310 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
Kinematics of W UMa-type binaries and evidences on the two types of formation
The kinematics of 129 W UMa binaries is studied and its implications on the
contact binary evolution is discussed. The sample is found to be heterogeneous
in the velocity space that kinematically younger and older contact binaries
exist in the sample. Kinematically young (0.5 Gyr) sub-sample (MG) is formed by
selecting the systems which are satisfying the kinematical criteria of moving
groups. After removing the possible MG members and the systems which are known
to be members of open clusters, the rest of the sample is called Field Contact
Binaries (FCB). The FCB has further divided into four groups according to The
orbital period ranges. Then a correlation has been found in the sense that
shorter period less massive systems have larger velocity dispersions than the
longer period more massive systems. Dispersions in the velocity space indicates
5.47 Gyr kinematical age for the FCB group. Comparing with the field
chromospherically active binaries (CAB), presumably detached binary progenitors
of the contact systems, the FCB appears to be 1.61 Gyr older. Assuming an
equilibrium in the formation and destruction of CAB and W UMa systems in the
Galaxy, this age difference is treated as empirically deduced lifetime of the
contact stage. Since the kinematical ages of the four sub groups of FCB are
much longer than the 1.61 Gyr lifetime of the contact stage, the pre-contact
stages of FCB must dominantly be producing the large dispersions. The
kinematically young (0.5 Gyr) MG group covers the same total mass, period and
spectral ranges as the FCB. But, the very young age of this group does not
leave enough room for pre-contact stages, thus it is most likely that those
systems were formed in the beginning of the main-sequence or during the
pre-main-sequence contraction phase.Comment: 19 pages, including 11 figures and 5 tables, accepted for publication
in MNRA
On the eclipsing cataclysmic variable star HBHA 4705-03
We present observations and analysis of a new eclipsing binary HBHA 4705-03.
Using decomposition of the light curve into accretion disk and hot spot
components, we estimated photometrically the mass ratio of the studied system
to be q=0.62 +-0.07. Other fundamental parameters was found with modeling. This
approach gave: white dwarf mass M_1 = (0.8 +- 0.2) M_sun, secondary mass
M_2=(0.497 +- 0.05) M_sun, orbital radius a=1.418 R_sun, orbital inclination i
= (81.58 +- 0.5) deg, accretion disk radius r_d/a = 0.366 +- 0.002, and
accretion rate dot{M} = (2.5 +- 2) * 10^{18}[g/s], (3*10^{-8} [M_sun/yr]).
Power spectrum analysis revealed ambiguous low-period Quasi Periodic
Oscillations centered at the frequencies f_{1}=0.00076 Hz, f_2=0.00048 Hz and
f_3=0.00036 Hz. The B-V=0.04 [mag] color corresponds to a dwarf novae during an
outburst. The examined light curves suggest that HBHA 4705-03 is a nova-like
variable star.Comment: 7 figures and 2 tables, accepted for publication in Acta Astronomic
On the Zero Point Constant of the Bolometric Correction Scale
Arbitrariness attributed to the zero point constant of the band
bolometric corrections () and its relation to "bolometric magnitude of a
star ought to be brighter than its visual magnitude" and "bolometric
corrections must always be negative" was investigated. The falsehood of the
second assertion became noticeable to us after IAU 2015 General Assembly
Resolution B2, where the zero point constant of bolometric magnitude scale was
decided to have a definite value ~. Since the zero
point constant of the scale could be written as , where
is the zero point constant of the visual magnitudes in the basic
definition , and , the zero point
constant () of the scale cannot be arbitrary anymore; rather, it
must be a definite positive number obtained from the two definite positive
numbers. The two conditions and are also sufficient for
, a similar case to negative numbers, which means that
"bolometric corrections are not always negative". In sum it becomes apparent
that the first assertion is misleading causing one to understand bolometric
corrections must always be negative, which is not necessarily true.Comment: 12 pages, including 3 figures and 1 table, accepted for publication
in Monthly Notices of the Royal Astronomical Societ
Kinematics of the chromospherically active binaries and evidence of an orbital period decrease in binary evolution
Kinematics of 237 Chromospherically Active Binaries (CAB) 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
super giants. The computed , , space velocities indicate the sample
is also heterogeneous in the velocity space. That is, both kinematically
younger and older systems exist among the non-evolved main sequence and the
evolved binaries containing giants and sub giants. The kinematically young
(0.95 Gyr) sub-sample (N=95), which is formed according to the kinematical
criteria of moving groups, was compared to the rest (N=142) of the sample (3.86
Gyr) in order to investigate observational clues of the binary evolution.
Comparing the orbital period histograms between the younger and older
sub-samples, evidences were found supporting Demircan's (1999) finding that the
CAB binaries 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 (), which is compared between the younger
(available only N=53 systems) and older sub-samples (available only N=66
systems). 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 sub samples according to the period ranges of ,
, and among the binaries in the older sub
sample.Comment: 26 pages, including 11 figures and 5 tables, 2004, MNRAS, 349, 106
- …