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\begin{document} 
\IBVShead{5822}{10 April 2008} 
 
\IBVStitletl{Photometric Sequences and Astrometric Positions}{ of Nova V\lowercase{ul} 2007 N.2 and Nova C\lowercase{yg} 2008}
  
\IBVSauth{Henden, Arne$^1$; Munari, Ulisse$^2$}

\IBVSinst{AAVSO, American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138, USA} 
\IBVSinst{INAF Osservatorio Astronomico di Padova, Sede di Asiago, I-36032 Asiago (VI), Italy} 
 
\SIMBADobj{Nova Cyg 2008}
\SIMBADobj{V459 Vul} 
\IBVStyp{ Nova } 
\IBVSkey{photometry, astrometry} 
\IBVSabs{Accurate BVRcIc photometric sequences to assist the monitoring of}
\IBVSabs{light- and color-evolution are provided for Nova Vul 2007 N.2}
\IBVSabs{and Nova Cyg 2008, together with accurate astrometric positions}
\IBVSabs{linked to the UCAC2 reference catalog.}


\begintext 

Nova Vul 2007 N.2 (= V459 Vul) was discovered by H. Kaneda at $\sim$8.7~mag
on Dec 25.35 UT (cf. Nakano, 2007). Spectroscopic confirmation was provided
by Yamaoka (2007) and Munari et al. (2007). The latter reported a peak
brightness $V=7.58$ and $B-V=+1.10$ on Dec. 27.75 UT. At that time the spectrum
was characterized by strong absorptions, with feeble emission components
visible only in H$\alpha$ and OI 7772~\AA. A day later, the absorption
spectrum weakened remarkably and a rich and strong emission line spectrum
appeared, typical of novae soon after maximum.

Nova Cyg 2008 (= V2468 Cyg) was also discovered by H. Kaneda, at
$\sim$8.2~mag on Mar 7.80 UT (cf. Nakano, 2008), and spectroscopic
confirmation was provided by Nogami et al. (2008). On Mar 8.8 UT, they
observed a rich emission line spectrum, with velocities and P-Cyg profiles
typical of novae close to maximum brightness.

In this note we present a $BVR_{\rm C}I_{\rm C}$ photometric sequence
around both novae, optimized for CCD observations and their color
corrections. To calibrate the sequences, we obtained CCD photometry with the
Sonoita Research Observatory 0.35-m robotic telescope on several distinct
photometric nights, using $BVR_{\rm C}I_{\rm C}$ filters and an SBIG
STL-1001E CCD camera.  Pixel size is 1\farcs 25/pix and the field
of view is 20\arcm$\times$20\arcm .  Observations on each photometric night
included following an extinction star from low to high airmass, along with
$BVR_{\rm C}I_{\rm C}$ exposures of Landolt standard fields (Landolt,
1983, 1992). The photometric sequences are presented in Figures~1 and 2.

Some very red stars are included in these sequences for the purpose of
extending over a wide color range the determination of the transformation
coefficients.  When intrinsic, such red colors are generally associated to
variable cool stars. However, both fields suffer from large reddenings. In
fact, both novae at maximum displayed colors reddened by $E(B-V)\geq0.6$ and
in both cases blue field stars are missing. Thus, the very red stars
included in the sequences are such at least in part because of the large
reddenings and not necessarily because they are intrinsically very cool.
Nevertheless, these stars have not been observed sufficiently often to
guard against possible variability.


Astrometry was performed using SLALIB (Wallace, 1994) linear plate
transformation routines in conjunction with the UCAC2 reference catalog.
Errors in coordinates were less than 0.1 arcsec in both
coordinates, referred to the mean coordinate zero point of the reference
stars in each field.

