Patrick Palmer

Hyperfine Interactions and Electron Spin Distribution in Triplet‐State Naphthalene

The anisotropic proton hyperfine interaction of the triplet‐state electrons of the naphthalene molecule have been measured at the boiling point of N2. The naphthalene molecules were oriented in single crystal solid solutions in durene. The effects of various substitutions of D for H were investigated. The spin density distribution deduced from these experiments was ρα=+0.219, ρβ=+0.062, ργ=—0.063. These results were compared with the results of theoretical calculations and with experimental results for the naphthalene negative ion.

Radio continuum and radio recombination line observations of Sagittarius B2

VLA radio continuum and H110α radio recombination line observations of Srg B2 (G0.7-0.0) are presented with spatial resolutions ranging from 3″ to 20″. The goals of the continuum study were (1) imaging the extended component of Sgr B2. The flux density of this component accounts for ∼50% of the total flux density of the region at 20 cm. (2) examination of the less well studied compact sources of this region. Several shell-like and cometary H II regions were discovered. Physical parameters, such as emission measures and electron densities, were derived.

Cyanoacetylene in dense interstellar clouds

Statistical equilibrium calculations were performed and matched to the observations of several sources. These calculations indicate the following: homogeneous cloud models are inadequate for at least one source, Sgr B2, for which a two-component (core-halo) model is presented; the observed lines of HC/sub 3/N are usually, if not always, optically thin; fairly high densities (> or =10/sup 4/ cm/sup -3/) are generally required to account for the observed lines; the J=1..-->..0 transition of HC/sub 3/N in Sgr B2 probably a weak maser. Several sources are discussed individually. (AIP)

A Sensitive Very Large Array Search for Small-Scale Glycine Emission Toward OMC-1

We have conducted a deep Q-band (� � 7 mm) search with the Very Large Array (VLA) toward OMC-1 for the lowest energy conformation (conformer I) of glycine (NH2CH2COOH) in four rotational transitions: 615–514 ,6 24–523 ,7 17–616, and 707–606. Our VLA observations sample the smallest scale structures to date in the search for glycine toward OMC-1. No glycine emission features were detected. Thus, if glycine exists in OMC-1, it is below our detection limit, or it is more spatially extended than other large molecules in this source, or it is primarily in its high-energy form (conformer II). Our VLA glycine fractional abundance limits in OMC-1 are comparable to those determined from previous IRAM 30 m measurements—somewhat better or worse depending on the specific source model—and the entire � 1 0 primary beam of the VLA was searched while sensitive to an areal spatial scale � 150 times smaller than the 24 00 beam of the IRAM single-element telescope. In the course of this work, we detected and imaged the 414–313 A and E transitions of methyl formate (HCOOCH3) and also the 202–101 transition of formic acid (HCOOH). Since formic acid is a possible precursor to glycine, our glycine limits and formic acid results provide a constraint on this potential formation chemistry route for glycine in OMC-1. Subject headings: ISM: abundances — ISM: clouds — ISM: individual (OMC-1) — ISM: molecules — radio lines: ISM

Radio detection of formaldehyde emission from Comet Halley

The J(K-1 K1) = -1(11) -10(10) transition of H/sub 2/CO was detected in emission at 4829.659 MHz from Comet Halley. The H/sub 2/CO emission line had a peak intensity of 2.66 + or - 0.78 mJy/beam with a small blueshift of -0.76 + or - 0.40 km/s, which is consistent with the anisotropic outgassing of the nucleus in the solar direction found for other cometary species. Data analysis suggests that cometary H/sub 2/CO was produced from an extended source in the coma as well as directly from the nucleus and that it was not refrigerated as in interstellar dark nebulae. The derived H/sub 2/CO production rate of 1.5 x 10 to the 28th molecules/s is obtained which is consistent with observational and theoretical findings. 37 references.

Dispersal of dense protostellar material - NH3 hot cores and outflows in Sagittarius B2

VLA observations of Sgr B2 in six ammonia transitions have uncovered two 200-K condensations with approximately 0.2 pc diameters associated with water maser sources which are similar to the Orion hot core but are more massive. Total NH3 mass of the northern source is 1000 times higher than in the Orion hot core. The hot core emission traces dense gas around newly formed massive stars, and is produced during a relatively brief stage after the star begins to heat the surrounding medium and before the dense gas is dispersed by outflow and the emergence of an expanding H II region. 36 references.

