On the formation of TW Crv optical radiation

We present the analysis of the optical radiation of the young pre-cataclysmic variable TW Crv. Spectroscopic and photometric observations were obtained at the SAO RAS 6-m BTA telescope and at the Russian-Turkish RTT-150 telescope. The light curves of the system posses nearly sinusoidal shapes with the amplitudes of Δ_m > 0.^m7, what is typical for young pre-cataclysmic variables with sdO-subdwarfs and orbit inclinations of less than 45?. The optical spectrum contains dominant radiation of the hot subdwarf with the HI and He II absorption lines and strong emission lines, which are formed in the atmosphere of the secondary owing to the reflection effects. Radial velocities of the cool star were measured by analyzing the λλ 4630–4650 Å Bowen blend, which for the first time allowed to determine the component masses. A numerical simulation of the light curves and spectra of TW Crv, obtaining a complete set of systems fundamental parameters was carried out. The hot star parameters prompt its belonging to the sdOsubdwarf class at the stage of transition to the cooling white dwarf sequence. The absence of its observable planetary nebula is caused by a long-lasting evolution of the system after the common envelope state. The secondary component has a luminosity excess, which is typical for other young sdO-subdwarf precataclysmic variables. Its position on the “age??luminosity excess” diagram points at the accuracy of the obtained set of TW Crv fundamental parameters and at the similarity of its evolutionary and physical conditions with that of other BE UMa-type objects.     

Mapping of seagrass meadows from the lakshadweep islands (India), using aerial photographs

Seagrass meadows from the Lakshadweep islands were mapped with the help of black and white aerial photographs. A maximum of 40 ha seagrass cover was estimated in the lagoon of Minicoy, followed by Kavaratti (34 ha). The total seagrass cover from six major islands of Lakshadweep was estimated to be 112 ha with standing crop of ca 800 metric tonnes. The dominant seagrass species observed wasThalassia hemprichii whileCymodocea rotundata, Halophila ovata, Syringodium isoetifolium andHalodule uninervis were common to these islands.     

Possible variability of the magnetic field of T Tau

Using the Main Stellar Spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a polametric analyzer, we measured the longitudinal magnetic field component B_∥ for the T Tauri stars T Tau and AS 507 on January 16 and 18 and February 15, 2003. For both stars, we determined only the upper limits on B_∥ from photospheric lines: +15±30 G for T Tau and ?70±90 G for AS 507. The magnetic field of AS 507 was not measured previously, while B_∥ for T Tau is lower than its values that we obtained in 1996 and 2002 (B_∥?150±50G), suggesting that the longitudinal magnetic field component in the photosphere of T Tau is variable. We also measured the longitudinal magnetic field component for T Tau in the formation region of the He I 5876 Å emission line. We found B_∥ in this region to be ?+650, ?+350, and ?+1100 G on January 16, 18, and February 15, 2003, respectively. Our observations on January 18 and February 15 correspond to virtually the same phase of the star's rotation period, but the profiles of the He I 5876 Å line differ markedly on these two nights. Therefore, we believe that the threefold difference between the B_∥ values on these nights does not result from observational errors. We discuss the possible causes of the B_∥ variability in the photosphere and the magnetosphere of T Tau.     

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.     

Microvariability of line profiles in the spectra of OB stars: δOri A

We have studied variability of the spectral lines of the OB star δOri A—the brightest component of the δOri triple system. Forty spectra with signal-to-noise ratios ≈500–800 and a time resolution of four minutes were obtained. We detected variability in the HeIIλ4686, HeIλ4713, and Hβ absorption and the CIIIλ5696 emission profiles. The amplitude of the variability is ≈(0.5–1)% of the continuum intensity. The dynamical wavelet spectrum of the profile variations reveals large-scale components in the interval 25–50 km/s that move within the-V sin i to V sin i band for the primary star of the system, Aa¹, with a band crossing time of 4^h–5^h. However, some of the variable features go outside the band, presumably due to either imhomogeneities in the stellar wind from δOri Aa¹ or nonradial pulsations of the weaker components of the system, Aa² or Ab. The detected variability may be cyclic with a period of ≈4^h. We suggest that it is associated with nonradial pulsations of the primary in the sector mode (l,m) = (2, ?2).     

Spectral variability of LBV star V 532 (Romano’s star)

We present the results of studying the spectral and photometric variability of the luminous blue variable star V532 in M33. The photometric variations are traced from 1960 to 2010, spectral variations—from 1992 to 2009. The star has revealed an absolute maximum of visual brightness (1992–1994, high/cold state) and an absolute minimum (2007–2008, low/hot state) with a brightness difference of ΔB ≈ 2.3 ^m . The temperature estimates in the absolute maximum and absolute minimum were found to be T ∼ 22000 K and T ∼ 42000 K, respectively. The variability of the spectrum of V532 is fully consistent with the temperature variations in its photosphere, while both permitted and forbidden lines are formed in an extended stellar atmosphere. Broad components of the brightest lines were found, the broadening of these components is due to electron scattering in the wind parts closest to the photosphere. We measured the wind velocity as a difference between the emission and absorption peaks in the PCyg type profiles. The wind velocity clearly depends on the size of the stellar photosphere or on the visual brightness, when brightness declines, the wind velocity increases. In the absolute minimum a kinematic profile of the V532 atmosphere was detected. The wind velocity increases and its temperature declines with distance from the star. In the low/hot state, the spectral type of the star corresponds to WN8.5h, in the high/cold state—to WN11. We studied the evolution of V532 along with the evolution of AGCar and the massive WR binary HD5980 in SMC. During their visual minima, all the three stars perfectly fit with the WNL star sequence by Crowther and Smith (1997). However, when visual brightness increases, all the three stars form a separate sequence. It is possible that this reflects a new property of LBV stars, namely, in the high/cold states they do not pertain to the bona fide WNL stars.     

Magnetic fields and rotation of the white dwarfs 40 Eri B and WD 0009+501

We describe the results of our magnetometric monitoring of two white dwarfs: 40 Eri B and WD 0009+501. We found periodic variations in the longitudinal magnetic field of 40 Eri B. The field variability with an amplitude of ～4 kG and a zero mean is discussed in terms of an oblique rotator model. The rotation period is ～5 h 17 min, but there is another period of 2 h 25 min that may be related to nondipolar field components. The published projected rotational velocities of 40 Eri B measured from a narrow non-LTE Hα peak V sin i?8 km s^?1 are in good agreement with our measurements of the magnetic field and the rotation period. The combined effect of magnetic and rotational broadening of the central Hα component constrains the rotation period, P? 5.2 h. We discovered the rotation period (1.83 h) of the magnetic white dwarf WD 0009+501. The period was found from the periodically varying magnetic field of the star with a mean 〈B_e〉 = ?42.3±5.4 kG and a half-amplitude of 32.0±6.8 kG.     

Moderate-resolution holographic spectrograph

We present a new scheme of a moderate-resolution spectrograph based on a cascade of serial holographic gratings each of which produces an individual spectrum with a resolution of about 6000 and a bandwidth of 80 nm. The gratings ensure centering of each part of the spectrum they produce so as to provide uniform coverage of the broadest possible wavelength interval. In this study we manage to simultaneously cover the 430–680 nm interval without gaps using three gratings. Efficiency of the spectrograph optical system itself from the entrance slit to the CCD detector is typically of about 60% with a maximum of 75%. We discuss the advantages and drawbacks of the new spectrograph scheme as well as the astrophysical tasks for which the instrument can be used.