Spectroscopic Study of Be Star β Lyrae

Abstract

We present the spectroscopic observation of β Lyrae, an interacting eclipsing binary, with orbital rotation period of 12.9 days, with one component known as the B-emission (Be) star. The primary star is a B6-B8II of 3 M⊙ and the secondary is a 13 M⊙ B0.5V star. The secondary star is embedded in the accretion disk produced by the infalling matter from the primary star, and this disk is estimated as the source of the emission lines. The observations were conducted at Bosscha Observatory, Lembang, Indonesia from May to August 2018, using 10” Meade LX-200R Telescope (D = 254 f/D = 9.84), equipped with a Littrow High Resolution Spectrograph (LHIRES) III, grating of 1200 grooves/mm yielding in the resolution of R∼5900, and CCD SBIG ST-402 XME camera with backfocus at 17.5 mm. Seeing during observation was estimated to be 2 arc seconds. During this period, we have obtained 15 spectra in various wavelength coverage, 4 spectra covering around λλ = 5779 – 6046 ÅÅ (typical S/N = 0.02), 1 spectrum covering around λλ = 6430.257 – 6694.434 ÅÅ (typical S/N = 0.06), and 10 spectra covering around λλ = 6487 – 6752 ÅÅ (typical S/N = 0.06). The observed spectra show Hα-emission profiles with V/R variation, He I 6678 Å with P-Cygni profiles, and He I 5876 Å with P-Cygni profiles. These variations are due to the fact that β Lyrae is a binary star system, and also it is suspected that another possible mechanism might be involved.