ASAS-SN Discovery of 3 Cataclysmic Variables

ATel #4987; B. Shappee, C. S. Kochanek, K. Z. Stanek, J. Jencson, J. F. Beacom (Ohio State), J. L. Prieto (Princeton), A. Talabere (Metro High School/OSU), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), M. Dubberley, M. Elphick, S. Foale, E. Hawkins, D. Mullens, W. Rosing, R. Ross, Z. Walker (Las Cumbres Observatory), D. Gifford (University of Michigan), J. Rich (Carnegie Observatories)
on 17 Apr 2013; 04:14 UT
Credential Certification: Jose L. Prieto (jose@obs.carnegiescience.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the double 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered three new transient sources:

 
Object       RA (J2000)  DEC (J2000)     Disc. UT Date    Disc. V mag 
ASASSN-13aa  12:14:13.4  +65:40:29.0    2013 April 5.34       14.8 
ASASSN-13ab  17:59:08.7  +14:51:33.8    2013 April 5.53       14.5 
ASASSN-13ac  19:47:10.4  -18:07:26.4    2013 April 6.58       14.0 

ASASSN-13aa was present in images obtained on 2013 UT Apr. 5 and Apr. 10., but undetected down to our magnitude limit of V~17 on 2013 UT Mar. 20 and earlier. SDSS DR9 imaging of the field reveals a blue stellar source (u=19.9, g=20.0, r=19.88) at RA = 12:14:13.33, DEC = +65:40:23.8 (J2000.0), about 5" from our initial position (within 7.5"/pixel of Brutus). Follow-up photometry obtained by D. Gifford on UT Apr. 11 with the MDM 2.4-m telescope and the OSMOS imaging spectrograph revealed that our transient source is indeed at the position of the SDSS archival source, with the following SDSS magnitudes: g = 15.1, r = 15.3, i = 15.4, z = 15.6 (+/- 0.05 mag). A spectrum obtained with OSMOS on UT Apr. 12.2 shows Balmer lines in absorption. This is consistent with a CV around maximum.

ASASSN-13ab was present in images obtained on 2013 UT Apr. 5, but undetected down to our magnitude limit of V~17 on 2013 UT Mar. 26. and earlier. We checked Vizier and find an optical source detected at RA = 17:59:08.62, DEC = +14:51:30.9 (J2000) in the GSC2.2 with B = 18.9 and R = 17.3 mag (within 3.2" of the ASAS-SN coordinates). There is also a mid-IR source at this position detected in WISE with W1 = 14.6 and W2 = 14.5 mag. An optical spectrum obtained by J. Rich on UT Apr. 13.3 with WFCCD mounted on the du Pont 2.5-m telescope at Las Campanas Observatory, shows a blue continuum with broad (FWHM ~ 900 km/s) and asymmetric Balmer lines in emission, as well as He I and He II lines. This spectrum is characteristic of a CV after maximum.

ASASSN-13ac was present in images obtained 2013 UT Apr. 6 and Apr. 7, but undetected down to our magnitude limit of V~17 on 2013 UT Mar. 26 and earlier. We checked in Vizier and find a faint source with B~19.6 mag detected 0.7-0.9" from our ASAS-SN position in the NOMAD and GSC2.3 catalogs. An optical spectrum obtained by J. Rich on UT Apr. 13.3 with WFCCD mounted on the du Pont telescope, shows a blue continuum with Balmer lines in absorption. The H-alpha line is filled and has a faint emission component. The spectrum is characteristic of a CV close to peak. We note that this transient was discovered independently on Apr. 8.77 and reported in the CBAT TOCP as TCP J19471043-1807262.

A plot with the spectra of ASASSN-13ab and ASASSN-13ac can be found here.