CO near the Pleiades: Encounter of a star cluster with a small molecular cloud

Although there is a large amount of interstellar matter near the Pleiades star cluster, the observed dust and gas is not a remnant of the placental molecular cloud from which the star cluster was formed. Carbon monoxide (CO) associated with the visible reflection nebulae was discovered by Cohen (1975). Its radial velocity differs from that of the cluster by many times the cluster escape velocity, which implies that the cloud-cluster association is the result of a chance encounter. This circumstance and the proximity of the Pleiades to the sun creates an unique opportunity for study of interstellar processes at high spatial resolution. To study the molecular component of the gas, a 1.7 square degree field was mapped with the AT&T Bell Laboratories 7-meter antenna (1.7' beam) on a 1' grid in the J=1.0 C(12)O line, obtaining over 6,000 spectra with 50 kHz resolution. The cloud core was mapped in the J=1-0 line of C(13)O. Further observations include an unsuccessful search for CS (J=2-1) at AT&T BL, and some C(12)O J=2-1 spectra obtained at the Millimeter Wave Observatory of the University of Texas

Energy and ash contents of sandy beach macrofauna from the West Coast of South Africa

The energy values and ash contents of 15 species of macrolauna found on three exposed sandy beaches on the west coast of South Africa were examined over an 18-month period. The values obtained ranged from a mean of 26,65 kJ.g−1 ash-free dry weight (AFDW) in the haustoriid amphipod Urothoe grimaldii to 19,83 kJ.g−1 for the bivalve Donax serra and the values obtained are applied to biomass data for the three beaches. A pattern of decreasing energy content with increasing mean body weight was observed. No patterns of seasonal or regional variation were detected in either energy values or ash contents. Ash contents depended on taxonomic group (owing to morphological effects) and the mean size of the species; in the case of the Crustacea increasing with size within a given taxonomic grouping. The mean energy value for the 15 species was 23,81 kJ.g−1, higher than the 23,09 kJ.g−1 conversion factor obtained by Brey, Rumohr & Ankar (1988) for aquatic macrobenthic invertebrates in general, and in accordance with the suggestion by Slobodkin & Richman (1961) that energy contents are affected by the extent of storage for adverse conditions

The curious morphology and orientation of Orion proplyd HST-10

HST-10 is one of the largest proplyds in the Orion Nebula and is located approximately 1' SE of the Trapezium. Unlike other proplyds in Orion, however, the long-axis of HST-10 does not align with theta 1 C Ori, but is instead aligned with the rotational axis of the HST-10 disk. This cannot be easily explained using current photo-evaporation models. In this letter, we present high spatial resolution near-infrared images of the Orion proplyd HST-10 using Keck/NIRC2 with the Laser Guide Star Adaptive Optics system, along with multi-epoch analysis of HH objects near HST-10 using Hubble Space Telescope WFPC2 and ACS cameras. Our narrow-band near-IR images resolve the proplyd ionization front (IF) and circumstellar disk down to 23 AU at the distance to Orion in Br gamma, He I, H_2, and PAH emission. Br gamma and He I emission primarily trace the IF (with the disk showing prominently in silhouette), while the H_2 and PAH emission trace the surface of the disk itself. PAH emission also traces small dust grains within the proplyd envelope which is asymmetric and does not coincide with the IF. The curious morphology of the PAH emission may be due to UV-heating by both theta 1C Ori and theta 2A Ori. Multi-epoch HST images of the HST-10 field show proper motion of 3 knots associated with HH 517, clearly indicating that HST-10 has a jet. We postulate that the orientation of HST-10 is determined by the combined ram-pressure of this jet and the FUV-powered photo-ablation flow from the disk surface.Comment: 12 pages, 2 figures. Accepted for publication in ApJ Letters, 4 Nov 201

A Little-known waterlily from Tanganyika

Volume: XX

East African Succulents VI

Volume: XVII

East African Succulents, Part I

Volume: X

Ab Initio Treatment of Collective Correlations and the Neutrinoless Double Beta Decay of 48^{48}Ca

Working with Hamiltonians from chiral effective field theory, we develop a novel framework for describing arbitrary deformed medium-mass nuclei by combining the in-medium similarity renormalization group with the generator coordinate method. The approach leverages the ability of the first method to capture dynamic correlations and the second to include collective correlations without violating symmetries. We use our scheme to compute the matrix element that governs the neutrinoless double beta decay of $^{48}$Ca to $^{48}$Ti, and find it to have the value $0.61$, near or below the predictions of most phenomenological methods. The result opens the door to ab initio calculations of the matrix elements for the decay of heavier nuclei such as $^{76}$Ge, $^{130}$Te, and $^{136}$Xe.Comment: 6 pages, 4 figures and 1 table. supplementary material included. version to be publishe

A CS J = 2 1 survey of the galactic center region

A CS map of the galactic center region is presented consisting of 15,000 spectra covering -1 deg. less than 3. deg. 6 min., -0 deg.4 min. less than b less than 0 deg. 4 min., each having an rms noise of 0.15 K in 1 MHz filters. CS is a high-excitation molecule, meaning that it is excited into emission only when the ambient density is less than n much greater than or approx. 2 x 10 to the 4th power/cu cm CS emission in the inner 2 deg. of the galaxy is nearly as pervasive as CO emission, in stark contrast to the outer galaxy where CS emission is confined to cloud cores. Galactic center clouds are on average much more dense than outer Galaxy clouds. This can be understood as a necessary consequence of the strong tidal stresses in the inner galaxy

A new mid-infrared map of the BN/KL region using the Keck telescope

We present a new mid-infrared (12.5micron) map of the BN/KL high-mass star-forming complex in Orion using the LWS instrument at Keck I. Despite poor weather we achieved nearly diffraction-limited images (FWHM = 0.38'') over a roughly 25'' X 25'' region centered on IRc2 down to a flux limit of ~250 mJy. Many of the known infrared (IR) sources in the region break up into smaller sub-components. We have also detected 6 new mid-IR sources. Nearly all of the sources are resolved in our mosaic. The near-IR source ''n'' is slightly elongated in the mid-IR along a NW--SE axis and perfectly bisects the double-peaked radio source ''L''. Source n has been identified as a candidate for powering the large IR luminosity of the BN/KL region (L = 10^5 L_sun). We postulate that the 12 micron emission arises in a circumstellar disk surrounding source n. The morphology of the mid-IR emission and the Orion ''hot core'' (as seen in NH_3 emission), along with the location of water and OH masers, is very suggestive of a bipolar cavity centered on source n and aligned with the rotation axis of the hypothetical circumstellar disk. IRc2, once thought to be the dominant energy source for the BN/KL region, clearly breaks into 4 sub-sources in our mosaic, as seen previously at 3.8 -- 5.0 micron. The anti-correlation of mid-IR emission and NH_3 emission from the nearby hot core indicates that the IRc2 sources are roughly coincident (or behind) the dense hot core. The nature of IRc2 is not clear: neither self-luminous sources (embedded protostars) nor external heating by source I can be definitively ruled out. We also report the discovery of a new arc-like feature SW of the BN object, and some curious morphology surrounding near-IR source ''t".Comment: To appear in The Astronomical Journal, July 2004 (16 pages, 7 figures