Spectral Observations of Subfuors (Exors). II. V1143 Ori

Spectral observations of the subfuor (exor) V 1143 Ori during the outburst of 1992-93 are reported. Data on the behavior of the Ca II infrared triplet before and during the outburst are presented for the first time. The amplitudes of the outbursts during 1982-94 show that their maxima do not vary greatly on the average. Between outbursts, when the star is in the minimum of its active period, the spectrum of V 1143 Ori is typical of a WTTS and during an outburst, of a CTTS.     

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.     

The BM Ori System. I. Anomaly in the Radial Velocity

The radial velocities of the star BM Ori are determined from spectra obtained by the HST and IUE satellites, as well as from spectra obtained with the BTA telescope. An analysis of this data shows that the radial velocities of the main star and its satellite experience an irregular positive shift by 20-30 km/s. This fact can only be interpreted in terms of the presence of yet another star in the binary system. The new observations have made it possible to significantly improve the accuracy of the spectroscopic elements of the orbit of the close binary system and to estimate the orbital characteristics of the third body. The preliminary values of the elements are: Ep=JD2444744, P=1302^d, =11km/s, e=0.92, K=20km/s, and =1.6rad.     

The system Bm Ori. V. Improved photometric elements

The times of individual minima taken from the literature are used to plot the dependence of O-C on revolution number for the eclipsing star BM Ori. A least squares fit of this plot yields the following photometric elements: Min I=JD2440265.331(5)+6.470524(3)·E. __________ Translated from Astrofizika, Vol. 51, No. 3, pp. 501–503 (August 2008).     

Spectroscopic observations of V1118 Ori in 1989

The spectra of the star V1118 Ori obtained during the fuor-like outburst in 1989 are typical of classical T Tau stars. The Balmer emission lines of hydrogen and Call are the most prominent lines in the spectrum. A short-wavelength absorption component of the H line shifted –500 km/sec from the H peak was observed in the spectrum of December 19, 1989, which indicates an strong outflow of material from the star. The rate of fuor-like outbursts for V1118 Ori during its active period has been once every three years on the average. There is some similarity between slow out bursts and the outbursts of EXors (subfuors).Translated fromAstrofizika, Vol. 39, No. 3, pp. 365–374, July–September, 1996.     

The BM Ori System. III. The Depth of the Minimum in the Infrared

The depth of the minimum of the BM Ori eclipsing system is studied in the infrared. For this purpose, observations have been made in the JHKLM bands outside the eclipse and in the JHKL bands near the central phase of the eclipse. The depth of the minimum is found to have a complicated wavelength dependence. In the short wavelength region of the spectrum this depth decreases from the U band to the R band (λ=0.36–0.71 mm), which is explained in terms of eclipsing of the principal star by a dust cloud surrounding the companion and by the disk of the companion. In the IR the depth of the minimum increases sharply from the I to the L band (λ=0.97–3.5 mm). This effect can be explained by partial obscuring of the hot region of the dust cloud by the disk of the companion. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 565–573 (November 2005).     

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).     

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.     

HST Observations of Sakurai's Object (V4334 Sgr) and Related Stars

We describe our ongoing program of HST observations of Sakurai's Object(V4334 Sgr). Direct WFPC2 imaging from August 1996 through August 2000 revealsno transient features (such as light echoes), and documents the decline of thestar to below 24th visual magnitude in 2000. The surrounding planetary nebulahas shown no changes from 1996 through 2000. There are no obvious peculiarfeatures (such as blobs or knots) in the immediate vicinity of the star. Wealso have in place a target-of-opportunity program to obtain UV spectra withHST in the event that the star begins to retrace its evolution back to highsurface temperature. We also present older HST FOC imaging of V605 Aql. The central object is aresolved nebula that emits in [O III] (but not in hydrogen), whose 0.6diameter is consistent with a dust cloud ejected during the 1919 outburst. Thecentral star itself is not seen due to its being embedded in the nebula.Several other central stars (including H 3-75, IC 2120, and Abell 14) havelate-type nuclei and no evidence for hot companions. They may be furthercandidates for born-again red-giant nuclei.     

Photoelectric Observations of V448 CYGNAE

The research literature on the star V448 Cyg is reviewed in more detail. An analysis of three color photoelectric observations made at Abastumani is reported in detail with corresponding tables and graphs. In particular, the gaseous structure and evolutionary status of the system are discussed. Newly published spectroscopic data suggest that our light curves might be interpreted by more modern nonclassical methods assuming a new model. Thus, comparing data obtained in this fashion with the new spectroscopic data may help improve the evolutionary status and model for the V448 Cyg system. It is also seems possible to obtain better values of the physical parameters for circumstellar structures and obtain more precise information on the physical conditions in the atmospheres of the stars and on the structure of the circumstellar shells.     

Spectral and photometric observations of the star Y Ori

Data are presented from a spectral and photometric study of the long-period variable star Y Ori, which we have classified as a type M7IIIe near its brightness minimum. In the blue part of the spectrum, features from a star of an earlier spectral class are superimposed on the spectrum of a cool giant, so that a variable excess emission is observed at wavelengths of 4000–4200 Å. As opposed to the monotonically decreasing intensity of the Balmer lines (EWHα > EWHβ > EWHγ > EWHδ) in normal stars belonging to the earlier spectral classes, a reverse relationship, with EWHγ < EWHδ is detected in Y Ori. Translated from Astrofizika, Vol. 51, No. 4, pp. 567–575 (November 2008).     

