STEREO observations of hybrid stars V775 Tau and V483 Tau

In this study, pulsational and physical characteristics of two \(\delta\) Scuti stars, V775?Tau and V483?Tau, are analysed by using four-year high-precision photometric data of the STEREO satellite. Thus, it is aimed to gain new insights into behaviours of these pulsators and evolution of \(\delta\) Scuti, \(\gamma\) Dor and Am type stars. The data are taken between 2007–2011 and examined with the help of the Lomb–Scargle method. The detection precision in the four-year combined data is around \(10^{-5}\) cd^?1 in frequency and \(10^{-5}\) mag in amplitude. It is revealed that V775?Tau exhibits weak pulsation characteristic which is interpreted as the existence of the interaction between the helium loss in the partial ionization zone and pulsation intensities. It is also considered that the absence of strong pulsations is also related to the evolution status of the star. Further, its periodogram shows low-frequency peaks. If these oscillations are g-modes, V775?Tau can be thought to be one of the rare stars that show all \(\gamma\) Dor, \(\delta\) Scuti and Am type variations. V483?Tau is comparatively more luminous, hotter and has higher rotational velocity. Therefore, although it shares the same region with V775?Tau in the H–R diagram, it is not considered to be an Am star. Yet, it exactly overlaps with the \(\gamma\) Dor stars. These clues as well as g-modes detected in its periodogram indicate that V483?Tau is a hybrid star. Finally, both V775?Tau and V483?Tau display period changes whose rates are between \(10^{-3}\) and \(10^{-4}\) yr^?1. Considering the \(\delta\) Scuti nature, it may be speculated that these changes are non-evolutionary.     

Spectrophotometric studies of two Be stars,α Leo and 17 Tau

The present work deals with spectrophotometric studies of two Be stars ( Leo and 17 Tau) using 74 telescope at Kottamia observatory.The results obtained revealed the presence of variations in the general shape and the equivalent width of the profiles of hydrogen lines in the spectrum of both stars within short period interval.     

Be星ζTau的光谱研究

A long sequence of observations of ( Tau obtained using the grating spectrograph at the 60 / 90 cm Schmidt telescoope during 1978 Dec.-1990 Feb. and the All-Fiber-Coupler grating CCD spectrograph at the 216 cm telescope after 1990 at the Xing-long Station of Beijing Observatory is presented. The reciprocal linear dispersions of the spectra were 17 A/mm, 50 A/mm and 96 A/mm. In order to study spectroscopic behaviour in detail, we measure the radial velocities of the shell absorption lines and the equivalent width and V/ R ratio of the Hα emission line. The results show that:1. The variations of the radial velocity of the shell absorption lines appeared cycle in 1978-1985. First cycle ceased around 1982 but second one lasted shorter and the amplitude was less. During 1986-1990, the velocity values conspicuously diminished and the cyclic variation also disappeared. It is a pity that we locked the radial velocity material since 1990.2. The variations of the V / R ratio of Hα is in phase with the radial ve     

Extended (15 × 6 AU) Hα Emission Around T Tau N

We present an image of T Tauri N reconstructed from speckle interferometry observations made at the 3.6 m Canada-France-Hawaii telescope (CFHT). Two spectral windows, at Hα [6540-6580 Å] and red continuum [6580-6840 Å] were used. The star is unresolved in the continuum (θ ≤ 0″038), setting an upper limit for its size of ≤ 5.3 AU (assuming a 140 pc distance). At Hα (continuum subtracted) two components are observed, an unresolved one with 70% of the Hα flux and a resolved 0″106 × 0″043 (15 × 6 AU) with 30 %. The extended component is elongated in the North-South direction. The extended Hα component scale, it's non-detection in the continuum, and TTau Hα profile shape suggest that the extension is a disk corona.     

Study of the optical variability of T Tau in the period 1962–2003

We present the results of our long-term U BV R observations of the star T Tauri performed at Mt. Maidanak Observatory from 1986 until 2003. These data, together with previous photoelectric observations of other authors, suggest that the long-term variations of the light curve are not periodic, but have a cycle with a time scale of 6–9 yr. The light curve also exhibits slower variations with time scales of ～30–40 yr. We confirm the existence of periodic brightness variations with a period of \(P = 2\mathop .\limits^d 798\) over many years; this process is peculiar in that the phase and shape of the phase curve change from season to season. We analyze the color behavior of the star. We found evidence of a strong flare occurred on October 5, 1999, when the brightness of the star reached \(9\mathop .\limits^m 22\). This is the strongest flare recorded during its photoelectric observations.     

