Study of the Hydrogen and Helium II Lines in a High-Temperature Subdwarf.

Abstract

view Abstract Citations (21) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Study of the Hydrogen and Helium II Lines in a High-Temperature Subdwarf. Münch, Guido Abstract The problem of line formation in a scheme of pure absorption is considered For the case of a source function depending linearly on mean optical depth, r, and a ratio, , of line to continuous absorption coefficients independent of r, an approximate expression for the line depth is derived similar in form to the Minnaert- interpolation formula It is shown that this formula, for a given equivalent width, underestimates the frequency-independent part of77 by a factor equal to the central depth of the line, both for lines broadened by linear Stark effect and for Doppler-broadened lines A procedure defining the mean level of formation of the various parts of the contour of a line with `7depending arbitrarily on r is developed. The representative depths for the formation of a line as a whole, when it is broadened by linear Stark effect, are also evaluated. The use of the theoretical developments is illustrated by an analysis of the lines He ii x 4686 and H + He ii X 4340 observed in the spectrum of the 0-type subdwarf HZ 44. Preliminary values of the electron pressure, p (r = 23), the effective temperature, T , and the helium number abundance, Y, are derived from the observed strength of X 4686, its ratio to 4340, and the ionization equilibrium between the ions N Ir and N iii, assuming = Constant. On the basis of the model log p, = 4.0, T, = 34000 K, and V = 0 28 thus obtained, the line intensities are again calculated, allowing for the r-dependence of 77. The parameters p, and T, of the zero approximation model atmosphere are found not to change significantly on this account; but the value of V is reduced to V = 0.23 A surface gravity g = 10' 7 cm/sec2 and a visual absolute magnitude M, = +37 if the mass were 1 0 and M = +12 if = 10 0, are estimated. Publication: The Astrophysical Journal Pub Date: May 1958 DOI: 10.1086/146496 Bibcode: 1958ApJ...127..642M full text sources ADS |