High Rydberg State Carbon Recombination Lines from Interstellar Clouds

We report observations of carbon recombination lines near 34.5 MHz (qunatum number n=578) and 325 MHz (n=272) made towards Cas A, the Galactic centre and about ten other directions in the galactic plane. Constraints on the physical conditions in the line forming regions are derived from these and other existing observations. The CII regions that produce the low-frequency lines are most likely associated with the neutral HI component of the ISM.Comment: 4 pages, 3 figures; Presented at the workshop on "New Perspects on the Interstellare Medium", Penticton, Canada, Aug 199

Discovery of a Non-Thermal Galactic Center Filament (G358.85+0.47) Parallel to the Galactic Plane

We report the discovery of a new non-thermal filament, G358.85+0.47, the ``Pelican'', located ~225 pc in projection from SgrA, and oriented parallel to the Galactic plane. VLA continuum observations at 20 cm reveal that this 7' (17.5 pc) structure bends at its northern extension and is comprised of parallel strands, most apparent at its ends. Observations at 6 and 3.6 cm reveal that the Pelican is a synchrotron-emitting source and is strongly linearly polarized over much of its extent. The spectral index of the filament changes from alpha(20/6)=-0.8 to alpha(6/3.6)=-1.5. The rotation measures exhibit a smooth gradient, with values ranging from -1000 rad/m2 to +500 rad/m2. The intrinsic magnetic field is well-aligned along the length of the filament. Based on these properties, we classify the Pelican as one of the non-thermal filaments unique to the Galactic center. Since these filaments (most of which are oriented perpendicular to the Galactic plane) are believed to trace the overall magnetic field in the inner Galaxy, the Pelican is the first detection of a component of this field parallel to the plane. The Pelican may thus mark a transition region of the magnetic field orientation in the inner kiloparsec of the Galaxy.Comment: 6 pages, 4 figures, to appear in ApJ Letters; Figs. 2 & 3 are color .ps files and best viewed in colo

Low density ionized gas in the inner galaxy - Interpretation of recombination line observations at 325 MHz

The recent survey of H 272α recombination line (324.99 MHz) in the direction of 34 Hn regions, 12 SNRs and 6 regions of continuum minimum ('blank' regions) in the galactic plane is used to derive the properties of diffuse ionized gas in the inner Galaxy. The intensity of radio recombination lines at high frequencies is dominated by spontaneous emission in high-density gas and that at low frequencies (325 MHz) by stimulated emission in low-density gas. We have used this property to obtain the electron density in the gas in the direction of blank regions and SNRs, by combining the H 272 α measurements (preceeding paper) with the published data at higher frequencies. Further, we have imposed constraints on the electron temperature and pathlength through this gas using the observed high-frequency continuum emission, average interstellar electron density and geometry of the line-emitting regions. The derived properties of the gas are (i) electron density 0.5-6 cm-3, (ii) electron temperature 3000-8000 K and (iii) emission measures 500-3000 pc cm-6 The corresponding pathlengths are 50-200 pc. As the derived sizes of the low-density regions are small compared to the pathlength through the Galaxy, the low-frequency recombination lines cannot be considered as coming from a widely distributed component of the interstellar medium. The Hn regions studied in the above survey cannot themselves produce the H 272α lines detected towards them because of pressure broadening, optical depth, and beam dilution. However, the agreement in velocity of these lines with those seen at higher frequencies suggests that the low-frequency recombination lines arise in low-density envelopes of the Hn regions. Assuming that the temperature of the envelopes are similar to those of the cores and invoking geometrical considerations we find that these envelopes should have electron densities in the range 1-10 cm-3 and linear sizes of 30-300 pc in order to produce the observed H 272α lines

Transfer hydrogenation; a convenient method for removal of some commonly used protecting groups in peptide synthesis

N-Benzyloxycarbonyl and benzyl ester groups in peptidescan be conveniently removed by transfer hydrogenation with cyclohexene and 10% palladium-carbon catalyst. If freshly prepared palladium black catalyst is used, other commonly used protecting groups like Nτ-benzyl (histidine), benzyl ether (tyrosine, serine), and nitro (arginine) can also be removed much more rapidly than in the case of the usually employed catalytic hydrogenation

On the origin of the Galactic Ridge recombination lines

Radio recombination lines are known to be observable at positions along the galactic ridge which are free of discrete continuum sources. Based on the results of a recent survey of H272α lines it is shown that most of the observed galactic ridge recombination lines can be explained as emission from outer low-density envelopes of normal HII regions. The distribution of low-density ionized gas and discrete HII regions as a function of the distance from the galactic centre is also derived

A survey of recombination line emission from the galactic plane at 325 MHz

A survey of the H 272 α recombination line at 325 MHz has been made towards 53 directions in the galactic plane using the Ooty Radio Telescope (ORT). 34 of these directions correspond to well-known Hn regions, 12 to SNRs and 6 to 'blank' areas selected so that the 5 GHz continuum is a minimum over the telescope beam of 2° × 6 arcmin. Observing procedure and spectra of 47 sources towards which lines are detected are presented. Hydrogen recombination lines have been detected towards all the observed directions having l<40°. Carbon recombination lines are identified in 12 of the directions. The hydrogen line intensities are found to correlate well with the total continuum intensity (which includes the nonthermal galactic background) indicating that most of the lines arise due to stimulated emission by the background radiation. A preliminary discussion on the nature of the line-emitting regions is also presented

K. M. Sivanandaiah (1931-2011)

K. M. Sivanandaiah, an eminent teacher and an internationally renowned peptide chemist, from the Department of Chemistry, Central College, Bangalore, passed away on 2 October 2011 in Bangalore