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Observations of a Unique Minimum of RR Tau in the Optical and Near Infrared
We present observations of the UX Ori star RR Tau in the optical(UBVRI)and near infrared (JHKLM)acquired between November 2000 and April2001. We recorded a uniquely long (about half a year) Algol-like minimumwith an amplitude of ΔV≈2.9. The dimming of RR Tau wasaccompanied by an increase of the linear polarization, typical of UX Oristars and testifying to the eclipsing nature of the minimum. The J and Hinfrared fluxes varied synchronously with the optical variations.However, the K and L brightness changes were in the opposite sense: theflux in these two bands increased for the entire duration of the opticalminimum. Our analysis suggests that the source of the K and L radiationis the dust cloud itself, moving at a distance of about 1 AU from thestar. The flux increase in these bands was not due to an increase in thedust temperature, but instead to an increase in the number of emittinggrains in the cloud. This could be associated either with an actualincrease in the number of fine grains due to sublimation and thedisruption of larger grains or with the distortion and disruption of thecloud due to tidal perturbation, permitting the star’s light topenetrate and heat the densest regions of the cloud. Based on theobserved L fluxes, we estimate the mass of the emitting dust in thecloud to be ≈1023 g. Taking into account the presence of cool dustand a gaseous component in the cloud in addition to the dust heated bythe star’s radiation, and adopting a ratio for the masses of thedust and gas components similar to that in the interstellar medium(1:100), we estimate the cloud’s total mass to be ≥1025 g.Judging from this value and the duration of the minimum, we observed anextremely rare episode associated with a giant gas and dust cloud with atotal mass on the order of 0.1 lunar mass or higher, which passed verynear the young star (and may be falling onto it).
| Dust around young stars. Photopolarimetric activity of the classical Herbig Ae/Be star RR Tauri.
The classical Herbig Ae/Be (HAeBe) star RR Tau is known as a highlyvariable young star with an amplitude of variability of about 4mag inthe V pass-band. In this paper we present the results of coordinatedCrimea-Dodaira multi-band photo-polarimetric observations of this starwhich cover fully the observed interval of its brightness changes.Within the observed interval of its light variations the linearpolarization of RR Tau anti-correlates with its brightness changes. Thedependence of the linear polarization on the stellar magnitude agreeswell with the model according to which the main source of the intrinsicpolarization of RR Tau is scattered radiation by the circumstellar (CS)disk-like dust envelope (probably the protoplanetary disk) seen edge-onor under a small inclination to the line-of-sight, and that thebrightness variations are caused by variable obscuration of the star byrevolving circumstellar dust clouds. A comparison with previousphoto-polarimetric observations of this star shows that the Stokesparameters of its polarized radiation are quite stable on a time scaleof about 7 years. By using this fact we have separated the interstellarand intrinsic components of the observed polarization. The numericalmodeling of the intrinsic linear polarization together with thecolour-magnitude diagrams of RR Tau show that the circumstellardisk-like envelope around this star is strongly flattened and that thecharacteristic size of the grains is intermediate between that ofinterstellar dust and dust in the old protoplanetary disk of βPictoris. We assume on the basis of this analysis that RR Tau issurrounded by a young protoplanetary disk and that it can be consideredas a young progenitor of β Pictoris.
| UBVRI photometry and polarimetry of the optical component of the X-ray source A 0535 + 26 = V 725 Tau
Attention is given to results obtained at the Crimean AstrophysicalObservatory of five-color photometric and polarimetric observations ofthe Be-star HDE 245770 = V 725 Tau optical component of the transientX-ray source A 0535 + 26 and of a number of stars in its vicinity. Ananalysis of brightness changes during 1983-1985 reveals that with anincrease in brightness, the star becomes redder. This behavior is commonfor Be stars at which a highly-flattened envelope is seen nearly'pole-on'. Sometimes the brightness is coupled with blueness suggestingthe complicated and variable structure of the gaseous envelope. Aninvestigation of the linear polarization revealed that at V725 Tau,there is interstellar variable polarization of its radiation. The basiccharacteristics of this polarization are rapid variability in terms ofits magnitude and direction, a strong dependence of the position of theoscillation plane on wavelength, and the absence of a correlation withbrightness variations. These characteristics distinguish it frompolarization typical of Be-stars.
| Results of narrow-band photometry of the magnetically variable star Beta CrB
The SPh-68 spectrophotometer was used to observe the emission flux fromBeta CrB in the dispersion band of 5215 A with respect to the referencestar Gamma CrB. Analysis of the observational data revealed theexistence of short-period flux variations with periods of 196.9, 158.3,and 53.57 min, and amplitudes of 0.005, 0.004, and 0.004 mag,respectively. In addition, sharp flux variations with stellar rotationphase can be explained within the framework of a model of an obliquerotator. It is suggested that line intensity variations are the reasonfor flux variations in the depression.
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