|
Hasmik Andreasyan, T. Yu. Magakian, T. A. Movsessian Kateryna Andrych, I.L.Andronov, K.D.Andrych, V.V.Breus, L.L.Chinarova, S.V.Kolesnikov, L.S.Kudashkina, V.I.Marsakova, M.G.Tkachenko Odessa Mechnikov National University, Ukraine MONITORING OF VARIABLE STARS AT SMALL TELESCOPES. SOME HIGHLIGHTS The use of small telescopes allows studies of time behavior of selected objects. In our group, the monitoring has started 40 years ago from the magnetic cataclysmic variable AM Herculis, the prototype of “polars”. Since 1989, the polarimetric monitoring of some magnetic objects (AM Her, QQ Vul, BY Cam et al.) was carried out using the 2.6m Shain telescope. A huge international observational campaign “Inter-Longitude Astronomy” was organized, based on transient working groups. A CCD monitoring is carried out for a group of most interesting variable stars: classical polars (including eclipsing polars), asynchronous polars, intermediate polars, outbursting intermediate polars, magnetic and non-magnetic dwarf novae, nova-like systems, “spotted” and “not spotted” eclipsing binaries, including “Extreme Direct Impactors”, pulsating stars of different types: DSct, HADS, RR, RV, SR, M. More than 1900 objects have been analyzed. These objects exhibit dozens of type! s of mono- and multi- component variability according to a variety of combinations of the properties of the components and possible accretion stream/column, or a hot spot/line. Naira Azatyan Byurakan Astrophysical Observatory, Armenia Investigation of the stellar content in the IRAS 05168+3634 star-forming region I report investigation results of a cluster in the star-forming region around IRAS 05168+3634 (also known as Mol 9) using a photometric data of UKIDSS-DR6 JHK and Spitzer GLIMPSE [3.6], [4.5] μm surveys. It has been used multi-color criteria to identify the candidate of young stellar objects (YSOs). We used color-magnitude diagram and K luminosity function (KLF) for determining the basic parameters of stellar objects (spectral classes, masses, ages). For study of YSOs associated with MSX sources the radiative transfer models are used. Based on color-color and color-magnitude diagrams, we identified a rich population of embedded YSO candidates with infrared excesses (Class 0/I and Class II), associated with the IRAS 05168+3634 region. Out of 83/87 revealed pre-main sequence (PMS) objects 36.8% (32 PMS) and 35.6% (31 PMS) of all members in IRAS 05168+3634 star-forming region are classified as Class I and Class II stars, respectively. The local distribution of identified young stellar objects frequently shows elongation and subclustering. The color-magnitude diagrams of the cluster suggest very young stellar population. According to the SED fitting tool, the mass and luminosity of the central source IRAS 05168+3634 associated with a MSX G170.6575−00.2685 source, is estimated of 8 Msun and 10^3-10^4 Lsun, respectively. We construct the K luminosity function (KLF) of the cluster and we find that the slope of the KLF of IRAS 05168+3634 region is lower than the typical values reported for young embedded clusters. According to the value of the slope of KLF, the age of the IRAS 05168+3634 star-forming region can be estimated as 0.3 Myr. Grigor Broutian, V. V. Mkhitarian Byurakan Astrophysical Observatory, Armenia On The History of the Discovery of Stellar Associations Andrei Dambis, A.M.Mel'nik Sternberg Astronomical Institute of M.V.Lomonosov Moscow State University, Russia Kinematics of OB-associations in Gaia epoch We use stellar proper motions from the TGAS catalog to study the kinematics of OB-associations. The TGAS proper motions of OB-associations generally agree well with the Hipparcos proper motions. The parameters of the Galactic rotation curve obtained with TGAS and Hipparcos proper motions agree within the errors. The average one-dimensional velocity dispersion inside 18 OB-associations with more than 10 TGAS stars is sigma_v=3.9 km s-1, which is considerably smaller, by a factor of 0.4, than the velocity dispersions derived from Hipparcos data. The effective contribution from orbital motions of binary OB-stars into the velocity dispersion sigma_v inside OB-associations is sigma_b=1.2 km s-1. The median virial and stellar masses of OB-associations are equal to 7.1 10^5 and 9.0 10^3 Ms, respectively. Thus OB-associations must be unbound objects provided they do not include a lot of dense gas. The median star-formation efficiency is epsilon=2.1 percent. Nearly one third of stars of OB-associations must lie outside their tidal radius. We found that the Per OB1 and Car OB1 associations are expanding with the expansion started in a small region of 11--27 pc 7--10 Myr ago. The average expansion