[vsnet-alert 17937] ASASSN-14fv (ATEL)

[Taichi Kato]

ASASSN-14fv (ATEL)

===

ATEL #6669							     ATEL #6669

Title:	Identification of a New Candidate Outbursting AM CVn System
		from ASAS-SN
Author:	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)
Queries:	mwagner at lbto.org
Posted:	5 Nov 2014; 17:25 UT
Subjects:Optical, Cataclysmic Variable, Transient

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 &le; 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&#8217;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.