\documentstyle[epsfig,epsf,twoside]{article}
\input ibvs2.sty


\begin{document}

\IBVShead{5433}{26 June 2003}

\IBVStitle{V516 C\lowercase{as}, an RR\lowercase{ab} Star at the Galactic Plane}

\IBVSauth{BENK\H{O}, J. M.$^1$; GAB\'ANYI, K. \'E.$^{2,3}$}

\IBVSinst{Konkoly Observatory, P.O. Box 67, H-1525 Budapest, Hungary; 
e-mail: benko@konkoly.hu}
\IBVSinst{Department of Astronomy, E\"otv\"os University, P\'azm\'any P. 
s. 1/A, H-1117 Budapest, Hungary; e-mail: gabanyik@mailbox.hu }
\IBVSinst{Max-Planck-Institut f\"ur Radioastronomie, Auf dem H\"ugel 69,
D-53121 Bonn, Germany; \\
e-mail: gabanyik@mpifr-bonn.mpg.de}


\SIMBADobj{V516 Cas}
\IBVSabs{We report here BVIc CCD observations of the V516 Cas.}
\IBVSabs{The first light curve, periods and other fundamental parameters are }
\IBVSabs{presented. Colour excess and interstellar reddening coefficient }
\IBVSabs{are also determined.}


\begintext

   The variable star V516~Cas was discovered by Romano 
(1971) who classified it as an RR Lyrae type star.
Although Simbad database includes this 
variable with an erroneous position due to the wrong 
coordinates given by the discoverer, on the base of
Romano's finding chart it can be identified unambiguously and
the electronic edition of the ``GCVS with Improved Coordinates'' 
(Samus et al., 2002) gives also the correct position:
$\alpha_{2000}=0\hr35\mm21\fsec75$,
$\delta_{2000}=52\deg59\arcm53\farcs8$.

Since no observations were published on this star, we wanted to verify 
its variability and type. We observed it during 4 nights using two
different CCD cameras attached to the 1m RCC telescope of the Konkoly Observatory mountain
station at Piszk\'estet\H{o}. On three nights in December 2002 a camera 
was used which had been built by Photometrics Inc. 
containing a Thomson TH7896M 16 bits chip with $1024\times1024$ pixels. 
It yields a $5\arcm\times5\arcm$ field of view (FOV). 
On the night in February 2003 we used a camera made by Wright Instruments
including an EEV CCD05-20 16 bits chip with $800\times1200$ pixels.
This equipment yields abut $4\arcm\times6\arcm$ FOV. 
For detailed technical
description of the CCDs we refer to the paper of Bakos (2000). 
The observational log is shown in Table~1.
The filters used were standard Johnson $B,V$ and Cousins $I_{\rm C}$, 
and the exposure times were between 4-6 minutes for all colours, 
the value of typical seeing was between $1\farcs5$--$3\farcs5$. 

The basic reduction steps: flat fielding, overscan correction were
carried out by {\sc Iraf}\footnote{IRAF is
distributed by the NOAO, operated by the Association of Universities for
Research in Astronomy Inc., under contract with the NSF.}, similarly
to the aperture photometry. 
Since the stars in our field were well 
separated, an aperture photometry was done.
A relative photometry to the comparison star (comp) GSC-2.2 N311030314105
(=1425-00833847 USNO-A2.0, Monet et al., 1998), 
and check star (check) GSC-2.2 N311030313722 (=1425-00838472 USNO-A2.0)
were done and no variability was found in our data
over $\sigma=0.01$ for all three bands. 
Therefore we have used the relative magnitudes V516~Cas minus comp. 
The extinction was corrected in the usual way taking into account 
the first order extinction coefficients.    
To tie the comparisons into the standard photometric system, we 
observed the open cluster M52 on two nights (09/12/02 and 10/12/02).
We used photometric results of $\sim$50 relatively bright and separated 
stars from the paper of Pandey et al. (2001) as reference magnitudes for all
three colours. Applying the colour equations with the 
determined telescope constants and
zero points, the magnitudes and colours for comparison and
check stars are $V=13\fmm82$, 
$(B-V)=0\fmm516$, 
$(V-I_{\rm C})=0\fmm573$ and 
$V=13\fmm63$,
$(B-V)=0\fmm775$, 
$(V-I_{\rm C})=0\fmm819$, respectively, 
where the estimated accuracies are $\pm0.025$.  

