Investigating the nature of the Fried Egg nebula^⋆

CO mm-line and optical spectroscopy of IRAS 17163–3907

¹ Department of Earth and Space SciencesChalmers University of Technology, Onsala Space Observatory, 439-92 Onsala, Sweden
email: sofia.wallstrom@chalmers.se
² Department of Astronomy, Cornell University, Ithaca, NY 14853-6801, USA
³ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁴ Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan, 200D, 3001 Leuven, Belgium
⁵ Jodrell Bank Center For Astrophysics, The University of Manchester, Manchester, M13 9PL, UK

Received: 20 March 2013
Accepted: 12 December 2014

Abstract

Through CO mm-line and optical spectroscopy, we investigate the properties of the Fried Egg nebula IRAS 17163–3907, which has recently been proposed to be one of the rare members of the yellow hypergiant class. The CO J = 2−1 and J = 3−2 emission arises from a region within 20″ of the star and is clearly associated with the circumstellar material. The CO lines show a multi-component asymmetrical profile, and an unexpected velocity gradient is resolved in the east-west direction, suggesting a bipolar outflow. This is in contrast with the apparent symmetry of the dust envelope as observed in the infrared. The optical spectrum of IRAS 17163–3907 between 5100 and 9000 Å was compared with that of the archetypal yellow hypergiant IRC+10420 and was found to be very similar. These results build on previous evidence that IRAS 17163–3907 is a yellow hypergiant.