\documentstyle[twoside,epsf]{article}

\input{ibvs2.sty}

\begin{document}

\IBVShead{4926}{21 July 2000}

\IBVStitletl{A Study of the Variability of LD 345}


\IBVSauth{Guilbault, P.R.$^1$; Hager, T.$^2$; Henden, A.$^3$; Kroll, P.$^4$; Kurochkin, N.E.$^5$; Moro, D.$^6$;\\ \indent Splittgerber, E.$^7$}

\IBVSinst{P.O. Box 287, Chepachet, Rhode Island 02814, USA,
 e-mail: pete1199@aol.com}
\IBVSinst{34 Mount Tom Road, New Milford, Connecticut 06776, USA,
 e-mail: thager@pcnet.com}
\IBVSinst{Universities Space Research Association/U. S. Naval Observatory,
P.O. Box 1149, Flagstaff, AZ 86002-1149, \\
\indent USA, e-mail: aah@nofs.navy.mil}
\IBVSinst{Sonneberg Observatory, Sternwartestr. 32, D-96515 Sonneberg,
Germany, e-mail: pk@stw.tu-ilmenau.de}
\IBVSinst{Sternberg Astronomical Institute, Universitetskij Prospect, 13,
Moscow, 119899, Russia}
\IBVSinst{Asiago Astrophysical Observatory, Department of Astronomy,
University of Padova, 36012 Asiago, (VI) \\
\indent Italy, e-mail: moro@pd.astro.astro.it}
\IBVSinst{Sonneberg Observatory, Sternwartestr. 32, D-96515 Sonneberg,
Germany, e-mail: splitti@stw.tu-ilmenau.de}

\IBVSabs{This report discusses the nature of LD 345.}

\SIMBADobj{LD 345}

\begintext

LD 345 (GSC 3530-2757) is located at 18\hr31\mm13\fsec83,
$+$46\deg58\arcm34\farcs7 (J2000).  Lennart Dahlmark discovered
variability during a photographic variable star search (Dahlmark,
2000a).  In the discovery report LD 345 is listed as an eclipsing binary type
variable of no known period.  Brian Skiff of the Lowell Observatory
generated interest in this star when he notified several AAVSO members
of its unusual behavior. Dahlmark reported the star had appeared to
enter a deep decline lasting at least two years.  The long duration of
the decline caused speculation as to the possibility that LD 345 may be
an eclipsing binary with a very long period or belong to a more exotic
class of variables such as the R Coronae Borealis or symbiotic stars.

In this paper we present the results of our investigation
of the classification of LD 345.  As part of our study Henden
performed high precision photometry in order to determine the
color indices and magnitudes of the variable and suitable comparison
and check stars. We also conducted a photographic plate survey
of LD 345 using the plate collections located at the Asiago
Astrophysical Observatory, the Harvard College Observatory,
the Sonneberg Observatory, and the Sternberg State Astronomical
Institute (SAI) of the Moscow State University.  In addition to
these archival plate collections, the photographic observations
of Dahlmark were used.

Dahlmark indicated 18 exposures were taken between 1967 and 1982,
and another 48 were taken between 1995 and May 2000.  On all but three plates
the star remains constant at $m_v = 11.4$, $m_{pg} = 13.1$, where
$m_v$ are photovisual (yellow) magnitudes and $m_{pg}$ are photographic
(blue) magnitudes. On the three plates,
exposed in July 1972, July 1973 and June 1974, the star had faded
more than three magnitudes to $m_v < 14.7$.

Guilbault and Hager visited the Harvard College Observatory
and examined approximately 200 patrol plates from the RH and Damon
series for evidence of variability.  Those plates encompassed
the years 1928 to 1952, a single plate from 1962, and 1975 to 1989.
At the Sternberg State Astronomical Institute Kurochkin measured
LD 345 on 172 plates taken with the 40-cm astrograph of the
SAI Crimean station. He examined four plates from 1905 to 1908,
one each from 1940 and 1942, and the remainder from 1978 to 1995.
No additional minima were found nor could we confirm
Dahlmark's observations at minimum since no exposures of the
field were taken at Harvard or Moscow during the
years 1972 to 1974.