The Formaldehyde Masers in NGC 7538 and G29.96-0.02: Very Long Baseline Array, Multielement Radio-linked Interferometer Network, and Very Large Array Observations

The 6 cm formaldehyde (H2CO) maser sources in the compact H II regions NGC 7538 IRS 1 and G29.96-0.02 have been imaged at high resolution (?beam < 50 mas). Using the Very Long Baseline Array and MERLIN, we find the angular sizes of the NGC 7538 masers to be ~10 mas (30 AU), corresponding to brightness temperatures ~108 K. The angular sizes of the G29.96-0.02 masers are ~20 mas (130 AU), corresponding to brightness temperatures ~107 K. Using the VLA, we detect 2 cm formaldehyde absorption from the maser regions. We detect no emission in the 2 cm line, indicating the lack of a 2 cm maser and placing limits on the 6 cm excitation process. We find that both NGC 7538 maser components show an increase in intensity on 5-10 yr timescales while the G29.96-0.02 masers show no variability over 2 yr. A search for polarization provides 3 ? upper limits of 1% circularly polarized and 10% linearly polarized emission in NGC 7538 and of 15% circularly polarized emission in G29.96-0.02. A pronounced velocity gradient of 28 km s-1 arcsec-1 (1900 km s-1 pc-1) is detected in the NGC 7538 maser gas.The 6 cm formaldehyde (H 2 CO) maser sources in the compact H II regions NGC 7538-IRS1 and G29.96-0.02 have been imaged at high resolution (θ beam < 50 mas). Using the VLBA and MERLIN, we find the angular sizes of the NGC 7538 masers to be ∼ 10 mas (30 AU) corresponding to brightness temperatures ∼ 10 8 K. The angular sizes of the G29.96-0.02 masers are ∼ 20 mas (130 AU) corresponding to brightness temperatures ∼ 10 7 K. Using the VLA, we detect 2 cm formaldehyde absorption from the maser regions. We detect no emission in the 2 cm line, indicating the lack of a 2 cm maser and placing limits on the 6 cm excitation process. We find that both NGC 7538 maser components show an increase in intensity on 5-10 year timescales while the G29.96-0.02 masers show no variability over 2 years. A search for polarization provides 3-σ upper limits of 1% circularly polarized and 10% linearly polarized emission in NGC 7538 and of 15% circularly polarized emission in G29.96-0.02. A pronounced velocity gradient of 28 km s −1 arcsecond −1 (1900 km s −1 pc −1) is detected in the NGC 7538 maser gas.

Observations of Interstellar Formaldehyde

Rotational transition of interstellar formaldehyde in absorption in direction of galactic and extragalactic objects

A bipolar outflow of ionized gas in K3-50A: H76 alpha radio recombination line and continuum observations of K3-50

The H II regions near K3-50 (G70.3 + 1.6) have been imaged at high angular resolution (approximately 1 sec .3) in the continuum and the recombination lines H76(sub alpha and He76(sub alpha) using the Very Large Array (VLA). The helium line is detected in only the brightest component K3-50A while the hydrogen line is detected in three components (K3-50A, B and C1). K3-50A shows a pronounced velocity gradient of approximately 150 km/sec/pc along its major axis (P.A. = 160 deg); in addition a wide range of line widths are observed, from 20 to 65 km/sec. Kinematics from the line data and the morphology of the continuum emission suggest that the ionized material associated with K3-50A is undergoing a high-velocity bipolar outflow.

Dynamical collapse of the W51 star-forming region

High-resolution molecular line and 3.4 mm continuum observations of a 2.3 arcmin field centered on W51 IRS 1 in the W51 molecular core are presented. The HCO(+) spectra show deep, wide absorptions redshifted in the cases of W51e2 and W51 IRS 2, both redshifted and blueshifted in the case of W51 IRA 1. The latter two absorptions can be explained by postulating that the W51 cloud is undergoing a large-scale dynamic collapse toward materials centered near W51e2. The HCO(+) maps reveal the presence of many clumps of emission with lower mass limits ranging from 20-50 solar and upper limits of 90 solar, suggesting that many of these clumps are gravitationally bound. H(C-13)N and SO maps reveal three molecular peaks which coincide with the NH3(3,3) peaks seen by Ho et al. (1983) and are therefore warm. A previously undetected molecular peak, H(C-13)N-4, coincides with a 3.4 mm continuum peak due to thermal dust. 48 refs.