Optical spectroscopy of Galactic field Classical Be stars

Abstract

In this study, we analyze the emission lines of different species present in 118 Galactic field classical Be stars in the wavelength range of 3800 - 9000 Å. We re-estimated the extinction parameter (A${}_V$) for our sample stars using the newly available data from Gaia DR2 and suggest that it is important to consider A${}_V$ while measuring the Balmer decrement (i.e. $D_{34}$ and $D_{54}$) values in classical Be stars. Subsequently, we estimated the Balmer decrement values for 105 program stars and found that $\approx$ 20\% of them show $D_{34}$ $\ge$ 2.7, implying that their circumstellar disc are generally optically thick in nature. One program star, HD 60855 shows H$\alpha$ in absorption -- indicative of discless phase. From our analysis, we found that in classical Be stars, H$\alpha$ emission equivalent width values are mostly lower than 40 Å, which agrees with that present in literature. Moreover, we noticed that a threshold value of $\sim$ 10 Å~of H$\alpha$ emission equivalent width is necessary for Fe{\sc ii} emission to become visible. We also observed that emission line equivalent widths of H$\alpha$, P14, Fe{\sc ii} 5169 and O{\sc i} 8446 Å~for our program stars tend to be more intense in earlier spectral types, peaking mostly near B1-B2. Furthermore, we explored various formation regions of Ca{\sc ii} emission lines around the circumstellar disc of classical Be stars. We suggest the possibility that Ca{\sc ii} triplet emission can originate either in the circumbinary disc or from the cooler outer regions of the disc, which might not be isothermal in nature.

arXiv comment20 pages, 9 figures, accepted for publication in MNRAS

References in corpus (38)

• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• A 3D Dust Map Based on Gaia, Pan-STARRS 1 and 2MASS
• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• NLTE Monte Carlo Radiative Transfer: I. The Thermal Properties of Keplerian Disks around Classical Be Stars
• The Thermal Structure of the Circumstellar Disk Surrounding the Classical Be Star gamma Cassiopeia
• Origins of the H, He I, and Ca II Line Emission in Classical T Tauri Stars
• First direct detection of a Keplerian rotating disk around the Be star $\alpha$ Arae using the VLTI/AMBER instrument
• Non-LTE Monte Carlo Radiative Transfer: II. Non-Isothermal Solutions for Viscous Keplerian Disks
• Prevalence of SED turndown among classical Be stars: Are all Be stars close binaries?
• The first determination of the viscosity parameter in the circumstellar disk of a Be Star
• Clues about the scarcity of stripped-envelope stars from the evolutionary state of the sdO+Be binary system phi Persei
• Be phenomenon in open clusters: Results from a survey of emission-line stars in young open clusters
• Empirical Bolometric Fluxes and Angular Diameters of 1.6 Million Tycho-2 Stars and Radii of 350,000 Stars with \emph{Gaia} DR1 Parallaxes
• The Remarkable Be+sdOB Binary HD 55606 I: Orbital and Stellar Parameters
• VLTI/MIDI atlas of disks around low- and intermediate-mass young stellar objects
• A representative sample of Be stars III: H band spectroscopy
• 3D Interstellar Extinction Map within the Nearest Kiloparsec
• Evidence for Different Disk Mass Distributions Between Early and Late-Type Be Stars in the BeSOS Survey
• The Effect of Density on the Thermal Structure of Gravitationally-Darkened Be Star Disks
• Spectroscopic atlas of Halpha and Hbeta in a sample of northern Be stars
• Stellar parameters of Be stars observed with X-shooter
• Benchmarking Atomic Data for Astrophysics: Be-like Ions between B II and Ne VII
• Short-term variability and mass loss in Be stars IV. Two groups of closely spaced, approximately equidistant frequencies in three decades of space photometry of $\nu$ Puppis (B7-8 IIIe)
• A Catalog of Calibrator Stars for Next-Generation Optical Interferometers
• Is there a propeller neutron star in $\gamma$ Cas?
• Short-term variability and mass loss in Be stars V. Space photometry and ground-based spectroscopy of $\gamma$ Cas
• A representative sample of Be stars V: Hα variability
• L-band spectra of 13 outbursting Be stars
• Study of candidate Be stars in the Magellanic Clouds using NIR photometry and optical spectroscopy
• A study of the role of Lyman β fluorescence on OI line strengths in Be stars
• Infrared studies of the Be star X Per
• Measurements of Ca II Infrared Triplet Lines of Young Stellar Objects
• Short-term Hα line variations in Classical Be stars: 59 Cyg and OT Gem
• The H$\alpha$ line emission of the Be star $\beta$ Psc: the last 40 years
• A peculiar interacting Be star binary in the Small Magellanic Cloud
• Calcium Emission in Interacting Binary Be Stars
• Spectroscopic study of Be-shell stars: 4 Her and 88 Her

Cited by in corpus (9)

• Identification of new Classical Ae stars in the Galaxy using LAMOST DR5
• Discovery of 2716 hot emission-line stars from LAMOST DR5
• Multiple giant eruptions and X-ray emission in the recoiling AGN/LBV candidate SDSS1133
• Decoding the X-ray flare from MAXI J0709-159 using optical spectroscopy and multi-epoch photometry
• Spectroscopic study of Herbig Ae/Be stars in the Galactic Anti-center region from LAMOST DR5
• Identification of emission-line stars in transition phase from pre-main sequence to main sequence
• HD 63021: Chromospheric Activity and Mass Transfer in a Close Binary
• Study of Classical Be stars in open clusters older than 100 Myr
• Study of the transient nature of classical Be stars using multi-epoch optical spectroscopy