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\begin{document} 
\IBVShead{5834}{28 May 2008} 
 
\IBVStitletl{Photometric Sequences and Astrometric Positions}{ of Nova C\lowercase{yg} 2008 N.2 and Nova S\lowercase{gr} 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{V2491 Cyg}
\SIMBADobjAlias{Nova Sgr 2008}{V5579 Sgr} 
\IBVStyp{ Nova } 
\IBVSkey{photometry, astrometry} 
\IBVSabs{Accurate BVRcIc photometric sequences to assist the monitoring}
\IBVSabs{of their light- and color-evolution are provided for}
\IBVSabs{Nova Cyg 2008 N.2 and Nova Sgr 2008, together with accurate}
\IBVSabs{astrometric position liked to UCAC2 reference catalog.}


\begintext 

Nova Cyg 2008 N.2 (= V2491 Cyg) was discovered by K. Nishiyama and F.
Kabashima at $\sim$7.7~mag on Apr. 10.728 UT (cf. Nakano, 2008a). 
Spectroscopic confirmation was provided by Ayani and Matsumoto (2008) on Apr.
11.72 UT, that observed a FWHM of 4500~km/s for the H$\alpha$ emission line.
P-Cyg absorption components for Balmer lines at $-$4000~km/s were reported by
Tomov et al (2008a) for Apr. 11.99 and 13.95 spectra, together with presence
of an additional emission component at +2300~km/s and a classification as a
FeII-type nova given the numerous FeII multiplets seen in emission. A
classification as He/N-type nova was instead preferred by Lynch et al.
(2008) on the base of their near-IR spectra of Apr. 12.56 UT that displayed a
FWHM of 5500~km/s for the emission lines that included HeI, NI, NII and OI.
From the intensity of OI emission lines at 0.84 and 1.13 $\mu$m on Apr. 17.6
UT, Rudy et al. (2008) estimated a reddening $E_{B-V}$$\sim$0.43. The FWHM
of the emission lines in the near-IR spectra of Ashok~et~al.~(2008) for Apr.~18
 and 20 were $\sim$4100~km/s, while it ranged from 4200 to 5400~km/s
depending from the given emission line in the optical spectra for Apr. 27.3
and 28.4 UT of Helton~et~al.~(2008) who also remarked on the appearance of
HeII and NIII emission lines in the spectra and the disappearance of P-Cyg
absorption components from all emission lines. A detailed description of the
spectral appearance on Apr 15 and 17 was presented by Tomov~et~al.~(2008b),
who revised their classification to that of a He/N-type nova.

Ibarra and Kuulkers (2008) were the first to note the positional coincidence
of Nova Cyg 2008 N.2 with an X-ray source observed before outburst by Rosat,
Swift and XMM-Newton satellites. A greater number of details of such
pre-outburst X-ray observations were reported by Ibarra et al. (2008), that
noted how the source was largely variable on time scales of $\sim$4~days,
sometimes displaying a very soft energy distribution. The~only other nova
detected in X-rays {\em before} the outburst is Nova Oph 1998 (=V2487 Oph,
Hernanz and Sala, 2002). The nova was not-detected by Swift on Apr. 11 and
instead positively observed by the X-ray satellite on Apr. 15, at a much
lower count rate than before the outburst (Kuulkers et al., 2008).

Finally, Balman, Pekon and Kiziloglu (2008) reported that their serendipitous 
monitoring on the nova field from July to November 2007 failed to reveal
any source at the nova position brighter than the $R_{\rm C}$=18.2~mag 
limiting magnitude of their observations.

Nova Sgr 2008 (= V5579 Sgr) was also discovered by  K. Nishiyama and F.   
Kabashima, at $\sim$8.4~mag on Apr 18.784 UT (cf. Nakano et al., 2008b). 
Spectroscopic confirmation was provided by M. Fujii on Apr. 19.82 UT 
(cf. Yamaoka, 2008) who noted a prominent P-Cyg profile for H$\alpha$.

