A photometric study of the star V1016 Ori

New photoelectric UBVRI observations of the eclipsing variable V 1016 Ori have been obtained with the AZT-11 telescope at Crimean Astrophysical Observatory and with the Zeiss-600 telescope at Mount Maidanak Observatory. Light curves are constructed from the new observations and from published and archival data. We use a total of 340, 348, 386, 185, and 62 magnitude estimates in the bands from U to I, respectively. An analysis of these data has yielded the following results. The photometric elements were refined; their new values are $Min I = JDH 2441966.820 + 65\mathop .\limits^d 4331E$ . The UBVRI magnitudes outside eclipse were found to be $5\mathop .\limits^m 95$ , $6\mathop .\limits^m 77$ , $6\mathop .\limits^m 75$ , $6\mathop .\limits^m 68$ , and $6\mathop .\limits^m 16$ , respectively. No phase effect was detected. We obtained two light-curve solutions: (1) assuming that the giant star was in front of the small one during eclipse, we determined the stellar radii, r _s=0.0141 and r _g=0.0228 (in fractions of the semimajor axis of the orbit); and (2) assuming that the small star was in front of the giant one, we derived r _g=0.0186 and r _s=0.0180 for the V band. The brightness of the primary star in the bands from U to I is L ₁=0.96, 0.92, 0.90, 0.89, and 0.88, the orbital inclination is $i = 87^\circ .1$ , and the maximum eclipse phase is α₀= 0.66. In both cases, we accepted the U hypothesis, assumed the orbit to be elliptical, and took into account the flux from the star Θ¹ Ori E that fell within the photometer aperture. The first solution leads to a discrepancy between the primary radius determined by solving the light curve and the radial-velocity curve and its value estimated from the luminosity and temperature. This discrepancy is eliminated in the second solution, and it turns out that, by all parameters, the primary corresponds to a normal zero-age main-sequence star.     

A spectroscopic study of V1016 Ori

Two CCD spectra of the star V1016 Ori were obtained with the echelle spectrograph of the 6-m (BTA) telescope. An analysis of these spectra allowed us to estimate the star's atmospheric parameters (T _eff=29700 K, logg=4.4) and projected rotational velocity (Vsini=60 km s^?1) and to determine its chemical composition. Chemical anomalies were found. The Fe abundance is nearly solar; He, C, O, Mg, Al, Si are underabundant; and Ne, S, Zn are overabundant. The “spectroscopic” radius of the primary is in satisfactory agreement with its radius determined from the light and radial-velocity curves if the small star is assumed to lie in front of the giant star during an eclipse. The paradox of the primary's anomalous radius is thus resolved. A table of line equivalent widths and a portion of the star's spectrum are given in Appendices 1 and 2.     

Improved photometric elements for the eclipsing system V1016 Ori

Published observations of the times of individual minima are analyzed by a least squares technique to determine O-C as a function of orbit number for the eclipsing system V1016 Ori. The following photometric elements are found: MinI=JD2441966.831(4)+65.43284(5)E.     

Mechanism for cyclical activity of the Herbig Ae star BF Ori

The photometric activity of the star BF Ori, which belongs to the family of UX Ori-type stars, is studied. New data obtained with the ASAS robotic telescope confirm the existence of a cyclical component in the light curve for this star with a duration of roughly 11-12 years. The form of the photometric cycle resembles the theoretical light curves for a young binary system with a low-mass secondary component, and which is accreting matter from a surrounding common disk. Alternative mechanisms for the cyclical variability of UX Ori stars are also discussed.     

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).     

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.     

Spectrum of the star BM Ori at minimum light

Two spectra of the star BM Ori were obtained with the 2.6-m Crimean Astrophysical Observatory telescope near its maximum eclipse phase. The light detector was a CCD array. The wavelength range 5305–5373 Å was chosen in such a way that it contained no strong primary lines. Optimum filtration of the spectra yielded a signal-to-noise ratio of ～300. Eighteen secondary lines are seen in the spectrum. Atmospheric parameters of the secondary star were determined: T _eff=5740 K and logg=3.0; the secondary was classified by these parameters as being of spectral type G2 III. The best agreement between observed and synthetic spectra is achieved for metallicity [M/H]=?0.5 and microturbulence ξ_t=0 km s^?1. The projected rotational velocity is Vsini=60 km s^?, in agreement with the synchronous velocity in the hypothesis that assumes a total eclipse by the secondary star. Atmospheric elemental abundances in the secondary are estimated. Nickel, chromium, and iron exhibit an underabundance of ～1 dex.     

