Search

We present our analysis of new and archived observations of two candidate magnetic cataclysmic variables, namely 1RXS J174320.1-042953 and YY Sex. 1RXS J174320.1-042953 was observed in two distinctive high and low states where a phase shift was seen, which could be due to the changes in the shape, size, and (or) location of the accretion region. We find that its orbital X-ray modulations only persist in the soft (0.3-2.0 keV) energy band, which could be attributed to the photoelectric absorption in the accretion flow. The X-ray spectra exhibit a multi-temperature post-shock region where the hard X-rays are absorbed through a thick absorber with an equivalent hydrogen column of $\sim$7.5 $\times$ 10$^{23}$ cm$^{-2}$, which partially covers $\sim$56 per cent of the emission. No soft X-ray excess was found to be present; however, a soft X-ray emission with a blackbody temperature of $\sim$97 eV describes the spectra. Extensive TESS observations of YY Sex allow us to refine its orbital period to 1.5746 $\pm$ 0.0011 h. We did not find any signature of previously reported spin or beat periods in this system. Furthermore, our new polarimetric observations show clear circular polarization modulated on the orbital period only. Finally, both systems show strong Balmer and He II 4686 A$^\circ$ emission lines in the optical spectra, further indicative of their magnetic nature., 16 pages, 12 figures, and 7 tables (accepted for publication in MNRAS)

We present stellar variability towards the young open cluster NGC\,6823. Time series $V$- and $I$-band CCD photometry led to identification and characterization of 88 variable stars, of which only 14 have been previously recognized. We ascertain the membership of each variable with optical $UBVI$ and infrared photometry, and with Gaia EDR3 parallax and proper motion data. Seventy two variable stars are found to be cluster members, of which 25 are main sequence stars and 48 are pre-main-sequence stars. The probable cluster members collectively suggest an isochrone age of the cluster to be about 2~Myrs based on the GAIA photometry. With the color and magnitude, as well as the shape of the light curve, we have classified the main sequence variables into $\beta$~Cep, $\delta$~Scuti, slowly pulsating B type, and new class variables. Among the pre-main-sequence variables, eight are classical T Tauri variables, and four are Herbig Ae/Be objects, whereas the remaining belong to the weak-lined T Tauri population. The variable nature of 32 stars is validated with TESS light curves. Our work provides refined classification of variability of pre-main-sequence and main-sequence cluster members of the active star-forming complex, Sharpless\,86. Despite no strong evidence of the disk-locking mechanism in the present sample of TTSs, one TTS with larger $\Delta(I-K)$ is found to be slow rotator., Comment: 19 pages, 19 figures, accepted for publication in MNRAS

All available databases of molecular and gas-dust clouds in the Galaxy and other galaxies including their main properties such as position, angular and linear dimensions, distances, radial velocities, atomic and molecular hydrogen mass and column densities, temperatures, masses and others available are briefly described in the paper. An initial list of about 10 000 entries was condensed into a cross-identified all-sky catalogue containing molecular and gas-dust clouds. Some relationships were studied between main physical features of clouds. Finally, we prepared the complex observing program and address prospective work for gaining the gaps.

Preliminary results on observations of open clusters are presented. The project has been initiated in the framework of the Uzbek-Taiwan and Taiwan-Baltic collaboration, mainly to upgrade and make use of facilities at Maidanak Observatory. We present detailed, multiwavelength studies of the young cluster NGC 6823 and the associated complex nebulosity, to diagnose the young stellar population and star formation history in the region. In addition, 7 compact open clusters have been monitored for stellar variability. We show how observations like these could feasibly be used to look for exoplanet transit events. We also expect to join the Whole-Earth Telescope effort in future campaigns for asteroseismology.

The Maidanak One-meter Telescope (MOT) is a Ritchey-Chretien telescope by Carl Zeiss, located atop Maidanak in Uzbekistan, where site parameters indicate excellent atmospheric seeing conditions. An effort to computerize the MOT, jointly made by an Uzbek, Taiwanese and Baltic consortium, is expected to complete in 2005. Monitoring the variability of star clusters will be among the first scientific projects to be carried out. Equipped with sensitive CCD cameras, the MOT, with its middle-Asia geographic location, will be a desirable addition to the Whole Earth Telescope (WET) network. We describe the upgrade engineering and instrumentation of the telescope and how the system can be used in future campaigns.

