[vsnet-alert 10675] (fwd) Strong Neon Emission in CSS081007:030559+054715: A Possible Oxygen/Neon Nova (OT_J030558.6+054715)

[Taichi Kato]

   If this object is indeed a nova, the maximum should have been
very bright.  Could it have totally escaped detection, or anyone
photographed in twilight??  The relatively high galactic latitiude
is unusual for such a nova.

===

Strong Neon Emission in CSS081007:030559+054715: A Possible 
Oxygen/Neon Nova 

ATel #1835; J. L. Prieto, K. Denney, O. Pejcha, & R. M. Wagner (Ohio 
State University) 
on 7 Nov 2008; 21:54 UT 
Password Certification: Jose Prieto (prieto at astronomy.ohio-state.edu) 

Subjects: Optical, Novae, Transients 

On 2008 October 30.4 we obtained low-resolution optical spectra 
(range 3350-4800 Angstroms) of the transient CSS081007:030559+054715 
using the Boller & Chivens CCD Spectrograph on the 1.3m McGraw-Hill 
telescope at MDM Observatory. The most striking feature in this 
spectral region is very strong, double-peaked [Ne V] at 3426 
Angstroms. The two peaks are offset by -1700 and 1100 km/s with 
respect to the rest wavelength. The equivalent width of this line is 
about five times higher than of Halpha in our previous spectrum (ATEL 
#1825). The HWZI of this line is 3100 km/s. Similar double-peaked 
structure with the same wavelength shifts are observed in 
substantially weaker lines of [Ne III] at 3869 and 3968 Angstroms. 
The bright emission line between 4650 and 4760 Angstroms, that we 
observed in ATEL #1825, is due to [Ne IV] 4721 blended with He II 
4686. 

Apart from Catalina Real-time Transient Survey, 
CSS081007:030559+054715 was observed by several other surveys. The 
All Sky Automated Survey (Pojmanski, 2002, Acta Astronomica, 52, 397) 
detected the object four times, specifically on 2008 Jan 14.19 UT at 
V=16.09(7), 2008 Jul 17.4 UT at V=14.26(5), 2008 Jul 24.4 UT at 
V=14.37(5), and 2008 Aug 3.4 UT at V=15.06(5). John Greaves brought 
to our attention that CSS081007:030559+054715 was measured by SDSS on 
2004 Dec 14.2 UT to have u=18.61(2), g=18.56(1), r=18.52(1), 
i=18.57(1) and z=18.68(5). 

Photometry on our RETROCAM images from 2008 Oct 27.35 UT give 
g=15.94(5), r=16.12(5) and i=16.28(5). Two other recent photometric 
measurements are provided by CRTS followup and indicate that 
CSS081007:030559+054715 is slowly fading, but with fairly rapid 
decline in the g-band. 

The ASAS measurements from 2008 Jul and Aug are very close to the 
limiting magnitude of that survey, but seem to indicate that the 
object was brighter during the seasonal gap. Our blue spectrum is 
similar to the late nebular phase spectrum of the very fast Nova Sgr 
1991 (V4160 Sgr, see Figure 10 of Williams et al. 1994, ApJS, 90, 
297), which developed very strong and broad forbidden neon emission 
lines. The exceptional strength of the forbidden Ne emission lines in 
the spectrum of CSS081007:030559+054715 suggests that it is a member 
of the class of neon novae which may originate on massive ONeMg white 
dwarfs and the outburst occurred during its seasonal gap, i.e., 
around JD 2454600. 

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

We thank K. Z. Stanek for useful discussions and suggestions.