The results of the polarization observations of T Tau, RY Tau and of field stars are presented (Fig.1). The ratio p/Av for RY Tau is equal to 0.066 and is larger than the same ratio for surrounding field stars. The observed variations of the polarization parameters of T Tau and RY Tau as well as the maximum value of the ratio p/Av for RY Tau have permited already in 1964 to suggest that these stars have intrinsic polarization.

Recent results on observations and models of polarization of T Tauri stars (TTS) and other young stellar objects (YSO's) are presented. In particular, the difference in polarization properties between the classical T Tauri stars (CTTS) and the weak-line T Tauri stars (WTTS) is made. A correlation between polarization and rotation period is searched for but not found. Observations of polarization maps for many young stars are considered. Two types of models have been proposed to explain these observations. Current evidence favors single and multiple scattering in flattened, optically thick, structures, i.e. disks, around many TTS. In particular, the size of the optically thick part of the disks, and their inclination to our line of sight can determined for published polarization maps.

The preliminary analysis of UBVRI photometric and polarimetric observations of the naked T Tau star HDE 283572 indicates that:

(i)there is intrinsic and variable component of polarisation;

(ii) the distribution and the area of the active regions on stellar surface are variable on time scale of a year.

Periods of the rotational modulation of the brightness of BY Dra-type stars, Pleiades spotted stars, naked T Tau stars and T Tau-type stars are compared with absolute bolometric stellar magnitudes. Arguments are given that the majority of BY Dra-type stars have the age of 10∗∗8 years and relatively fast as well as slowly rotating objects are met between them.

An overview of the characteristics of short-term light variability on T Tauri stars is given. The evidence of the occurrence of flares comes from observations mainly at X-ray energies and from patrole observations in the ultraviolet spectral region. From such observations some limits on the peak fluxes and total energies of the largest flare-like events can be set. In addition, the frequency of such events can be deduced for a number of stars. It is demonstrated that there appears to be a qualitative difference between powerful flare-like events on the weak-line T Tauri stars (NTTs) and those on strong-line stars (CTTs). While it appears that the concept of surface flares occurring on NTTs may be correct there is the evidence that the disk-stars in addition produce flare-like events of a different nature. These events could be related to processes occurring not on the stars but in their circumstellar environment, for instance in a circumstellar disk. We also point at observations that could be of importance in clarifying the cause of flare-like activity on T Tauri stars and also comment on how this activity changes with stellar age.

T Tauri stars and flare stars are both magnetically active late-type stars of low mass and low to moderate luminosities. The flares observed in these two classes of variables show similar properties and, thus, probably have the same physical origin. On the other hand, at least the majority of the classical T Tauri stars seem to be surrounded by cool, dusty (accretion) disks, which are absent or undetectable in most classical flare stars.

On the basis of investigations concerning the character and the behaviour of circumstellar shells at T Tauri stars it is shown that the position of these objects in the colour magnitude diagram, below and above the main sequence, is caused by cosmogonic circumstellar effects originated by the mass loss of the stars.

Ejection and accretion of gas clouds in the vicinity of RY Tau were discovered. The existense of large scale “stellar prominences” around young stars is suggested.

A [S II] emission-line image of T Tauri and its surrounding nebulosity suggests the presence of a precessing jet in the system.

Summary of the works on emission line stars and Herbig-Haro objects done by visiting astronomers at Kiso is presented.

The FU Orionis phenomenon has attracted increasing attention in recent years, and is now accepted as a crucial element in the early evolution of low mass stars. The general characteristics of FUors are outlined and individual members of the class are discussed. The discovery of a new FUor, BBW 76, is presented, together with a discussion of photometric and spectroscopic observations of the star. The evidence for circumstellar disks around T Tauri stars is briefly outlined, and the FUor phenomenon is discussed in the context of a disk accretion model. A large increase in the accretion rate through a circumstellar disk makes the disk self-luminous with a luminosity two or more orders larger than that of the star. Massive cool winds rise from FUors, and it is conceivable that they are related to the initiation of Herbig-Haro flows. The FUor phenomenon appears to be repetitive, and newborn low-mass stars may be cycling between the FUor state and the T Tauri state.

