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\input ibvs2.sty 
 
\begin{document} 
\IBVShead{5387}{3 March 2003} 
 
\IBVStitletl{Photometric Observations of VW LM\lowercase{i}}{ and the New Binary System V345 G\lowercase{em}} 
 
\IBVSauth{G\'omez-Forrellad, J. M.$^{1,2}$; Vidal-S\'ainz, J.$^1$; S\'anchez-Bajo, F.$^3$; Garc\'{\i}a-Melendo, E.$^2$} 
 
\IBVSinst{Grup d'Estudis Astron\`omics, Apartado 9481, 08080 Barcelona, Spain; e-mail: jmgomez@astrogea.org} 
 
\IBVSinst{Esteve Duran Observatory Foundation, Avda Montseny 46, El Montany\`a, 08553 Seva, Barcelona, Spain; e-mail: duranobs@astrogea.org} 
 
\IBVSinst{Departamento de Electr\'onica e Ingenier\'{\i}a Electromec\'anica, Escuela de Ingenier\'{\i}as Industriales, Universidad de Extremadura, Avda de Elvas s/n, 06071 Badajoz, Spain; e-mail: fsanbajo@unex.es} 
 
\IBVStyp{ CWA } 
\IBVSkey{photometry} 
\SIMBADobj{VW LMi}
\SIMBADobj{V345 Gem}
 
\begintext 
 
In this paper we present new observations of the HIPPARCOS 
variables VW LMi and V345 Gem from Mollet and Monegrillo 
Observatories. At both places telescopes were fitted with a SX 
Starlight CCD camera with a Sony ICX027BL chip cooled by a Peltier 
system to about $-$25\deg C. Dark frames and flat fields were 
obtained and used to perform image cleaning. Photometric 
observations were taken in the $B$ and $V$ bands, and reductions 
were carried out using a synthetic aperture differential magnitude 
extraction method and the software package {\tt LAIA} (Laboratory for 
Astronomical Image Analysis). Table 1 summarizes the observational 
log for both stars. Table 2 gives some additional basic data for 
these objects. 
 
\begin{table}[!hc]
\centerline{Table 1. Observational log} 
\begin{center} 
\begin{tabular}{ccccc} 
\hline 
Star & HIP number & Observation period & Comparison star & Remarks$^*$ \\ 
\hline 
VW LMi & HIP 54003 & 27 Dec 1997-24 Apr 1998 & HIP 53969 & 1 \\ 
V345 Gem & HIP 37197 & 25 Dec 1998-21 Mar 1999 & HD 60913 & 2 \\ 
\hline 
\end{tabular} 
\end{center} 
\vskip -7pt 
$^*${\small 1: Mollet Observatory, 41 cm Newtonian telescope.\\} 
\phantom{$^*$}{\small 2: Mollet and Monegrillo Observatories, 41 cm Newtonian
telescope.} 
\end{table} 

\begin{table}[!hc]
\centerline{Table 2. Basic data} 
\begin{center} 
\begin{tabular}{cccc} 
\hline 
Star & Spectral type & Equatorial coordinates (epoch 2000.0) & $B-V^{**}$ \\ 
\hline 
VW LMi & F3V & $\alpha$ = 11\hr 02\mm 51\fsec909 $\delta$ = +30\deg 24\arcm 54\farcs71 & 0.410 $\pm$ 0.015 \\ 
V345 Gem & F0 & $\alpha$ = 07\hr 38\mm 30\fsec224 $\delta$ = +33\deg 42\arcm 41\farcs51  & 0.476 $\pm$ 0.015 \\ 
\hline 
\end{tabular} 
\end{center} 
$^{**}${\small Spectral type and $B-V$ colour index retrieved from the HIPPARCOS 
Catalogue (ESA 1997).}\\ 
\end{table} 

VW LMi is a variable star discovered by the HIPPARCOS mission (ESA, 1997) 
and catalogued as an EW in the 74th Special Name-List 
(Kazarovets \textit{et al.}, 1999). Dumitrescu (2000) reported ground-based photometric observations on this star and four minimum timings. In the HIPPARCOS catalogue the following 
ephemeris is given: 
 
\begin{center} 
${\rm Min.~I} = {\rm BJD~} 2448500.1960(10) + 0\fday477547(3)\!\times\!{\rm E}$ \\ 
\end{center} 
 
We performed a new period analysis based on our new photometric data and the 
already existing observations. The new $B$ and $V$ light-curves 
also allowed computing a first estimate of some physical 
parameters for this binary system. 
 