New photometric investigation of the low-mass-ratio contact binary star V1853 Orionis

Four-color charge-coupled device(CCD) light curves in the B, V, Rc and I c bands of the totaleclipsing binary system V1853 Orionis(V1853 Ori) are presented. By comparing our light curves with those published by previous investigators, it is determined that the O'Connell effect on the light curves has disappeared. By analyzing those multi-color light curves with the Wilson-Devinney code(W-D code),it is discovered that V1853 Ori is an A-type intermediate-contact binary with a degree of contact factor of f = 33.3%(3.7%) and a mass ratio of q = 0.1896(0.0013). Combining our 10 newly determined times of light minima together with others published in the literature, the period changes of the system are investigated. We found that the general trend of the observed minus calculated(O-C) curve shows a downward parabolic variation that corresponds to a long-term decrease in the orbital period with a rate of d P/dt =-1.96(0.46)×10^-7 d yr^-1. The long-term period decrease could be explained by mass transfer from the more-massive component to the less-massive one. By combining our photometric solutions with data from Gaia DR_2, absolute parameters were derived as M_1 = 1.20 M⊙, M_2 = 0.23 M⊙, R_1 = 1.36 R⊙and R_2 = 0.66 R⊙. The long-term period decrease and intermediate-contact configuration suggest that V1853 Ori will evolve into a high fill-out overcontact binary.     

Photometric investigation of the K-type extremely shallow contact binary V1799 Orion

New multi-color light curves of the very short period K-type eclipsing binary V1799 Ori were obtained and analyzed with the Wilson-Devinney code. The photometric solutions reveal that the system is a W-type shallow-contact binary with a mass ratio of q = 1.335(±0.005) and a degree of contact of about f = 3.5(±1.1)%.In general, the results are in good agreement with what is reported by Samec. Dramatic manifestations of the O'Connell effect that appear in the light curves can be explained well by employing starspots on the binary surface, which confirms that the system is active at present. Several new times of light minimum were obtained. All the available times of light minimum were collected, along with the recalculated and newly obtained values. Applying a least-squares method to the constructed O- C diagram,a new ephemeris is derived for V1799 Ori. The orbital period is found to show a continuous weak increase at a rate of 1.8(±0.6) × 10-8d yr-1. The extremely shallow contact, together with the period increase, suggests that the binary may be at a critical stage predicted by thermal relaxation oscillation theory.     

Detection of superhumps in XTE J1118+480 approaching quiescence

We present the results of our monitoring of the halo black hole soft X-ray transient (SXT) XTE J1118+480 during its decline to quiescence. The system has decayed 0.5 mag from 2000 December to its present near-quiescent level at   R ≃18.65  (2001 June). The ellipsoidal light curve is distorted by an additional modulation that we interpret as a superhump of   P _sh=0.17049(1) d  i.e. 0.3 per cent longer than the orbital period. This implies a disc precession period   P _prec∼52 d  . After correcting the average phase-folded light curve for veiling, the amplitude difference between the minima suggests that the binary inclination angle lies in the range   i =71–82°  . However, we urge caution in the interpretation of these values because of residual systematic contamination of the ellipsoidal light curve by the complex form of the superhump modulation. The orbital-mean H α profiles exhibit clear velocity variations with ∼500 km s⁻¹ amplitude. We interpret this as the first spectroscopic evidence of an eccentric precessing disc.     

Spectral Observations of the Flare Star HU Del

Results are presented from a study of 27 spectra of the flare star HU Del obtained during 2000–2002 on the 2.6 meter telescope at the Byurakan Observatory. Two flares were detected, along with a weak correlation between the equivalent widths of the Hα and Hβ emission lines. At the time of the photometric maximum of a flare the equivalent widths of both these lines are minimal and reach their maximum only significantly afterward. A strong increase in the Hβ line intensity is observed which appears to be the consequence of a photometrically undetected, short-duration flare. A possible relationship between the binary (multiple) character and the physical activity of this star is examined briefly in terms of current theoretical models.__________Translated from Astrofizika, Vol. 48, No. 3, pp. 335–348 (August 2005).     

The ultraviolet line spectrum of the soft X-ray transient XTE J1118+480: a CNO-processed core exposed

We compare ultraviolet (UV) spectra of the recent soft X-ray transients XTE J1118+480 and XTE J1859+226. The emission line strengths in XTE J1118+480 strongly suggest that the accreting material has been CNO processed. We show that this system must have come into contact with a secondary star of about 1.5 M_⊙, and an orbital period ∼15 h, very close to the bifurcation value at which the nuclear and angular momentum loss time-scales are similar. Subsequent evolution to the current period of 4.1 h was driven by angular momentum loss. In passing through a period of 7.75 h the secondary star would have shown essentially normal surface abundances. XTE J1118+480 could thus represent a slightly later evolutionary stage of A0620-00. We briefly discuss the broad Ly α absorption wings in XTE J1118+480.     

Results of Photometric and Polarimetric Observations of the Fuor V1057 Cyg from the Time of an Outburst to the Present

Observations of the brightness, color, and polarization of the fuor V1057 Cyg over more than 30 years are presented and briefly discussed. Variability of the linear polarization was found.     

Measurement of the longitudinal magnetic-field component for FU Ori

The Main Stellar Spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a polarimetric analyzer was used to measure the longitudinal magnetic-field component of FU Ori on January 24, 2002. The following (3σ) upper limits were obtained for the magnetic field B_‖: B_‖<350–400 G in the formation region of Fe I, Ni I, and Ca I absorption lines (disk + wind), and B_‖<200 G in the formation region of the absorption component of the Hα line with a P Cyg profile. We conclude that the strength of a large-scale magnetic field capable of collimating the disk wind does not exceed 300 G. For the region where the emission component of the Hα line is formed, we found that B_‖<100 G. Such a low value may have been obtained because the magnetic field lines in this region were almost perpendicular to the line of sight at the time of our observations.