479 research outputs found
The Social Status of Priestly and Levite Women
An analysis of pentateuchal laws pertaining to women either born or married into priestly and levitical families in ancient Israel
An Update on the 0Z Project
We give an update on our 0Z Survey to find more extremely metal poor (EMP)
stars with [Fe/H] < -3 dex through mining the database of the Hamburg/ESO
Survey. We present the most extreme such stars we have found from ~1550
moderate resolution follow up spectra. One of these, HE1424-0241, has highly
anomalous abundance ratios not seen in any previously known halo giant, with
very deficient Si, moderately deficient Ca and Ti, highly enhanced Mn and Co,
and low C, all with respect to Fe. We suggest a SNII where the nucleosynthetic
yield for explosive alpha-burning nuclei was very low compared to that for the
hydrostatic alpha-burning element Mg, which is normal in this star relative to
Fe. A second, less extreme, outlier star with high [Sc/Fe] has also been found.
We examine the extremely metal-poor tail of the HES metallicity distribution
function (MDF). We suggest on the basis of comparison of our high resolution
detailed abundance analyses with [Fe/H](HES) for stars in our sample that the
MDF inferred from follow up spectra of the HES sample of candidate EMP stars is
heavily contaminated for [Fe/H](HES) < -3 dex; many of the supposed EMP stars
below that metallicity are of substantially higher Fe-metallicity, including
most of the very C-rich stars, or are spurious objects.Comment: to appear in conference proceedings "First Stars III", ed. B. O'Shea,
A. Heger & T.Abel, 4 pages, 2 figure
MagAO: Status and on-sky performance of the Magellan adaptive optics system
MagAO is the new adaptive optics system with visible-light and infrared
science cameras, located on the 6.5-m Magellan "Clay" telescope at Las Campanas
Observatory, Chile. The instrument locks on natural guide stars (NGS) from
0 to 16 -band magnitude, measures turbulence
with a modulating pyramid wavefront sensor binnable from 28x28 to 7x7
subapertures, and uses a 585-actuator adaptive secondary mirror (ASM) to
provide flat wavefronts to the two science cameras. MagAO is a mutated clone of
the similar AO systems at the Large Binocular Telescope (LBT) at Mt. Graham,
Arizona. The high-level AO loop controls up to 378 modes and operates at frame
rates up to 1000 Hz. The instrument has two science cameras: VisAO operating
from 0.5-1 m and Clio2 operating from 1-5 m. MagAO was installed in
2012 and successfully completed two commissioning runs in 2012-2013. In April
2014 we had our first science run that was open to the general Magellan
community. Observers from Arizona, Carnegie, Australia, Harvard, MIT, Michigan,
and Chile took observations in collaboration with the MagAO instrument team.
Here we describe the MagAO instrument, describe our on-sky performance, and
report our status as of summer 2014.Comment: 13 pages, 11 figures, to appear in Proc. SPIE 9148-
Deriving Iodine-free spectra for high-resolution echelle spectrographs
We describe a new method to derive clean, iodine-free spectra directly from
observations acquired using high-resolution echelle spectrographs equipped with
iodine cells. The main motivation to obtain iodine-free spectra is to use
portions of the spectrum that are superimposed with the dense forest of iodine
absorption lines, in order to retrieve lines that can be used to monitor the
magnetic activity of the star, helping to validate candidate planets. In short,
we provide a straight-forward methodology to clean the spectra by using the
forward model used to derive radial velocities, the Line Spread Function
information plus the stellar spectrum without iodine to reconstruct and
subtract the iodine spectrum from the observations. We show our results using
observations of the star Ceti acquired with the PFS, HIRES and UCLES
spectrographs, reaching an iodine-free spectrum correction at the 1% RMS
level. We additionally discuss the limitations and further applications of the
method.Comment: 15 pages, 7 figures. Accepted for publication in A
Neutron-Capture Nucleosynthesis in the First Stars
Recent studies suggest that metal-poor stars enhanced in carbon but
containing low levels of neutron-capture elements may have been among the first
to incorporate the nucleosynthesis products of the first generation of stars.
We have observed 16 stars with enhanced carbon or nitrogen using the MIKE
Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the
Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present
radial velocities, stellar parameters, and detailed abundance patterns for
these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and
other heavy elements are detected. In four stars, these heavy elements appear
to have originated in some form of r-process nucleosynthesis. In one star, a
partial s-process origin is possible. The origin of the heavy elements in the
rest of the sample cannot be determined unambiguously. The presence of elements
heavier than the iron group offers further evidence that zero-metallicity
rapidly-rotating massive stars and pair instability supernovae did not
contribute substantial amounts of neutron-capture elements to the regions where
the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor
stars with low levels of neutron-capture elements were enriched by products of
zero-metallicity supernovae only, then the presence of these heavy elements
indicates that at least one form of neutron-capture reaction operated in some
of the first stars.Comment: Accepted for publication in the Astrophysical Journal (36 pages, 26
figures
A Detailed Study of Giants and Horizontal Branch Stars in M68: Atmospheric Parameters and Chemical Abundances
In this paper, we present a detailed high-resolution spectroscopic study of
post main sequence stars in the Globular Cluster M68. Our sample, which covers
a range of 4000 K in , and 3.5 dex in , is comprised of
members from the red giant, red horizontal, and blue horizontal branch, making
this the first high-resolution globular cluster study covering such a large
evolutionary and parameter space. Initially, atmospheric parameters were
determined using photometric as well as spectroscopic methods, both of which
resulted in unphysical and unexpected , , , and
[Fe/H] combinations. We therefore developed a hybrid approach that addresses
most of these problems, and yields atmospheric parameters that agree well with
other measurements in the literature. Furthermore, our derived stellar
metallicities are consistent across all evolutionary stages, with
[Fe/H] = 2.42 ( = 0.14) from 25 stars. Chemical
abundances obtained using our methodology also agree with previous studies and
bear all the hallmarks of globular clusters, such as a Na-O anti-correlation,
constant Ca abundances, and mild -process enrichment.Comment: Accepted to the Astronomical Journa
Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. III. Power spectrum analysis and excess isotropic component of fluctuations
The cosmic infrared background (CIB) radiation is the cosmic repository for
energy release throughout the history of the universe. Using the all-sky data
from the COBE DIRBE instrument at wavelengths 1.25 - 100 mic we attempt to
measure the CIB fluctuations. In the near-IR, foreground emission is dominated
by small scale structure due to stars in the Galaxy. There we find a strong
correlation between the amplitude of the fluctuations and Galactic latitude
after removing bright foreground stars. Using data outside the Galactic plane
() and away from the center () we extrapolate
the amplitude of the fluctuations to cosec. We find a positive intercept
of nW/m2/sr at 1.25, 2.2,3.5 and 4.9 mic
respectively, where the errors are the range of 92% confidence limits. For
color subtracted maps between band 1 and 2 we find the isotropic part of the
fluctuations at nW/m2/sr. Based on detailed numerical and
analytic models, this residual is not likely to originate from the Galaxy, our
clipping algorithm, or instrumental noise. We demonstrate that the residuals
from the fit used in the extrapolation are distributed isotropically and
suggest that this extra variance may result from structure in the CIB. For
2\deg< \theta < 15^\deg, a power-spectrum analysis yields firm upper limits
of (\theta/5^\deg) \times\delta F_{\rm rms} (\theta) < 6, 2.5, 0.8, 0.5
nW/m2/sr at 1.25, 2.2, 3.5 and 4.9 mic respectively. From 10-100 mic, the upper
limits <1 nW/m2/sr.Comment: Ap.J., in press. 69 pages including 24 fig
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