\documentstyle[twoside, epsf]{article} 
 
\input ibvs2.sty 
 
\begin{document} 
\IBVShead{5803}{25 October 2007} 
 
\IBVStitletl{Photometric Sequences and Astrometric Positions}{ of Nova S\lowercase{gr} 2007 and Nova V\lowercase{ul} 2007}
  
\IBVSauth{Henden, Arne$^1$; Munari, Ulisse$^2$}

\IBVSinst{AAVSO, American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138, USA} 
\IBVSinst{INF Osservatorio Astronomico di Padova, Sede di Asiago, I-36032 Asiago (VI), Italy} 
 
\SIMBADobjAlias{V5558 Sgr}{Nova Sgr 2007}
\SIMBADobjAlias{V458 Vul}{Nova Vul 2007} 
\IBVStyp{ Nova } 
\IBVSkey{photometry, astrometry} 


\begintext 

Nova Sgr 2007 (= V5558 Sgr) was discovered by Y. Sakurai at $\sim$10.3~mag
on Apr~14.777 UT (cf. Nakano 2007a). It was recovered on prediscovery images
by K. Haseda at mag~11.2 on Apr. 11.792 UT (cf. Yamaoka 2007). On April 20,
spectroscopic confirmation was provided by Iijima (2007a), who argued that
the object could be a rather peculiar nova seen in the pre-maximum phase,
and by Naito et al. (2007), who concluded the object is probably not a
classical nova. Later, Iijima (2007b) recapped the spectroscopic evolution
until mid July and concluded the object is indeed a nova with a very
peculiar behaviour. A detailed description of the first three months of
photometric and spectroscopic evolution of Nova Sgr 2007 was provided by
Munari et al. (2007a), that also highlighted the similarity with Nova Cas
1995 (V723 Cas) and reported about their positive detection of the nova in
the X-rays with the SWIFT satellite. Further evolution in optical and
infrared spectra were reported by Kiss and Sarneczky (2007a) and Lynch et
al. (2007). According to Munari et al. (2007a), maximum brightness occurred
around July 10.0 UT with $V=6.53$, $B-V=+0.96$, $V-I_{\rm C}=+1.22$.
According to the AAVSO International Database, Nova Sgr 2007 went through
five further progressively fainter maxima.

Nova Vul 2007 (= V458 Vul) was discovered on August 8.54 UT by H. Abe at 9.5~mag (cf. Nakano 2007b). Spectroscopic confirmation was obtained on the
following day by Munari et al. (2007b), Buil (2007) and Fujii (2007). A
description of the spectrum for August 18 was reported by Kiss and Sarneczky
(2007b).  According to the AAVSO International Database, Nova Vul 2007 went
through three distinct maxima of similar $\sim$8.2 mag brightness on August
9, 13 and 19, before entering a stable decline.

In this note we present a $BVR_{\rm C}I_{\rm C}$ photometric sequence
around both novae. These sequences are based on the visual sequences used by the
AAVSO, with a wider color range for CCD calibration.
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.

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 Sgr 2007 are 
$\alpha_{\rm J2000}$ = 18\hr 10\mm 18\fsec258 ($\pm$0\fsec 046),
$\delta_{\rm J2000}$ = $-$18\deg 46\arcm 51\farcs95 ($\pm$0\farcs 047),
close to the coordinates reported by Nakano (2007a) at position end figures
18\fsec 27 and 52\farcs 1, and by Koff (2007) at position end figures 18\fsec 21 and 51\farcs 8. No progenitor is visible on POSS plates within a few arcsec from this position, which would set the outburst amplitude to $\Delta B\geq 13.4$
mag.  7.2~arcsec north of the nova lies field star GSC2 S9JJ000329, for
which we measured psf-fit magnitudes as given in Table 1 and position
(J2000) $\alpha$=18\hr 10\mm 17\fsec 99, $\delta$=$-$18\deg 46\arcm 46\farcs 0.

