Evidence for ablated flows in the shell of the nova DQ Herculis

High-resolution long-slit Hα spectra of the shell of the old nova DQ Herculis have been obtained with the William Herschel Telescope using the ISIS spectrograph. An equatorial expansion velocity of  370 ± 14   km s⁻¹  is derived from the spectra which, in conjunction with a narrow-band Hα image of the remnant, allows a distance estimate of 525 ± 28 pc. An equatorial ring which exhibits enhanced [N  ii ] emission has also been detected and the inclination angle of the shell is found to be     with respect to the line of sight. The spectra also reveal tails extending from the clumps in the shell, which have a radial velocity increasing along their length. This suggests the presence of a stellar wind, collimated in the polar direction, which ablates fragments of material from the clumps and accelerates them into its stream up to a terminal velocity of the order of 800–900 km s⁻¹.     

Outbursts of selected dwarf novas and postnovas

Observations are presented of selected cataclysmic variables (the dwarf novas V1504 Cyg and GO Com and the postnovas Q Cyg, V446 Her, and DI Lac) carried out at the Crimean Astrophysical Observatory and the Crimean Laboratory of the Sternberg Astronomical Institute in 1995–2007. The outburst parameters and the behavior of these objects on the “magnitude (V)-color (V-R)” diagram are described. The tracks of postnova outbursts on this diagram are similar to the dwarf-nova behavior. On average, all the studied systems show a break on the “brightness-color” dependence. The color V-R before the break increases more weakly than after it or does not increase at all.     

The oEA stars QY Aql, BW Del, TZ Dra, BO Her and RR Lep: photometric analysis, frequency search and evolutionary status

New and complete multi-band light curves of the oEA stars QY Aql, BW Del, TZ Dra, BO Her and RR Lep were obtained and analysed with the Wilson-Devinney code. The light curves residuals were further analysed with the Fourier method in order to derive the pulsation characteristics of the oscillating components. All the reliable observed times of minimum light were used to examine orbital period irregularities. The orbital period analyses revealed secular changes for QY Aql and BW Del, while the Light-Time Effect seems to be the best explanation for the cyclic period changes in TZ Dra and BO Her. RR Lep has a rather steady orbital period. Light curve solutions provided the means to calculate the absolute parameters of the components of the systems, which subsequently were used to make an estimate of their present evolutionary status.     

Spectroscopic study of Be-shell stars: 4 Her and 88 Her

We present an optical spectroscopic study based on 41 spectra of 4 Her and 32 spectra of 88 Her,obtained over a period of 6 months.We estimate the rotational velocity of these stars from Hel lines in the blue spectral region(4000-4500 ?).We find that these stars are likely to be rotating at a fractional critical rotation of~0.80.We measure the average I_p/I_c ratio to quantify the strength of the Hα line and obtain1.63 for 4 Her and 2.06 for 88 Her.The radius of the Ha emission region is estimated to be R_d/R_*~5.0,assuming a Keplerian disk.These stars are thus found to be fast rotators with a relatively small Ha emission region.We detect V/R variation of the Ha spectral line during the observed period.We re-estimate the periods for both stars and obtain a period of ~46 d and its harmonic of 23.095 d for 4 Her,and a period of~86 d for 88 Her.As these two cases are shell stars with binaries and have low Ha EW with the emission region closer to the central star,the V/R variation and a change in period may be an effect of the binary on the circumstellar disk.     

Spatial and velocity structure of circumstellar water masers

We discuss the results of our study of water masers at 22 GHz with the Very Large Array. We conclude, from the anticorrelation between the intensity and linewidth of the maser features, that they are unsaturated; turbulence must exist in order to explain the large observed opacities. For most sources, we are able to place the masers on an expanding shell around the central star, finding that the overall sizes of the maser regions increase with mass loss rate. We compare the extent of the water maser emitting region with the region of dust formation.     

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).     

