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\IBVShead{4881}{20 April 2000}

\IBVStitle{New Field Variable Stars II}


\IBVSauth{Cs\'ak, B.$^{1,4}$; Kiss, L.L.$^{2,4}$; Szil\'adi, K.$^{2,4}$; S\'arneczky, K.$^{3,4}$; Szab\'o$^{2,4}$, Gy.}

\IBVSinst{Department of Optics \& Quantum Electronics and Astronomical
Observatory, University of Szeged,\\ \indent
P.O. Box 406, H-6701 Hungary, e-mail: csakb@neptun.physx.u-szeged.hu}

\IBVSinst{Department of Experimental Physics and Astronomical Observatory,
University of Szeged}

\IBVSinst{Department of Physical Geography, ELTE University, Hungary}

\IBVSinst{Guest Observer at the Konkoly Observatory}

\SIMBADobj{GSC 708-95}                % = V14
\SIMBADobj{USNO-A2.0 0825-07948896}   % = V17
\SIMBADobj{USNO-A2.0 1125-06366938}   % = V16
\SIMBADobj{GSC 705-728}               % = V15
\SIMBADobj{GSC 689-1745}              % = V13
\SIMBADobj{USNO-A2.0 1200-01646388}   % = V12

\IBVStyp{ EW, DSCT }
\IBVSkey{CCD photometry}
\IBVSabs{We report the discovery of six new field variable stars based on}
\IBVSabs{CCD observations carried out between April 1998 and January 2000. The}
\IBVSabs{obtained light curves do not allow an accurate classification. The}
\IBVSabs{shapes of light curves suggest eclipsing binary nature for the}
\IBVSabs{majority of new variable stars. Approximate spectral types are given}
\IBVSabs{based on low-resolution objective prism spectra taken in February,}
\IBVSabs{2000 at the Konkoly Observatory.}

\begintext

In the course of photometric and astrometric observations of
selected minor planets, we obtained more than 4000 individual
CCD frames at the Konkoly Observatory between April, 1998
and January, 2000. We have surveyed all of the time-series
CCD photometric observations in order to identify and/or discover
variable stars observed by chance in these images. We have
discovered 17 new variable stars and the first 11 was presented
in the first part of this series (Cs\'ak et al.\ 2000, Paper~I).
The remaining 6 stars are in the focus of this paper.

\IBVSfig{17cm}{4881-f1.eps}{Light curves of 6 new variable stars}

\vskip-11pt
The observations, the instruments and the applied methods of analysis
were the same as described in Paper~I.  The individual data shown in
Figs.~1 and~2 are available upon request from the first author.  The
sparse phase coverage did not allow reliable classification of the
variable stars, though the majority seem to be eclipsing binaries. V17
has the best data series, because we made 3-hour long follow-up
observations on two nights in January 2000 (Fig.~2). This enabled a
more accurate period determination which resulted in a period
of $0.1275\pm0.0001$ days. The unfavourable data distribution caused
all data to cover very similar phases, therefore, any multiplet of this shortest value cannot be ruled out.  Basic data (identifications,
celestial coordinates and magnitudes) of the new variables are
summarized in Table\ 1.  The given types of variability (based on the
light curve shapes and USNO-A2.0 colours) should be considered only as
approximate ones.

\begin{table*}
\begin{center}
\caption{Basic data of the new variables. The coordinates,
red and blue magnitudes were taken from USNO-A2.0}
\vskip 3mm
\begin{tabular} {clcclll}
\hline
Variable & R.A. (2000) & Dec.\ (2000) & Red mag. & Blue mag. & Sp.\ type & Type\\
\hline
V12 & 03\hr36\mm27\fsec60 & +36\deg22\arcm27\farcs03 & 15.5 & 16.9 & -- & EW\\
V13 & 05\hr02\mm53\fsec72 & +10\deg36\arcm49\farcs93 & 15.2 & 16.1 & -- & EW\\
V14 & 05\hr26\mm30\fsec92 & +12\deg57\arcm27\farcs33 & 12.8 & 14.0 & G4 & EW\\
V15 & 05\hr31\mm34\fsec58 & +10\deg33\arcm59\farcs49 & 14.0 & 14.8 & F3 & --\\
V16 & 11\hr42\mm15\fsec70 & +27\deg33\arcm05\farcs33 & 14.9 & 14.8 & G3 & EW\\
V17 & 13\hr14\mm47\fsec64 &$-$03\deg54\arcm42\farcs70 & 13.6 & 14.3 & F8 & EW\\
\hline
\end{tabular}
\end{center}
\end{table*}

