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Wootten, A.

Publications and source records attributed to Wootten, A..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Deuterated Water in Comet C/1996 B2 (Hyakutake) and its Implications for the Origin of Comets

The close approach to the Earth of comet C/1996 B2 (Hyakutake) in March 1996 allowed searches for minor volatile species outgassing from the nucleus. We report the detection of deuterated water (HDO) through its 1(sub 01)-0(sub 00) rotational transition at 464.925 GHz using the Caltech Submillimeter Observatory. We also present negative results of a sensitive research for the J(5-4) line of deuterated hydrogen cyanide (DCN) at 362.046 GHz. Simultaneous observations of two rotational lines of methanol together with HDO in the same spectrum allow us to determine the average gas temperature within the telescope beam to be 69 +/- 10 K. We are thus able to constrain the excitation conditions in the inner coma and determine reliably the HDO production rate as (1.20 +/- 0.28) x 10(exp 26)/s on March 23-24, 1996. Available IR, UV and radio measurements lead to a water production rate of (2.1 +/- 0.5) x 10(exp 29)/s at the time of our HDO observations. The resulting D/H ratio in cometary water is thus (29 +/- 10) x 10(exp -5) in good agreement with the values of (30.8(sub - 5.3, sup +3.8) (Balsiger et al. 1995) and (31.6 +/- 3.4) x 10(exp -5) (Eberhardt et al. 1995) determined in comet P/Halley from in situ ion mass spectra. The inferred 3 a upper limit for the D/H ratio in HCN is 1%. Deuterium abundance is a key parameter for studying the origin and the early evolution of the Solar System and of its individual bodies. Our HDO measurement confirms that, in cometary water, deuterium is enriched by a factor of at least 10 relative to the protosolar ratio, namely the D/H ratio in H2 in the primitive Solar Nebula which formed from the collapse of the protosolar cloud. This indicates that cometary water has preserved a major part of the high D/H ratio acquired in this protosolar cloud through ion-molecule isotopic exchanges or grain-surface reactions and was not re-equilibrated with H2 in the Solar Nebula. Scenarios of formation of comets consistent with these results are discussed.

Bockelee-Morvan, D.↗
NASA NTRS1982

Observations of neutral carbon in the NGC 1977 bright rim

Strong neutral carbon emission at 610 microns (492 GHz) has been detected from a bright-rimmed cloud abutting the H II region NGC 1977. The similarity of velocity and width between (C-13)O and C I lines suggests that both lines originate in the same region. A model for the density and temperature structure of the cloud, based on (C-13)O and (C-12)O observations, has been used to estimate the carbon abundance. The abundances of both C I and (C-13)O increase with depth into the cloud away from the rim. The carbon abundance reaches its peak value nearer the rim than does the (C-13)O abundance. This variation in the relative abundance distributions of CO and C I confirms the importance of photodissociation in the chemistry of molecular clouds, and of the C I line to studies of the interaction of hot stars with clouds.

Wootten, A.↗
NASA NTRS1980

Models of molecular clouds and the abundances of H2CO and HCO/+/

Observations of HCO(+) and H2CO in a sample of 13 molecular clouds have been analyzed by construction of uniform, spherical cloud models. The total densities and the abundance of HCO(+) and H2CO relative to H2 which result from these models fall into two domains: one group of clouds has a low temperature, moderate density, and high abundances; the other group has higher temperature and density, but lower abundances. The factor distinguishing these groups may be depletion onto grains in the denser sources.

Wootten, A.↗
NASA NTRS1979

The determination of electron abundances in interstellar clouds

An independent method is proposed for the determination of electron abundances in dense clouds based upon the abundance ratio of HCO(+) and CO. The method is derived from a simple application of gas phase ion molecule interstellar chemistry. It is noted that unlike the fractionation of deuterated molecules, it applies to warm as well as to cool clouds. The method is illustrated with the results of the recent abundance survey of Wooten et al. (1978). Finally, it is shown that in cases where deuterium enhancement is measured, an upper limit can be obtained for the cosmic ray ionization rate.

Wootten, A.↗
NASA NTRS1978

Detection of star formation regions near supernova remnant W44

Observations of two infrared objects embedded in molecular clouds near the supernova remnant W44 are presented. W44-IRS1 offers compelling evidence that it is a star whose formation was recently induced by expansion of the supernova remnant. W44-IRS2 lies beyond the remnant, possibly apart from the region of its influence.

Wootten, A.↗