1,840 research outputs found
A Refutation of Modern Higher Critical Arguments Against the Authenticity of the Davidic Psalms
Setting out to inspect literary productions, the higher critics seek to ascertain their dates, their authors and their value as they themselves may yield the evidence. It is our purpose here, however, to deal only with their considerations advanced in opposition to the conservative view, that David is the author of those Psalms ascribed to him in their titles (seventy-three in all), and in favor of the critical view, advocating a late origin in either exilic or post-exilic times. In classifying their arguments we find that there are essentially three modes of attack used against the authenticity of the Davidic Psalms
Contribution of White Dwarfs to Cluster Masses
I present a literature search through 31 July 1997 of white dwarfs (WDs) in
open and globular clusters. There are 36 single WDs and 5 WDs in binaries known
among 13 open clusters, and 340 single WDs and 11 WDs in binaries known among
11 globular clusters. From these data I have calculated WD mass fractions for
four open clusters (the Pleiades, NGC 2168, NGC 3532, and the Hyades) and one
globular cluster (NGC 6121). I develop a simple model of cluster evolution that
incorporates stellar evolution but not dynamical evolution to interpret the WD
mass fractions. I augment the results of my simple model with N-body
simulations incorporating stellar evolution (Terlevich 1987; de la Feunte
Marcos 1996; Vesperini & Heggie 1997). I find that even though these clusters
undergo moderate to strong kinematical evolution the WD mass fraction is
relatively insensitive to kinematical evolution. By comparing the cluster mass
functions to that of the Galactic disk, and incorporating plausibility
arguments for the mass function of the Galactic halo, I estimate the WD mass
fraction in these two populations. I assume the Galactic disk is ~10 Gyrs old
(Winget et al. 1987; Liebert, Dahn, & Monet 1988; Oswalt et al. 1996) and that
the Galactic halo is ~12 Gyrs old (Reid 1997b; Gratton et al. 1997; Chaboyer et
al. 1998), although the WD mass fraction is insensitive to age in this range. I
find that the Galactic halo should contain 8 to 9% (alpha = -2.35) or perhaps
as much as 15 to 17% (alpha = -2.0) of its stellar mass in the form of WDs. The
Galactic disk WD mass fraction should be 6 to 7% (alpha = -2.35), consistent
with the empirical estimates of 3 to 7% (Liebert, Dahn, & Monet 1988; Oswalt et
al. 1996). (abridged)Comment: 20 pages, uuencoded gunzip'ed latex + 3 postscrip figures, to be
published in AJ, April, 199
On the Spectral Evolution of Cool, Helium-Atmosphere White Dwarfs: Detailed Spectroscopic and Photometric Analysis of DZ Stars
We present a detailed analysis of a large spectroscopic and photometric
sample of DZ white dwarfs based on our latest model atmosphere calculations. We
revise the atmospheric parameters of the trigonometric parallax sample of
Bergeron, Leggett, & Ruiz (12 stars) and analyze 147 new DZ white dwarfs
discovered in the Sloan Digital Sky Survey. The inclusion of metals and
hydrogen in our model atmosphere calculations leads to different atmospheric
parameters than those derived from pure helium models. Calcium abundances are
found in the range from log (Ca/He) = -12 to -8. We also find that fits of the
coolest objects show peculiarities, suggesting that our physical models may not
correctly describe the conditions of high atmospheric pressure encountered in
the coolest DZ stars. We find that the mean mass of the 11 DZ stars with
trigonometric parallaxes, = 0.63 Mo, is significantly lower than that
obtained from pure helium models, = 0.78 Mo, and in much better agreement
with the mean mass of other types of white dwarfs. We determine hydrogen
abundances for 27% of the DZ stars in our sample, while only upper limits are
obtained for objects with low signal-to-noise ratio spectroscopic data. We
confirm with a high level of confidence that the accretion rate of hydrogen is
at least two orders of magnitude smaller than that of metals (and up to five in
some cases) to be compatible with the observations. We find a correlation
between the hydrogen abundance and the effective temperature, suggesting for
the first time empirical evidence of a lower temperature boundary for the
hydrogen screening mechanism. Finally, we speculate on the possibility that the
DZA white dwarfs could be the result of the convective mixing of thin
hydrogen-rich atmospheres with the underlying helium convection zone.Comment: 67 pages, 32 figures, accepted for publication in Ap
The Chemical Composition of an Extrasolar Minor Planet
We report the relative abundances of 17 elements in the atmosphere of the
white dwarf star GD 362, material that, very probably, was contained previously
in a large asteroid or asteroids with composition similar to the Earth/Moon
system. The asteroid may have once been part of a larger parent body not unlike
one of the terrestrial planets of our solar system.Comment: ApJ, in pres
Impact of Systematics on SZ-Optical Scaling Relations
One of the central goals of multi-wavelength galaxy cluster cosmology is to
unite all cluster observables to form a consistent understanding of cluster
mass. Here, we study the impact of systematic effects from optical cluster
catalogs on stacked SZ signals. We show that the optically predicted
Y-decrement can vary by as much as 50% based on the current 2 sigma systematic
uncertainties in the observed mass-richness relationship. Mis-centering and
impurities will suppress the SZ signal compared to expectations for a clean and
perfectly centered optical sample, but to a lesser degree. We show that the
level of these variations and suppression is dependent on the amount of
systematics in the optical cluster catalogs. We also study X-ray
luminosity-dependent sub-sampling of the optical catalog and find that it
creates Malmquist bias increasing the observed Y-decrement of the stacked
signal. We show that the current Planck measurements of the Y-decrement around
SDSS optical clusters and their X-ray counterparts are consistent with
expectations after accounting for the 1 sigma optical systematic uncertainties
using the Johnston mass richness relation.Comment: 6 pages, 4 figures. Revised to match version accepted in the
Astrophysical Journa
Rocky Planetesimals as the Origin of Metals in DZ Stars
{Abridged}. An analysis of the calcium and hydrogen abundances, Galactic
positions and kinematics of 146 DZ stars from the Sloan Digital Sky Survey
demonstrates that interaction with the interstellar medium cannot account for
their externally polluted atmospheres. The calcium-to-hydrogen ratios for the
37 DZA stars are dominated by super-solar values, as are the lower limits for
the remaining 109 DZ stars. All together their metal-contaminated convective
envelopes contain 10^{20+-2} g of calcium, commensurate with the masses of
calcium inferred for large asteroids. It is probable that these stars are
contaminated by circumstellar matter; the rocky remains of terrestrial
planetary systems. In this picture, two predictions emerge: 1) at least 3.5% of
all main sequence A- and F-type stars build terrestrial planets; and 2) the DZA
stars are externally polluted by both metals and hydrogen, and hence constrain
the frequency and mass of water-rich, extrasolar planetesimals.Comment: Accepted to MNRA
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