The discovery of a shell-like event in the O-type star HD 120678
R. Gamen,1 J. I. Arias,2 and R. H. Barbá,3 and N. I. Morrell,4 and N. R. Walborn,5 and A. Sota,6 J. Maíz Apellániz,6 E. J. Alfaro61 Instituto de Astrofísica de La Plata (CONICET) and Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina
2 Departamento de Física, Universidad de La Serena, Cisternas 1200 Norte, La Serena, Chile
3 Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE-CONICET), Avda España 1512 Sur, J5402DSP, San Juan, Argentina
4 Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile
5 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218
6 Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008, Granada, Spain
Aims. We report the detection of a shell-like event in the Oe-type star HD 120678.
Methods. HD 120678 has been intensively observed as part of a high-resolution spectroscopic monitoring program of southern Galactic O stars and Wolf-Rayet stars of the nitrogen sequence.
Results. An optical spectrogram of HD 120678 obtained in June 2008 shows strong H and He I absorption lines instead of the double-peaked emission profiles observed both previously and subsequently, as well as a variety of previously undetected absorption features, mainly of O II, Si III and Fe III. Photometric data reveal that the development of the absorption spectrum coincided with a remarkable dip in the V-band lightcurve. The "shell phase" of HD 120678 did not persist for very long: the V magnitude recovered its previous average value in fewer than 120 days, whereas H and He emission lines became detectable one year later. Similar spectral variations have been observed in a few Be stars, and they are usually interpreted as changes in the circumstellar disk.
Accepted by A&A
Preprints from http://dx.doi.org/10.1051/0004-6361/201118725