\IBVSfig{6cm}{4881-f2.eps}{Follow-up observations of V17}

\vskip-11pt
In addition to the photometry, we obtained low-resolution spectra
with an objective prism at the Konkoly Observatory in February, 2000.
The telescope and the detector were the same as above, while
the prism has a refracting angle of 5\deg\ giving 580 \AA/mm resolution
at H$\gamma$ (Kun 1992). Since the observations were unfiltered, a wide
spectral region (approximately between 3800 \AA\ and 9000 \AA)
was detected limited by the spectral response of the CCD and the
atmospheric transmission.

We took 10-minute spectra of all stars, but V12 and V13 turned out to
be too faint. Almost 300 MK spectral standards taken from Jaschek et
al.\ (1964) were observed to form a homogeneous basis for a preliminary
spectral type determination that makes use of integral properties of
the obtained digital spectra. The spectral extraction was done with a
newly developed software which automatically detects the boundaries of
the spectral images. The extracted spectra were adjusted to match the
strongest atmospheric telluric band O$_2$ at 7594 \AA\ (see, e.g.,
Appendix E in Gray, 1992) and normalized to their maximum values near
7500 \AA.  The wavelength calibration was based on the hydrogen Balmer
series lines in the spectrum of $\alpha$~Lyr. The spectral response
function of the CCD chip was calibrated with the same spectrum of Vega,
knowing its tabulated absolute flux spectrum taken from Gray (1992).
All of the observed spectra were divided by the resulting spectral
response function. Sample spectra are plotted in Fig.~3.

\IBVSfig{8cm}{4881-f3.eps}{Sample spectra of standard
stars and V14. The marked spectral standards are the following
ones: HD150553 (F0V), HD72905 (G0V), HD112859 (G6V) and HD75632 (K5V).}

\IBVSfig{8cm}{4881-f4.eps}{The relation between the integrated
parameter $A$ and spectral type.}

\vskip-11pt
We calculated a simple empirical parameter ($A$) by integrating the
normalized and calibrated spectra between 4600 and 7500 \AA\
($A=\sum_{4600}^{7500} i(\lambda)\Delta \lambda$). $A$ is related with
the mean slope of the continuum, which is a considerably tight function
of the spectral type (Gray 1992).  The spectral type was parametrized
by assigning 20 to B0, 30 to A0, \dots\ being one of the usual ways in
semi-automatic spectral type determinations (e.g.\ Stock 1994).  We
determined a linear fit to estimate the spectral types of new variables
with an error of 3 subclass (see Fig.~4). Since this method suffers
from the possible effects of the interstellar reddening, the spectral
class was also checked by visual comparison of different standards (as
in Fig.~3). The fact that we did not have to change the resulting
spectral class of any of the variables indicates the usefulness of the
method.

This work has been supported by Hungarian OTKA Grant \#F032258,
Pro Renovanda Cultura Hungariae Foundation Grant DT 1999 \'apr./36.
and Szeged Observatory Foundation. The warm hospitality of the staff
of the Konkoly Observatory and their provision of telescope time
is gratefully acknowledged. We used the SIMBAD database,
operated at CDS, Strasbourg, France.

\references

Balog, Z., Moitinho, A., Vink\'o, J., Delgado, A.J., Alfaro, E.J.,
F\H{u}r\'esz, G., Kasz\'as, G., 2000, {\it MNRAS}, in preparation

Cs\'ak, B., Kiss, L.L., Szab\'o, Gy., S\'arneczky, K., Szil\'adi, K.,
2000, {\it IBVS}, No.\ 4875

Gray, D.F., 1992, Observations and analysis of stellar photospheres,
Cambridge University Press, New York

Jaschek, C., Conde, H., de Sierra, A.C., 1964, Serie Astronomica, La
Plata, Observatorio Astronomico de la Universidad de la Plata

Kun, M., 1992, {\it A\&AS}, {\bf 92}, 875

Stock, J., 1994, {\it Rev.\ Mex.\ Astron.\ Astrofis.}, {\bf 28}, 153

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