Analysis of the variability of the luminous emission line star MWC 314^*

¹ Laboratoire d'Astrophysique de Marseille, 2 Place le Verrier, 13248 Marseille Cedex 04, France e-mail: gerard.muratorio@oamp.fr
² Dipartimento di Fisica, Università “La Sapienza”, Piazzzale A. Moro 2, 00185 Roma, Italy e-mail: corinne.rossi@roma1.infn.it
³ Institut d'Astrophysique, 98 bis Boulevard Arago, 75014 Paris, France e-mail: fried@iap.fr

Received: 27 October 2007
Accepted: 20 May 2008

Abstract

Context. We investigated the surroundings of MWC 314 in the framework of the study of hot emission line star environments using the SAC method. This star is either a B[e] supergiant or a luminous blue variable and appears to be extremely luminous and massive.

Aims. We determine the structure and physical conditions of the emitting region and study the possible variations.

Methods. We measured the absorption and emission line radial velocities and the emission line fluxes on high-resolution spectra obtained with Aurelie at the 1.52 m OHP telescope in July 1998, with Elodie at the 1.93 m OHP telescope at various epochs, and with echelle spectrographs of the Asiago and Loiano observatories (Italy) in 2006. We used the statistical approach of the self-absorption curve method (SAC) to derive physical parameters of the line-emitting region.

Results. We detected drastic variations of the photospheric absorption line radial velocities with time, while the emission line velocities appear to be stable. The Cr II, Ti II, and Fe II emission lines have a complex structure. They are double-peaked, and each of these two 60 km s^-1 separated components, is composed of a narrow and a broad component, while the [Fe II] line components are narrower. The fit of the various components of the Fe II lines to a SAC curve indicates that their intensities are affected by some self absorption. We obtained a Boltzmann-type population law whose mean excitation temperature is  K for the narrow component lower and upper levels. We obtained a higher Boltzmann-type population law of  K for the forbidden transition upper levels.

Conclusions. From the absorption lines we confirm the binarity for MWC 314. The periodicity has nevertheless to be improved with a higher sampling frequency. Our results from the emission lines are consistent with line formation in a rotating disk around a star. The typical minimum radius of the line emitting region obtained from the SAC study is 3.5  10¹³ cm (2.0  10¹³ cm < R < 6.3  10¹³ cm). We argue, in the framework of a very simplified geometrical model, that the [Fe II] lines are emitted farther out than the permitted Cr II, Ti II, and Fe II lines, in a disk inclined 25 ± 5 degrees to the plane of sky. If the rotation of the disk is Keplerian, the Fe II lines are emitted in a zone defined by 4  10¹² cm < R < 7  10¹³ cm, while for a rotation with conservation of angular momentum, they are emitted from 4  10¹² cm < R < 2  10¹³ cm.