\vskip 1cm
\centerline{Table 1.  Nova optical companions}
\vskip 3mm
\begin{center}
\begin{tabular}{lcccccccc}
\hline
{\em companion to:} & $V$  & ($B-V$) & ($V-R_c$) & ($R_c-I_c$) \\
\hline
V5558 Sgr & 12.25 $\pm$0.05 & +1.39 $\pm$0.05 & +0.77 $\pm$0.08 & +0.73 $\pm$0.06 \\
V458 Vul & 15.96 $\pm$0.05 & +1.80 $\pm$0.08 & +1.01 $\pm$0.05 &+ 0.97 $\pm$0.08 \\
\hline
\end{tabular}
\end{center}
\vskip 1cm

Our coordinates for Nova Vul 2007 are: $\alpha_{\rm J2000}$ = 19\hr 54\mm 24\fsec 628 ($\pm$0\fsec 061),
\\$\delta_{\rm J2000}$ = $+$20\deg 52\arcm 52\farcs 02 ($\pm$0\farcs 049),
close to the coordinates reported by Nakano (2007b) at position end figures
24\fsec 64 and 51\farcs 9. Within 0.61 arcsec from our position of the nova lies
USNO-B1.0 1108-0460444, at catalog $B$=18.2 and $R$=17.8 mag. The blue color
and $\Delta B$=10.5 mag outburst amplitude make this object a viable
progenitor for the nova. 7.4~arcsec south of the nova lies USNO-B1.0
1108-0460435, for which we measured psf-fit magnitudes as given in
Table 1 and position (J2000) $\alpha$=19\hr 54\mm 24\fsec 52, $\delta$=+20\deg 52\arcm 44\farcs 8

\IBVSfig{18cm}{5803-f1.eps}{$BVR_{\rm C}I_{\rm C}$ photometric
comparison sequence around Nova Vul 2007. 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 $V$=16.5. The dashed
6\arcm $\times$6\arcm\ area is zoomed in on the left panel.
$\alpha$~=~HD~345257~(K5), $\beta$~=~HD~345267 (K2), $\gamma$~=~HD~345266
(B5), $\delta$~=~HD~345268 (B8), $\epsilon$~=~HD~345256 (G5) and
$\zeta$~=~HD~345264 (A2).}
\IBVSfigKey{5803-f1.eps}{Nova Vul 2007}{photometric sequence}

\IBVSfig{18cm}{5803-f2.eps}{$BVR_{\rm C}I_{\rm C}$ photometric
comparison sequence around Nova Sgr 2007. 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 $V$=16.2. The dashed
6\arcm $\times$6\arcm\ area is zoomed in on the left panel.
$\alpha$~=~HD~166240~(K0III), $\beta$~=~HD~166322 (B9IV),
$\gamma$=~HD~166145 (G5/G6III), $\delta$~=~HD~312752 (A0),
$\epsilon$~=~HD~166189 (B9II) and $\zeta$~=~HD~312750.}
\IBVSfigKey{5803-f2.eps}{Nova Sgr 2007}{photometric sequence}

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.

\IBVSedata{5803-t2.txt}
\IBVSdataKey{5803-t2.txt}{V458 Vul}{sequence}
\AladinChart{5803-t2}
\IBVSecomment{photometric sequence}

\IBVSedata{5803-t3.txt}
\IBVSdataKey{5803-t3.txt}{V5558 Sgr}{sequence}
\AladinChart{5803-t3}
\IBVSecomment{photometric sequence}


\references 

Buil, C., 2007, {\it IAUC}, {\bf 8862}

Fujii, M., 2007, {\it IAUC}, {\bf 8862}

Iijima, T., 2007a, {\it CBET}, {\bf 934}

Iijima, T., 2007b, {\it CBET}, {\bf 1006}

Kiss L., Sarneczky, K., 2007a, {\it CBET}, {\bf 1039}

Kiss L., Sarneczky, K., 2007b, {\it CBET}, {\bf 1038}

Koff, R., 2007, {\it IAUC}, {\bf 8832}

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

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

Lynch D. et al., 2007, {\it IAUC}, {\bf 8874}

Munari, U. et al., 2007a, {\it CBET}, {\bf 1010}

Munari, U. et al., 2007b, {\it CBET}, {\bf 1029}

Nakano, S., 2007a, {\it IAUC}, {\bf 8832}

Nakano, S., 2007b, {\it IAUC}, {\bf 8861}

Naito, H., Matsuda K., Yamaoka H., 2007, {\it CBET}, {\bf 934}

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

Yamaoka, H., 2007, {\it IAUC}, {\bf 8832}

\endreferences 

\end{document}

