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\input{ibvs2.sty}

\begin{document}

\IBVShead{5170}{13 September 2001}

\IBVStitle{UZ CV\lowercase{n}: a Century of Period Increase}

\IBVSauth{Vandenbroere, Jacqueline$^{1}$; Berthold, Thomas$^{2,3}$}

\IBVSinst{Group Europ\'een d'Observations Stellaires (GEOS), 
23 Parc de Levesville, F--28300 Bailleau l'Ev\"{e}que, France,\\ \indent
e-mail: j.vandenbroere@skynet.be}

\IBVSinst{Bundesdeutsche Arbeitsge\-mein\-schaft f\"{u}r Ver\"{a}nderliche 
Sterne e.V. (BAV), Munsterdamm 90, \\ \indent
D--12169 Berlin, Germany}

\IBVSinst{Bruno-H.-B\"{u}rgel-Sternwarte Hartha, T\"{o}pelstr.\ 43, D--04746 
Hartha, Germany, e-mail: tb.stwhartha@web.de}

\SIMBADobj{UZ CVn}

\IBVStyp{ RRab }
 
\begintext

UZ CVn (= BV 96 = HIP 61029 = GSC 3018 255, 12\hr30\mm27\fsec7 ,
+40\deg30\arcm31\farcs9, 2000.0), was discovered by Kippenhahn (1955)
and found to be a pulsating star of RRab type by Strohmeier and Knigge
(1961).  Their elements, listed in the GCVS (Kholopov, 1985),
\begin {equation}
\begin{array}{r@{}r@{}l}
{\rm Max. = HJD}~2426427.3806 & {} + 0\fday6977829 & {} \times E \\
\end{array}
\end {equation}
were derived from photographic plates They are obviously no longer
valuable because the period has changed continuously.  In order to
study the evolution of the period of UZ CVn during the last century, we
have gathered all the instants of maximum light published in the
literature and we have also performed our own measurements.

There are only 13 photoelectric measurements in $V$ and $R$ made between March 
1990 and December 1991 resulting in the determination of one instant of 
maximum (Schmidt et al., 1995).  The 127 CCD transits accepted from the 
Hipparcos satellite measurements (1990--1993) were studied by Fernley et al.\ 
(1998) who obtained a period of 0\fday697783 with a very scattered light 
curve.  We took into account the epoch of the Hipparcos catalogue only.  The 
photographic data are very scattered instants of bright light obtained from 
the inspection of sky patrol plates.  The first 59 times of maximum found from 
Bamberg and Sonneberg plates taken between 1931 and 1960, including 5 instants 
published before by Filatov (1960) and 38 instants derived by D\"{o}ppner
from Sonneberg plates, were published by Strohmeier and Knigge (1961), 
establishing ephemeris (1). A re-inspection of the Sonneberg plates done by 
one of us (T.B.) has evidenced the timings assigned to D\"{o}ppner to be in fact 
geocentric! They have been corrected for further analysis. Later on, a further 
set of 80 instants of bright light was published by Strohmeier and Bauernfeind 
(1968) as a result of the investigation of Harvard photographic plates taken 
between 1901 and 1953.

\IBVSfig{9cm}{5170-f1.ps}{$V$ lightcurve of UZ CVn according to
ephemeris (2)}

\IBVSfig{9cm}{5170-f2.ps}{$O-C$ diagram of UZ CVn  according ephemeris
(2). \\The symbols refer to the kind of observation: $\times$ (visual),
$+$ (photographic), $\ast$ (photographic normal maxima), $\circ$
(HIPPARCOS), $\bullet$ (photoelectric)}

\vskip-22pt

A GEOS team made 26 photoelectric measurements of UZ CVn in the $B$ and
$V$ filters of the Geneva system at the Jungfraujoch observatory during
two nights in January 1997. A new time of maximum could be determined.
Seven additional measurements were obtained at the same observatory in
1998 (see Figure~1). Two visual observers, J.-P. Verrot and J.
Vandenbroere, determined 20 further instants of maximum from their
estimates made between 1994 and 2001.  To close the remaining gap in
the data between 1960 and 1990, T.B. has used 554 Sonneberg Observatory
sky patrol plates taken between 1959 and 1993. From 69 newly found
instants, 7 normal maxima in consecutive intervals were derived for
further analysis.

Taking into account all the available material, we are able to document
the behaviour of the period of an RR Lyrae star over a whole century.
The complete list of all the observed times of maximum is available
from the IBVS website as file 5170-t1.txt.  A linear least-squares fit,
made with 163 instants of maximum, consisting of two photoelectric
instants ($w=10$), seven photographic normal maxima ($w=4$), one
Hipparcos and 20 visual instants ($w=3$) and 133 photographic instants
($w=1$), covering the years from 1901 to 2001, has yielded the
following ephemeris:
\begin {equation}
\begin{array}{r@{}r@{}l}
{\rm Max. = HJD}~2415423.9927 & {} + 0\fday69778714 & {} \times E. \\
{} \pm 74 & {} \pm 47 \\
\end{array}
\end {equation}
\IBVSedata{5170-t1.txt}

As Figure 2 points out, the trend of the $O-C$ values can be represented either by an abrupt period
change around epoch 28000 or by a parabolic fit.  

From JD 2415400 (approx.)\ to JD 2435000 (approx.):
\begin {equation}
\begin{array}{r@{}r@{}l}
{\rm Max. = HJD}~2415424.1137 & {} + 0\fday69777993 & {} \times E. \\
{} \pm 120 & {} \pm 66 \\
\end{array}
\end {equation}

From JD 2435000 (approx.)\ to JD 2452100 (approx.):
\begin {equation}
\begin{array}{r@{}r@{}l}
{\rm Max. = HJD}~2450460.6095 & {} + 0\fday69779191 & {} \times E. \\
{} \pm 67 & {} \pm 15 \\
\end{array}
\end {equation}

Alternatively, the quadratic least squares fit yields the following elements:
\begin{equation}
\begin{array}{r@{}r@{}r@{}l}
{\rm Max. = HJD~} 2415424.1453 & {} + 0\fday69777362 & {} \times E + 2.19 & {} \times 10^{-10} \times E^{2}. \\
                        \pm 91 &              \pm 69 &             \pm 11 \\
\end{array}
\end{equation}

Assuming the last case, the period of UZ CVn has been established to
have increased by a constant rate of $dP = 6\fday28 \times 10^{-10}$
per day during the last century and thus has increased by 1.98s in the
same time. Such rates are found to be typical in numerous cases among
RR Lyrae variables.


\bigskip
We want to acknowledge M. Dumont (GEOS) and L. Zimmerman (Cercle
Astronom\-ique de Bruxelles) for discussion and Peter Kroll (Sonneberg
Observatory) for the use of the plate archive. This research made use
of the SIMBAD database operated by the CDS at Strasbourg.

\references 

Fernley, J., et al., 1998, {\it Astron.\ Astrophys.}, {\bf 330}, 515

Filatov, G.S., 1960, {\it Astron.\ Circ.}, {\bf 215}, 17

Kholopov, P.N., et al., 1985, GCVS, IVth edition, Nauka, Moscow

Kippenhahn, R., 1955, {\it Kl.\ Ver.\ Bamberg}, {\bf 11}

Schmidt, E.G., et al., 1995, {\it Astron.\ Journ.}, {\bf 109}, 1239

Strohmeier, W., and Bauernfeind, H., 1968, {\it Bamberg Ver.}, {\bf VII}, 77

Strohmeier, W., and Knigge, R., 1961, {\it Bamberg Ver.}, {\bf V}, 11

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