To recompute the period of VW LMi, an analysis of $O-C$ 
residuals based on times of minimum was performed. Table 3 lists 
the timings based on our observations. When the HIPPARCOS 
period (0.477547 days) was used, it was found to be a short 
estimate of the real one as indicated by an increasing trend of 
positive $O-C$ residuals. Assuming no period changes from 1991 to 
2000, the trend was removed after a least squares linear fit, 
resulting in a new revolving time of 0.4775942(3) days for the 
binary system. Figure~1 shows the folded light-curves in the $B$ 
and $V$ bands using the new period. Although longer surveillance 
is still needed in the long term to monitor the behaviour of VW 
LMi, the satellite data and our photometry could be merged and 
satisfactorily folded on the new refined period, suggesting that it has remained 
stable during the 1991-2000 interval. 
 
\begin{table}[!hc]
\centerline{Table 3. Minimum timings for VW LMi} 
\begin{center} 
\begin{tabular}{ccc} 
\hline 
Minimum & Photometric band & Epoch \\ 
\hline 
2450809.6214 $\pm$ 0.0002 & $V$ & 4836.0 \\ 
2450835.6495 $\pm$ 0.0002 & $V$ & 4890.5 \\ 
2450872.4224 $\pm$ 0.0001 & $V$ & 4967.5 \\ 
2450877.4658 $\pm$ 0.0001 & $V$ & 4978.0 \\ 
2450921.3707 $\pm$ 0.0002 & $B$ & 5070.0 \\ 
\hline 
\end{tabular} 
\end{center} 
\end{table} 

\IBVSfig{6cm}{5387-f1.eps}{Differential $B$ and $V$ light-curves of 
VW LMi, folded with the period of 0.47754916 days obtained in this 
work} 
%%\IBVSfigKey{5387-f1.eps}{VW LMi}{light curve}
 
\vskip -0.5cm 
The differential $B$ and $V$ data were analysed using the 
Wilson-Devinney method (Wilson, 1998), assuming convective 
envelopes and a temperature of the primary ($T_{1}$~=~6700~K) 
according to the spectral type of VW LMi. Because the lack of 
information about the mass ratio, we varied it from 0.3 to 0.8 in 
steps of 0.1, performing for each value a complete set of cycles 
of refinement. The solution corresponding to the minimum residual 
(obtained for $q$ = 0.4) suggests a system with an inclination of 
about 70\deg and relative luminosities (in both $B$ and $V$ 
bands) of 0.7 and 0.3 for the primary and secondary, respectively. \\

V345 Gem was also discovered by the HIPPARCOS mission, and 
catalogued as a periodic variable (ESA 1997) with a period of 
0.1373890(5) days. An origin for maximum light was given at the 
BJD = 2448500.0260 (10), but no variable type was specified. In a 
preliminary search for EW candidates among the HIPPARCOS 
variables, Duerbeck (1997) classified V345 Gem as a suspected 
pulsating variable. This star was afterwards included in the 74th 
Special Name-List (Kazarovets et al., 1999) as DSCT. In subsequent 
literature, this object is still referred to as a $\delta$ Sct 
star (Rodriguez \textit{et al.}, 2000), but later on Rodriguez and 
Breger (2001) indicated that it might be an EW with a 0.275-day period. 
V345 Gem is also the visual binary CCDM 07385+3343AB (Dommanget 
and Nys, 1994), consisting of a pair of 8.2 and 9.5 $V$ magnitude 
stars separated by 3.0 arcseconds. Kazarovets \textit{et al.} 
(1999) commented that ``variability [of V345 Gem] might be due to 
the fainter (B) component''. 
 
