The discovery of a shell-like event in the O-type star HD 120678

Gamen, R.; Arias, J. I.; Barbá, R. H.; Morrell, N. I.; Walborn, N. R.; Sota, A.; Maíz Apellániz, J.; Alfaro, E. J.
Astronomy & Astrophysics, Volume 546, id.A92, 7 pp. (2012).


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.

Based on observations collected at the Complejo Astronómico El Leoncito (CASLEO), the Las Campanas Observatory, and the European Organisation for Astronomical Research in the Southern Hemisphere (proposals: 079.D-0564, 086.D-0997, and 087.D-0946).Table 2 and Fig. 4 are available in electronic form at Reduced spectra is available at the CDS via anonymous ftp to ( or via