velocity is 6.3 km s-1. Serguei Dodonov, S. Kotov, T. Movsessian, M. Gevorgian Special Astrophysical Observatory, Russia 1-m Schmidt Telescope : New Observational Possibilities. During several years we worked under reconstruction 1-m Schmidt Telescope of the Byurakan Observatory (Armenia). This well-known Telescope (Markarian Survey was developed on it) up today remains one of the largest Schmidt cameras in the world. A new control system and modern driving motors were installed on the Telescope. A CCD detector (4k x 4k Apogee 16M CCD with liquid cooling system, RON ~ 11.1 e) and a filter wheel were installed in the Telescope focus. As a result we obtained near 1 sq. degree field of view with 0.868 arcsec/pixel image scale. The filter set contain 20 medium band (FWHM = 250 A, permanently cover 4000 – 9000 A) and 5 broad band (u,g,r,i,z SDSS) filters. First light on renewed Telescope was obtained in October 2015, since this time we begun several observational programs on the Telescope. In report I will describe current status and some results obtained on 1-m Schmidt Telescope in deep broad band photometry of the outer parts of the galaxies, search for the AGNs with low selection effects with medium band filters to AB=23m. Vardan Elbakyan, E. Vorobyov Research Institute of Physics, Southern Federal University, Russia Formation of giant planets at tens-of-AU distances Planets form in the disks of gas and dust around young stars. One of possible scenarios for giant planet formation is gravitational fragmentation of protostellar disks. Here we show that massive gaseous fragments that have formed in the outer regions of a protostellar disk may become perturbed by other fragments and quickly migrate toward the central star (during ~ few 104 years). However, some fragments halt their migration at a distance of a few tens of AU, while losing a substantial fraction of their outer envelope via tidal torques and keeping only a dense and hot nucleus. At the same time, the central temperature of these truncated fragments may exceed the hydrogen dissociation temperature (~2000 K) and the central region of the fragment can collapse into a gas giant planet, which provides a potential explanation for the existence of giant planets at distances of tens of AU. Vladimir Grinin Pulkovo Observatory, St. Petersburg, Russia "Long-Livers" among Pre-Main-Seaquence Stars. The case of RZ Psc Maryam Habibi, S. Gillessen, F. Martins, F. Eisenhauer, P. M. Plewa, O. Pfuhl, E. George, J. Dexter, I. Waisberg, T. Ott, S. von Fellenberg, M. Bauboeck, A. Jimenez-Rosales, and R. Genzel Max Planck Institute for extraterrestrial Physics, Germany TWELVE YEARS OF SPECTROSCOPIC MONITORING IN THE GALACTIC CENTER: THE CLOSEST LOOK AT S-STARS NEAR THE BLACK HOLE We study the young S-stars within a distance of 0.04 pc from the supermassive black hole in the center of our Galaxy. Given how inhospitable the region is for star formation, their presence is more puzzling the younger we estimate their ages. In this study, we analyse the result of 12 years of high resolution spectroscopy within the central arcsecond of the Galactic Center (GC). Using deep H-band spectra, we show that these stars must be high surface gravity (dwarf) stars. We compare these deep spectra to detailed model atmospheres to infer the stellar parameters. All the available observables are then compared to stellar evolution models to constrain the final stellar parameters of the stars including their evolutionary stages and masses. The inferred stellar parameters imply a spectral type of B0-B3V for these stars. The masses lie within 8–14Msun. We derive an age of 6.6 {+3.4,-4.7} Myr for the star S2, which is compatible with the age of the clockwise rotating young stellar disk in the GC. We estimate the age of all other studied S-stars to be less than 15 Myr, which are compatible with the age of S2 within the uncertainties. The relatively low ages for all S-stars we have investigated favor a scenario in which the stars formed in a local disk rather than the field-binary-disruption scenario throughout a longer period of time. Valeri Hambaryan Astrophysical Institute of Friedrich-Schiller-University Jena, Germany Identifying birth places of high-velocity stars We have searched for the high-velocity and isolated neutron stars that encountered in the past with a stellar cluster/association closer than 20 pc. For this purpose, we took more than 216 000 stars with the measured proper motions and trigonometric parallaxes from the Gaia DR1 catalogue and their radial velocities from the RAVE5 catalogue. We used a full gravitational potential of the Galaxy to calculate the motion of a stellar cluster/association and a high-velocity