Search

We present intensive optical, infrared, and radio monitoring observations of the BL Lac object OJ 287, taken between the years 1993-1998. Two large optical outbursts were detected at the predicted times in November 1994 and December 1995. The detection of these outbursts supports the binary black hole model for OJ 287. Optical and radio polarisation observations show large variability in the degree of polarisation and position angle, very similar to those observed during the 1983/84 outburst in OJ 287. The polarisation position angles show very similar behaviour during these observations, indicating that, at least, the magnetic field orientations in radio and optical bands are related in OJ 287. Optical and infrared light curves show continuous variability in time scales ranging from tens of minutes to years. In the radio bands we have observed some of the lowest ever measured flux levels. During the first optical outburst in November 1994 the observed radio flux was very low, but during the second optical outburst radio bands also showed high flux levels. This is a puzzling observation, which can hopefully be used for discriminating between different outburst models. On top of the large outbursts OJ 287 has displayed flaring activity in time scales from days to weeks and shorter time scale flickering.

We present results of optical monitoring of quasars and blazars obtained at Tuorla Observatory between September 1995 and May 1997. The aim of our monitoring is to provide well sampled optical light curves for quasar and blazar studies. During the observing period the V-band brightness of S2 0109+224, 3C 66A, and ON 231 (W Comae) reached some of the brightest values ever measured for these objects. A strong outburst was observed in Mrk 421 and the large outburst, which was predicted earlier, in OJ 287 was confirmed. CTA 102 had over one magnitude outburst which happened in a timescale of a few days. For OI 090.4 we measured one of the faintest V-band brightness values ever.

Over 13600 continuum observations of extragalactic sources are presented. These observations of 157 sources at 22, 37 and 87 GHz more than doubles the millimeter observations of these sources. The data are between 1990.5 and 1995.5, and combined with our earlier published data they form a 15 year database.

We present the results of the optical and radio monitoring of the BL Lac object AO 0235+164 during a faint state. In both optical and radio bands the source has been observed at the faintest ever recorded levels, reaching $V=19.80$and $F_{\rm 22GHz} = 0.34$Jy. In the optical bands we still see variability with amplitudes up to 1.5 magnitudes on timescales from days to weeks. The radio variability is less dramatic, but in general follows the optical behaviour. A correlation between general trends in the optical and radio behaviour of AO 0235+164 may be recognized in the data from the present monitoring as well as in the historical light curves, suggesting a "base” mechanism responsible for the emission at both frequencies. A good candidate is a synchrotron process in the relativistic jet. Optical flares with no corresponding radio counterparts have been observed too. These events may be interpreted in terms of microlensing by a foreground galaxy.

We present results from a two year intensive monitoring of BL Lac object 3C 66A (PKS 0219+428). This object was observed in outburst during these two years. It reached the brightest ever observed magnitude on V=13.59 (1.2.1995) and on K=10.59 (15.2.1994). The optical and infrared light curves are characterised by randomly distributed fast flares, lasting a few days and well defined outbursts lasting a week or two. On top of these flares we can occasionally see small amplitude microvariability. No clear correlation can be found between the spectral behaviour and the occurrence of these flares. In the radio bands 3C 66A was quite faint and very stable compared to the optical variations. The light curves will be presented with preliminary analysis and discussions on the possible causes for the observed variations.

We present the most continuous data base of optical multiband data ever published on the BL Lacertae object ON 231 (W Com). The data have been collected during an intensive and coordinated $BVR_{\rm c}I_{\rm c}$monitoring campaign carried out in the period from March 1994 to March 1997. During our campaign, the source brightness was at the highest level ever observed. The light curve shows a complex structure, characterized by the presence of three major outbursts having the observed maxima in March 1995, February 1996, and January 1997, when ON 231 reached its historical maximum ($B \simeq 14.2$). Variability on time scales from a few hours up to a month have frequently been observed and the light curve seems to be the superposition of many flares with different amplitudes and time scales. The broad-band optical spectral energy distribution is characterized by a spectral slope which correlates with the flux level. In particular, the higher is the flux the flatter is the spectrum.

In the Canes Venatici cloud, eighteen dwarf irregular galaxies were observed in $B,\ V$bands at the Nordic Optical Telescope under a seeing of one arcsec. Most of the galaxies having radial velocities $V_0 <$500 km/s have been resolved into stars for the first time. The galaxy distances were derived based on photometry of their brightest blue stars. Distances to some of the galaxies: UGC 6782, UGC 7131 and, probably, K 215, which are located at the CVn southern edge, were estimated to be about 15 Mpc, which is typical of the Virgo cluster outskirts. For two LSB galaxies, K 200 and K 215, the distances may be overestimated, probably because of a lack of young massive stars. For the remaining galaxies: UGC 7559, UGC 7599, UGC 7605, UGC 7639, UGC 7698, UGCA 290, UGCA 292, UGC 7866, UGC 8024, UGC 8638, UGC 8651, UGC 8760, and UGC 8833 the estimated distances range from 2.3 to 8.0 Mpc, indicating their actual membership in the CVn cloud.
Several objects studied here (UGC 7605, UGC 7639, UGC 8638, UGC 8833) have a well-resolved bluish core and regular yellow outer parts, which may point to composite (new and old) populations. The galaxy UGCA 292 = CVn dwA has unusual global parameters: $(B-V)_{\rm T}$=+0.08, $M_{\rm T}=-11.4$, $M({\rm HI})/L_B = 6\ M_\odot/L_\odot$and $M({\rm HI})/M_{\rm T} =0.7$, being, perhaps, one of the youngest known objects in the Local Universe.

We present results of optical monitoring of quasars and blazars obtained at Tuorla Observatory between September 1995 and May 1997. The aim of our monitoring is to provide well sampled optical light curves for quasar and blazar studies. During the observing period the $V$ -band brightness of S2 0109+224, 3C 66A, and ON 231 (W Comae) reached some of the brightest values ever measured for these objects. A strong outburst was observed in Mrk 421 and the large outburst, which was predicted earlier, in OJ 287 was confirmed. CTA 102 had over one magnitude outburst which happened in a timescale of a few days. For OI 090.4 we measured one of the faintest $V$ -band brightness values ever.