The identification of the optical/IR counterpart of the 29.5-s transient X-ray pulsar GS 1843+009^*

¹ Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monteporzio Catone, Italy
² Observatoire Astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
³ SAX Science Data Center, ASI c/o Telespazio, via Corcolle 19, 00131 Roma, Italy
⁴ Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
⁵ Dept. of Physics & Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁶ Dipartimento di Fisica, Università degli Studi "La Sapienza", Piazza A. Moro 5, 00185 Roma, Italy

Corresponding author: G. L. Israel, Gianluca.Israel@oar.mporzio.astro.it

Received: 21 December 2000
Accepted: 19 March 2001

Abstract

We report on the identification of the optical/IR counterpart of the 29.5-s transient X-ray pulsar GS 1843+009. We re-analysed an archival ROSAT HRI observation of GS 1843+009 obtaining a new refined position. The optical and IR follow-up observations carried out for the new error circle allowed us to find a relatively faint () and variable early type reddened star (). The optical spectra show the Balmer and Paschen series in emission, while the IR observations confirm the presence of a flux excess (, ), suggesting that the star is surrounded by a circumstellar envelope. Spectroscopic and photometric data together indicate a B0-B2 IV-Ve spectral-type star located at a distance of ≥ 10 kpc confirming the Be-star/X-ray binary nature of GS 1843+009.