We use the Yohkoh soft X-ray telescope (SXT) full-disk images made from 1993 to 2000 to manually identify X-ray bright points (XBPs). We also employ the National Solar Observatory (Kitt Peak) full-disk longitudinal magnetograms made between 1992 April and 2001 April and an automatic procedure to identify photospheric bipoles whose magnetic field strength is above 20 G, with a pole size (cross-section) between 5'' and 552, and with pole separation between 55 and 483. We use these data to study statistical properties of XBPs and photospheric bipoles during the declining phase of solar cycle 22 and the rising phase of cycle 23. The XBP number follows well-known anti-cycle variation. The average number of XBPs (~10 per disk image) remained approximately the same from 1993 to 1994. Beginning in 1995 it grew, reached a maximum around 1996 December (~50 XBPs per image), and then dropped back to pre-1995 levels in 1998. By contrast, the average number of photospheric bipoles remained approximately the same (~250 per disk image) between 1992 and 2001, despite sunspot activity changes from high (1992, cycle 22) to low (1996, solar minimum) and a return to high activity again in 2000 (solar maximum, cycle 23). Since we expect that a fraction of photospheric bipoles associated with X-ray bright points is independent of solar activity, we see this as a clear indication that the anti-cycle variation of XBP numbers is not real. Most likely, the variation in XBP numbers is the result of a change in the background brightness of the quiet-Sun corona, which is affected by the presence of active regions. On the other hand, annual latitudinal histograms of XBPs show an excess of coronal bright points at active region latitudes, contrary to the effect of changing background brightness. Photospheric bipoles show no enhancement of their distribution at active latitudes. We consider two alternative explanations for this inconsistency.

A brief overview for some aspects of astronomical investigations at Maidanak is given. An excursus is made into its history and past research. Future plans and their requirements are described.

The value of different forms of energy contained in TDC region as well as the structure and physical characteristics of star formation in the Taurus Dark Clouds are analyzed.

We present photoelectric observations in B and V, as well as spectroscopic observations of the 7.3 day period double-lined eclipsing binary V364 Lacertae. From the analysis of the light curves and the radial velocity curves we have determined the absolute dimensions of the components with high precision (1%). The masses for the primary and secondary are MA = 2.333 ± 0.015 M⊙ and MB = 2.296 ± 0.025 M⊙, respectively, and the radii are RA = 3.307 ± 0.038 R⊙ and RB = 2.985 ± 0.035 R⊙. We derive also effective temperatures of T = 8250 ± 150 K and T = 8500 ± 150 K, and projected rotational velocities of vA sin i = 45 ± 1 km s-1 and vB sin i = 15 ± 1 km s-1. Evolutionary tracks from current stellar evolution models are in good agreement with the observations for a system age of log t = 8.792 (6.2 × 108 yr) and for solar metallicity. Hints of a lower metallicity from spectroscopy and photometry appear to be ruled out by these models, but a definitive comparison must await a more accurate spectroscopic abundance determination. Analysis of all available eclipse timings along with our radial velocities of this moderately eccentric system (e = 0.2873 ± 0.0014) has revealed a small but significant motion of the line of apsides of = 0.00258 ± 0.00033 deg cycle-1, corresponding to an apsidal period of U = 2810 ± 360 yr. The contribution from general relativity effects is significant (~17%). A comparison with predictions from interior structure models shows the real stars to be less concentrated in mass than expected. Our measurements of the projected rotational velocities indicate that the primary star is essentially pseudosynchronized (synchronized at periastron), while the secondary is spinning 3 times more slowly and is not yet synchronized. Both the rotational status of the stars and the nonzero eccentricity of the orbit are consistent with the predictions from tidal theory, specifically for the radiative damping mechanism.

In this project, all available databases of molecular and gas-dust clouds in the Galaxy were cross-identi ed by taking into account available properties, including position, angular dimensions, velocity,density, temperature and mass. An initial list of about 7000 entries was condensed into a cross-identi edall-sky catalogue containing molecular and gas-dust clouds. Some relationships were studied between themain physical features of clouds. Finally, we prepared a complex observing program and address futurework for lling in the gaps.Key words: Galaxy: structure{Galaxy: disk { Galaxy: kinematics and dynamics - ISM: structure {ISM: clouds - radio lines: ISM - Catalogs1. INTRODUCTIONAt the present time the rapid progress both in in-strumentation and observing technology creates con-ditions for in-depth study of the interstellar medium(ISM) in the Galaxy as well as in other galaxies such asLMC, SMC, M31, M33, M51, M77, M83, M110, IC10,NGC185, NGC1569, NGC2976, NGC3077, NGC4038/9,NGC4214, NGC4449, NGC4605, etc. A signi cant frac-tion of the baryon mass of the ISM in the Galaxy andobserved galaxies is concentrated in the form of nebulaor clouds with molecular content in the densest parts(see, e.g., Draine 2011). Naturally, the molecular clouds(MoC) should be closely related to cold dust-gas clouds,particularly HI ones. They have to play a key-role inthe star forming processes as well as in the kinematicsand dynamics of the Galaxy on the whole. The abovereasons prove the importance of the census, systematicstudy and survey of MoC populations.2. CENSUS AND CATALOGTo attempt to nd solutions for at least some issues re-garding the physics and evolution of the MoC systemin our Galaxy and their impact on the dynamics andevolution of the Galaxy generally, and to extend theresults to MoC systems in other galaxies, we drafteda consolidated and uni ed composite all-sky catalog ofmolecular and dust-gas clouds that are observable fromthe Earth based on recent data. The preliminary re-sults were reported in Hojaev et al. (2013). Electronicdata bases and webservices such as VizieR, SIMBAD atCDS, 2MASS (Ks Atlas) and DSS as well as originalhttp://pkas.kas.orgpapers, reports and other publications were used. Thegeneral catalog has been divided into 3 sub-catalogs: 1)large and giant MoCs; 2) MoCs with moderate massesand sizes; 3) small MoCs including clumps and cores.All main catalogs and subcatalogs contain the coordi-nates, sizes, distances, masses and other physical pa-rameters (such as density, temperature, radial velocity,etc.) that are available for the di erent clouds. In ourGalaxy there are about 200 large and giant molecularclouds, more than 2500 smaller cold dark clouds (includ-ing clumps and cores this value exceeds approximately6000 objects) observed in the Solar vicinity and neigh-borhood up to 11 kpc away.3. ANALYSIS AND DISCUSSIONBased on the data in the combined catalog, we analysedphysical conditions in the MoCs and searched for re-lations between the physical parameters of the MoCsobserved. Due to the space limitations, we restrictourselves to discussing only a few. In Figure 1, wepresent a plot of the column density of molecular hy-drogen as a function of the cloud virial mass. The lin-ear t to the data is: N(H

