Volume 544, August 2012
|Number of page(s)||8|
|Section||Stellar structure and evolution|
|Published online||09 August 2012|
1 INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, 40129 Bologna, Italy
2 Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, via per Arnesano, 73100 Lecce, Italy
3 INFN – Istituto Nazionale di Fisica Nucleare, Sezione di Lecce, via per Arnesano, 73100 Lecce, Italy
4 INAF – Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133 Roma, Italy
Received: 3 April 2012
Accepted: 5 July 2012
The X-ray source 1RXS J180431.1−273932 has been proposed as a new member of the symbiotic X-ray binary (SyXB) class of systems, which are composed of a late-type giant that loses matter to an extremely compact object, most likely a neutron star. In this paper, we present an optical campaign of imaging plus spectroscopy on selected candidate counterparts of this object. We also reanalyzed the available archival X-ray data collected with XMM-Newton. We find that the brightest optical source inside the 90% X-ray positional error circle is spectroscopically identified as a magnetic cataclysmic variable (CV), most likely of intermediate polar type, through the detection of prominent Balmer, He i, He ii, and Bowen blend emissions. On either spectroscopic or statistical grounds, we discard as counterparts of the X-ray source the other optical objects in the XMM-Newton error circle. A red giant star of spectral type M5 III is found lying just outside the X-ray position: we consider this latter object as a fore-/background one and likewise rule it out as a counterpart of 1RXS J180431.1−273932. The description of the X-ray spectrum of the source using a bremsstrahlung plus black-body model gives temperatures of kTbr ~ 40 keV and kTbb ~ 0.1 keV for these two components. We estimate a distance of d ~ 450 pc and a 0.2−10 keV X-ray luminosity of LX ~ 1.7 × 1032 erg s-1 for this system and, using the information obtained from the X-ray spectral analysis, a mass MWD ~ 0.8 M⊙ for the accreting white dwarf (WD). We also confirm an X-ray periodicity of 494 s for this source, which we interpret as the spin period of the WD. In summary, 1RXS J180431.1−273932 is identified as a magnetic CV and its SyXB nature is excluded.
Key words: X-rays: individuals: 1RXS J180431.1 / 273932 / novae, cataclysmic variables / stars: dwarf novae / techniques: spectroscopic / astrometry
Partly based on observations collected at the Italian Telescopio Nazionale Galileo, located at the Observatorio del Roque de los Muchachos (Canary Islands, Spain).
Reduced data used for imaging and spectra is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/544/A114
© ESO, 2012
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