Journal Article

SDSS J080449.49+161624.8: a peculiar AM CVn star from a colour-selected sample of candidates

G. H. A. Roelofs, P. J. Groot, D. Steeghs, A. Rau, E. De Groot, T. R. Marsh, G. Nelemans, J. Liebert and P. Woudt

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 394, issue 1, pages 367-374
Published in print March 2009 | ISSN: 0035-8711
Published online March 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14288.x
SDSS J080449.49+161624.8: a peculiar AM CVn star from a colour-selected sample of candidates

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We describe a spectroscopic survey designed to uncover an estimated ∼40 AM Canum Venaticorum (AM CVn) stars hiding in the photometric data base of the Sloan Digital Sky Survey. We have constructed a relatively small sample of about 1500 candidates based on a colour selection, which should contain the majority of all AM CVn binaries while remaining small enough that spectroscopic identification of the full sample is feasible.

We present the first new AM CVn star discovered using this strategy, SDSS J080449.49+161624.8, the ultracompact binary nature of which is demonstrated using high-time-resolution spectroscopy obtained with the Magellan telescopes at Las Campanas Observatory, Chile. A kinematic ‘S-wave’ feature is observed on a period Porb= 44.5 ± 0.1 min, which we propose is the orbital period, although the present data cannot yet exclude its nearest daily aliases.

The new AM CVn star shows a peculiar spectrum of broad, single-peaked helium emission lines with unusually strong series of ionized helium, reminiscent of the (intermediate) polars among the hydrogen-rich cataclysmic variables. We speculate that SDSS J0804+1616 may be the first magnetic AM CVn star. The accreted material appears to be enriched in nitrogen, to N/O ≳ 10 and N/C > 10 by number, indicating CNO cycle hydrogen burning, but no helium burning, in the prior evolution of the donor star.

Keywords: accretion, accretion discs; binaries: close; stars: individual: SDSS J080449.49+161624.8; novae, cataclysmic variables; white dwarfs

Journal Article.  5952 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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