105 research outputs found
Ultra-stripped supernovae and double neutron star systems
The evolution of close-orbit progenitor binaries of double neutron star (DNS)
systems leads to supernova (SN) explosions of ultra-stripped stars. The amount
of SN ejecta mass is very limited from such, more or less, naked metal cores
with envelope masses of only 0.01-0.2 Msun. The combination of little SN ejecta
mass and the associated possibility of small NS kicks is quite important for
the characteristics of the resulting DNS systems left behind. Here, we discuss
theoretical predictions for DNS systems, based on Case BB Roche-lobe overflow
prior to ultra-stripped SNe, and briefly compare with observations.Comment: 6 pages, 3 figures, BN3 talk presented at the Marcel Grossmann
Meeting (MG14), Rome, July 201
Maximum speed of hypervelocity stars ejected from binaries
The recent detection of hypervelocity stars (HVSs) as late-type B-stars and
HVS candidate G/K-dwarfs raises the important question of their origin. In this
Letter, we investigate the maximum possible velocities of such HVSs if they are
produced from binaries which are disrupted via an asymmetric supernova
explosion. We find that HVSs up to ~770 and ~1280 km/s are possible in the
Galactic rest frame from this scenario for these two subclasses of HVSs,
respectively. We conclude that whereas a binary origin cannot easily explain
all of the observed velocities of B-type HVSs (in agreement with their proposed
central massive black hole origin) it can indeed account for the far majority
(if not all) of the recently detected G/K-dwarf HVS candidates.Comment: 6 pages, 6 figures, including appendix, in press, MNRAS Letters
(Updated and a comment added on the spin axis of SN-induced HVSs
Five and a half roads to form a millisecond pulsar
In this review I discuss the characteristics and the formation of all classes
of millisecond pulsars (MSPs). The main focus is on the stellar astrophysics of
X-ray binaries leading to the production of fully recycled MSPs with white
dwarf (WD) or substellar semi-degenerate companions. Depending on the nature of
the companion star MSPs are believed to form from either low-mass X-ray
binaries (LMXBs) or intermediate-mass X-ray binaries (IMXBs). For each of these
two classes of X-ray binaries the evolutionary status of the donor star -- or
equivalently, the orbital period -- at the onset of the Roche-lobe overflow
(RLO) is the determining factor for the outcome of the mass-transfer phase and
thus the nature of the MSP formed. Furthermore, the formation of binary MSPs is
discussed in context of the (P,P_dot)-diagram, as well as new interpretations
of the Corbet diagram. Finally, I present new models of Case A RLO of IMXBs in
order to reproduce the two solar mass pulsar PSR J1614-2230.Comment: 17 pages, 9 figures (color). Invited review at ESO workshop
"Evolution of Compact Binaries", March 2011, Vina del Mar (Chile), ASP Conf.
Series. Fig.7 is available in high resolution on reques
Recycled Pulsars: Spins, Masses and Ages
Recycled pulsars are mainly characterized by their spin periods, B-fields and
masses. All these quantities are affected by previous interactions with a
companion star in a binary system. Therefore, we can use these quantities as
fossil records and learn about binary evolution. Here, I briefly review the
distribution of these observed quantities and summarize our current
understanding of the pulsar recycling process.Comment: Brief summary of invited review talk @ MODEST-16. 4 pages, 3 figures.
To appear in: "Cosmic-Lab: Star Clusters as Cosmic Laboratories for
Astrophysics, Dynamics and Fundamental Physics", F.R Ferraro & B. Lanzoni
eds, Mem. SAIt, Vol 87, n.
The formation of low-mass helium white dwarfs orbiting pulsars: Evolution of low-mass X-ray binaries below the bifurcation period
Millisecond pulsars (MSPs) are generally believed to be old neutron stars
(NSs) which have been spun up to high rotation rates via accretion of matter
from a companion star in a low-mass X-ray binary (LMXB). However, many details
of this recycling scenario remain to be understood. Here we investigate binary
evolution in close LMXBs to study the formation of radio MSPs with low-mass
helium white dwarf companions (He WDs) in tight binaries with orbital periods
P_orb = 2-9 hr. In particular, we examine: i) if such observed systems can be
reproduced from theoretical modelling using standard prescriptions of orbital
angular momentum losses (i.e. with respect to the nature and the strength of
magnetic braking), ii) if our computations of the Roche-lobe detachments can
match the observed orbital periods, and iii) if the correlation between WD mass
and orbital period (M_WD, P_orb) is valid for systems with P_orb < 2 days.
