116 research outputs found
Massive star evolution : rotation, winds, and overshooting vectors in the Mass-Luminosity plane I. A calibrated grid of rotating single star models
We aim to constrain massive star evolution models using the unique testbed
eclipsing binary HD166734 with new grids of MESA stellar evolution models,
adopting calibrated prescriptions of overshooting, mass loss, and rotation. We
introduce a novel tool: the "mass-luminosity plane" or "M-L plane", as an
equivalent to the traditional HR diagram, utilising it to reproduce the testbed
binary HD166734 with newly calibrated MESA stellar evolution models for single
stars. We can only reproduce the Galactic binary system with an enhanced amount
of core overshooting (alpha = 0.5), mass loss, and rotational mixing. We can
utilise the gradient in the M-L plane to constrain the amount of mass loss to
0.5 - 1.5 times the standard Vink et al. 2001 prescriptions, and we can exclude
extreme reduction or multiplication factors. The extent of the vectors in the
M-L plane leads us to conclude that the amount of core overshooting is larger
than is normally adopted in contemporary massive star evolution models. We
furthermore conclude that rotational mixing is mandatory to get the nitrogen
abundance ratios between the primary and secondary components to be correct
(3:1) in our testbed binary system. Our calibrated grid of models, alongside
our new M-L plane approach, present the possibility of a widened main sequence
due to an increased demand for core overshooting. The increased amount of core
overshooting is not only needed to explain the extended main sequence, but the
enhanced overshooting is also needed to explain the location of the
upper-luminosity limit of the red supergiants. Finally, the increased amount of
core overshooting has -- via the compactness parameter -- implications for
supernova explodibility.Comment: Revised version, 14 pages, 19 figures, accepted for publication by
Astronomy & Astrophysic
The hydrogen clock to infer the upper stellar mass
The most massive stars dominate the chemical enrichment, mechanical and
radiative feedback, and energy budget of their host environments. Yet how
massive stars initially form and how they evolve throughout their lives is
ambiguous. The mass loss of the most massive stars remains a key unknown in
stellar physics, with consequences for stellar feedback and populations. In
this work, we compare grids of very massive star (VMS) models with masses
ranging from 80-1000Msun, for a range of input physics. We include enhanced
winds close to the Eddington limit as a comparison to standard O-star winds,
with consequences for present-day observations of ~50-100Msun stars. We probe
the relevant surface H abundances (Xs) to determine the key traits of VMS
evolution compared to O stars. We find fundamental differences in the behaviour
of our models with the enhanced-wind prescription, with a convergence on the
stellar mass at 1.6 Myr, regardless of the initial mass. It turns out that Xs
is an important tool in deciphering the initial mass due to the chemically
homogeneous nature of VMS above a mass threshold. We use Xs to break the
degeneracy of the initial masses of both components of a detached binary, and a
sample of WNh stars in the Tarantula nebula. We find that for some objects, the
initial masses are unrestricted and, as such, even initial masses of the order
1000Msun are not excluded. Coupled with the mass turnover at 1.6 Myr, Xs can be
used as a 'clock' to determine the upper stellar mass.Comment: Accepted for publication in MNRAS, 14 figure
Stellar Wind Yields of Very Massive Stars
The most massive stars provide an essential source of recycled material for
young clusters and galaxies. While very massive stars (VMS, M>100M) are
relatively rare compared to O stars, they lose disproportionately large amounts
of mass already from the onset of core H-burning. VMS have optically thick
winds with elevated mass-loss rates in comparison to optically thin standard
O-star winds. We compute wind yields and ejected masses on the main sequence,
and we compare enhanced mass-loss rates to standard ones. We calculate solar
metallicity wind yields from MESA stellar evolution models in the range 50 -
500M, including a large nuclear network of 92 isotopes, investigating not only
the CNO-cycle, but also the Ne-Na and Mg-Al cycles. VMS with enhanced winds
eject 5-10 times more H-processed elements (N, Ne, Na, Al) on the main sequence
in comparison to standard winds, with possible consequences for observed
anti-correlations, such as C-N and Na-O, in globular clusters. We find that for
VMS 95% of the total wind yields is produced on the main sequence, while only
~5% is supplied by the post-main sequence. This implies that VMS with enhanced
winds are the primary source of 26Al, contrasting previous works where
classical Wolf-Rayet winds had been suggested to be responsible for Galactic
26Al enrichment. Finally, 200M stars eject 100 times more of each heavy element
in their winds than 50M stars, and even when weighted by an IMF their wind
contribution is still an order of magnitude higher than that of 50M stars.Comment: Accepted for publication in MNRAS. 14 pages, 10 figure
Persistent holes in a fluid
We observe stable holes in a vertically oscillated 0.5 cm deep aqueous
suspension of cornstarch for accelerations a above 10g. Holes appear only if a
finite perturbation is applied to the layer. Holes are circular and
approximately 0.5 cm wide, and can persist for more than 10^5 cycles. Above a =
17g the rim of the hole becomes unstable producing finger-like protrusions or
hole division. At higher acceleration, the hole delocalizes, growing to cover
the entire surface with erratic undulations. We find similar behavior in an
aqueous suspension of glass microspheres.Comment: 4 pages, 6 figure
Stellar wind yields of very massive stars
