Publications (4)0 Total impact
-
[show abstract]
[hide abstract]
ABSTRACT: 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 17000 F-type and G-type dwarfs using selection of colour, log
g, and uncertainty on derived space motion, calculate for each star a
probabilistic (kinematic) population assignment to 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 to young thin disc and to older thin disc stars. We derive a
metallicity gradient as a function of Galactocentric radial distance, i.e.
d[M/H]/dR_m=-0.051+/-0.005 dex kpc^-1, for the youngest sample, F-type stars
with vertical orbital eccentricities e_V<=0.04. Samples biased to older thin
disc stars show systematically shallower abundance gradients.
09/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The second RAdial Velocity Experiment (RAVE) Data Release (DR2) derives log g
values but we present a simpler and cleaner method of identifying dwarfs and
giants using only magnitudes, which does not require spectroscopic analysis. We
confirm the Bilir et al. (2006) procedure which estimates the number of dwarfs
and giants via their positions in the J-V two magnitude diagram by applying it
to RAVE DR2. It is effective in estimating the number of dwarfs and giants at
J-H>0.4 compared to RAVE's log g values. For J-H<=0.4, where dwarfs and
subgiants show a continuous transition in the J magnitude histogram, we used
the Besancon Galaxy model predictions to statistically isolate giants. The
percentages of giants for red stars and for the whole sample are 85% and 34%,
respectively. If we add the subgiants, the percentage of evolved stars for the
whole sample raises to 59%. For the first time in the literature, we analysed
the effect of CHISQ on RAVE's log g values (CHISQ is the penalised chi^2 from
RAVE's technique of finding an optimal match between the observed spectrum and
synthetic spectra to derive stellar parameters). Neither the CHISQ values nor
the signal-to-noise ratio bias RAVE log g values. Therefore the method of
identifying dwarfs and giants via the two magnitude diagram has been verified
against an unbiased dataset.
07/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We present colour transformations for the conversion of the W1 and W2
magnitudes of WISE photometric system to the Johnson-Cousins' BVRI, SDSS (gri),
and 2MASS (JHK_s) photometric systems, for dwarfs. The W3 and W4 magnitudes
were not considered due to their insufficient signal to noise ratio (S/N). The
coordinates of 825 dwarfs along with their BVRI, gri, and JHK_s data, taken
from Bilir et al. (2008) were matched with the coordinates of stars in the
preliminary data release of WISE (Wright et al., 2010) and a homogeneous dwarf
sample with high S/N ratio have been obtained using the following constraints:
1) the data were dereddened, 2) giants were identified and excluded from the
sample, 3) sample stars were selected according to data quality, 4)
transformations were derived for sub samples of different metallicity range,
and 5) transformations are two colour dependent. These colour transformations,
coupled with known absolute magnitudes at shorter wavelenghts, can be used in
space density evaluation for the Galactic (thin and thick) discs, at distances
larger than the ones evaluated with JHK_s photometry.
07/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We used the data of 701 stars covering the colour index interval
0.32<B-V<=1.16, with metallicities -1.76<=[Fe/H]<=+0.40 dex, which were taken
from PASTEL catalogue and estimated metallicity dependent guillotine factors
which provide a more accurate metallicity calibration. We reduced the
metallicities of 11 authors to the metallicities of Valenti & Fischer (2005),
thus obtained a homogeneous set of data which increased the accuracy of the
calibration, i.e. [Fe/H]=-14.316*delta^{2}_{0.6}-3.557*delta_{0.6}+0.105.
Comparison of the metallicity residuals, for two sets of data, based on the
metallicity dependent guillotine factors with the ones obtained via metal free
guillotine factors, shows that metallicities estimated by means of new
guillotine factors are more accurate than the other ones. This advantage can be
used in the metallicity gradient investigation of the Galactic components, i.e.
thin disc, thick disc and halo.
02/2011;
