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\IBVShead{4444}{28 February 1997}


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\large
{\ft DETECTION OF 43 NEW BRIGHT VARIABLE STARS} \\
{\ft BY THE TYCHO INSTRUMENT OF THE HIPPARCOS SATELLITE}\\
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\begintext

The Tycho experiment on board of the Hipparcos satellite has led to a
photometric catalogue that promises to improve our knowledge about variable
stars greatly (Mauder, H{\o}g, 1987). For about one million stars up to B=12 (completeness up to
10.7 mag) the brightness in two spectral bands (Tycho-V and Tycho-B,
similar to Johnson-V and Johnson-B) is given at 100 to 400 moments,
which are spread over the four-year lifetime of the satellite (1989-1993).

This database has great advantages against archived photoplates that are
usually used to search for new variable stars. On the one hand, the brightness
is given in magnitudes, no further photometric reduction is necessary.
On the other hand, the moments of observations are almost completely independent
of seasons and daytimes. This is important for variables having a period of
about one day or one year, what makes them hardly detectable by ground-based
observations.

We have searched the Tycho Mean Photometric Catalogue (TPMC) and the
Tycho Photometric Observations Catalogue (TPOC 2) for new variable stars
using merely two criteria. The first one is that variability causes a
scattering of the brightnesses at single observations with respect
to their median value. Therefore, the error of this median will be larger
than one would expect for a constant star, if the amplitude of the
variability is strong enough (Grossmann, private communication).
 The other criterion does only affect
periodic variables. Periodogram analysis (Horne, Baliunas 1985) has been done
with the time series from the catalogue. The height of maxima in the
periodogram yields a probability for a correct period determination
(Scargle 1982), that is usually more than $99\%$ for the stars presented here.

This analysis is strongly affected by the extremely uneven sampling.
The smallest time interval between two single measurements is about one
second, but there can be several months without any observation of the star. 
This leads to instabilities of maxima in the periodogram. We tried to
overcome this problem by computing the periodogram over different time
intervals, but this is only an improvement and not a complete solution.
The measurement technique of Tycho causes another problem: The presence
of field stars in the neighborhood of a program star and especially an
unknown multiplicity of the star can simulate a variability that in fact
does not exist. For these reasons we encourage astronomers to observe
the stars that are presented here. This will lead to a better confidence
for the variability and -- especially -- the period determinations.

