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\IBVShead{4179}{31 March 1995}      

\centerline{\ft THE FIRST PERIOD CHANGE DISCOVERED IN}
\centerline{\ft THE BRIGHT ALGOL SYSTEM UV LEONIS}
\vskip 2mm
\centerline{(BAV  Mitteilungen  No. 77)}
\vskip 8mm

\begintext

The UV Leo system consists of two detached main sequence stars of solar type 
and nearly equal properties (m$_1$=0.99, m$_2$=0.92, R$_1$=1.00, R$_2$=1.11 solar masses 
and radii, according to Giuricin et al. [11]). Hoffmeister [14] discovered the 
variability and the system has soon classified as an eclipsing binary by Jensch 
[16]. The depth of the primary and the secondary minima is nearly equal,
nevertheless some small night-to-night fluctuation in the light curve has been 
observed [3], probably due to intrinsic variability of one or both of the 
components. The magnitude outside eclipse is given as V=8.91 by Popper [33], 
so the system is fairly bright.

The correct period very near to 0.600 days was first derived by Schneller 
[35]. McCluskey [22] demonstrated that the period of UV Leo had been constant since 
at least 1933. This finding can also be extended back to 1897 on base of data 
from sky-patrol plates given by Gaposchkin [10]. The period change claimed by 
Ahnert [1] around the year 1952 could not be confirmed. Elements published by
Rafert [34] -- also cited in the 4th edition of the GCVS -- describe the light 
variations well from 1897 up to the early eighties:
\vskip 1mm
\hspace*{3cm}Hel.Min.\,I  = J.D.\,2438440.72633  +  0\fd 60008478 $\times$ E \hfill  (1)
\vskip 1mm
At N\"urnberg Observatory UV Leonis has been observed photoelectrically since 
1964 ([9, 17, 18, 26-32]). We continued monitoring the system using a 0.34 m 
Cassegrain telescope, equipped with a 1P21 phototube, and V filter.  Five new 
times of minima, determined from the light curves, are included in Table 1, 
which lists all available times of minima from the literature and their O$-$C
residuals, computed against elements (1). The data given by Soliman et al. [36] 
was not included, since it seems to suffer from systematic error.
\epsfysize=6cm
\centerline{\epsffile{4179-f1.ps}}
\centerline{Figure 1.}
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\centerline{2}
\vskip 1mm
\centerline{Table 1}
\vskip 1mm
\begin{center}
\small
\begin{tabular}{lrllllrll}
\hline
Hel. JD   &   (O$-$C)$_1$&  E  & Observer    & &    Hel. JD  & (O$-$C)$_1$   &  E &  Observer\\
2400000+  &   days     &cycle& and Ref. No.& & 	24400000+  &  days &      cycle&  and Ref. No.\\
\hline
\\
32951.4513&	 0.0005&$-$9147.5&Perek [24]&	&	35905.370&	 0.002\	&$-$4225&Szczepan. [37]\\
32981.4535&	$-$0.0015&$-$9097.5&Perek [24]&	&	35934.4708&	$-$0.0014&$-$4176.5&Broglia [4]\\
32995.5559&	$-$0.0011&$-$9074&Perek [24]&	&        35935.373&	 0.001\	&$-$4175&Szczepan. [37]\\
32997.3561&	$-$0.0012&$-$9071&Perek [24]&	&	37017.324&	$-$0.001\ &$-$2372&Herczeg [8]\\
32999.4559&	$-$0.0017&$-$9067.5&Perek [24]&     &	37758.7310&	 0.0010	&$-$1136.5&McCluskey [22]\\
33000.3565&	$-$0.0012&$-$9066&Perek [24]&	&	37764.7313&	 0.0005	&$-$1126.5&McCluskey [22]\\
33006.3571&	$-$0.0014&$-$9056&Perek [24]&	&	37765.6316&	 0.0007	&$-$1125&McCluskey [22]\\
33021.3615&	 0.0008&$-$9031&Perek [24]&	&	38111.5809&	 0.0011	&$-$548.5&McCluskey [22]\\
33024.3602&	$-$0.0009&$-$9026&Perek [24]&	&	38416.7243&	 0.0014	&$-$40	&McCluskey [22]\\
33027.3627&	 0.0012&$-$9021&Perek [24]&	&	38440.7275&	 0.0012	&0	&McCluskey [22]\\
33030.361&	$-$0.001\ &$-$9016&Piotrowski [25]& &	38470.7315&	 0.0010	&50	&McCluskey [22]\\
33030.3619&	 0.0000&$-$9016&Perek [24]&	&	38474.6325&	 0.0014	&56.5	&McCluskey [22]\\
33033.3618&	$-$0.0005&$-$9011&Perek [24]&	&	38495.6353&	 0.0012	&91.5	&McCluskey [22]\\
33039.360&	$-$0.003\ &$-$9001&Piotrowski [25]& &	38512.438&	 0.002\	&119.5	&M\"uller [28]\\
33039.3639&	 0.0007&$-$9001&Perek [24]&	&	38852.384&	 0.000\	&686	&Krausser [28]\\
