The He I line profiles in normal B type spectra.
Abstract
The primary aim of this study is to determine to what extent the proffles of a large number of He r lines, as observed over the entire range of B spectral types, can be matched by theoretical proffles computed in LTE. Detailed proffle analyses of as many as 11 He I lines, carried out for the stars 134 Tau (B9 IV), Cet (B7 V), HR 2154 (B5 IV), Her (B3 V), Peg (B2 V), HR 1861 (B1 V) and v Ori (B0 V), are summarized. Original, high dispersion proffle data are presented for five of these stars. Stellar logg and Tv values are estimated from H and H6 proffles and spectrophotometric data, reduced to the new standard calibration of Vega by Oke and Schild (1970). The observed Mg U 4481 proffles yield V sin i values <30 km/s for all the stars considered and yield an average log N (Mg)/N(H) + 12 = 7.8 + 0.1. For most of the He I lines considered at spectral types B1 and B0, one cannot match simultaneously an observed line core and the observed line wings with an LTE proffle; the observed cores are systematically deeper and broader than predicted. For certain lines ( 4471, 5876, 6678 and possibly 4026, 4388) this problem persists over the entire range of spectral types considered (B0B9). The observed singlet/triplet equlvalent width ratios are well reproduced by the LTE calculations in spite of evident deviations from LTE in the line cores. Estimated He/H ratios, obtained on the basis of theoretical fits to the weaker He I lines and to the wings of the strong lines, are given for six of the seven stars considered. An overall average N(He)/N(H) = 0.106 is obtained for these stars, from a total of 46 lines, with little scatter being noted in the results obtained from line to line for a given star. Virtually no scatter exists in the derived He/H ratios among the six stars considered. It is un]ikely that the more obvious sources of possible systematic errors could push the average N(He)/N(H) for these stars outside the range 0.0950.125. Derived He/H ratios for V Ori and HR 1861, members of the Orion association, are in excellent agreement with the results of recent optical studies of the Orion nebula. The need for a rigorous theoretical test of the LTE assumption for the weak He I lines and the wings of the strong lines is stressed. Key words: B stars  helium abundances  line proffles  non LTE
 Publication:

Astronomy and Astrophysics
 Pub Date:
 April 1971
 Bibcode:
 1971A&A....11..387L