599 research outputs found
Comets at radio wavelengths
Comets are considered as the most primitive objects in the Solar System.
Their composition provides information on the composition of the primitive
solar nebula, 4.6 Gyr ago. The radio domain is a privileged tool to study the
composition of cometary ices. Observations of the OH radical at 18 cm
wavelength allow us to measure the water production rate. A wealth of molecules
(and some of their isotopologues) coming from the sublimation of ices in the
nucleus have been identified by observations in the millimetre and
submillimetre domains. We present an historical review on radio observations of
comets, focusing on the results from our group, and including recent
observations with the Nan\c{c}ay radio telescope, the IRAM antennas, the Odin
satellite, the Herschel space observatory, ALMA, and the MIRO instrument aboard
the Rosetta space probe.Comment: Proceedings of URSI France scientific days, "Probing Matter with
Electromagnetic Waves", 24-25 March 2015, Paris. To be published in C. R.
Physiqu
Observations of the 18-cm OH lines of comet 103P/Hartley 2 at Nan\c{c}ay in support to the EPOXI and Herschel missions
The 18-cm radio lines of the OH radical were observed in comet 103P/Hartley 2
with the Nan\c{c}ay radio telescope in support to its flyby by the EPOXI
mission and to observations with the Herschel Space Observatory. The OH lines
were detected from 24 September to 15 December 2010. These observations are
used to estimate the gas expansion velocity within the coma to 0.83 \pm 0.08
km/s in October 2010. The water production increased steeply but progressively
before perihelion, and reached 1.9 \pm 0.3 X 10E28 s-1 just before the EPOXI
flyby.Comment: Accepted for publication in Icarus (6 pages, 4 figures
The chemical diversity of comets
A fundamental question in cometary science is whether the different dynamical
classes of comets have different chemical compositions, which would reflect
different initial conditions. From the ground or Earth orbit, radio and
infrared spectroscopic observations of a now significant sample of comets
indeed reveal deep differences in the relative abundances of cometary ices.
However, no obvious correlation with dynamical classes is found. Further
results come, or are expected, from space exploration. Such investigations, by
nature limited to a small number of objects, are unfortunately focussed on
short-period comets (mainly Jupiter-family). But these in situ studies provide
"ground truth" for remote sensing. We discuss the chemical differences in
comets from our database of spectroscopic radio observations, which has been
recently enriched by several Jupiter-family and Halley-type comets.Comment: In press in Earth, Moon and Planets (proceedings of the workshop
"Future Ground-based Solar System Research: Synergies with Space Probes and
Space Telescopes", Portoferraio, Isola d'Elba, Livorno (Italy), 8-12
September 2008). 6 pages with 2 figure
Model of Dust Thermal Emission of Comet 67p-Churyumov-Gerasimenko for the Rosetta-MIRO Instrument
The ESA's Rosetta spacecraft will arrive at comet 67P/Churyumov-Gerasimenko in 2014. The study of gas and dust emission is primary objective of several instruments on the Rosetta spacecraft, including the Microwave Instrument for the Rosetta Orbiter (MIRO). We developed a model of dust thermal emission to estimate the detectability of dust in the vicinity of the nucleus with MIRO. Our model computes the power received by the MIRO antenna in limb viewing as a function of the geometry of the observations and the physical properties of the grains. We show that detection in the millimeter and submillimeter channels can be achieved near perihelion
The Composition of Comets
This paper is the result of the International Cometary Workshop, held in
Toulouse, France in April 2014, where the participants came together to assess
our knowledge of comets prior to the ESA Rosetta Mission. In this paper, we
look at the composition of the gas and dust from the comae of comets. With the
gas, we cover the various taxonomic studies that have broken comets into groups
and compare what is seen at all wavelengths. We also discuss what has been
learned from mass spectrometers during flybys. A few caveats for our
interpretation are discussed. With dust, much of our information comes from
flybys. They include {\it in situ} analyses as well as samples returned to
Earth for laboratory measurements. Remote sensing IR observations and
polarimetry are also discussed. For both gas and dust, we discuss what
instruments the Rosetta spacecraft and Philae lander will bring to bear to
improve our understanding of comet 67P/Churyumov-Gerasimenko as "ground-truth"
for our previous comprehensive studies. Finally, we summarize some of the
initial Rosetta Mission findings.Comment: To appear in Space Science Review
Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy)
The presence of numerous complex organic molecules (COMs; defined as those containing six or more atoms) around protostars shows that star formation is accompanied by an increase of molecular complexity. These COMs may be part of the material from which planetesimals and, ultimately, planets formed. Comets represent some of the oldest and most primitive material in the solar system, including ices, and are thus our best window into the volatile composition of the solar protoplanetary disk. Molecules identified to be present in cometary ices include water, simple hydrocarbons, oxygen, sulfur, and nitrogen-bearing species, as well as a few COMs, such as ethylene glycol and glycine. We report the detection of 21 molecules in comet C/2014 Q2 (Lovejoy), including the first identification of ethyl alcohol (ethanol, C_2H_5OH) and the simplest monosaccharide sugar glycolaldehyde (CH_2OHCHO) in a comet. The abundances of ethanol and glycolaldehyde, respectively 5 and 0.8% relative to methanol (0.12 and 0.02% relative to water), are somewhat higher than the values measured in solar-type protostars. Overall, the high abundance of COMs in cometary ices supports the formation through grain-surface reactions in the solar system protoplanetary disk
Leveraging the ALMA Atacama Compact Array for Cometary Science: An Interferometric Survey of Comet C/2015 ER61 (PanSTARRS) and Evidence for a Distributed Source of Carbon Monosulfide
We report the first survey of molecular emission from cometary volatiles
using standalone Atacama Compact Array (ACA) observations of the Atacama Large
Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS)
carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst.
