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Optical/IR studies of Be stars in NGC 6834 with emphasis on two specific stars

Research in Astronomy and Astrophysics 2014年第9期14卷 1173-1192页

作者： Blesson Mathew Watson P. Varricatt Annapurni Subramaniam N. M. Ashok D. P. K. Banerjee Centre for Astrophysics & Supercomputing Swinburne University Hawthorn VIC 3122Australia Astronomy and Astrophysics Division Physical Research Laboratory NavrangapuraAhmedabad - 380 009 Gujarat India Joint Astronomy Centre 660 N. Aohoku Pl. Hilo HI 96720 USA Indian Institute of Astrophysics Bangalore - 560 034 India

We present optical and infrared photometric and spectroscopic studies of two Be stars in the 70-80-Myr-old open cluster NGC 6834. NGC 6834（1） has been reported as a binary from speckle interferometric studies whereas NGC 6834（2） may possibly be a γ Cas-like variable. Infrared photometry and spectroscopy from the United Kingdom Infrared Telescope （UKIRT）, and optical data from various facilities are combined with archival data to understand the nature of these candidates. High signal-to-noise near-IR spectra obtained from UKIRT have enabled us to study the optical depth effects in the hydrogen emission lines of these stars. We have explored the spectral classification scheme based on the intensity of emission lines in the H and K bands and contrasted it with the conventional classification based on the intensity of hydrogen and helium absorption lines. This work also presents hitherto unavailable UBV CCD photometry of NGC 6834, from which the evolutionary state of the Be stars is identified.

关键词： stars: emission-line Be -- circumstellar matter -- infrared: stars -- line profiles -- (Galaxy:) open clusters and associations: individual (NGC 6834)

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Spectroscopic study of Be-shell stars:4 Her and 88 Her

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Research in Astronomy and Astrophysics 2016年第5期16卷 47-58页

作者： Shruthi S Bhat Paul KT Annapumi Subramaniam Blesson Mathew Department of Physics Christ UniversityBangalore 560029India Indian Institute of Astrophysics II BlockKormangalaBangalore 560034India Department of Astronomy&Astrophysics Tata Institute of Fundamental ResearchHomi Bhabha RoadMumbai400005India

We present an optical spectroscopic study based on 41 spectra of 4 Her and 32 spectra of 88 Her, obtained over a period of 6 months. We estimate the rotational velocity of these stars from HeI lines in the blue spectral region （4000-4500 A）. We find that these stars are likely to be rotating at a fractional critical rotation of -0.80. We measure the average Ip/lc ratio to quantify the strength of the Ha line and obtain 1.63 for 4 Her and 2.06 for 88 Her. The radius of the Ha emission region is estimated to be Ra/R. -5.0, assuming a Keplerian disk. These stars are thus found to be fast rotators with a relatively small Hoe emission region. We detect V/R variation of the Ha spectral line during the observed period. We re-estimate the periods for both stars and obtain a period of ,-46 d and its harmonic of 23.095 d for 4 Her, and a period of -86 d for 88 Her. As these two cases are shell stars with binaries and have low Ha EW with the emission region closer to the central star, the V/R variation and a change in period may be an effect of the binary on the circumstellar disk.

关键词： stars: emission-line Be -- circumstellar matter -- stars: individual (4 Her 88 Her) -- stars:rotation -- techniques: spectroscopic

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