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\IBVShead{5141}{18 July 2001}

\IBVStitletl{The Identity of DO V\lowercase{ul}}

\IBVSauth{Henden, A. A.$^1$; Thorstensen, J. R.$^2$; Sumner, B.$^3$}

\IBVSinst{USRA/USNO, Flagstaff Station, P. O. Box 1149, Flagstaff, AZ 86002 USA,\\
\indent e-mail: aah@nofs.navy.mil}
\IBVSinst{Dept.\ Physics and Astronomy, Dartmouth College, 6127
Wilder Laboratory, Hanover, NH 03755-3528 USA,
\indent e-mail: thorsten@partita.dartmouth.edu}
\IBVSinst{Astronomical Society of Victoria, GPO Box 1059J, Melbourne
VIC 3001, Australia, \\
\indent e-mail: b.sumner@bom.gov.au}

\SIMBADobj{DO Vul}
\IBVStyp{ cataclysmic }

\IBVSabs{This report discusses the identification of DO Vul.}

\begintext

DO Vul (AN 25.1928) is a variable star discovered by Baade (1928)
during his Bergedorfer days.  The GCVS lists it as a UG cataclysmic
variable with an outburst magnitude of $m_{\rm pg}=14.0$ and a quiescent
magnitude fainter than $m_{\rm pg}=17.4$.
Skiff (1997), in acquiring proper identification
for Baade's variables, found that most of Baade's positions
in the Sagitta field were quite accurate, with typical errors
less than 2 arcsec.  However, Skiff could not locate DO Vul
at the Baade position on the DSS\@.  Downes and Shara (1993, DS93)
identified DO Vul only as the northwestern star of a close
faint pair (with a further comment that it could be a faint
companion); no additional identification was given in
Downes, Webbink and Shara (1997, DWS97) though the coordinates
were changed slightly.  The identification of DO Vul has been uncertain
since this is a crowded field and there has been no modern
epoch visual outburst (Mattei 2001).  Tsesevich (1978) reported
nine faint outbursts ($m_{\rm pg}=16.0$ to $m_{\rm pg}=17.1$) in the
interval October 1960 through July 1976 on Moscow plates;
these bursts were only above the plate limit for a day or less.

During the course of various monitoring studies, we have
been able to observe the field for DO Vul and unambiguously
determine which star is the variable.  Shown in Figure~1
is an image of the field, taken with the MDM Observatory 2.4-m telescope,
while DO Vul was at quiescence.  Figure 2 shows the same
field, taken with the USNO Flagstaff STation 1.0-m telescope, while DO Vul
was in outburst (May 19, 1999 UT).

There have been several reported positions for the variable.
We list the three normal ones in Table 1,
along with our measured (using USNO-A2.0) outburst and quiescent positions.
The star originally identified as DO Vul in DS93 lies 2.4 arcsec
east of the star identified here; its coordinates
are given in Table 1 as well.  

The photometry for DO Vul and for the nearby companion
is given in Table 2.  The field zero point
was set from the secondary standards given in Henden (2001).

We would like to thank Bill Fenton for taking the data
at MDM.

\IBVSfig{15cm}{5141-f1.eps}{Quiescent $V$-band image of field on
010522 UT; the scale mark is one arcmin}
\IBVSfig{15cm}{5141-f2.eps}{Outburst $V$-band image of field on 990519 UT}

\begin{table}
\begin{center}
\caption{Coordinates for DO Vul} \vskip2mm
\begin{tabular}{lll}
\hline
Source & RA(J2000) & Dec(J2000) \\
\hline

Baade & 19\hr52\mm10\fsec6 &$+$19\deg34\arcm44\arcs \\
DS93 & 19\hr52\mm11\fsec0 &$+$19\deg34\arcm39\arcs \\
DWS97 & 19\hr52\mm11\fsec0 &$+$19\deg34\arcm42\arcs \\
Quiescent & 19\hr52\mm10\fsec71 &$+$19\deg34\arcm42\farcs5 \\
Outburst & 19\hr52\mm10\fsec74 &$+$19\deg34\arcm42\farcs4 \\
Companion & 19\hr52\mm10\fsec88 &$+$19\deg34\arcm42\farcs4 \\

\hline
\end{tabular}

\caption{Photometry of DO Vul} \vskip2mm
\begin{tabular}{lcccc}
\hline
State & $V$ & $B-V$ & $U-B$ & $V-I$ \\
\hline
Quiescent & $20.73 \pm 0.05$ & $+0.08  \pm 0.10$ & $-0.99 \pm 0.17$ & $+0.64 \pm 0.10$ \\
Outburst & $16.427 \pm 0.016$ & $+0.167 \pm 0.019$ &  &  \\
Companion & $19.670 \pm 0.020$ & $+1.65 \pm 0.06$ & $+0.24 \pm 0.36$  & $+2.504 \pm 0.021$ \\
\hline
\end{tabular}
\end{center}
\end{table}

\references

Baade, W., 1928, {\it Astron.\ Nach.}, {\bf 232}, 65

Downes, R. A., Shara, M. M., 1993, {\it PASP}, {\bf 105}, 127

Downes, R., Webbink, R. F., Shara, M. M., 1997, {\it PASP}, {\bf 109}, 345

Henden,\,A.,\,2001,\,{\tt
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/sequence/dovul.dat}

Mattei, J., 2001, priv.\ comm.

Skiff, B., 1997, {\it IBVS}, No.\ 4459

Tsesevich, V. P., 1978, Kiev, Izdatel'stvo Naukova Dumka

\endreferences


\IBVSedata{5141-t3.txt}

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