The present study deals with the problem of the orbital and physical parameters' estimation of the ac- tive eclipsing binary WZ Cep based on the interpretation of its photometric observations. The B and V light curves (Homann 1984), as well as the new ones obtained at the Maidanak Observatory in the B, V and R passbands dur- ing 1995, are analysed and discussed. These two groups of light curves show large dierences in their shape and in the depth of the primary minimum. Homann's light curves show big asymmetry, especially conspicuous in the dierent height of the successive maxima. The new obser- vations give light curves that are almost symmetric having signicantly shallower primary minimum. They are analysed in the framework of the Roche computer model (Djura sevi c 1992a) by applying the inverse problem method (Djura sevi c 1992b) based on Marquardt's (1963) algorithm. The model is generalised for the case of an overcontact conguration also. To ex- plain these light curves asymmetries and variations, the model involved spotted regions on the components. The analysis shows that WZ Cep system is in a slight overcon- tact conguration and that best tting is achieved with spotted regions on the primary star (SpF5), with the tem- perature contrast between the spotted area and the sur- rounding photosphere being As = Ts=T1 0:70. The mass ratio was estimated at the valueq =m2=m1 0:33, based on the light-curve analysis. The basic parameters of the system and of the spot- ted areas are estimated for all foregoing mentioned light curves. The obtained solutions show that there are no sig- nicant variations of the system's basic parameters es- timated by analysing these two groups of very dierent light curves. Consequently, the main variations in the light curves can be explained by the change of the position and the size of the spotted areas on the primary.

A brief description of International Aerospace School (IASS) is given.

From a series of 4° objective-prism plates obtained on the 1 m Schmidt telescope of the Byurakan Astrophysical Observatory, 20 new Hα emission line stars were found. The intensity of Hα emission line was evaluated for these stars. An additional sample of probable Hα emission stars was also found. We present here details and some observational features of these stars. The total number of Hα emission line stars estimated for the surveyed area is about 80.

Some intra-day variable, compact extra-galactic radio sources show brightness temperatures severely exceeding 10^{12} K, the limit set by catastrophic inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation. The violation of the IC limit, possible under non-stationary conditions, would lead to IC avalanches in the soft-gamma-ray energy band during transient periods. For the first time, broadband signatures of possible IC catastrophes were searched for in S5 0716+71. A multifrequency observing campaign targetting S5 0716+71 was carried out in November 2003 under the framework of the European Network for the Investigation of Galactic nuclei through Multifrequency Analysis (ENIGMA) together with a campaign by the Whole Earth Blazar Telescope (WEBT), involving a pointing by the soft-gamma-ray satellite INTEGRAL, optical, near-infrared, sub-millimeter, millimeter, radio, and Very Long Baseline Array (VLBA) monitoring. S5 0716+71 was very bright at radio frequencies and in a rather faint optical state during the INTEGRAL pointing; significant inter-day and low intra-day variability was recorded in the radio regime, while typical fast variability features were observed in the optical band. No correlation was found between the radio and optical emission. The source was not detected by INTEGRAL, neither by the X-ray monitor JEM-X nor by the gamma-ray imager ISGRI, but upper limits to the source emission in the 3-200 keV energy band were estimated. A brightness temperature Tb>2.1x10^{14} K was inferred from the radio variability, but no corresponding signatures of IC avalanches were recorded at higher energies. The absence of IC-catastrophe signatures provides either a lower limit delta>8 to the Doppler factor affecting the radio emission or strong constraints for modelling of the Compton catastrophes in S5 0716+71., 15 pages, 3 EPS figures, 3 tables, to appear in A&A

The first attempt at a census of all molecular clouds (MoC) in the Milky Way observed to date is presented. The catalog of MoC includes all observed and estimated physical parameters. The data will be used to compute a model of the MoC system in the Galaxy.