARS

Sigut, T. A. A.; Patel, P.

doi:10.1088/0004-637x/765/1/41

Cited by 39 publications

(39 citation statements)

References 74 publications

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“…Identifying Outburst Variation Because Be star outbursts show a large range in their amplitude, duration, and morphology, they are difficult to rigorously define. In what follows, a feature in a light curve is considered an outburst if there is a sharp departure from baseline (either brightening or fading) followed by a gradual return towards baseline (Sigut & Patel 2013). Despite this simple description, there are numerous difficulties involved with detecting outbursts.…”

Section: Notesmentioning

confidence: 99%

Photometric Variability of the Be Star Population

Labadie-Bartz

Pepper

McSwain

et al. 2017

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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, baseline of up to ten 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 nonradial pulsations (25%), outbursts (36%), and long term trends in the circumstellar disk (37%), and show how these are correlated with spectral sub-type. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectral Database (BeSS) allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk.

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Section: Notesmentioning

confidence: 99%

Photometric Variability of the Be Star Population

Labadie-Bartz

Pepper

McSwain

et al. 2017

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“…As suggested by Vieira et al (2017), disk growth and dissipation phases can be represented with different combinations of the parameters n and ρ 0 . During these formation/dissipation phases, the star is expected to describe a loop in the CMD (Dougherty et al 1994;de Wit et al 2006;Sigut & Patel 2013). Figure 14 shows our confirmed Be stars together with models of disk growth and dissipation phases, similar to those presented by Vieira et al (2017): first the disk forms and grows in size, represented by a decrease in n from 4 to 3.5 for a constant ρ 0 , and then subsequently dissipates, represented by a decrease in ρ 0 and decreasing n. For each stellar model, two different values of ρ 0 at the beginning of the disk growth were considered in an attempt to mimmick two different disk mass loss rates.…”

Section: Disk Growth and Dissipation Phasesmentioning

confidence: 99%

Quiescent and Active Phases in Be Stars: A WISE Snapshot of Young Galactic Open Clusters

Granada

Jones

Sigut

et al. 2018

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Through the modelling of near-infrared photometry of star plus disk systems with the codes bedisk/beray, we successfully describe the WISE photometric characteristics of Be stars in five young open clusters, NGC 663, NGC 869, NGC 884, NGC 3766 and NGC 4755, broadly studied in the literature. WISE photometry allows previously known Be stars to be detected and to find new Be candidates which could be confirmed spectroscopically. The location of Be stars in the WISE colour-magnitude diagram, separates them in two groups; active (Be stars hosting a developed circumstellar disk) and quiescent objects (Be stars in a diskless phase), and this way, we can explore how often stars are observed in these different stages. The variability observed in most active variable Be stars is compatible with a disk dissipation phase. We find that 50 percent of Be stars in the studied open clusters are in an active phase. We can interpret this as Be stars having a developed circumstellar disk half of the time. The location of Be stars with a developed disk in the CMD require mass loss rates in agreement with values recently reported in the literature. For these objects, we expect to have a tight relation between the equivalent width of the Hα line and the mass of the disk, if the inclination is known. Also, near-infrared photometry of Be stars in stellar clusters has the potential of being useful to test whether there is a preferential viewing angle.

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“…This technique has the advantage that it does not rely on an assumption like that used in the Dunstall et al (2011). In addition, the full range of behavior of the disk's effect on the spectrum is possible; for example at low inclinations (pole-on star, face-on disk), it is reasonable to expect the disk contribution to be added continuum emission, like that assumed by Dunstall et al (2011); however, for higher inclination systems, the photosphere can be viewed through the disk, and there is the possibility of a reduction in the photospheric spectrum due to this obscuration (see Sigut & Patel 2013). Another advantage of direct Hα modelling is that an estimate of the system inclination is obtained as the morphology of the Hα line (singly-peaked, doubly-peaked, shell absorption) depends strongly on the inclination.…”

Section: Circumstellar Disk Emissionmentioning

confidence: 97%

Rotational mixing in Be stars: nitrogen abundances for a sample of Be stars from the MiMeS survey

Ahmed

Sigut

2017

Monthly Notices of the Royal Astronomical Society

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Photospheric nitrogen abundances for a sample of 26 Be stars and 16 normal B stars were found using high-resolution spectra from the Magnetism in Massive Stars (MiMeS) spectroscopic survey. Nitrogen abundances were obtained using non-LTE equivalent widths and line profiles, and Monte Carlo simulation was used to determine the error bounds of the measured nitrogen abundances due to uncertainties in the adopted stellar parameters, continuum normalization, and atomic data. In addition, the effects of the gravitational darkening and disk contamination on the measured Be star nitrogen abundances were investigated. About one third of the sample Be stars and half of the normal B-type stars have nitrogen enrichments that may be due to rotational mixing in these rapidly rotating objects. Corrections for gravitational darkening and disk contamination do not significantly change the overall results for the Be star sample. The average nitrogen abundance of the B and Be star samples coincide with the solar abundance, although the dispersion in the nitrogen abundances is much larger in the Be star sample. The Be star sample also has a significant fraction of sub-solar nitrogen abundance objects which are not present in significant numbers in the B star sample. This may point to yet unresolved systematic errors in the analysis of the Be stars.

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THE CORRELATION BETWEEN Hα EMISSION AND VISUAL MAGNITUDE DURING LONG-TERM VARIATIONS IN CLASSICAL Be STARS

Cited by 39 publications

References 74 publications

Photometric Variability of the Be Star Population

Photometric Variability of the Be Star Population

Quiescent and Active Phases in Be Stars: A WISE Snapshot of Young Galactic Open Clusters

Rotational mixing in Be stars: nitrogen abundances for a sample of Be stars from the MiMeS survey

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