33349.3052&	$-$0.0018&$-$8484.5&Wallenquist [24]& &	38882.388&	$-$0.001\ &736	&Pohl [28]\\
33354.4025&	$-$0.0052&$-$8476.5&Wallenquist [24]& &	39940.339&	 0.001\	&2499	&Bickel [29]\\
33386.811&	$-$0.001\ &$-$8422&Nason [23]& &	39978.445&	 0.001\	&2562.5	&Kurutac [29]\\
33390.713&	 0.000\ &	 $-$8415.5&Nason [23]& &	40291.388& 0.000\ &3084	&Ibanoglu [29]\\
34454.363&	 0.000\ &	 $-$6643&Szczepan. [37]& &	41060.395&$-$0.001\ &4365.5	&H\"olzl [17]\\
34456.462&	$-$0.001\ &$-$6639.5&Wellmann [38]& &	41390.441&	$-$0.002\ &4915.5	&Grampp [18]\\
34457.362&	$-$0.001&\ $-$6638&Wellmann [38]	& &	41466.3544&0.0006	&5042	&Akinci [18]\\
34475.366&	 0.000\ &	 $-$6608&Wellmann [38]	& &	41766.3971& 0.0009	&5542	&Ebersberger [18]\\
34477.464&	$-$0.002\ &$-$6604.5&Wellmann [38]& &	42147.4502&	 0.0002	&6177	&Ebersberger [30]\\
34479.565&	$-$0.002\ &$-$6601&Wellmann [38]	& &	42453.4937& 0.0004	&6687	&Besold [31]\\
34481.366&	$-$0.001\ &$-$6598&Wellmann [38]	& &	42838.4473&$-$0.0003&7328.5&Ebersberger [32]\\
34487.364&	$-$0.004\ &$-$6588&Wellmann [38]	& &	43266.3065&$-$0.0016&8041.5&Ertan [9]\\
34488.565&	$-$0.003\ &$-$6586&Wellmann [38]	& &	43608.3540&$-$0.0024&8611.5&Chwastek [27]\\
34489.468&	 0.000\ &$-$6584.5&Wellmann [38]& &	44292.4549&	 0.0019	&9751.5	&Bode [26]\\
34493.365&	$-$0.004\ &$-$6578&Wellmann [38]	& &	44404.3702& 0.0014	&9938	&Elias [19]\\
34496.365&	$-$0.004\ &$-$6573&Wellmann [38]	& &	44716.412& $-$0.001\	&10458	&Diethelm [20]\\
34501.468&	$-$0.002\ &$-$6564.5&Wellmann [38]& &	45061.4657&	 0.0040	&11033	&Fernandes [2]\\
34803.611&	$-$0.001\ &$-$6061&Fracastoro [3]	& &	46521.4739& 0.0060	&13466	&Ells [15]\\
34808.4108&	$-$0.0023&$-$6053&Fracastoro [3]& &	46903.4273&	 0.0054	&14102.5&Diethelm [21]\\
34827.315&	$-$0.001\ &$-$6021.5&Fracastoro [3]&  &	47270.3801&	 0.0063	&14714	&Diethelm [5]\\
34844.416&	$-$0.002\ &$-$5993&Fracastoro [3]	& &	47615.4315& 0.0090	&15289	&Wunder [39]\\
35846.558&	$-$0.002\ &$-$4323&Broglia [4]	& &	47616.3325&	 0.0099	&15290.5&Wieck/Wund. [39]\\
35850.758&	$-$0.002\ &$-$4316&Broglia [4]	& &	47945.479&	 0.001\	&15839	&Hudecek [12]\\
35867.5619&	$-$0.0008&$-$4288&Broglia [4]	& &	48332.535&	 0.011\	&16484	&Paschke [6]\\
35871.4616&	$-$0.0017&$-$4281.5&Broglia [4]	& &	48358.3399&	 0.0124	&16527	&Bl\"attler [6]\\
35873.5622&	$-$0.0014&$-$4278&Broglia [4]	& &	48700.3886&	 0.0128	&17097	&Diethelm [29]\\
35895.4654&	$-$0.0013&$-$4241.5&Broglia [4]	& &	48757.3963&	 0.0125	&17192	&Wunder [39]\\
35897.5661&	$-$0.0009&$-$4238&Broglia [4]	& &	49475.3986&	 0.0133	&18388.5&Diethelm [30]\\
35901.467&	$-$0.001\ &$-$4231.5&Broglia [4]	& &	49775.4436&	 0.0160	&18888.5&Wunder [39]\\
35904.469&	 0.001\ &	$-$4226.5&Szczepan. [37]& &	49776.3439&	 0.0161	&18890	&Wund./Traub [39]\\
\hline
\end{tabular}
\end{center}
\large
\vfill \eject

\centerline{3}
\vskip 1mm

From the O$-$C diagram in Figure 1 it is obvious that the period of UV Leonis 
increased at around JD\,2444000. This is the first reliable period change  in 
the system discovered yet. Calculating new elements for the time since 
JD\,2444000, the least squares method yields:
\vskip 1mm
\hspace*{2cm}Hel.Min. I  = J.D.\,2447615.43178  +  0\fd 60086414 $\times$ E\hfill(2)
\hspace*{75mm}�$\pm$31\ \ \,\hspace*{14mm}$\pm$ 52
\vskip 1cm


\beginauthors
\authorsrightcol
E. WUNDER
Bundesdeutsche Arbeitsgemeinschaft
f\"ur Ver\"anderliche Sterne e.V. (BAV)
N\"urnberg Observatory
Regiomontanusweg 1
90317  N\"urnberg
Germany
\endauthors

%references section modified for HTML links - Wed Apr  9  2003
\references

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%Corrected: Mon Sep 26 12:21:44 MEST 2005

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\vfill \eject

\centerline{4}
\vskip 1mm 

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this paper [39]

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