These measurements of HCN, CS, CHOH, HCO, and HNC (along with continuum
emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric
outgassing and discerning parent from daughter/distributed source species. This
work presents spectrally integrated flux maps, autocorrelation spectra,
production rates, and parent scale lengths for each molecule, and a stringent
upper limit for CO. HCN is consistent with direct nucleus release in C/2015
ER61, whereas CS, HCO, HNC, and potentially CHOH are associated with
distributed sources in the coma. Adopting a Haser model, parent scale lengths
determined for HCO (L 2200 km) and HNC (L 3300 km)
are consistent with previous work in comets, whereas significant extended
source production (L 2000 km) is indicated for CS, suggesting
production from an unknown parent in the coma. The continuum presents a
point-source distribution, with a flux density implying an excessively large
nucleus, inconsistent with other estimates of the nucleus size. It is best
explained by the thermal emission of slowly-moving outburst ejectas, with total
mass 5--8 10 kg. These results demonstrate the power of the ACA
for revealing the abundances, spatial distributions, and locations of molecular
production for volatiles in moderately bright comets such as C/2015 ER61
Low NH/HO ratio in comet C/2020 F3 (NEOWISE) at 0.7 au from the Sun
A lower-than-solar elemental nitrogen content has been demonstrated for
several comets, including 1P/Halley and 67P/C-G with independent in situ
measurements of volatile and refractory budgets. The recently discovered
semi-refractory ammonium salts in 67P/C-G are thought to be the missing
nitrogen reservoir in comets. The thermal desorption of ammonium salts from
cometary dust particles leads to their decomposition into ammonia and a
corresponding acid. The NH/HO ratio is expected to increase with
decreasing heliocentric distance with evidence for this in near-infrared
observations. NH has been claimed to be more extended than expected for a
nuclear source. Here, the aim is to constrain the NH/HO ratio in
comet C/2020 F3 (NEOWISE) during its July 2020 passage. OH emission from comet
C/2020 F3 (NEOWISE) was monitored for 2 months with NRT and observed from GBT
on 24 July and 11 August 2020. Contemporaneously with the 24 July 2020 OH
observations, the NH hyperfine lines were targeted with GBT. The
concurrent GBT and NRT observations allowed the OH quenching radius to be
determined at km on 24 July 2020, which
is important for accurately deriving . C/2020 F3 (NEOWISE) was a
highly active comet with molec
s one day before perihelion. The upper limit for
is at au from the
Sun. The obtained NH/HO ratio is a factor of a few lower than
measurements for other comets at such heliocentric distances. The abundance of
NH may vary strongly with time depending on the amount of water-poor dust
in the coma. Lifted dust can be heated, fragmented, and super-heated; whereby,
ammonium salts, if present, can rapidly thermally disintegrate and modify the
NH/HO ratio.Comment: Accepted for publication in A&A; 18 pages, 8 figures, 6 table
The effects of time-restricted eating and weight loss on bone metabolism and health: a 6-month randomized controlled trial.
OBJECTIVE
This study explored the impact of time-restricted eating (TRE) versus standard dietary advice (SDA) on bone health.
METHODS
Adults with ≥1 component of metabolic syndrome were randomized to TRE (ad libitum eating within 12 hours) or SDA (food pyramid brochure). Bone turnover markers and bone mineral content/density by dual energy x-ray absorptiometry were assessed at baseline and 6-month follow-up. Statistical analyses were performed in the total population and by weight loss response.
RESULTS
In the total population (n = 42, 76% women, median age 47 years [IQR: 31-52]), there were no between-group differences (TRE vs. SDA) in any bone parameter. Among weight loss responders (≥0.6 kg weight loss), the bone resorption marker β-carboxyterminal telopeptide of type I collagen tended to decrease after TRE but increase after SDA (between-group differences p = 0.041), whereas changes in the bone formation marker procollagen type I N-propeptide did not differ between groups. Total body bone mineral content decreased after SDA (p = 0.028) but remained unchanged after TRE (p = 0.31) in weight loss responders (between-group differences p = 0.028). Among nonresponders (<0.6 kg weight loss), there were no between-group differences in bone outcomes.
CONCLUSIONS
TRE had no detrimental impact on bone health, whereas, when weight loss occurred, it was associated with some bone-sparing effects compared with SDA
The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI): instrument and pre-launch testing
This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI), to be launched onboard of ESA's Herschel Space Observatory, by 2008. It includes the first results from the instrument level tests. The instrument is designed to be electronically tuneable over a wide and continuous frequency range in the Far Infrared, with velocity resolutions better than 0.1 km/s with a high sensitivity. This will enable detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies. The instrument comprises 5 frequency bands covering 480-1150 GHz with SIS mixers and a sixth dual frequency band, for the 1410-1910 GHz range, with Hot Electron Bolometer Mixers (HEB). The Local Oscillator (LO) subsystem consists of a dedicated Ka-band synthesizer followed by 7 times 2 chains of frequency multipliers, 2 chains for each frequency band. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarization front-ends to provide instantaneous frequency coverage of 4 GHz, with a set of resolutions (140 kHz to 1 MHz), better than < 0.1 km/s. After a successful qualification program, the flight instrument was delivered and entered the testing phase at satellite level. We will also report on the pre-flight test and calibration results together with the expected in-flight performance
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