936 research outputs found
Interferometric mapping of the 3.3-mm continuum emission of comet 17P/Holmes after its 2007 outburst
Comet 17P/Holmes underwent a dramatic outburst in October 2007, caused by the
sudden fragmentation of its nucleus and the production of a large quantity of
grains scattering sunlight. We report on 90 GHz continuum observations carried
out with the IRAM Plateau de Bure interferometer on 27.1 and 28.2 October 2007
UT, i.e., 4-5 days after the outburst. These observations probed the thermal
radiation of large dust particles, and therefore provide the best constraints
on the mass in the ejecta debris. The thermal emission of the debris was
modelled and coupled to a time-dependent description of their expansion after
the outburst. The analysis was performed in the Fourier plane. Visibilities
were computed for the two observing dates and compared to the data to measure
their velocity and mass. Optical data and 250-GHz continuum measurements
published in the literature were used to further constrain the dust kinematics
and size distribution. Two distinct dust components in terms of kinematic
properties are identified in the data. The large-velocity component, with
typical velocities V0 of 50-100 m/s for 1 mm particles, displays a steep size
distribution with a size index estimated to q = -3.7 (\pm0.1), assuming a
minimum grain size of 0.1 \mum. It corresponds to the fast expanding shell
observed in optical images. The slowly-moving "core" component (V0 = 7-9 m/s)
detected near the nucleus has a size index |q| < 3.4 and contains a higher
proportion of large particles than the shell. The dust mass in the core is in
the range 0.1-1 that of the shell. Using optical constants pertaining to porous
grains (50% porosity) made of astronomical silicates mixed with water ice (48%
in mass), the total dust mass Mdust injected by the outburst is estimated to
4-14 x 10**11 kg, corresponding to 3-9% the nucleus mass.Comment: 15 pages with 11 figures and 7 tables. Accepted for publication in
Astronomy & Astrophysic
From Spirals to Low Surface Brightness galaxies
We show that simple models of the chemical and spectrophotometric evolution
of galaxies can be used to explore the properties of present-day galaxies and
especially the causes of the observed variety among disc galaxies. We focus on
the link between ``classical'' spirals and Low Surface Brightness galaxies.Comment: 4 pages, To appear in the Proceedings of the Euroconference The
Evolution of Galaxies: III. From simple approaches to self-consistent models
(Kluwer
Millimetre continuum observations of comet C/2009 P1 (Garradd)
Little is known about the physical properties of the nuclei of Oort cloud
comets. Measuring the thermal emission of a nucleus is one of the few means for
deriving its size and constraining some of its thermal properties. We attempted
to measure the nucleus size of the Oort cloud comet C/2009 P1 (Garradd). We
used the Plateau de Bure Interferometer to measure the millimetric thermal
emission of this comet at 157 GHz (1.9 mm) and 266 GHz (1.1 mm). Whereas the
observations at 266 GHz were not usable due to bad atmospheric conditions, we
derived a 3-sigma upper limit on the comet continuum emission of 0.41 mJy at
157 GHz. Using a thermal model for a spherical nucleus with standard thermal
parameters, we found an upper limit of 5.6 km for the radius. The dust
contribution to our signal is estimated to be negligible. Given the water
production rates measured for this comet and our upper limit, we estimated that
Garradd was very active, with an active fraction of its nucleus larger than
50%.Comment: Accepted for publication in Astronomy & Astrophysics. 5 pages, 2
figure
Complex organic molecules in comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy): detection of ethylene glycol and formamide
A spectral survey in the 1 mm wavelength range was undertaken in the
long-period comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy) using the 30 m
telescope of the Institut de radioastronomie millim\'etrique (IRAM) in April
and November-December 2013. We report the detection of ethylene glycol
(CHOH) (aGg' conformer) and formamide (NHCHO) in the two comets.
