Distinguishing post-AGB impostors in a sample of pre-main sequence stars

¹ Universidade de São Paulo, IAG – Rua do Matão, 1226, 05508-900 São Paulo, SP, Brazil
e-mail: vieira@astro.iag.usp.br
² Universidade Federal do ABC, CECS, Rua Santa Adélia, 166, 09210-170 Santo André, SP, Brazil
³ Observatoire de Meudon, LUTH, 5 Place Jules Janssen, 92190 Meudon, France
⁴ N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland

Received: 16 August 2010
Accepted: 16 September 2010

Abstract

Context. A sample of 27 sources, cataloged as pre-main sequence stars by the Pico dos Dias Survey (PDS), is analyzed to investigate a possible contamination by post-AGB stars. The far-infrared excess due to dust present in the circumstellar envelope is typical of both categories: young stars and objects that have already left the main sequence and are suffering severe mass loss.

Aims. The two known post-AGB stars in our sample inspired us to seek for other very likely or possible post-AGB objects among PDS sources previously suggested to be Herbig Ae/Be stars, by revisiting the observational database of this sample.

Methods. In a comparative study with well known post-AGBs, several characteristics were evaluated: (i) parameters related to the circumstellar emission; (ii) spatial distribution to verify the background contribution from dark clouds; (iii) spectral features; and (iv) optical and infrared colors.

Results. These characteristics suggest that seven objects of the studied sample are very likely post-AGBs, five are possible post-AGBs, eight are unlikely post-AGBs, and the nature of seven objects remains unclear.