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\IBVShead{5351}{10 December 2002}

\IBVStitle{FR C\lowercase{nc} = BD +16\deg 1753 - A Young Active Main-Sequence Star}

\IBVSauth{Pandey, J. C.$^{1}$; Singh, K. P.$^2$; Sagar, R.$^1$; Drake, S. A.$^3$}

\IBVSinst{State Observatory, Naini Tal - 263129, India}
\IBVSinst{Tata Institute of Fundamental Research, Mumbai 400005, India}
\IBVSinst{USRA \& Code 662, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA}


\SIMBADobj{FR Cnc}
 
\begintext
 
\vskip 0.2in
 
  The star BD +16\deg 1753 ($\alpha_{2000}=08\hr32\mm30\fsec5$ and
$\delta_{2000}= +15\deg49\arcm26\arcs$)  of $V$ = 10.43~mag and spectral type K8V is 
an optical counterpart of the bright soft X-ray source 1ES 0829 + 15.9 $=$
1RXS J083230.9+154940 (Elvis et al. 1992; Schachter et al. 1996; Voges et al.
1999). BD +16\deg 1753 is $33 \pm 2$ pc distant (Perryman et al. 1997) implying
an absolute magnitude of 7.8 and a ratio of X-ray to bolometric luminosity
$f_x/f_{bol}$ of $\sim10^{-3}$ which shows that the star has an active corona at at the `saturation' limit. It has been classified as an 
`unsolved' Hipparcos variable star (FR Cnc) of 0.17 magnitudes amplitude variability
(Perryman et al., 1997), and as a suspected BY Dra-type variable, i.e.,
having variability due to the rotational modulation of starspots, 
by Kazarovets et al. (1999). Using the mean radial velocity of 25.5 km/s 
(Upgren et al. 2002) and the Hipparcos Catalogue distance and proper motions, 
the galactic space velocity components (U,\ V,\ W) of BD +16\deg 1753 are 
$(-24.1,-22.8,-5.1)$ km/s. This clearly places the star inside the young disk 
population boundaries in the (U,\ V) and (V,\ W) diagram (Montes et al. 2001). 
 
Broad band BVR photometric observations of FR Cnc were carried out from 
the State Observatory Naini Tal using the $2K \times 2K$  CCD camera during 
the years 2001 - 2002.   We have also taken low resolution spectra 
from 104-cm telescope at State Observatory
Naini Tal using the  HR-320 spectrograph with the $1K \times 1K$ CCD camera.
The dispersion of the spectrograph was 100 ${\rm \AA}$/mm.

Both photometric and spectroscopic data were reduced using
the standard packages under IRAF\footnote{IRAF is distributed by the National Optical Astronomy Observatories, USA}. 
We have been able to do accurate differential photometry as both the 
comparison (S1) and
check (S2) stars are within the  $13\arcm \times 13\arcm $ field of view of the CCD 
camera as shown in Fig 1.
The corresponding  USNO-A2.0 numbers for S1 and S2 are 1050-05766844 and
1050-05766589.
The comparison star (S1) is also identified as TYC 1392 2110 1.
Correlated periodic variations have been observed in
the $V$ magnitude and the $(V-R)$ colour of FR Cnc. 
The top and the middle panels of Fig. 2 show the
differential magnitude and the $(V-R)$ colour variations folded against 
the most significant period of $0\fday827$ found (see below).   
An arbitrary epoch of JD 2451943.1980 has been used. 
The data shown are from observations carried out in 
27 November - 5 December 2001 (Fig. 2a), 11 December 2001 - 1 January 
2002 (Fig 2b) 
and 31 January - 4 February 2002 (Fig. 2c).
The star was found to become redder when fainter and bluer when brighter.
The differential magnitudes of the check star with respect to the comparison 
star are also plotted in Fig. 2 (bottom panels). 
No significant light variation was detected  between the different measures 
of the comparison and check stars, indicating that the light of the comparison 
star was indeed constant during the observations.
The full set of data was analysed using the standard period finding
techniques and photometric period $0\fday827\pm 0.002$ was found. 
The amplitude of variation
in $V$ band and change in phase of the minima are tabulated in Table 1. 
The errors in determination of $\Delta V$ and  phase minima are  
$\pm 0.003$ mag and $\pm 0.03$ to $ \pm 0.06$, respectively.
The light curves for the epochs (a) and (c) clearly show the secondary minima indicating
the presence of two
spots (or groups of spots) separated by 0.5 in phase. Secondary minima could not  be determined  during
the epoch (b) observation. 

