Marina V. Zabolotskikh

Kinematic parameters of young subsystems and the galactic rotation curve

We analyze the space velocities of blue supergiants, long-period Cepheids, and young open star clusters (OSCs), as well as the H I and H II radial-velocity fields by the maximum-likelihood method. The distance scales of the objects are matched both by comparing the first derivatives of the angular velocity Ω′ determined separately from radial velocities and proper motions and by the statistical-parallax method. The former method yields a short distance scale (for R0=7.5 kpc, the assumed distances should be increased by 4%), whereas the latter method yields a long distance scale (for R0=8.5 kpc, the assumed distances should be increased by 16%). We cannot choose between these two methods. Similarly, the distance scale of blue supergiants should be shortened by 9% and lengthened by 3%, respectively. The H II distance scale is matched with the distance scale of Cepheids and OSCs by comparing the derivatives Ω′ determined for H II from radial velocities and for Cepheids and OSCs from space velocities. As a result, the distances to H II regions should be increased by 5% in the short distance scale. We constructed the Galactic rotation curve in the Galactocentric distance range 2–14 kpc from the radial velocities of all objects with allowance for the difference between the residual-velocity distributions. The axial ratio of the Cepheid+OSC velocity ellipsoid is well described by the Lindblad relation, while σu≈σv for gas. The following rotation-curve parameters 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.

Mid-infrared period–luminosity relations for globular cluster RR Lyrae

The period - metallicity - WISE W1- and W2-band luminosity relations are derived for RR Lyrae stars based on WISE epoch photometry for 360 and 275 stars in 15 and 9 Galactic globular clusters, respectively. Our final relations have the form =γW1 -(2.381±0.097)log PF + (0.096±0.021)[Fe/H] and =γW2 -(2.269±0.127)log PF + (0.108±0.021)[Fe/H], where [Fe/H] values are on the scale of Carretta et al. (2009). We obtained two appreciably discrepant estimates for the zero points γW1 and γW2 of both relations: one based on a statistical-parallax analysis – γW1=-0.829±0.093 and γW2=-0.776±0.093 and another, significantly brighter one, based on HST FGS trigonometric parallaxes – γW1,HST=-1.150±0.077and γW2,HST=1.105±0.077. The period-metallicity-luminosity relations in the two bands yield highly consistent distance moduli for the calibrator clusters and the distance moduli computed using the W1- and W2-band relations with the HST zero points agree well with those computed by Sollima et al. (2006) based on their derived period-metallicity-Kband luminosity relation whose zero point is tied to the HST trigonometric parallax of RR Lyrae itself (�DM0 = 0.04 and 0.06, respectively, with a scatter of only 0.06).

Galactic masers: Kinematics, spiral structure and the disk dynamic state

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 V0 ≈ (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 fR ≈ −6.9 ± 1.4 km s−1, fΘ ≈ +2.8 ± 1.0 km s−1. The kinematic data yield a solar Galactocentric distance of R0 ≈ 8.24 ± 0.12 kpc. Based on rotation curve parameters and the asymmetric drift we infer the exponential disk scale HD ≈ 2.7 ± 0.2 kpc assuming marginal stability of the intermediate-age disk, and also estimate the minimum local surface disk density, Σ(R0) > 26 ± 3M⊙ pc−2.

Photometric study of open clusters Berkeley 96, Berkeley 97, King 12, NGC 7261, NGC 7296 and NGC 7788

We present BV RcIc CCD photometry in the fields of six Galactic open clusters toward the Perseus spiral arm. These data, complemented with J, H, and KS magnitudes from 2MASS, have been used to determine the ages, distances, and colour excesses E(B V ) for these clusters: 40 Myr, 3180 +440 380 pc, 0.54±0.03 mag (Berkeley 96); 250 Myr, 2410 +220 200 pc, 0.77±0.06 mag (Berkeley 97); 70 Myr, 2490 +180 170 pc, 0.51±0.05 mag (King 12); 160 Myr, 2830 +160 150 pc, 0.88 ± 0.09 mag (NGC 7261); 280 Myr, 2450 +190 170 pc, 0.24 ± 0.03 mag (NGC 7296); and 160 Myr, 2750 +220 210 pc, 0.49 ± 0.02 mag (NGC 7788). We found gaps in the mass function of clusters Be 97, King 12, and NGC 7788 in the mass intervals of [1.3–1.5], [1.4–1.6], and [1.5–1.7] solar masses, respectively.

