The CN isotopic ratios in comets Manfroid, J.; Jehin, E.; Hutsemékers, D. ...
Astronomy and astrophysics (Berlin),
08/2009, Letnik:
503, Številka:
2
Journal Article, Web Resource
Recenzirano
Odprti dostop
Our aim is to determine the isotopic ratios 12C/13C and 14N/15N in a variety of comets and link these measurements to the formation and evolution of the solar system. The 12C/13C and 14N/15N isotopic ...ratios are measured for the CN radical by means of high-resolution optical spectra of the R branch of the B-X (0, 0) violet band. 23 comets from different dynamical classes have been observed, sometimes at various heliocentric and nucleocentric distances, in order to estimate possible variations of the isotopic ratios in parent molecules. The 12C/13C and 14N/15N isotopic ratios in CN are remarkably constant (average values of, respectively, 91.0 ± 3.6 and 147.8 ± 5.7) within our measurement errors, for all comets whatever their origin or heliocentric distance. While the carbon isotopic ratio does agree with the terrestrial value (89), the nitrogen ratio is a factor of two lower than the terrestrial value (272), indicating a fractionation in the early solar system, or in the protosolar nebula, common to all the comets of our sample. This points towards a common origin of the comets independently of their birthplaces, and a relationship between HCN and CN.
From millimeter and optical observations of the Jupiter-family comet 17P/Holmes performed soon after its huge outburst of 2007 October 24, we derive super(14)N/ super(15)N = 139 plus or minus 26 in ...HCN and super(14)N/ super(15)N = 165 plus or minus 40 in CN, establishing that HCN has the same nonterrestrial isotopic composition as CN. The same conclusion is obtained for the long-period comet C/1995 01 (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 super(15)N excess relative to the Earth's 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 super(12)C/ super(13)C ratios in HCN and CN are measured to be consistent with the terrestrial value.
The last decade has revealed an unexpected fungal diversity associated with natural rocks, often collected in environments influenced by harsh climatic conditions. Yet the phylogenetic affiliations ...and the taxonomy of many of these extreme fungi, mainly within Dothideomycetes, the largest class of Ascomycota, have only partially been described. In the present study we confirm that most rock inhabiting-fungi (RIF) are highly polyphyletic among Dothideomycetidae, mainly within the order Capnodiales, an order otherwise incorporating several families of major plant pathological importance. Novel taxa were identified within the two major and distinct clades of
Teratosphaeriaceae
, both comprising meristematic black fungi. Thirty one novel species and 13 new genera are proposed, based on ITS and partial nucLSU,
RPB2
and
BT2
sequences.
Isotopic abundance ratios are excellently suited to probe the origin of solar system matter. We review the recent measurements of the isotopic ratios of the light elements (D/H,
12
C/
13
C,
16
O/
18
...O,
14
N/
15
N,
32
S/
34
S) in cometary dust and gas and discuss briefly their implications. Special emphasis will be put on the determinations and progress performed in the field over the past years thanks to high resolution spectroscopy of cometary comae obtained with the ESO Very Large Telescope. Future perspectives from space missions and ground-based observations with new large and extremely large telescopes operating in the optical, infrared and submillimeter wavelengths will be presented.
The 16OH/18OH and OD/OH isotope ratios are measured in the Oort-Cloud comet C/2002 T7 (LINEAR) through ground-based observations of the OH $A\,^{2}\Sigma^{+} - X\,^{2}\Pi_{i}$ ultraviolet bands at ...3063 Å (0, 0) and 3121 Å (1, 1) obtained with the Very Large Telescope (VLT) feeding the Ultraviolet-Visual Echelle Spectrograph (UVES). From the 16OH/18OH ratio, we find 16O/18O = $425 \pm 55$, equal within the uncertainties to the terrestrial value and to the ratio measured in other comets, although marginally smaller. We also estimate OD/OH from which we derive ${\rm D/H} = 2.5 \pm 0.7\times 10^{-4}$ in water. This value is compatible with the water D/H ratios evaluated in other comets and is marginally higher than the terrestrial value.
