91 research outputs found
Mid-Infrared Ethane Emission on Neptune and Uranus
We report 8- to 13-micron spectral observations of Neptune and Uranus from
the NASA Infrared Telescope Facility spanning more than a decade. The
spectroscopic data indicate a steady increase in Neptune's mean atmospheric
12-micron ethane emission from 1985 to 2003, followed by a slight decrease in
2004. The simplest explanation for the intensity variation is an increase in
stratospheric effective temperature from 155 +/- 3 K in 1985 to 176 +/- 3 K in
2003 (an average rate of 1.2 K/year), and subsequent decrease to 165 +/- 3 K in
2004. We also detected variation of the overall spectral structure of the
ethane band, specifically an apparent absorption structure in the central
portion of the band; this structure arises from coarse spectral sampling
coupled with a non-uniform response function within the detector elements. We
also report a probable direct detection of ethane emission on Uranus. The
deduced peak mole fraction is approximately an order of magnitude higher than
previous upper limits for Uranus. The model fit suggests an effective
temperature of 114 +/- 3 K for the globally-averaged stratosphere of Uranus,
which is consistent with recent measurements indicative of seasonal variation.Comment: Accepted for publication in ApJ. 16 pages, 10 figures, 2 table
HERSCHEL-HIFI spectroscopy of the intermediate mass protostar NGC7129 FIRS 2
HERSCHEL-HIFI observations of water from the intermediate mass protostar
NGC7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this
star formation environment. Six spectral settings, covering four H216O and two
H218O lines, were observed and all but one H218O line were detected. The four
H2 16 O lines discussed here share a similar morphology: a narrower, \approx 6
km/s, component centered slightly redward of the systemic velocity of NGC7129
FIRS 2 and a much broader, \approx 25 km/s component centered blueward and
likely associated with powerful outflows. The narrower components are
consistent with emission from water arising in the envelope around the
intermediate mass protostar, and the abundance of H2O is constrained to \approx
10-7 for the outer envelope. Additionally, the presence of a narrow
self-absorption component for the lowest energy lines is likely due to
self-absorption from colder water in the outer envelope. The broader component,
where the H2O/CO relative abundance is found to be \approx 0.2, appears to be
tracing the same energetic region that produces strong CO emission at high J.Comment: 6 pages, 4 figures, accepted by A&
Sensitive limits on the abundance of cold water vapor in the DM Tau protoplanetary disk
We performed a sensitive search for the ground-state emission lines of ortho-
and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI
instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s
channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the
1_{11}--0_{00} line. We report a very tentative detection, however, of the
1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of
T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s.
The latter constitutes a 6sigma detection. Regardless of the reality of this
tentative detection, model calculations indicate that our sensitive limits on
the line strengths preclude efficient desorption of water in the UV illuminated
regions of the disk. We hypothesize that more than 95-99% of the water ice is
locked up in coagulated grains that have settled to the midplane.Comment: 5 pages, 3 figures. Accepted for publication in the Herschel HIFI
special issue of A&
Hydrides in Young Stellar Objects: Radiation tracers in a protostar-disk-outflow system
Context: Hydrides of the most abundant heavier elements are fundamental
molecules in cosmic chemistry. Some of them trace gas irradiated by UV or
X-rays. Aims: We explore the abundances of major hydrides in W3 IRS5, a
prototypical region of high-mass star formation. Methods: W3 IRS5 was observed
by HIFI on the Herschel Space Observatory with deep integration (about 2500 s)
in 8 spectral regions. Results: The target lines including CH, NH, H3O+, and
the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J=1-0 lines
are found mostly in absorption, but also appear to exhibit weak emission
(P-Cyg-like). Emission requires high density, thus originates most likely near
the protostar. This is corroborated by the absence of line shifts relative to
the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong
absorption components at a velocity shifted relative to W3 IRS5, which are
attributed to foreground clouds. Conclusions: The molecular column densities
derived from observations correlate well with the predictions of a model that
assumes the main emission region is in outflow walls, heated and irradiated by
protostellar UV radiation.Comment: Astronomy and Astrophysics Letters, in pres
Water in massive star-forming regions: HIFI observations of W3 IRS5
We present Herschel observations of the water molecule in the massive
star-forming region W3 IRS5. The o-H17O 110-101, p-H18O 111-000, p-H2O 22
