EDP Sciences
Free access
Volume 386, Number 2, May I 2002
Page(s) 487 - 491
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020224

A&A 386, 487-491 (2002)
DOI: 10.1051/0004-6361:20020224

HST observations rule out the association between Cir X-1 and SNR G321.9-0.3

R. P. Mignani1, A. De Luca2, 3, P. A. Caraveo2 and I. F. Mirabel4, 5

1  ESO, Karl Schwarzschild Str. 2, 85748 Garching bei München, Germany
2  Istituto di Fisica Cosmica del CNR "G. Occhialini", Via Bassini 15, 20133 Milan, Italy
3  Universitá di Milano Bicocca, Dipartimento di Fisica, Piazza della Scienza 3, 20126 Milano, Italy
4  Service d'Astrophysique / CEA, CE-Saclay, 91191 Gif-sur-Yvette, France
5  Instituto de Astronomía y Física del Espacio/CONICET. cc5, 1428 Bs As, Argentina

(Received 21 December 2001 / Accepted 5 February 2002 )

Cir X-1 is one of the most intriguing galactic X-ray sources. It is a $\sim $16.6 days variable X/radio source, a type-I X-ray burster and a QPO emitter. In spite of an uncertain optical counterpart classification, all these properties identify the source as an LMXB. The morphology of the surrounding radio nebula has suggested an association with the nearby ( $\sim $25 arcmin) SNR G321.9-0.3, implying that Cir X-1 is a runaway binary originated from the supernova explosion ${\approx} 10^5$ years ago. To investigate this hypothesis, we carried out a proper motion measurement of the Cir X-1 $m \sim 19$ optical counterpart using a set of HST/WFC and WFPC2 observations taken ~8.6 years apart. We obtained a $3 \sigma$ upper limit of $\approx$5 mas yr -1 on the source proper motion. Since the runaway hypothesis would have implied a proper motion due North ranging between 15 and 75 mas yr -1, depending on the actual age of the SNR, our result definitively rules out the association between Cir X-1 and SNR G321.9-0.3.

Key words: X-ray: binaries -- ISM: individual objects: SNR G321.9-0.3 -- stars: individual: Cir X-1

Offprint request: R. P. Mignani, rmignani@eso.org

SIMBAD Objects

© ESO 2002