A sensitive search for methanol line emission toward evolved stars

 

José F. Gómez,¹ Lucero Uscanga,² Olga Suárez,³ J. Ricardo Rizzo,⁴ and Itziar de Gregorio-Monsalvo^5,6

 

¹ Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, E-18080 Granada, Spain. (jfg@iaa.es).

² Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, I. Metaxa & V. Pavlou, P. Penteli, 15236 Athens, Greece. (lucero@astro.noa.gr).

³ Laboratoire Lagrange, UMR 7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de laCôte d'Azur, 06300 Nice, France. (olga.suarez@oca.eu).

⁴ Centro de Astrobiología, INTA-CSIC, Ctra. M-108, km. 4, E-28850 Torrejón de Ardoz, Spain. (ricardo@cab.inta-csic.es).

⁵ European Southern Observatory, Karl Schwarzschild Str 2, 85748 Garching bei München, Germany. (idegrego@alma.cl).

 

Received 2013 December 11.
Accepted 2014 January 24.

 

RESUMEN

Presentamos una búsqueda muy sensible de emisión de líneas de metanol a 1 cm en estrellas evolucionadas, con el fin de detectar, por primera vez, máseres de metanol en este tipo de objetos. Nuestra muestra incluye estrellas post-AGB y nebulosas planetarias (NP) jóvenes, cuyos procesos de pérdida de masa y sus estructuras circunestelares se asemejan a los de objetos estelares jóvenes (OEJ), en los que se detectan máseres de metanol. Buscamos máseres de Clase I en 73 objetos y de Clase II en 16. No encontramos ninguna detección. La ausencia de detecciones de máseres de Clase I indica que la producción de metanol en granos de polvo, o el incremento de su abundancia en las zonas de choque de objetos evolucionados no es tan eficiente como en OEJs. Proponemos que las NPs relativamente más evolucionadas podrían tener una mayor probabilidad de detección de máseres de Clase II.

 

ABSTRACT

We present a sensitive search for methanol line emission in evolved stars at 1 cm, aiming to detect, for the first time, methanol masers in this type of objects. Our sample comprised post-AGB stars and young planetary nebulae (PNe), whose mass-loss processes and circumstellar structures resemble those of young stellar objects(YSOs), where methanol masers are detected. Class I masers were searched for in 73 objects, whereas Class II ones were searched in 16. No detection was obtained. The non-detection of Class I methanol masers indicated that methanol production in dust grains and/or the enhancement of its gas-phase abundance in the shocked regions of evolved objects are not as effcient as in YSOs. We suggest that relatively more evolved PNe might have a better probability of harboring Class II masers.

Key Words: ISM: molecules — masers — stars: AGB and post-AGB.

 

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ACKNOWLEDGMENTS

JFG, OS, and IdG acknowledge support from MICINN (Spain) AYA2011-30228-C03 grant (including FEDER funds). L.U. acknowledges support from grant PE9-1160 of the Greek General Secretariat for Research and Technology in the framework of the program Support of Postdoctoral Researchers. JRR acknowledges support from MICINN grants CSD2009-00038, AYA2009-07304, and AYA201232032. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This work is partially based on observations done at MDSCC (Robledo), under the Host Country Radio Astronomy program. Part of the data in this paper was reduced using the GILDAS software package (http://www.iram.fr/IRAMFR/GILDAS/).

 

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