盾牌座δ型变星V647 Tau的脉动频率──第八次STEPHI联测结果

１９９７年１１月-１２月,我们对昴星团盾牌座δ型变星Ｖ６４７Ｔａｕ及二个比较星进行了国际多址连续快速测光．分析结果表明Ｖ６４７Ｔａｕ具有５个激发脉动频率．这些频率包含了径向与非径向模式．１９７２年观测得出的主频ｆ＝２０．４０８次／天,已降至目前的第二个频率,且对应的脉动振幅也下降了．     

盾牌座δ型变星V647Tau的脉动频率——第八次TEPHI联测结果

１９９７年１１月－１２月,我们对昴星团盾牌座δ型变星Ｖ６４７Ｔａｕ及二个比较星进行了国际多址连续快速测光,分析结果表明Ｖ６４７Ｔａｕ具有５个激光脉动频率。这些频率包含了径向与非径向模式。１９７２年观测得出的主频ｆ＝２０．４０８次／天,已降至目前的第二个频率,且对应的脉动振幅也下降了。     

The (O–C) diagram problem of triple pre-cataclysmic system V471 Tau solved

V471 Tau was discovered as a spectroscopic binary by Wilson (General Catalogue of Stellar Radial Velocities, p. 44, 1953). It is the prototype of a post-common envelope system and a progenitor of a cataclysmic binary. The system consists of a cool red dwarf, K2 V, very probably a main sequence star and a hot white dwarf. The object was classified as a close binary with an orbital period of around 0.5 days. Moreover, on the light curve are observed light variations with a period of 191 days, which are connected with an ellipsoidal shape of the red dwarf as well as with the migration of spots on the surface of this cool component. The eclipse of the white dwarf in the binary remains 49 minutes and declines to the minimum and the increase from the minimum takes only 55 s. Such photometric behaviour hinders obtaining good eclipses. In this paper we have obtained during four years seven eclipses with high time resolution with all four contacts to reach precise times of minima. Fortunately these times of the minima show a change of trend in the (O–C) diagram, and we were able to decide about the physical processes responsible for the behaviour of the (O–C) diagram. We showed that this behaviour is caused by a third body in the system with an orbital period of 33.2 years, and its physical and geometrical parameters are presented. For an inclination larger than 35° we get the mass of this body below the stable hydrogen-burning limit and thus most probably the candidate would be a brown dwarf.     

美国(Datum)FTS Inc.代表访问陕西天文台——介绍 Sigma Tau 氢钟技术及其它

在时频技术和设备研制方面颇有影响的美国(Datum)FTS(Frequency and Time Systems,Inc.)公司副总裁 David S.Briggs 先生于今年3月初访问陕西天文台,介绍 Sigma Tau 氢钟(ActiveHydrogen MASERs)及其它时频技术。原先在美国 NASA 哥达德航天中心工作的 Harry Peters 于1977年创建 Sigma Tau 公司。1982年为 VLBA 射电天文观测,开发研制新型氢脉泽——更新设计原子束光学系统、腔谐振调节     

Overshooting and semiconvection: structural changes and asteroseismic signatures

Overshooting and semiconvection are two poorly known mechanisms which affect the extent and the efficiency of chemical mixing outside classical convection zones in stars. We discuss the uncertainties and the inferences of those processes in main sequence stars burning hydrogen in a convective core. We then focus on the asteroseismic signatures of partially or fully mixed zones surrounding the convective core, through the detailed shape of the induced chemical composition profile. We emphasize the potential power of asteroseismology to determine the internal structure of stars and thus to help us understand the physical processes at work inside the stars.     

A Survey and Statistics of Interstellar OH and H_2O Masers

We present a statistical analysis of a sky survey of interstellar H2O and OH masers. These masers can be classified into three categories: isolated H2O masers, isolated OH masers, and simple OH/H2O maser associations. The total number of sources in each category is of the same order of magnitude, and as an evolutionary phase they can maintain -105 yr. An improved radiative pumping mechanism is proposed. This model avoids some of the deficiencies of previous radiative models, such as shortage of exciting photons. The statistical results obtained from the survey can be interpreted by the new mechanism together with the evolutionary model in which the gravitational force of the central stellar objects is responsible for the HII region.     

X-Ray Afterglows of GRBs 050318 and 060124 and their External Shock Origin

The observations with Swift X-ray telescope (XRT) challenge the conventional gamma-ray burst model in many aspects. The XRT light curves are generally composed of four consecutive segments, i.e., a steep decay segment, a shallow decay segment, a normal decay segment, a jet-like steep decay segment, and sometimes erratic flares as well. The phys-ical origin of the X-ray emission is highly debatable. We focus here on the physical origin of the X-ray emissions of GRBs 050318 and 060124. We present the XRT light curves and spectra of the two bursts. The light curve decay slopes of the two bursts are normal, and their relations to the spectral indices are consistent with the prediction of the standard forward shock model. The multi-wavelength light curves at 0.5keV, 1.0keV, 2.0keV and 4.0keV can be reproduced by this model with an isotropic kinetic energy Ek = 2.2×1052 erg, e = 0.04, B = 0.01 for GRB 050318 and Ek = 4.2×1053 erg, e = 0.05, B = 0.01 for GRB 060124. These facts suggest that the normal decay phases of the X-rays for the two bursts are of the forward shock origin.     

