Spectroscopic analysis of four post-AGB candidates

 

R. E. Molina,¹ S. Giridhar,² C. B. Pereira,³ A. Arellano Ferro,^4,5 and S. Muneer⁶

 

¹ Laboratorio de Investigación en Física Aplicada y Computacional, Universidad Nacional Experimental del Táchira, Venezuela (rmolina@unet.edu.ve).

² Indian Institute of Astrophysics, Bangalore 560034, India (giridhar@iiap.res.in).

³ Observatório Nacional/MCTI, Rua Gen. José Cristino 77, Sao Cristovao, Rio de Janeiro, CEP 20921-400, Brazil (claudio@on.br).

⁴ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 70-264, 04510, México, D. F., México (armando@astro.unam.mx).

⁵ European Southern Observatory, München, Germany.

⁶ CREST Campus, Indian Institute of Astrophysics, Hosakote, India (muneers@iiap.res.in).

 

Received 2014 January 6.
Accepted 2014 May 27.

 

RESUMEN

Hemos efectuado un análisis detallado de las abundancias químicas de cuatro objetos candidatos a post-AGB: IRAS 13110-6629, IRAS 17579-3121, IRAS 183211401 y IRAS 18489-0629, usando espectros de alta resolución. Hemos construido las distribuciones de energía espectral (SEDs) para cada objeto usando datos fotométricos existentes, combinados con los flujos infrarrojos. Para todos los objetos en la muestra, las SEDs exhiben dos picos en la distribución de energía, con el pico IR bien definido, mostrando con ello la presencia de material circunestelar. Las abundancias de CNO muestran la producción de N por la vía del ciclo CN, mientras que el cociente [C/Fe] observado señala una mezcla de carbono producida por la combustión del He aunque el cociente C/O se mantiene menor que 1. Se observa un efecto moderado de separación gas-polvo en IRAS 18489-0629 y en IRAS 17579- 3121 mientras que sólo se observa una gran dispersión en la remoción selectiva en IRAS 18321 -1401 y en IRAS 13110- 6629, lo que indica que otros procesos afectan los patrones de abundancias observadas.

 

ABSTRACT

We have done a detailed abundance analysis of four unexplored candidate post-Asymptotic Giant Branch(AGB) stars IRAS 13110-6629, IRAS 17579-3121, IRAS 18321-1401 and IRAS 18489-0629 using high resolution spectra. We have constructed Spectral Energy Distributions (SED) for these objects using the existing photometric data combined with infrared (IR) fluxes. For all sample stars, the SEDs exhibit double peaked energy distribution with well separated IR peaks showing the presence of dusty circumstellar material. The CNO abundances indicate the production of N via CN cycling, but observed [C/Fe] indicates the mixing of carbon produced by He burning by third dredge up although C/O ratio remains less that 1. A moderate DG-effect is clearly seen for IRAS 18489-0629 and IRAS 17579-3121 while a large scatter observed in depletion plots for IRAS 18321-1401 and IRAS 13110-6629 indicate the presence of other processes affecting the observed abundance pattern.

Key Words: stars: abundances — stars: AGB and post-AGB — stars: evolution.

 

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ACKNOWLEDGMENTS

AAF acknowledges the support of DGAPA-UNAM grant through Project IN104612. This work has made extensive use of SIMBAD database, 2MASS (Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation), IRAS, AKARI/IRC data (a JAXA project with participation of ESA), WISE(Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration), MSX6C (Midcourse Space Experiment funded by the Ballistic Missile Defense Organization with additional support from NASA Office of Space Science) and the ADS-NASA to which we are thankful. We would also like to express our gratitude to an anonymous referee for his/her comments which have helped to considerably improve the paper.

 

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