S. Bilir

Local stellar kinematics from RAVE data – I. Local standard of rest

We analyze a sample of 82850 stars from the RAVE survey, with well-determined velocities and stellar parameters, to isolate a sample of 18026 high-probability thin-disc dwarfs within 600 pc of the Sun. We derive space motions for these stars, and deduce the solar space velocity with respect to the Local Standard of Rest. The peculiar solar

A catalogue of chromospherically active binary stars (third edition)

The catalogue of chromospherically active binaries (CABs) has been revised and updated. With 203 new identifications, the number of CAB stars is increased to 409. The catalogue is available in electronic format where each system has a number of lines (suborders) with a unique order number. The columns contain data of limited numbers of selected cross references, comments to explain peculiarities and the position of the binarity in case it belongs to a multiple system, classical identifications (RS Canum Venaticorum, BY Draconis), brightness and colours, photometric and spectroscopic data, a description of emission features (Ca II H and K, Hα, ultraviolet, infrared), X-ray luminosity, radio flux, physical quantities and orbital information, where each basic entry is referenced so users can go to the original sources.

Transformations between 2MASS, SDSS and BVRI photometric systems: bridging the near-infrared and optical

We present colour transformations for the conversion of the Two Micron All Sky Survey (2MASS) photometric system to the Johnson–Cousins UBVRI system and further into the Sloan Digital Sky Survey (SDSS) ugriz system. We have taken SDSS gri magnitudes of stars measured with the 2.5-m telescope from SDSS Data Release 5 (DR5), and BVRI and JHKs magnitudes from Stetson’s catalogue and Cutri et al., respectively. We matched thousands of stars in the three photometric systems by their coordinates and obtained a homogeneous sample of 825 stars by the following constraints, which are not used in previous transformations: (1) the data are dereddened, (2) giants are omitted and (3) the sample stars selected are of the highest quality. We give metallicity, population type and transformations dependent on two colours. The transformations provide absolute magnitude and distance determinations which can be used in space density evaluations at short distances where some or all of the SDSS ugriz magnitudes are saturated. The combination of these densities with those evaluated at larger distances using SDSS ugriz photometry will supply accurate Galactic model parameters, particularly the local space densities for each population.

A different approach for the estimation of Galactic model parameters

We estimated the Galactic model parameters by means of a new approach based on the comparison of the observed space density functions per absolute magnitude interval with a unique density law for each population individually, and via the procedure in situ for the field SA 114 (α = 22 h 40 m 00 s , δ = 00 o 00 ′ 00 ′′ ; l = 68 o .15, b = 48 o .38; 4.239 square-degree; epoch 2000). The separation of stars into different populations has been carried out by their spatial distribution. The new approach reveals that model parameters are absolute magnitude dependent. The scale height for thin disk decreases monotonously from absolutely bright (M(g ′ )=5) to absolutely faint (M(g ′ ) = 13) stars in a range 265-495 pc, but there is a discontunity at the absolute magnitude M(g ′ ) = 10 where the squared secans hiperbolicus density law replaces the exponential one. The range of the scale-height for thick disk, dominant in the absolute magnitude interval 5 < M(g ′ ) � 9, is less: 805-970 pc. The local space density for thick disk relative to thin disk decreases from 9.5% to 5.2% when one goes from the absolutely bright to faint magnitudes. Halo is dominant in three absolute magnitude intervals, i.e. 5 < M(g ′ ) � 6, 6 < M(g ′ ) � 7, and 7 < M(g ′ ) � 8 and the axial ratio for this component is almost the same for these intervals where c/a � 0.7. The same holds for the local space density relative to the thin disk with range (0.02-0.15)%. The model parameters estimated by comparison of the observed space density functions combined for three populations per absolute magnitude interval with the combined density laws agree with the cited values in the literature. Also each parameter is equal to at least one of the corresponding parameters estimated for different absolute magnitude intervals by the new approach. We argue that the most appropriate Galactic model parameters are those, that are magnitude dependent.

Estimation of Galactic model parameters in high latitudes with 2MASS

Context. In general, studies focused on the Milky Ways structure show a range of values when deriving different Galactic parameters, such as radial scalelengths, vertical scaleheights, or local space densities. Those values are also dependent on the Galactic coordinates under consideration for the corresponding analysis, as a direct consequence of observing a structure (our Galaxy) that is far from being as smooth and well-behaved as models usually treat. Aims. In this paper, we try to find any dependence of the Galactic structural parameters on the Galactic longitude for either the thin disc or the thick disc of the Milky Way that would indicate possible inhomogeneities or asymmetries in those Galactic components. Methods. Galactic model parameters have been estimated for a set of 36 high-latitude fields with Two Micron All Sky Survey (2MASS) photometry. Possible variations with the Galactic longitude in either the scaleheight and the local space density of these components are explored. Results. Galactic model parameters for the different fields show that they are Galactic longitude-dependent. The thick disc scaleheight changes from ∼800 pc at 150° < l < 230° to ∼1050 pc at |l| < 30°. A plausible explanation for this finding might be the effect of the flare on this Galactic component, which changes the scaleheight (h z ) with Galactocentric distance (R) following the approximate law: h z (R) = (940 ± 20) x [1 - (0.12 ± 0.02)(R - R ⊙ )]. The effect of the flare is more prominent in some lines of sight than in others, producing the observed changes in the parameters with the Galactic coordinates used to derive them.

