133

Astron. Nachr., Bd. zgz, H. 3 (1970)

Light outburst of a compact galaxy LORE and NIKOLAUS B. RICHTER, Tautenburg

With z figures. (Received 19% November I I)

Von 750 kompakten Galaxien in einem Feld nahe M3, von dem U,B,V-Aufnahmen von 1963 bis 19% vor- liegen, zeigt ein Objekt im Zeitraum 1966/67 im BBereich eine Aufhellung um I mag.

In a fieldnearM3photographed in U,B,Vfrom 1963 to 1g6g one of 750 compact galaxiesshows a brighten- ing of I mag in B during 1966/67.

During a photometric statistical investigation of 750 compact galaxies in a field round M3 a galaxy was detected which had a light outburst of one magnitude (System B). The coordinates of the object are

aIg50.0 = 13h 4" 33' I

dxg50.0 = +3O0I0' - In Fig. xa and Ib, which may be used as finding charts too, the galaxy is to be seen before and during the outburst.

Fig. I a. Galaxy before outburst 1966 June IO/II Fig. I b. Galaxy during outburst 1967 Febr. 14/15 System B, scales: I' = 8.5 mm

Fig. 2 shows the variation of its magnitude from 1963 March till 1969 June in U, B, V. These magnitudes were determined from plates taken with the Tautenburg I34/200/400 cm Schmidt camera, measured with an iris photometer.

From this figure we find that the light outburst must have happened between the middle of 1966 and the beginning of 1967. The increasing of light in B amounts to one magnitude. In V it is about half a magnitude. Unfortunately there exist no plates in U during the outburst. It seems that a small preceding outburst in B happened in 1966 March. The most interesting feature in Fig. z is, that in System B the brigthness of the object diminished after the outburst rather quickly within one year to its normal magnitude. In system V on the contrary its brightness remained on the outburst magnitude or ascended even a little. This means, that the galaxy changed its color after the outburst and became more reddened. In the following table the photometric data of the galaxy are compiled.

134 L. and N. B. RICHTER: Light outburst of a compact galaxy

I U I B I V ' I U-B mag I B - v mag

beforeoutbhp[ 1c81 1 18m44 I 164196 I -by37 -1 +I.oO +1.48 during outburst 17-45 16.45 after outburst 18.81 18.38 16-37 +0.43 +2.01

As to the photometric accuracy of the magnitudes the following may be told. As standards we used JOHNSON and SANDAGE'S') photoelectric sequences in M3. Unfortunately the galaxy is lying more than 1.8 degrees apart from the cluster (12.75 cm on the plates) and mostly near the border of the plates. Therefore the photometric connection was difficult. This may be one reason of the large scattering of brightness on the different plates. But the main reason may be that the galaxy has a small halo, especially in V, and is not exactly starlike concentrated. So its brightness depends still from the limiting magnitudes of the plates. This effect is wellknown, especially in system Vr).

1967 1968 I 1969 I

Fig. 2. Development of brightness in U, B, V between 1963 and 19%. The large dots in system V are the mean of bright- ness derived from more than z plates during the same night

A d d e n d u m (1970 July 23)

Further plates of the field round M 3 were taken by F. BORNGEN between 1970 March 30 and April 8. B. BALASZ (Budapest), during a stay at Tautenburg, measured the brightness of the galaxy on these plates with the iris photometer. His result from 6 plates in B is 18F44; this is exactly the brightness before the outburst. From 4 plates in U he found 18m50, more than 0.3 mag brighter than before the outburst.

I) H. L. JOHNSON and A. R. SANDAGE, Three-color photometry in the globular cluster M3. Astrophys. J. 124.379 ('956).

2) N. RICHTER, Zwei bemerkenswerte Galaxientriplets. Monatsberichte DAW, Bd. 9, Heft 9/10 (1967) = Mitt. Karl-Schwarzschild-Obs. Nr. 39