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Alteration and Oxidiation of an Olivine Lamprophyre Dike from Southern Utah, USA: An Analog for Mars
We report on oxidized basaltic dike intrusions on the Colorado Plateau as analog for Martian basalt oxidation
Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements VI. Ni II
We present the first detailed ab initio quantum mechanical calculations for
total and state-specific recombination rate coefficients for e + Ni III --> Ni
II. These rates are obtained using a unified treatment for total electron-ion
recombination that treats the nonresonant radiative recombination and the
resonant dielectronic recombination in a self-consistent unified manner in the
close coupling approximation. Large-scale calculations are carried out using a
49-state wavefunction expansion from core configurations 3d^8, 3d^74s, and
3d^64p that permits the inclusion of prominent dipole allowed core transitions.
These extensive calculations for the recombination rates of Ni II required
hundreds of CPU hours on the Cray T90. The total recombination rate
coefficients are provided for a wide range of temperature. The state-specific
recombination rates for 532 bound states of doublet and quartet symmetries, and
the corresponding photoionization cross sections for leaving the core in the
ground state, are presented. Present total recombination rate coefficients
differ considerably from the currently used data in astrophysical models.Comment: ApJ Suppl. (submitted), 4 figure
Origin of entropy convergence in hydrophobic hydration and protein folding
An information theory model is used to construct a molecular explanation why
hydrophobic solvation entropies measured in calorimetry of protein unfolding
converge at a common temperature. The entropy convergence follows from the weak
temperature dependence of occupancy fluctuations for molecular-scale volumes in
water. The macroscopic expression of the contrasting entropic behavior between
water and common organic solvents is the relative temperature insensitivity of
the water isothermal compressibility. The information theory model provides a
quantitative description of small molecule hydration and predicts a negative
entropy at convergence. Interpretations of entropic contributions to protein
folding should account for this result.Comment: Phys. Rev. Letts. (in press 1996), 3 pages, 3 figure
The Rich Mid-Infrared Environments of Two Highly-Obscured X-ray Binaries: Spitzer Observations of IGR J16318-4848 and GX 301-2
We present the results of Spitzer mid-infrared spectroscopic observations of
two highly-obscured massive X-ray binaries: IGR J16318-4848 and GX301-2. Our
observations reveal for the first time the extremely rich mid-infrared
environments of this type of source, including multiple continuum emission
components (a hot component with T > 700 K and a warm component with T ~ 180 K)
with apparent silicate absorption features, numerous HI recombination lines,
many forbidden ionic lines of low ionization potentials, and pure rotational H2
lines. This indicates that both sources have hot and warm circumstellar dust,
ionized stellar winds, extended low-density ionized regions, and
photo-dissociated regions. It appears difficult to attribute the total optical
extinction of both sources to the hot and warm dust components, which suggests
that there could be an otherwise observable colder dust component responsible
for the most of the optical extinction and silicate absorption features. The
observed mid-infrared spectra are similar to those from Luminous Blue
Variables, indicating that the highly-obscured massive X-ray binaries may
represent a previously unknown evolutionary phase of X-ray binaries with
early-type optical companions. Our results highlight the importance and utility
of mid-infrared spectroscopy to investigate highly-obscured X-ray binaries.Comment: To appear in ApJ Letter
Reionization Constraints on the Contribution of Primordial Compact Objects to Dark Matter
Many lines of evidence suggest that nonbaryonic dark matter constitutes
roughly 30% of the critical closure density, but the composition of this dark
matter is unknown. One class of candidates for the dark matter is compact
objects formed in the early universe, with typical masses M between 0.1 and 1
solar masses to correspond to the mass scale of objects found with microlensing
observing projects. Specific candidates of this type include black holes formed
at the epoch of the QCD phase transition, quark stars, and boson stars. Here we
show that accretion onto these objects produces substantial ionization in the
early universe, with an optical depth to Thomson scattering out to z=1100 of
approximately tau=2-4 [f_CO\epsilon_{-1}(M/Msun)]^{1/2} (H_0/65)^{-1}, where
