308,805 research outputs found
Laboratory Astrophysics and the State of Astronomy and Astrophysics
Laboratory astrophysics and complementary theoretical calculations are the
foundations of astronomy and astrophysics and will remain so into the
foreseeable future. The impact of laboratory astrophysics ranges from the
scientific conception stage for ground-based, airborne, and space-based
observatories, all the way through to the scientific return of these projects
and missions. It is our understanding of the under-lying physical processes and
the measurements of critical physical parameters that allows us to address
fundamental questions in astronomy and astrophysics. In this regard, laboratory
astrophysics is much like detector and instrument development at NASA, NSF, and
DOE. These efforts are necessary for the success of astronomical research being
funded by the agencies. Without concomitant efforts in all three directions
(observational facilities, detector/instrument development, and laboratory
astrophysics) the future progress of astronomy and astrophysics is imperiled.
In addition, new developments in experimental technologies have allowed
laboratory studies to take on a new role as some questions which previously
could only be studied theoretically can now be addressed directly in the lab.
With this in mind we, the members of the AAS Working Group on Laboratory
Astrophysics, have prepared this State of the Profession Position Paper on the
laboratory astrophysics infrastructure needed to ensure the advancement of
astronomy and astrophysics in the next decade.Comment: Position paper submitted by the AAS Working Group on Laboratory
Astrophysics (WGLA) to the State of the Profession (Facilities, Funding and
Programs Study Group) of the Astronomy and Astrophysics Decadal Survey
(Astro2010
XMM-Newton unveils the complex iron K alpha region of Mrk 279
We present the results of a ~160 ks-long XMM-Newton observation of the
Seyfert 1 galaxy Mrk 279. The spectrum shows evidence of both broad and narrow
emission features. The Fe K alpha line may be equally well explained by a
single broad Gaussian (FWHM~10,000 km/s) or by two components: an unresolved
core plus a very broad profile (FWHM~14,000 km/s). For the first time we
quantified, via the "locally optimally emitting cloud" model, the contribution
of the broad line region (BLR) to the absolute luminosity of the broad
component of the Fe K alpha at 6.4 keV. We find that the contribution of the
BLR is only ~3%. In the two-line component scenario, we also evaluated the
contribution of the highly ionized gas component, which produces the FeXXVI
line in the iron K region. This contribution to the narrow core of the Fe K
alpha line is marginal <0.1%. Most of the luminosity of the unresolved,
component of Fe K alpha may come from the obscuring torus, while the very-broad
associated component may come from the accretion disk. However, models of
reflection by cold gas are difficult to test because of the limited energy
band. The FeXXVI line at 6.9 keV is consistent to be produced in a high column
density (N_H~10^23 cm^{-2}), extremely ionized (log\xi~5.5-7) gas. This gas may
be a highly ionized outer layer of the torus.Comment: 10 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
The VLT-FLAMES survey of massive stars: Wind properties and evolution of hot massive stars in the LMC
[Abridged] We have studied the optical spectra of 28 O- and early B-type
stars in the Large Magellanic Cloud, 22 of which are associated with the young
star-forming region N11. Stellar parameters are determined using an automated
fitting method, combining the stellar atmosphere code FASTWIND with the
genetic-algorithm optimisation routine PIKAIA. Results for stars in the LH9 and
LH10 associations of N11 are consistent with a sequential star formation
scenario, in which activity in LH9 triggered the formation of LH10. Our sample
contains four stars of spectral type O2, of which the hottest is found to be
~49-54 kK (cf. ~45-46 kK for O3 stars). The masses of helium-enriched dwarfs
and giants are systematically lower than those implied by non-rotating
evolutionary tracks. We interpret this as evidence for efficient
rotationally-enhanced mixing, leading to the surfacing of primary helium and to
an increase of the stellar luminosity. This result is consistent with findings
for SMC stars by Mokiem et al. For bright giants and supergiants no such
mass-discrepancy is found, implying that these stars follow tracks of modestly
(or non-)rotating objects. Stellar mass-loss properties were found to be
intermediate to those found in massive stars in the Galaxy and the SMC, and
comparisons with theoretical predictions at LMC metallicity yielded good
agreement over the luminosity range of our targets, i.e. 5.0 < log L/L(sun) <
6.1
Toward detailed prominence seismology - II. Charting the continuous magnetohydrodynamic spectrum
Starting from accurate MHD flux rope equilibria containing prominence
condensations, we initiate a systematic survey of their linear
eigenoscillations. To quantify the full spectrum of linear MHD eigenmodes, we
require knowledge of all flux-surface localized modes, charting out the
continuous parts of the MHD spectrum. We combine analytical and numerical
findings for the continuous spectrum for realistic prominence configurations.