The abundances relative to water of ethylene glycol and formamide are 0.2-0.3%
and 0.02% in the two comets, similar to the values measured in comet C/1995 O1
(Hale-Bopp). We also report the detection of HCOOH and CHCHO in comet
C/2013 R1 (Lovejoy), and a search for other complex species (methyl formate,
glycolaldehyde).Comment: Accepted for publication as a Letter in Astronomy and Astrophysic
Ammonia and other parent molecules in comet 10P/Tempel 2 from Herschel/HIFI and ground-based radio observations
The Jupiter-family comet 10P/Tempel 2 was observed during its 2010 return
with the Herschel Space Observatory. We present here the observation of the (J,
K) = (1, 0)-(0, 0) transition of ammonia at 572 GHz in this comet with the
Heterodyne Instrument for the Far Infrared (HIFI) of Herschel. We also report
on radio observations of other molecules (HCN, CH3OH, H2S and CS) obtained
during the 1999 return of the comet with the CSO telescope and the JCMT, and
during its 2010 return with the IRAM 30-m telescope. Molecular abundances
relative to water are 0.09%, 1.8%, 0.4%, and 0.08% for HCN, CH3OH, H2S, and CS,
respectively. An abundance of 0.5% for NH3 is obtained, which is similar to the
values measured in other comets. The hyperfine structure of the ammonia line is
resolved for the first time in an astronomical source. Strong anisotropy in the
outgassing is present in all observations from 1999 to 2010 and is modelled to
derive the production rates.Comment: 6 pages and 8 figures. Accepted for publication in Astronomy &
Astrophysic
The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence
We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6m photometry for > 2000
galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue
Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which
is populated by irregular and spiral galaxies, and is mainly driven by changes
in the formation timescale () and a degeneracy between and dust
reddening. The tightness of the GBS provides an unprecedented way of
identifying star-forming galaxies and objects that are just evolving to (or
from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS,
at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated
by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the
optical red sequence. We find no such dichotomy in terms of stellar mass
(measured by ), since both massive () blue and red sequence galaxies are identified. The type that is
proportionally more often found in the GGV are the S0-Sa's and most of these
are located in high-density environments. We discuss evolutionary models of
galaxies that show a rapid transition from the blue to the red sequence on
timescale of years.Comment: 7 pages, 4 figures, 1 table. Accepted for publication in ApJ
Large excess of heavy nitrogen in both hydrogen cyanide and cyanogen from comet 17P/Holmes
From millimeter and optical observations of the Jupiter-family comet
17P/Holmes performed soon after its huge outburst of October 24, 2007, we
derive 14 N/15N = 139 +/- 26 in HCN, and 14N/15N = 165 +/- 40 in CN,
establishing that HCN has the same non-terrestrial isotopic composition as CN.
The same conclusion is obtained for the long-period comet C/1995 O1 (Hale-Bopp)
after a reanalysis of previously published measurements. These results are
compatible with HCN being the prime parent of CN in cometary atmospheres. The
15N excess relative to the Earth atmospheric value indicates that N-bearing
volatiles in the solar nebula underwent important N isotopic fractionation at
some stage of Solar System formation. HCN molecules never isotopically
equilibrated with the main nitrogen reservoir in the solar nebula before being
incorporated in Oort-cloud and Kuiper-belt comets. The 12C/13C ratios in HCN
and CN are measured to be consistent with the terrestrial value.Comment: Accepted for publication in the Astrophysical Journal (Letters) 4
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Imaging of crystalline and amorphous surface regions using time-of-flight secondary-ion mass spectrometry (ToF-SIMS): application to pharmaceutical materials
The structure of a material, in particular the extremes of crystalline and amorphous forms, significantly impacts material performance in numerous sectors such as semiconductors, energy storage, and pharmaceutical products, which are investigated in this paper. To characterize the spatial distribution for crystalline−amorphous forms at the uppermost molecular surface layer, we performed time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) measurements for quench-cooled amorphous and recrystallized samples of the drugs indomethacin, felodipine, and acetaminophen. Polarized light microscopy was used to localize crystallinity induced in the samples under controlled conditions. Principal component analysis was used to identify the subtle changes in the ToF-SIMS spectra indicative of the amorphous and crystalline forms for each drug. The indicators of amorphous and crystalline surfaces were common in type across the three drugs, and could be explained in general terms of crystal packing and intermolecular bonding, leading to intramolecular chain scission in the formation of secondary ions. Less intramolecular scission occurred in the amorphous form, resulting in a greater intensity of molecular and dimer secondary ions. To test the generality of amorphous−crystalline differentiation using ToF-SIMS, a different recrystallization method was investigated where acetaminophen single crystals were recrystallized from supersaturated solutions. The findings indicated that the ability to assign the crystalline/amorphous state of the sample using ToF-SIMS was insensitive to the recrystallization method. This demonstrates ToF-SIMS capabilities of detecting and mapping ordered crystalline and disordered amorphous molecular materials forms at micron spatial resolution in the uppermost surface of a material
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