RX J0806.3+1527: A double degenerate binary with the shortest known orbital period (321s)

Free access article

Issue		A&A Volume 386, Number 1, April IV 2002


Page(s)		L13 - L17
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20020314

A&A 386, L13-L17 (2002)
DOI: 10.1051/0004-6361:20020314

Letter

RX J0806.3+1527: A double degenerate binary with the shortest known orbital period (321s)

G. L. Israel¹, W. Hummel², S. Covino³, S. Campana³, I. Appenzeller⁴, W. Gässler^{5, 6}, K.-H. Mantel⁵, G. Marconi^{7, 1}, C. W. Mauche⁸, U. Munari⁹, I. Negueruela¹⁰, H. Nicklas¹¹, G. Rupprecht², R. L. Smart¹², O. Stahl⁴ and L. Stella¹

¹ INAF - Osservatorio Astronomico di Roma, V. Frascati 33, 00040 Monteporzio Catone, Italy
² European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching, Germany
³ INAF - Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate, Italy
⁴ Landessternwarte Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁵ Institut für Physik, Universitäts-Sternwarte München, Scheinerstr. 1, 81673 München, Germany
⁶ Subaru Telescope, NAOJ, 650 North A'ohoku Place, Hilo, Hawaii, HI 96720, USA
⁷ European Southern Observatory, Casilla 19001, Santiago, Chile
⁸ Lawrence Livermore National Laboratory, L-43, 7000 East Avenue, Livermore, CA 94550, USA
⁹ INAF - Osservatorio Astronomico di Padova, Sede di Asiago, 36012 Asiago, Italy
¹⁰ Observatoire Astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
¹¹ Universitätssternwarte Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany
¹² INAF - Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025, Pino Torinese (To), Italy

(Received 12 February 2002 / Accepted 1 March 2002 )

Abstract
We carried out optical observations of the field of the X-ray pulsator RX J0806.3+1527. A blue V = 21.1 star was found to be the only object consistent with the X-ray position. VLT FORS spectra revealed a blue continuum with no intrinsic absorption lines. Broad ( $v \sim$ 1500 km s ^-1), low equivalent width (~-1 $\div$ -6 Å) emission lines from the HeII Pickering series were clearly detected. B, V and R time-resolved photometry revealed the presence of ~15% pulsations at the ~321 s X-ray period, confirming the identification. These findings, together with the period stability and absence of any additional modulation in the 1 min -5 hr period range, argue in favour of the orbital interpretation of the 321 s pulsations. The most likely scenario is thus that RX J0806.3+1527 is a double degenerate system of the AM CVn class. This would make RX J0806.3+1527 the shortest orbital period binary currently known and one of the best candidates for gravitational wave detection.

Key words: stars: individual: -- RX J0806.3+1527, 1BMW J080622.8+152732 -- binaries: close -- stars: white dwarfs -- stars: emission-line -- X-rays: stars

Offprint request: G. L. Israel, gianluca@mporzio.astro.it

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