15,961 research outputs found
The Solar Neighborhood VIII: Discovery of New High Proper Motion Nearby Stars Using the SuperCOSMOS Sky Survey
Five new objects with proper motions between 1.0 arcsec/yr and 2.6 arcsec/yr
have been discovered via a new RECONS search for high proper motion stars
utilizing the SuperCOSMOS Sky Survey. The first portion of the search,
discussed here, is centered on the south celestial pole and covers declinations
-90 degrees to -57.5 degrees.
Photographic photometry from SuperCOSMOS and JHKs near-infrared photometry
from 2MASS for stars nearer than 10 pc are combined to provide a suite of new
M_Ks-color relations useful for estimating distances to main sequence stars.
These relations are then used to derive distances to the new proper motion
objects as well as previously known stars with mu >= 1.0 arcsec/yr (many of
which have no trigonometric parallaxes) recovered during this phase of the
survey.
Four of the five new stars have red dwarf colors, while one is a nearby white
dwarf. Two of the red dwarfs are likely to be within the RECONS 10 pc sample,
and the white dwarf probably lies between 15 and 25 pc. Among the 23 known
stars recovered during the search, there are three additional candidates for
the RECONS sample that have no trigonometric parallaxes.Comment: 17 pages, 5 figures; accepted for publication in Astronomy Journa
Computing NodeTrix Representations of Clustered Graphs
NodeTrix representations are a popular way to visualize clustered graphs;
they represent clusters as adjacency matrices and inter-cluster edges as curves
connecting the matrix boundaries. We study the complexity of constructing
NodeTrix representations focusing on planarity testing problems, and we show
several NP-completeness results and some polynomial-time algorithms. Building
on such algorithms we develop a JavaScript library for NodeTrix representations
aimed at reducing the crossings between edges incident to the same matrix.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Static and Dynamic Spectroscopy of (Al,Ga)As/GaAs Microdisk Lasers with Interface Fluctuation Quantum Dots
We have studied the steady state and dynamic optical properties of
semiconductor microdisk lasers whose active region contains interface
fluctuation quantum dots in GaAs/(Ga,Al)As quantum wells. Steady-state
measurements of the stimulated emission via whispering gallery modes yield a
quality factor and a coupling constant . The
broad gain spectrum produces mode hopping between spectrally adjacent
whispering gallery modes as a function of temperature and excitation power.
Time- and energy-resolved photoluminescence measurements show that the emission
rise and decay rates increase significantly with excitation power. Marked
differences are observed between the radiative decay rates in processed and
unprocessed samples.Comment: To appear in Phys. Rev.
Evidence for Non-Hydrostatic Gas from the Cluster X-ray to Lensing Mass Ratio
Using a uniform analysis procedure, we measure spatially resolved weak
gravitational lensing and hydrostatic X-ray masses for a sample of 18 clusters
of galaxies. We find a radial trend in the X-ray to lensing mass ratio: at
r2500 we obtain a ratio MX/ML=1.03+/-0.07 which decreases to MX/ML=0.78+/-0.09
at r500. This difference is significant at 3 sigma once we account for
correlations between the measurements. We show that correcting the lensing mass
for excess correlated structure outside the virial radius slightly reduces, but
does not eliminate this trend. An X-ray mass underestimate, perhaps due to
nonthermal pressure support, can explain the residual trend. The trend is not
correlated with the presence or absence of a cool core. We also examine the
cluster gas fraction and find no correlation with ML, an important result for
techniques that aim to determine cosmological parameters using the gas
fraction.Comment: 8 pages, minor modifications, accepted for publication in MNRA
Cluster Mass Estimate and a Cusp of the Mass Density Distribution in Clusters of Galaxies
We study density cusps in the center of clusters of galaxies to reconcile
X-ray mass estimates with gravitational lensing masses. For various mass
density models with cusps we compute X-ray surface brightness distribution, and
fit them to observations to measure the range of parameters in the density
models. The Einstein radii estimated from these density models are compared
with Einstein radii derived from the observed arcs for Abell 2163, Abell 2218,
and RX J1347.5-1145. The X-ray masses and lensing masses corresponding to these
Einstein radii are also compared. While steeper cusps give smaller ratios of
lensing mass to X-ray mass, the X-ray surface brightnesses estimated from
