[vsnet-newvar 2736] SDSS J080449.49+161624.8

[Taichi Kato]

   This object might be of interest.  ASAS-3 possibly detected an outburst
(a noise?)  The system paparmeter might suggest a helium dwarf nova
like CP Eri.

  YYYYMMDD(UT)   mag  observer
  20050113.1530 14.303V  (ASAS (Pojmanski, G. 2002, Acta Astron. 52,397))
  20050113.1530 14.325V  (ASAS (Pojmanski, G. 2002, Acta Astron. 52,397))
  20050113.1824 <14.50V  (ASAS (Pojmanski, G. 2002, Acta Astron. 52,397))

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arXiv:0811.3974

    Title: SDSS J080449.49+161624.8: A peculiar AM CVn star from a colour-selected sample of candidates
    Authors: G.H.A. Roelofs (CfA), P.J. Groot (Nijmegen), D. Steeghs (Warwick), A. Rau (Caltech), E. de Groot (Nijmegen), T.R. Marsh (Warwick), G. Nelemans (Nijmegen), J. Liebert (U. Arizona), P. Woudt (Cape Town)
    Comments: Accepted to MNRAS
    Subjects: Astrophysics (astro-ph)

    We describe a spectroscopic survey designed to uncover an 
estimated ~40 AM CVn stars hiding in the photometric database of the 
Sloan Digital Sky Survey (SDSS). 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 at the Magellan telescopes at Las Campanas Observatory, 
Chile. A kinematic 'S-wave' feature is observed on a period 
44.5+/-0.1min, 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 
ionised 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.