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Alexey S. Rastorguev

Bio: Alexey S. Rastorguev is an academic researcher from Moscow State University. The author has contributed to research in topics: Cepheid variable & Open cluster. The author has an hindex of 19, co-authored 83 publications receiving 1108 citations. Previous affiliations of Alexey S. Rastorguev include Sternberg Astronomical Institute.


Papers
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Journal ArticleDOI
TL;DR: In this article, the mean velocities of the RR Lyrae populations in the solar neighbourhood were determined using UCAC4 proper motions and WISE W1-band apparent magnitudes intensity-mean.
Abstract: We use UCAC4 proper motions and WISE W1-band apparent magnitudes intensity-mean for almost 400 field RR Lyrae variables to determine the parameters of the velocity distribution of Galactic RR Lyrae population and constrain the zero points of the metallicity- relation and those of the period-metallicity- -band and period-metallicity- -band luminosity relations via statistical parallax We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be (U0(Halo), V0(Halo), W0(Halo)) = (-7 +/- 9, -214 +/- 10, -10 +/- 6) km/s and (U0(Disc), V0(Disc), W0(Disc)) =(-13 +/- 7, -37 +/- 6, -17 +/- 4) km/s, respectively, and the corresponding components of the velocity-dispersion ellipsoids, (sigma VR(Halo), sigma Vphi(Halo), sigma Vtheta(Halo)) = (153 +/- 9, 101 +/- 6, 96 +/- 5) km/s and (sigma VR(Disc), sigma Vphi(Disc), sigma Vtheta(Disc)) = (46 +/- 7, 37 +/- 5, 27 +/- 4) km/s, respectively The fraction of thick-disc stars is estimated at 022 +/- 003 The corrected IR period-metallicity-luminosity relations are = -0769 +0088 [Fe/H]- 233 mathoprm log PF and = -0825 + 0088 [Fe/H] -233 mathoprm log PF, and the optical metallicity-luminosity relation, [Fe/H]- , is = +1094 + 0232 [Fe/H], with a standard error of +/- 0089, implying an LMC distance modulus of 1832 +/- 009, a solar Galactocentric distance of 773 +/- 036 kpc, and the M31 and M33 distance moduli of DM(M31) = 2424 +/- 009 (D = 705 +/- 30 kpc) and DM(M33) = 2436 +/- 009 (D = 745 +/- 31 kpc), respectively Extragalactic distances calibrated with our RR Lyrae star luminosity scale imply a Hubble constant of ~80 km/s/Mpc Our results suggest marginal prograde rotation for the population of halo RR Lyraes in the Milky Way

98 citations

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TL;DR: In this paper, the authors applied the statistical-parallax technique to derive the kinematical parameters of the maser sample with 136 sources, including the overall rotation of the Galactic disk and the spiral density-wave effects, and the variation of radial velocity dispersion with Galactocentric distance.
Abstract: We applied the currently most comprehensive version of the statistical-parallax technique to derive the kinematical parameters of the maser sample with 136 sources. Our kinematic model comprises the overall rotation of the Galactic disk and the spiral density-wave effects, and the variation of radial velocity dispersion with Galactocentric distance. The best description of the observed velocity field is provided by the model with constant radial and vertical velocity dispersions, (σU0, σW0) ≈ (9.4 ± 0.9, 5.9 ± 0.8) kms−1. The resulting Galactic rotation curve proved to be flat over the Galactocentric distance interval from 3 to 15 kpc and we find the local circular rotation velocity to be V 0 ≈ (235 − 238) ± 7 km s−1. We determine the parameters of the four-armed spiral pattern (pitch angle i ≈ −10. ◦ 4 ± 0.3◦ and the phase of the Sun χ0 ≈ 125◦ ± 10◦). The amplitudes of radial and tangential spiral perturbations are about f R ≈ −6.9 ± 1.4 km s−1, f Θ ≈ +2.8 ± 1.0 km s−1. The kinematic data yield a solar Galactocentric distance of R 0 ≈ 8.24 ± 0.12 kpc. Based on rotation curve parameters and the asymmetric drift we infer the exponential disk scale H D ≈ 2.7 ± 0.2 kpc assuming marginal stability of the intermediate-age disk, and also estimate the minimum local surface disk density, Σ(R 0) > 26 ± 3M ⊙ pc−2.

