Mid-infrared PL 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 = gamma(W1) - (2.381 +/- 0.097) log PF + (0.096 +/- 0.021)[Fe/H] and = gamma(W2)-(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 gamma(W1) and gamma(W2) of both relations: one based on a statistical-parallax analysis -- gamma(W1) = -0.829 +/- 0.093 and gamma(W2)=-0.776 +/- 0.093 and another, significantly brighter one, based on HST FGS trigonometric parallaxes -- gamma(W1, HST) =-1.150 +/- 0.077 and gamma(W2, 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 \citet{sollima} based on their derived period-metallicity-K-band luminosity relation whose zero point is tied to the HST trigonometric parallax of RR Lyrae itself (Delta DM0 = +0.04 and +0.06, respectively, with a scatter of only 0.06).Comment: 11 pages, 9 figures, 6 tables. Accepted for publication in MNRA

Effect of multiplicity of stellar encounters and the diffusion coefficients in the uniform stellar medium: no classical divergence ?

Agekyan lambda-factor that accounts for the effect of multiple distant encounters with large impact factors is used for the first time to compute the diffusion coefficients in the velocity space of a stellar system. It is shown that in this case the cumulative effect - the total contribution of distant encounters to the change in the velocity of the test star - is finite, and the logarithmic divergence inherent to the classical description disappears, as also was earlier noted by Kandrup (1981). At the same time, the formulas for the diffusion coefficients, as before, contain the logarithm of the ratio of two independent scale factors that fully characterize the state of the stellar system: the average interparticle distance and the impact parameter of a close encounter. However, the physical meaning of this factor is no longer associated with the classical logarithmic divergence.Comment: 12 pages, 4 figures; Submitted to MNRA

The Baade-Becker-Wesselink technique and the fundamental astrophysical parameters of 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.Comment: arXiv admin note: substantial text overlap with arXiv:1011.330

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

We applied the currently most comprehensive version of the statistical-parallax technique to derive 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. We take into account the variation of radial velocity dispersion with Galactocentric distance. The best description of the velocity field is provided by the model with constant radial and vertical velocity dispersions, $(\sigma U0, \sigma W0) \approx (9.4 \pm 0.9~, 5.9 \pm 0.8)~ km/s$. We compute flat Galactic rotation curve over the Galactocentric distance interval from 3 to 15 kpc and find the local circular rotation velocity to be $V_0 \approx (235-238)$~ km/s $\pm 7$~ km/s. We also determine the parameters of the four-armed spiral pattern (pitch angle $i \approx (-10.4 \pm 0.3)^\circ$ and the phase of the Sun $\chi_0 \approx (125 \pm 10) ^\circ$). The radial and tangential spiral perturbations are about $f_R \approx (-6.9 \pm 1.4)$~km/s, $f_\Theta \approx (+2.8 \pm 1.0$) ~km/s. The kinematic data yield a solar Galactocentric distance of $R_0 \approx (8.24 \pm 0.12)~kpc$. Based on rotation curve parameters and the asymmetric drift we Infer the exponential disk scale $H_D \approx (2.7 \pm 0.2)$ ~kpc under assumption of marginal stability of the intermediate-age disk, and finally we estimate the minimum local surface disk density, $\Sigma (R_0) > (26 \pm 3) ~ M_\odot pc^{-2}$.Comment: 16 pages, 8 figures, 5 table

RR Lyrae variables: visual and infrared luminosities, intrinsic colours, and kinematics

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 0.22 +/- 0.03. The corrected IR period-metallicity-luminosity relations are = -0.769 +0.088 [Fe/H]- 2.33 mathoprm log PF and = -0.825 + 0.088 [Fe/H] -2.33 mathoprm log PF, and the optical metallicity-luminosity relation, [Fe/H]-, is = +1.094 + 0.232 [Fe/H], with a standard error of +/- 0.089, implying an LMC distance modulus of 18.32 +/- 0.09, a solar Galactocentric distance of 7.73 +/- 0.36 kpc, and the M31 and M33 distance moduli of DM(M31) = 24.24 +/- 0.09 (D = 705 +/- 30 kpc) and DM(M33) = 24.36 +/- 0.09 (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.Comment: 17 pages, 5 tables, 11 figures. To be published in the Monthly Notices of the Royal Astronomical Societ

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 $R_V$ ~ 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.Comment: 17 pages, 14 figures, 2 tables. Accepted by MNRA

