Crimean Astrophysical Observatory

Crimea, Ukraine

Crimean Astrophysical Observatory

Crimea, Ukraine
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Grankin K.N.,Crimean Astrophysical Observatory
Astronomy Letters | Year: 2016

Long-term homogeneous photometry for 35 classical T Tauri stars (CTTS) in the Taurus–Auriga star-forming region has been analyzed. Reliable effective temperatures, interstellar extinctions, luminosities, radii, masses, and ages have been determined for the CTTS. The physical parameters and evolutionary status of 35 CTTS from this work and 34 weak-line T Tauri stars (WTTS) from previous studies have been compared. The luminosities, radii, and rotation periods of low-mass (0.3–1.1 M⊙) CTTS are shown to be, on average, greater than those of low-mass WTTS, in good agreement with the evolutionary status of these two subgroups. The mean age of the younger subgroup of WTTS from our sample (2.3 Myr) essentially coincides with the mean duration of the protoplanetary disk accretion phase (2.3 Myr) for a representative sample of low-mass stars in seven young stellar clusters. The accretion disk dissipation time scale for the younger subgroup of CTTS (<4 Myr) in the Taurus–Auriga star-forming region is shown to be no greater than 0.4 Myr, in good agreement with the short protoplanetary disk dissipation time scale that is predicted by present-day protoplanetary disk evolution models. © 2016, Pleiades Publishing, Inc.


The X-ray emission of the kiloparsec-scale jets of core-dominant quasars is usually interpreted as inverse Compton scattering on the cosmic microwave background (CMB) emission (Sample I). By analogy with the situation on parsec scales, ultrarelativistic motion along a jet oriented at a small angle to the line of sight is usually invoked to explain the X-ray emission while also satisfying the condition of equipartition between the energies associated with the relativistic particles and the magnetic field on kiloparsec scales. This leads to an increase in the energy flux of the CMB radiation in the rest frame of the kiloparsec-scale jets. Consequently, the intensity of the CMB radiation is enhanced to the level required for detectable X-ray emission. This suggests that kiloparsec jets of quasars with similar extents and radio flux densities that are not detected in the X-ray (Sample II) could have subrelativistic speeds and larger angles to the line of sight, due to deceleration and bending of the jet between parsec and kiloparsec scales. This suggests the possible presence of differences in the distributions of the difference between the position angle for the parsec-scale and kiloparsec-scale jets for these two groups of quasars; this is not confirmed by a statistical analysis of the data for Samples I and II. It is deduced that most of the sources considered exhibit bending of their jets by less than about 1.5 times the angle of the parsec-scale jet to the line of sight. This suggests that the X-ray emission is generated by other mechanisms that there is no equipartition. © 2016, Pleiades Publishing, Ltd.


Kotov V.A.,Crimean Astrophysical Observatory
Advances in Space Research | Year: 2015

Measurements of the general magnetic field of the Sun seen as a star were performed over last 45 years by the CrAO and five other observatories (1968-2012, nearly 23 thousand daily strengths B). Analysis of the B time series showed that the most substantial long-term period of the field variation is the Hale's cycle 22 years, which cannot be explained by dynamo theory. It reveals a saw-edged profile, indicating perhaps a cosmic origin of the cycle. © 2014 COSPAR.


Kotov V.A.,Crimean Astrophysical Observatory
Advances in Space Research | Year: 2015

The 41-year measurements of the Doppler effect of the photosphere performed at the Crimean Astrophysical Observatory, discovered two periods of global oscillations of the Sun: 9600.606(12) s and 9597.929(15) s. Their beat period, 398.4(2.9) d, well agrees with a synodic orbital period of Jupiter, PJ = 398.9 d, raising a new problem for solar physics, cosmogony and cosmology. A hypothesis is advanced that the PJ beating of the Sun is induced by gravitation of Jupiter, revolving in a privileged reference system "the Sun - the Earth". © 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.


Tarasova T.N.,Crimean Astrophysical Observatory
Astronomy Reports | Year: 2013

Spectral variations of the nova V2468 Cyg were studied over 1.5 years following the beginning of its outburst, during its smooth fading and the star's rebrightenings. Following the rebrightening on March 25, 2008, the profiles of H I lines had changed, from a two-component structure with peaks at -220 and 670 km/s to a four-component structure with peaks at -640, -260, 255, and 620 km/s. The profiles of [N II] 5755 Å, [O III] 5007 Å, He II 4686 Å, and [Fe VII] 6086 Å lines varied throughout the interval of our observations. During rebrightenings, the lines profiles changed and the line intensities significantly decreased. The width of the [Fe VII] 6086 Å profile varied, in addition to its shape and intensity; this profile differed from the profiles of other lines during the nebular phase. Estimates of chemical-element abundances in the nova's envelope indicate enhanced abundances of nitrogen and oxygen, compared to the Sun, and solar abundances of neon and argon. The helium abundance was somewhat higher than the solar value. The mass of the ejected envelope is estimated to be 5 × 10-5M⊙. © 2013 Pleiades Publishing, Ltd.


