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Zuckerman, B.

Publications and source records attributed to Zuckerman, B..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Molecular hydrogen emission from W51

The detection of emission from the v = 1 approaches 0 S(1) quadrupole transition of H2 toward the cluster of intense infrared and H2O maser sources in W51 (north) is reported. The apparent luminosity of this line in W51 (north) is only about 4% of the luminosity of the same line toward the Kleinmann-Low infrared cluster in Orion; however, additional line-of-sight extinction and spatial extent of the source may account for the lower apparent power in W51. Similarity in the infrared and H2O properties of these clusters is addressed. The implications of the H2 emission for mass loss in the W51 region is discussed and some proposed models of radiation-driven mass outflow from pre-main sequence stars are briefly considered.

Beckwith, S.↗
NASA NTRS1980

On ultracold molecular gas toward the galactic center

Several positions near the galactic center (Sgr A) in the J=1-0 rotational transitions of (C-12)O, (C-13)O, and C(O-18) were observed in order to better understand the nature of the 'very cold' molecular gas whose existence was first stressed by Liszt and his colleagues (1975, 1977). It is established that several dips in the (C-12)O spectra are due to optically thick clouds of foreground CO with relatively low excitation temperatures (T sub ex). T sub ex is found to be greater than about 5.3 K for all such (C-12)O clouds in all five observed directions. Such clouds fall at the extreme low end of the measured range of T sub ex for nearby dark clouds, but would, nonetheless, generally be detected in sensitive emission surveys of galactic CO.

Zuckerman, B.↗
NASA NTRS1980

Further observational studies of the high velocity molecular source /'plateau'/ in Orion

Sensitive measurements have been made of the profiles of various molecular lines in the direction of the BN/KL infrared complex in Orion. Similar line shapes are found for the high velocity wings ('plateau') of most lines observed. The position of the high velocity source was found in SO and HCO(+) relative to the SiO maser. A search for high velocity emission in other sources was unsuccessful.

Kuiper, T. B. H.↗
NASA NTRS1979

CO observations of mass outflow from the infrared star CIT 6

Results are presented for observations of CO emission from the molecular envelope surrounding the carbon star CIT 6 (IRC + 30219) made at five epochs spanning 17 months. There is no evidence for any variation in the CO line intensity on this time scale, but the intensity is much lower than that reported by previous authors. In addition, an earlier report of (C-13)O line emission cannot be confirmed, and the carbon isotope ratio C-12/C-13 is measured to be greater than 20. The shape of the CO emission line observed at all epochs can be fitted by a uniformly expanding cloud model in which the CO is optically thin except through the longest lines of sight.

Knapp, G. R.↗
NASA NTRS1978

Spectral line shapes in spherically symmetric radially moving clouds

We present a method for the analysis of spectral line shapes arising in homogeneous, moving gas clouds in which velocity and molecular line excitation have power-law dependences on radial distance from the center. Analytical expressions are obtained for radial flows, for both optically thick and optically thin lines. The additional case of an optically thick line from a differentially rotating cloud is considered qualitatively. The method is applied to the interpretation of the C(12)O line observed in the direction of the Kleinmann-Low infrared nebula in Orion. While gravitational collapse and accelerated outflows would produce lines qualitatively similar to the observed profile, it does not appear to be possible to fit either model to the observations in detail.

Kuiper, T. B. H.↗
NASA NTRS1978

Deuterated ammonia toward the Orion Nebula

The detection of transitions in NH2D at 85926.2 and 110153.4 MHz from the Orion molecular cloud is reported. An 11-m radio telescope with an 80-120 GHz cooled Cassegrain receiver and a tunable quasi-optical rejection filter was used in the investigations. Equations of statistical equilibrium for the lowest 34 energy levels of NH2D were solved. It seems unlikely that the observed lines arise in the very extended CO cloud. However, they could originate either in the molecular 'ridge' or the unresolved (Kleinmann-Low) core of the cloud or both. A column density of about 50 trillion/sq cm is deduced. The NH2D spectra, with 1 MHz resolution, are shown in a graph. Using previously reported column densities for NH3, a value of 0.05 with an estimated maximum uncertainty factor of 10 is found for the ratio NH2D/NH3.

