arXiv subjects

A. K. Dambis

Publications and source records attributed to A. K. Dambis.

22 records · Page 2Linked to original sources

arXiv2009

Kinematics of OB-associations and the new reduction of the Hipparcos data

The proper motions of OB-associations computed using the old (Hipparcos 1997} and new (van Leeuwen 2007) reductions of the Hipparcos data are in a good agreement with each other. The Galactic rotation curve derived from an analysis of line-of-sight velocities and proper motions of OB-associations is almost flat in the 3-kpc neighborhood of the Sun. The angular rotation velocity at the solar distance is Omega_0=31 +/-1 km s-1 kpc-1. The standard deviation of the velocities of OB-associations from the rotation curve is sigma=7.2 km s-1. The distance scale for OB associations (Blaha & Humphreys 1989) should be shortened by 10-20%. The residual velocities of OB-associations calculated for the new and old reductions differ, on average, by 3.5 km s-1. The mean residual velocities of OB-associations in the stellar-gas complexes depend only slightly on the data reduction employed.

astro-ph.GA↗

arXiv2008

Periodic Pattern in the Residual-Velocity Field of OB Associations

An analysis of the residual-velocity field of OB associations within 3 kpc of the Sun has revealed periodic variations in the radial residual velocities along the Galactic radius vector with a typical scale length of lambda=2.0(+/-0.2) kpc and a mean amplitude of fR=7(+/-1) km/s. The fact that the radial residual velocities of almost all OB-associations in rich stellar-gas complexes are directed toward the Galactic center suggests that the solar neighborhood under consideration is within the corotation radius. The azimuthal-velocity field exhibits a distinct periodic pattern in the region 0<l<180 degrees, where the mean azimuthal-velocity amplitude is ft=6(+/-2) km/s. There is no periodic pattern of the azimuthal-velocity field in the region 180<l<360 degrees. The locations of the Cygnus arm, as well as the Perseus arm, inferred from an analysis of the radial- and azimuthal-velocity fields coincide. The periodic patterns of the residual-velocity fields of Cepheids and OB associations share many common features.

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arXiv2003

Age Dependence of the Vertical Distribution of Young Open Clusters: Implications for Local Mass Density, Stellar Evolution, and Star Formation

The ages of 203 open clusters from the list of Dambis (1999) are computed in terms of the evolutionary tracks of Pols et al. (1998) with and without the allowance for convective overshooting. The vertical scaleheight of the cluster layer at Galactocentric distances R_0-1 kpc < R_g< R_0+ 1 kpc varies nonmonotonically with age, exhibiting a wavelike pattern similar to the one earlier found for the Cepheid population (Joeveer 1974), with a period of P_Z = 74 +/- 2 Myr and P_Z = 92 +/- 2 Myr if cluster ages are computed in terms of evolutionary models without and with overshooting, respectively. The period of vertical oscillations can be reconciled with the known local mass density only if cluster ages are computed with no or just mild overshooting: the overshooting-based ages imply a local mass density of rho = 0.075 +/- 0.003 M_Sun/pc^3, which is incompatibe with the recent Hipparcos-based estimate of rho = 0.102 M_Sun/pc^3 (Holmberg and Flynn 2000). Our results imply a maximum local dark-mass density of rho_DM <= 0.027 M_Sun/pc^3. At the time of their formation open clusters have, on the average, excess vertical kinetic energy and as a population are not in virial equilibrium; moreover, their initial vertical coordinates (at the time of birth) are strongly and positively correlated with initial vertical velocities (r = 0.81 +/-0.08), thus favoring a scenario where star formation in the disk is triggered by some massive objects falling onto the Galactic plane.

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arXiv2003

The Kinematics and Zero Point of the log P -- Relation for Galactic Field RR Lyrae Variables via Statistical Parallax

The kinematical parameters of the local field RR Lyrae population and the zero point of the log P-- relation for these variables are inferred by applying the statistical parallax (maximum-likelihood) technique to a sample of 182 RR Lyraes with known periods, radial-velocities, metallicities, K-band photometry, and absolute proper motions on the ICRS system. The K-band magnitudes were adopted from the list of Fernley et al. (1998) and the 2MASS Second Incremental Data Release. The parameters of the velocity distribution are found to be (U_0,V_0,W_0) = (-10 +/- 10, -51 +/- 8, -14 +/- 5) km/s, (sigma_U, sigma_V, sigma_W) = (62 +/- 10, 45 +/- 8, 28 +/- 6) km/s and (U_0,V_0,W_0) = (-23 +/- 13, -213 +/- 12, -5 +/- 8) km/s, (sigma_U, sigma_V, sigma_W) = (157 +/- 12, 98 +/- 8, 91 +/- 7) km/s for the thick-disk (41 stars) and halo (141 stars) objects, respectively. The zero point of the infrared PL relation of Jones et al. (1992) (based on the results obtained using the Baade-Wesselink method) is confirmed: we find = -2.33 log P_F-0.82 +/- 0.12 compared to = -2.33 log P_F-0.88 as inferred by Jones et al. (1992). A conversion of the resulting log P- relation to V-band luminosities yields the metallicity-luminosity relation = +1.04 + 0.14 [Fe/H] +/- 0.11. Our results imply a solar Galactocentric distance of R_0 = 7.6 +/- 0.4 kpc and an LMC distance modulus of DM_LMC = 18.18 +/- 0.12 (cluster RR Lyraes) or DM_LMC = 18.11 +/- 0.12 (field RR Lyraes), thereby favoring the so-called short distance scale.

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