star from their current positions to the proximity epoch. For this calculations we used a numerical integration in rectangular, Galactocentric coordinates. We used a covariance matrices of the astrometric data for each star to estimate the accuracy of the obtained proximity distance and epoch. To this aim we used a Monte Carlo method, replaced each star with 10 000 of its simulations and studied the distribution of their individual close passages near a stellar cluster/association. In addition we investigated a neutron star/runaway star pairs very likely both ejected during the same supernova event. Hayk Harutyunyan Byurakan Astrophysical Observatory, Armenia On some consequences of Universe expansion on smaller scales Gayane Kostandyan, N. Mauron, K. Gigoyan Byurakan Astrophysical Observatory Armenia NEW ASYMPTOTIC GIANT BRANCH CARBON STARS IN THE GALACTIC HALO. We first present eight confirmed or candidate carbon ( C ) stars found mainly from objective-prism plates. By using the Catalina database of light curves, we find that all these stars are pulsating, allowing a distance to be estimated through the K - band Period – Luminosity ( PL ) relation. This relation does not depend on spectral type ( M or C ) and distances are reliable even for C candidates. Seven stars are more than 10 kpc from the galactic plane, suggesting they do not belong to the galactic disk. We also find one star located at about 180 kpc from the Sun, being one of the most distant star in the Galaxy. Many of these new C stars are relatively blue. Some comments are also provided on seven other known halo carbon stars for which either a pulsation period is obtained, or because they were not included in previous works on halo C stars. Tigran Magakian Byurakan Astrophysical Observatory, Armenia FUors and EXors: Attempt of revised classification Powerful eruptions of middle and low mass stars attracted attention from 70ies. The classes of FUors, EXors and some others were identified. The criteria for classification were selected; however, they should be carefully used. An important feature of these stars is their extreme rarity, which makes the classification even more difficult. We present the revised list of FUors, FUor-like stars and EXors, based on the existing references and our own observations. The features of these stars, especially related to collimated mass outflows, are discussed. Some part of stars are considered as “intermediate” objects. Several other unusual objects in star forming regions are discussed: V1318 Cyg S (mixed EXor/Uxor?), CPM 19 (strong infrared source, which unexpectedly became visible in optical range), V350 Cep (extremely active T Tau type star with long-lasting eruption). Tigran Movsessian, T.Magakian Byurakan Observatory Armenia Jets from young stellar objects Elena Nikoghosyan, N. Azatyan Byurakan Astrophysical Observatory, Armenia Variability of Ha emission of PMS stellar objects in IC 348 Based on the observations made on the 2.6 m telescope of the Byurakan Observatory between 2009 and 2016, in the young star cluster IC 348 the variability of Ha emission of PMS stars was studied. The observations were carried out by using the slit-less method. Data processing shows, that among 127 stellar objects located in the field of our observation 90 (70%) have the significant variability. The 20 of them change their evolutionary classes (CTTau/WTTau) and show the largest value of Lx/Lbol. When these objects are excluded, the correlation between the evolutionary phases according Ha emission and the infrared excess reaches almost 100%. The variable CTTau have a much larger accretion rate than non-variable ones. Elena Nikoghosyan, N. Azatyan Byurakan Astrophysical Observatory, Armenia New eruptive variable in the massive star-forming region associated with IRAS 18507+0121 We report the discovery of a strong outburst of the embedded young stellar object (YSO) UKIDSS-J185318.36+012454.5, located in the star-forming region associated with IRAS 18507+0121 and the ultra-compact H II region GAL 034.4+00.23. Using archival photometric data and images, we determined the amplitude and the epoch of the outburst as well as the evolution stage and the basic parameters of the object. According to the near- and mid-infrared colors and spectral energy distribution, we classify the object as an intermediate mass YSO with Class 0/I evolution stage. The outburst apparently started between May 2003 and April 2004. The amplitude of the outburst is at least 5:0 mag in Ks band. The summation of the photometric and spectral data does not allow classifying UKIDSS-J185318.36+012454.5 as an FU Orionis (FUor) or EX Orionis (EXor) object. We can consider it as an eruptive