658 research outputs found
Lensed Arcs and Inner Structure of Abell 697
We present new optical observations of the z=0.282 cluster Abell 697 from the
Keck II telescope. Images show an unusual disturbed structure in the cD halo
and a previously unknown faint gravitational lens arc. A spectrum of the arc
did not yield a redshift, but its spectrum and colors suggest it lies at z>1.3.
We construct models to reproduce the arc that show the potential is likely to
be highly elliptical. We suggest that this cluster may have undergone a recent
merger and is in the process of forming its cD galaxy. Analysis of X-ray data
from ROSAT and ASCA suggests that the merging process is sufficiently advanced
that the gas in the cluster has relaxed, and A697 lies near the L_x-T_x
relation for normal clusters.Comment: LaTeX; 12 pages, 3 figures, submitted to ApJ Letter
A Lensed Arc in the Low Redshift Cluster Abell 2124
We report the discovery of an arc-like object 27" from the center of the cD
galaxy in the redshift cluster A2124. Observations with the Keck II
telescope reveal that the object is a background galaxy at ,
apparently lensed into an arc of length \sim 8 \farcs5 and total R magnitude
. The width of the arc is resolved; we estimate it to be
0\farcs6 after correcting for seeing. A lens model of the A2124 core mass
distribution consistent with the cluster galaxy velocity dispersion reproduces
the observed arc geometry and indicates a magnification factor \gta 9. With
this magnification, the strength of the [OII] \lambda 3727 line implies a
star-formation rate of SFR \sim 0.4 h^{-2}\msun yr^{-1}$. A2124 thus appears to
be the lowest redshift cluster known to exhibit strong lensing of a distant
background galaxy.Comment: 6 pages using emulateapj.sty; 4 Postscript figures; Figure 4 uses
color. Accepted for publication, but ApJ Letters' new policy of counting data
images makes the manuscript too long; will appear in main journal. This final
version has minor correction
Constaints on the shape and scale of the galactic gravitational potential
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994.Includes bibliographical references (leaves 212-213).by Mark Robert Metzger.Ph.D
A Search for Distant Galactic Cepheids Toward l=60
We present results of a survey of a 6-square-degree region near l=60, b=0 to
search for distant Milky Way Cepheids. Few MW Cepheids are known at distances
>~ R_0, limiting large-scale MW disk models derived from Cepheid kinematics;
this work was designed to find a sample of distant Cepheids for use in such
models. The survey was conducted in the V and I bands over 8 epochs, to a
limiting I~=18, with a total of ~ 5 million photometric observations of ~ 1
million stars. We present a catalog of 578 high-amplitude variables discovered
in this field. Cepheid candidates were selected from this catalog on the basis
of variability and color change, and observed again the following season. We
confirm 10 of these candidates as Cepheids with periods from 4 to 8 days, most
at distances > 3 kpc. Many of the Cepheids are heavily reddened by intervening
dust, some with implied extinction A_V > 10 mag. With a future addition of
infrared photometry and radial velocities, these stars alone can provide a
constraint on R_0 to 8%, and in conjunction with other known Cepheids should
provide good estimates of the global disk potential ellipticity.Comment: 18 pages, 4 tables, 13 figures (LaTeX / AASTeX
Matched cohort study of germline BRCA mutation carriers with triple negative breast cancer in brightness
The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for band Surface Brightness Fluctuation (SBF) magnitudes,
V-I colors, and distance moduli for 300 galaxies. The Survey contains E, S0 and
early-type spiral galaxies in the proportions of 49:42:9, and is essentially
complete for E galaxies to Hubble velocities of 2000 km/s, with a substantial
sampling of E galaxies out to 4000 km/s. The median error in distance modulus
is 0.22 mag.
We also present two new results from the Survey. (1) We compare the mean
peculiar flow velocity (bulk flow) implied by our distances with predictions of
typical cold dark matter transfer functions as a function of scale, and find
very good agreement with cold, dark matter cosmologies if the transfer function
scale parameter , and the power spectrum normalization are
related by . Derived directly from
velocities, this result is independent of the distribution of galaxies or
models for biasing. The modest bulk flow contradicts reports of large-scale,
large-amplitude flows in the Mpc diameter volume surrounding our
Survey volume. (2) We present a distance-independent measure of absolute galaxy
luminosity, \Nbar, and show how it correlates with galaxy properties such as
color and velocity dispersion, demonstrating its utility for measuring galaxy
distances through large and unknown extinction.Comment: Accepted for publication in ApJ (10 January 2001); 23 page
Generation of Transplantable Beta Cells for Patient-Specific Cell Therapy
Islet cell transplantation offers a potential cure for type 1 diabetes, but it is challenged by insufficient donor tissue and side effects of current immunosuppressive drugs. Therefore, alternative sources of insulin-producing cells and isletfriendly immunosuppression are required to increase the efficiency and safety of this procedure. Beta cells can be transdifferentiated from precursors or another heterologous (non-beta-cell) source. Recent advances in beta cell regeneration from somatic cells such as fibroblasts could circumvent the usage of immunosuppressive drugs. Therefore, generation of patient-specific beta cells provides the potential of an evolutionary treatment for patients with diabetes
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