IUE observations of star formation in a cooling flow

Star formation in cooling flows is usually found to have an initial mass function deficient in massive stars, but the center of the cooling flow in Hydra A has been shown to contain a significant number of early type stars. Here we use UV-spectra obtained with the IUE satellite together with ground based data to constrain the nature of this young population. The data is compatible with a burst of star formation with a Salpeter-like initial mass function, a burst age of about 4 107 yr, and a total mass ≈ 108 M⊙. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromospheric activity on the late-type star V1355 Ori using Lijiang 1.8-m and 2.4-m telescopes

We obtained new high-resolution spectra using the Lijiang 1.8-m and 2.4-m telescopes to investigate the chromospheric activities of VI355 Ori as indicated in the behaviors of Ca Ⅱ HK,Hδ,Hγ,Hβ,Na Ⅰ D_1,D_2,Hα and Ca Ⅱ infrared triplet(IRT) lines.The observed spectra show obvious emissions above the continuum in Ca II HK lines,absorptions in the Hδ,Hγ,Hβ and Na Ⅰ D_1,D_2 lines,variable behavior(filled-in absorption,partial emission with a core absorption component or emission above the continuum)in the Hα line,and weak self-reversal emissions in the strong filled-in absorptions of the Ca Ⅱ IRT lines.We used a spectral subtraction technique to analyze our data.The results show no excess emission in the Hδ and Hγ lines,very weak excess emissions in the Na Ⅰ D_1,D_2 lines,excess emission in the Hβ line,clear excess emission in the Hα line,and excess emissions in the Ca Ⅱ IRT lines.The value of the ratio of EW_(8542)/EW_(8498) is in the range 0.9 to 1.7,which implies that chromospheric activity might have been caused by plage events.The value of the ratio E_(Hα)/E_(Hβ) is above 3,indicating that the Balmer lines would arise from prominence-like material.We also found time variations in light curves associated with equivalent widths of chromospheric activity lines in the Na Ⅰ D_1,D_2,Ca Ⅱ IRT and Hα lines in particular.These phenomena can be explained by plage events,which are consistent with the behavior of chromospheric activity indicators.     

Periodic variabilities in the IUE spectra of SS Cygni

The analysis of the IUE low resolution spectra of SS Cyg in quiescence clearly shows modulations with the orbital phase of the continuum and the emission lines total area. The shape of such modulations is depending on the type of the optical outburst preceding the quiescent phase in which the UV spectra were collected. This behaviour, together with those in other wavelength regions, could be explained within the framework of the intermediate polar models.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Analysis of HST and IUE ultraviolet spectra for T Tauri stars: DF Tau

We analyze ultraviolet spectra of DF Tau, a binary system whose primary component is a classical T Tauri star. The spectra were obtained from the Hubble Space Telescope and the IUE satellite. The stellar emission in the wavelength range covered is shown to originate in an accretion shock wave. The gas infall velocity is ～250 km s^?1. The accreted-gas density is typically N ₀≤10¹¹ cm^?3, but it can occasionally be higher by one and a half orders of magnitude. The continuum intensity near λ=1900 Å was found to be virtually constant for such a significant change in N ₀. The star’s photometric variability is probably attributable to variations in accreted-gas density and velocity, as well as to variations in the area of a hot spot on the stellar surface and in its orientation relative to the observer. The mean accretion rate is $\dot M \sim 3 \times 10^{ - 9} M_ \odot yr^{ - 1}$ . The interstellar extinction for DF Tau is $A_V \simeq 0\mathop .\limits^m 5$ , the stellar radius is ≤2R _⊙, and the luminosity of the primary component is most likely no higher than 0.3 L _⊙. We argue that the distance to DF Tau is about 70 pc. Upper limits are placed on the primary’s coronal emission measure: EM(T=10⁷ K)<3×10⁵⁴ cm^?3 and EM(T=1.3×10⁶ K)<3×10⁵⁵ cm^?3. Absorption lines originating in the stellar wind were detected in the star’s spectrum. Molecular hydrogen lines have essentially the same radial velocity as the star, but their full width at half maximum is FWHM ?50 km s^?1. We failed to explain why the intensity ratio of the C IV λ1550 doublet components exceeds 2.     

A Model Atmosphere Analysis of the F6V Star π3 Ori

Model atmosphere analysis, based on Kurucz models has been applied to study the F6V star π³ Ori (=BS1543=HD30652). The following values of the effective temperature, surface gravity and microturbulence velocity were obtained: = 6270±200 K, log g = 3.80.2, ξ_t =3.5±0.5 km/s. The abundances of 10 elements were determined. The resulting element abundances for the π³ Ori were found to be about three times lower with respect to the Sun. From evolutionary calculations we derived a mass, radius and luminosity for π³ Ori of M =1.3 M_⊙, R =2.38 R_⊙, L =7.9 L_⊙. Hence this star should be classified F6IV instead of F6 V. This revised version was published online in July 2006 with corrections to the Cover Date.