Rodriguez Kuiper, E. N.↗
NASA NTRS1977

Unidentified lines in molecular clouds and a search for C-14 in IRC +10216

Two spectral features have been detected toward the Kleinmann-Low infrared nebula in Orion that agree in frequency with the 7(25)-7(16) and 7(35)-7(26) rotational transitions of the ring-structured molecule ethylene oxide (CH2)2O. A feature agreeing in frequency with the 8(24)-8(45) transition probably also was detected; however, seven other transitions in (CH2)2O were not. Additional unidentified lines were detected in Ori A and Sgr B2. Searches for H(C-14)N and (C-14)O in the luminous carbon star IRC +10216 were unsuccessful. However, an unidentified line was found in IRC +10216 that was not detected in the KL nebula.

Kuiper, E. N. R.↗
NASA NTRS1977

Observations of formaldehyde absorption in the region of NGC 2264 and other Bok globules

The paper reports observations of 6-cm H2CO absorption over an extended region surrounding the globule in NGC 2264 and toward the globules B68, B72, B133, B134, B227, B238, and B335. The lines observed from the globules are similar to those seen in more extended dark clouds. It is inferred that physical conditions are similar in the two types of region. Negative results for several other globules are reported.

Rickard, L. J.↗
NASA NTRS1976

High-velocity gas in the Orion infrared nebula

Sensitive observations of carbon monoxide toward the Kleinmann-Low (KL) infrared nebular in Orion have revealed the presence of low-level emission extending over a radial velocity range of at least 150 km/s. The high-velocity emission appears to be localized in a region not exceeding about 1 arcmin in diameter centered on KL. The high-velocity gas is probably associated with pre-rather than post-main-sequence object(s). However, the intensity of line radiation at these high velocities is not easily explained with simple models of mass outflow, gravitational collapse, or rotation.

Zuckerman, B.↗
NASA NTRS1976

Radio continuum measurements of compact H II regions and other sources

Results are reported for measurements of the flux densities of 33 sources at wavelengths of 13, 4, and 2 cm, which were conducted using the NASA/JPL Deep Space Network 64-m antenna at Goldstone, Calif. Besides compact H II regions, the sources included five Uhuru X-ray sources, several IR sources, an extragalactic radio source, and a H2O maser. The Lyman continuum flux is derived from the measured radio flux and the assumed distance and temperature for 10 possible H II regions; the spectra of previously known sources are extended to higher frequencies, and upper limits are placed on the flux densities for the five X-ray sources. New compact H II regions are found in the bright nebula M78, the nebula K5, and the Ophiuchus dark cloud/IR region.

Matsakis, D. N.↗
NASA NTRS1975

Detection of 2.6-millimeter radiation probably due to nitrogen sulfide

Results are reported for observations of millimeter-wavelength radiation in Sgr B2 at two frequencies corresponding to the transitions between the J = 5/2 and J = 3/2 Lambda-doublet sublevels in the 2 Pi(1/2) state of nitrogen sulfide. Difficulties in making a positive identification of the source of this radiation are discussed which result from the apparently anomalous ratio of the hyperfine components. However, it is noted that observations of the d-state by Gottlieb et al. (1975) showing the hyperfine components more exactly in their optically thin ratio confirm that the observed radiation is due to nitrogen sulfide.

Kuiper, T. B. H.↗
NASA NTRS1972

Interstellar sodium lines and the two-component model of galactic H I regions.

The intensities and widths of the interstellar sodium lines are considered as possible discriminants between two different two-component models recently proposed for galactic H I regions. Depending on the model, the observed sodium lines are either formed entirely in the clouds or, alternatively, in both the clouds and the intercloud medium. Present observational evidence is insufficient to distinguish between these two possibilities.

Hobbs, L. M.↗