Vol 16, No 5

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

Shruthi S Bhat, Paul KT, Annapurni Subramaniam, Blesson Mathew


Abstract 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 He I lines in the blue spectral region (4000–4500 Å). We find that these stars are likely to be rotating at a fractional critical rotation of ~0.80. We measure the average Ip/Ic ratio to quantify the strength of the Hα line and obtain 1.63 for 4 Her and 2.06 for 88 Her. The radius of the Hα emission region is estimated to be Rd/R∗~5.0, assuming a Keplerian disk. These stars are thus found to be fast rotators with a relatively small Hα emission region. We detect V/R variation of the Hα 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 Hα 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.


Keywords stars: emission-line, Be — circumstellar matter — stars: individual (4 Her, 88 Her) — stars: rotation — techniques: spectroscopic

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