Identification of a New Candidate Outbursting AM CVn System from ASAS-SN

ATel #6669; R. M. Wagner (Ohio State/LBTO), A. Kaur (Clemson), A. Porter (Clemson), A. Wilber (Arizona State), C. E. Woodward (Minnesota), S. G. Starrfield (Arizona State), D. H. Hartmann (Clemson), A. B. Davis (Ohio State), T. W.-S. Holoien (Ohio State), G. Simonian (Ohio State), K. Z. Stanek (Ohio State), C. S. Kochanek (Ohio State), B. J. Shappee (Carnegie Observatories), and J. L. Prieto (Diego Portales, MAS)
on 5 Nov 2014; 17:25 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

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We report the identification of a new candidate outbursting AM CVn system designated ASASSN-14fv discovered during the course of the All Sky Automated Survey for SuperNovae (ASAS-SN; http://www.astronomy.ohio-state.edu/~assassin/index.shtml ). The source was discovered by ASAS-SN on 2014 August 15.47 UT at V = 15.7 and was classified as a possible cataclysmic variable based on its outburst amplitude of about 4-5 mag and its likely association with a faint B = 20.5 point source on the DSS. On 2014 August 13.47 UT, the transient was undetected (V > 17.0).

We obtained an optical spectrum (range: 390-740 nm; resolution: 0.7 nm) of ASASSN-14fv on 2014 August 25.34 UT using the 2.4 m Hiltner Telescope (+CCDS) of the MDM Observatory on Kitt Peak. The spectrum exhibits relatively symmetrical absorption lines of He I superposed on a blue continuum. Identified He I absorption lines include 392.6, 402.3, 414.3, 416.9:, 438.8, 443.8, 447.1, 492.2, 501.5:, 504.8:, and 587.5 nm (the latter may be blended with a contribution from Na I D). The equivalent width of He I 447.1 absorption was 0.36 nm and with a resolution-corrected full width at the continuum level of about 4.7 nm and a FWHM of about 2.1 nm. The Balmer lines of hydrogen and emission from He II 468.6 nm are not present.

The light curve obtained by ASAS-SN on five epochs between 2014 August 15.5 and 27.5 UT shows the source fluctuating between V = 15.7 and 16.4 and declining to V = 16.8 on 2014 August 31.4 UT. The source was undetected (V > 16.3) until 2014 September 13.5 UT when it was detected again at V = 14.59 and then subsequently declined to V = 15.24 on 2014 Sep 14.52. The source was undetected (V > 16.5) in 10 observations between 2014 Sep 16.5 and Oct 9.4 UT. Thus, the light curve of ASASSN-14fv exhibited at least two outbursts between 2014 August 15.5 and September 14.52 UT which were characterized by a rapid rise (< 2 d) from V > 17 to outbursts with V ≤ 15.7.

Our spectrum and the ASAS-SN light curve of ASASSN-14fv both suggest that the source is a new outbursting AM CVn system. The spectrum obtained during a high state is dominated by He I absorption lines that lack the Stark-broadened wings characteristic of higher gravity DB white dwarfs and shows no trace of detectable hydrogen lines similar to the spectra of other AM CVn systems in their high states. In fact, our spectrum is reminiscent of the spectrum of the AM CVn-type system V803 Cen in its high state (O’Donoghue and Kilkenny 1989, MNRAS, 236, 319). A spectrum of ASASSN-14fv during its low state and photometric observations are required to measure the orbital period and to confirm the nature of the object.