Photospheric spectrum of the pre-fuor V1331 Cyg: a star or a disk?
The T Tauri variable V1331 Cyg is distinguished by its intensive emission line spectrum, spectral signatures of high mass-loss and the presence of circular reflection nebulae. With these characteristics the star can be considered as a candidate pre-FUor. The photospheric spectrum of the star has not been registered so far. In this paper we analyse the high-resolution spectra of V1331 Cyg, obtained by G. H. Herbig with the HIRES spectrograph at Keck-1 telescope in 2004 and 2007. For the first time the numerous photospheric lines of the star were detected and the spectral type was estimated: G7–K0 IV. Projected rotational velocity was found to be less than the width of instrumental profile (v sin i < 6 km s-1), thus indicating a low inclination. Radial velocity of the star, derived from the photospheric lines, is RV = -15.0±0.3 km s-1, with no significant difference between 2004 and 2007. The photospheric spectrum is veiled considerably, but the amount of veiling is not the same in different lines. It depends on the line strength in the template spectrum of G7 IV star: the weakest measured lines (EW = 5–10 mÅ in template spectrum) are veiled by factor of ≈ 1 and rise to 4–5 in stronger lines. The Hα and Hβ lines show classical P Cyg profiles indicating a powerfull wind with terminal velocity of ≈ 400 km s-1. Besides of these, emission lines of Fe ii, Mg i, K i and some other species are accompanied by narrow blue-shifted absorptions at -150... - 250 km s-1. The emission spectrum is rich in narrow (FWHM = 30–50 km s-1) lines of neutrals and ionised metals, indicating excitation temperature Texc = 3800±300 K. The stellar mass M*≈ 3 M⊙ and radius R*≈ 5 R⊙ are estimated.
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