Relative Velocities and Linewidths in a Coronal Hole and Outside

Relative Doppler velocities and spectral linewidths in a coronal hole and in the quiet Sun region outside have been obtained from Solar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer (CDS) observations. Five strong emission lines in the CDS wavelength range (namely, O? iii 599 Å, O?v 630 Å, Ne?vi 562.8 Å, He?ii 304 Å, and Mg?ix 368 Å), whose formation temperatures represent different heights in the solar atmosphere from the lower transition region to the inner corona, have been used in the study. As reported earlier, relative velocities in the coronal hole are generally blueshifted with respect to the quiet Sun, and the magnitude of the blueshifts increases with height. It has been found that the polar coronal hole has larger relative velocities than the equatorial extension in the inner corona. Several localized velocity contours have been found mainly on network brightenings and in the vicinity of the coronal hole boundary. The presence of velocity contours on the network may represent network outflows whereas the latter could be due to localized jets probably arising from magnetic reconnection at the boundary. All spectral lines have larger widths in the coronal hole than in the quiet Sun. In O?v 630 Å an extended low-linewidth region is seen in the coronal hole?–?quiet Sun boundary, which may indicate fresh mass transfer across the boundary. Also polar coronal holes have larger linewidths in comparison with the equatorial extension. Together with larger relative velocities, this suggests that the solar wind emanating from polar hole regions is faster than that from equatorial hole regions.     

DEFPOS and Its First Results

A spectrometer was built to examine the interstellar medium (ISM) using the hydrogen Balmer a line. It is called Dual Etalon Fabry-Perot Optical Spectrometer (DEFPOS). DEFPOS will be coupled to coude exit of the 150 cm telescope (RTT150) installed at TUBITAK National Observatory (TUG). DEFPOS was ready for observations about two years ago, but work was still continuing on the RTT150 coude exit alignment. So we have started observing HII regions with DEFPOS without the RTT150. We present here some characteristics of the instrument and some of the results obtained.     

Solar Activity and Classical Physics

1 INTRODUCTION The Sun is close enough to observe in some detail, and it shows that a star is more than the traditional stable self-gravitating thermonuclear body established half a celltury ago. For the fact is that out of sight beneath the visible surface the outward flow of heat from the thermonuclear core drives hydrodynamics that generates magnetic fields. It is the complicated dynamics of those magnetic fields that produces the modern mysteries of the active Sun. The…     

Type II bursts in Meter and Decameter – Hectometer Wavelength Ranges and Their Relation to Flares and CMEs

Statistical analysis of the relationship between type II radio bursts appearing in the metric (m) and decameter-to-hectometer (DH) wavelength ranges is presented. The associated X-ray flares and coronal mass ejections (CMEs) are also reported. The sample is divided into two classes using the frequency-drift plots: Class I, representing those events where DH-type-II bursts are not continuation of m-type-II bursts and Class II, where the DH-type-II bursts are extensions of m-type-II bursts. Our study consists of three steps: i) comparison of characteristics of the Class I and II events; ii) correlation of m-type-II and DH-type-II burst characteristics with X-ray flare properties and iii) correlation of m-type-II and DH-type-II burst characteristics with CME properties. We have found no clear correlation between properties of m-type-II bursts and DH-type-II bursts. For example, there is no correlation between drift rates of m-type-II bursts and DH-type-II bursts. Similarly there is no correlation between their starting frequencies. In Class I events we found correlations between X-ray flare characteristics and properties of m-type-II bursts and there is no correlation between flare parameters and DH-type-II bursts. On the other hand, the correlation between CME parameters and m-type-II bursts is very weak, but it is good for CME parameters and DH-type-II bursts. These results indicate that Class I m-type-II bursts are related to the energy releases in flares, whereas DH-type-II bursts tend to be related to CMEs. On the contrary, for Class II events in the case of m-type-II and DH-type-II bursts we have found no clear correlation between both flare and CMEs.     

Photometry and spectroscopy of Ⅱ Peg,IM Peg and UX Ari

V band photometry of three RS CVn stars, II Peg, IM Peg and UX Ari, is carried out to study the physical properties of these variables. We verified the significant and regular optical photometric variability to be present in all three stars. The strong photometric variability and emission of Hα and Ca II H K using high resolution optical spectroscopy with the Hanle Echelle Spectrograph(HESP),which operates in conjunction with the Himalayan Chandra Telescope, verify the strong chromospheric activity which is present in RS CVn stars. The photometric studies of II Peg, UX Ari and IM Peg were subjected to light curve analysis for spot parameters using a two-starspot model.     

Infrared radiometry of Uranus and Neptune at 21 and 32 μm

Radiometric measurement of Uranus and Neptune near 21 and 32 μm have been made with filters with widths of 8 and 5 μm, respectively. The observations at 21 μm, made on 1985 June 19 at the NASA Infrared telescope facility at Mauna Kea, Hawaii, were calibrated against α Boo and corresponded to brightness temperatures of 54.1 ± 0.3 K for Uranus and 58.1 ± 0.3 K for Neptune. The observations at 32 μm were made on three nights: 1983 May 1 and 1984 May 30 and 31, also at the NASA IRTF. Calibrated against the Jovian satellites Callisto (J4) and Ganymede (J3), these measurements corresponded to brightness temperatures of 51.8 ± 1.5 K for Uranus and 55.6 ± 1.2 K for Neptune. The observations are consistent with higher-resolution studies and confirm the general decrease of brightness temperatures going from about 20 to 30 μm.