Institute of Astronomy of the Russian AS

Kabardino Balkaria, Russia

Institute of Astronomy of the Russian AS

Kabardino Balkaria, Russia
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Galazutdinov G.,Católica del Norte University | Galazutdinov G.,Pulkovo Observatory | Strobel A.,Nicolaus Copernicus University | Musaev F.A.,Institute of Astronomy of the Russian AS | And 2 more authors.
Publications of the Astronomical Society of the Pacific | Year: 2015

The rotation curve of the Galaxy is generally thought to be flat. However, using radial velocities from interstellar molecular clouds, as is common in rotation curve determination, seems to be incorrect and may lead to wrongly inferring that the rotation curve is flat indeed. Tests based on photometric and spectral observations of bright stars may also be misleading. The rotation tracers (OB stars) are affected by motions around local gravity centers and by pulsation effects seen in such early-type objects. To get rid of the latter involves extensive observing work. We introduce a method of studying the kinematics of the thin disk of our Galaxy outside the solar orbit in a way that avoids these problems. We propose a test based on observations of interstellar Ca II H and K lines that determines both radial velocities and distances. We implemented the test using stellar spectra of thin disk stars at Galactic longitudes of 135° and 180°. Using this method, we constructed the rotation curve of the thin disk of the Galaxy. The test leads to the obvious conclusion that the rotation curve of the thin gaseous galactic disk, represented by the Ca ii lines, is Keplerian outside the solar orbit rather than flat. © 2015. The Astronomical Society of the Pacific. All rights reserved.

Zacs L.,Vilnius University | Zacs L.,University of Latvia | Sperauskas J.,Vilnius University | Grankina A.,University of Latvia | And 4 more authors.
Astrophysical Journal | Year: 2015

Radial velocity measurements, BVRC photometry, and high-resolution spectroscopy in the wavelength region from blue to near-infrared are employed in order to clarify the evolutionary status of the carbon-enhanced metal-poor star HD 112869 with a unique ratio of carbon isotopes in the atmosphere. An LTE abundance analysis was carried out using the method of spectral synthesis and new self-consistent 1D atmospheric models. The radial velocity monitoring confirmed semiregular variations with a peak-to-peak amplitude of about 10 km and a dominating period of about 115 days. The light, color, and radial velocity variations are typical of the evolved pulsating stars. The atmosphere of HD 112869 appears to be less metal-poor than reported before, [Fe/H] = -2.3 ± 0.2 dex. Carbon-to-oxygen and carbon isotope ratios are found to be extremely high, C/O 12.6 and12C/13C ≳ 1500, respectively. The s-process elements yttrium and barium are not enhanced, but neodymium appears to be overabundant. The magnesium abundance seems to be lower than the average found for CEMP stars, [Mg/Fe] < +0.4 dex. HD 112869 could be a single low-mass halo star in the stage of asymptotic giant branch evolution. © 2015. The American Astronomical Society. All rights reserved.

Sperauskas J.,Vilnius University | Zacs L.,Vilnius University | Zacs L.,University of Latvia | Raudeliunas S.,Vilnius University | And 2 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Recent detection of a yellow supergiant star as a possible progenitor of a supernova has posed serious questions about our understanding of the evolution of massive stars. Aims. The spectroscopic binary star HD 50975 with an unseen hot secondary was studied in detail with the main goal of estimating fundamental parameters of both components and the binary system. Methods. A comprehensive analysis and modeling of collected long-term radial velocity measurements, photometric data, and spectra was performed to calculate orbital elements, atmospheric parameters, abundances, and luminosities. The spectrum in an ultraviolet region was studied to clarify the nature of an unseen companion star. Results. The orbital period was found to be 190.22 ± 0.01 days. The primary star (hereafter HD 50975A) is a yellow supergiant with an effective temperature Teff = 5900 ± 150 K and a surface gravity of log≠(g) = 1.4 ± 0.3 (cgs). The atmosphere of HD≠50975 A is slightly metal deficient relative to solar, [Fe/H] =-0.26 ± 0.06 dex. Abundances of Si and Ca are close to the scaled solar composition. The r-process element europium is enhanced, [Eu/H] = + 0.61 ± 0.07. The bolometric magnitude of the primary was estimated to be Mbol =-5.5 ± 0.3 mag and its mass to be 10.7 ± 2.0 M. The secondary (hereafter HD 50975B) is a hot star of spectral type B2 near ZAMS with an effective temperature of Teff 21000 K and a mass M 8.6 M. The distance between HD 50975A and B is about 370 R. The binary star is near a semi-detached configuration with a radius, RA 107 R, and a radius of Roche lobe of about 120 R for the primary star. © 2014 ESO.

Zacs L.,University of Latvia | Alksnis O.,University of Latvia | Barzdis A.,University of Latvia | Laure A.,University of Latvia | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

The results of local thermodynamic equilibrium (LTE) abundance analysis are presented for four red giants in the fields of open clusters NGC1545 and Tr2. The membership of HD27276, HD27292 and HD16068 was confirmed and the age of NGC1545 was updated: log age(yr) = 7.95. A mild deficiency of iron-group elements was found on average for NGC1545 and Tr2, [Fe/H]=-0.13 and -0.07 with an uncertainty of about 0.08dex. Oxygen and carbon are moderately depleted in all cluster giants, [O/Fe]=-0.23 ± 0.05dex and [C/Fe]=-0.56 ± 0.07dex on average. Nitrogen is enhanced, [N/Fe] values in range +0.4 to +1.2dex, and lithium depleted. Sodium is slightly enhanced, [Na/Fe]=+0.26 ± 0.04dex on average. Modified abundances are in agreement with the chemical evolution of intermediate-mass stars on the red giant branch. Some occasional radial velocity variations are probably due to convection in the atmospheres of luminous giants. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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