flatter cusps are better fits to the observations. For Abell 2163 and Abell
2218, although the isothermal sphere with a finite core cannot produce giant
arc images, a density model with a central cusp can produce a finite Einstein
radius, which is smaller than the observed radii. We find that a total mass
density profile which declines as produces the largest radius
in models which are consistent with the X-ray surface brightness profile. As
the result, the extremely large ratio of the lensing mass to the X-ray mass is
improved from 2.2 to 1.4 for Abell 2163, and from 3 to 2.4 for Abell 2218. For
RX J1347.5-1145, which is a cooling flow cluster, we cannot reduce the mass
discrepancy.Comment: 23 pages, 10 figures, Latex, uses aasms4.sty, accepted for
publication in ApJ, Part
IMMUNOLOGIC REACTIONS TO HAPTENS ON AUTOLOGOUS CARRIERS : I. PARTICIPATION OF BOTH THYMUS-DERIVED AND BONE MARROW-DERIVED CELLS IN THE SECONDARY IN VITRO RESPONSE
Both thymus-derived (T) and bone marrow-derived (B) lymphocytes participate in the response to a hapten 4-hydroxy-3-iodo-5-nitrophenylacetic acid (NIP), coupled to a nonimmunogenic isologous carrier, mouse gamma globulin (MGG). Spleen cells from mice immunized with NIP-MGG show increased DNA synthesis in vitro when cultured with NIP-MGG. The participation of and requirement for T cells in the response was demonstrated by treating the spleen cells with anti-θ serum. This treatment resulted in a 77% inhibition of the antigen response. Furthermore, adoptively transferred normal thymus cells could be specifically "activated" by NIP-MGG in vivo and they responded secondarily to the antigen in vitro. The active participation of B cells in the secondary response was demonstrated by passing the immune spleen cells through a column coated with polyvalent anti-MGG serum. Column filtration reduced the number of NIP-specific plaque-forming cells and NIP-specific rosette-forming cells (both functions of B cells) and produced a 47% inhibition of the NIP-MGG response. The ability of the cells to respond to phytohemagglutinin (PHA) was not affected by column filtration showing that T cells were not being selectively removed. The participation of B cells in the in vitro NIP-MGG response was also shown by treatment of the spleen cells with antiserum specific for MGG and MGG determinants. B cells were removed by treatment with anti-IgM or polyvalent anti-MGG serum plus complement, resulting in a respective 46 and 49% inhibition of the response to NIP-MGG. (Treatment with anti-IgM serum had no effect on T cells.) The contribution of the hapten NIP to stimulation of T cells was investigated using NIP-MGG-activated thymus cells. These activated T cells responded in vitro very well to the NIP-MGG complex but not to the MGG carrier alone demonstrating the requirement of the hapten for T cell stimulation. The response was also partially inhibited (41%) by incubating the activated cells with NIP coupled to a single amino acid (epsilon-aminocaproic acid) before addition of NIP-MGG. These results demonstrated that T cells recognize the hapten NIP when it is coupled to the isologous carrier MGG
The Rotation Period of the Planet-Hosting Star HD 189733
We present synoptic optical photometry of HD 189733, the chromospherically
active parent star of one of the most intensively studied exoplanets. We have
significantly extended the timespan of our previously reported observations and
refined the estimate of the stellar rotation period by more than an order of
magnitude: days. We derive a lower limit on the
inclination of the stellar rotation axis of 56\arcdeg (with 95% confidence),
corroborating earlier evidence that the stellar spin axis and planetary orbital
axis are well aligned.Comment: To appear in A
Five New Transits of the Super-Neptune HD 149026
We present new photometry of HD 149026 spanning five transits of its
"super-Neptune" planet. In combination with previous data, we improve upon the
determination of the planet-to-star radius ratio: R_p/R_star =
0.0491^{+0.0018}_{-0.0005}. We find the planetary radius to be 0.71 +/- 0.05
R_Jup, in accordance with previous theoretical models invoking a high metal
abundance for the planet. The limiting error is the uncertainty in the stellar
radius. Although we find agreement among four different ways of estimating the
stellar radius, the uncertainty remains at 7%. We also present a refined
transit ephemeris and a constraint on the orbital eccentricity and argument of
pericenter, e cos(omega) = -0.0014 +/- 0.0012, based on the measured interval
between primary and secondary transits.Comment: To appear in ApJ [19 pages
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