167 research outputs found
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
Study of Eclipsing Binary and Multiple Systems in OB Associations: I. Ori OB1a - IM Mon
All available photometric and spectroscopic observations were collected and
used as the basis of a detailed analysis of the close binary IM Mon. The
orbital period of the binary was refined to 1.19024249(0.00000014) days. The
Roche equipotentials, fractional luminosities (in (B, V) and H_p bands) and
fractional radii for the component stars in addition to mass ratio q,
inclination i of the orbit and the effective temperature T_eff of the secondary
cooler less massive component were obtained by the analysis of light curves. IM
Mon is classified to be a detached binary system in contrast to the contact
configuration estimations in the literature. The absolute parameters of IM Mon
were derived by the simultaneous solutions of light and radial velocity curves
as M_1,2=5.50(0.24)M_o and 3.32(0.16)M_o, R1,2=3.15(0.04)R_o and 2.36(0.03)R_o,
T_eff1,2=17500(350) K and 14500(550) K implying spectral types of B4 and B6.5
ZAMS stars for the primary and secondary components respectively. The modelling
of the high resolution spectrum revealed the rotational velocities of the
component stars as V_rot1=147(15) km/s and V_rot2=90(25) km/s. The photometric
distance of 353(59) pc was found more precise and reliable than Hipparcos
distance of 341(85) pc. An evolutionary age of 11.5(1.5) Myr was obtained for
IM Mon. Kinematical and dynamical analysis support the membership of the young
thin-disk population system IM Mon to the Ori OB1a association dynamically.
Finally, we derived the distance, age and metallicity information of Ori OB1a
sub-group using the information of IM Mon parameters.Comment: 26 pages, 5 figures and 6 tables, accepted for publication in
Publication of the Astronomical Society of Japa
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
Study of Eclipsing Binary and Multiple Systems in OB Associations II. The Cygnus OB Region: V443 Cyg, V456 Cyg and V2107 Cyg
Three presumably young eclipsing binary systems in the direction of the
Cygnus OB1, OB3 and OB9 associations are studied. Component spectra are
reconstructed and their orbits are determined using light curves and spectra
disentangling techniques. V443 Cyg and V456 Cyg have circular orbits, while the
light curve of V2107\,Cyg imposes a slightly eccentric orbit
(. V443 Cyg harbours F-type stars, and not young early-A stars
as previously suggested in the literature based on photometry solely. It
appears to be situated in the foreground (distance kpc) of the
young stellar populations in Cygnus. V456 Cyg, at a distance of
kpc consists of a slightly metal-weak A--type and an early--F star. The age of
both systems, on or very near to the main sequence, remains uncertain by an
order of magnitude. V2107 Cyg is a more massive system ( and
) at kpc and, also kinematically, a strong
candidate-member of Cyg OB1. The more massive component is slightly evolved and
appears to undergo non-radial -type pulsations. The Doppler signal
of the secondary is barely detectable. A more extensive study is important to
fix masses more precisely, and an asteroseismological study would then become
appropriate. Nevertheless, the position of the primary in the HR-diagram
confines the age already reasonably well to Myr, indicating for Cyg
OB1 a similar extent of star formation history as established for Cyg OB2.Comment: 27 pages, including 9 figures and 6 tables, accepted for publication
in Astronomical Journa
The Spectroscopic Orbits of Three Double-lined Eclipsing Binaries: I. BG Ind, IM Mon, RS Sgr
We present the spectroscopic orbit solutions of three double-lines eclipsing
binaries, BG Ind, IM Mon and RS Sgr. The first precise radial velocities (RVs)
of the components were determined using high resolution echelle spectra
obtained at Mt. John University Observatory in New Zealand. The RVs of the
components of BG Ind and RS Sgr were measured using Gaussian fittings to the
selected spectral lines, whereas two-dimensional cross-correlation technique
was preferred to determine the RVs of IM Mon since it has relatively short
orbital period among the other targets and so blending of the lines is more
effective. For all systems, the Keplerian orbital solution was used during the
analysis and also circular orbit was adopted because the eccentricities for all
targets were found to be negligible. The first precise orbit analysis of these
systems gives the mass ratios of the systems as 0.894, 0.606 and 0.325,
respectively for BG Ind, IM Mon and RS Sgr. Comparison of the mass ratio
values, orbital sizes and minimum masses of the components of the systems
indicates that all systems should have different physical, dynamical and
probable evolutionary status.Comment: 17 pages, 6 figures and 4 tables, accepted for publication in New
Astronom
Dynamical evolution of active detached binaries on log Jo - log M diagram and contact binary formation
Orbital angular momentum (Jo), 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 Jo - log P, log M - log P
and log Jo-log M were formed from 119 CAB and 102 W UMa stars. The log Jo-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 Jo - log M
diagram. Since orbital size (a) and period (P) of binaries are determined by
their current Jo, M and mass ratio q, the rates of orbital angular momentum
loss (dlog Jo/dt) and mass loss (dlog M/dt) are primary parameters to determine
the direction and the speed of the dynamical evolution. A detached system
becomes a contact system if its own dynamical evolution enables it to pass the
contact border on the log Jo - log M diagram. Evolution of q for a mass loosing
detached system is unknown unless 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 cent of current CAB stars would transform to W UMa systems
if their nuclear evolution permits them to live 2, 4 and 6 Gyrs respectively.Comment: 28 pages, including 6 figures and 2 tables, accepted for publication
in MNRA
- …