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THE ASTRONOMER Electronic Circular No 2332      2007 May 05 18.49UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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V2467 CYGNI
D.Steeghs (CfA), et. al., report on Astronomer's Telegram 1031 their 
detection of the likely progenitor to Nova Cygni 2007 = V2476 Cyg using 
images from the INT Photometric H-Alpha Survey (IPHAS;
http://www.iphas.org).

The field containing the classical nova was observed on several
occasions with the Isaac Newton Telescope at La Palma Observatory and 
its Wide Field Camera. The closest point source in the IPHAS database to 
the reported position of V2467 Cyg was found at
RA 20:28:12.47, DEC +41:48:36.4 (2000). This is consistent with the 
outburst position reported in IAUC #8821, CBET #894 and less than 0.3" 
from the USNO-A2.0 object 1275-13944467.

Three sets of r', i' and narrow-band H-alpha measurements were obtained 
in good observing conditions on 2004 August 8 & 9, from which they can 
derive reliable r', i' magnitudes and a measure of H-alpha excess (see 
Drew et al. 2005 for a discussion of the IPHAS survey and its point 
source photometry). They obtain r'=18.46+/-0.01, i'=17.49+/-0.01 and 
hence r'-i'=0.97+/-0.02. Comparing the IPHAS r'-i' and r'-Halpha colours 
with those of other field stars within the same INT/WFC pointing 
suggests a source consistent with either a lightly reddened K dwarf with 
no significant H-alpha emission or a bluer, more heavily reddened object 
with an r'-H-alpha excess of ~0.2 magnitudes. Given the absolute 
magnitude of K dwarfs (M~7), a distance of ~2kpc is implied in the first
scenario. This seems hard to reconcile with a lightly reddened object, 
in particular when considering the considerable galactic extinction 
along the line of sight.

In order to further disentangle these two possibilities, they comment 
that a source consistent with our IPHAS position is present in the 2MASS 
catalog at K=14.74+/-0.12 and with J-H=0.60+/-0.10 and H-K=0.39+/-0.13. 
For the low reddening scenario, the 2MASS magnitudes imply a M5 dwarf, 
not consistent with our r',i' magnitudes and also not consistent with an 
unreddened cataclysmic variable (CV) that would be the nova progenitor. 
However, an E(B-V) of 1.0-1.5 would make the 2MASS colours more in line 
with that of a high mass transfer rate CV. Applying this reddening to 
the IPHAS colours suggests a progenitor with an optical SED analogous to 
that of an A/F dwarf, and exhibiting a modest H-alpha excess.

For distances of more than ~1 kpc, the sight line of V2467 Cyg traverses 
molecular gas in the Cygnus-X star forming region and this amount of 
reddening would be unremarkable. Hence a relatively blue SED with some 
line emission offers a consistent fit to both optical and NIR 
photometry. An early A-type spectral type with weak H-alpha emission is 
consistent with the appearance of an optically thick accretion disc, as 
found in a number of high mass transfer rate cataclysmic variables.

They conclude that they have likely detected the progenitor to Nova 
Cygni 2007. It is a moderately reddened point source that showed H-alpha 
emission in 2004 and is consistent with a cataclysmic variable 
progenitor accreting at a high rate. Given the unreddened magnitude of 
r'~16 and a typical absolute magnitude of 3-5 for such CVs leads us to a 
distance estimate of 1.5-4kpc for V2467 Cyg. Finally, they remark that 
the outburst amplitude of ~12 magnitudes is very typical for a 
FeII-class galactic nova.

Guy M Hurst