\documentstyle[twoside, epsf]{article}

\input ibvs2.sty

\begin{document}
\IBVShead{5222}{16 January 2002}

\IBVStitletl{J AND K INFRARED LIGHT CURVES}{ OF THE ACTIVE BINARY BH V\lowercase{ir}}


\IBVSauth{Ar\'evalo, M. J.$^1$; L\'azaro, C.$^1$; Barrera, E.$^1$; Dominguez, R. M.$^2$;}

\IBVSinst{Departamento de Astrof\'\i sica, Universidad de la Laguna,
38271 La Laguna, Tenerife, Spain  and Instituto de Astrof\'\i sica de Canarias, 38205 La Laguna, Tenerife, Spain. e-mail: mam@ll.iac.es, clh@ll.iac.es}
\IBVSinst{Telescopio Nazionale Galileo, Centro Galileo Galilei, P.O. Box 565, 38700 Santa Cruz de La Palma, Spain, e-mail: domingue@tng.iac.es}

\SIMBADobj{BH Vir}

\begintext

We have carried out a monitoring program devoted to the
photometric infrared observation of  active  RS CVn short-period systems (Ar\'evalo, 1994). These binaries display  vast  solar-type activity phenomena. Over the
last two decades efforts have been made  to understand the
nature of this activity. One aim of these
studies has been to model the physical properties of starspots
evident from  distorted photometric light curves.
Once the distortion wave are removed the clean light curves are analyzed
with the aim of determining reliable parameters. For this reason it is 
important to analyze  IR light curves in order to determine
the physical parameters of these binaries.
Light curves observed in the infrared bands have revealed that this spectral
region
is not exempt from the known variability presented in the visible spectral range,
but it seems clear that  the amplitude of the observed irregularities in the light curves generally decreases at longer wavelengths (Ar\'evalo, 1994).

Before discussing  the results it is interesting to give   a summary of some of the 
known
features of BH Vir, currently considered a member of the RS CVn short-period group. 
Photometric visible light curves  have been published  regularly since 1957
 (See Zeilik {\it et al.} 1990  and  Xiang, Deng and Liu 2000, for references). 
 Zeilik {\it et al.} (1990)
  studied all the visible
photometric  light curves observed from
1953 to 1986   parameterizing the photometric distortion waves presented in  the light curves of BH Vir by a
dark circular spot model on the primary star. When the starspot contribution was subtracted 
from the  light curves the latter  were analyzed in order to
obtain the physical parameters.
 Later Xiang, Deng and Liu (2000)  modeled the
photometric distortion, also
 considering  active regions on the secondary star.
Complete  Str\"omgren {\it uvby}  light curves with the distortion wave
removed were
analyzed by Clement {\it et al.} (1997), who concluded that BH Vir appears to be
 a binary system with G0 and G2 main sequence solar-type stars.  There are slight disagreements  among the  results of the analysis performed by different authors using different fitting programs. Vincent, Piskunov and Tuominen (1993),
by means of surface imaging technique, pointed out that BH Vir has a total secondary eclipse. 

 Concerning  spectroscopic mass ratio $ q=m_2/m_1$ determination,
different authors give different  values, ranging from 1.02 to 0.903
(e.g., Abt 1965; Popper 1997; Xiang, Deng and Liu, 2000).
From photometric and spectroscopic studies,  it seems 
 that the primary component in BH Vir is approaching the end of its main sequence life. 


 
\par
  The observations presented in this paper were performed  over  7 nights in 1998  March and June
with the 1.5 m Carlos Sanchez Telescope at
 the  Observatorio del Teide (Canary Islands, Spain) (Table 1). We used a CVF photometer with a focal plane chopper, an InSb detector cooled with liquid nitrogen and standard broadband J and K filters. Both the chopping amplitudes and the aperture diameter were 15$''$.  The estimated photometry  errors were less than 0.01 mag. The main comparison star was HD 121299. The orbital phases were calculated using the ephemeris given by Koch (1967); namely, Min I (HJD)= 
 2438107.19047+0\fday81687099E. 
The orbital period of BH Vir shows no obvious changes,  as 
was determined by Xiang, Deng and Liu (2000).

Our infrared light curves show equal maxima, especially in the K filter. 
In order to determine new geometrical elements from the IR light curves, we used the code developed by Budding and Zeilik (1987). This program,
based on the Information Limit Optimization Technique (ILOT), is extensively described in  Banks (1993) and references therein. The limb darkening coefficients were interpolated from the values given by Claret {\it et al.} (1995). 
The  mean stellar surface temperatures used to calculate the gravity darkening
exponents were $T_1$ = 6100 K and $T_2$ = 5800 K.
We attempted to find solutions assuming  an initial set of parameter values corresponding to the previously existing determinations. In fact, the radii ratio $k=r_2/r_1$ was varied as an initial parameter  from 0.80--1.10. Solutions
with a radius ratio in the range  0.91--0.97 fit  the observed light curves 
 well, but
the smallest $\chi$$^2$ corresponds to the lower 0.92 value. The  inclination
angle was always very close to 87\deg.  The infrared light curve solutions are in good agreement with
Zeilik {\it et al.} (1990) determinations
from the UBVRI light curves ILOT analysis. In order to stand out these results, in
 Table 2 we have included  Zeilik {\it et al.} (1990) solutions together
with our J and K 
accepted parameters. The J and K filter models are plotted with the observations
in Figure 1.

