650 research outputs found
A Broad 22 Microns Emission Feature in the Carina Nebula H II Region
We report the detection of a broad 22 microns emission feature in the Carina
nebula H II region by the Infrared Space Observatory (ISO) Short Wavelength
Spectrometer. The feature shape is similar to that of the 22 microns emission
feature of newly synthesized dust observed in the Cassiopeia A supernova
remnant. This finding suggests that both of the features are arising from the
same carrier, and that supernovae are probably the dominant production source
of this new interstellar grain. A similar broad emission dust feature is also
found in the spectra of two starburst galaxies from the ISO archival data. This
new dust grain could be an abundant component of interstellar grains and can be
used to trace the supernova rate or star formation rate in external galaxies.
The existence of the broad 22 microns emission feature complicates the dust
model for starburst galaxies and must be taken into account correctly in the
derivation of dust color temperature. Mg protosilicate has been suggested as
the carrier of the 22 microns emission dust feature observed in Cassiopeia A.
The present results provide useful information in studies on chemical
composition and emission mechanism of the carrier.Comment: 7 pages, 6 figures, to appear in ApJ Letter
Chemical Constraints on the Water and Total Oxygen Abundances in the Deep Atmosphere of Saturn
Thermochemical equilibrium and kinetic calculations for the trace gases CO,
PH3, and SiH4 give three independent constraints on the water and total oxygen
abundances of Saturn's deep atmosphere. A lower limit to the water abundance of
H2O/H2 > 1.7 x 10^-3 is given by CO chemistry while an upper limit of H2O/H2 <
5.5 x 10^-3 is given by PH3 chemistry. A combination of the CO and PH3
constraints indicates a water enrichment on Saturn of 1.9 to 6.1 times the
solar system abundance (H2O/H2 = 8.96 x 10^-4). The total oxygen abundance must
be at least 1.7 times the solar system abundance (O/H2 = 1.16 x 10^-3) in order
for the SiH4 to remain below a detection limit of SiH4/H2 < 2 x 10^-10. A
combination of the CO, PH3, and SiH4 constraints suggests that the total oxygen
abundance on Saturn is 3.2 to 6.4 times the solar system abundance. Our results
indicate that oxygen on Saturn is less enriched than other heavy elements (such
as C and P) relative to a solar system composition. This work was supported by
NASA NAG5-11958.Comment: 19 pages, 2 figures, accepted for publication in the Astrophysical
Journa
ISOPHOT observations of 3CR quasars and radio galaxies
In order to check for consistency with the radio-loud AGN unification scheme, ISOPHOT data obtained for two small sets of intermediate redshift steep-spectrum 3CR radio galaxies and quasars are being examined. Supplementary submillimeter and centimeter radio data for the quasars are also taken into account, in order to assess the magnitude of any beamed nonthermal radiation. The fact that we find broad-lined objects to be somewhat more luminous in their far-infrared output than narrow-lined objects, hints at a contradiction to the unification scheme. However, as the sample objects are not particularly well matched, the sample size is small, and the FIR radiation may still be partly anisotropic, this evidence is, at the moment, weak
Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei
We report a detection of water in emission in the spectrum of the M2
supergiant atar mu Cep (M2Ia) observed by the Short Wavelength Spectrometer
(SWS) aboard Infrared Space Observatory (ISO) and now released as the ISO
Archives. The emission first appears in the 6 micron region (nu2 fundamental)
and then in the 40 micron region (pure rotation lines) despite the rather
strong dust emission. The intensity ratios of the emission features are far
from those of the optically thin gaseous emission. Instead, we could reproduce
the major observed emission features by an optically thick water sphere of the
inner radius about two stellar radii (1300Rsun), Tex = 1500K, and Ncol (H2O) =
3.0E+20/cm2. This model also accounts for the H2O absorption bands in the near
infrared (1.4, 1.9, and 2.7 micron) as well. The detection of water in emission
provides strong constraints on the nature of water in the early M supergiant
stars, and especially its origin in the outer atmosphere is confirmed against
other models such as the large convective cell model. We finally confirm that
the early M supergiant star is surrounded by a huge optically thick sphere of
the warm water vapor, which may be referred to as MOLsphere for simplicity.
