Engineering topics

Wootten, H. A.

Publications and source records attributed to Wootten, H. A..

9 records

NASA NTRS1997

Collisional quenching of OH radio emission from comet Hale-Bopp

Observations of comets in the 18-cm OH transitions offer a means to probe gas production, kinematics, and OH excitation in comets. We present initial results of OH observations of comet Hale-Bopp obtained with the NRAO 43 m antenna located in Greenbank, WV. Maps of the emission provide strong constraints on the amount of quenching of the inversion of the OH ground state A-doublet in the coma. Analysis of the total radio OH flux and maps of its radial brightness distribution indicate a quenched region on the order of approximately 500,000 km during March and April 1997. This large value is generally consistent with previous observations of radio OH quenching in lower production rate comets when the high production rate of comet Hale-Bopp is considered.

NASA Discipline Exobiology↗

NASA NTRS1987

Deuterated C3H2 as a clue to deuterium chemistry

The deuterated cyclopropenylidene ring molecule, C3HD, has been detected toward several sources in four rotational lines, at 19, 79, 104, and 107 GHz. The relative integrated intensities of the 2-sub-12 - 1-sub-01 lines of C3HD and C3H2 are found in the ratio 1:5, indicating a high deuterium fractionation ratio for cyclopropenylidene. The detection of the C-13 isotope of C3H2 at the same position allows a determination of the optical thickness (about 3) of the line. The detection of such a large enhancement in the deuterated form of C3H2 very strongly suggests that a molecular ion is the chemical precursor of the molecules. Consideration of the amount of the enhancement relative to that in other molecules suggests that the precursor ion is C3H3+.

Gerin, M.↗

NASA NTRS1983

Neutral carbon in the Egg Nebula (AFGL 2688)

A search for sub-mm C I emission from seven stars that are surrounded by dense molecular gas shells has led to the detection, in the case of the 'Egg Nebula' (AFGL 2688), of an 0.9 K line implying a C I/CO value greater than 5. The material surrounding this star must be extremely carbon-rich, and it is suggested that the apparently greater extent of the C I emission region may be due to the effects of the the galactic UV field on the shell's chemistry, as suggested by Huggins and Glassgold (1982).

Huggins, P. J.↗

NASA NTRS1983

The molecular cloud complex associated with ON 1

Observations of CO with different resolutions near the compact H II region/maser source ON 1 are presented, as well as new H2CO and HCO(+) observations. ON 1 is part of an extended molecular cloud complex with overall dimensions of 25 x 60 pc at a distance of 1.4 kpc; it appears to be the only site of star formation in at least the western part of the complex. ON 1 coincides with a compact and dense molecular cloud core (size 0.8 pc) that shows little sign of disruption indicating that ON 1 has only recently turned on. The isolation and apparent youth of ON 1 suggest that the very beginning of the star formation phase of a molecular cloud complex is observed here.

Israel, F. P.↗

NASA NTRS1982

An upper limit to the atomic carbon abundance in the Orion plateau

Observations made of the atomic carbon line at 492 GHz toward OMC-1 show no evidence for the high velocity dispersion wings observed for many molecular rotational lines. The 3sigma upper limit to the CI column density, NCI, is 6.9 x 10 to the 17th per sq cm for velocities greater than or equal to 4 km per sec from the line center. This upper limit corresponds to a ratio of CI to CO abundances as low as less than 0.13, depending on the assumed CO column density. Atomic carbon is apparently depleted by a factor as large as five in the hot plateau gas, relative to its abundance in other molecular clouds. The lack of CI in the plateau source may mean that the shocks thought to be present in the region are not dissociative in nature and thus do not produce the UV radiation required to convert CO into CI.

Beichman, C. A.↗

NASA NTRS1981

Compact radio source 1413 + 135 is a far-IR extragalactic object

The radio source 1413 + 135 is shown to be one of the strongest known emitters of millimeter radiation. The energy distribution of this object, measured between meter and X-ray wavelengths, reveals that most of the power emitted by this object comes out at millimeter and far-IR wavelengths. If the emission at 1 mm is due to incoherent synchrotron radiation, then the source must be very compact, with a size around 25 micron arc sec, and contain a magnetic field larger than 10 G. The steep spectral index in the near-IR is attributed to a high-energy cutoff in the distribution of synchrotron emitting electrons at a Lorentz factor of approximately 300.

Beichman, C. A.↗

NASA NTRS1981

Extremely red compact radio sources - The empty field objects

Radiation of 10 microns has been detected from 1413+135, one of the very red objects discovered by Rieke, Lebofsky, and Kinman (1979) at near-infrared wavelengths. The spectrum of this object flattens at wavelengths longer than 2.2 microns. Upper limits are also given for the 10-micron emission from 2255+14, 0026+34, and 0406+121. Photometry between 1.25 and 2.2 microns confirms the variability of 1413+135, 2255+41, and 0406+121. Five percent resolution spectra of 1413+135 and 0406+121 between 1.5 and 2.4 microns show no emission or absorption lines. The spectral data rule out the possibility that 1413+135 is a quasar with normal line strengths and a redshift less than 1.3 and greater than 4. The lack of features of the 1.5-2.4-micron spectra, the rapid variability, and the overall shape of the radio, infrared, and X-ray energy distributions are consistent with a BL Lac nature for these objects.

Beichman, C. A.↗

NASA NTRS1977

Observations of DCO/plus/ - The electron abundance in dark clouds

The J equals 2-1 rotational line of DCO(plus) has been definitely detected in five molecular clouds, including three dark clouds, L63, L134, and L134 N, and marginally detected in four others. The DCO(plus) emission has been mapped in L134 N and extends over a region of 3 arcmin. The DCO(plus)/HCO(plus) abundance ratio found at the centers of dark clouds is large and implies a fractional electron abundance of less than one hundred millionth. This low electron density sets constraints on the metals and possibly CO as well as on the hydrogen density.

Guelin, M.↗

NASA NTRS1973

Spectroscopic observations of HZ Herculis. II

Preliminary results from an extensive series of spectroscopic observations of the HZ Her optical counterpart of the eclipsing, pulsating X-ray binary Her X-1. Spectrograms with a dispersion of 30 A/mm reveal a spectral type as late as F5 near minimum in the light curve with the G-band and metallic lines present. Narrow Fe lines show that HZ Her is not a rapid rotator. Low-dispersion (115 A/mm) spectra, obtained with 10-minute time resolution, reveal rapid (10-min) variations in the 4640 N III emission and in the 4471 He I absorbtion features. The H-beta absorption is variable in equivalent width, and shows evidence of being partially filled with emission.

Bopp, B. W.↗