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\IBVShead{4620}{10 August 1998}

\IBVStitletl{Period Determinations for the RR\lowercase{c}}{ Variable CI COMAE BERENICES}

\IBVSauth{R. Diethelm}
\IBVSinsto{BBSAG, Rennweg 1, CH-4118 Rodersdorf, Switzerland,\\
and Astronomisches Institut der Universit\"at Basel, Venusstrasse 7, CH-4102 Binningen, Switzerland\\
e-mail: diethelm@astro.unibas.ch}
\SIMBADobj{CI Com}
\IBVStyp{ RRc }
\IBVSkey{CCD photometry}

\begintext

The variability of CI Comae Berenices = S\,9780 = GSC\,872.326
($\alpha_{J2000}:12\hr 14\mm 11\fsec 3$; $\delta_{J2000}:+14\deg
01\arcm 50\arcs$) was discovered by Hoffmeister (1967). He found a
possible RR Lyrae nature and gave two approximate moments of maximum
light based on photographic plates. Splittgerber (1979), from another
study employing the photographic plates secured at Sonneberg
Observatory, Germany, could not determine a period of variation, but he
mentioned a possible EW classification. No further source of
information was found through a bibliographical search with the SIMBAD
data base.
\vskip-3mm

\IBVSfig{10cm}{4620-f1.eps}{CCD light curve of CI Comae Berenices using the elements (1)}


We have observed CI Com with a SBIG ST-6 CCD camera attached to the
0.35 m S-C-telescope of the R. Szafraniec Observatory at Metzerlen,
Switzerland. GSC\,872.598 (GSC magnitude: 11.29) served as comparison
star, while GSC\,872.499 was used as check star. Both these stars
turned out to be constant at the $0\fmm 02$ level. A total of 84 CCD
measurements (without using a filter) during 17 nights from JD\,2450895
to JD\,2450988 have been obtained. Due to the proximity of the
comparison stars to the variable, no correction for differential
extinction was applied to the data.

These measurements were subjected to a period search algorithm. For
this purpose, we employed the program ``Period98'' written by Sperl
(1998). With the highest peak corresponding to a frequency of $P^{-1} =
2.77799$ our measurements can be represented to within the accuracy of
the photometry ($0\fmm 03$). The following elements of variation are
found:
$$
{\rm JD}(max,hel) = 2450925.467 (10) + 0.359972 (3) \times E \eqno(1)
$$

In Figure 1, we show all our CCD data folded with the elements (1).


The slight asymmetry of the light curve as well as the range of variation ($13\fmm 51-13\fmm 95$) and the value for the period leads us to classify CI Com as an RRc type pulsating variable. Since no information on the colour variation is available, this conclusion is in need of confirmation.

This research has made use of the SIMBAD data base operated by the CDS,
Strasbourg, France. The CCD photometry at the R. Szafraniec Observatory is supported by the ``Emilia Guggenheim-Schnurr Foundation''.

\references

Hoffmeister, C., 1967, {\it Astr.\ Nachr.}, {\bf 290}, 43

Sperl, M., 1998, {\it Masters thesis}, Institut f\"ur Astronomie, Universit\"at Wien

Splittgerber, E., 1979, {\it MVS}, {\bf 8}, 100

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