11,134 research outputs found
A deeper understanding of white dwarf interiors
A detailed record of the physical processes that operate during
post-main-sequence evolution is contained in the internal chemical structure of
white dwarfs. Global pulsations allow us to probe the stellar interior through
asteroseismology, revealing the signatures of prior nuclear burning, mixing,
and diffusion in these stars. I review the rapid evolution of structural models
for helium-atmosphere variable (DBV) white dwarfs over the past five years, and
I present a new series of model-fits using recent observations to illustrate
the relative importance of various interior structures. By incorporating
physically motivated C/O profiles into double-layered envelope models for the
first time, I finally identify an optimal asteroseismic model that agrees with
both diffusion theory and the expected nuclear burning history of the
progenitor. I discuss the implications of this fundamental result, and I
evaluate the prospects for continued progress in the future.Comment: 5 pages, 2 figures, 1 table, Accepted for MNRAS Letter
Crowdfunding Astronomy Research with Google Sky
For nearly four years, NASA's Kepler space telescope searched for planets
like Earth around more than 150,000 stars similar to the Sun. In 2008 with
in-kind support from several technology companies, our non-profit organization
established the Pale Blue Dot Project, an adopt-a-star program that supports
scientific research on the stars observed by the Kepler mission. To help other
astronomy educators conduct successful fundraising efforts, I describe how this
innovative crowdfunding program successfully engaged the public over the past
seven years to help support an international team in an era of economic
austerity.Comment: 7 pages, 3 figures, Journal of Astronomy & Earth Sciences Education,
accepted. Project website is at http://adoptastar.whitedwarf.or
The Citation Impact of Digital Preprint Archives for Solar Physics Papers
Papers that are posted to a digital preprint archive are typically cited
twice as often as papers that are not posted. This has been demonstrated for
papers published in a wide variety of journals, and in many different subfields
of astronomy. Most astronomers now use the arXiv.org server (astro-ph) to
distribute preprints, but the solar physics community has an independent
archive hosted at Montana State University. For several samples of solar
physics papers published in 2003, I quantify the boost in citation rates for
preprints posted to each of these servers. I show that papers on the MSU
archive typically have citation rates 1.7 times higher than the average of
similar papers that are not posted as preprints, while those posted to astro-ph
get 2.6 times the average. A comparable boost is found for papers published in
conference proceedings, suggesting that the higher citation rates are not the
result of self-selection of above-average papers.Comment: 5 pages, 1 table, Solar Physics accepte
The Consequences of assuming m=0 for Global Model-fitting
A recent re-analysis of Whole Earth Telescope observations of GD 358 obtained
in 1990 suggests that asteroseismology of additional DBV white dwarfs can lead
to independent constraints on the important, but poorly determined,
^{12}C(alpha,gamma)^{16}O nuclear reaction rate. Data exist for several other
DBV white dwarfs, but relatively few modes are detected and there is often no
multiplet structure to aid in the identification of the spherical harmonic
indices (l,m). I use a new grid of one million DBV models covering a broad
range of masses, temperatures, and surface helium layer masses to investigate
the consequences of assuming m=0 for global model-fitting. I find that when the
spherical degree is known and the rotation period is of order 1 day, the
model-fitting procedure applied to modes with unknown m-values will still
correctly identify the_families_ of possible solutions, and has a high
probability of identifying the same globally optimal solution found when the
m-value is known.Comment: 5 pages, 2 figures, to appear in proceedings of the 6th Whole Earth
Telescope worksho
WhiteDwarf.org - Establishing a permanent endowment for the Whole Earth Telescope
White Dwarf Research Corporation is a 501(c)(3) non-profit organization
dedicated to scientific research and public education on topics relevant to
white dwarf stars. It was founded in 1999 in Austin, Texas to help fulfill the
need for an alternative research center where scarce funding dollars could be
used more efficiently, and to provide a direct link between astronomers who
study white dwarf stars and the general public. Due to its administrative
simplicity, WDRC can facilitate the funding of multi-institutional and
international collaborations, provide seamless grant portability, minimize
overhead rates, and actively seek non-governmental funding sources. I describe
the motivation for, and current status of, one of the long-term goals of WDRC:
to establish a permanent endowment for the operation of the Whole Earth
Telescope. I pay particular attention to fund-raising efforts through the
website at http://WhiteDwarf.org/donate/Comment: 5 pages, to appear in proceedings of the 6th Whole Earth Telescope
worksho
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