The equations governing all eigenmodes for translationally symmetric,
gravitating equilibria containing an axial shear flow, are analyzed, along with
their flux-surface localized limit. The analysis is valid for general 2.5D
equilibria, where either density, entropy, or temperature vary from one flux
surface to another. We analyze the mode couplings caused by the poloidal
variation in the flux rope equilibria, by performing a small gravity parameter
expansion. We contrast the analytical results with continuous spectra obtained
numerically. For equilibria where the density is a flux function, we show that
continuum modes can be overstable, and we present the stability criterion for
these convective continuum instabilities. Furthermore, for all equilibria, a
four-mode coupling scheme between an Alfvenic mode of poloidal mode number m
and three neighboring (m-1, m, m+1) slow modes is identified, occurring in the
vicinity of rational flux surfaces. For realistically prominence equilibria,
this coupling is shown to play an important role, from weak to stronger gravity
parameter g values. The analytic predictions for small g are compared with
numerical spectra, and progressive deviations for larger g are identified. The
unstable continuum modes could be relevant for short-lived prominence
configurations. The gaps created by poloidal mode coupling in the continuous
spectrum need further analysis, as they form preferred frequency ranges for
global eigenoscillations.Comment: Accepted by Astronmy & Astrophysics, 21 pages, 15 figure
Astrophysics
Historical account of astrophysics development based on photometry and spectroscop
Nuclear Astrophysics
Nuclear physics has a long and productive history of application to
astrophysics which continues today. Advances in the accuracy and breadth of
astrophysical data and theory drive the need for better experimental and
theoretical understanding of the underlying nuclear physics. This paper will
review some of the scenarios where nuclear physics plays an important role,
including Big Bang Nucleosynthesis, neutrino production by our sun,
nucleosynthesis in novae, the creation of elements heavier than iron, and
neutron stars. Big-bang nucleosynthesis is concerned with the formation of
elements with A <= 7 in the early Universe; the primary nuclear physics inputs
required are few-nucleon reaction cross sections. The nucleosynthesis of
heavier elements involves a variety of proton-, alpha-, neutron-, and
photon-induced reactions, coupled with radioactive decay. The advent of
radioactive ion beam facilities has opened an important new avenue for studying
these processes, as many involve radioactive species. Nuclear physics also
plays an important role in neutron stars: both the nuclear equation of state
and cooling processes involving neutrino emission play a very important role.
Recent developments and also the interplay between nuclear physics and
astrophysics will be highlighted.Comment: To be published in the Proceedings of 19th Lake Louise Winter
Institute (15-21 February 2004). 9 pages, 3 figure
Young and intermediate-age massive star clusters
An overview of our current understanding of the formation and evolution of
star clusters is given, with main emphasis on high-mass clusters. Clusters form
deeply embedded within dense clouds of molecular gas. Left-over gas is cleared
within a few million years and, depending on the efficiency of star formation,
the clusters may disperse almost immediately or remain gravitationally bound.
Current evidence suggests that a few percent of star formation occurs in
clusters that remain bound, although it is not yet clear if this fraction is
truly universal. Internal two-body relaxation and external shocks will lead to
further, gradual dissolution on timescales of up to a few hundred million years
for low-mass open clusters in the Milky Way, while the most massive clusters (>
10^5 Msun) have lifetimes comparable to or exceeding the age of the Universe.
The low-mass end of the initial cluster mass function is well approximated by a
power-law distribution, dN/dM ~ M^{-2}, but there is mounting evidence that
quiescent spiral discs form relatively few clusters with masses M > 2 x 10^5
Msun. In starburst galaxies and old globular cluster systems, this limit
appears to be higher, at least several x 10^6 Msun. The difference is likely
related to the higher gas densities and pressures in starburst galaxies, which
allow denser, more massive giant molecular clouds to form. Low-mass clusters
may thus trace star formation quite universally, while the more long-lived,
massive clusters appear to form preferentially in the context of violent star
formation.Comment: 21 pages, 3 figures. To appear as invited review article in a special
issue of the Phil. Trans. Royal Soc. A: Ch. 9 "Star clusters as tracers of
galactic star-formation histories" (ed. R. de Grijs). Fully peer reviewed.
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