32 research outputs found
Opacity Effects on Pulsations of Main-Sequence A-Type Stars
Opacity enhancements for stellar interior conditions have been explored to
explain observed pulsation frequencies and to extend the pulsation instability
region for B-type main-sequence variable stars. For these stars, the pulsations
are driven in the region of the opacity bump of Fe-group elements at
200,000 K in the stellar envelope. Here we explore effects of opacity
enhancements for the somewhat cooler main-sequence A-type stars, in which
-mode pulsations are driven instead in the second helium ionization region
at 50,000 K. We compare models using the new LANL OPLIB vs. LLNL OPAL
opacities for the AGSS09 solar mixture. For models of 2 solar masses and
effective temperature 7600 K, opacity enhancements have only a mild effect on
pulsations, shifting mode frequencies and/or slightly changing kinetic-energy
growth rates. Increased opacity near the bump at 200,000 K can induce
convection that may alter composition gradients created by diffusive settling
and radiative levitation. Opacity increases around the hydrogen and 1st He
ionization region (13,000 K) can cause additional higher-frequency modes to
be excited, raising the possibility that improved treatment of these layers may
result in prediction of new modes that could be tested by observations. New or
wider convective zones and higher convective velocities produced by opacity
increases could also affect angular momentum transport during evolution. More
work needs to be done to quantify the effects of opacity on the boundaries of
the pulsation instability regions for A-type stars.Comment: 14 pages, 12 figures. Accepted version for MDPI Atoms Special Issue
"Atomic and Molecular Opacity Data for Astrophysics", Published 4 June 2018,
Atoms 2018, 6(2), 31, https://doi.org/10.3390/atoms602003
Model Atmospheres for X-ray Bursting Neutron Stars
The hydrogen and helium accreted by X-ray bursting neutron stars is
periodically consumed in runaway thermonuclear reactions that cause the entire
surface to glow brightly in X-rays for a few seconds. With models of the
emission, the mass and radius of the neutron star can be inferred from the
observations. By simultaneously probing neutron star masses and radii, X-ray
bursts are one of the strongest diagnostics of the nature of matter at
extremely high densities. Accurate determinations of these parameters are
difficult, however, due to the highly non-ideal nature of the atmospheres where
X-ray bursts occur. Observations from X-ray telescopes such as RXTE and NuStar
can potentially place strong constraints on nuclear matter once uncertainties
in atmosphere models have been reduced. Here we discuss current progress on
modeling atmospheres of X-ray bursting neutron stars and some of the challenges
still to be overcome.Comment: 25 pages, 14 figure
Spectra and Light Curves of Failed Supernovae
Astronomers have proposed a number of mechanisms to produce supernova
explosions. Although many of these mechanisms are now not considered primary
engines behind supernovae, they do produce transients that will be observed by
upcoming ground-based surveys and NASA satellites. Here we present the first
radiation-hydrodynamics calculations of the spectra and light curves from three
of these "failed" supernovae: supernovae with considerable fallback, accretion
induced collapse of white dwarfs, and energetic helium flashes (also known as
type .Ia supernovae).Comment: 33 pages, 14 figure
Interpolated kilonova spectra models: necessity for a phenomenological, blue component in the fitting of AT2017gfo spectra
In this work, we present a simple interpolation methodology for spectroscopic
time series, based on conventional interpolation techniques (random forests)
implemented in widely-available libraries. We demonstrate that our existing
library of simulations is sufficient for training, producing interpolated
spectra that respond sensitively to varied ejecta parameter, post-merger time,
and viewing angle inputs. We compare our interpolated spectra to the AT2017gfo
spectral data, and find parameters similar to our previous inferences using
broadband light curves. However, the spectral observations have significant
systematic short-wavelength residuals relative to our models, which we cannot
explain within our existing framework. Similar to previous studies, we argue
that an additional blue component is required. We consider a radioactive
heating source as a third component characterized by light, slow-moving,
lanthanide-free ejecta with , c,
and cm/g. When included as part of our radiative
transfer simulations, our choice of third component reprocesses blue photons
into lower energies, having the opposite effect and further accentuating the
blue-underluminosity disparity in our simulations. As such, we are unable to
overcome short-wavelength deficits at later times using an additional
radioactive heating component, indicating the need for a more sophisticated
modeling treatment.Comment: 11 pages, 7 figures, presenting at April APS session F13.0000
Allele-specific antibodies to Plasmodium vivax merozoite surface protein-1: prevalence and inverse relationship to haemoglobin levels during infection.
BACKGROUND: Antigenic polymorphisms are considered as one of the main strategies employed by malaria parasites to escape from the host immune responses after infections. Merozoite surface protein-1 (MSP-1) of Plasmodium vivax, a promising vaccine candidate, is a highly polymorphic protein whose immune recognition is not well understood. METHODS AND RESULTS: The IgG responses to conserved (MSP-119) and polymorphic (block 2 and block 10) epitopes of PvMSP-1 were evaluated in 141 P. vivax infected patients. Ten recombinant proteins corresponding to block 2 (variants BR07, BP29, BP39, BP30, BEL) and block 10 (BR07, BP29, BP39, BP01, BP13) often observed in Brazilian P. vivax isolates were assessed by ELISA in order to determine levels of specific antibodies and their respective seroprevalence. The magnitude and the frequency of variant-specific responses were very low, except for BR07 variant (>40%), which was the predominant haplotype as revealed by block 10 PvMSP-1 gene sequencing. By contrast, 89% of patients had IgG against the C-terminal conserved domain (PvMSP-119), confirming the high antigenicity of this protein. Using multiple linear and logistic regression models, there was evidence for a negative association between levels of haemoglobin and several IgG antibodies against block 2 variant antigens, with the strongest association being observed for BP39 allelic version. This variant was also found to increase the odds of anaemia in these patients. CONCLUSIONS: These findings may have implications for vaccine development and represent an important step towards a better understanding of the polymorphic PvMSP-1 domain as potential targets of vaccine development. These data highlight the importance of extending the study of these polymorphic epitopes of PvMSP-1 to different epidemiological settings
The Los Alamos Supernova Light Curve Project: Computational Methods
We have entered the era of explosive transient astronomy, in which upcoming
real-time surveys like the Large Synoptic Survey Telescope (LSST), the Palomar
Transient Factory (PTF) and Panoramic Survey Telescope and Rapid Response
System (Pan-STARRS) will detect supernovae in unprecedented numbers. Future
telescopes such as the James Webb Space Telescope may discover supernovae from
the earliest stars in the universe and reveal their masses. The observational
signatures of these astrophysical transients are the key to unveiling their
central engines, the environments in which they occur, and to what precision
they will pinpoint cosmic acceleration and the nature of dark energy. We
present a new method for modeling supernova light curves and spectra with the
radiation hydrodynamics code RAGE coupled with detailed monochromatic opacities
in the SPECTRUM code. We include a suite of tests that demonstrate how the
improved physics is indispensable to modeling shock breakout and light curves.Comment: 18 pages, 19 figures, published in ApJ Supplement