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\farcs25/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 Cyg 2008 N.2 are 
$\alpha_{\rm J2000}$ = 19\hr 43\mm 01\fsec980 ($\pm$0\fsec030),
$\delta_{\rm J2000}$ = +32\deg 19\arcm 13\farcs55 ($\pm$0\farcs017),
close to the coordinates reported by Sostero and Guido (2008) at position end figures
01\fsec98 and 13\farcs5. Within 0.9 arcsec of this position there is the very faint
star USNO-B1.0	1223-0482965 ($R$=15.9 mag), with no counterpart in the 2MASS~catalog.
Its position end figures are 02\fsec04 and 13\farcs8 (0.4 arcsec error). If this
was indeed the progenitor, the amplitude of the outburst in the $R$ band reached 9 mag.

Our coordinates for Nova Sgr 2008 are: $\alpha_{\rm J2000}$ = 18\hr 05\mm 58\fsec92 ($\pm$0\fsec08), \\$\delta_{\rm J2000}$ = $-$27\deg 13\arcm 55\farcs9
($\pm$0\farcs25), close to the coordinates reported by Nakano
(2008b) at position end figures 58\fsec88 and 56\farcs0. The field is extremely crowded,
with several very faint field stars laying within 4 arcsec from nova position and
not listed in USNO B1 or 2MASS catalogs.


\references 

Ashok, N.M., Banerjee, D.P.K., Naik, S., 2008, {\it CBET}, {\bf 1354}

Ayani, K., Matsumoto, K., 2008, {\it CBET}, {\bf 1334}

Balman, S., Pekon, Y., Kiziloglu, U., 2008, {\it ATel}, {\bf 1504}

Helton, L.A., Woodward, C.E., Vanlandingham, K., Schwarz, G.J., 2008, {\it CBET},  {\bf 1379}

Hernanz, M., Sala, G., 2002, {\it Science}, {\bf 298}, 393 

Ibarra, A., Kuulkers, E., 2008, {\it ATel}, {\bf 1473}

Ibarra, A. et al., 2008, {\it ATel}, {\bf 1478}

Kuulkers, E. et al., 2008, {\it ATel}, {\bf 1480}

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

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

Lynch, D.K., Russell, R.W., Rudy, R.J., Woodward, C.E., Schwarz, G.J., 2008, {\it IAUC}, {\bf 8935}

Nakano, S., 2008a, {\it IAUC}, {\bf 8934}

Nakano, S. et al., 2008b, {\it IAUC}, {\bf 8937}

Rudy, R.J., Lynch, D.K., Russell, R.W., Woodward, C.E., Covey, K., 2008, {\it IAUC}, {\bf 8938}

Sostero, G., Guido, E., 2008, {\it IAUC}, {\bf 8934}

Tomov, T. et al., 2008a, {\it ATel}, {\bf 1475} 

Tomov, T. et al., 2008b, {\it ATel}, {\bf 1475} 

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

Yamaoka, H., 2008, {\it CBET}, {\bf 1344}


\endreferences 


\IBVSfig{19cm}{5834-f1.eps}{$BVR_{\rm C}I_{\rm C}$ photometric
comparison sequence around Nova Cyg 2008 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
covers a 6\arcm$\times$6\arcm\ area centered on the nova
and shows stars down to $V$=18.2. Star $a$ is HD~331150.}
\IBVSfigKey{5834-f1.eps}{Nova Cyg 2008 N.2.}{finding chart}

\IBVSedata{5834-t1.txt}
\IBVSfigKey{5834-t1.txt}{V2491 Cyg}{sequence}
\AladinChart{5834-t1}
\IBVSecomment{photometric sequence}


\IBVSfig{16cm}{5834-f2.eps}{$BVR_{\rm C}I_{\rm C}$ photometric
comparison sequence around Nova Sgr 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 on the right covers a 20\arcm$\times$20\arcm\ area centered on
the nova and shows stars down to $V$=16.0. The dashed
6\arcm$\times$6\arcm\ area is zoomed in on the left panel.}
\IBVSfigKey{5834-f2.eps}{Nova Sgr 2008}{finding chart}

\IBVSedata{5834-t2.txt}
\IBVSfigKey{5834-t2.txt}{Nova Sgr 2008}{sequence}
\AladinChart{5834-t2}
\IBVSecomment{photometric sequence}


\end{document}
