551 research outputs found
Infrared Observations of Hot Gas and Cold Ice toward the Low Mass Protostar Elias 29
We have obtained the full 1-200 um spectrum of the low luminosity (36 Lsun)
Class I protostar Elias 29 in the Rho Ophiuchi molecular cloud. It provides a
unique opportunity to study the origin and evolution of interstellar ice and
the interrelationship of interstellar ice and hot core gases around low mass
protostars. We see abundant hot CO and H2O gas, as well as the absorption bands
of CO, CO2, H2O and ``6.85 um'' ices. We compare the abundances and physical
conditions of the gas and ices toward Elias 29 with the conditions around
several well studied luminous, high mass protostars. The high gas temperature
and gas/solid ratios resemble those of relatively evolved high mass objects
(e.g. GL 2591). However, none of the ice band profiles shows evidence for
significant thermal processing, and in this respect Elias 29 resembles the
least evolved luminous protostars, such as NGC 7538 : IRS9. Thus we conclude
that the heating of the envelope of the low mass object Elias 29 is
qualitatively different from that of high mass protostars. This is possibly
related to a different density gradient of the envelope or shielding of the
ices in a circumstellar disk. This result is important for our understanding of
the evolution of interstellar ices, and their relation to cometary ices.Comment: 18 pages and 14 figures, accepted for publication in A&
Detection of H2 pure rotational line emission from the GG~Tau binary system
We present the first detection of the low-lying pure rotational emission
lines of H2 from circumstellar disks around T~Tauri stars, using the Short
Wavelength Spectrometer on the Infrared Space Observatory. These lines provide
a direct measure of the total amount of warm molecular gas in disks. The J=2->0
S(0) line at 28.218 mum and the J=3->1 S(1) line at 17.035 mum have been
observed toward the double binary system GG Tau. Together with limits on the
J=5->3 S(3) and J=7->5 S(5) lines, the data suggest the presence of gas at
T_kin=110+-10 K with a mass of (3.6+-2.0)x10^-3 M_sol (3sigma). This amounts to
~3% of the total gas + dust mass of the circumbinary disk as imaged by
millimeter interferometry, but is larger than the estimated mass of the
circumstellar disk(s). Possible origins for the warm gas seen in H2 are
discussed in terms of photon and wind-shock heating mechanisms of the
circumbinary material, and comparisons with model calculations are made.Comment: 14 pages including 1 figure. To appear in Astrophysical Journal
Letter
ISO observations toward the reflection nebula NGC 7023: A nonequilibrium ortho- to para-H2 ratio
We have observed the S(0), S(1), S(2), S(3), S(4) and S(5) rotational lines
of molecular hydrogen (H2) towards the peak of the photodissociation region
(PDR) associated with the reflection nebula NGC 7023. The observed H2 line
ratios show that they arise in warm gas with kinetic temperatures ~300 - 700 K.
However, the data cannot be fitted by an ortho- to para- (OTP) ratio of 3. An
OTP ratio in the range ~1.5 - 2 is necessary to explain our observations. This
is the first detection of a non-equilibrium OTP ratio measured from the H2
pure-rotational lines in a PDR. The existence of a dynamical PDR is discussed
as the most likely explanation for this low OTP ratio.Comment: 4 pages, 3 figure
Neon and Sulfur Abundances of Planetary Nebulae in the Magellanic Clouds
The chemical abundances of neon and sulfur for 25 planetary nebulae (PNe) in
the Magellanic Clouds are presented. These abundances have been derived using
mainly infrared data from the Spitzer Space Telescope. The implications for the
chemical evolution of these elements are discussed. A comparison with similarly
obtained abundances of Galactic PNe and HII regions and Magellanic Clouds HII
regions is also given. The average neon abundances are 6.0x10(-5) and
2.7x10(-5) for the PNe in the Large and Small Magellanic Clouds respectively.