Star-forming regions at the periphery of the supershell surrounding the Cyg OB1 association – I. The star cluster vdB 130 and its ambient gas and dust medium

Stellar population and the interstellar gas-dust medium in the vicinity of the open star cluster vdB 130 are analysed using optical observations taken with the 6-m telescope of the SAO RAS and the 125-cm telescope of the SAI MSU along with the data of Spitzer and Herschel. Based on proper motions and BV and JHKs 2MASS photometric data, we select additional 36 stars as probable cluster members. Some stars in vdB 130 are classified as B stars. Our estimates of minimum colour excess, apparent distance modulus and the distance are consistent with young age (from 5 to 10 Myrs) of the cluster vdB 130. We suppose the large deviations from the conventional extinction law in the cluster direction, with

The Baade–Becker–Wesselink technique and the fundamental astrophysical parameters of Cepheids

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MID-INFRARED PERIOD-METALLICITY-LUMINOSITY RELATIONS AND KINEMATICS OF RR LYRAE VARIABLES

~ 4 - 5. The cluster vdB 130 appears to be physically related to the supershell around Cyg OB1, a cometary CO cloud, ionized gas, and regions of infrared emission. There are a few regions of bright mid-infrared emission in the vicinity of vdB 130. The largest of them is also visible on H-alpha and [SII] emission maps. We suggest that the infrared blobs that coincide in projection with the head of the molecular cloud are HII regions, excited by the cluster B-stars. Some signatures of a shock front are identified between these IR-bright regions.

A search for new open clusters hosting cepheids

The BBW method remains one of most demanded tool to derive full set of Cepheid astrophysical parameters. Surface brightness version of the BBW technique was preferentially used during last decades to calculate Cepheid radii and to improve PLC relations. Its implementation requires a priory knowledge of Cepheid reddening value. We propose a new version of the Baade--Becker--Wesselink technique, which allows one to independently determine the colour excess and the intrinsic colour of a radially pulsating star, in addition to its radius, luminosity, and distance. It is considered to be a generalization of the Balona light curve modelling approach. The method also allows the function F(CI_0) = BC + 10 log Teff for the class of pulsating stars considered to be calibrated. We apply this technique to a number of classical Cepheids with very accurate light and radial-velocity curves. The new technique can also be applied to other pulsating variables, e.g. RR Lyraes. We discuss also possible dependence of the projection factor on the pulsation phase.

Kinematic Properties of Young Subsystems and the Rotation Curve of our Galaxy

We use ALLWISE data release W1- and W2-band epoch photometry collected by the Wide-Field Infrared Survey Explorer (WISE) to determine slopes of the period-luminosity relations for RR Lyrae stars in 15 globular clusters in the corresponding bands. We further combine these results with V- and K-band photometry of Galactic eld RR Lyrae stars to determine the metallicity slopes of the log P F -[Fe/H]-M K , log P F - [Fe/H]-M W1 , and log P F - [Fe/H]- M W2 period-metallicity-luminosity relations. We infer the zero points of these relations and determine the kinematical parameters of thick-disk and halo RR Lyraes via statistical parallax, and estimate the RR Lyrae-based distances to 18 Local-Group galaxies including the center of the Milky Way.

Proper-Motion Based Kinematics Study of Galactic RR Lyraes

Abstract We analyze yet-unknown genetic links between open star clusters (OSCs) and galactic Cepheids and report the results of the new search for Cepheids – probable OSC members. A sample of 25% of the stars from a new catalog by Berdnikov (published in Melnik et al. 2015) which lists 674 Cepheids with reliable parameters was investigated. Based on photometric and kinematic data, we selected 17 Cepheids that are likely to be related to star clusters, four of which being new OSCs discovered by us.