432 research outputs found
Characterizing the AB Doradus Moving Group Via High Resolution Spectroscopy and Kinematic Traceback
We present a detailed analysis of 10 proposed F and G members of the nearby,
young moving group AB Doradus (ABD). Our sample was obtained using the 2.7m
telescope at the McDonald Observatory with the coude echelle spectrograph,
achieving R 60,000 and S/N 200. We derive spectroscopic
T, log(g), [Fe/H], and microturbulance (v) using a bootstrap
method of the TGVIT software resulting in typical errors of 33K in T,
0.08 dex in log(g), 0.03 dex in [Fe/H], and 0.13 km s in v.
Characterization of the ABD sample is performed in three ways: (1) Chemical
homogeneity, (2) Kinematic Traceback, and (3) Isochrone fitting. We find the
average metal abundance is [M/H] = -0.03 0.06 with a traceback age of 125
Myrs. Our stars were fit to 3 different evolutionary models (Siess et al. 2000,
Baraffe et al. 1998, and YREC) and we found the best match to our ABD sample is
the YREC [M/H] = -0.1 model. In our sample of 10 stars, we identify 1 star
which is a probable non-member, 3 enigmatic stars, and 6 stars with confirmed
membership. We also present a list of chemically coherent stars from this study
and the Barenfeld et al. (2013) study.Comment: 34 pages, 9 figures, 6 table
Red Clump Stars in the Sagittarius Tidal Streams
We have probed a section (l ~ 150, b ~ -60) of the trailing tidal arm of the
Sagittarius dwarf spheroidal galaxy by identifying a sample of Red Clump stream
stars. Red Clump stars are not generally found in the halo field, but are found
in significant numbers in both the Sagittarius galaxy and its tidal streams,
making them excellent probes of stream characteristics. Our target sample was
selected using photometric data from the Sloan Digital Sky Survey, Data Release
6, which was constrained in color to match the Sagittarius Red Clump stars.
Spectroscopic observations of the target stars were conducted at Kitt Peak
National Observatory using the WIYN telescope. The resulting spectroscopic
sample is magnitude limited and contains both main sequence disk stars and
evolved Red Clump stars. We have developed a method to systematically separate
these two stellar classes using kinematic information and a Bayesian approach
for surface gravity determination. The resulting Red Clump sample allows us to
determine an absolute stellar density of {\rho} = 2.7 +/- 0.5 RC stars kpc-3 at
this location in the stream. Future measurements of stellar densities for a
variety of populations and at various locations along the streams will lead to
a much improved understanding of the original nature of the Sagittarius galaxy
and the physical processes controlling its disruption and subsequent stream
generation.Comment: 16 figures, 5 tables, accepted to A
Young Blue Straggler Stars in the Galactic Field
In this study we present an analysis of a sample of field blue straggler (BS)
stars that show high ultra violet emission in their spectral energy
distributions (SED): indication of a hot white dwarf (WD) companion to BS.
Using photometry available in the Sloan Digital Sky Survey (SDSS) and Galaxy
Evolution Explorer (GALEX ) surveys we identified 80 stars with UV excess. To
determine the parameter distributions (mass, temperature and age) of the WD
companions, we developed a fitting routine that could fit binary model SEDs to
the observed SED. Results from this fit indicate the need for a hot WD
companion to provide the excess UV flux. The WD mass distribution peaks at
, suggesting the primary formation channel of field BSs
is case B mass transfer, i.e. when the donor star is in red giant phase of its
evolution. Based on stellar evolutionary models, we estimate the lower limit of
the binary mass transfer efficiency to be .Comment: 8 pages, 3 Figures, Accepted by MNRA
Young Blue Straggler Stars in the Galactic Field
In this study, we present an analysis of a sample of field blue straggler (BS) stars that show high ultra violet emission in their spectral energy distributions (SEDs): indication of a hot white dwarf (WD) companion to BS. Using photometry available in the Sloan Digital Sky Survey (SDSS) and Galaxy Evolution Explorer (GALEX) surveys, we identified 80 stars with ultraviolet (UV) excess. To determine the parameter distributions (mass, temperature, and age) of the WD companions, we developed a fitting routine that could fit binary model SEDs to the observed SED. Results from this fit indicate the need for a hot WD companion to provide the excess UV flux. The WD mass distribution peaks at ā¼0.4Māā , suggesting the primary formation channel of field BSs is case B mass transfer, i.e. when the donor star is in red giant phase of its evolution. Based on stellar evolutionary models, we estimate the lower limit of the binary mass transfer efficiency to be Ī² ā¼ 0.5
Comparison of Three CD3-Specific Separation Methods Leading to Labeled and Label-Free T Cells
T cells are an essential part of the immune system. They determine the specificity of the immune response to foreign substances and, thus, help to protect the body from infections and cancer. Recently, T cells have gained much attention as promising tools in adoptive T cell transfer for cancer treatment. However, it is crucial not only for medical purposes but also for research to obtain T cells in large quantities, of high purity and functionality. To fulfill these criteria, efficient and robust isolation methods are needed. We used three different isolation methods to separate CD3-specific T cells from leukocyte concentrates (buffy coats) and Ficoll purified PBMCs. To catch the target cells, the Traceless Affinity Cell Selection (TACSĀ®) method, based on immune affinity chromatography, uses CD-specific low affinity Fab-fragments; while the classical Magnetic Activated Cell Sorting (MACSĀ®) method relies on magnetic beads coated with specific high affinity monoclonal antibodies. The REAleaseĀ® system also works with magnetic beads but, in contrast to MACSĀ®, low-affinity antibody fragments are used. The target cells separated by TACSĀ® and REAleaseĀ® are ālabel-freeā, while cells isolated by MACSĀ® still carry the cell specific label. The time required to isolate T cells from buffy coat by TACSĀ® and MACSĀ® amounted to 90 min and 50 min, respectively, while it took 150 min to isolate T cells from PBMCs by TACSĀ® and 110 min by REAleaseĀ®. All methods used are well suited to obtain T cells in large quantities of high viability (>92%) and purity (>98%). Only the median CD4:CD8 ratio of approximately 6.8 after REAleaseĀ® separation differed greatly from the physiological conditions. MACSĀ® separation was found to induce proliferation and cytokine secretion. However, independent of the isolation methods used, stimulation of T cells by anti CD3/CD28 resulted in similar rates of proliferation and cytokine production, verifying the functional activity of the isolated cells
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