An infrared study of galactic OH/IR stars ^*,**,***

I. An optical/near-IR atlas of the Arecibo sample

¹ VILSPA Satellite Tracking Station, Apartado de Correos 50727, 28080 Madrid, Spain
² Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: Francisco.Jimenez-Esteban@hs.uni-hamburg.de
³ ISO Data Centre, Science Operations and Data Systems Division, Research and Scientific Support Department of ESA, Villafranca del Castillo, Apartado de Correos 50727, 28080 Madrid, Spain

Received: 22 July 2004
Accepted: 11 October 2004

Abstract

In this paper we present optical and near-infrared finding charts, accurate astrometry (≈1´´) and single-epoch near-infrared photometry for 371 IRAS sources, 96% of those included in the so-called “Arecibo sample of OH/IR stars” (Eder et al. [CITE], ApJS, 66, 183; Lewis et al. [CITE], ApJ, 362, 634; Chengalur et al. [CITE], ApJS, 89, 189). The main photometric properties of the stars in the sample are presented and discussed as well as the problems found during the process of identification of the optical/near-infrared counterparts. In addition, we also identify suitable reference stars in each field to be used for differential photometry purposes in the future.
We find that 39% of the sources (144 in number) have no optical counterpart, 8 of them being invisible even at near infrared wavelengths. The relative distribution of sources with and without optical counterpart in the IRAS two-colour diagram and their characteristic near infrared colours are interpreted as the consequence of the increasing thickness of their circumstellar shells. Among the objects not detected at near infrared wavelengths four non-variable sources are proposed to be heavily obscured post-AGB stars which have just very recently left the AGB. Eight additional objects with unusually bright and/or blue near-infrared colours are identified as candidate post-AGB stars and/or proto-planetary nebulae.