Photometric Variability of the Be Star Population

Abstract

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.

The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars

“…Similar findings were reported in the Galaxy (e.g. Rivinius et al 2013;Labadie-Bartz et al 2017). For a complete characterisation the disc life cycles a census of the number of bumps present during the timespan of OGLE-II and OGLE-III observations (roughly 12 years) would be required .…”

“…(iii) Late-type Be stars tend to show less variability (Rivinius et al 2013;Labadie-Bartz et al 2017, see also next subsections), which would make it less probable to identify bumps in their light curves.…”

Variability Properties of Four Million Sources in the TESS Input Catalog Observed with the Kilodegree Extremely Little Telescope Survey

“…KELT observations have surveyed more than 70% of the celestial sphere, down to a limiting magnitude near V ∼ 13, with a baseline of 9 yrs using KELT North (hereafter, KELT-N) and 5 yrs using KELT South (hereafter, KELT-S). Initially deployed to detect exoplanet transits around bright (V < 10) stars, the survey has contributed discoveries to supernovae (Siverd et al 2015), the monitoring of Be Stars (Labadie-Bartz et al 2017), eclipses of stars by disks (Rodriguez et al 2013), gyrochronology of young stars (Cargile et al 2014), pre-identification of young variable objects to be observed by K2 (Rodriguez et al 2017a,b;Ansdell et al 2017), more than 21 confirmed transiting planets (with 19 in press Pepper et al 2013;Collins et al 2014;Bieryla et al 2015;Fulton et al 2015;Eastman et al 2016;Kuhn et al 2016;Rodriguez et al 2016c;Zhou et al 2016;Gaudi et al 2017;McLeod et al 2017;Oberst et al 2017;Pepper et al 2017;Stevens et al 2017;Temple et al 2017;Lund et al 2017;Siverd et al 2017)) and 1 short period, transiting brown dwarf .…”

An investigation of the photometric variability of confirmed and candidate Galactic Be stars using ASAS-3 data

“…While single non-radial pulsation modes are not suited to trigger mass loss, beating effects may produce higher amplitudes (Neiner et al 2002;Rivinius et al 2013;Labadie-Bartz et al 2017) and a connection between pulsational amplitude and circumstellar activity has been established (Carciofi et al 2008;Neiner et al 2013). Interestingly, so-called 'difference frequencies' (∆ frequencies) may show amplitudes in excess of the amplitude sum of their associated pulsational base frequencies, influencing the mass transfer to the circumstellar environment (Baade et al , 2017a.…”