358 research outputs found
Spatial distribution and galactic model parameters of cataclysmic variables
The spatial distribution, galactic model parameters and luminosity function
of cataclysmic variables (CVs) in the solar neighbourhood have been determined
from a carefully established sample of 459 CVs. The sample contains all of the
CVs with distances computed from the Period-Luminosity-Colours (PLCs) relation
of CVs which has been recently derived and calibrated with {\em 2MASS}
photometric data. It has been found that an exponential function fits best to
the observational z-distributions of all of the CVs in the sample, non-magnetic
CVs and dwarf novae, while the sech^{2} function is more appropriate for
nova-like stars and polars. The vertical scaleheight of CVs is 15814 pc
for the {\em 2MASS} J-band limiting apparent magnitude of 15.8. On the other
hand, the vertical scaleheights are 12820 and 1605 pc for dwarf novae
and nova-like stars, respectively. The local space density of CVs is found to
be pc^{-3} which is in agreement with the lower limit of
the theoretical predictions. The luminosity function of CVs shows an increasing
trend toward higher space densities at low luminosities, implying that the
number of short-period systems should be high. The discrepancies between the
theoretical and observational population studies of CVs will almost disappear
if for the z-dependence of the space density the sech^{2} density function is
used.Comment: 29 pages, 9 figures and 5 tables, accepted for publication in New
Astronom
Metallicity Calibration and Photometric Parallax Estimation: I. UBV photometry
We present metallicity and photometric parallax calibrations for the F and G
type dwarfs with photometric, astrometric and spectroscopic data. The sample
consists of 168 dwarf stars covering the colour, iron abundance and absolute
magnitude intervals mag, dex and
mag, respectively. The means and standard deviations of the
metallicity and absolute magnitude residuals are small, i.e.
and dex, and and mag, respectively, which indicate
accurate metallicity and photometric parallax estimations.Comment: 13 pages, 11 figures and 2 tables, accepted for publication in
Astrophysics and Space Scienc
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