SBS 1150+599A: An extremely oxygen-poor planetary nebula in the Galactic halo?

¹ OAN, Instituto de Astronomía, UNAM, México
² DAEC, Observatoire de Meudon, 92195 Meudon Cedex, France e-mail: grazyna.stasinska@obspm.fr
³ Instituto Nacional de Astrofísica Optica y Electrónica, AP 51 y 216, Puebla, Pue., México e-mail: vahram@inaoep.mx
⁴ Instituto de Astrofísica de Canarias, Ave. Via Láctea s/n, 38200 La Laguna, Tenerife, Spain e-mail: cgc@ll.iac.es

Corresponding author: G. Tovmassian, gag@astrosen.unam.mx

Received: 6 November 2000
Accepted: 7 February 2001

Abstract

We report results of a spectrophotometric study of SBS 1150+599A and discuss the nature of this object based upon our data. Our study shows that SBS 1150+599A is most probably a planetary nebula located in the Galactic halo and not a cataclysmic variable as originally proposed by the authors of the Second Byurakan Survey from low resolution spectroscopy. We have further elaborated on the properties of SBS 1150+599A (now becoming PN G135.9+55.9) with tools used for planetary nebula analysis. Our photoionization models show that, in order to match the observational constraints, the oxygen abundance in the nebula is probably extremely low, around 1/500 solar, which is one order of magnitude lower than the most oxygen-poor planetary nebulae known so far. This finding has strong implications on our understanding of the formation of planetary nebulae and of the evolution of the Galactic halo.