COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                    NUMBER 620

                                      Konkoly Observatory
                                      Budapest
                                      1972 January 28


            SOME RECENT OBSERVATIONS OF UV CETI


Introduction

Investigation of the flare Star UV Ceti (R.A.=01h37.2m. Dec.=-18deg08'
(1966.0), Mag vis. 12.9, spectrum type dM5.5e) have been made from Boyden
Observatory using the 40 cm aperture Nishimura (Cassegrain) Reflector.
Observations have all been with a solid carbon-dioxide cooled EMI type 6256
photomultiplier tube photometer fitted with a Johnson B. filter. The
photometric accuracy was considered to be just within five per cent and the
associated time constant of the photometer was one second.

Observations

Details of the monitoring carried out during the recent International
Co-operative period from 11th-27th October, 1971 are given in the following
table.

Results

Eight flares were recorded during the observational period. The level of
activity was quite high; with an average (I_0+f-I_0)/I_0 of 1.37. The flares
all showed the typical characteristic flash phase of UV Ceti type flare stars
followed by a gradual decline. In one (flare No. 3) there is the usual rapid
decline after the flash phase followed by a secondary maximum and then a slow
fall off in intensity. Several similar flares have been previously recorded by
Jarrett and Eksteen (1969, 1970).

Deductions

Using the data in the table along with that from UV Ceti flares observed in
recent years at Boyden by Jarrett and Eksteen (1969, 1970), involving 70 flares
in all, we conclude that there is a flare recurrence period of very nearly 24^h
(or an integral multiple thereof as the recorded flares were not always on
consecutive nights), with a probable error of +4 minutes.

Monitoring Table of UV Ceti

Date                       Total   Flare   U.T.    Duration   I_0+f-I_0
1971      U.T.             Hours    No.     of               -----------
Okt.                        per           Flare                 I_0
                           Night
12     22^h03^m- 23^h28^m  1^h35^m   1    23^h12^m.9  3.1    0.86
18     19  46  - 21  58              2    19  07.6    4.4    1.77
       22  48  - 23  13    2  37     3    19  56.6    5.6    1.11
19     17  40  - 21  58              4    18  37.5    0.5    1.10
       22  20  - 23  00    4.58      5    20  10.0    8.5    2.19
20     17  39  - 19  03
       22  18  - 23  45    2.51
21     18  36  - 18  50
       21  10  - 21  45
       22  24  - 22  46    1  11
25     18  29  - 21  20              6    19  17.1    2.9    1.14
       22  10  - 23  03    3  44
26     18  07  - 21  16              7    18  44.3    2.0    1.10
       21  53  - 23  59    5  15     8    19  56.3    3.0    1.70

Total                     22^h11^m            I_0+f-I_0
                                       Mean ------------ = 1.37
                                                I_0

Note: I_0 is the intensity deflection less sky background of the quiet star.
I_0+f is the total intensity deflection less sky background of the star plus
flare at maximum.


A.H. JARRETT and J.P. EKSTEEN
Boyden Observatory, Astronomy Department,
University of the Orange Free State,
South Africa

References:

A.H. Jarrett and J.P. Eksteen, 1969, IBVS, No. 349.
A.H. Jarrett and J.P. Eksteen, 1969, IBVS, No. 406.
A.H. Jarrett and J.P. Eksteen, 1970, IBVS, No. 412.
A.H. Jarrett and J.P. Eksteen, 1970, IBVS, No. 484.
A.H. Jarrett and J.P. Eksteen, 1970, Monthly Notices of the Astronomical
   Society of Southern Africa, XXIX, No. 8, 115. [BIBCODE 1970MNSSA..29..115J ]


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