High resolution spectroscopy of the post-red supergiant IRC+10420

Abstract

A high resolution optical spectrum of the post-red supergiant candidate IRC+10420 is presented. The Utrecht Echelle Spectrograph observations, with a total integration time of more than 9 hours! provide a spectral coverage front 3850 Angstrom to 1 mu m, and a spectral resolution of 9 km s(-1). The spectrum is shown, and an identification list of lines in the spectrum is provided. From a preliminary analysis of the spectrum we find that the spectral type of IRC+10420 has changed from F8I(+) in 1973 to mid- to early A type now, confirming the results of Oudmaijer et al. (1996), who claimed a change in temperature based on photometric changes. It is shown that most of the emission lines in the spectrum of IRC+10420 are blue-shifted with respect to the systemic velocity traced by circumstellar rotational CO emission. while the (few) absorption lines - with the exception of some high excitation lines are red-shifted by 25 km s(-1), which may suggest infall of material onto the star. Finally, it is found that the interstellar extinction towards IRC+10420 as traced by the Diffuse Interstellar Bands is very large, with an inferred E(B-V) of 1.4 +/- 0.5 compared to a total E(B-V) of 2.4.