COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3614

                                               Konkoly Observatory
                                               Budapest
                                               4 June 1991

                                               HU ISSN 0374 - 0676



          THE OUTBURSTS OF THE DWARF NOVA FS AURIGAE


The variability of FS Aur (S 3946) was discovered by Hoffmeister (1949), who
pointed out the rapid variations in the range 15.4m and 16.2m, outbursts to
14.4m with the shortest interval between them 35d. This value of the cycle
length was recently confirmed by Gessner (1389). The strong emission lines of
H alpha - H epsilon and helium were found by Williams (1983). Howell and
Szkody (1988) suspected the photometric period P = 97+-10 minutes, which is
characteristic for SU UMa-type stars.

The star was observed on 180 archive photographic plates of the Sternberg State
Astronomical Institute. The comparison stars were linked to the BV sequence of
Christian (1980) on 6 plates by using the Iris-photometer of the Sternberg
Institute. They are shown in Fig. 1. The sigma_m value of am corresponds to
the mean-squared deviation from the mean. Normally sigma_m<=0.15m, but for the
stars p, y, q the larger value of sigma_m may argue for the possible brightness
variations, and they were not used as comparison stars.

The histogram (Fig. 2) is characteristic for Dwarf Novae, as well as the light
curve, some parts of which are shown in Fig. 3. The brightness changed from
14.0m to 17.2m (pg), its mean value <m>=16.02m and the mean-squared deviation
sigma_m=0.67m. For the observations in 'quiescent' state m_pg >15.0m,
<m>=16.22m, sigma_m=0.39m. The brightenings were observed on 20 plates
corresponding to 12 outbursts. As one may see from the Table 1, the shortest
time interval between the subsequent observed outbursts is equal to 24d, two
are twice longer (50d and 53d). Only one interval (33d) derived from the
Moscow plates is near the value 35d, which was previously suspected by
Hoffmeister (1949) and Gessner (1989). From these values one may suppose that
the cycle length may be near C~=12d. From the revised `Amplitude-Cycle`
relation derived by Richter and Brauer (1989), one may obtain the value C~=13d
for the amplitude 2.2m. Obviously, this statistical relationship corresponds
to the relative accuracy 100 per cent, thus such a value must be revised by the
future observations.


                                [FIGURE 1]

                 Fig. 1. Comparison stars for FS Aur

                   *	m_pg	sigma_m	n
                   a	13.00	0.08	6
                   b	13.22	0.09	6
                   c	13.60	0.06	6
                   d	13.75	0.05	6
                   e	13.89	0.09	6
                   f	14.04	0.10	6
                   g	14.06	0.07	6
                   h	14.22	0.09	6
                   k	14.28	0.07	5
                   l	14.39	0.08	4
                   m	14.58	0.17	6
                   n	14.64	0.10	6
                   p	14.80	0.22	6
                   q	14.80	0.15	6
                   r	15.11	0.14	5
                   s	15.12	0.15	6
                   t	15.56	0.19	5
                   u	15.68	0.09	4
                   w	15.83	0.09	5
                   x	16.52	0.27	4
                   y	17.20	0.16	3

                               [FIGURE 2]

        Fig. 2. The histogram for the brightness of FS Aurigae


The ascending branch of the light curve lasts no more than 1d (Fig. 3c), the
descending branch lasts from 2d (Fig. 3c) to 3.5d (Fig. 3f). The value of the
full outburst width W=3.0d, which may be derived from the statistical `W-P'
relation of Gicger (1987), is in excellent agreement with our data. From the
statistical relation between P and the rate of decline tau=dt/dm (van Paradijs,
1983), one may calculate the value of tau=0.95+-0.21 days/mag. For different
outbursts we obtained the values of tau from 0.6 (Fig. 3f) to 1.0 (Fig. 3c).
Thus the estimated characteristics agree with that observed in other Dwarf
Novae with similar orbital periods.

However, no superoutbursts were detected (or recognized), which may be
achieved, if P<=2h. The amplitude of brightness variations during one night
varies with characteristic time from ~0.4m at outburst to ~0.9m at
'quiescence'. However, the time resolution ~40 min is insufficient to study
the possible orbital or superhump variability.


                                 [FIGURE 3]

           Fig. 3. The fragments of the light curve of FS Aur


                  Table I

               The outbursts of FS Aurigae
26351.2   G+   38472.3   G+     42449.3   G       44900.6   14.1
26687.4   G    40148.5   G++    42812.4   14.9    44987.4   14.1
27046.5   G+   41322.4   G+     42836.3   15.0    45263.6   14.0
27424.3   G+   41330.3   G+     42869.3   14.1    45313.4   14.8
27459.4   G+   42009.5   14.0   43050.5   14.5    46147.4   G
27582.6   G+   42093.4   14.4   43161.5   14.6    46307.5   K13.5
27718.5   G    42336.5   14.6   44254.5   G       46335.6   K14.0
31530.4   G                                       46420.0   K14.7

Remarks:  The (JD-2400000) of the observations near the outburst are given. G
corresponds to the photographic observations of Gessner(1989) with `normal` and
'larger' (G+) brightenings, K - to the visual estimates of Kinnunen (1985). The
values without letter correspond to our observations.


                                I. L. ANDRONOV
                Department of Astronomy, Odessa State University
                              Odessa 270014 USSR

References

Christian, C.A.: 1980, Astron. J. 85, No. 6, p.700 [BIBCODE 1980AJ.....85..700C ]
Gessner, G. : 1989, Mitt. veranderl. Sterne 11, No 8, p.186 [BIBCODE 1989MitVS..11R.186G ]
Gicger, A.: 1987, Acta Astr. 37, 29 [BIBCODE 1987AcA....37...29G ]
Hoffmeister, C. : 1949, Veroff. Sternw. Sonneberg 1, 3
Howell, S.B., Szkody P.: 1988, Publ. Astron. Soc. Pacific. 100, 224 [BIBCODE 1988PASP..100..224H ]
Kinnunen, E.: 1985, Rep. Scand. Var. Star Obs. 2, 90 pp.
van Paradijs, J.: 1983, Astron. Astrophys. 125, L 18 [BIBCODE 1983A&A...125L..16V ]
Richter, G.A., Brauer, H.-J.: 1989, Astron. Nachr. 309, 413 [BIBCODE 1989AN....310..413R ]
Williams, G.: 1983, Astrophys. J. Suppl. 53, No. 3, p.523 [BIBCODE 1983ApJS...53..523W ]