The periodic lightcurves shown here were produced as follows: The data were
phased with respect to the period taken from the periodogram and then
binned into 20 equal parts of the period. The figures show to cycles. 
The reason for this binning is that single observations may be disturbed
and can lead to wrong conclusions, if they are taken too seriously.
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Figure 9. Phased lightcurve (P=5\fd 252) of the star HD\,61551 in V.
This may be an eclipsing binary of $\beta$ Lyr type
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Figure 21. Phased lightcurve (P=122\fd 0) of the star HD\,114267 in V
(triangles) and B (squares). Note the variability of the
colour index B$-$V
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Figure 38. Phased lightcurve (P=2\fd 91) of the star HD\,213233 in V (triangles) and B (squares)
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\centerline{3} 
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\centerline{Table 1. Results on the 43 new variables}
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\begin{tabular}{cllllcc}
\hline
No.& TICID\footnote{}& Cross & RA 2000.0 & Dec. 2000.0  &  Period &  Type\\
   &                 &Identification&     &              & [days]   &         \\
\hline
\\
1  & 3303/979/1  & HD\,15992  & 02\fh 31\fmm 48\fss 65  & +49\degr 51\farcmm 38\farcs 0 & 0.40 &  RRc \\
2  & 9152/1800/1 & HD\,22909  & 03 35 53.0   & $-$69 11 35 2 &     &  L   \\
3  & 2429/274/1  & HD\,43476  & 06 18 02.7   & +35 35 51 5 & 28.4 &     \\
4  & 8535/222/1  & HD\,44363  & 06 18 22.3   & $-$54 24 15 6 &     &  L  \\
5  & 3769/1982/1 & HD\,46101  & 06 34 32.73  & +55 21 10 5 & 62.9 & SR \\
6  & 2426/414/1  & HD\,46552  & 06 35 37.63  & +32 34 37 1 & 0.53  & EW \\
7  & 4539/864/1  & HD\,60062  & 07 46 52.6   & +81 40 56 8 &      &   \\
8  & 8551/1508/1 & HD\,60649  & 07 32 46.24  & $-$53 33 19 3 & 0.49 & EW \\
9  & 5405/2897/1 & HD\,61551  & 07 39 27.2   & $-$11 33 50 9 & 5.52 & EB \\
10 & 8911/2750/1 & HD\,65321  & 07 54 29.4   & $-$61 12 15 8 & 50.3 & SR \\
11 & 2504/188/1  & HD\,84615  & 09 47 20.12  & +32 46 57 5 &      & L  \\
12 & 8606/502/1  & HD\,85025  & 09 47 02      & $-$57 21      &      & L  \\
13 & 8600/3290/1 & HD\,90371  & 10 24 39.66  & $-$54 19 19 1 &      & L  \\
14 & 9219/2587/1 & HD\,93325  & 10 44 10.2   & $-$72 03 51   & 1.19 & EB \\
15 & 8958/2448/1 & HD\,95687  & 11 01 35.75  & $-$61 02 55 4 & 2.91 &   \\
16 & 8628/1620/1 & HD\,98434  & 11 18 43.92  & $-$58 11 11 3 & 1.71 &   \\
17 & 8959/2596/1 & HD\,98817  & 11 21 06      & $-$60 50      &      & L \\
18 & 8972/291/1  & HD\,101104 & 11 37 34.4   & $-$60 54 12 4 & 2.05 &   \\
19 & 7240/1270/1 & HD\,106865 & 12 17 29.58  & $-$34 30 17 4 & 217  & SR \\
20 & 881/680/1   & HD\,109983 & 12 38 51.5   & +13 48 13 5 &      & L  \\
21 & 5537/1087/1 & HD\,114267 & 13 09 36.05  & $-$07 46 50 5 & 122 &  SR \\
22 & 323/930/1   & HD\,125488 & 14 19 37.8   & +05 53 46 8 & 0.20 & RRb \\
23 & 8682/2013/1 & HD\,125687 & 14 22 52.1   & $-$55 57 43 0 & 109  & SR \\
24 & 3038/566/1  & HD\,126080 & 14 22 17.6   & +41 27 03 5 & 0.69 & RRa \\
25 & 7851/500/1  & HD\,143996 & 16 05 01.1   & $-$39 12 57 8 & 12.5 &    \\
26 & 9039/2221/1 & HD\,152982 & 17 00 36.6   & $-$61 24 16 8 &      &  L  \\
27 & 8354/1640/1 & HD\,158479 & 17 32 10.4   & $-$51 04 25 1 &      & L \\
28 & 9297/1770/1 & HD\,160326 & 17 46 22.4   & $-$72 49 18   & 349  & SR \\
29 & 8344/931/1  & HD\,162985 & 17 56 08.32  & $-$45 09 20 8 & 0.78 & EA \\
30 & 3913/1509/1 & HD\,172022 & 18 34 26.3   & +57 48 06 4 &      &    \\
31 & 1073/1391/1 & HD\,192689 & 20 15 53.5   & +07 40 13 0 &      & L \\
32 & 6929/1233/1 & HD\,197785 & 20 46 40.13  & $-$27 13 59 9 & 11.1 & EB \\
33 & 1656/2033/1 & HD\,200271 & 21 01 53.2   & +18 59 54 9 &      & L \\
34 & 8818/1040/1 & HD\,204611 & 21 32 00.6   & $-$58 48 54 4 &      & L \\
35 & 7990/374/1  & HD\,208016 & 21 54 22.2   & $-$41 15 57 7 & 97.1 & SR \\
36 & 8825/1029/1 & HD\,210741 & 22 14 02.4   & $-$57 13 06 3 &      & L \\
37 & 8442/1011/1 & HD\,212508 & 22 25 46.05  & $-$49 49 34 7 & 6.15 &   \\
38 & 3619/2726/1 & HD\,213233 & 22 28 58.24  & +50 57 47 4 & 2.91 & $\delta$ Cep\\
39 & 9127/307/1  & HD\,223470 & 23 49 58.0   & $-$61 08 08 6 & 1.47 &   \\
40 & 2772/1716/1 & HD\,224326 & 23 56 57.97  & +32 20 14 3 & 27.95 &  \\
41 & 2091/1465/1 & HD\,341508 & 18 03 19.15  & +23 48 53 0 & 5.89 & $\delta$ Cep\\
42 & 6497/892/1  & SAO 170690 & 05 40 58.7 & $-$27 57 07 3 &   & L \\
43 & 8958/3540/1 & CSI-60-11041 1 & 11 06 09.0 & $-$60 31 21 & 0.33 & RRb \\
\hline
\end{tabular}
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\normalsize

1) The TICID is the ``name'' of a star in the Tycho Catalogue. The first number gives the GSC-region, the second one is a running number inside this region, and the last one numbers components of multiple systems. 
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Because the space is limited, not all of the 43 lightcurves can be
presented here. They are available on the IBVS ftp site: ftp.konkoly.hu/pub/ibvs/4401/4444-f$<$No.$>$.ps where No. is the serial
number in Table 1.
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{\it Acknowledgements}: I am thankful to Prof. Horst Mauder, T\"ubingen,
for giving me the possibility to work with Tycho-data. Andreas Wicenec and
Volkmar Grossmann helped me very much in doing my diploma thesis. This
research has made use of the SIMBAD database, operated at CDS, France.

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\beginauthors
\authorsrightcol
J. WOITAS
Max-Planck-Institut f\"ur Astronomie
D-69117 Heidelberg
Germany
e-mail: woitas@mpia-hd.mpg.de 
\endauthors


\references

Horne, J., Baliunas, S., 1985, {\it  ApJ}, {\bf 302}, 757 

Mauder, H., H{\o}g, E., 1987, {\it A\&A}, {\bf 185}, 349

Scargle, J., 1982, {\it ApJ}, {\bf 263}, 835 



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