Globular clusters: absolute proper motions and Galactic orbits

We cross-match objects from several different astronomical catalogs to determine the absolute proper proper motions of stars within the 30-arcmin radius fields of 115 Milky-Way globular clusters with the accuracy of 1--2~mas/yr. The proper motions are based on positional data recovered from the USNO-B1, 2MASS, URAT1, ALLWISE, UCAC5, and GAIA DR1 surveys with up to 10 positions spanning an epoch difference of up to $\sim$~65~years, and reduced to GAIA DR1 TGAS frame using UCAC5 as the reference catalog. Cluster members are photometrically identified by selecting horizontal- and red-giant branch stars on color-magnitude diagrams, and the mean absolute proper motions of the clusters with a typical formal error of $\sim$~0.4~mas/yr are computed by averaging the proper motions of selected members. The inferred absolute proper motions of clusters are combined with available radial-velocity data and heliocentric distance estimates to compute the cluster orbits in terms of the Galactic potential models based on Miyamoto and Nagai disk, Hernquist spheroid, and modified isothermal dark-matter halo (axisymmetric model without a bar) and the same model + rotating Ferre's bar (non-axisymmetric). Five distant clusters have higher-than-escape velocities, most likely due to large errors of computed transversal velocities, whereas the computed orbits of all other clusters remain bound to the Galaxy. Unlike previously published results, we find the bar to affect substantially the orbits of most of the clusters, even those at large Galactocentric distances, bringing appreciable chaotization, especially in the portions of the orbits close to the Galactic center, and stretching out the orbits of some of the thick-disk clusters.Comment: 14 pages, 14 figures, 3 tables, to appear in Astrophysical Bulletin. Table 1 replaced by corrected version (Tables 2 and 3 are based on correct data and remain unchanged

The period-luminosity relation for Cepheids derived from multiphase temperature measurements and Cepheids kinematics based on GAIA DR2 data

Calibration of the period-luminosity relation (PLR) for Cepheids has always been one of the biggest goals of stellar astronomy. Among a considerable number of different approaches, the Baade-Becker-Wesselink (BBW) method stands in the foreground as one of the most universal and precise methods. We present a new realization of the BBW method which is considered to be the generalization of surface brightness (\citealt{Barnes+Evans+1976}) and \cite{Balona+1977} approaches first proposed by \cite{Rastorguev+Dambis+2010} and described in \cite{Paper1}. One of the main features of this method is using measured effective temperature variations to determine the main parameters of Cepheid, such as distance, radius, luminosity, colour excess, intrinsic colour. We apply this method to 45 Cepheids of Northern sky, for which multiphase temperature data are available. We take into account the effect of shock waves, whose presence in stellar atmosphere distorts the observational data and the calibrations used in this work. Within $0.0-0.87$ phase interval we derived PL relation $_I=-(2.67 \pm 0.17)\cdot logP - (1.58 \pm 0.16)$. It was used to calculate the distances, rotation curve and kinematical parameters of the sample of 435 Cepheids with GAIA DR2 proper motions.Comment: 8 pages, 6 figure

Herbig-Haro flows around BBWo 192E (GM 1-23) nebula

We studied a small comet-shape reflection nebula, located in the dark cloud SL 4 in the Vela Molecular Ridge cloud C, known as BBWo 192E (GM 1-23), and a young infrared cluster embedded into the nebula, for the evidences of recent star formation. We obtained the images of BBWo 192E in Halpha and [SII] lines and in SDSS i' with Blanco telescope at the Cerro Tololo Interamerican Observatory to discover new Herbig-Haro (HH) flows. 2MASS and WISE surveys were used for the search of the additional member stars of the cluster. We also studied proper motions and parallaxes of the cluster members with the aid of GAIA DR2. Five new groups containing at least 9 HH objects tracing several distinct outflows were revealed. A previously unreported reflection nebula and a number of probable outflow sources were found in the infrared range. The proper motions allowed selecting eight probable member stars in the visual range. Their parallaxes correspond to a mean distance 800 +/- 100 pc for this cluster. The bolometric luminosities of the brightest cluster members are 1010 L(sun) (IRAS 08513-4201,the strong source in the center of the cluster) and 2 to 6 L(sun) for the five other stars. The existence of the optical HH flows around the infrared cluster of YSOs suggests that star formation in this cloud is on-going around the more massive HAeBe star. By its morphology and other features this star-forming region is similar to the zone of star formation near CPM 19.Comment: 8 pages, 11 figure

New version of the Baade--Becker--Wesselink method based on multiphase effective temperature measurements of Cepheids

A new version of the Baade--Becker--Wesselink (hereafter BBW) method is proposed, based on direct spectroscopic measurements of effective temperatures of 45 northern Cepheids, made in different pulsating phases. By comparing the temperature estimates obtained from the calibration of effective temperature by normal color with real temperature measurements we were able not only to determine the color excess with an accuracy of 0.01 mag, but also to derive new color calibration of the effective temperature immediately for all available measurements with taking into account the differences in [Fe/H] and log g values: log Teff = 3.88 - 0.20 (B-V)o + 0.026 (B-V)o^2 + 0.009 log g - 0.010 (B-V)o log g - 0.051 [Fe/H] + 0.051 (B-V)o [Fe/H], which is accurate to about 1.1%. We also showed the complete identity of the two main versions of the BBW technique: surface brightness method proposed by Barnes and Evans (1976) and maximum likelyhood method of Balona (1977), refined later by Rastorguev and Dambis (2010).Comment: 7 pages, 2 figure