\begin{table}[t]
\begin{center}
\caption{Log of observations of V516~Cas}
\centerline{}
\begin{tabular}{ccc}
    Date    &   No  & Camera \\
            &	$B$ $V$ $I_{\rm C}$ &   \\
09/12/2002  &   20, 20, 20          & Photometrics \\ 
10/12/2002  &   20, 20, 20          & Photometrics \\ 
11/12/2002  &   14, 14, 13          & Photometrics \\ 
02/02/2003  &       25              & Wright \\ 
\end{tabular}
\end{center}
\end{table}

A period search was done for $V$ light curve 
using a Fourier-method realized by {\sc Mufran} 
program package (Koll\'ath, 1990). The following 
ephemeris was obtained:
\[
V_{\rm max}({\rm HJD})=2452618.460+0.403913 E.
\]
The $B$, $V$ and $I_{\rm C}$-band light curves of the V516~Cas folded by
the above period are
shown in Fig.~1. The observational data are available by electronic
form via the IBVS-website, as 5433-t2.txt, 5433-t3.txt, 5433-t4.txt 
\IBVSedata{5433-t2.txt}
%\IBVSdataKey{5433-t2.txt}{V516 Cas}{photometry}
\IBVSedata{5433-t3.txt}
%\IBVSdataKey{5433-t3.txt}{V516 Cas}{photometry}
\IBVSedata{5433-t4.txt}
%\IBVSdataKey{5433-t4.txt}{V516 Cas}{photometry}
The magnitude and intensity averaged mean
magnitudes and colours are $\langle V \rangle=14\fmm652$,
 $\langle B-V \rangle=0.523$,  
 $\langle V-I_{\rm C} \rangle=0.721$,  
 and $\overline{V}=14\fmm576$, 
$\overline{B-V}=0.474$,
$\overline{V-I_{\rm C}}=0.669$,  
respectively. 
Concerning the shape of the
phase diagram and the period 
V516~Cas is truly an RR~Lyrae star 
as it was suggested by Romano.

In the past years
empirical relations have been found among the Fourier
coefficients of $V$ light curves and fundamental physical parameters 
of RRab stars. The calculated metal abundance of V516~Cas is
[Fe/H]=$-0.65$ using the formula of Jurcsik \& Kov\'acs (1996), while
the mean absolute magnitude is $\langle M_V \rangle=0\fmm88$
by Kov\'acs \& Walker (2001) with the zero point of Kinman (2002).
Using the three parameter formula for reddening free $B-V$ colour index
by Kov\'acs \& Walker (2001) and comparing them with the measured value
we can determined the colour excess along the line of sight as
$E(B-V)=0.23$. It agrees well with 
the value of $E(B-V)=0.24$
from dust map of Schlegel et al. 
(1998) constructed from IRAS and COBE/DIRBE data.