variable with mixed characteristics or as an MNor type object. Hovhannes Pikichyan Byurakan Astrophysical Observatory: Armenia Inverse problem of the statistical determination of the total number, luminosity function and the variability features for the T Tauri stars in the stellar aggregates Alexey Rastorguev , Zabolotskikh M.V., Utkin N.D. Lomonosov Moscow State University, Russia Kinematics of young population Using the most complete version of the statistical parallax method, the kinematics of the population of galactic masers and the cepheids of the Galaxy have been studied. The rotation curve of the Galaxy in the galactocentric distance interval from 3 to 15 kpc is constructed and the main kinematic parameters of the disk are determined. At the same time, the parameters of the four-arm spiral pattern are determined. Based on the new proper motions taken from GAIA TGAS release and precise radial velocities, the distance scale of cepheids was corrected and their kinematic parameters are also determined. It is shown that the distances of cepheids with periods of less than 9 days are systematically underestimated, which can be explained by the presence of unidentified overtone cepheids in the sample. In general, kinematical parameters of cepheids and maser sources are very similar. Iraj Safaei, Sadollah Nasiri Geydari, Hosein Safari University of Kashan, Iran It is well-known that increasing the resolving power in spectroscopy, the detectable wavelength range decreases. As a result of this fact also the flux of the photons in each band decreases and this poses the main limitation on the spectroscopy of stars with small telescopes. In the present work the rather small 16inch diameter telescope of the University of Kashan Observatory (UKO) has been used to measure stellar rotational velocities with the hydrogen-beta line. Due to the limitation in the total flux received from the stars, we had to measure the rotation speed of the brightest ones of the fast-moving star: Altair, Alderamin, Regulus, Alkaid, Denebola Hereby we compared the rotational Doppler broadening with measurements by other methods and show that our results are in the acceptable range. In our calculations thermal Doppler broadening only had a slight effect, and we ignored it together with other possible effects for now. Evgeni Semkov, S.Peneva, S.Ibryamov, A.Mutafov Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, Bulgaria Long-term optical photometric monitoring in the star formation regions Photometric variability is a basic feature of the pre-main sequence objects. Using new optical photometric data and data from photographic plate archives, we try to construct the long-term light curves of the variable stars of the types: FU Ori, EX Lup, UX Ori, T Tau etc. Meanwhile the received photometric observations are used for the discovery of new young variable stars in the fields of star formation. In order to collect the necessary photometric data, we mainly use the observation facilities of the Rozhen National Astronomical Observatory (Bulgaria) - three telescopes designed for optical observations. Most suitable for long-term photometric study are the plate archives of the big Schmidt telescopes that have a large field of view, as the 105/150 cm Schmidt telescope at Kiso Observatory (Japan), the 67/92 cm Schmidt telescope at Asiago Observatory (Italy), the Palomar Schmidt telescope and others. Our results show that usually the young variable stars indicate various types of variability: outbursts with different amplitudes and duration, eclipses from circumstellar clumps of matter or discs, periodic and non-periodic variability in brightness. In many cases, two or more types of variability can be observed on the same object. In this report we present our results from photometric studies of the young stellar objects in two areas of star formation: the North America (NGC 7000) and Pelican Nebula (IC 5070) complex and the reflection nebula NGC 7129. Particular attention is paid to the following objects: V2493 Cyg, V2492 Cyg, FHO 27, FNO 29, V521 Cyg, V1716 Cyg, V1929 Cyg, V350 Cep and V391 Cep. Ararat Yeghikyan Byurakan Astrophysical Observatory, Armenia On the effectivity of particle acceleration under WR starwind-ISM postshock conditions An attempt is made to calculate the differential intensity of the energetic protons accelerated to energies of 1-100 MeV by the WR-shock wave. The estimate for the intensity yields a value 3-4 orders of magnitude higher than the mean galactic intensity value. The proposed one-parameter formula for estimating the intensity at 1 MeV, when applied to the heliosphere, shows good agreement with the Voyager-1 data, to within a factor of less than 2. |