Structure of the inner region of the accretion disk of the Herbig Ae star CQ Tau based on long-term monitoring data

Results from simultaneous spectral and photometric monitoring of the Herbig Ae star CQ Tau in the neighborhood of the Hα and resonance sodium doublet Na I D lines are presented. It is shown that the inner structure of the accretion disk of CQ Tau is nonuniform and consists of two regions with quite different kinematic characteristics. Region I is characterized by relative stability and a smooth long-term variation in the velocity of the gas along the line of sight. Region II is distinguished by the highest velocities and a variability in their maximum values over time scales from a few days to 700 days. The dust clouds which produse the star’s brightness minima may also be the source of cold gas and contribute to the observed spectral variability. We assume that region I of the disk coincides with the accretion disk of the star. The kinematic differences in region II may be caused by dissipation of circumstellar dust clouds which, moving in elongated orbits, are able to approach the star quite closely. __________ Translated from Astrofizika, Vol. 50, No. 1, pp. 39–55 (February 2007).     

Large-scale photometric activity of UX Ori type stars

Radical readjustments in the photometric activity of young stars owing to sudden changes in the circumstellar extinction are discussed using the light curves of two UX Ori type stars, CQ Tau and V1184 Tau, as examples. Changes of this sort can be caused by large deviations from axial symmetry in the distribution of circumstellar dust, as well as by large variations in the mass accretion rate in circumstellar disks. A large amount of dust may also appear in the vicinity of a young star owing to collisions of planetesimals. __________ Translated from Astrofizika, Vol. 51, No. 1, pp. 5–13 (February 2008).     

The Herbig Ae/Be Star V586 Ori

Studies of the Herbig Ae/Be star V586 Ori based on photoelectric observations in the Strömgren system are reported. It is found that as the brightness decreases, the Balmer discontinuity index initially increases and then begins to drop. As the star fades, the index decreases. We have previously found similar variations in the indices and C for UX Ori, RR Tau, and V351 Ori. It is shown that V586 Ori has the characteristics of a shell-star.     

Analysis of magnetic field measurements for T Tau

The presence of hot spots on the surface of T Tau attributable to mass accretion from the protoplanetary disk is shown to have virtually no effect on the accuracy of estimating the magnetic field strength for this star. By comparing the magnetic field strengths for T Tau at the photospheric level measured by various methods, we found that if the angle i at which we see T Tau does not exceed 10°, then the magnetic field of the star could be dipolar with the angle between the dipole axis and the rotation axis of the star ?85°. If, however, it later emerges that i > 10°, its magnetic field is essentially nondipolar and/or nonstationary.     

Rotational Brightness Modulation and Starspots on the RS CVn-type Stars IN Com, IL Com, UX Ari, and V711 Tau

UBVRI photometric observations and models of spotting are presented for four noneclipsing RS CVn systems: IN Com (G5III/IV), IL Com (F8V+F8V), UX Ari (K01V+G5V), and V711 Tau (K1IV+G5V). A low amplitude variability caused by cold (T=1700K)spots which can occupy up to 19% of the star's surface is confirmed for the little-studied star IL Com. Long-term light curves are constructed and the stellar magnitudes and color indices of the unspotted photospheres are estimated for IN com, UX Ari, and V711 Tau. It is shown that UX Ari becomes bluer with decreasing brightness, so its variability cannot be fully explained in terms of cold spots. Models of spotting on In Com and V711 Tau are constructed from the full set of available photometric observations. The spots on both of these variables lie at middle latitudes and occupy up to 22% (In Com) and 33% (V711 Tau) of the stars' surfaces. Both stars manifest a tendency for the width of the spots to decrease as their area increases. This is a crude analog of the Maunder butterflies. These stars experience cyclical spot activity and have a differential rotation of the type found on the sun.     

Photometric activity of the UX Ori star V1184 Tau in the optical and near-infrared spectral ranges

We present the results of our infrared JHK photometry for the unusual UX Ori star V1184 Tau. Comparison with previous observations performed before the catastrophic decline in its optical brightness in 2004 (when the star faded approximately by a factor of 100) has shown the following: the star faded approximately by 2 ^m and 1 ^m in the J and H bands, respectively, while its K brightness remained almost constant. This pattern of infrared variability seems incompatible with the mechanism of variable circumstellar extinction responsible for the dramatic decline in the star’s optical brightness. However, if this mechanism is considered in the context of an accretion disk model with a puffed-up inner rim in the dust sublimation zone and with a disk wind producing an expanding gas-dust atmosphere above the disk surface, then the paradox can be resolved. In this model, the photometric activity of V1184 Tau in both visible and near-infrared spectral ranges, including the sharp brightness decline in 2004, can be explained by an increase in the geometric thickness of the disk in the dust sublimation zone caused by enhanced accretion of circumstellar matter onto the star. There is reason to believe that such events occur periodically and result from the presence of a companion to V1184 Tau moving in a highly eccentric orbit. The offered interpretation of the photometric activity of V1184 Tau allows this object to be classified as an UX Ori star based on the observed photometric effect and, at the same time, as a FU Ori star based on the pattern of the physical process that produced this effect.     