There is no object in the Galactic position
of V516~Cas ($l=120\fdeg46$, $b=-9\fdeg8$) in  
the ``Catalogue of dust clouds in the Galaxy'' 
(Dutra \& Bica, 2002), so this considerable reddening  
should be caused by the diffuse interstellar matter. 
Our light curves allow us to calculate the 
selective interstellar absorption coefficients $R_V=A_V/E(B-V)$. 
Following Kov\'acs \& Jurcsik (1997)=KJ97 we have applied
the formula  
$I_0=\langle I_{\rm C} \rangle-d-R_{I_{\rm c}}E(B-V)$, where
$I_0$ is the calculated averaged magnitude from the Fourier 
coefficients and $R_{I_{\rm c}}=0.751R_V-0.485$. 
The distance modulus $d=X-X_0$, where 
$X=\langle I_{\rm C} \rangle -\beta \langle V-I_{\rm C} \rangle$, 
$\beta=R_{I_{\rm c}}/(R_V-R_{I_{\rm c}})$
and the reddening free quantity $X_0$ has also an expression 
containing Fourier parameters (see KJ97 for the details). 
The only unknown parameter is $R_V$ which can be calculated 
from the above equations simply.
We have found it as $R_V=3.06\pm0.5$, which agrees with  
the widely used $R_V=3.14$. The error 
given here is
derived from the formal errors of the applied formulae so it may be
overestimated.   
We have estimated the
distance of V516~Cas from the previously obtained quantities: 
$r\approx4.1$~kpc.
All the above information shows that V516~Cas is a relatively young, 
metal rich RRab variable lying in the Galactic disk. 

As we have seen,
from $BVI_{\rm C}$ light curves of
an RRab variable we can derive the colour excess and 
interstellar absorption coefficients, directly.
In this manner we could scan the distribution of 
the interstellar matter at a much better angular resolution than 
that the known maps are yielded. 

JMB thanks to G. Kov\'acs for his suggestions and to OTKA Grant No~T043504 
for the financial support.

\IBVSfig{10.5cm}{5433-f1.eps}{Phase diagrams of $B$, $V$ and $I_{\rm 
C}$-band photometric magnitudes of V516~Cas.}
%%\IBVSfigKey{5433-f1.eps}{V516 Cas}{light curve}

\vspace{-1.2cm}


\references

Bakos, G. \'A., 2000, {\it Occ. Tech. Notes Konkoly Obs.}, No~11.\\
{\tt http://www.konkoly.hu/Mitteilungen/Mitteilungen.html}

Dutra, C. M., \& Bica, E., 2002, {\it A\&A}, {\bf 383}, 631
%%\BIBCODE{2002A&A...383..631D}

Jurcsik, J., \& Kov\'acs, G., 1996, {\it A\&A}, {\bf 312}, 111
%%\BIBCODE{1996A&A...312..111J}

Kinman, T. D., 2002, {\it IBVS}, No~5354
%%\BIBCODE{2002IBVS.5354....1K}

Koll\'ath, Z., 1990, {\it Occ. Tech. Notes Konkoly Obs.}, No~1.\\
{\tt http://www.konkoly.hu/Mitteilungen/Mitteilungen.html}

Kov\'acs, G., \& Jurcsik, J., 1997, {\it A\&A}, {\bf 322}, 218
%%\BIBCODE{1997A&A...322..218K}

Kov\'acs, G., \& Walker, A.R., 2001, {\it A\&A}, {\bf 371}, 579
%%\BIBCODE{2001A&A...371..579K}

Monet, D., Bird, A., Canzian B., Dahn, C., Guetter, H., et al., 
1998,\vphantom { } 
The USNO-A2 Catalogue, US Naval Obs., Flagstaff
%%\BIBCODE{1998yCat.1252....0M}

Pandey, A. K., Nilakshi, Ogura, K., Sagar, R., \& Tarusawa, K., 
2001, {\it A\&A}, {\bf 374}, 504
%%\BIBCODE{2001A&A...374..504P}


Romano, G., 1971,
{\it Mem. Soc. Astron. Italiana}, {\bf 42}, 639
%%\BIBCODE{1971MmSAI..42..639R} 

Samus, N. N., Goranskii, V. P., Durlevich, O. V., Zharova, A. V., 
Kazarovets, E. V., et al.,
2002, {\it Pis'ma Astron. Zh.}, {\bf 28}, 201
\BIBCODE{2002AstL...28..174S}

Schlegel, D. J., Finkbeiner, D. P. \& Davis, M., 1998,
{\it ApJ}, {\bf 500}, 525
%%\BIBCODE{1998ApJ...500..525S}

\endreferences

\end{document}