Figure 3 shows a low-resolution normalized spectrum of FR Cnc 
taken on 29 April 2002.  $H_{\alpha}$ emission is clearly seen.
In late type stars $H_{\alpha}$ emission is a good indicator of 
chromospheric activity. Changes of the photometric amplitude and phase 
on a time scale of a few rotations are quite commonly seen among active 
stars as their spot distributions vary. The observed rotational 
period of FR Cnc is unusually short, however.
 
 
\IBVSfig{9cm}{5351-f1.eps}{Identification chart of FR Cnc, Where S1 and S2 are comparison and check stars, respectively.}


\begin{table}
\begin{center}
\caption{Maximum amplitude in $V$ band ($\Delta V$) and phase of the minima at different epochs }
\vspace{0.2cm}
\begin{tabular}{lccc}\hline
Epoch&  ~~~~~~~$\Delta V$ (mag)~~~~~~~&\multicolumn{2}{c}{~~~Phase minima~~~}\\
 &  &~~~~~I~~~~~~ & ~~~~~II~~~~~  \\
\hline
(a)27 Nov - 5 Dec 2001&0.06&~0.40~ &~0.90~ \\
(b)11 Dec 2001 - 1 Jan 2002&0.10 &~0.30~ &~--\\
(c)31 Jan - 4 Feb 2002&0.10&~0.27~ &~0.78~ \\
\hline
\end{tabular}
\end{center}
\end{table}

\IBVSfig{6cm}{5351-f2.eps}{Differential $V$ and $(V-R)$ light curves of the star BD +16\deg 1753 and differential $V$ light curve of the comparison star:
(a) during 27 November - 5 December 2001; (b) 11 December 2001 - 1 January 2002; and (c) 31 January - 4 February 2002}

\IBVSfig{10cm}{5351-f3.eps}{Low-resolution spectrum of BD +16\deg 1753} 

\vspace*{-1.5cm}

Its youth, amplitude variation, phase change, $H_{\alpha}$ emission and
soft X-ray emission suggest that the star FR Cnc is an active and
spotted star with photometric period of $0\fday827 \pm 0.002$ (the likely
stellar rotation period).  It is more likely to
be a single star than a binary star, given the lack of radial velocity
variations (based on two measurements!), although the fact that its absolute 
magnitude is $\sim 0.8$ magnitudes brighter than that of a canonical K8 V star
is a weak evidence for a binary status.
However, to further understand the nature of this star,
high-resolution spectroscopic observations coordinated with simultaneous 
photometric observations are urgently needed.  We are accordingly planning to 
monitor this object further. 
 

\references

Elvis, M., Plummer, D., Schachter, J. and Fabbiano, G., 1992, {\it ApJS}, {\bf 80}, 257.

Kazarovets, A. V., Samus, N. N., Durlevich, O. V., Frolov, M. S., Antipin, S. V. et al., 1999, {\it IBVS}, No. 4659.

Montes, D., L\'{o}pez-Santiago, J., G\'{a}lvez, M. C., Fern\'{a}ndez-Figueroa, M. J., De Castro, E. and Cornide, M., 2001, {\it MNRAS}, {\bf 328}, 45.

Perryman, M. A. C., Lindegren, L., Kovalevsky, J., Hoeg, E., Bastian, U. et al., 1997, {\it A\&A}, {\bf 323}, L49.

Schachter, J. F., Remillard, R., Sarr, S. H., Favata, F., Sciortino, S. and
Barbera, M., 1996, {\it ApJ}, {\bf 463}, 747.

Upgren, A. R., Sperauskas J. and Boyle R. P., 2002, {\it Baltic Astronomy}, {\bf 11}, 91

Voges, W., Aschenbach, B., Boller, Th., Br\"{a}uninger, H., Briel, U. et al., 1999, {\it A\&A}, {\bf 349}, 389.

\endreferences

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