Thus, the outer atmosphere of M supergiant stars should have a complicated
hierarchical and/or hybrid structure with at least three major constituents
including the warm MOLsphere (T about 1.0E+3K) together with the previously
known hot chromosphere (T about 1.0E+4K) and cool expanding gas-dust envelope
(T about 1.0E+2K).Comment: 14 pages, 5 postscript figures, to appear in ApJ
OH rotational lines as a diagnostic of the warm neutral gas in galaxies
We present Infrared Space Observatory (ISO) observations of several OH, CH
and H2O rotational lines toward the bright infrared galaxies NGC253 and
NGC1068. As found in the Galactic clouds in SgrB2 and Orion, the extragalactic
far-IR OH lines change from absorption to emission depending on the physical
conditions and distribution of gas and dust along the line of sight. As a
result, most of the OH rotational lines that appear in absorption toward NGC253
are observed in emission toward NGC1068. We show that the far-IR spectrum of OH
can be used as a powerful diagnostic to derive the physical conditions of
extragalactic neutral gas. In particular, we find that a warm (Tk~150 K, n(H2)<
5 10^4 cm^-3) component of molecular gas with an OH abundance of 10^{-7} from
the inner <15'' can qualitatively reproduce the OH lines toward NGC253. Similar
temperatures but higher densities (5 10^5 cm^-3) are required to explain the OH
emission in NGC1068.Comment: 5 pages, 4 figures, accepted in ApJ Part I (2004, October 6
Spitzer-IRS high resolution spectroscopy of the 12\mu m Seyfert galaxies: I. First results
The first high resolution Spitzer IRS 9-37um spectra of 29 Seyfert galaxies
(about one quarter) of the 12um Active Galaxy Sample are presented and
discussed. The high resolution spectroscopy was obtained with corresponding
off-source observations. This allows excellent background subtraction, so that
the continuum levels and strengths of weak emission lines are accurately
measured. The result is several new combinations of emission line ratios,
line/continuum and continuum/continuum ratios that turn out to be effective
diagnostics of the strength of the AGN component in the IR emission of these
galaxies. The line ratios [NeV]/[NeII], [OIV]/[NeII], already known, but also
[NeIII]/[NeII] and [NeV]/[SiII] can all be effectively used to measure the
dominance of the AGN. We extend the analysis, already done using the 6.2um PAH
emission feature, to the equivalent width of the 11.25um PAH feature, which
also anti-correlates with the dominance of the AGN. We measure that the 11.25um
PAH feature has a constant ratio with the H_2 S(1) irrespective of Seyfert
type, approximately 10 to 1. Using the ratio of accurate flux measurements at
about 19um with the two spectrometer channels, having aperture areas differing
by a factor 4, we measured the source extendness and correlated it with the
emission line and PAH feature equivalent widths. The extendness of the source
gives another measure of the AGN dominance and correlates both with the EWs of
[NeII] and PAH emission. Using the rotational transitions of H we were able
to estimate temperatures (200-300K) and masses (1-10 x 10^6 M_sun), or
significant limits on them, for the warm molecular component in the galaxies
observed.Comment: submitted to ApJ, Aug.2007, revised, in the refereeing proces
Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity
We examine the spectra and infrared colors of the cool methane-dominated
atmospheres at Teff < 1400 K expected for young gas giant planets. We couple
these spectral calculations to an updated version of the Marley et al. (2007)
giant planet thermal evolution models that include formation by core
accretion-gas capture. These relatively cool "young Jupiters" can be 1-6
magnitudes fainter than predicted by standard cooling tracks that include a
traditional initial condition, which may provide a diagnostic of formation. If
correct, this would make true Jupiter-like planets much more difficult to
detect at young ages than previously thought. Since Jupiter and Saturn are of
distinctly super-solar composition, we examine emitted spectra for model
planets at both solar metallicity and a metallicity of 5 times solar. These
metal-enhanced young Jupiters have lower pressure photospheres than field brown
dwarfs of the same effective temperatures arising from both lower surface
gravities and enhanced atmospheric opacity. We highlight several diagnostics
for enhanced metallicity. A stronger CO absorption band at 4.5 m for the
warmest objects is predicted. At all temperatures, enhanced flux in band is
expected due to reduced collisional induced absorption by H. This leads to
correspondingly redder near infrared colors, which are redder than solar
metallicity models with the same surface gravity by up to 0.7 in and 1.5
in . Molecular absorption band depths increase as well, most significantly
for the coolest objects. We also qualitatively assess the changes to emitted
spectra due to nonequilibrium chemistry.Comment: Accepted to ApJ. Most figures in colo
Identification of SH ro-vibrational lines in R And
We report the identification of SH ro-vibrational lines in the
published high-resolution infrared spectrum of the S-type star, R And. This is
the first astronomical detection of this molecule. The lines show inverse
P-Cygni profiles, indicating infall motion of the molecular layer due to
stellar pulsation. A simple spherical shell model with a constant infall
velocity is adopted to determine the condition of the layer. It is found that a
single excitation temperature of 2200 K reproduces the observed line
intensities satisfactory. SH is located in a layer from 1.0 to ~1.1 stellar
radii, which is moving inward with a velocity of 9 km s-1. These results are
consistent with the previous measurements of CO transitions. The
estimated molecular abundance SH/H is 1x10^-7, consistent with a thermal
equilibrium calculation.Comment: 10 pages, 2 figures. Accepted for publication in ApJ Letter
Infrared Spectroscopy of Molecular Supernova Remnants
We present Infrared Space Observatory spectroscopy of sites in the supernova
remnants W28, W44, and 3C391, where blast waves are impacting molecular clouds.
Atomic fine-structure lines were detected from C, N, O, Si, P, and Fe. The S(3)
and S(9) lines of H2 were detected for all three remnants. The observations
require both shocks into gas with moderate (~ 100 /cm3) and high (~10,000 /cm3)
pre-shock densities, with the moderate density shocks producing the ionic lines
and the high density shock producing the molecular lines. No single shock model
can account for all of the observed lines, even at the order of magnitude
level. We find that the principal coolants of radiative supernova shocks in
moderate-density gas are the far-infrared continuum from dust grains surviving
the shock, followed by collisionally-excited [O I] 63.2 and [Si II] 34.8 micron
lines. The principal coolant of the high-density shocks is
collisionally-excited H2 rotational and ro-vibrational line emission. We
systematically examine the ground-state fine structure of all cosmically
abundant elements, to explain the presence or lack of all atomic fine lines in
our spectra in terms of the atomic structure, interstellar abundances, and a
moderate-density, partially-ionized plasma. The [P II] line at 60.6 microns is
the first known astronomical detection. There is one bright unidentified line
in our spectra, at 74.26 microns. The presence of bright [Si II] and [Fe II]
lines requires partial destruction of the dust. The required gas-phase
abundance of Fe suggests 15-30% of the Fe-bearing grains were destroyed. The
infrared continuum brightness requires ~1 Msun of dust survives the shock,
suggesting about 1/3 of the dust mass was destroyed, in agreement with the
depletion estimate and with theoretical models for dust destruction.Comment: 40 pages; 10 figures; accepted by ApJ July 11, 200
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