[vsnet-alert 10652] OT_J030558.6+054715 = Catalina transient, emission-line object of unknown class

[Taichi Kato]

> OT_J030558.6+054715 = Catalina transient
>
>   This transient is a slowly brightening, unusual transient.
> There is a non-red 18-19 mag counterpart in USNO catalog.

   This object is indeed an emission-line object of unknown class.
The presence of [O III] (?) line is unusual if this is a nova in the
rising stage.

===

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 

Password Certification: Jose Prieto (prieto at astronomy.ohio-state.edu) 
Subjects: Optical, Novae, Transients 

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 AV = 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.