459 research outputs found
Isotopic Anomalies in Primitive Solar System Matter: Spin-state Dependent Fractionation of Nitrogen and Deuterium in Interstellar Clouds
Organic material found in meteorites and interplanetary dust particles is
enriched in D and 15N. This is consistent with the idea that the functional
groups carrying these isotopic anomalies, nitriles and amines, were formed by
ion-molecule chemistry in the protosolar nebula. Theoretical models of
interstellar fractionation at low temperatures predict large enrichments in
both D and 15N and can account for the largest isotopic enrichments measured in
carbonaceous meteorites. However, more recent measurements have shown that, in
some primitive samples, a large 15N enrichment does not correlate with one in
D, and that some D-enriched primitive material displays little, if any, 15N
enrichment. By considering the spin-state dependence in ion-molecule reactions
involving the ortho and para forms of H2, we show that ammonia and related
molecules can exhibit such a wide range of fractionation for both 15N and D in
dense cloud cores. We also show that while the nitriles, HCN and HNC, contain
the greatest 15N enrichment, this is not expected to correlate with extreme D
enrichment. These calculations therefore support the view that Solar System 15N
and D isotopic anomalies have an interstellar heritage. We also compare our
results to existing astronomical observations and briefly discuss future tests
of this model.Comment: Submitted to ApJ
Observations of Isotope Fractionation in Prestellar Cores: Interstellar Origin of Meteoritic Hot Spot?
Isotopically fractionated material is found in many solar system objects, including meteorites and comets. It is thought, in some cases, to trace interstellar material that was incorporated into the solar system without undergoing significant processing. Here, we show the results of models and observations of the nitrogen and carbon fractionation in proto-stellar cores
Observations of Nitrogen Fractionation in Prestellar Cores: Nitriles Tracing Interstellar Chemistry
Primitive materials provide important clues on the processes that occurred during the formation and early evolution of the Solar System. Space-based and ground-based observations of cometary comae show that comets appear to contain a mixture of the products of both interstellar and nebular chemistries. Significant 15-nitrogen enrichments have been measured in CN and HCN towards a number of comets and may suggest an origin of interstellar chemical fractionation. Additionally, large N-15 enhancements are found in meteorites and has also led to to the view that the N-15 traces material formed in the interstellar medium (ISM), although multiple sources cannot be excluded. Here, we show the results of observations of the nitrogen and carbon fractionation in prestellar cores for various N-bearing species to decipher the origin of primitive material isotopic enrichments
Spin-State-Dependent Ion-Molecule Chemistry as the Origin of N-15 and D Isotopic Anomalies in Primitive Matter.
Many meteoritic and interplanetary dust particle (IDP) samples contain bulk enhancements and hotspots rich in N-15. Similarly low C(14)N/C(15)N ratios have been observed in numerous comets, An almost constant enrichment factor in comets from disti'nct formation zones in the nebular disk (i.e. both Jupiter Family and Oort Cloud comets), strongly suggests that this fractionation is primordial and was set in the protsolar cloud core. Deuterium enrichment is observed in both meteorites and IDP
Measuring molecular abundances in comet C/2014 Q2 (Lovejoy) using the APEX telescope
Comet composition provides critical information on the chemical and physical
processes that took place during the formation of the Solar system. We report
here on millimetre spectroscopic observations of the long-period bright comet
C/2014 Q2 (Lovejoy) using the Atacama Pathfinder Experiment (APEX) band 1
receiver between 2015 January UT 16.948 to 18.120, when the comet was at
heliocentric distance of 1.30 AU and geocentric distance of 0.53 AU. Bright
comets allow for sensitive observations of gaseous volatiles that sublimate in
their coma. These observations allowed us to detect HCN, CH3OH (multiple
transitions), H2CO and CO, and to measure precise molecular production rates.
Additionally, sensitive upper limits were derived on the complex molecules
acetaldehyde (CH3CHO) and formamide (NH2CHO) based on the average of the
strongest lines in the targeted spectral range to improve the signal-to-noise
ratio. Gas production rates are derived using a non-LTE molecular excitation
calculation involving collisions with H2O and radiative pumping that becomes
important in the outer coma due to solar radiation. We find a depletion of CO
in C/2014 Q2 (Lovejoy) with a production rate relative to water of 2 per cent,
and relatively low abundances of Q(HCN)/Q(H2O), 0.1 per cent, and
Q(H2CO)/Q(H2O), 0.2 per cent. In contrast the CH3OH relative abundance
Q(CH3OH)/Q(H2O), 2.2 per cent, is close to the mean value observed in other
comets. The measured production rates are consistent with values derived for
this object from other facilities at similar wavelengths taking into account
the difference in the fields of view. Based on the observed mixing ratios of
organic molecules in four bright comets including C/2014 Q2, we find some
support for atom addition reactions on cold dust being the origin of some of
the molecules.Comment: 10 pages, 7 figures, to be published in MNRA
On the nature of the enigmatic object IRAS 19312+1950: A rare phase of massive star formation?