Dahlmark indicated to Guilbault that the Asiago Astrophysical
Observatory had taken photographic plates during the years
in question (Dahlmark, 2000b).  As a result, Moro was contacted at
Asiago and she measured the brightness of LD 345 on 6 Schmidt
plates taken between 1967 and 1970, and 10 plates from 1974
to 1976. Comparison star magnitudes were determined using the
GSC--ACT (Gray, 1999) and the USNO--A2.0 catalogue
(Monet et al., 1998). Subsequently, additional observations
were made using the Sonneberg plate collection.  Splittgerber
and Kroll examined 111 photovisual
plates of the Sonneberg Sky Patrol taken from 1970 to 1977.
The star appears faint at maximum but just above the plate limit
of $m_v = 13.0$.  Between December 1971 and September 1974,
however, the star is not visible on the plates.
Photographic observations near or at minimum appear along with those
of Dahlmark in Table 1.

\begin{center}
{\normalsize Table 1. Photographic Observations of Minimum of LD345} \\
\begin{tabular}{ccccc} \hline
Julian date & Date & Magnitude & Type & Observer \\ \hline
2440750 & 1970-06-12 & $13.3$ & $m_{pg}$ & Moro \\
2440773 & 1970-07-05 & $13.1$ & $m_{pg}$ & Dahlmark \\
2441153 & 1971-07-21 & $13.1$ & $m_{pg}$ & Dahlmark \\
2441248 & 1972-03-15 & $11.8$ & $m_v$ & Kroll/Splittgerber \\
2441391 & 1972-03-15 & $<12.7$ & $m_v$ & Kroll/Splittgerber \\
2441394 & 1972-03-18 & $<12.9$ & $m_v$ & Kroll/Splittgerber \\
2441512 & 1972-07-14 & $<14.7$ & $m_v$ & Dahlmark \\
2441892 & 1973-07-29 & $<14.7$ & $m_v$ & Dahlmark \\
2442220 & 1974-06-22 & $<14.7$ & $m_v$ & Dahlmark \\
2442246 & 1974-07-16 & $16.8$ & $m_{pg}$ & Moro \\
2442248 & 1974-07-19 & $16.8$ & $m_{pg}$ & Moro \\
2442305 & 1974-09-14 & $15.6$ & $m_{pg}$ & Moro \\
2442307 & 1974-09-16 & $15.6$ & $m_{pg}$ & Moro \\
2442360 & 1974-11-08 & $14.7$ & $m_{pg}$ & Moro \\
2442551 & 1975-05-18 & $13.3$ & $m_{pg}$ & Moro \\
2442599 & 1975-07-06 & $13.1$ & $m_{pg}$ & Dahlmark \\
\hline
\end{tabular}
\end{center}

These observations confirm both the occurrence and the depth of the
decline as reported by Dahlmark and allow constraints to be
applied so that the duration of the minimum and the descending
and ascending branches of the light curve can be reasonably determined.
The duration of the minimum is $\sim1000$--1200 days.  The recovery from
the observed minimum of $16.8\ m_{pg}$ occurs within $\sim150$--200 days.
Assuming a symmetrical light curve with a flat bottom and minimum
at $\sim16.8 m_{pg}$, constant light lasts $\sim700$--800 days.