A Search for Water Vaporization on Ceres Rousselot, P; Jehin, E; Manfroid, J ...
The Astronomical journal,
10/2011, Letnik:
142, Številka:
4
Journal Article, Web Resource
Recenzirano
Odprti dostop
There are hints that the dwarf planet (1) Ceres may contain a large amount of water ice. Some models and previous observations suggest that ice could be close enough to the surface to create a flux ...of water outward through the regolith. This work aims to confirm a previous detection of OH emission off the northern limb of Ceres with the International Ultraviolet Explorer (IUE). Such emission would be evidence of water molecules escaping from the dwarf planet. We used the Ultraviolet and Visual Echelle Spectrograph of the Very Large Telescope to obtain spectra off the northern and southern limbs of Ceres at several epochs. These spectra cover the 307-312 nm wavelength range corresponding to the OH (0,0) emission band, which is the brightest band of this radical, well known in the cometary spectra. These new observations, five times more sensitive than those from IUE, did not permit detection of OH around Ceres. We derive an upper limit for the water production of about ~7 X 1025 molecules s--1 and estimate the minimum thickness of the dust surface layer above the water ice layer (if present) to be about 20 m.
We report on observations of comet 9P/Tempel 1 carried out before, during, and after the NASA Deep Impact event (UT July 4), with the optical spectrometers UVES and HIRES mounted on the telescopes ...Kueyen of the ESO VLT (Chile) and Keck I on Mauna Kea (Hawaii), respectively. A total observing time of about 60 hr, distributed over 15 nights around the impact date, allowed us (1) to find a periodic variation of 1.709 c 0.009 days in the CN and NH flux, explained by the presence of two major active regions; (2) to derive a lifetime >5 x 10 super(4) s (at 1.5 AU) for the parent of the CN radical from a simple modeling of the CN light curve after the impact; (3) to follow the gas and dust spatial profiles' evolution during the 4 hr following the impact and derive the projected velocities (400 and 150 m s super(-1), respectively); and (4) to show that the material released by the impact has the same carbon and nitrogen isotopic composition as the surface material ( super(12)C/ super(13)C = 95 c 15 and super(14)N/ super(15)N = 145 c 20).
Anomalous Nitrogen Isotope Ratio in Comets Arpigny, Claude; Jehin, Emmanuël; Manfroid, Jean ...
Science (American Association for the Advancement of Science),
09/2003, Letnik:
301, Številka:
5639
Journal Article, Web Resource
Recenzirano
High-resolution spectra of the$CN B^2 \Sigma^+-X^2 \Sigma^+$(0,0) band at 390 nanometers yield isotopic ratios for comets C/1995 O1 (Hale-Bopp) and C/2000 WM1 (LINEAR) as follows:$165 \pm 40$and$115 ...\pm 20$for12C/13C,$140 \pm 35$and$140 \pm 30$for14N/15N. Our N isotopic measurements are lower than the terrestrial$^{14}N/^{15}N = 272$and the ratio for Hale-Bopp from measurements of HCN, the presumed parent species of CN. This isotopic anomaly suggests the existence of other parent(s) of CN, with an even lower N isotopic ratio. Organic compounds like those found in interplanetary dust particles are good candidates.