This star was included in our observing program after concluding 
that its light-curve morphology, based on the HIPPARCOS 
photometric data folded on a 0.274778-days period (doubling that 
given in the HIPPARCOS Catalogue), suggested an EW or ELL type 
instead of a pulsating variable. Observations confirm that this 
star is an EW variable (Figure 2) with $V$ and $B$ amplitudes of 
0.07 magnitudes, and primary minima about 0.005 magnitudes deeper 
than secondary minima in both $B$ and $V$ bands. Times of minimum from 
ground-based observations are listed in Table 4, which allowed, 
along with the HIPPARCOS data, to compute the following ephemeris: 
 
\begin{center} 
${\rm Min.~I} = {\rm BJD~} 2448362.7224(10) + 0\fday2747736(2)\!\times\!{\rm E}$ \\ 
\end{center} 
 
Since our photometry actually consists of joint light measurements 
of the visual double system, if star A is the variable then the 
$V$ amplitude is 0.10 mag, or 0.34 mag if component B is the 
eclipsing binary system. 
 
\vskip 0.5cm 
\centerline{Table 4. Minimum timings for V345 Gem} 
\begin{center} 
\begin{tabular}{ccc} 
\hline 
Minimum & Photometric band & Epoch \\ 
\hline 
2451185.3344 $\pm$ 0.0004 & $B$ & 10272.5 \\ 
2451185.4730 $\pm$ 0.0003 & $B$ & 10273.0 \\ 
2451186.4350 $\pm$ 0.0003 & $B$ & 10276.5 \\ 
2451192.3396 $\pm$ 0.0004 & $B$ & 10298.0 \\ 
2451192.4772 $\pm$ 0.0008 & $B$ & 10298.5 \\ 
2451215.4217 $\pm$ 0.0002 & $V$ & 10382.0 \\ 
2451221.3292 $\pm$ 0.0002 & $V$ & 10403.5 \\ 
2451222.4275 $\pm$ 0.0002 & $V$ & 10407.5 \\ 
2451223.3904 $\pm$ 0.0005 & $V$ & 10411.0 \\ 
2451226.4131 $\pm$ 0.0005 & $B$ & 10422.0 \\ 
2451227.3723 $\pm$ 0.0006 & $B$ & 10425.5 \\ 
2451258.4240 $\pm$ 0.0004 & $B$ & 10538.5 \\ 
\hline 
\end{tabular} 
\end{center} 
 
\IBVSfig{9cm}{5387-f2.eps}{Differential $B$ and $V$ light-curves 
of V345 Gem} 
%%\IBVSfigKey{5387-f2.eps}{V345 Gem}{light curve}
 
\textit{Acknowledgements}: We would like to thank Joan A. Cano and Rafael Barber\'a for writing the software for obtaining and reducing the CCD frames. Use has been made of the SIMBAD database operated at the Centre de Donn\'ees Astronomiques (CDS, Strasbourg, France) and the Astrophysics Data System (ADS). 

\newpage
 
\references 
 
Dommanget, J., \& Nys, O., 1994, {\it CoORB}, {\bf 115}, 1 
 
Duerbeck, H. W., 1997, {\it IBVS}, No. 4513 
 
Dumitrescu, A., 2000, {\it IBVS}, No. 4952 
 
ESA, 1997, {\it The Hipparcos and Tycho Catalogues}, ESA SP-1200 
 
Kazarovets, A. V., Samus, N. N., Durlevich, O. V., Frolov, S. V., 
Antipin, S. V., Kireeva, N. N., Pastukhova, E. E., 1999, {\it IBVS}, 
No. 4659 
 
Rodr\'{\i}guez, E., L\'opez-Gonz\'alez, M. J., \& L\'opez de Coca, 
P., 2000, {\it A\&AS}, {\bf 144}, 469 
 
Rodr\'{\i}guez, E., \& Breger, M., 2001, {\it A\&A}, {\bf 366}, 
178 
 
Wilson, R. E., 1998, \textit{Computing Binary Star Observables} 
(Reference Manual to the Wilson-Devinney Program), Department of 
Astronomy, University of Florida, Gainesville, FL, 1998 Edition 

\endreferences 

\IBVSerratum{5065}

The coordinates for NSV 03007 given in IBVS 5065 are in error. The actual
ones (2000), according to its identification with GSC 3376-0287 and SIMBAD
database are:

$$
		{\rm R.A.}\ =\ 06\hr 32\mm 46\fsec2
$$
$$
		{\rm Dec.}\ =\ +46\deg 23\arcm 32\farcs82\,.
$$
\hfill {\it Enr\'\i que Garc\'\i a-Melendo}

 
\end{document}
