370 research outputs found
Numerical models for the circumstellar medium around Betelgeuse
The nearby red supergiant (RSG) Betelgeuse has a complex circumstellar medium
out to at least 0.5 parsecs from its surface, shaped by its mass-loss history
within the past 0.1 Myr, its environment, and its motion through the
interstellar medium (ISM). In principle its mass-loss history can be
constrained by comparing hydrodynamic models with observations. Observations
and numerical simulations indicate that Betelgeuse has a very young bow shock,
hence the star may have only recently become a RSG. To test this possibility we
calculated a stellar evolution model for a single star with properties
consistent with Betelgeuse. We incorporated the resulting evolving stellar wind
into 2D hydrodynamic simulations to model a runaway blue supergiant (BSG)
undergoing the transition to a RSG near the end of its life. The collapsing BSG
wind bubble induces a bow shock-shaped inner shell which at least superficially
resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is
the larger-scale retreating bow shock generated by the now defunct BSG wind's
interaction with the ISM. We investigate whether this outer shell could explain
the bar feature located (at least in projection) just in front of Betelgeuse's
bow shock.Comment: 5 pages, 3 figures; to appear in proceedings of the Betelgeuse 2012
Workshop, Paris, Nov. 201
The Connection Between Pulsation, Mass Loss and Circumstellar Shells in Classical Cepheids
Recent observations of Cepheids using infrared interferometry and Spitzer
photometry have detected the presence of circumstellar envelopes (CSE) of dust
and it has been hypothesized that the CSE's are due to dust forming in a
Cepheid wind. Here we use a modified Castor, Abbott & Klein formalism to
produce a Cepheid wind, and this is used to estimate the contribution of mass
loss to the Cepheid mass discrepancy Furthermore, we test the OGLE-III
Classical Cepheids using the IR fluxes from the SAGE survey to determine if
Large Magellanic Cloud Cepheids have CSE's. It is found that IR excess is a
common phenomenon for LMC Cepheids and that the resulting mass-loss rates can
explain at least a fraction of the Cepheid mass discrepancy, depending on the
assumed dust-to-gas ratio in the wind.Comment: 5 pages, 3 figures, proceeding for "Stellar Pulsation: Challenges for
Theory and Observation", Santa Fe 200
Period-Luminosity Relations Derived from the OGLE-III Fundamental Mode Cepheids
In this Paper, we have derived Cepheid period-luminosity (P-L) relations for
the Large Magellanic Cloud (LMC) fundamental mode Cepheids, based on the data
released from OGLE-III. We have applied an extinction map to correct for the
extinction of these Cepheids. In addition to the VIW band P-L relations, we
also include JHK and four Spitzer IRAC band P-L relations, derived by matching
the OGLE-III Cepheids to the 2MASS and SAGE datasets, respectively. We also
test the non-linearity of the Cepheid P-L relations based on
extinction-corrected data. Our results (again) show that the LMC P-L relations
are non-linear in VIJH bands and linear in KW and the four IRAC bands,
respectively.Comment: 6 pages, 3 figures and 3 tables, ApJ accepte
Heat transfer studies of vapor condensing at high velocities in straight tubes interim progress report, 1 nov. 1964 - 30 apr. 1965
Heat transfer of vapor condensing at high velocities in straight tube
Celecoxib does not appear to affect prosthesis fixation in total knee replacement: A randomized study using radiostereometry in 50 patients
Background and purpose After joint replacement, a repair process starts at the interface between bone and cement. If this process is disturbed, the prosthesis may never become rigidly fixed to the bone, leading to migration—and with time, loosening. Cox-2 inhibitors are widely used as postoperative analgesics, and have adverse effects on bone healing. This could tamper prosthesis fixation. We investigated whether celecoxib, a selective Cox-2 inhibitor, increases prosthesis migration in total knee replacement (TKR)
Stellar Astrophysics and Exoplanet Science with the Maunakea Spectroscopic Explorer (MSE)
The Maunakea Spectroscopic Explorer (MSE) is a planned 11.25-m aperture
facility with a 1.5 square degree field of view that will be fully dedicated to
multi-object spectroscopy. A rebirth of the 3.6m Canada-France-Hawaii Telescope
on Maunakea, MSE will use 4332 fibers operating at three different resolving
powers (R ~ 2500, 6000, 40000) across a wavelength range of 0.36-1.8mum, with
dynamical fiber positioning that allows fibers to match the exposure times of
individual objects. MSE will enable spectroscopic surveys with unprecedented
scale and sensitivity by collecting millions of spectra per year down to
limiting magnitudes of g ~ 20-24 mag, with a nominal velocity precision of ~100
m/s in high-resolution mode. This white paper describes science cases for
stellar astrophysics and exoplanet science using MSE, including the discovery
and atmospheric characterization of exoplanets and substellar objects, stellar
physics with star clusters, asteroseismology of solar-like oscillators and
opacity-driven pulsators, studies of stellar rotation, activity, and
multiplicity, as well as the chemical characterization of AGB and extremely
metal-poor stars.Comment: 31 pages, 11 figures; To appear as a chapter for the Detailed Science
Case of the Maunakea Spectroscopic Explore
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