7,235 research outputs found
The population of hot subdwarf stars studied with Gaia II. The Gaia DR2 catalogue of hot subluminous stars
Based on data from the ESA Gaia Data Release 2 (DR2) and several
ground-based, multi-band photometry surveys we compiled an all-sky catalogue of
hot subluminous star candidates selected in Gaia DR2 by means of
colour, absolute magnitude and reduced proper motion cuts. We expect the
majority of the candidates to be hot subdwarf stars of spectral type B and O,
followed by blue horizontal branch stars of late B-type (HBB), hot post-AGB
stars, and central stars of planetary nebulae. The contamination by cooler
stars should be about . The catalogue is magnitude limited to Gaia
and covers the whole sky. Except within the Galactic plane
and LMC/SMC regions, we expect the catalogue to be almost complete up to about
. The main purpose of this catalogue is to serve as input
target list for the large-scale photometric and spectroscopic surveys which are
ongoing or scheduled to start in the coming years. In the long run, securing a
statistically significant sample of spectroscopically confirmed hot subluminous
stars is key to advance towards a more detailed understanding of the latest
stages of stellar evolution for single and binary stars.Comment: 13 pages, A&A, accepte
Analysis of cool DO-type white dwarfs from the Sloan Digital Sky Survey Data Release 10
We report on the identification of 22 new cool DO-type white dwarfs (WD)
detected in Data Release 10 (DR10) of the Sloan Digital Sky Survey (SDSS).
Among them, we found one more member of the so-called hot-wind DO WDs, which
show ultrahigh excitation absorption lines. Our non-LTE model atmosphere
analyses of these objects and two not previously analyzed hot-wind DO WDs,
revealed effective temperatures and gravities in the ranges Teff=45-80kK and
log g= 7.50-8.75. In eight of the spectra we found traces of C (0.001-0.01, by
mass). Two of these are the coolest DO WDs ever discovered that still show a
considerable amount of C in their atmospheres. This is in strong contradiction
with diffusion calculations, and probably, similar to what is proposed for DB
WDs, a weak mass-loss is present in DO WDs. One object is the most massive DO
WD discovered so far with a mass of 1.07 M_sun if it is an ONe-WD or 1.09 M_sun
if it is a CO-WD. We furthermore present the mass distribution of all known hot
non-DA (pre-) WDs and derive the hot DA to non-DA ratio for the SDSS DR7
spectroscopic sample. The mass distribution of DO WDs beyond the wind limit
strongly deviates from the mass distribution of the objects before the wind
limit. We address this phenomenon by applying different evolutionary input
channels. We argue that the DO WD channel may be fed by about 13% by
post-extreme-horizontal branch stars and that PG1159 stars and O(He) stars may
contribute in a similar extent to the non-DA WD channel.Comment: 13 pages, accepted for publication in A&
The Field White Dwarf Mass Distribution
We revisit the properties and astrophysical implications of the field white
dwarf mass distribution in preparation of Gaia applications. Our study is based
on the two samples with the best established completeness and most precise
atmospheric parameters, the volume-complete survey within 20 pc and the Sloan
Digital Sky Survey (SDSS) magnitude-limited sample. We explore the modelling of
the observed mass distributions with Monte Carlo simulations, but find that it
is difficult to constrain independently the initial mass function (IMF), the
initial-to-final-mass relation (IFMR), the stellar formation history (SFH), the
variation of the Galactic disk vertical scale height as a function of stellar
age, and binary evolution. Each of these input ingredients has a moderate
effect on the predicted mass distributions, and we must also take into account
biases owing to unidentified faint objects (20 pc sample), as well as unknown
masses for magnetic white dwarfs and spectroscopic calibration issues (SDSS
sample). Nevertheless, we find that fixed standard assumptions for the above
parameters result in predicted mean masses that are in good qualitative
agreement with the observed values. It suggests that derived masses for both
studied samples are consistent with our current knowledge of stellar and
Galactic evolution. Our simulations overpredict by 40-50% the number of massive
white dwarfs (M > 0.75 Msun) for both surveys, although we can not exclude a
Salpeter IMF when we account for all biases. Furthermore, we find no evidence
of a population of double white dwarf mergers in the observed mass
distributions.Comment: 15 pages, 16 figures, accepted for publication in MNRA
Experimental measurement and model validation of COD in pipe under bending with off-centered circumferential crack
The leak area of circumferential through-thickness crack in pipe under bending depends on the position of the crack with respect to the bending plane. In leak-before-break (LBB) analysis, the assumption that the crack is symmetrically placed with respect to the bending plane is not necessarily conservative. In this work, the crack opening of circumferential cracks, off-centered with respect to the bending plane, was investigated experimentally. Here, three pipe geometries and two crack lengths were investigated. For each crack, the centred and two off-centered configuration were examined. The crack opening displacement (COD) distribution along the crack length was measured for two selected bending load levels using digital image correlation (DIC) technique. These measurements have been used for verifying the solution provided by the hodograph cone method (HCM) as proposed by Bonora [1]
Magnetic Fields in the Center of the Perseus Cluster
We present Very Long Baseline Array (VLBA) observations of the nucleus of NGC
1275, the central, dominant galaxy in the Perseus cluster of galaxies. These
are the first observations to resolve the linearly polarized emission from
3C84, and from them we determine a Faraday rotation measure (RM) ranging from
6500 to 7500 rad/m^2 across the tip of the bright southern jet component. At 22
GHz some polarization is also detected from the central parsec of 3C84,
indicating the presence of even more extreme RMs that depolarize the core at
lower frequencies. The nature of the Faraday screen is most consistent with
being produced by magnetic fields associated with the optical filaments of
ionized gas in the Perseus Cluster.Comment: Accepted for publication in MNRA
Profiling Metacognition in Binge Eating Disorder
© 2020, The Author(s). Research has shown that metacognition may play a role in problem eating. In this study we explored whether aspects of metacognition are relevant to the understanding of binge eating in patients with Binge Eating Disorder. We aimed to ascertain: (1) the presence of metacognitive beliefs about binge eating; (2) the goal of, and stop signal for, binge eating; and (3) the impact of binge eating on self-consciousness. Ten Binge Eating Disorder patients took part in the study and were assessed using the metacognitive profiling semi-structured interview. Results suggested that all patients endorsed both positive and negative metacognitive beliefs about binge eating. The goals of binge eating were stop thinking about personal concerns and improve emotional state. All patients reported that they did not know when these goals had been reached. The stop signals for binge eating included physical discomfort, beliefs about binge eating not being the best way to solve problems, and environmental stimuli. All patients also confirmed that a reduction in self-consciousness occurred during a binge eating episode. The results of this study confirm that metacognition may indeed be relevant to the understanding of Binge Eating Disorder
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