The coordinates we derived for Nova Vul 2007 N.2 are 
$\alpha_{\rm J2000}$ = 19\hr 48\mm 08\fsec 866 ($\pm$0\fsec 026),
$\delta_{\rm J2000}$ = +21\deg 15\arcm 26\farcs 67 ($\pm$0\farcs 027),
close to the coordinates reported by Kaneda (2007) at position end figures
08\fsec 89 and 26\farcs 8. Within 0.1 arcsec of this position there is the very faint
star USNO-B1.0 1112-0430634, detected only on red POSS-II plates
at $R=20$ mag and with no counterpart in the 2MASS catalog.
Its position end figures are 08\fsec 87 and 26\farcs 8 (1 arcsec error). If this
was the progenitor, the amplitude of the outburst in the $B$ band exceeded
12.5 mag.

Our coordinates for Nova Cyg 2008 are: $\alpha_{\rm J2000}$ = 19\hr 58\mm 33\fsec 36
($\pm$0\fsec 18), $\delta_{\rm J2000}$ = $+$29\deg 52\arcm 06\farcs 6
($\pm$0\farcs 31), close to the coordinates reported by Nakano
(2008) at position end figures 33\fsec 39 and 06\farcs 5. Three arcsec away there
is the very faint star USNO-B1 1198-0459968 ($R=18$ mag) at position end
figures 33\fsec 16 and 06\farcs 4 (1 arcsec error), visible only on POSS-II red
plates and not on blue ones,with no counterpart in the 2MASS catalog. If
this star was the progenitor, the amplitude of the outburst was larger than
12 mag in the $B$ band.

We would like to thank J. Gross, W. Cooney and D. Terrell for their help in
setting up the SRO observations and relinquishing their observing time.


\references 

 Kaneda, H., 2008, {\it IAUC}, {\bf 8907}

 Landolt, A.U.,  1983, {\it AJ}, {\bf 88}, 439

 Landolt, A.U., 1992, {\it AJ}, {\bf 104}, 340

 Munari, U., Siviero, A., Valisa, P., Frigo, A., Dallaporta, S., Cherini,
 G., Dalla Via G., 2007, {\it CBET}, {\bf 1183}

 Nakano, S., 2008, {\it IAUC}, {\bf 8907}

 Nakano, S., 2008, {\it IAUC}, {\bf 8927}

 Wallace, P., 1994, {\it ASP Conf. Ser.}, {\bf 61}, 481, 
	Astronomical Data Analysis Software and Systems III

 Yamaoka, H., 2007, {\it CBET}, {\bf 1181}


\endreferences 

\IBVSfig{18cm}{5822-f1.eps}{$BVR_{\rm C}I_{\rm C}$ photometric
comparison sequence around Nova Vul 2007 N.2. The cross indicates the nova. 
$N$ is the number of nights in which the given star has been measured
in the given band. The error in $\alpha$ and $\delta$ are in arcsec.  The
panel on the right covers a 20\arcm$\times$20\arcm\ area centered on
the nova and shows stars down to $V$=17.0. The dashed
6\arcm$\times$6\arcm\ area is zoomed in on the left panel.}
\IBVSfigKey{5822-f1.eps}{Nova Vul 2007 N.2}{sequence}


\IBVSfig{18cm}{5822-f2.eps}{$BVR_{\rm C}I_{\rm C}$ photometric
comparison sequence around Nova Cyg 2008. The cross indicates the nova.  $N$
is the number of nights in which the given star has been measured in the
given band. The error in $\alpha$ and $\delta$ are in arcsec. The panel
covers a 6\arcm$\times$6\arcm\ area centered on the nova
and shows stars down to $V$=17.0. Star $b$ is HD~33314.}
\IBVSfigKey{5822-f2.eps}{Nova Cyg 2008}{sequence}

\IBVSedata{5822-t1.txt}
\IBVSdataKey{5822-t1.txt}{Nova Vul 2007 N.2}{photometry}
\AladinChart{5822-t1}
\IBVSecomment{photometric sequence}

\IBVSedata{5822-t2.txt}
\IBVSdataKey{5822-t2.txt}{Nova Cyg 2008}{photometry}
\AladinChart{5822-t2}
\IBVSecomment{photometric sequence}

\end{document}