Abstract Objectives We aimed to provide a consensus statement by the International Rapid Eye Movement Sleep Behavior Disorder Study Group (IRBD-SG) on devising controlled active treatment studies in ...rapid eye movement sleep behavior disorder (RBD) and devising studies of neuroprotection against Parkinson disease (PD) and related neurodegeneration in RBD. Methods The consensus statement was generated during the fourth IRBD-SG symposium in Marburg, Germany in 2011. The IRBD-SG identified essential methodologic components for a randomized trial in RBD, including potential screening and diagnostic criteria, inclusion and exclusion criteria, primary and secondary outcomes for symptomatic therapy trials (particularly for melatonin and clonazepam), and potential primary and secondary outcomes for eventual trials with disease-modifying and neuroprotective agents. The latter trials are considered urgent, given the high conversion rate from idiopathic RBD (iRBD) to Parkinsonian disorders (i.e., PD, dementia with Lewy bodies DLB, multiple system atrophy MSA). Results Six inclusion criteria were identified for symptomatic therapy and neuroprotective trials: (1) diagnosis of RBD needs to satisfy the International Classification of Sleep Disorders, second edition, (ICSD-2) criteria; (2) minimum frequency of RBD episodes should preferably be ⩾2 times weekly to allow for assessment of change; (3) if the PD-RBD target population is included, it should be in the early stages of PD defined as Hoehn and Yahr stages 1–3 in Off (untreated); (4) iRBD patients with soft neurologic dysfunction and with operational criteria established by the consensus of study investigators; (5) patients with mild cognitive impairment (MCI); and (6) optimally treated comorbid OSA. Twenty-four exclusion criteria were identified. The primary outcome measure for RBD treatment trials was determined to be the Clinical Global Impression (CGI) efficacy index, consisting of a four-point scale with a four-point side-effect scale. Assessment of video-polysomnographic (vPSG) changes holds promise but is costly and needs further elaboration. Secondary outcome measures include sleep diaries; sleepiness scales; PD sleep scale 2 (PDSS-2); serial motor examinations; cognitive indices; mood and anxiety indices; assessment of frequency of falls, gait impairment, and apathy; fatigue severity scale; and actigraphy and customized bed alarm systems. Consensus also was established for evaluating the clinical and vPSG aspects of RBD. End points for neuroprotective trials in RBD, taking lessons from research in PD, should be focused on the ultimate goal of determining the performance of disease-modifying agents. To date no compound with convincing evidence of disease-modifying or neuroprotective efficacy has been identified in PD. Nevertheless, iRBD patients are considered ideal candidates for neuroprotective studies. Conclusions The IRBD-SG provides an important platform for developing multinational collaborative studies on RBD such as on environmental risk factors for iRBD, as recently reported in a peer-reviewed journal article, and on controlled active treatment studies for symptomatic and neuroprotective therapy that emerged during the 2011 consensus conference in Marburg, Germany, as described in our report.
We report on the composition of the Halley-family comet (HFC) 8P/Tuttle investigated with high-dispersion near-infrared spectroscopic observations. The observations were carried out at the ESO VLT ...(Very Large Telescope) with the CRIRES instrument as part of a multi-wavelength observation campaign of 8P/Tuttle performed in late January and early February 2008. Radar observations suggested that 8P/Tuttle is a contact binary, and it was proposed that these components might be heterogeneous in chemistry. We determined mixing ratios of organic volatiles with respect to H2O and found that mixing ratios were consistent with previous near infrared spectroscopic observations obtained in late December 2007 and in late January 2008. It has been suggested that because 8P/Tuttle is a contact binary, it might be chemically heterogeneous. However, we find no evidence for chemical heterogeneity within the nucleus of 8P/Tuttle. We also compared the mixing ratios of organic molecules in 8P/Tuttle with those of both other HFCs and long period comets (LPCs) and found that HCN, C2H2, and C2H6 are depleted whereas CH4 and CH3OH have normal abundances. This may indicate that 8P/Tuttle was formed in a different region of the early solar nebula than other HFCs and LPCs. We estimated the conversion efficiency from C2H2 to C2H6 by hydrogen addition reactions on cold grains by employing the C2H6/(C2H6+C2H$_{2})$ ratio. The C2H6/(C2H6+C2H$_{2})$ ratio in 8P/Tuttle is consistent with the ratios found in other HFCs and LPCs within the error bars. We also discuss the source of C2 and CN based on our observations and conclude that the abundances of C2H2 and C2H6 are insufficient to explain the C2 abundances in comet 8P/Tuttle and that the abundance of HCN is insufficient to explain the CN abundances in the comet, so at least one additional parent is needed for each species, as pointed out in previous study.
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