The most massive stars provide an essential source of recycled material for young clusters and galaxies. While very massive stars (VMSs, M>100) are relatively rare compared to O stars, they lose disproportionately large amounts of mass already from the onset of core H-burning. VMS have optically thick winds with elevated mass-loss rates in comparison to optically thin standard O-star winds. We compute wind yields and ejected masses on the main sequence, and we compare enhanced mass-loss rates to standard ones. We calculate solar metallicity wind yields from MESA stellar evolution models in the range 50-500, including a large nuclear network of 92 isotopes, investigating not only the CNO-cycle, but also the Ne-Na and Mg-Al cycles. VMS with enhanced winds eject 5-10 times more H-processed elements (N, Ne, Na, Al) on the main sequence in comparison to standard winds, with possible consequences for observed anticorrelations, such as C-N and Na-O, in globular clusters. We find that for VMS 95 per cent of the total wind yields is produced on the main sequence, while only ∼5 per cent is supplied by the post-main sequence. This implies that VMS with enhanced winds are the primary source of 26Al, contrasting previous works where classical Wolf-Rayet winds had been suggested to be responsible for galactic 26Al enrichment. Finally, 200 stars eject 100 times more of each heavy element in their winds than 50 stars, and even when weighted by an IMF their wind contribution is still an order of magnitude higher than that of 50 stars
Stellar wind yields of very massive stars
The most massive stars provide an essential source of recycled material for young clusters and galaxies. While very massive stars (VMS, M>100 ) are relatively rare compared to O stars, they lose disproportionately large amounts of mass already from the onset of core H-burning. VMS have optically thick winds with elevated mass-loss rates in comparison to optically thin standard O-star winds. We compute wind yields and ejected masses on the main sequence, and we compare enhanced mass-loss rates to standard ones. We calculate solar metallicity wind yields from MESA stellar evolution models in the range 50 – 500 , including a large nuclear network of 92 isotopes, investigating not only the CNO-cycle, but also the Ne-Na and Mg-Al cycles. VMS with enhanced winds eject 5-10 times more H-processed elements (N, Ne, Na, Al) on the main sequence in comparison to standard winds, with possible consequences for observed anti-correlations, such as C-N and Na-O, in globular clusters. We find that for VMS 95% of the total wind yields is produced on the main sequence, while only ∼ 5% is supplied by the post-main sequence. This implies that VMS with enhanced winds are the primary source of 26Al, contrasting previous works where classical Wolf-Rayet winds had been suggested to be responsible for Galactic 26Al enrichment. Finally, 200 stars eject 100 times more of each heavy element in their winds than 50 stars, and even when weighted by an IMF their wind contribution is still an order of magnitude higher than that of 50 stars
Bringing Stellar Evolution & Feedback Together: Summary of proposals from the Lorentz Center Workshop, 2022
Stars strongly impact their environment, and shape structures on all scales
throughout the universe, in a process known as ``feedback''. Due to the
complexity of both stellar evolution and the physics of larger astrophysical
structures, there remain many unanswered questions about how feedback operates,
and what we can learn about stars by studying their imprint on the wider
universe. In this white paper, we summarize discussions from the Lorentz Center
meeting `Bringing Stellar Evolution and Feedback Together' in April 2022, and
identify key areas where further dialogue can bring about radical changes in
how we view the relationship between stars and the universe they live in.Comment: Accepted to the Publications of the Astronomical Society of the
Pacifi
Impact of H1N1 on Socially Disadvantaged Populations: Systematic Review
The burden of H1N1 among socially disadvantaged populations is unclear. We aimed to synthesize hospitalization, severe illness, and mortality data associated with pandemic A/H1N1/2009 among socially disadvantaged populations.Studies were identified through searching MEDLINE, EMBASE, scanning reference lists, and contacting experts. Studies reporting hospitalization, severe illness, and mortality attributable to laboratory-confirmed 2009 H1N1 pandemic among socially disadvantaged populations (e.g., ethnic minorities, low-income or lower-middle-income economy countries [LIC/LMIC]) were included. Two independent reviewers conducted screening, data abstraction, and quality appraisal (Newcastle Ottawa Scale). Random effects meta-analysis was conducted using SAS and Review Manager.Sixty-two studies including 44,777 patients were included after screening 787 citations and 164 full-text articles. The prevalence of hospitalization for H1N1 ranged from 17-87% in high-income economy countries (HIC) and 11-45% in LIC/LMIC. Of those hospitalized, the prevalence of intensive care unit (ICU) admission and mortality was 6-76% and 1-25% in HIC; and 30% and 8-15%, in LIC/LMIC, respectively. There were significantly more hospitalizations among ethnic minorities versus non-ethnic minorities in two studies conducted in North America (1,313 patients, OR 2.26 [95% CI: 1.53-3.32]). There were no differences in ICU admissions (n = 8 studies, 15,352 patients, OR 0.84 [0.69-1.02]) or deaths (n = 6 studies, 14,757 patients, OR 0.85 [95% CI: 0.73-1.01]) among hospitalized patients in HIC. Sub-group analysis indicated that the meta-analysis results were not likely affected by confounding. Overall, the prevalence of hospitalization, severe illness, and mortality due to H1N1 was high for ethnic minorities in HIC and individuals from LIC/LMIC. However, our results suggest that there were little differences in the proportion of hospitalization, severe illness, and mortality between ethnic minorities and non-ethnic minorities living in HIC
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