Optical spectroscopy of microquasar candidates at low Galactic latitudes

¹ Departamento de Física, Escuela Politécnica Superior, Universidad de Jaén, Virgen de la Cabeza 2, 23071 Jaén, Spain e-mail: jmarti@ujaen.es
² Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain e-mail: jmparedes@ub.es
³ Harvard Society of Fellows, 78 Mount Auburn Street, Cambridge, MA 02138, USA
⁴ Harvard-Smithsonian Center for Astrophysics, MC 20, 60 Garden Street, Cambridge, MA 02138, USA e-mail: jbloom@cfa.harvard.edu
⁵ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38200 La Laguna, Tenerife, Canary Islands, Spain e-mail: jcv@ll.iac.es
⁶ Service d'Astrophysique, CEA Saclay, Bât. 709, L'Orme des Merisiers, 91191 Gif-sur-Yvette, Cedex, France e-mail: mribo@discovery.saclay.cea.fr
⁷ Smithsonian Institution, F. L. Whipple Observatory, PO Box 97, 670 Mount Hopkins, Amado, AZ 85645, USA e-mail: falco@cfa.harvard.edu

Corresponding author: J. Martí, jmarti@ujaen.es

Received: 2 June 2003
Accepted: 22 September 2003

Abstract

We report optical spectroscopic observations of a sample of 6 low-galactic latitude microquasar candidates selected by cross-identification of X-ray and radio point source catalogs for . Two objects resulted to be of clear extragalactic origin, as an obvious cosmologic redshift has been measured from their emission lines. For the rest, none exhibits a clear stellar-like spectrum as would be expected for genuine Galactic microquasars. Their featureless spectra are consistent with being extragalactic in origin although two of them could be also highly reddened stars. The apparent non-confirmation of our candidates suggests that the population of persistent microquasar systems in the Galaxy is more rare than previously believed. If none of them is galactic, the upper limit to the space density of new Cygnus X-3-like microquasars within 15 kpc would be pc^-3. A similar upper limit for new LS 5039-like systems within 4 kpc is estimated to be pc^-3.