Spectral line ratios as indicators in solar-like stars

¹ Dipartimento di Fisica, Università di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italia e-mail: penza@roma2.infn.it
² Consorzio Interuniversitario per la Fisica Spaziale (CIFS)
³ Osservatorio astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italia e-mail: gomez@na.astro.it

Corresponding author: B. Caccin, caccin@roma2.infn.it

Received: 22 November 2001
Accepted: 5 February 2002

Abstract

The ratios of spectral line depths are often used as indicators of the stellar effective temperature T_eff. In particular, Gray & Livingston ([CITE]) calibrated the temperature sensitivity of the ratios between the central depths of the line C I 538.032 nm and either the Fe I 537.958 or the Ti II 538.103, making use of observed spectra of several solar-like stars. The ultimate reason for choosing these lines was the subsequent application of their calibration to a long series of solar data, collected at Kitt Peak (in disk-integrated light) from 1978 to 1992, in order to get the T_eff variation of the Sun during its 11-yr magnetic cycle (Gray & Livingston [CITE]). We propose a theoretical calibration that includes a careful treatment of convective transport and fits the stellar data very well , showing, at the same time, that the empirical calibration of Gray and Livingston incorporates in the T_eff sensitivity an undesired dependence of line ratios on the surface gravities of the individual stars they used. A possible dependence of the calibration upon stellar rotation is also explored.