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Spectroscopic Classification of AT 2017ggq/ATLAS17jsu as a Galactic Cataclysmic Variable

ATel #10771; J. Vinko (Konkoly Obs.; U Szeged; UT Austin), J. C. Wheeler (UT Austin), K. Sarneczky, O. Hanyecz, B. Cseh (Konkoly)
on 24 Sep 2017; 17:06 UT
Credential Certification: Jozsef Vinko (vinko@astro.as.utexas.edu)

Subjects: Optical, Cataclysmic Variable, Transient

AT 2017ggq was discovered by the ATLAS transient survey (Tonry et al., ATel #8680) on 2017-08-06, and it was classified as a featureless blue transient a few days later by Stritzinger et al. (ATel #10672).

Optical follow-up photometry taken with the 0.6/0.9m Schmidt telescope through Bessell BVRI filters indicates that the transient has been fading continuously since discovery with a rate of Delta m_15 ~ 1 mag. The following magnitudes have been obtained via PSF-fitting and tied to PS1 photometry of local comparison stars:

 
  JD        B     Err.   V     Err.   R    Err.    I     Err. 
57993.84  19.107 0.100 18.830 0.094 18.857 0.091 19.043 0.206 
57994.94  18.894 0.055 19.004 0.078 18.910 0.080 18.830 0.120 
57995.92  19.147 0.090 19.018 0.050 18.995 0.061 18.979 0.132 
57996.91  19.261 0.067 19.285 0.081 19.023 0.120 19.411 0.204 
58011.83  19.854 0.075 19.838 0.064 20.003 0.114   --    -- 

An optical spectrum, taken with the LRS2 spectrograph on the 10m Hobby-Eberly Telescope at McDonald Observatory by Matthew Shetrone on 2017-09-22.2 UT, shows a blue continuum with weak H-alpha and relatively strong Na D features at zero redshift. The spectrum indicates that AT 2017ggq is a new Galactic Cataclysmic Variable, likely a dwarf nova.

Our classification spectrum can be accessed on the Transient Name Server: http://wis-tns.weizmann.ac.il/object/2017ggq/