Polarimetric and photometric observations of the star m cephei

The results of photometric and polarimetric observations of the star Μ Cep at Byurakan Observatory are presented. Some interesting correlations between the parameters of the star’s brightness variation and the degree of polarization of the light are obtained. It is suggested that the recorded rapid changes in the degree of polarization may result from Μ Cep being a double star. Translated from Astrofizika, Vol. 43, No. 2, pp. 219-228, April–June, 2000.     

Effects of Wind-Wind Collision in Close Binary Stars

Various observational appearences of the effects of wind-wind collision for binary stellar systems have been discovered recently in X-ray, UV, optical, IR and radio ranges. Recent 3D gas-dynamic simulations of the wind-wind collision regions in WR+O, O+O and symbiotic binary systems allow to understand the physics of wind-wind collision effects, provide interpretation of observational data and constrain basic parameters of winds as well as those of binary systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optical spectrum of the infrared source IRAS 23304+6147

Based on CCD spectra obtained with the PFES echelle spectrometer of the 6-m telescope, we have determined for the first time the effective temperature T _eff=5900 K, surface gravity logg=0.0, and detailed chemical composition of the faint star identified with the infrared source IRAS 23304+6147 by the model-atmosphere method. Its metallicity indicates that the object belongs to the old Galactic disk (the mean abundance of the iron-group elements V, Cr, and Fe for IRAS 23304+6147 is [X/H]=?0.61 dex). The stellar atmosphere exhibits an enhancement of carbon and nitrogen, [C/Fe]=+0.98, [N/Fe]=+1.36, and C/O>1. Significant overabundances of lanthanides were detected: the mean [X/Fe]=+1.04 for La, Ce, Pr, Nd, and Eu. The elemental abundances suggest that the atmospheric chemical composition of IRAS 23304+6147 was modified mainly by nucleosynthesis followed by mixing. By modeling the object's spectrum, we revealed absorption features at the positions of well-known absorption diffuse interstellar bands (DIBs). An analysis of radial-velocity and intensity measurements for these DIBs leads us to conclude that, for IRAS 23304+6147, the DIBs originate mostly in its circumstellar dust envelope expanding at a velocity of about 20 km s^?1. Molecular C₂ Swan emission bands were detected in the object's spectrum, which also originate in the circumstellar envelope. There is a close match between the object's atmospheric effective temperatures determined independently by the model-atmosphere method and by modeling its optical and infrared energy distribution, within the accuracy of the methods.     

Spectral analysis of the 91bg-like Type Ia SN 2005bl: low luminosity, low velocities, incomplete burning

The properties of underluminous Type Ia supernovae (SNe Ia) of the 91bg subclass have yet to be theoretically understood. Here, we take a closer look at the structure of the dim SN Ia 2005bl. We infer the abundance and density profiles needed to reproduce the observed spectral evolution between −6 d and  +12.9 d  with respect to B maximum. Initially, we assume the density structure of the standard explosion model W7; then we test whether better fits to the observed spectra can be obtained using modified density profiles with different total masses and kinetic energies. Compared to normal SNe Ia, we find a lack of burning products especially in the rapidly expanding outer layers  ( v ≳ 15 000 km s⁻¹)  . The zone between ∼8500 and 15 000 km s⁻¹ is dominated by oxygen and includes some amount of intermediate-mass elements. At lower velocities, intermediate-mass elements dominate. This holds down to the lowest zones investigated in this work. This fact, together with negligible-to-moderate abundances of Fe-group elements, indicates large-scale incomplete Si burning or explosive O burning, possibly in a detonation at low densities. Consistently with the reduced nucleosynthesis, we find hints of a kinetic energy lower than that of a canonical SN Ia: the spectra strongly favour reduced densities at  ≳13 000 km s⁻¹  compared to W7, and are very well fitted using a rescaled W7 model with original mass  (1.38 M_⊙)  , but a kinetic energy reduced by ∼30 per cent (i.e. from  1.33 × 10⁵¹  to  0.93 × 10⁵¹ erg  ).     

Trace constituents of Europa's atmosphere

Europa is bombarded by intense radiation that erodes the surface, launching molecules into a thin “atmosphere” representative of surface composition. In addition to atoms and molecules created in the mostly water ice surface such as H₂O, O₂, H₂, the atmosphere is known to have species representative of trace surface materials. These trace species are carried off with the 10-10⁴ H₂O molecules ejected by each energetic heavy ion, a process we have simulated using molecular dynamics. Using the results of those simulations, we found that a neutral mass spectrometer orbiting ∼100 km above the surface could detect species with surface concentrations above ∼0.03%. We have also modeled the atmospheric spatial structure of the volatile species CO₂ and SO₂ under a variety of assumptions. Detections of these species with moderate time and space resolution would allow us to constrain surface composition, chemistry and to study space weathering processes.     

Comparison of parallel group velocity of ECH waves with electron resonant velocity: Implication for electron diffusion by ECH waves

We have investigated the role of group velocity in the calculation of pitch-angle diffusion coefficients by electron cyclotron harmonic (ECH) waves in planetary magnetospheres. The assumption which is generally made that the parallel group velocity can be neglected in comparison with particle parallel velocity is examined in detail. It is found that for lowest harmonic band this assumption is quite good. It is found that in general it is not possible to ignore the parallel group velocity. However, for lowest harmonic band this assumption is quite good at low electron temperatures.     

On the width distribution of penumbral filaments in sunspots

The mean width and distribution of penumbral filaments of a sunspot have been estimated, using white light photographs obtained with a vacuum, Newtonian type, telescope. Three areas corresponding to the penumbra of a sunspot have been analysed. Data were collected during the solar eclipse of June 1973. The photometric profiles of the Moon limb over the photosphere have been analysed to obtain useful information on both, atmospheric and instrumental perturbation on each exposure. The mean value of the width of penumbral filaments is 0.37 arc sec.Now at INTA-Villafranca, S.T.S., P.O. Box 54065, Madrid, Spain.     

Intensity ratios of spectral cores Ca ii K to H across a sunspot

Ratios of the intensity in the core of the Ca ii K line to the intensity of the H line core across a sunspot (SPO 5007) were determined from measurements of spectra made simultaneously with the Echelle spectrograph at the Vacuum Tower Telescope, Sacramento Peak Observatory. The measured values averaged over the neighboring nonspot region, the penumbra and the umbra are found to be 1.13 ± 0.04, 1.19 ± 0.05, and 1.25 ± 0.03, respectively.This work was supported by the U.S.-Republic of Korea Cooperative Science Program (K-24).     

Unique components of the WZ Sge-type dwarf nova SDSS J080434.20+510349.2

Detailed photometrical monitoring of the cataclysmic variable SDSS J080434.20+510349.2 began at the Crimean Astrophysical Observatory (Ukraine) and the Apache Point Observatory (United States) before the 2006 outburst, continued during the outburst, as well as the following two years. We established the unique nature of the primary and secondary components of the binary. We performed a comprehensive study of the white dwarf’s pulsations over the course of five months, two years after the 2006 outburst. It is shown that the most stable pulsations are equal to or double a period of 12.6 min. On the basis of all the available observations, more precise values for the orbital and the superhump periods were found to be 0.0590048(3) days and 0.059729(4) days, respectively. Our estimation of the mass of the secondary component lies in the range of solar mass from 0.037 to 0.087. This confirms the previous suggestion that the secondary component is most probably a brown dwarf.