79 citations

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TL;DR: In this paper, the angular velocity of young objects was determined from stellar radial velocities alone by using the Lindblad relation, and good agreement between the inferred angular velocity and their calculations based on space velocity was obtained.
Abstract: were obtained: Ω0 =( 27.5 ± 1.4) km s −1 kpc −1 and A =( 17.1 ± 0.5) km s −1 kpc −1 for the short distance scale (R0 =7 .5 kpc); and Ω0 =( 26.6 ± 1.4) km s −1 kpc −1 and A =( 15.4 ± 0.5) km s −1 kpc −1 for the long distance scale (R0 =8 .5 kpc). We propose a new method for determining the angular velocity Ω0 from stellar radial velocities alone by using the Lindblad relation. Good agreement between the inferred Ω0 and our calculations based on space velocities suggests that the Lindblad relation holds throughout the entire sample volume. Our analysis of the heliocentric velocities for samples of young objects reveals noticeable streaming motions (with a velocity lag of ∼7 km s −1 relative to the LSR), whereas a direct computation of the perturbation amplitudes in terms of the linear density-wave theory yields a small amplitude for the tangential perturbations. c � 2002 MAIK “Nauka/Interperiodica”.

68 citations

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TL;DR: By directly comparing the photometric distances of Blaha and Humphreys (1989) to OB associations and field stars with the corresponding Hipparcos trigonometric parallaxes, this article showed that the BH distance scale is overestimated, on average, by 10-20%.
Abstract: By directly comparing the photometric distances of Blaha and Humphreys (1989) (BH) to OB associations and field stars with the corresponding Hipparcos trigonometric parallaxes, we show that the BH distance scale is overestimated, on average, by 10–20%. This result is independently corroborated by applying the rigorous statistical-parallax method and its simplified analog (finding a kinematically adjusted rotation-curve solution from radial velocities and proper motions) to a sample of OB associations. These two methods lead us to conclude that the BH distance scale for OB associations should be shrunk, on average, by 11±6 and 24±10%, respectively. Kinematical parameters have been determined for the system of OB associations: u0 = 8.2 ± 1.3 km s−1, v0 = 11.9 ± 1.1 km s−1, w0 = 9.5 ± 0.9 km s−1, σu = 8.2 ± 1.1 km s−1, σv = 5.8 ± 0.8 km s−1, σw = 5.0 ± 0.8 km s−1, Ω0 = 29.1 ± 1.0 km s−1 kpc−1, Ω0′ = −4.57 ± 0.20 km s−1 kpc−2, and Ω0″ = 1.32 ± 0.14 km s−1 kpc−3. The distance scale for OB associations reduced by 20% matches the short Cepheid distance scale (Berdnikov and Efremov 1985; Sitnik and Mel’nik 1996). Our results are a further argument for the short distance scale in the Universe.

59 citations


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TL;DR: Van Kampen as mentioned in this paper provides an extensive graduate-level introduction which is clear, cautious, interesting and readable, and could be expected to become an essential part of the library of every physical scientist concerned with problems involving fluctuations and stochastic processes.
Abstract: N G van Kampen 1981 Amsterdam: North-Holland xiv + 419 pp price Dfl 180 This is a book which, at a lower price, could be expected to become an essential part of the library of every physical scientist concerned with problems involving fluctuations and stochastic processes, as well as those who just enjoy a beautifully written book. It provides an extensive graduate-level introduction which is clear, cautious, interesting and readable.

3,647 citations

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TL;DR: In this paper, a stellar library for stellar population synthesis modelling is presented, which consists of 985 stars spanning a large range in atmospheric parameters and is obtained at the 2.5m Isaac Newton Telescope and cover the range λλ 3525-7500 A at 2.3 A spectral resolution.
Abstract: A new stellar library developed for stellar population synthesis modelling is presented. The library consists of 985 stars spanning a large range in atmospheric parameters. The spectra were obtained at the 2.5-m Isaac Newton Telescope and cover the range λλ 3525–7500 A at 2.3 A (full width at half-maximum) spectral resolution. The spectral resolution, spectral-type coverage, flux-calibration accuracy and number of stars represent a substantial improvement over previous libraries used in population-synthesis models.

