199 research outputs found
The non-uniform, dynamic atmosphere of Betelgeuse observed at mid-infrared wavelengths
We present an interferometric study of the continuum surface of the red
supergiant star Betelgeuse at 11.15 microns wavelength, using data obtained
with the Berkeley Infrared Spatial Interferometer each year between 2006 and
2010. These data allow an investigation of an optically thick layer within 1.4
stellar radii of the photosphere. The layer has an optical depth of ~1 at 11.15
microns, and varies in temperature between 1900 K and 2800 K and in outer
radius between 1.16 and 1.36 stellar radii. Electron-hydrogen atom collisions
contribute significantly to the opacity of the layer. The layer has a
non-uniform intensity distribution that changes between observing epochs. These
results indicate that large-scale surface convective activity strongly
influences the dynamics of the inner atmosphere of Betelgeuse, and mass-loss
processes.Comment: 13 pages, 5 figures, in press (ApJ
Distributed Management of Massive Data: an Efficient Fine-Grain Data Access Scheme
This paper addresses the problem of efficiently storing and accessing massive
data blocks in a large-scale distributed environment, while providing efficient
fine-grain access to data subsets. This issue is crucial in the context of
applications in the field of databases, data mining and multimedia. We propose
a data sharing service based on distributed, RAM-based storage of data, while
leveraging a DHT-based, natively parallel metadata management scheme. As
opposed to the most commonly used grid storage infrastructures that provide
mechanisms for explicit data localization and transfer, we provide a
transparent access model, where data are accessed through global identifiers.
Our proposal has been validated through a prototype implementation whose
preliminary evaluation provides promising results
Imaging the dynamical atmosphere of the red supergiant Betelgeuse in the CO first overtone lines with VLTI/AMBER
We present the first 1-D aperture synthesis imaging of the red supergiant
Betelgeuse in the individual CO first overtone lines with VLTI/AMBER. The
reconstructed 1-D projection images reveal that the star appears differently in
the blue wing, line center, and red wing of the individual CO lines. The 1-D
projection images in the blue wing and line center show a pronounced,
asymmetrically extended component up to ~1.3 stellar radii, while those in the
red wing do not show such a component. The observed 1-D projection images in
the lines can be reasonably explained by a model in which the CO gas within a
region more than half as large as the stellar size is moving slightly outward
with 0--5 km s^-1, while the gas in the remaining region is infalling fast with
20--30 km s^-1. A comparison between the CO line AMBER data taken in 2008 and
2009 shows a significant time variation in the dynamics of the CO line-forming
region in the photosphere and the outer atmosphere. In contrast to the line
data, the reconstructed 1-D projection images in the continuum show only a
slight deviation from a uniform disk or limb-darkened disk. We derive a
uniform-disk diameter of 42.05 +/- 0.05 mas and a power-law-type limb-darkened
disk diameter of 42.49 +/- 0.06 mas and a limb-darkening parameter of (9.7 +/-
0.5) x 10^{-2}. This latter angular diameter leads to an effective temperature
of 3690 +/- 54 K for the continuum-forming layer. These diameters confirm that
the near-IR size of Betelgeuse was nearly constant over the last 18 years, in
marked contrast to the recently reported noticeable decrease in the mid-IR
size. The continuum data taken in 2008 and 2009 reveal no or only marginal time
variations, much smaller than the maximum variation predicted by the current
3-D convection simulations.Comment: 21 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
- …