343 research outputs found
Testing eccentricity pumping mechanisms to model eccentric long period sdB binaries with MESA
Hot subdwarf-B stars in long-period binaries are found to be on eccentric
orbits, even though current binary-evolution theory predicts those objects to
be circularised before the onset of Roche-lobe overflow (RLOF). We aim to find
binary-evolution mechanisms that can explain these eccentric long-period
orbits, and reproduce the currently observed period-eccentricity diagram. Three
different processes are considered; tidally-enhanced wind mass-loss,
phase-dependent RLOF on eccentric orbits and the interaction between a
circumbinary disk and the binary. The binary module of the stellar-evolution
code MESA (Modules for Experiments in Stellar Astrophysics) is extended to
include the eccentricity-pumping processes. The effects of different input
parameters on the final period and eccentricity of a binary-evolution model are
tested with MESA. The end products of models with only tidally-enhanced wind
mass-loss can indeed be eccentric, but these models need to lose too much mass,
and invariably end up with a helium white dwarf that is too light to ignite
helium. Within the tested parameter space, no sdBs in eccentric systems are
formed. Phase-dependent RLOF can reintroduce eccentricity during RLOF, and
could help to populate the short-period part of the period-eccentricity
diagram. When phase-dependent RLOF is combined with eccentricity pumping via a
circumbinary disk, the higher eccentricities can be reached as well. A
remaining problem is that these models favour a distribution of higher
eccentricities at lower periods, while the observed systems show the opposite.
The models presented here are potentially capable of explaining the
period-eccentricity distribution of long-period sdB binaries, but further
theoretical work on the physical mechanisms is necessary.Comment: 18 pages, 9 figures, accepted for publication in A&
Holography for bulk states in 3D quantum gravity
In this work we discuss the holographic description of states in the Hilbert
space of (2+1)-dimensional quantum gravity, living on a time slice in the bulk.
We focus on pure gravity coupled to pointlike sources for heavy spinning
particles. We develop a formulation where the equations for the backreacted
metric reduce to two decoupled Liouville equations with delta-function sources
under pseudosphere boundary conditions. We show that both the semiclassical
wavefunction and the gravity solution are determined by a universal object,
namely a classical Virasoro vacuum block on the sphere. In doing so we derive a
version of Polyakov's conjecture, as well as an existence criterion, for
classical Liouville theory on the pseudosphere. We also discuss how some of
these results are modified when considering closed universes with compact
spatial slices.Comment: 39 pages, 4 figures, 2 appendice
Observed binary populations reflect the Galactic history. Explaining the orbital period-mass ratio relation in wide hot subdwarf binaries
Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes
of stable mass transfer from evolved red giants. The orbits of these binaries
show a strong correlation between their orbital periods and mass ratios. The
origins of this correlation have, so far, been lacking a conclusive
explanation. We aim to find a binary evolution model which can explain the
observed correlation. Radii of evolved red giants, and hence the resulting
orbital periods, strongly depend on their metallicity. We have performed a
small but statistically significant binary population synthesis study with the
binary stellar evolution code MESA. We have used a standard model for binary
mass loss and a standard Galactic metallicity history. The resulting sdBs were
selected based on the same criteria as used in observations and then compared
with the observed population. We have achieved an excellent match to the
observed period - mass ratio correlation without explicitly fine-tuning any
parameters. Furthermore, our models produce a good match to the observed period
- metallicity correlation. We predict several new correlations which link the
observed sdB binaries to their progenitors, and a correlation between the
period, metallicity and core mass for subdwarfs and young low-mass He white
dwarfs. We also predict that sdB binaries have distinct orbital properties
depending on whether they formed in the bulge, thin or thick disc, or the halo.
We demonstrate, for the first time, how the metallicity history of the Milky
Way is imprinted in the properties of the observed post-mass transfer binaries.
We show that Galactic chemical evolution is an important factor in binary
population studies of interacting systems containing at least one evolved
low-mass (Mi < 1.6 Msol) component. Finally, we provide an observationally
supported model of mass transfer from low-mass red giants onto main-sequence
stars.Comment: Accepted for publication in A&A, updated references and language
editin
Faecal leukocyte esterase activity is an alternative biomarker in inflammatory bowel disease
Background: Leukocyte cytosolic proteins (e.g., calprotectin) are emerging biomarkers for inflammatory bowel disease. Leukocyte aryl esterase activity has been commonly used for sensitive detection of leukocytes in human body fluids such as urine. Urine test strip results are generally reported in categories. As automated strip readers allow quantitative data to be reported, sensitive quantitative detection of leukocytes in body fluids has become possible. Here, we explored the use of leukocyte esterase as a potential alternative faecal biomarker for inflammatory bowel disease.
