5,078 research outputs found
White Light Flare Continuum Observations with ULTRACAM
We present sub-second, continuous-coverage photometry of three flares on the
dM3.5e star, EQ Peg A, using custom continuum filters with WHT/ULTRACAM. These
data provide a new view of flare continuum emission, with each flare exhibiting
a very distinct light curve morphology. The spectral shape of flare emission
for the two large-amplitude flares is compared with synthetic ULTRACAM
measurements taken from the spectra during the large 'megaflare' event on a
similar type flare star. The white light shape during the impulsive phase of
the EQ Peg flares is consistent with the range of colors derived from the
megaflare continuum, which is known to contain a Hydrogen recombination
component and compact, blackbody-like components. Tentative evidence in the
ULTRACAM photometry is found for an anti-correlation between the emission of
these components.Comment: 8 pages, 3 figures. Proceedings of the 16th Workshop on Cool Stars,
Stellar Systems, and the Sun (PASP conference series, in press
Observation of Collective-Emission-Induced Cooling inside an Optical Cavity
We report the observation of collective-emission-induced, velocity-dependent
light forces. One third of a falling sample containing 3 x 10^6 cesium atoms
illuminated by a horizontal standing wave is stopped by cooperatively emitting
light into a vertically oriented confocal resonator. We observe decelerations
up to 1500 m/s^2 and cooling to temperatures as low as 7 uK, well below the
free space Doppler limit. The measured forces substantially exceed those
predicted for a single two-level atom.Comment: 10 pages, 5 figure
33.8 GHz CCS Survey of Molecular Cores in Dark Clouds
We have conducted a survey of the CCS line toward 11 dark
clouds and star-forming regions at 30 arcsec spatial resolution and 0.054 km/s
velocity resolution. CCS was only detected in quiescent clouds, not in active
star-forming regions. The CCS distribution shows remarkable clumpy structure,
and 25 clumps are identified in 7 clouds. Seven clumps with extremely narrow
nonthermal linewidths < 0.1 km/s are among the most quiescent clumps ever
found. The CCS clumps tend to exist around the higher density regions traced by
NH_3 emission or submillimeter continuum sources, and the distribution is not
spherically symmetric. Variation of the CCS abundance was suggested as an
indicator of the evolutionary status of star formation. However, we can only
find a weak correlation between N(CCS) and . The velocity
distributions of CCS clouds reveal that a systematic velocity pattern generally
exists. The most striking feature in our data is a ring structure in the
position-velocity diagram of L1544 with an well-resolved inner hole of 0.04 pc
x 0.13 km/s and an outer boundary of 0.16 pc x 0.55 km/s. This
position-velocity structure clearly indicates an edge-on disk or ring geometry,
and it can be interpreted as a collapsing disk with an infall velocity
0.1 km/s and a rotational velocity less than our velocity resolution.
Nonthermal linewidth distribution is generally coherent in CCS clouds, which
could be evidence for the termination of Larson's Law at small scales,
0.1 pc.Comment: 21 pages, 25 ostscript figures, accepted for publication in the
Supplement Series of the Astrophysical Journal (May 2000
Representation theory of some infinite-dimensional algebras arising in continuously controlled algebra and topology
In this paper we determine the representation type of some algebras of
infinite matrices continuously controlled at infinity by a compact metrizable
space. We explicitly classify their finitely presented modules in the finite
and tame cases. The algebra of row-column-finite (or locally finite) matrices
over an arbitrary field is one of the algebras considered in this paper, its
representation type is shown to be finite.Comment: 33 page
MOST Observations of the Flare Star AD Leo
We present continuous, high-precision photometric monitoring data with 1
minute cadence of the dM3e flare star AD Leo with the {\it MOST} satellite. We
observed 19 flares in 5.8 days, and find a flare frequency distribution that is
similar to previous studies. The light curve reveals a sinusoidal modulation
with period of days that we attribute to the rotation of
a stellar spot rotating into and out of view. We see no correlation between the
occurrence of flares and rotational phase, indicating that there may be many
spots distributed at different longitudes, or possibly that the modulation is
caused by varying surface coverage of a large polar spot that is viewed nearly
pole-on. The data show no correlation between flare energy and the time since
the previous flare. We use these results to reject a simple model in which all
magnetic energy is stored in one active region and released only during flares.Comment: 20 Pages, 8 Figures, PASP Accepte
The Role of Bulge Formation in the Homogenization of Stellar Populations at as revealed by Internal Color Dispersion in CANDELS
We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy
Survey to study how the spatial variation in the stellar populations of
galaxies relate to the formation of galaxies at . We use the
Internal Color Dispersion (ICD), measured between the rest-frame UV and optical
bands, which is sensitive to age (and dust attenuation) variations in stellar
populations. The ICD shows a relation with the stellar masses and morphologies
of the galaxies. Galaxies with the largest variation in their stellar
populations as evidenced by high ICD have disk-dominated morphologies (with
S\'{e}rsic indexes ) and stellar masses between . There is a marked decrease in the ICD as the stellar mass and/or
the S\'ersic index increases. By studying the relations between the ICD and
other galaxy properties including sizes, total colors, star-formation rate, and
dust attenuation, we conclude that the largest variations in stellar
populations occur in galaxies where the light from newly, high star-forming
clumps contrasts older stellar disk populations. This phase reaches a peak for
galaxies only with a specific stellar mass range, , and prior to the formation of a substantial bulge/spheroid. In contrast,
galaxies at higher or lower stellar masses, and/or higher S\'{e}rsic index () show reduced ICD values, implying a greater homogeneity of their stellar
populations. This indicates that if a galaxy is to have both a quiescent bulge
along with a star forming disk, typical of Hubble Sequence galaxies, this is
most common for stellar masses and when the
bulge component remains relatively small ().Comment: 15 pages, 14 figure
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