Volume 546, October 2012
|Number of page(s)||7|
|Section||Stellar structure and evolution|
|Published online||10 October 2012|
1 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, USA
6 Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008, Granada, Spain
Received: 22 December 2011
Accepted: 4 September 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.
Key words: binaries: spectroscopic / stars: early-type / stars: emission-line, Be / stars: individual: HD 120678
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 http://www.aanda.org
Reduced spectra is available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A92
© ESO, 2012
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