IRAS 19312+1950 is a peculiar object that has eluded firm characterization
since its discovery, with combined maser properties similar to an evolved star
and a young stellar object (YSO). To help determine its true nature, we
obtained infrared spectra of IRAS 19312+1950 in the range 5-550 m using
the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a
compact, slightly asymmetric continuum source at 170 m, indicative of a
large, dusty circumstellar envelope. The far-IR CO emission line spectrum
reveals two gas temperature components: of material at
K, and of material at K. The OI 63
m line is detected on-source but no significant emission from atomic ions
was found. The HIFI observations display shocked, high-velocity gas with
outflow speeds up to 90 km s along the line of sight. From Spitzer
spectroscopy, we identify ice absorption bands due to HO at 5.8 m and
CO at 15 m. The spectral energy distribution is consistent with a
massive, luminous () central source surrounded by a
dense, warm circumstellar disk and envelope of total mass
-, with large bipolar outflow cavities. The combination
of distinctive far-IR spectral features suggest that IRAS 19312+1950 should be
classified as an accreting high-mass YSO rather than an evolved star. In light
of this reclassification, IRAS 19312+1950 becomes only the 5th high-mass
protostar known to exhibit SiO maser activity, and demonstrates that 18 cm OH
maser line ratios may not be reliable observational discriminators between
evolved stars and YSOs.Comment: 16 pages. Accepted for publication in Ap
Ground-Based Centimeter, Millimeter, and Submillimeter Observations of Comet 103P/Hartley 2
Comets provide important clues to the physical and chemical processes that occurred during the formation and early evolution of the Solar System, and could also have been important for initiating prebiotic chemistry on the early Earth [1]. Comets are comprised of molecular ices, that may be pristine interstellar remnants of Solar System formation, along with high-temperature crystalline silicate dust that is indicative of a more thermally varied history in the protosolar nebula [2]. Comparing abundances of cometary parent volatiles, and isotopic fractionation ratios, to those found in the interstellar medium, in disks around young stars, and between cometary families, is vital to understanding planetary system formation and the processing history experienced by organic matter in the so-called interstellar-comet connection [3]. We have conducted observations, at primarily millimeter and submillimeter wavelengths, where molecular emission is easily resolved, towards comets to determine important cosmogonic quantities, such as the ortl1o:pal'a ratio and isotope ratios, as well as probe the origin of cometary organics. Comets provide important clues to the processes that occurred during the formation and early evolution of the Solar System. Past observations, as well as laboratory measurements of cometary material obtained from Stardust, have shown that comets appear to contain a mixture of the products from both interstellar and nebular chemistries. A major observational challenge in cometary science is to quantify the extent to which chemical compounds can be linked to either reservoir
Ground-Based Centimeter, Millimeter, and Submillimeter Observations of Recent Comets
Comets provide important clues to the physical and chemical processes that occurred during the formation and early evolution of the Solar System, and could also have been important for initiating prebiotic chemistry on the early Earth [I]. Comets are comprised of molecular ices, that may be pristine interstellar remnants of Solar System formation, along with high-temperature crystalline silicate dust that is indicative of a more thermally varied history in the protosolar nebula [2]. Comparing abundances of cometary parent volatiles, and isotopic fractionation ratios, to those found in the interstellar medium, in disks around young stars, and between cometary families, is vital to understanding planetary system formation and the processing history experienced by organic matter in the so-called interstellar-comet connection [3]. In the classical picture, the long-period comets probably formed in the nebular disk across the giant planet formation region (5-40 AU) with the majority of them originating from the Uranus-Neptune region. They were subsequently scattered out to the Oort Cloud (OC) by Jupiter. The short-period comets (also known as ecliptic or Jupiter Family Comets - JFC) reside mainly in the Edgeworth-Kuiper belt where they were formed. Given the gradient in physical conditions expected across this region of the nebula, chemical diversity in this comet population is to be expected [4,5]. We have conducted observations of comets I 03P/Hartley 2 (JFC) and C/2009 PI (Garradd) (OC), at primarily millimeter and submillimeter wavelengths, to determine important cosmogonic quantities, such as the ortho:para ratio and isotope ratios, as well as probe the origin of cometary organics and if they vary between the two dynamic reservoirs
Validating Morphometrics with DNA Barcoding to Reliably Separate Three Cryptic Species of Bombus Cresson (Hymenoptera: Apidae)
Despite their large size and striking markings, the identification of bumble bees (Bombus spp.) is surprisingly difficult. This is particularly true for three North American sympatric species in the subgenus Pyrobombus that are often misidentified: B. sandersoni Franklin, B. vagans Smith B. perplexus Cresson. Traditionally, the identification of these cryptic species was based on observations of differences in hair coloration and pattern and qualitative comparisons of morphological characters including malar length. Unfortunately, these characteristics do not reliably separate these species. We present quantitative morphometric methods to separate these species based on the malar length to width ratio (MRL) and the ratios of the malar length to flagellar segments 1 (MR1) and 3 (MR3) for queens and workers, and validated our determinations based on DNA barcoding. All three measurements discriminated queens of B. sandersoni and B. vagans with 100% accuracy. For workers, we achieved 99% accuracy by combining both MR1 and MR3 measurements, and 100% accuracy differentiating workers using MRL. Moreover, measurements were highly repeatable within and among both experienced and inexperienced observers. Our results, validated by genetic evidence, demonstrate that malar measurements provide accurate identifications of B. vagans and B. sandersoni. There was considerable overlap in the measurements between B. perplexus and B. sandersoni. However, these species can usually be reliably separated by combining malar ratio measurements with other morphological features like hair color. The ability to identify bumble bees is key to monitoring the status and trends of their populations, and the methods we present here advance these efforts
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