Dynamical evolution of active detached binaries on the log Jo–log M diagram and contact binary formation

Orbital angular momentum (OAM, J o ), systemic mass (M) and orbital period (P) distributions of chromospherically active binaries (CAB) and W Ursae Majoris (W UMa) systems were investigated. The diagrams of log J o -logP, logM-logP and log J o -log M were formed from 119 CAB and 102 W UMa stars. The log J o -log M diagram is found to be most meaningful in demonstrating dynamical evolution of binary star orbits. A slightly curved borderline (contact border) separating the detached and the contact systems was discovered on the log J o -log M diagram. Since the orbital size (a) and period (P) of binaries are determined by their current J o , M and mass ratio, q, the rates of OAM loss (d log J o /dt) and mass loss (d log M/dt) are primary parameters to determine the direction and the speed of the dynamical evolution. A detached system becomes a eontact system if its own dynamical evolution enables it to pass the contact border on the log J o -log M diagram. The evolution of q for a mass-losing detached system is unknown unless the mass-loss rate for each component is known. Assuming q is constant in the first approximation and using the mean decreasing rates of Jo and M from the kinematical ages of CAB stars, it has been predicted that 11, 23 and 39 per cent of current CAB stars would transform to W UMa systems if their nuclear evolution permits them to live 2, 4 and 6 Gyr, respectively.

Local stellar kinematics from RAVE data – II. Radial metallicity gradient

We investigate radial metallicity gradients for a sample of dwarf stars from the RAdial Velocity Experiment (RAVE) Data Release 3 (DR3). We select a total of approximately 17 000 F-type and G-type dwarfs, using a selection of colour, log g and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thick or thin disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We additionally subsample by colour, to provide samples biased toward young thin-disc and older thin-disc stars. We derive a metallicity gradient as a function of Galactocentric radial distance, i.e. d[M/H]/dRm =− 0.051 ± 0.005 dex kpc −1 , for the youngest sample, F-type stars with vertical orbital eccentricities ev ≤ 0.04. Samples biased toward older thin-disc stars show systematically shallower abundance gradients.

Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution

The kinematics of 237 chromospherically active binaries (CABs) were studied. The sample is heterogeneous with different orbits and physically different components from F to M spectral-type main-sequence stars to G and K giants and supergiants. The computed U, V, W space velocities indicate that the sample is also heterogeneous in velocity space. That is, both kinematically younger and older systems exist among the non-evolved main sequence and the evolved binaries containing giants and subgiants. The kinematically young (0.95 Gyr) subsample (N = 95), which is formed according to the kinematical criteria of moving groups, was compared with the rest (N = 142) of the sample (3.86 Gyr) to investigate any observational clues of binary evolution. Comparing the orbital period histograms between the younger and older subsamples, evidence was found supporting the finding of Demircan that the CABs lose mass (and angular momentum) and evolve towards shorter orbital periods. The evidence of mass loss is noticeable on the histograms of the total mass (M h + M c ), which is compared between the younger (only N = 53 systems available) and older subsamples (only N = 66 systems available). The orbital period decrease during binary evolution is found to be clearly indicated by the kinematical ages of 6.69, 5.19 and 3.02 Gyr which were found in the subsamples according to the period ranges of log P ≤ 0.8, 0.8 < log P ≤ 1.7 and 1.7 < log P ≤ 3, respectively, among the binaries in the older subsample.

Estimation of Galactic Model Parameters in High Latitudes with SDSS

We estimated the Galactic model parameters for a set of 36 high-latitude fields included in the currently available Data Release 5 (DR 5) of the Sloan Digital Sky Survey (SDSS), to explore their possible variation with the Galactic longitude. The thick disc scaleheight moves from ~550 pc at 120 < l < 150° to ~720 pc at 250 < l < 290°, while the thin disc scaleheight is as large as ~195 pc in the anticenter direction and ~15% lower at |l| < 30°. Finally, the axis ratio (c/a) of the halo changes from a mean value of ~0.55 in the two first quadrants of the Galaxy to ~0.70 at 190 < l < 300°. For the halo, the reason for the dependence of the model parameters on the Galactic longitude arises from the well known asymmetric structure of this component. However, the variation of the model parameters of the thin and thick discs with Galactic longitude originates from the gravitational effect of the Galactic long bar. Moreover, the excess of stars in quadrant I (quadrant III) over quadrant IV (quadrant II) is in agreement with this scenario.

Mass loss and orbital period decrease in detached chromospherically active binaries

The secular evolution of the orbital angular momentum (OAM), the systemic mass (M = M1+M2) and the orbital period of 114 chromospherically active binaries (CABs) were investigated after determining the kinematical ages of the sub-samples which were set according to OAM bins. OAMs, systemic masses and orbital periods were shown to be decreasing by the kinematical ages. The first order decreasing rates of OAM, systemic mass and orbital period have been determined as u J = 3.48× 10 10 yr 1 per systemic OAM, u M = 1.30× 10 10 yr 1 per systemic mass and u P = 3.96 × 10 10 yr 1 per orbital period respectively from the kinematical ages. The ratio of dlog J/dlog M = 2.68, which were derived from the kinematics of the present sample, implies that there must be a mechanism which amplifies the angular momentum loss ¯ A = 2.68 times in comparison to isotropic angular momentum loss of hypothetical isotropic wind from the components. It has been shown that simple isotropic mass loss from the surface of a component or both components would increase the orbital period.