 
\vskip 1.truecm
\centerline { Table 1:
 Observing runs }.
\begin{center}
\begin{tabular}{ccccc}
\hline
Observation date & Observed Filters \\
\hline
 1--2 March 1998 & J, K \\
2--3 March 1998 & J, K \\
8--9 March 1998 & J, K \\
13--14 March 1998 & J, K \\
14--15 March 1998 & J, K \\
3--4  June 1998 & J, K \\
10--11 June 1998 & J, K \\
\hline
\end{tabular}
\end{center}

\newpage

\IBVSfig{17cm}{5222-f1.eps}{ Observed light curves and the fits obtained with {\it ILOT}. (a) J filter and (b) K filter}

\newpage

\centerline { Table 2: {\it ILOT} light curve solutions  }.
\begin{center}
\begin{tabular}{ccccc}
\hline
~ & U filter   & B filter   & V filter  &  R filter \\
\hline
L$_1$ & 0.649 $\pm$ 0.013 &  0.634 $\pm$ 0.008  & 0.616 $\pm$ 0.009  & 0.600 $\pm$ 0.009 \\
L$_2$ & 0.307 $\pm$ 0.008 & 0.336 $\pm$ 0.004  & 0.356 $\pm$ 0.005  & 0.374$\pm$ 0.005 \\
r$_1$ & 0.254 $\pm$ 0.003  & 0.255 $\pm$ 0.002  & 0.255 $\pm$ 0.003  & 0.255$\pm$ 0.003 \\
r$_2$& 0.233 $\pm$ 0.003  & 0.231 $\pm$ 0.002 & 0.233 $\pm$ 0.002 & 0.237$\pm$ 0.003 \\
{\it k}& 0.919  & 0.906  & 0.914  & 0.929 \\
{\it i} & 86\fdeg5$\pm$ 0.1   & 86\fdeg5$\pm$ 0.1   & 86\fdeg5$\pm$ 0.1  & 86\fdeg5$\pm$ 0.1 \\
$\chi$$^2$ & 227 & 195& 257& 162 \\
$\epsilon$ & 0.01  & 0.01 & 0.01 & 0.01 \\
N.Points & 199 &  199 &  194&  198 \\
\hline
\end{tabular}
\end{center}

\begin{center}
\begin{tabular}{cccc}
\hline
~ & I filter   & J filter  & K filter  \\
\hline
L$_1$ & 0.586 $\pm$ 0.010   & 0.566 $\pm$ 0.008 &  0.557 $\pm$0.007 \\
L$_2$ & 0.386 $\pm$ 0.005  & 0.433 $\pm$ 0.002 & 0.443 $\pm$ 0.002   \\
r$_1$ & 0.258 $\pm$ 0.003  & 0.255 $\pm$ 0.001 & 0.257$\pm$ 0.001  \\
r$_2$& 0.241 $\pm$ 0.002  & 0.237 $\pm$ 0.001 & 0.239 $\pm$ 0.001   \\
{\it k}& 0.934  & 0.929  &0.928  \\
{\it i} & 86\fdeg5$\pm$ 0.1   & 86\fdeg7$\pm$ 0.1  & 87\fdeg1$\pm$ 0.1   \\
$\chi$$^2$ & 242&  520& 499  \\
$\epsilon$ & 0.01 & 0.01 & 0.01  \\
N.Points & 199 &  258 & 256  \\
\hline
\end{tabular}
\end{center}

\references

Abt, H.A., 1965, {\it PASP}, {\bf 77}, 367

Ar\'evalo, M.J, 1994, PhD. thesis Univ. La Laguna

Banks, T. 1993, in Light Curve Modeling of Eclipsing Binary Stars, edited by 
E.F.  Milone (Springer, Berlin) p. 181

Budding, E., \& Zeilik, M., 1987, {\it ApJ}, {\bf 319}, 827

Claret, A., Diaz--Cordov\'es, J., \& Gim\'enez, A. 1995, {\it A\&AS}, {\bf 114}, 247

%(helyesen: Diaz--Cordov\'es, J., Claret, A., \& Gim\'enez, A. 1995, {\it A\&AS}, {\bf 110}, 329
%vagy:   1995A&AS..114..247C )


Clement, R., Reglero, V., Garcia. M., Fabregat, J. and Suso J. 1997, {\it A\&AS}, {\bf 124}, 499

Koch, R.H. 1967, {\it AJ},  {\bf 72}, 411

Popper, D.M. 1997, {\it AJ},  {\bf 114}, 1195

Vicent, A., Piskunov, N.E. and Tuominen, I., 1993, {\it A\&A}, {\bf 278}, 523

%(masodik szerzo helyesen: Piskunov, a harmadik: Tuominen)


Xiang, F.Y., Deng, S.F. and Liu, Q.Y. 2000, {\it A\&AS}, {\bf 146}, 7

Zeilik, M., Ledlow, M., Rhodes, M. Ar\'evalo, M.J. and Budding, E. 1990, 
{\it ApJ}, {\bf 354}, 352


\endreferences

\end{document}

