T. B. H. Kuiper

Study of Structure and Small-Scale Fragmentation in TMC-1

Large-scale C(sup 18)O maps show that the Taurus molecular cloud 1 (TMC-1) has numerous cores located along a ridge which extends about 12 minutes by at least 35 minutes. The cores traced by C(sup 18)O are about a few arcminutes (0.1-0.2 pc) in extent, typically contain about 0.5-3 solar mass, and are probably gravitationally bound. We present a detailed study of the small-scale fragmentary structure of one of these cores, called core D, within TMC-1 using very high spectral and spatial resolution maps of CCS and CS. The CCS lines are excellent tracers for investigating the density, temperature, and velocity structure in dense cores. The high spectral resolution, 0.008 km /s, data consist mainly of single-dish, Nyquist-sampled maps of CCS at 22 GHz with 45 sec spatial resolution taken with NASAs 70 m DSN antenna at Goldstone. The high spatial resolution spectral line maps were made with the Very Large Array (9 sec resolution) at 22 GHz and with the OVRO millimeter array in CCS and CS at 93 GHz and 98 GHz, respectively, with 6 sec resolution. These maps are supplemented with single-dish observations of CCS and CC(sup 34)S spectra at 33 GHz using a NASA 34 m DSN antenna, CCS 93 GHz, C(sup 34)S (2-1), and C(sup 18)O (1-0) single-dish observations made with the AT&T Bell Laboratories 7 m antenna. Our high spectral and spatial CCS and CS maps show that core D is highly fragmented. The single-dish CCS observations map out several clumps which range in size from approx. 45 sec to 90 sec (0.03-0.06 pc). These clumps have very narrow intrinsic line widths, 0.11-0.25 km/s, slightly larger than the thermal line width for CCS at 10 K, and masses about 0.03-0.2 solar mass. Interferometer observations of some of these clumps show that they have considerable additional internal structure, consisting of several condensations ranging in size from approx. 10 sec- 30 sec (0.007-0.021 pc), also with narrow line widths. The mass of these smallest fragments is of order 0.01 solar mass. These small-scale structures traced by CCS appear to be gravitationally unbound by a large factor. Most of these objects have masses that fall below those of the putative proto-brown dwarfs (approx. less than 0.1 solar mass). The presence of many small gravitationally unbound clumps suggests that fragmentation mechanisms other than a purely Jeans gravitational instability may be important for the dynamics of these cold dense cores.

Discovery of Water Maser Emission in Eight AGNs with 70 m Antennas of NASA’s Deep Space Network

We report the discovery of water maser emission in eight active galactic nuclei (AGNs) with the 70 m NASA Deep Space Network (DSN) antennas at Tidbinbilla, Australia, and Robledo, Spain. The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 σ (03 radio and 13 optical) and most likely mark the locations of the embedded central engines. The spectra of two sources, NGC 3393 and NGC 5495, display the characteristic spectral signature of emission from an edge-on accretion disk, with orbital velocities of ~600 and ~400 km s-1, respectively. In a survey with DSN facilities of 630 AGNs selected from the NASA Extragalactic Database, we have discovered a total of 15 water maser sources. The resulting incidence rate of maser emission among nearby (vsys < 7000 km s-1) Seyfert 1.8-2.0 and LINER systems is ~10% for a typical rms noise level of ~14 mJy over 1.3 km s-1 spectral channels. As a result of this work, the number of nearby AGNs (vsys < 7000 km s-1) observed with <20 mJy rms noise has increased from 130 to 449.

Methyl acetylene as a temperature probe for dense interstellar clouds

Methyl acetylene (propyne) appears to be a convenient and reliable probe of kinetic temperature for dense (> or approx. =few +- 10/sup 4/ cm/sup -3/) molecular clouds. A method is presented for fitting a (J+1)-J K-multiplet to obtain the kinetic temperature from a single observation, facilitating the direct construction of kinetic temperature maps. Observations of Tau MC1, Ori MC1, Sgr B2, DR 21, DR 21 (OH), and S140 are presented to demonstrate the validity of the technique. Determination of methyl acetylene column densities requires, in addition, knowledge of the rotational excitation temperature. The relative abundance of CH/sub 3/CCH appears to be within a factor of 2 of 2.5 +- 10/sup -9/. Because of the large uncertainties in estimates of total gas column density, it is not clear whether there is genuine source-to-source variation in the CH/sub 2/CCH relative abundance.

Measuring the Magnetic Field Strength in L1498 with Zeeman-splitting Observations of CCS

We have measured the Zeeman splitting of the CCS JN = 32-21 line at 33 GHz toward L1498, a dense preprotostellar core, in an effort to measure the line-of-sight component of its magnetic field. With approximately 35 hr of data on source (70 hr total) in good weather, the data suggest a line-of-sight component of the magnetic field in L1498 of 48 ± 31 μG, yielding an upper limit of Blos < 100 μG at the 95% confidence level. This upper limit provides some constraints on models. Our results show that the technique we have adopted to measure CCS Zeeman splitting holds great promise for determining magnetic field strengths in cloud cores using lower-frequency transitions, in particular the CCS JN = 10-00 line at 11 GHz. At this transition, the frequency splitting per gauss is 3 times that at 33 GHz, the brightness temperature is comparable to the 32-21 line, and receiver systems can be made more sensitive.

Shock enhancement of HCO

In the shocked gas associated with the supernova remnant IC 443, it is found that the HCO(+)/CO abundance is approximately 0.004. This is about 100 times greater than in the unshocked gas in this source where the ratio is typical of molecular clouds. This increase contradicts some current models for shock chemistry which predict a decrease of HCO(+) behind shock fronts.

Large Deployable Reflector (LDR): A Concept For An Orbiting Submillimeter-Infrared Telescope For The 1990S

The history and background of the Large Deployable Reflector (LDR) are reviewed. The results of the June 1982 Asilomar (California) workshop are incorporated into the LDR science objectives and telescope concept. The areas where the LDR may have the greatest scientific impact are in the study of star formation and planetary systems in our own and nearby galaxies and in cosmological studies of the structure and evolution of the early universe. The observational requirements for these and other scientific studies give rise to a set of telescope functional requirements. These, in turn, are satisfied by an LDR configuration which is a Cassegrain design with a 20 m diameter, actively controlled, segmented, primary reflector, diffraction limited at a wavelength of 30 to 50 um. Technical challenges in the LDR development include construction of high tolerance mirror segments, surface figure measurement, figure control, vibration control, pointing, cryogenics, and coherent detectors. Project status and future plans for the LDR are discussed.

Detection of 2.6-millimeter radiation probably due to nitrogen sulfide

Millimeter-wavelength radiation was seen in Sgr B2 at two frequencies which correspond to transitions between the J=5/2 and the J=3/2

Statistical Studies of Giant Pulse Emission from the Crab Pulsar

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Observations of heavy-element recombination lines in the Rho Ophiuchi dark cloud at 13 centimeters wavelength

-doublet sublevels in the

CO observations of galactic reflection nebulae

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