Photoelectric Investigation of the Herbig Ae/Be Star MWC 1080

The results of photoelectric observations of the Herbig Ae/Be star MWC 1080 in the Strömgren system are given. It was found that MWC 1080 undergoes rapid rises and falls in brightness with an amplitude of up to 0 ^m .25, occurring in a time interval of from several minutes to several hours. It is shown that MWC 1080 is similar to MWC 342 and MWC 419. It is suggested that there is a fundamental difference between the mechanisms of brightness variation of these three objects and of Herbig Ae/Be stars.     

Spot activity in the RS CVn binary UX arietis

Photoelectric observations of the RS CVn type non-eclipsing binary UX Arietis obtained at Nizamiah Observatory during the observing seasons of 1975–76, 1981–82 and 1982–83 are presented. The light curve of UX Ari showed a distortion wave with an amplitude inV varying from 0.02 mag during 1975–76 to 0.15 mag during 1982–83. An analysis of the available data shows that the light maximum is almost constant. It is also evident that the light-curve minimum decreases as the wave amplitude increases. The constant light at maximum,V = 6.51 ± 0.03 indicates the unspotted photospheric brightness. It is also suggested that the variation in meanV brightness is mainly due to spot activity and not due to intrinsic variation.     

Anomalous Behavior of the Linear Polarization of the Herbig Ae Star WW Vul during the 1997 Minimum

In the course of photopolarimetric monitoring of the Herbig Ae star WW Vul, an unusual variation of linear polarization upon energence from a deep minimum was recorded, which cannot be explained by the standard mechanism for such objects (UX Ori stars): a variable contribution of radiation scattered by circumstellar dust. An analysis of possible causes of the anomalous behavior of polarization shows that it was most likely due to the presence of aligned, aspherical dust grains in the dust cloud crossing the line of sight at that time.     

Surface inhomogeneities and line variability on DF Tau

We have mapped surface inhomogeneities on the classical T Tauri star DF Tau, using the Li  i doublet at 670.8 nm, the Ca  i lines at 612.2 nm and 643.9 nm and a calcium and iron blend at 646.3 nm. We find compelling evidence that there are hotspots with temperatures of more than 5000 K. Two of the hotspots produce line-profile deformations that can be traced as they move through the cross-correlated profiles. When one of the hotspots crosses the stellar disc, redshifted absorption components appear in the Na D lines. As these redshifted absorption features are usually tracers for mass-infall we interpret this hotspot as an accretion shock close to the stellar surface.   Parts of the surface of DF Tau are covered with a hot chromosphere that is visible in the Ca  ii infrared triplet lines and the narrow component of He  i . We find no correlation between the veiling and the lines that originate from the hot chromosphere, suggesting that the veiling and the chromospheric emission are produced in physically distinct regions.     

Spectrophotometric studies of CQ Cephei

Spectrophotometric and spectroscopic observations of CQ Cep — the shortest-period binary with WN component — are presented. Excepting the NV λ4603, the fluxes of all other emission lines show enhancement at minima. They can be explained by the Roche surfaces that take into account the strong wind of the WN7 component. Various radial velocity curves for emission and absorption give different orbital solutions with a general positive shift of λ axes. Although N IV λ4058 represents the true motion of the WN7 component, its flux variations are influenced by geometric effects. There is no signature of the companion. The extent of the atmosphere of CQ Cephei appears larger than in V444Cyg, another eclipsing binary with a Wolf-Rayet component.     

Photometric and Hα Observations of the Cataclysmic Star UX UMa

UBVRI photometry and spectroscopic observations around the H_α line of the cataclysmic star UX UMa are presented. The analysis of the 9-year photometry shows that the out-of-eclipse brightness of the system and the depth of the eclipse changes in different time scales while the width of the eclipse remains constant. The observed features of the light curves as well as the features of the two-peaked H_α profiles were attributed to an inhomogeneity of the accretion disk. “Spiral arm” model for a fitting of the light curves of UX UMa is proposed. It reproduces well the observational data. The obtained azimuthal extent of the spiral arms is of ∼90° and their light contribution is about 17–30of the total V flux of the disk. The obtained two dense structures at the outer disk covering partially the inner hot disk and the white dwarf at orbital phases ∼0.7 and ∼0.2 is in agreement with the predictions of the theoretical computations.