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Register a new userMetallicity and absolute magnitude calibrations for F-G type main-sequence stars in the Gaia era
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In this study, photometric metallicity and absolute magnitude calibrations were derived using F-G spectral type main-sequence stars in the Solar neighbourhood with precise spectroscopic, photometric and Gaia astrometric data for UBV photometry. The sample consists of 504 main-sequence stars covering the temperature, surface gravity and colour index intervals $5300<T_{eff} < 7300$ K, $log g > 4$ (cgs) and $0.3<(B-V)_0<0.8$ mag, respectively. Stars with relative trigonometric parallax errors $sigma_{pi}/pileq0.01$ were preferred from Gaia DR2 data for the estimation of their $M_V$ absolute magnitudes. In order to obtain calibrations, $(U-B)_0$ and $(B-V)_0$ colour indices of stars were preferred and a multi-variable second order equation was used. Calibrations are valid for main-sequence stars in the metallicity and absolute magnitude ranges $-2<{rm [Fe/H]}<0.5$ dex and $2.5<M_V<6$ mag, respectively. The mean value and standard deviation of the differences between original and estimated values for the metal abundance and absolute magnitude are $langleDelta {rm[Fe/H]}rangle=0.00pm0.11$ dex and $langleDelta M_V rangle=0.00pm0.22$ mag, respectively. In this work, it has been shown that more precise iron abundance and absolute magnitude values were obtained with the new calibrations, compared to previous calibrations in the literature.
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We estimated iron and metallicity gradients in the radial and vertical directions with the F and G type dwarfs taken from the RAVE DR4 database. The sample defined by the constraints Zmax<=825 pc and ep<=0.10 consists of stars with metal abundances and space velocity components agreeable with the thin-disc stars. The radial iron and metallicity gradients estimated for the vertical distance intervals 0<Zmax<=500 and 500<Zmax<=800 pc are d[Fe/H]/dRm=-0.083(0.030) and d[Fe/H]/dRm=-0.048(0.037 )dex/kpc; and d[M/H]/dRm=-0.063(0.011) and d[M/H]/dRm=-0.028(0.057) dex/kpc, respectively, where Rm is the mean Galactocentric distance. The iron and metallicity gradients for less number of stars at further vertical distances, 800<Zmax<=1500 pc, are mostly positive. Compatible iron and metallicity gradients could be estimated with guiding radius (Rg) for the same vertical distance intervals 0<Zmax<=500 and 500<Zmax<=800 pc, i.e. d[Fe/H]/dRg=-0.083(0.030) and d[Fe/H]/dRg=-0.065(0.039) dex/kpc; d[M/H]/dRg=-0.062(0.018) and d[M/H]/dRg=-0.055(0.045) dex/kpc. F and G type dwarfs on elongated orbits show a complicated radial iron and metallicity gradient distribution in different vertical distance intervals. Significant radial iron and metallicity gradients could be derived neither for the sub-sample stars with Rm<=8 kpc, nor for the ones at larger distances, Rm>8 kpc. The range of the iron and metallicity abundance for the F and G type dwarfs on elongated orbits, [-0.13, -0.01), is similar to the thin-disc stars, while at least half of their space velocity components agree better with those of the thick-disc stars. The vertical iron gradients estimated for the F and G type dwarfs on circular orbits are d[Fe/H]/dZmax=-0.176(0.039) dex/kpc and d[Fe/H]/dZmax=-0.119(0.036) dex/kpc for the intervals Zmax<= 825 and Zmax<=1500 pc, respectively.
Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed. 31 W UMa stars, which have the most accurate parallaxes ($sigma_{pi}/pi<0.15$) which are neither associated with a photometric tertiary nor with evidence of a visual companion, were selected for re-calibrating the Period--Luminosity--Color (PLC) relation of W UMa stars. Using the Lutz--Kelker (LK) bias corrected (most probable) parallaxes, periods ($0.26< P(day)< 0.87$), and colors (0.04<$(B-V)_{0}$<1.28) of the 31 selected W UMa, the PLC relation have been revised and re-calibrated. The difference between the old (revised but not bias corrected) and the new (LK bias corrected) relations are almost negligible in predicting the distances of W UMa stars up to about 100 parsecs. But, it increases and may become intolerable as distances of stars increase. Additionally, using $(J-H)_{0}$ and $(H-K_{s})_{0}$ colors from 2MASS (Two Micron All Sky Survey) data, a PLC relation working with infrared data was derived. It can be used with infrared colors in the range $-0.01<(J-H)_{0}<0.58$, and $-0.10<(H-K_{s})_{0}<0.18$. Despite {em 2MASS} data are single epoch observations, which are not guaranteed at maximum brightness of the W UMa stars, the established relation has been found surprisingly consistent and reliable in predicting LK corrected distances of W UMa stars.
Lutz-Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main-sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% ($sigma_{pi}/pileq0.15$). The calibration equations which provide the corrected absolute magnitude for optical and near-infrared pass bands are valid for wide ranges of colours and absolute magnitudes: $-0.18<(B-V)_{0}<0.91$, $-1.6<M_{V}<5.5$ and $-0.15<(J-H)_{0}<0.50$, $-0.02<(H-K_{s})_{0}<0.13$, $0<M_{J}<4$, respectively. The distances computed using the luminosity-colours (LCs) relation with optical (BV) and near-infrared ($JHK_{s}$) observations were compared to the distances found from various other methods. The results show that new absolute magnitude calibrations of this study can be used as a convenient statistical tool to estimate the true distances of detached binaries out of Hipparcos distance limit.
We present new empirical calibrations of the absolute magnitude of the tip of the red giant branch (TRGB) in the optical I and near-infrared J, H, and K bands in terms of the (V-K)_0, (V-H)_0, and (J-K)_0 colors of the red giant branch. Our calibrations are based on the measurements in 19 fields in the Large and Small Magellanic Clouds, which span a wide (V-K)_0 color range of the brightest part of the red giant branch. We use a simple edge detection technique based on the comparison of the star count difference in two adjacent bins with the estimated Poisson noise. Further, we include the reddening and geometrical corrections, as well as the precise and accurate to 2% distance to the Large Magellanic Cloud. The calibration based on a (V-K) colors can be a robust tool to calculate with a great precision the absolute magnitude of the TRGB.
The kinematic properties of young stars that have not yet reached the stage of the main sequence are studied. The selection of these stars was recently carried out by Marton et al. (2019) and Vioque et al. (2020) according to the Gaia DR2 catalog using a number of photometric infrared surveys. We have determined the rotation parameters of the Galaxy and the parameters of the ellipsoids of the residual velocities. The linear velocity of the circular rotation of a solar region around the center of the Galaxy, found using 4431 stars, is equal to V_0=229.1+-4.4 km/s. The following ellipsoid parameters of their residual velocities are found from low-mass stars (of type T Tau): $sigma_{1,2,3}=(9.45,6.99,6.61)pm(0.94,0.43,0.32)$ km/s. For stars of intermediate masses (Herbig Ae/Be stars), their values turned out to be somewhat larger $sigma_{1,2,3}=(13.67,9.25,7.26)pm(2.40,2.44,0.88)$ km/s. Distant stars from both Catalogs trace the local spiral arm well. For 1212 stars, a new estimate of the pitch angle of the Local spiral arm is equal to i=-8.9+-0.1 deg.
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