\epsilon_{-1} is the accretion efficiency \epsilon\equiv L/{\dot M}c^2 divided
by 0.1 and f_CO is the fraction of matter in the compact objects. The current
upper limit to the scattering optical depth, based on the anisotropy of the
microwave background, is approximately 0.4. Therefore, if accretion onto these
objects is relatively efficient, they cannot be the main component of
nonbaryonic dark matter.Comment: 12 pages including one figure, uses aaspp4, submitted to Ap
The first detection of near-infrared CN bands in active galactic nuclei: signature of star formation
We present the first detection of the near-infrared CN absorption band in the
nuclear spectra of active galactic nuclei (AGN). This feature is a recent star
formation tracer, being particularly strong in carbon stars. The equivalent
width of the CN line correlates with that of the CO at 2.3 microns, as expected
in stellar populations (SP) with ages between ~ 0.2 and ~ 2 Gyr. The presence
of the 1.1 microns CN band in the spectra of the sources is taken as an
unambiguous evidence of the presence of young/intermediate SP close to the
central source of the AGN. Near-infrared bands can be powerful age indicators
for star formation connected to AGN, the understanding of which is crucial in
the context of galaxy formation and AGN feedback.Comment: Accepted for publication in The Astrophysical Journal Letters. 4
pages, 3 figure
Fluorescent Excitation of Spectral Lines in Planetary Nebulae
Fluorescent excitation of spectral lines is demonstrated as a function of
temperature-luminosity and the distance of the emitting region from the central
stars of planetary nebulae. The electron densities and temperatures are
determined, and the method is exemplified through a detailed analysis of
spectral observations of a high excitation PN, NGC 6741, observed by Hyung and
Aller(1997). Fluorescence should also be important in the determination of
element abundances. It is suggested that the method could be generally applied
to determine or constrain the luminosity and the region of spectral emission in
other intensively radiative sources such as novae, supernovae, and active
galactic nuclei.Comment: 5 pages, 4 figures (fig.4 in color), ApJ (in press
K-band Spectroscopy of Clusters in NGC 4038/4039
Integral field spectroscopy in the K-band (1.9-2.4um) was performed on four
IR-bright star clusters and the two nuclei in NGC 4038/4039 (``The Antennae'').
Two of the clusters are located in the overlap region of the two galaxies, and
together comprise ~25% of the total 15um and ~10% of the total 4.8 GHz emission
from this pair of merging galaxies. The other two clusters, each of them
spatially resolved into two components, are located in the northern galaxy, one
in the western and one in the eastern loop of blue clusters. Comparing our
analysis of Brgamma, CO band-heads, He I (2.058um), Halpha (from archival HST
data), and V-K colors with stellar population synthesis models indicates that
the clusters are extincted (A_V ~ 0.7 - 4.3 mags) and young, displaying a
significant age spread (4-13 Myrs). The starbursts in the nuclei are much older
(65 Myrs), with the nucleus of NGC 4038 displaying a region of recent star
formation northward of its K-band peak. Using our derived age estimates and
assuming the parameters of the IMF (Salpeter slope, upper mass cut-off of 100
M_sun, Miller-Scalo between 1 M_sun and 0.1 M_sun), we find that the clusters
have masses between 0.5 and 5 * 10^6M_sun.Comment: 10 pages, 3 figures, ApJ accepte
A Near-Infrared Spectral Template for Quasars
We present a near-infrared quasar composite spectrum spanning the wavelength
range 0.58 - 3.5 um. The spectrum has been constructed from observations of 27
quasars obtained at the NASA IRTF telescope and satisfying the criteria Ks <
14.5 and Mi < -23; the redshift range is 0.118 < z < 0.418. The signal-to-noise
is moderate, reaching a maximum of 150 between 1.6 and 1.9 um. While a
power-law fit to the continuum of the composite spectrum requires two breaks, a
single power-law slope of alpha=-0.92 plus a 1260 K blackbody provides an
excellent description of the spectrum from H-alpha to 3.5 um, strongly
suggesting the presence of significant quantities of hot dust in this
blue-selected quasar sample. We measure intensities and line widths for ten
lines, finding that the Paschen line ratios rule out Case B recombination. We
compute K-corrections for the J, H, K, and Spitzer 3.6 um bands which will be
useful in analyzing observations of quasars up to z=10.Comment: 39 pages, 11 figures, accepted for publication in ApJ Spectra will be
made available in the online version of the journal, once published. Until
then, if you wish to obtain the composite spectrum send an email request to
eilatg[at]astro.columbia.ed
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