202-111, p-H2O 111-000, o-H2O 221-212, and o-H2O 212-101 lines, covering a
frequency range from 552 up to 1669 GHz, have been detected at high spectral
resolution with HIFI. The water lines in W3 IRS5 show well-defined
high-velocity wings that indicate a clear contribution by outflows. Moreover,
the systematically blue-shifted absorption in the H2O lines suggests expansion,
presumably driven by the outflow. No infall signatures are detected. The p-H2O
111-000 and o-H2O 212-101 lines show absorption from the cold material (T ~ 10
K) in which the high-mass protostellar envelope is embedded. One-dimensional
radiative transfer models are used to estimate water abundances and to further
study the kinematics of the region. We show that the emission in the rare
isotopologues comes directly from the inner parts of the envelope (T > 100 K)
where water ices in the dust mantles evaporate and the gas-phase abundance
increases. The resulting jump in the water abundance (with a constant inner
abundance of 10^{-4}) is needed to reproduce the o-H17O 110-101 and p-H18O
111-000 spectra in our models. We estimate water abundances of 10^{-8} to
10^{-9} in the outer parts of the envelope (T < 100 K). The possibility of two
protostellar objects contributing to the emission is discussed.Comment: Accepted for publication in the A&A HIFI special issu
The CHESS chemical Herschel surveys of star forming regions: Peering into the protostellar shock L1157-B1. I. Shock chemical complexity
We present the first results of the unbiased survey of the L1157-B1 bow
shock, obtained with HIFI in the framework of the key program Chemical Herschel
surveys of star forming regions (CHESS). The L1157 outflow is driven by a
low-mass Class 0 protostar and is considered the prototype of the so-called
chemically active outflows. The bright blue-shifted bow shock B1 is the ideal
laboratory for studying the link between the hot (around 1000-2000 K) component
traced by H2 IR-emission and the cold (around 10-20 K) swept-up material. The
main aim is to trace the warm gas chemically enriched by the passage of a shock
and to infer the excitation conditions in L1157-B1. A total of 27 lines are
identified in the 555-636 GHz region, down to an average 3 sigma level of 30
mK. The emission is dominated by CO(5-4) and H2O(110-101) transitions, as
discussed by Lefloch et al. (2010). Here we report on the identification of
lines from NH3, H2CO, CH3OH, CS, HCN, and HCO+. The comparison between the
profiles produced by molecules released from dust mantles (NH3, H2CO, CH3OH)
and that of H2O is consistent with a scenario in which water is also formed in
the gas-phase in high-temperature regions where sputtering or grain-grain
collisions are not efficient. The high excitation range of the observed tracers
allows us to infer, for the first time for these species, the existence of a
warm (> 200 K) gas component coexisting in the B1 bow structure with the cold
and hot gas detected from ground
Water in Star-Forming Regions with the Herschel Space Observatory (WISH): Overview of key program and first results
`Water In Star-forming regions with Herschel' (WISH) is a key program on the
Herschel Space Observatory designed to probe the physical and chemical
structure of young stellar objects using water and related molecules and to
follow the water abundance from collapsing clouds to planet-forming disks.
About 80 sources are targeted covering a wide range of luminosities and
evolutionary stages, from cold pre-stellar cores to warm protostellar envelopes
and outflows to disks around young stars. Both the HIFI and PACS instruments
are used to observe a variety of lines of H2O, H218O and chemically related
species. An overview of the scientific motivation and observational strategy of
the program is given together with the modeling approach and analysis tools
that have been developed. Initial science results are presented. These include
a lack of water in cold gas at abundances that are lower than most predictions,
strong water emission from shocks in protostellar environments, the importance
of UV radiation in heating the gas along outflow walls across the full range of
luminosities, and surprisingly widespread detection of the chemically related
hydrides OH+ and H2O+ in outflows and foreground gas. Quantitative estimates of
the energy budget indicate that H2O is generally not the dominant coolant in
the warm dense gas associated with protostars. Very deep limits on the cold
gaseous water reservoir in the outer regions of protoplanetary disks are
obtained which have profound implications for our understanding of grain growth
and mixing in disks.Comment: 71 pages, 10 figures, PASP, in pres
Herschel-HIFI observations of high-J CO lines in the NGC 1333 low-mass star-forming region
Herschel-HIFI observations of high-J lines (up to J_u=10) of 12CO, 13CO and
C18O are presented toward three deeply embedded low-mass protostars, NGC 1333
IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming
regions with Herschel (WISH) key program. The spectrally-resolved HIFI data are
complemented by ground-based observations of lower-J CO and isotopologue lines.
