Optical spectroscopy of transient CSS081007:030559+054715

ATel #1825; O. Pejcha, J. L. Prieto & K. Denney (Ohio State University)
on 31 Oct 2008; 17:11 UT
Credential Certification: Jose Prieto (prieto@astronomy.ohio-state.edu)

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We report on observations of a transient CSS081007:030559+054715 discovered by the Catalina Real-time Transient Survey (CRTS). According to CRTS photometry the object brightened by about 4 mag during the last year and is currently at about 16th magnitude. We obtained low resolution spectrum (range 4200-7500 Angstroms) on 2008 Oct 27.32 UT using Modspec instrument on 2.4m Hiltner telescope at the MDM Observatory. The spectrum shows blue continuum with very wide and prominent emission lines. The Halpha line shows three well-separated components with radial velocities of -1740, -160 and 1580 km/s. The total HWZI is 2900 km/s. Apparently similar structure is seen at the position of He II and [OIII]. Hbeta is detected but weak. There is a wide unresolved line or blend of lines at the position of Hgamma.

The plot of the MDM spectrum can be seen at http://www.astronomy.ohio-state.edu/~pejcha/crts_transient.

In addition, between 2008 Oct 27.41 and 27.48 UT we obtained 130 r band images with RETROCAM instrument also on the MDM 2.4m telescope. During that time the transient remained constant to within ~0.05 mag.

The transient is located at galactic coordinates of (l,b)=(172.627,-43.727), i.e. away from the Galactic center. The Schlegel et al. (1998) value of the interstellar extinction at this position is A_V = 0.48 mag.

Based on the similarity of the observed spectral features with spectra of recurrent nova CI Aql (see, e.g., Fig. 5 in Matsumoto et al. 2001, A&A, 378, 487), including large expansion velocities, we suggest that the transient CSS081007:030559+054715 represents a nova-like phenomenon, although with very unusual, gradual rise of the light curve. For any plausible distance within our Galaxy (i.e. less than 50 kpc), the absolute magnitude of CSS081007:030559+054715 is fainter than about -3 magnitudes, significantly less luminous than classical novae. However, note the large gap in the temporal coverage of the event, and the fact that it is still ongoing.

Further observations of this interesting transient are strongly encouraged.

We thank K. Z. Stanek and R. M. Wagner for useful discussions and suggestions.

Webpage with spectra of the object.