These are ~1/3 and 1/6 of the average abundances of Galactic planetary nebulae
to which we compare. The average sulfur abundances for the LMC and SMC are
respectively 2.7x10(-6) and 1.0x10(-6). The Ne/S ratio (23.5) is on average
higher than the ratio found in Galactic PNe (16) but the range of values in
both data sets is similar for most of the objects. The neon abundances found in
PNe and HII regions agree with each other. It is possible that a few (3-4) of
the PNe in the sample have experienced some neon enrichment, but for two of
these objects the high Ne/S ratio can be explained by their very low sulfur
abundances. The neon and sulfur abundances derived in this paper are also
compared to previously published abundances using optical data and
photo-ionization models.Comment: 13 pages, 4 tables, 5 figures. Accepted for publication in Ap
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
The 35Cl/37Cl isotopic ratio in dense molecular clouds: HIFI observations of hydrogen chloride towards W3A
We report on the detection with the HIFI instrument on board the Herschel
satellite of the two hydrogen chloride isotopologues, H35Cl and H37Cl, towards
the massive star-forming region W3A. The J=1-0 line of both species was
observed with receiver 1b of the HIFI instrument at 625.9 and 624.9 GHz. The
different hyperfine components were resolved. The observations were modeled
with a non-local, non-LTE radiative transfer model that includes hyperfine line
overlap and radiative pumping by dust. Both effects are found to play an
important role in the emerging intensity from the different hyperfine
components. The inferred H35Cl column density (a few times 1e14 cm^-2), and
fractional abundance relative to H nuclei (~7.5e^-10), supports an upper limit
to the gas phase chlorine depletion of ~200. Our best-fit model estimate of the
H35Cl/H37Cl abundance ratio is ~2.1+/-0.5, slightly lower, but still compatible
with the solar isotopic abundance ratio (~3.1). Since both species were
observed simultaneously, this is the first accurate estimation of the
[35Cl]/[37Cl] isotopic ratio in molecular clouds. Our models indicate that even
for large line opacities and possible hyperfine intensity anomalies, the H35Cl
and H37Cl J=1-0 integrated line-intensity ratio provides a good estimate of the
35Cl/37Cl isotopic abundance ratio.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel
special issue
Superconducting resonator circuits at frequencies above the gap frequency
The frequency response of three superconductive niobium resonating circuits, formed by a Nb microstrip and a Nb tunnel junction, is measured and analyzed at frequencies above the superconducting gap frequency. The circuits are placed in a waveguide system and the frequency response is determined with a Fourier transform spectrometer. The calculated and measured resonance frequencies and bandwidths are in good agreement with the extreme anomalous limit of the MattisâBardeen theory on the anomalous skin effect in superconductors [D.C. Mattis and J. Bardeen, Phys. Rev. 111, 412 (1958)]. The observed loss is higher than predicted by this theory, in agreement with previous observations on Nb films. The use of other materials for striplines as tuning circuits for heterodyne superconducting tunnel junction mixers is analyzed
ISO observations of far-infrared rotational emission lines of water vapor toward the supergiant star VY Canis Majoris
We report the detection of numerous far-infrared emission lines of water
vapor toward the supergiant star VY Canis Majoris. A 29.5 - 45 micron grating
scan of VY CMa, obtained using the Short Wavelength Spectrometer (SWS) of the
Infrared Space Observatory (ISO) at a spectral resolving power of approximately
2000, reveals at least 41 spectral features due to water vapor that together
radiate a total luminosity ~ 25 solar luminosities. In addition to pure
rotational transitions within the ground vibrational state, these features
include rotational transitions within the (010) excited vibrational state. The
spectrum also shows the doublet Pi 1/2 (J=5/2) <-- doublet Pi 3/2 (J=3/2) OH
feature near 34.6 micron in absorption. Additional SWS observations of VY CMa
were carried out in the instrument's Fabry-Perot mode for three water
transitions: the 7(25)-6(16) line at 29.8367 micron, the 4(41)-3(12) line
31.7721 micron, and the 4(32)-3(03) line at 40.6909 micron. The higher spectral
resolving power of approximately 30,000 thereby obtained permits the line
profiles to be resolved spectrally for the first time and reveals the "P Cygni"
profiles that are characteristic of emission from an outflowing envelope.Comment: 11 pages (inc. 2 figures), LaTeX, uses aaspp4.sty, accepted for
publication in ApJ Letter
The origin of short-lived radionuclides and the astrophysical environment of solar system formation
Based on early solar system abundances of short-lived radionuclides (SRs),
such as Al (T Myr) and Fe (T Myr),
it is often asserted that the Sun was born in a large stellar cluster, where a
massive star contaminated the protoplanetary disk with freshly
nucleosynthesized isotopes from its supernova (SN) explosion. To account for
the inferred initial solar system abundances of short-lived radionuclides, this
supernova had to be close ( 0.3 pc) to the young ( 1 Myr)
protoplanetary disk.
Here we show that massive star evolution timescales are too long, compared to
typical timescales of star formation in embedded clusters, for them to explode
as supernovae within the lifetimes of nearby disks. This is especially true in
an Orion Nebular Cluster (ONC)-type of setting, where the most massive star
will explode as a supernova 5 Myr after the onset of star formation,
when nearby disks will have already suffered substantial photoevaporation
and/or formed large planetesimals.
We quantify the probability for {\it any} protoplanetary disk to receive SRs
from a nearby supernova at the level observed in the early solar system. Key
constraints on our estimate are: (1) SRs have to be injected into a newly
formed ( 1 Myr) disk, (2) the disk has to survive UV
photoevaporation, and (3) the protoplanetary disk must be situated in an
enrichment zone permitting SR injection at the solar system level without disk
disruption. The probability of protoplanetary disk contamination by a supernova
ejecta is, in the most favorable case, 3 10
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