The 12CO 10-9 profiles are dominated by broad (FWHM 25-30 km s^-1) emission.
Radiative transfer models are used to constrain the temperature of this shocked
gas to 100-200 K. Several CO and 13CO line profiles also reveal a medium-broad
component (FWHM 5-10 km s^-1), seen prominently in H2O lines. Column densities
for both components are presented, providing a reference for determining
abundances of other molecules in the same gas. The narrow C18O 9-8 lines probe
the warmer part of the quiescent envelope. Their intensities require a jump in
the CO abundance at an evaporation temperature around 25 K, thus providing new
direct evidence for a CO ice evaporation zone around low-mass protostars.Comment: 8 pages, 9 figure
Water in low-mass star-forming regions with Herschel: HIFI spectroscopy of NGC1333
'Water In Star-forming regions with Herschel' (WISH) is a key programme
dedicated to studying the role of water and related species during the
star-formation process and constraining the physical and chemical properties of
young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on
the Herschel Space Observatory observed three deeply embedded protostars in the
low-mass star-forming region NGC1333 in several H2-16O, H2-18O, and CO
transitions. Line profiles are resolved for five H16O transitions in each
source, revealing them to be surprisingly complex. The line profiles are
decomposed into broad (>20 km/s), medium-broad (~5-10 km/s), and narrow (<5
km/s) components. The H2-18O emission is only detected in broad 1_10-1_01 lines
(>20 km/s), indicating that its physical origin is the same as for the broad
H2-16O component. In one of the sources, IRAS4A, an inverse P Cygni profile is
observed, a clear sign of infall in the envelope. From the line profiles alone,
it is clear that the bulk of emission arises from shocks, both on small (<1000
AU) and large scales along the outflow cavity walls (~10 000 AU). The H2O line
profiles are compared to CO line profiles to constrain the H2O abundance as a
function of velocity within these shocked regions. The H2O/CO abundance ratios
are measured to be in the range of ~0.1-1, corresponding to H2O abundances of
~10-5-10-4 with respect to H2. Approximately 5-10% of the gas is hot enough for
all oxygen to be driven into water in warm post-shock gas, mostly at high
velocities.Comment: Accepted for publication in the A&A HIFI special issu
Herschel-HIFI detections of hydrides towards AFGL 2591 (Envelope emission versus tenuous cloud absorption)
The Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel
Space Observatory allows the first observations of light diatomic molecules at
high spectral resolution and in multiple transitions. Here, we report deep
integrations using HIFI in different lines of hydrides towards the high-mass
star forming region AFGL 2591. Detected are CH, CH+, NH, OH+, H2O+, while NH+
and SH+ have not been detected. All molecules except for CH and CH+ are seen in
absorption with low excitation temperatures and at velocities different from
the systemic velocity of the protostellar envelope. Surprisingly, the CH(JF,P =
3/2_2,- - 1/2_1,+) and CH+(J = 1 - 0, J = 2 - 1) lines are detected in emission
at the systemic velocity. We can assign the absorption features to a foreground
cloud and an outflow lobe, while the CH and CH+ emission stems from the
envelope. The observed abundance and excitation of CH and CH+ can be explained
in the scenario of FUV irradiated outflow walls, where a cavity etched out by
the outflow allows protostellar FUV photons to irradiate and heat the envelope
at larger distances driving the chemical reactions that produce these
molecules.Comment: Accepted for publication in Astronomy and Astrophysics (HIFI first
results issue
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