38 research outputs found
The quest for companions to post-common envelope binaries. II. NSVS14256825 and HS0705+6700
We report new mid-eclipse times of the two close binaries NSVS14256825 and
HS0705+6700, harboring an sdB primary and a low-mass main-sequence secondary.
Both objects display clear variations in the measured orbital period, which can
be explained by the action of a third object orbiting the binary. If this
interpretation is correct, the third object in NSVS14256825 is a giant planet
with a mass of roughly 12 M_Jup. For HS0705+6700, we provide evidence that
strengthens the case for the suggested periodic nature of the eclipse time
variation and reduces the uncertainties in the parameters of the brown dwarf
implied by that model. The derived period is 8.4 yr and the mass is 31 M_Jup,
if the orbit is coplanar with the binary. This research is part of the
PlanetFinders project, an ongoing collaboration between professional
astronomers and student groups at high schools.Comment: Accepted by Astron. and Astrophy
Life after eruption - I. Spectroscopic observations of ten nova candidates
We have started a project to investigate the connection of post-novae with
the population of cataclysmic variables. Our first steps in this concern
improving the sample of known post-novae and their properties. Here we present
the recovery and/or confirmation of the old novae MT Cen, V812 Cen, V655 CrA,
IL Nor, V2109 Oph, V909 Sgr, V2572 Sgr, and V728 Sco. Principal photometric and
spectroscopic properties of these systems are discussed. We find that V909 Sgr
is a probable magnetic CV, and that V728 Sco is a high-inclination system. We
furthermore suggest that the two candidate novae V734 Sco and V1310 Sgr have
been misclassified and instead are Mira variables.Comment: 11 pages, 7 figures (some of them in lower resolution), to be
published in MNRA
The quest for companions to post-common envelope binaries: I. Searching a sample of stars from the CSS and SDSS
As part of an ongoing collaboration between student groups at high schools
and professional astronomers, we have searched for the presence of
circum-binary planets in a bona-fide unbiased sample of twelve post-common
envelope binaries (PCEBs) from the Catalina Sky Survey (CSS) and the Sloan
Digital Sky Survey (SDSS). Although the present ephemerides are significantly
more accurate than previous ones, we find no clear evidence for orbital period
variations between 2005 and 2011 or during the 2011 observing season. The
sparse long-term coverage still permits O-C variations with a period of years
and an amplitude of tens of seconds, as found in other systems. Our
observations provide the basis for future inferences about the frequency with
which planet-sized or brown-dwarf companions have either formed in these
evolved systems or survived the common envelope (CE) phase.Comment: accepted by A&
Formation of millisecond pulsars with CO white dwarf companions - I. PSR J1614-2230: Evidence for a neutron star born massive
The recent discovery of a 2 M_sun binary millisecond pulsar (Demorest et al.
2010) has not only important consequences for the equation-of-state of nuclear
matter at high densities but also raises the interesting question if the
neutron star PSR J1614-2230 was born massive. The answer is vital for
understanding neutron star formation in core collapse supernovae. Furthermore,
this system raises interesting issues about the nature of the progenitor binary
and how it evolved during its mass exchanging X-ray phase. In this paper we
discuss the progenitor evolution of PSR J1614-2230. We have performed detailed
stellar evolution modelling of intermediate-mass X-ray binaries undergoing Case
A Roche-lobe overflow (RLO) and applied an analytic parameterization for
calculating the outcome of either a common envelope evolution or the highly
super-Eddington isotropic re-emission mode. We find two viable possibilities
for the formation of the PSR J1614-2230 system: either it contained a 2.2-2.6
M_sun giant donor star and evolved through a common envelope and spiral-in
phase or, more likely, it descended from a close binary system with a 4.0-5.0
M_sun main sequence donor star via Case A RLO. We conclude that the neutron
star must have been born with a mass of ~1.95 M_sun or 1.7+-0.15 M_sun,
respectively - which significantly exceeds neutron star birth masses in
previously discovered radio pulsar systems. Based on the expected neutron star
birth masses from considerations of stellar evolution and explosion models, we
find that the progenitor star of PSR J1614-2230 is likely to have been more
massive than 20 M_sun.Comment: 15 pages, 10 figures, MNRAS in press. 3 pages added (mainly extended
discussion on neutron star birth masses
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Characterization of new hard X-ray Cataclysmic Variables
We aim at characterizing a sample of 9 new hard X-ray selected Cataclysmic
Variable (CVs), to unambiguously identify them as magnetic systems of the
Intermediate Polar (IP) type. We performed timing and spectral analysis by
using X-ray, and simultaneous UV and optical data collected by XMM-Newton,
complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse
arrival time were used to estimate the orbital periods. The X-ray spectra were
fitted using composite models consisting of different absorbing columns and
emission components. Strong X-ray pulses at the White Dwarf (WD) spin period
are detected and found to decrease with energy. Most sources are spin-dominated
systems in the X-rays, though four are beat dominated at optical wavelengths.