爆后新星武仙V 533的光度研究

老新星武仙V533(V533Her=武仙1963年新星)是一颗光度变化极其复杂的天体。本文给出了我们用双筒天体照相仪于1980年6月至1982年11月间对其所做的照相观测结果。从所得结果可以看到:(1)该星亮度在此期间已基本恢复到其爆前的宁静期亮度;(2)高时频观测指出V533 Her具有时标为小时级,变幅Δm～0.2~m的小幅度光变;(3)在此期间其亮度有上升趋势,上升幅度～1.5等。本文还讨论了V533 Her在爆发前后的光度变化情况,通过分析指出新星在爆发前可能有可觉察的光度变化。     

Possible Flare of the Red Dwarf HU Del

The results of spectroscopic observations of the red dwarf flare star HU Del are given. The observations were made in August 2000 with the 2.6-m telescope of the Byurakan Observatory equipped with a Byu FOSC integral-field spectrograph. A rapid flare evidently occurred on HU Del.     

Photometric study of the binary system NN Del

We present the results of the differential V light curve analysis of NN Del. We show that NN Del is an EA eclipsing binary system with a period of 99.27 days and a highly eccentric orbit. Photometric solutions obtained using the Russell and the Wilson-Devinney models seem to indicate that both components are very similar in radii and luminosities (assuming a F5 spectral type). Constraints imposed on the V luminosity of the system by the HIPPARCOS data suggest that the components of the system could be subgiants instead of main sequence stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spatial structure of gravity waves in the solar photosphere

Observations of the Fe I line are used to simulate spatial and temporal pressure variations in the solar photosphere. The local internal gravity waves, which are essentially structures that are quasi-periodic in space (on granular and mesogranular scales) and time and propagate along inclined paths at subsonic velocities, are isolated by appropriate filtering. The phase and group velocities of the wave trains are orthogonal; their z-projections are of the opposite sign.     

Spatial structure of transverse oscillations in the interplanetary magnetic field

The spatial structure of the transverse oscillations in the interplanetary magnetic field at 1 AU is studied by comparing the simultaneous observations by Explorer 33 and 35 satellites at the maximum separation of about 200R _E. The anisotropy characteristics of these oscillations suggest that the oscillations sampled are Alfvén waves. It is found that the size of the region of the wave coherence is related to the solar wind velocity; the size is 80R _E when the wind velocity is lower than 500 km s^–1 but becomes less than this when the wind velocity is higher. An inference is made that the solar atmospheric turbulence contributing to the faster solar wind is finer in scale than that associated with the slower wind.A postgraduate student at the Tokai University     

Observations and analysis of MT Her

Previously reportedBV photometry of MT Her is analysed with the aid of efficient curve-fitting techniques. There is insufficient overall data to allow a definitive parametrization of the binary, but we can confidently rule out the possibility of a classical Algol.A provisional model is advanced which consists of two close unevolved dwarfs: the primary a late F-type and the secondary a mid K-type. The system is located at a distance of about 250 pc in a region of fairly heavy interstellar extinction near the galactic disk. It may be a short-period RS CVn-type binary, but this possibility, as the provisional model itself, requires spectrographic confirmation.     

Study of the delta-Scuti star HR 1170

The light and colour curves of the δ-Scuti star HR 1170 are presented. The absolute and bolometric magnitudes are derived and the position of the star on the colour-colour diagram is also shown. The primary and beat periods estimated from the light curves are 0 _. ^d 098 299 and 0 _. ^d 392 06, respectively.     

Spatial and temporal structure of a high-latitude transient ULF pulsation

Auroral radar observations of transient ULF pulsations with latitudinally varying period have recently been reported. An event of this type is analysed using data from the Scandinavian Magnetometer Array, the STARE radar, and the GEOS-2 satellite. The magnetometers show long-period (～450 s) oscillations consistent with the pulsations observed in the ionosphere using STARE, and confirm that the geomagnetic field shells are resonating in the toroidal mode. There is also a localised, small-amplitude component with 250-s period South of the STARE pulsations. Electric field measurements at GEOS-2 show only an impulsively stimulated pulsation of 250-s period. The wave fields at GEOS-2 imply that the satellite was earthward of a localised toroidal standing-wave resonance, which mapped to the ionosphere at least one degree South of the expected position. A radial profile of equatorial plasma mass density is inferred from the GEOS-2 and STARE results. This shows a radially increasing density near GEOS-2, and a radially decreasing density outside the satellite position.An interpretation of the event is given in which a tailward propagating hydromagnetic impulse directly stimulates field shells outside 7 R_E to oscillate at their eigenperiods. In the region of increasing density near GEOS-2, a relatively highly-damped surface wave is excited. This feeds energy rapidly into a narrow monochromatic toroidal field-line resonance, which subsequently decays more slowly through ionospheric dissipation.