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\input ibvs2.sty 
 
\begin{document} 
\IBVShead{5410}{6 May 2003} 
 
\IBVStitle{Accurate astrometric position for M31-RV}
  
\IBVSauth{Munari, Ulisse$^{1}$; Henden, Arne$^{2}$; Boschi, Federico$^{1}$} 
 
\IBVSinst{Osservatorio Astronomico di Padova - INAF, Sede di Asiago, I-36032 Asiago (VI), Italy} 
\IBVSinst{Universities Space Research Association/U. S. Naval Observatory
Flagstaff Station, P. O. Box 1149, Flagstaff AZ 86002-1149, USA}

 
\IBVSobj{M31-RV}
\IBVSkey{astrometry} 
\IBVSabs{M31-RV, erupting in 1988 in the bulge of the Andromeda galaxy,}
\IBVSabs{was one of the most mysterious outbursts ever recorded, producing an}
\IBVSabs{M supergiant that at peak magnitude became the brightest cool star of}
\IBVSabs{the Local Group. Poor available astrometry and finding charts have}
\IBVSabs{plagued both the search for the remnant on HST images of the very}
\IBVSabs{ crowded M31 bulge field, as well as archival plate searches }
\IBVSabs{to better define the outburst light curve. Here we provide accurate }
\IBVSabs{astrometry (at 0.2 arcsec, more than an order of magnitude} 
\IBVSabs{better than previously available), and a good finding chart.}
 
\begintext 

A mysterious event took place in the Andromeda galaxy in the summer of
1988, when a star of the inner bulge region erupted, peaking at $M_V=-10.0$.
The event was different from other novae discovered in M31 (e.g. Rosino, 1973;
Ciardullo et al., 1990):  at peak brightness it displayed an
M supergiant spectrum, as revealed by observations with the Palomar 5m
telescope by Rich et al. (1989). The short duration of the event, the faint
apparent magnitude and the delay of the announcement until the outburst was already
over are responsible for limited observations on this very interesting and highly
unusual event, for which theorists have not yet agreed on a shared
interpretation.

The recent colorful happenings of V838~Mon, where a star erupted and 
became - within an expanding huge light echo - a supergiant with first K,
than M and later a spectrum dominated by such cool features as have been
observed only in brown dwarfs (Munari et al., 2002a; Geballe et al.,
2002; Bond et al., 2003), have revitalized the interest in the similar
red variable of M31, cited in literature as M31-RV or M31-RedVar.

The discovery that V838~Mon is a binary system where the companion to the
exploded star is a massive B3V star (Munari et al., 2002b) and that it has
developed a bright, huge and long lasting light-echo (Henden et al., 2002)
is a stimulus to a detailed investigation, in particular on HST archive
images, trying to locate the remnant - if any - of the \hbox{M31-RV} event. The
understandably very crowded HST images of the bulge of the Andromeda galaxy
would greatly benefit from the most precise astrometric position possible
for \hbox{M31-RV}. The same coordinates and a good finding chart would also support
the search in plate archives around the world for further
photometry of the 1988 event. The original frame grabbed from the TV screen
of the telescope guider and presented by Rich et al. (1989) as an
identification of the field is hardly suited for the task. Furthermore, good
coordinates and a finding chart could also stimulate screening of plate
archives around the world looking for a confirmation or dismissal of a
second, weaker outburst of M31-RV in 1967 allegedly reported by Sharov
(1990) which, if real, could dramatically affect the interpretation of the
event.

The position of M31-RV has been reported as 214\arcs\ E and
196\arcs\ S ($\pm$2\arcs) of M31 nucleus by Rich et
al. (1989), as 214\arcs\ E and 198\arcs\ S by Sharov
(1990) citing Rich et al., and as 3\arcm\ from the nucleus by Mould et
al. (1990). More precise positions of M31-RV (referred to J2000 equinox)
have been reported by Ciardullo et al. (1990, their nova N.36) as
\begin{displaymath}
\alpha = 00\hr 43\mm 02\fsec1 ~~~~\delta = +41\deg 12\arcm 55\arcs
\end{displaymath}
by Bryan and Royer (1992) as 
\begin{displaymath}
\alpha = 00\hr 43\mm 01\fsec7 ~~~~\delta = +41\deg 12\arcm 59\arcs
\end{displaymath}
and by Tomaney and Shafter (1992) as
\begin{displaymath}
\alpha = 00\hr 43\mm 02\fsec4 ~~~~\delta = +41\deg 12\arcm 56\arcs
\end{displaymath}
The scatter among these measures (4.6 arcsec) is large and unsuited to support identification
of the remnant on HST images.

\vspace*{1cm}

\begin{table}[!hb]
\caption[]{Asiago archive plates imaging the 1988 outburst of M31-RV.}
\centering
\begin{tabular}{cccccc}
         &       &    &        &        &            \\
\hline
         &       &    &        &        &            \\
plate N. &  date & UT &  emul. & filter & exp. (sec) \\
         &       &    &        &        &            \\
14197    & 13 Aug 1988 & 00:03 & 103a-E & RG-1 & 1800\\
14222    &~~~8 Sep 1988& 01:27 & 103a-E & RG-1 & 1800\\
         &       &    &        &        &            \\
\hline 
\end{tabular}
\end{table}

\vspace*{1cm}

We have located in the plate archive of the Asiago 67/92 cm Schmidt
telescope (205~cm focal length) two plates secured during the outburst of
M31-RV in 1988. Details of the plates are given in Table~1. The USNO-B catalog
uses plate material that is saturated near the nucleus of M31.  To properly
measure the position of M31-RV on the Asiago plates, a deep image of M31
was taken with the USNO Flagstaff Station 1.0m telescope.  USNO-B stars further
from the nucleus were used to place all stars visible on the Asiago plates
on the same astrometric system.  Measurement of M31-RV was then possible with respect
to these secondary astrometric standards, resulting in:
\begin{eqnarray}
{\rm plate} 14197 &~~~~& \alpha =  00\hr 43\mm 02\fsec42 ~~~~\delta = +41\deg 12\arcm 56\farcs7\\
{\rm plate} 14222 &~~~~& \alpha =  00\hr 43\mm 02\fsec41 ~~~~\delta = +41\deg 12\arcm 57\farcs1
\end{eqnarray}
The position on the two plates agrees within 0.2 arcsec, representing more
than an order of magnitude gain in accuracy compared to what available so
far in the literature, and making the search for the remnant on HST images now
more feasible. A finding chart from plate 14197 is presented in Figure~1.\\

\vspace*{1cm}

{\sl Acknowledgements}. We would like to thank Sergio Dalle Ave for his
skillful digital preparation of the plate material for successive astrometric
work, and Cesare Barbieri for useful suggestions on the plate digitization
technique (cf. Barbieri et al. 2003).

\IBVSfig{20cm}{5410-f1.eps}{Finding chart for M31-RV from Asiago archive plate 14197 (cf. Table~1).}
%%\IBVSfigKey{5410-f1.eps}{M31-RV}{finding chart}

\newpage

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\endreferences 

\vspace*{4cm}

\IBVSerratum{4807}

The original title of IBVS 4807 contained an error:

``Two New Eclipsing Binary Systems in Cepheus: the W UM\lowercase{a}
NSV 14312 and the Eccentric EA GSC 3992\_30847''

The correct GSC number is, as used in the body of the paper: 3992\_0847 .

\bigskip

\hfill {\it The Editors}

\end{document} 