1,396 citations

Journal ArticleDOI
TL;DR: In this article, the authors used the Very Long Baseline Array and the Japanese VLBI Exploration of Radio Astronomy project to measure trigonometric parallaxes and proper motions of masers found in high-mass star-forming regions across the Milky Way.
Abstract: We are using the Very Long Baseline Array and the Japanese VLBI Exploration of Radio Astronomy project to measure trigonometric parallaxes and proper motions of masers found in high-mass star-forming regions across the Milky Way. Early results from 18 sources locate several spiral arms. The Perseus spiral arm has a pitch angle of 16 degrees +/- 3 degrees, which favors four rather than two spiral arms for the Galaxy. Combining positions, distances, proper motions, and radial velocities yields complete three-dimensional kinematic information. We find that star-forming regions on average are orbiting the Galaxy approximate to 15 km s(-1) slower than expected for circular orbits. By fitting the measurements to a model of the Galaxy, we estimate the distance to the Galactic center R(0) = 8.4 +/- 0.6 kpc and a circular rotation speed Theta(0) = 254 +/- 16 km s(-1). The ratio Theta(0)/R(0) can be determined to higher accuracy than either parameter individually, and we find it to be 30.3 +/- 0.9 km s(-1) kpc(-1), in good agreement with the angular rotation rate determined from the proper motion of Sgr A*. The data favor a rotation curve for the Galaxy that is nearly flat or slightly rising with Galactocentric distance. Kinematic distances are generally too large, sometimes by factors greater than 2; they can be brought into better agreement with the trigonometric parallaxes by increasing Theta(0)/R(0) from the IAU recommended value of 25.9 km s(-1) kpc(-1) to a value near 30 km s(-1) kpc(-1). We offer a "revised" prescription for calculating kinematic distances and their uncertainties, as well as a new approach for defining Galactic coordinates. Finally, our estimates of Theta(0) and Theta(0)/R(0), when coupled with direct estimates of R(0), provide evidence that the rotation curve of the Milky Way is similar to that of the Andromeda galaxy, suggesting that the dark matter halos of these two dominant Local Group galaxy are comparably massive.

1,167 citations

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TL;DR: In this paper, the authors presented synthetic spectral energy distributions (SEDs) for single-age, single-metallicity stellar populations (SSPs) covering the full optical spectral range at moderately high resolution [full width at half-maximum (FWHM) = 2.3A].
Abstract: We present synthetic spectral energy distributions (SEDs) for single-age, single-metallicity stellar populations (SSPs) covering the full optical spectral range at moderately high resolution [full width at half-maximum (FWHM) = 2.3A]. These SEDs constitute our base models, as they combine scaled-solar isochrones with an empirical stellar spectral library [Medium resolution INT Library of Empirical Spectra (MILES)], which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients, not just on the stellar spectra, but also on extensive photometric libraries, which are used to determine the transformations from the theoretical parameters of the isochrones to observational quantities. The unprecedented stellar parameter coverage of the MILES stellar library allowed us to safely extend our optical SSP SED predictions from intermediate- to very-old-age regimes and the metallicity coverage of the SSPs from super-solar to [M/H] = -2.3. SSPs with such low metallicities are particularly useful for globular cluster studies. We have computed SSP SEDs for a suite of initial mass function shapes and slopes. We provide a quantitative analysis of the dependence of the synthesized SSP SEDs on the (in)complete coverage of the stellar parameter space in the input library that not only shows that our models are of higher quality than those of other works, but also in which range of SSP parameters our models are reliable. The SSP SEDs are a useful tool to perform the analysis of stellar populations in a very flexible manner. Observed spectra can be studied by means of full spectrum fitting or by using line indices. For the latter, we propose a new line index system to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. Apart from constant resolution as a function of wavelength, the system is also based on flux-calibrated spectra. Data can be analysed at three different resolutions: 5, 8.4 and 14A (FWHM), which are appropriate for studying globular cluster, low- and intermediate-mass galaxies, and massive galaxies, respectively. Furthermore, we provide polynomials to transform current Lick/IDS line index measurements to the new system. We provide line index tables in the new system for various popular samples of Galactic globular clusters and galaxies. We apply the models to various stellar clusters and galaxies with high-quality spectra, for which independent studies are available, obtaining excellent results. Finally, we designed a web page from which not only these models and stellar libraries can be downloaded but which also provides a suite of on-line tools to facilitate the handling and transformation of the spectra.

867 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented a 0.8-5 μm spectral library of 210 cool stars observed at a resolving power of R ≡ λ/Δλ ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii.
Abstract: We present a 0.8-5 μm spectral library of 210 cool stars observed at a resolving power of R ≡ λ/Δλ ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The stars have well-established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample not only contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S stars. In contrast to some other spectral libraries, the continuum shape of the spectra is measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using the Two Micron All Sky Survey photometry. Potential uses of the library include studying the physics of cool stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically obscured regions of galaxies and synthetic photometry. The library is available in digital form from the IRTF Web site.

795 citations