Henden used the USNO Flagstaff Station 1.0-m telescope and a
SITe/Tektronix $1024\times1024$ CCD to observe LD345 in standard
Johnson-Cousins UBVRI bandpasses on three photometric nights.
Comparison and check stars were standardized as follows:

\begin{center}
\normalsize
\begin{tabular}{ccccccccc} \hline
Star & GSC & RA (J2000) & DEC & $V$ & $B-V$ & $U-B$ & $V-R$ & $R-I$ \\ \hline
comp. & 3530-02670 & 18:31:06.40 & +46:55:52.7 & 11.919 &
1.126 & 1.007 & 0.588 & 0.518 \\
check & 3530-02617 & 18:31:02.86 & +46:58:15.8 & 12.164 &
0.974 &  0.642 & 0.519 & 0.466 \\
\hline
\end{tabular}
\end{center}

\noindent
with magnitude and color errors less than 0\fmm01.
More complete photometric information about all stars within
5 arcmin of the variable can be found in Henden (2000).
Using these stars, the magnitude and colors of LD345
for the three nights were:

\begin{center}
\begin{tabular}{cccccc} \hline
HJD${}-{}$2400000 & $V$ & $B-V$ & $U-B$ & $V-R$ & $R-I$ \\ \hline
51722.7493 & 11.748 & 1.611 & \dots & 0.924 & 1.162 \\
51727.8363 & 11.790 & 1.595 & 1.858 & 0.962 & 1.130 \\
51728.7805 & 11.783 & 1.610 & 1.866 & 0.957 & 1.137 \\
\hline
\end{tabular}
\end{center}

\noindent
with errors again less than 0.01mag.

\IBVSfig{10cm}{4926-f1.eps}{LD345 Photographic Light Curve}

Figure 1 shows the photographic light curve
from 1905 to 2000. For consistency and to improve the shape of
the decline, the photovisual (yellow) magnitudes and limits were
approximately converted to photographic (blue) values by adding
the mean (B--V) color of the variable as given above.  The data suggests
the star may be variable at maximum on the order of perhaps a few
tenths of a magnitude.  Evident in the light curve is the absence
of additional minima. If, in fact, the decline were the result of
an eclipse by a companion, based upon the available photographic
record the period would be very long indeed. Assuming that the
minima occur at equal intervals the period cannot be shorter than
17200 days, nearly twice that of Epsilon Aurigae. Minima could
have occurred during the gaps in photographic coverage, from
1908 to 1927, and 1953 to 1966, but in that case the declines
would occur at irregular intervals. The photographic record
does not seem to support the classification of LD 345 as an
eclipsing binary, but is more characteristic of the symbiotic
stars which can remain at maximum light for decades.   On the
other hand, the photometric colors are similar
to a typical M0III star, but atypical for RCB or symbiotic stars.

In spite of the photographic and photometric observations
presented in this report the classification of LD 345 remains
uncertain. We hope that others will study this interesting star.
AAVSO and VSnet observers have already begun visual monitoring
programs. This is important if a future decline occurs.
It would be valuable to search other archival plate collections
for additional minima and to better define the light curve that
we have presented here. Most importantly, spectroscopy is
needed to reveal the properties of LD 345.

We would like to thank Lennart Dahlmark for allowing us to
use his observations in this report. Guilbault and Hager
would like to express their gratitude to Dr. Martha Hazen,
Curator of the Harvard College Observatory Astronomical
Photograph Collection, for allowing them access to this
valuable resource. We also wish to thank Margareta Westlund
who sent us her very recent visual observations of LD 345.
We are grateful to Vitaly Goranskij of the SAI and Marvin
Baldwin, Chairman of the Eclipsing Binary Committee of the
AAVSO for their help in the preparation of this report.

\IBVSedata{4926-t2.txt}
\IBVSedata{4926-t3.txt}

\references
Dahlmark, L., 2000a, {\it IBVS}, No.\ 4898

Dahlmark, L., 2000b, Private Correspondence

Gray, W., 1999, {\tt http://www.projectpluto.com/gsc\_act.htm}

Monet et al., 1998, USNO--A2.0; U.S. Naval Observatory, Washington, DC

Henden,\,A.,\,2000,\,{\tt ftp://ftp.nofs.navy.mil/pub/outgoing/aah/sequence/ld345.dat}

\end{document}