Methods: We evaluated leukocyte esterase activity in faecal extracts and compared Cobas u 411 (Roche) quantitative reflectance data with calprotectin concentration for 107 routine samples. Stability of leukocyte esterase for trypsin digestion was carried out by adding trypsin to the extract. Incubation occurred at 37 ° C for 24 h or 48 h.
Results: Reproducibility of the reflectance signal was good (within-run imprecision: 6.1%; between-run imprecision: 6.2%). Results were linear in the range 10 3 – 10 6 WBC/100 mg faeces. The lower limit of detection was 4 WBC/ μ L and the lower limit of quantification was 5 WBC/ μ L. Stability of LE activity in stool and faecal matrix was good. An adequate correlation was obtained between leukocyte esterase activity and the faecal calprotectin concentration: log(y)  =  4.28 + 0.29log(x). In vitro experiments monitored the digestion of leukocyte esterase and faecal calprotectin. Leukocyte esterase activity was significantly less affected by trypsin activity than calprotectin immunoreactivity.
Conclusions: Quantitative leukocyte esterase activity of faecal extracts provides information about the leukocyte count in the gut lumen. Leukocyte esterase is a promising and affordable alternative biomarker for monitoring inflammatory bowel disease
The first heavy-metal hot subdwarf composite binary SB 744
A radial velocity follow-up of the long-period sdOB+G1V type spectroscopic
binary SB 744 revealed strong lines of fluorine and lead in the optical
spectrum of the sdOB star and subsolar metallicity in the G1V companion. With
high-quality observations and Gaia astrometric data, we aim at measuring the
chemical composition and Galactic kinematics of the system to put it in context
with known populations of hot subdwarfs. Such binary systems have high
potential, as they give insights into the late stages of binary evolution as
well as into the mysterious formation of stripped core helium-burning stars. We
have analyzed the optical spectra with homogeneous atmospheric models to derive
surface parameters of the binary members from a direct wavelength space
decomposition and independently measured the atmospheric properties of the cool
companion. The two independent methods reached consistent results, which,
amended with constraints from spectral energy distributions provided a subdwarf
mass. The Gaia astrometry allowed us to derive the Galactic kinematics of the
system. SB 744 turned out to be an old, Population II system, that has gone
through dramatic events. The hot subdwarf star belongs to the heavy-metal
subclass of sdOB stars and we report super-solar abundances of lead, based on
Pb III/IV lines. The He abundance of the hot subdwarf is the lowest among the
known heavy-metal sdOB stars. The presence of fluorine implies that SB 744 was
once a hierarchical triple system and the inner binary has merged in the near
past. As an alternative scenario, single-star evolution through late core
helium flash and atmospheric mixing can also produce the observed fluorine
abundances. The atmospheric metal over-abundances currently observed are
perhaps the results of a combination of mixing processes during formation and
radiative support.Comment: Accepted for publication in Astronomy and Astrophysic
The orbital period -- mass ratio relation of wide sdB+MS binaries and its application to the stability of RLOF
Wide binaries with hot subdwarf-B (sdB) primaries and main sequence
companions are thought to form only through stable Roche lobe overflow (RLOF)
of the sdB progenitor near the tip of the red giant branch (RGB). We present
the orbital parameters of eleven new long period composite sdB binaries based
on spectroscopic observations obtained with the UVES, FEROS and CHIRON
spectrographs. Using all wide sdB binaries with known orbital parameters, 23
systems, the observed period distribution is found to match very well with
theoretical predictions. A second result is the strong correlation between the
orbital period (P) and the mass ratio (q) in the observed wide sdB binaries. In
the P-q plane two distinct groups emerge, with the main group (18 systems)
showing a strong correlation of lower mass ratios at longer orbital periods.
The second group are systems that are thought to be formed from higher mass
progenitors. Based on theoretical models, a correlation between the initial
mass ratio at the start of RLOF and core mass of the sdB progenitor is found,
which defines a mass-ratio range at which RLOF is stable on the RGB.Comment: accepted for publication in MNRAS, 16 pages, 16 figure
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