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\input ibvs2.sty 
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\IBVShead{5839}{9 July 2008} 
 
\IBVStitletl{Plate archive photometry of the progenitors of}{ Nova Cyg 2008 N.2 and Nova Sgr 2008}
  
\IBVSauth{Jurdana-Sepic, Rajka$^1$; Munari, Ulisse$^2$}

\IBVSinst{Physics Department, University of Rijeka, Omladinska 14, HR 51000 Rijeka, Croatia} 
\IBVSinst{INAF Osservatorio Astronomico di Padova, Sede di Asiago, I-36032 Asiago (VI), Italy} 
 
\SIMBADobj{V2491 Cyg}
\SIMBADobjAlias{Nova Sgr 2008}{V5579 Sgr} 
\IBVStyp{ Nova } 
\IBVSkey{photometry} 
\IBVSabs{The plate archives of the Asiago Schmidt telescopes have been}
\IBVSabs{searched for plates covering the position of Nova Cyg 2008 N.2 and}
\IBVSabs{Nova Sgr 2008. The position of Nova Cyg 2008 N.2 is imaged on 87}
\IBVSabs{plates covering the time span 1970 - 1986, that show the progenitor}
\IBVSabs{stable at <B>=17.9 (with a dispersion of 0.2 mag) <V>=17.1}
\IBVSabs{(with a dispersion of 0.2 mag), and <B-V>=+0.82 mag. The position of}
\IBVSabs{Nova Sgr 2008 is imaged on 58 plates covering the time span}
\IBVSabs{1961 - 1977, and it has always been fainter than plate limit(B>18).}
 
\begintext 

Nova Cyg 2008 N.2 (= V2491 Cyg) and Nova Sgr 2008 (= V5579 Sgr) were
discovered on 10 April 10 and 18 April 2008, respectively. A summary of the
discovery circumstances and early studies of these two novae has been
presented by Henden and Munari (2008). To the aim of providing more
information on the nature of these two novae, we have searched the archives
of the Asiago Schmidt telescopes for photographic plates imaging their
progenitors.

Henden and Munari (2008) found
the position of Nova Cyg 2008 N.2 to be coincident with the faint star USNO-B1.0
1223-042965 (within 0.9 arcsec). We located 131 Asiago photographic plates
covering the position of Nova Cyg 2008 N.2, 44 of which were later discarded
for various reasons (too bright sky background, poor focus or guiding, too
bright limiting magnitude, or other plate defects). A total of 87 good $B$ and $V$
plates (exposed between Oct 4, 1970 and Oct 10, 1986) were then retained,
and the magnitude of the progenitor was eye-estimated at the microscope against
the $BVR_{\rm C}I_{\rm C}$ photometric calibration sequence of Henden
and Munari (2008). The results are given in Table~1 (available electronic
only) and plotted for the $B$-band in Figure 1. During the 16 years covered
by the Asiago archive plates, no outburst or large variability was detected.
The progenitor remained stable around the mean values:
\begin{eqnarray}
<B> & = & 17.88  ~~{\rm (dispersion ~0.20 ~mag)} \\
<V> & = & 17.06  ~~{\rm (dispersion ~0.22 ~mag)} \\
<B-V> & = & + 0.82 \\
<V> - ~R_{\rm C}^{POSS-II} & = & + 0.73
\end{eqnarray}
The $V - R_{\rm C}$ is obtained by comparison with POSS-II plate on which
the progenitor shines at $R_{\rm C}$$\approx$16.33~mag. Comparing with
maximum brightness attended by the nova, the outburst amplitude has been
$\Delta B$=8.9, $\Delta V$=8.5~mag and $\Delta R_{\rm C}$=8.7.  Such a
limited amplitude is in sharp contrast with the rapid decline of Nova Cyg
2008 N.2. A 8.7~mag amplitude would correspond to a mean decline time
$t_2$$\approx$200~days (cf. Warner 1995, his Figure 5.4), a dozen times
slower than the observed $t_2$$\sim$17~days (Munari et al. 2008).

\IBVSedata{5839-t1.txt}
\IBVSdataKey{5839-t1.txt}{}{}

\IBVSfig{6cm}{5839-f1.ps}{B band photometry of the progenitor of Nova Cyg 2008 N.2 
from photographic plates of the Asiago Schmidt telescopes archives, showing its
constancy in brightness over the period 1970-1986.}

\IBVSfigKey{5839-f1.ps}{Nova Cyg 2008 N.2}{light curve}

A serendipitous monitoring of the field of Nova Cyg 2008 N.2 was carried out
by Balman et al. (2008) from July to November 2007. They failed
to reveal any source at the nova position brighter than the $R_{\rm
C}$=18.2~mag limiting magnitude of their observations. Balman et al. (2008) do 
not specify what is the astrometric position they assumed for the nova. They
linked their magnitude scale to USNO-B1 $R_{\rm C}$ 
magnitudes of the surrounding stars. By
comparing with the Henden and Munari (2008) photometric sequence, no
systematic offset larger than 0.1 mag is likely to affect the USNO-B1 $R_{\rm
C}$ values. This would imply that the progenitor of Nova Cyg 2008 N.2, which
was photometrically stable over the period 1970-1986, should have turned
fainter by $\Delta R_{\rm C}$$\geq$2~mag for several months right before to
erupt as a nova. This behavior would be highly peculiar and has no correspondence
among other novae, which instead in some cases tend to show an {\em
increase} in their luminosities in the years before the outburst (cf.
Robinson 1975). It seems therefore worthwhile that Balman et al. (2008) 
specify the
astrometric position they assumed for the nova and possibly publish a zoomed
picture of the field from their piled-up CCD $R_{\rm C}$ observations.

Similarly for Nova Cyg 2008 N.2, we searched the Asiago Schmidt plate
archives also for Nova Sgr 2008, and found 106 plates covering its position.
After plate inspection, 58 good $B$ and $I_{\rm C}$ band plates were finally
retained. We adopted nova position and photometric comparison sequence from
Henden and Munari (2008). The 58 good plates cover the period June 16, 1961
to 24 July, 1977, with an average limiting magnitude $B$$\sim$18, $I_{\rm
C}$$\sim$15.5. They are listed in Table~2 (available electronic only). The
progenitor was below limiting magnitude on all the plates.

\IBVSedata{5839-t2.txt}
\IBVSdataKey{5839-t2.txt}{}{}

\references 

Balman, S., Pekon, Y., Kiziloglu, U. 2008, ATel 1504 

Henden, A., Munari, U. 2008, IBVS 5834

Munari, U., et al. 2008, in preparation

Robinson, E.L. 1975, AJ 80, 515

Warner, B. 1995, Cataclysmic Variable Stars, Cambridge University Press

\endreferences 

\end{document}
