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V418 Ser: A Sub-Period Minimum CV With Hydrogen

ATel #6287; P. Garnavich, C. Littlefield (Notre Dame), D. Terndrup and S. Adams (Ohio State)
on 3 Jul 2014; 16:43 UT
Credential Certification: Peter Garnavich (pgarnavi@gmail.com)

Subjects: Optical, Cataclysmic Variable

We obtained spectra of the cataclysmic variable V418 Ser, which was recently found by the VSNET collaboration (Kato et al. 2004, PASJ, 56, 1) to have an orbit shorter than the period minimum for hydrogen-rich CVs (Littlefield, VSNET-alert 17321; de Miguel, VSNET-alert 17322).

The spectrum was taken with the Large Binocular Telescope (LBT) and MODS spectrograph on 2014 June 30, and covers wavelengths from 320 nm to 1 micron. The spectrum shows doubled peaked emission lines characteristic of a quiescent accretion disk. Hydrogen is clearly present indicating that this is not an AM CVn star, but the Helium to Hydrogen ratio is large when compared with long period CVs.

Overall the spectrum is very similar to the short period system SBS 1108+574 (CSS 120422:111127+571239; Littlefield et al. 2013, AJ, 145, 145; Carter et al. 2013, MNRAS, 431, 372) making V418 Ser a new member of a small but growing number of sub-period minimum binaries accreting some hydrogen.