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Astron. Astrophys. 347, L51-L54 (1999)

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Letter to the Editor

Magnitude, color and spectral type of Aql X-1 in quiescence *

Claude Chevalier 1, Sergio A. Ilovaisky 1, Pierre Leisy 2 and Ferdinando Patat 2

1 Observatoire de Haute-Provence (CNRS), F-04870 St.Michel l'Observatoire, France (chevalier, ilovaisky@obs-hp.fr)
2 European Southern Observatory, Casilla 19001, Santiago 9, Chile

Received 14 May 1999 / Accepted 16 June 1999


Direct I and V-band imaging of Aql X-1 in quiescence and during outburst maximum shows that the true optical counterpart is the interloper located 0.48" West of the previously known star. We find for the new counterpart V = 21.6 and [FORMULA] = 2.2 in quiescence, when its contribution to the total light was 12% in V and 22% in I. Analysis of this photometry and of low-resolution spectra of the sum of both stars, also taken during quiescence, shows that the likely spectral types for the previously known star and the optical counterpart are late G and late K, respectively, reddened by [FORMULA] = 0.5[FORMULA]0.1.

Key words: stars: binaries: close – stars: individual: Aql X-1 – stars: neutron – X-rays: stars

* Based on observations obtained at the European Southern Observatory, La Silla, Chile

Send offprint requests to: C.Chevalier

© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999