Numerical calculations with a detailed stellar evolution code were used to
trace the mass-transfer phase in ~ 400 close LMXB systems with different
initial values of donor star mass, NS mass, orbital period and the so-called
gamma-index of magnetic braking. Subsequently, we followed the orbital and the
interior evolution of the detached low-mass (proto) He WDs, including stages
with residual shell hydrogen burning. We find that a severe fine-tuning is
necessary to reproduce the observed MSPs in tight binaries with He WD
companions of mass < 0.20 M_sun, which suggests that something needs to be
modified or is missing in the standard input physics of LMXB modelling. We
demonstrate that the theoretically calculated (M_WD, P_orb)-relation is in
general also valid for systems with P_orb < 2 days, although with a large
scatter in He WD masses between 0.15-0.20 M_sun. The results of the thermal
evolution of the (proto) He WDs are reported in a follow-up paper (Paper II).Comment: 14 pages, 13 figures, 1 table, A&A, accepte
Progenitors of ultra-stripped supernovae
The explosion of ultra-stripped stars in close binaries may explain new
discoveries of weak and fast optical transients. We have demonstrated that
helium star companions to neutron stars (NSs) may evolve into naked metal cores
as low as ~1.5 Msun, barely above the Chandrasekhar mass limit, by the time
they explode. Here we present a new systematic investigation of the progenitor
evolution leading to such ultra-stripped supernovae (SNe), in some cases
yielding pre-SN envelopes of less than 0.01 Msun. We discuss the nature of
these SNe (electron-capture vs iron core-collapse) and their observational
light-curve properties. Ultra-stripped SNe are highly relevant for binary
pulsars, as well as gravitational wave detection of merging NSs by LIGO/VIRGO,
since these events are expected to produce mainly low-kick NSs in the mass
range 1.10-1.80 Msun.Comment: 7 pages, 5 figures, NS4 talk presented at the Marcel Grossmann
Meeting (MG14), Rome, July 201
Formation of the Galactic Millisecond Pulsar Triple System PSR J0337+1715 - a Neutron Star with Two Orbiting White Dwarfs
The millisecond pulsar in a triple system (PSR J0337+1715, recently
discovered by Ransom et al.) is an unusual neutron star with two orbiting white
dwarfs. The existence of such a system in the Galactic field poses new
challenges to stellar astrophysics for understanding evolution, interactions
and mass-transfer in close multiple stellar systems. In addition, this system
provides the first precise confirmation for a very wide-orbit system of the
white dwarf mass-orbital period relation. Here we present a self-consistent,
semi-analytical solution to the formation of PSR J0337+1715. Our model
constrains the peculiar velocity of the system to be less than 160 km/s and
brings novel insight to, for example, common envelope evolution in a triple
system, for which we find evidence for in-spiral of both outer stars. Finally,
we briefly discuss our scenario in relation to alternative models.Comment: ApJ Letters, in press (6 pages, 3 figures, 1 table
The timescale of low-mass proto-helium white dwarf evolution
A large number of low-mass (< 0.20 M_sun) helium white dwarfs (He WDs) have
recently been discovered. The majority of these are orbiting another WD or a
millisecond pulsar (MSP) in a close binary system; a few examples are found to
show pulsations or to have a main-sequence star companion. There appear to be
discrepancies between the current theoretical modelling of such low-mass He WDs
and a number of key observed cases, indicating that their formation scenario
remains to be fully understood. Here we investigate the formation of detached
proto-He WDs in close-orbit low-mass X-ray binaries (LMXBs). Our prime focus is
to examine the thermal evolution and the contraction phase towards the WD
cooling track and investigate how this evolution depends on the WD mass. Our
calculations are then compared to the most recent observational data. Numerical
calculations with a detailed stellar evolution code were used to trace the
mass-transfer phase in a large number of close-orbit LMXBs. Subsequently, we
followed the evolution of the detached low-mass proto-He WDs, including stages
with residual shell hydrogen burning and vigorous flashes caused by unstable
CNO burning. We find that the time between Roche-lobe detachment until the
low-mass proto-He WD reaches the WD cooling track is typically Delta_t_proto =
0.5 - 2 Gyr, depending systematically on the WD mass and therefore on its
luminosity. The lowest WD mass for developing shell flashes is ~0.21 M_sun for
progenitor stars of mass M2 <= 1.5 M_sun (and ~0.18 M_sun for M2 = 1.6 M_sun).
The long timescale of low-mass proto-He WD evolution can explain a number of
recent observations, including some MSP systems hosting He WD companions with
very low surface gravities and high effective temperatures. We find no evidence
for Delta_t_proto to depend on the occurrence of flashes and thus question the
suggested dichotomy in thermal evolution of proto-WDs.Comment: 6 pages, 6 figures, 2 tables, A&A Letters, accepte
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