Grankin K.N.,Crimean Astrophysical Observatory
Astronomy Letters | Year: 2013

We have analyzed a sample of 74 magnetically active stars toward the Taurus-Auriga starforming region. Based on accurate data on their basic physical parameters obtained from original photometric observations and published data on their proper motions, X-ray luminosities, and equivalent widths of the Hα and Li lines, we have refined the evolutionary status of these objects. We show that 50 objects are young stars with ages of 1-40 Myr and belong to the Taurus-Auriga star-forming region. Other 20 objects have a controversial evolutionary status and can belong to both Taurus-Auriga starforming region and the Gould Belt. The remaining four objects with ages of 70-100 Myr belong to the zero-age main sequence. We have analyzed the relationship between the rotation period, mass, and age for 50 magnetically active stars. The change in the angular momentum of the sample stars within the first 40 Myr of their evolution has been investigated. An active star-protoplanetary disk interaction is shown to occur on a time scale from 0.7 to 10Myr. © 2013 Pleiades Publishing, Ltd.


Grankin K.N.,Crimean Astrophysical Observatory
Astronomy Letters | Year: 2013

We have analyzed homogeneous long-term photometric observations of 28 well-known weakline T Tauri stars (WTTS) and 60 WTTS candidates detected by the ROSAT observatory toward the Taurus-Auriga star-forming region. We show that 22 known WTTS and 39 WTTS candidates exhibit periodic light variations that are attributable to the phenomenon of spotted rotational modulation. The rotation periods of these spotted stars lie within the range from 0. 5 to 10 days. Significant differences between the long-term photometric behaviors of known WTTS and WTTS candidates have been found. We have calculated accurate luminosities, radii, masses, and ages for 74 stars. About 33% of the sample of WTTS candidates have ages younger than 10 Myr. The mean distance to 24 WTTS candidates with reliable estimates of their radii is shown to be 143 ± 26 pc. This is in excellent agreement with the adopted distance to the Taurus-Auriga star-forming region. © 2013 Pleiades Publishing, Ltd.


Lovkaya M.N.,Crimean Astrophysical Observatory
Astronomy Reports | Year: 2013

The fine temporal structure of two flares observed on the red-dwarf flare star AD Leo on February 4, 2003 with the 1.25-m telescope of the Crimean Astrophysical Observatory in a rapidphotometry mode is studied. One flare lasted approximately 5 min and another was longer than 8 min. The amplitudes in the U band were 1.65m and 1.76m. A detailed color analysis shows that the flare parameters at the maximum brightnesses corresponded to blackbody radiation with temperatures of approximately 14 000 and 13 000 K, enabling the monitoring of temperature - the rapid cooling of flare plasma near the flare maxima-for the first time. During 1.5 and 3.5 min at the maxima, the flares radiated as blackbodies, but these behaved as optically thick plasmas in the Balmer continuum on the second half of the descending branches. At the end of the first flare, the plasma became optically thin in the Balmer continuum; the final stage of the second flare was not observed. The flare areas at the luminosity maxima were 2.1 × 1018 and 3.0×1018 cm2 in a blackbody approximation, or 0.07%and 0.11%of the visible stellar disk. The occurrence of quasi-periodic brightness pulsations during red-dwarf flares on time scales of approximately ten seconds is confirmed. © 2013 Pleiades Publishing, Ltd.


Tarasov A.E.,Crimean Astrophysical Observatory
Astronomy Letters | Year: 2016

Based on high-resolution spectra taken near the He I 6678 Å line for the massive binary system 103 Tau, we have detected a weak absorption component belonging to the binary’s secondary component. We have measured the radial velocities of both components, improved the previously known orbital parameters, and determined the new ones. The binary has an orbital period Porb = 58.305d, an orbital eccentricity e = 0.277, a radial velocity semi-amplitude of the bright component KA = 44.8 km s−1, and a component mass ratio MA/MB = 1.77. The absence of photometric variability and the estimates of physical parameters for the primary component suggest that the binary most likely has a considerable inclination of the orbital plane to the observer, i ≈ 50°−60°. In this case, the secondary component is probably a normal dwarf of spectral type B5–B8. Based on the spectra taken near the Hα line, we have studied the variability of the emission profile. It is shown to be formed in the Roche lobe of the secondary component, but no traces of active mass exchange in the binary have been detected. © 2016, Pleiades Publishing, Inc.


Tkachenko A.,Thuringer Landessternwarte TLS | Lehmann H.,Thuringer Landessternwarte TLS | Mkrtichian D.,Crimean Astrophysical Observatory
Astronomical Journal | Year: 2010

TWDra is a well-known short-period Algol-type system. It belongs to the class of oEA stars (Algol-type systems with a δScuti-like oscillating primary component). We investigate the TWDra system based on high-resolution spectra taken in 2007 and in 2008 to derive precise stellar and system parameters and to check for phases of active mass transfer. We derived a precise orbital solution and the extracted spectra of the stellar components of the TWDra system. The analysis of the spectrum of the primary shows that it is a normal A5-type star with a chemical composition close to solar. By means of the Shellspec07-inverse program we calculated precise stellar and system parameters from the composite spectra. All results agree with those from the most recent photometric study. During both epochs of observations, the system can be well modeled without counting for mass transfer effects, assuming a spherical configuration of the primary and a Roche-lobe filling secondary. Thus, we conclude that the star was in quiet phases during both epochs of observations. © 2010 The American Astronomical Society.

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