Results of spectral and photometric observations of Sugano star = V1143 Ori in brightness minimum and near it are given. Emission lines of HI, CaII, FeI, TiI, TiII and TiO absorption bands are detected. The appearing envelope is observed also in minimum. A brightness increase of Shanalstar V1118 Ori is observed. In its spectrum lines of HI, CaII, FeI, FeII are found, testifying to formation of an envelope.

During the last ten years data on T Tau type stars which have fuor-like outburst-subfuors were obtained. Two such stars were found in Orion association. These are V1118 Ori [1] and V 1143 Ori [2,3]. In recent years, in Byurakan observatory observations of these stars have been made.

Correlations between different eruptive phenomena (fast and slow flares, large-scale eruptive variations up to fuor phenomenon) in stellar instability during stage of evolution are analysed A conclusion is drawn on the difference in natures of eruptive phenomena lasting some ten minutes and slower variations lasting more than one day.

During observations made in August and November 1987 with the ultraviolet telescope “Glasar” [1] installed at the module “Kwant” of the “Mir” Space Station a very blue star HD 269665 = Sk −68°110 in the region of the LMC was detected.

Ratio between number OB-stars and that of comparatively bright flare stars in star forming reions are discussed.

The results of spectral investigations of collimatee outflows from young stellar objects, including HL/XZ Tau, L723, Bernes 48, RNO 43N, CoKu Tau/1, obtained on 6-m telescope BTA with two-dimensional photon counting system in 1986-1988 are presented.

The region of the H2O megamaaer emission in Orion KL had been studied by VLBI method. The structure is a chain of the compact components oriented under the angle X ≅ −80°. The size of the components is ⩽ 0.1 A.U., the brightness temperature Tb ≅ 1017 K, the linewidth of each component is Δ f ⋜ 7 kHz. The emission has linear polarization P ⋝ 80 % and position angle is changed by 9.2 degree / A.U. The velocity of the components has a gradient 0.41 km/sec A.U. The masers are unsaturated, the kinetic temperature Tk ≤ 120 K. The structure corresponds to an expanding protoplanet rings, radius of which is equal R = 6 A.U. The rotation and the expanding velocities are equal 5 and 3.8 km/s accordingly. Mass of a protostar is ~ 0.7 M⊙.

The results of observations of H2O maser sources Ori A and W49N at 1.35cm made the RATAN-600 radio telescope from June 1981 till December 1988 are presented. The light curves of these sources showed several outbursts. Duration of the strongest outbursts for the Ori A and W49N are approximately 1 and 1.5yr respectively. The maximum of the total luminosity (assuming isotropic emission) of these sources for the velocity range ±8km.s-1 is egual to 1×1047 ph.s-1 and 2×1049 ph.s-1 respectively. The time behaviour of the water maser source in W49N during more than 7yr is monitored for the first time.

The connection between the IRAS point sources catalog and following objects is studied: 1. H2O masers, 2. Herbig - Haro objects, 3. Cometary nebulae, 4. Compact nebulae, situated in the large nebulae, and 5. Dark globules. It is shown, that more than 50% of the 1, 2, 3, and 4 type objects are connected with the IRAS sources. More than 10 new H2O masers, connected with IRAS sources are found, one of them having very unusual properties. More than 10 dark globules are found in the Cep OB2 association, which are connected with IRAS sources. One of these sources consists of 4 components, forming a Trapezium-like configuration.

The infrared IRAS data for supposed sources of optical outflows and young stars in Taurus-Auriga complex are studied. It is shown that there exists a group of stars with extremely low optical and infrared luminosities. It's suggested, that they are the stars with anisotropic sourface activity.