[vsnet-alert 17733] ASASSN-14ei: AM CVn-type (ATEL)

[Taichi Kato]

ASASSN-14ei: AM CVn-type (ATEL)

ATEL #6475							     ATEL #6475

Title:	Follow-up of ASASSN-14ei show He lines in the spectra and Swift/XRT
		X-ray detection
Author:	J. L. Prieto (Universidad Diego Portales; MAS), N. Morrell
		(LCO), D. Grupe (Morehead State), K. Z. Stanek, C. S. Kochanek, T.
		W.-S. Holoien, A. B. Davis, U. Basu, J. F. Beacom (Ohio State), D.
		Bersier (LJMU), B. J. Shappee (Carnegie Observatories), J. Brimacombe
		(Coral Towers Observatory), D. Szczygiel, G. Pojmanski (Warsaw University
		Observatory)
Queries:	jose.prietok at mail.udp.cl
Posted:	15 Sep 2014; 21:50 UT
Subjects:Optical, Ultra-Violet, X-ray, Cataclysmic Variable, Transient

We report follow-up optical spectra and Swift X-ray/UV/optical imaging
of the unusual optical transient ASASSN-14ei (ATel #6340). We obtained
medium/low resolution optical spectra on UT 2014 Jul 28.4 and Aug 01.4
with the B&C spectrograph mounted on the du Pont 2.5m telescope at LCO.
The spectra show a blue continuum with relatively narrow He I and He II
lines in emission at redshift z=0 (see <a href="http://www.astronomy.ohio-state.edu/~assassin/followup/asassn14ei_spec.png">this
figure</a>). This is consistent with a He dwarf nova (AM CVn system in
outburst) classification for the object, which was proposed from the periodic
variations observed in the optical light curve of ~43 min and other light
curve characteristics (see <a href="http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/17575">vsnet-alerts
17575</a> and <a href="http://cbastro.org/pipermail/cba-public/2014-September/000927.html">CBA
news</a>). The optical light curve of ASASSN-14ei from AAVSO and ASAS-SN
shows 6 short brightening episodes since 2014 July 5 (UT July 10.4, July
24.4, August 03.4, August 14.2, August 28.2, and September 10.5) with V
= 11.9-13.2 mag at peak brightness and V ~ 15-17 mag between outbursts
(see the optical light curve <a href="http://www.astronomy.ohio-state.edu/~assassin/followup/asassn14ei_lc.png">here</a>,
with the dashed vertical lines showing the times when spectra were obtained).
The times between consecutive brightening peaks in the optical light curve
observed so far is between 10 and 14 days.  

We also obtained TOO observations of ASASSN-14ei with Swift UVOT and XRT
on four epochs between UT July 24.9 and UT July 26.5, within 2 days of
the peak of the second recorded outburst. The source was bright and blue
in UVOT photometry, with v=12.35 +/- 0.04, b=12.15 +/- 0.03, uvw1=10.27
+/- 0.04, uvm2=10.08 +/- 0.04, uvw2=10.04 +/- 0.04 on UT July 26.1. It
was also strongly detected in X-rays with the XRT in 1ks exposures. The
XRT data is well-modeled with a power-law with photon index of 1.7-2.0
and flux of 3.7-4.2 x 10<sup>-12</sup> erg/cm<sup>2</sup>/s (0.3-10 keV).

We thank the Swift team for making these observations possible. For more
information about the ASAS-SN project see the <a href=http://www.astronomy.ohio-state.edu/~assassin/index.shtml>ASAS-SN

Homepage</a> and also <a href=http://www.astronomy.ohio-state.edu/~assassin/transients.html>ASAS-SN
Transients</a>.