A&A 373, 993-997 (2001)
A method to estimate the effect of line blanketing in NLTE radiative transfer calculationsI. Busá, V. Andretta, M. T. Gomez and L. Terranegra
Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
(Received 5 February 2001 / Accepted 2 May 2001)
We present a method to estimate the contribution of line opacity to the total opacity as a function of wavelength. The estimated line-opacity function can then be used to simulate line-blanketing in NLTE radiative transfer calculations. Given a reference flux distribution (either observed or theoretical), our method allows to obtain a good estimate of the spectrum without the need for considering in detail all the millions of lines contributing to line blanketing. We applied the method to the spectra computed from a sample of photospheric models with effective temperatures Teff = 4200, 5200 and 6200 K, = 4.0, 4.5, 5.0 and [A/H] = 0.0, -1.0, -2.0, taken from the NextGen database (Allard & Hauschildt 1995). The computed flux distributions agree quite well with the corresponding LTE line-blanketed NextGen fluxes when we introduce the estimated line-opacity contribution as a multiplicative factor of the continuum opacity in the radiative transfer calculations. In particular we discuss the importance of a correct estimate of the continuum flux, mainly in the UV, in the NLTE formation of the CaII H & K, the CaII InfraRed Triplet (IRT: 8498, 8542, 8662), NaI D, LiI and KI resonance lines.
Key words: stars: atmospheres -- radiative transfer -- line: formation -- ultraviolet: stars
Offprint request: I. Busá, firstname.lastname@example.org
© ESO 2001