165 research outputs found
The orbital periods of subdwarf B binaries produced by the first stable Roche overflow channel
Long-orbital-period subdwarf B (sdB) stars with main-sequence companions are
believed to be the product of stable Roche Lobe overflow (RLOF), a scenario
challenged by recent observations. Here we represent the results of a
systematic study of the orbital-period distribution of sdB binaries in this
channel using detailed binary evolution calculations. We show that the observed
orbital-period distribution of long-period sdB binaries can be well explained
by this scenario. Furthermore, we find that, if the progenitors of the sdB
stars have initial masses below the helium flash mass, the sdB binaries
produced from stable RLOF follow a unique mass -- orbital period relation for a
given metallicity ; increasing the orbital period from to \,d corresponds to increasing the mass of the sdB star from to
for . We suggest that the longest sdB binaries
(with orbital period \,d) could be the result of atmospheric RLOF. The
mass -- orbital period relation can be tested observationally if the mass of
the sdB star can be determined precisely, e.g.\ from asteroseismology. Using
this relation, we revise the orbital period distribution of sdB binaries
produced by the first stable RLOF channel for the best fitting model of Han et
al (2003), and show that the orbital period has a peak around 830\,d.Comment: 8 pages, 2 figures, accepted for publication in MNRA
Formation of hot subdwarf B stars with neutron star components
Binary population synthesis predicts the existence of subdwarf B stars (sdBs)
with neutron star (NS) or black hole (BH) companions. We systematically
investigate the formation of sdB+NS binaries from binary evolution and aim to
obtain some clues for a search for such systems. We started from a series of
MS+NS systems and determined the parameter spaces for producing sdB+NS binaries
from the stable Roche-lobe overflow (RLOF) channel and from the common envelope
(CE) ejection channel. Various NS accretion efficiencies and NS masses were
examined to investigate the effects they have. We show the characteristics of
the produced sdB+NS systems, such as the mass of components, orbital period,
the semi-amplitude of the radial velocity (K), and the spin of the NS
component. In the stable RLOF channel, the orbital period of sdB+NS binaries
produced in this way ranges from several days to more than 1000 days and moves
toward the short-period (~ hr) side with increasing initial MS mass. the sdB+NS
systems that result from CE ejection have very short orbital periods and then
high values of K (up to 800km s^-1). Such systems are born in very young
populations (younger than 0.3 Gyr) and are potential gravitational wave sources
that might be resolved by the Laser Interferometer Space Antenna (LISA) in the
future. Gravitational wave radiation may again bring them into contact on a
timescale of only ~Myr. As a consequence, they are rare and hard to discover.
The pulsar signal is likely a feature of sdB+NS systems caused by stable RLOF,
and some NS components in sdB binaries may be millisecond pulsars.Comment: 12 pages, 6 figures, 4 tables. Accepted for publication in A&
Primordial Binary Evolution and Blue Stragglers
In this paper, we systematically studied blue stragglers produced from
primordial binary evolution via a binary population synthesis approach, and
examined their contribution to the integrated spectral energy distributions of
the host clusters. The mass transfer efficiency, , is an important
parameter for the final products (then blue stragglers) after mass transfer,
and it is set to be 0.5 except for case A binary evolution. The study shows
that primordial binary evolution may produce blue stragglers at any given times
and that different evolutionary channels are corresponding for blue stragglers
in different visual magnitude regions (in V band) on the colour-magnitude
diagram (CMD) of clusters. The specific frequency of blue stragglers obtained
from primordial binary evolution decreases with time first, and then increases
again when the age is larger than 10Gyr, while that from angular momentum loss
induced by magnetic braking in low-mass binaries increases with time and
exceeds that of primordial binary evolution in a population older than 3 Gyr.
Meanwhile, blue stragglers resulting from primordial binary evolution are
dominant contributors to the ISEDs in ultraviolet and blue bands in a
population between 0.3 and 2.0 Gyr. The value of significantly affects
on the final results. For old open clusters, the assumption of when
the primary is in HG at the onset of mass transfer matches the observations
better than that of from the locations of BSs on the CMDs. Our
study also shows that, for most Galactic open clusters, the specific frequency
of blue stragglers obtained from our simulations is lower than that of
observations, which is puzzling.Comment: 17 pages, 13 figures. accepted by MNRAS(Feb.19, 2009
The progenitors of type Ia supernovae in the semidetached binaries with red giant donors
Context. The companions of the exploding carbon-oxygen white dwarfs (CO WDs)
for producing type Ia supernovae (SNe Ia) are still not conclusively confirmed.
A red-giant (RG) star has been suggested to be the mass donor of the exploding
WD, named as the symbiotic channel. However, previous studies on the this
channel gave a relatively low rate of SNe Ia. Aims. We aim to systematically
investigate the parameter space, Galactic rates and delay time distributions of
SNe Ia from the symbiotic channel by employing a revised mass-transfer
prescription. Methods. We adopted an integrated mass-transfer prescription to
calculate the mass-transfer process from a RG star onto the WD. In this
prescription, the mass-transfer rate varies with the local material states.
Results. We evolved a large number of WD+RG systems, and found that the
parameter space of WD+RG systems for producing SNe Ia is significantly
enlarged. This channel could produce SNe Ia with intermediate and old ages,
contributing to at most 5% of all SNe Ia in the Galaxy. Our model increases the
SN Ia rate from this channel by a factor of 5. We suggest that the symbiotic
systems RS Oph and T CrB are strong candidates for the progenitors of SNe Ia.Comment: 8 pages, 6 figure
Spectroscopic triples and a chance alignment. A solution for a problem of suspicious mass ratios for SB2s from Wilson method
We selected three double-lined spectroscopic binary systems which have
extreme mass ratios, if measured using the Wilson method. We analysed medium
resolution spectroscopic observations and space-based photometry and find that
all these systems are not SB2, but rather triple systems and a chance alignment
of another star with SB1 that have an unseen component. Therefore suspicious
mass ratios determined by the Wilson method for some double-lined spectroscopic
binary systems aren't correct as these systems are more complex.Comment: 10 pages, accepted in MNRA
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