We estimated the orbital period in all system (except for IGR J16500-3307),
providing the first estimate for IGR J08390-4833, IGR J18308-1232, and IGR
J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX
J0636+3535 posses a soft X-ray optically thick component at kT 80 eV. An
intense K_alpha Fe line at 6.4 keV is detected in all sources. An absorption
edge at 0.76 keV from OVII is detected in IGR J08390-4833. The WD masses and
lower limits to the accretion rates are estimated. We found all sources to be
IPs. IGR J08390-4833, V2069 Cyg, and IGR J16500-3307 are pure disc accretors,
while IGR J18308-1232, IGR J1509-6649, IGR J17195-4100, and RX J0636+3535
display a disc-overflow accretion mode. All sources show a temperature gradient
in the post-shock regions and a highly absorbed emission from material located
in the pre-shock flow which is also responsible for the X-ray pulsations.
Reflection at the WD surface is likely the origin of the fluorescent iron line.
There is an increasing evidence for the presence of a warm absorber in IPs. The
addition of 2 systems to the subgroup of soft X-ray IPs confirms a \sim 30%
incidence.Comment: 23 pages, 11 figures, 7 tables, accepter for publication in A&A in
April 201
Observational Constraints on the Common Envelope Phase
The common envelope phase was first proposed more than forty years ago to
explain the origins of evolved, close binaries like cataclysmic variables. It
is now believed that the phase plays a critical role in the formation of a wide
variety of other phenomena ranging from type Ia supernovae through to binary
black holes, while common envelope mergers are likely responsible for a range
of enigmatic transients and supernova imposters. Yet, despite its clear
importance, the common envelope phase is still rather poorly understood. Here,
we outline some of the basic principles involved, the remaining questions as
well as some of the recent observational hints from common envelope phenomena -
namely planetary nebulae and luminous red novae - which may lead to answering
these open questions.Comment: 29 pages, 8 figures. To appear in the book "Reviews in Frontiers of
Modern Astrophysics: From Space Debris to Cosmology" (eds. Kabath, Jones and
Skarka; publisher Springer Nature) funded by the European Union Erasmus+
Strategic Partnership grant "Per Aspera Ad Astra Simul"
2017-1-CZ01-KA203-03556
Relativistic Binaries in Globular Clusters
Galactic globular clusters are old, dense star systems typically containing
10\super{4}--10\super{7} stars. As an old population of stars, globular
clusters contain many collapsed and degenerate objects. As a dense population
of stars, globular clusters are the scene of many interesting close dynamical
interactions between stars. These dynamical interactions can alter the
evolution of individual stars and can produce tight binary systems containing
one or two compact objects. In this review, we discuss theoretical models of
globular cluster evolution and binary evolution, techniques for simulating this
evolution that leads to relativistic binaries, and current and possible future
observational evidence for this population. Our discussion of globular cluster
evolution will focus on the processes that boost the production of hard binary
systems and the subsequent interaction of these binaries that can alter the
properties of both bodies and can lead to exotic objects. Direct {\it N}-body
integrations and Fokker--Planck simulations of the evolution of globular
clusters that incorporate tidal interactions and lead to predictions of
relativistic binary populations are also discussed. We discuss the current
observational evidence for cataclysmic variables, millisecond pulsars, and
low-mass X-ray binaries as well as possible future detection of relativistic
binaries with gravitational radiation.Comment: 88 pages, 13 figures. Submitted update of Living Reviews articl
Post common envelope binaries from SDSS
Context. Post-common-envelope binaries (PCEBs) consisting of a white dwarf (WD) and a main-sequence secondary star are ideal systems to constrain models of common-envelope (CE) evolution. Until very recently, observed samples of PCEBs have been too small to fully explore this potential, however the recently identified large and relatively homogenous sample of PCEBs from the Sloan Digital Sky Survey (SDSS) has significantly changed this situation.
Aims. We here analyze the orbital period distributions of PCEBs containing He- and C/O-core WDs separately and investigate whether the orbital period of PCEBs is related to the masses of their stellar components.
Methods. We performed standard statistical tests to compare the orbital period distributions and to determine the confidence levels of possible relations.
Results. The orbital periods of PCEBs containing He-core WDs are significantly shorter than those of PCEBs containing C/O-core WDs. While the He-core PCEB orbital period distribution has a median value of Porb ~ 0.28 d, the median orbital period for PCEBs containing C/O-core WDs is Porb ~ 0.57 d. We also find that systems containing more massive secondaries have longer post-CE orbital periods, in contradiction to recent predictions.
Conclusions. Our observational results provide new constraints on theories of CE evolution. However we suggest future binary population models to take selection effects into account that still affect the current observed PCEB sample