Scientific Results in Press

Warm H₂ in the Galactic center region

N.J. Rodríguez-Fernández(¹), J. Martín-Pintado(¹), A. Fuente(¹), P. de Vicente(¹), T.L. Wilson(²),(³) and S. Hüttemeister(⁴)
(¹)Observatorio Astronómico Nacional, IGN, Apartado 1143, E-28800 Alcalá de Henares, Spain, (²)Max-Planck-Institut für Radioastronomie, Postfach 2024, D-53010 Bonn, Germany, (³)Sub-mm Telescope Observatory, Steward Observatory, The University of Arizona, Tucson, AZ 85728, USA, (⁴)Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

Abstract:
We present ISO observations of several H₂ pure-rotational lines (from S(0) to S(5)) towards a sample of 16 molecular clouds distributed along the central $\sim 500$ pc of the Galaxy. We also present C¹⁸O and ¹³CO $J=1\rightarrow0$

NbN $_{\mbox{x}}$ Thin Film Resistors for Cryogenic Application

M. Schicke(¹), P. Sabon(¹), and K.-F. Schuster(¹)
(¹)Institut de Radio Astronomie Millimétrique, Domaine Universitaire de Grenoble, F-38406 St. Martin d'Hères, France

Abstract:
We report on the deposition and characterization of highly resistive NbN $_{\mbox{x}}$ films for cryogenic planar resistors. Radio frequency (RF) sputtering of Nb in a N₂/Ar mixture resulted in films with a temperature independent resistivity of 220 $\mu \Omega \cdot \mbox{cm}$ for temperatures down to at least 2.3 K. Sheet resistances of 25 $\Omega / \fbox{}$ were obtained for films of 90 nm thickness, which implies the application of even thicker films, advantageous for step-edge coverage, thickness tolerances, and interface effects. The films are thermally stable up to 200$^{\circ}$C and exhibit only minor surface oxidation. Both the film deposition and trimming by reactive ion etching (RIE) will be described.
Keywords: Sputtering -Electronic devices - Niobium nitride - Resistors

Submitted to: Thin Solid Films, October 2000

High-resolution observations at $\lambda =3$mm of the OH231.8+4.2 molecular outflow

Sánchez-Contreras(¹),(²), C.; Bujarrabal(¹), V.; Neri, R.(³) and Alcolea, J.(¹)
(¹)Observatorio Astronomico Nacional, Ap. 1143, 28800 Alcala de Henares, Spain, (²)Departamento de Astrofisica, Facultad CC. Fisicas, Universidad Complutense, 28040 Madrid, Spain, (³)IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France

Abstract:
We present high spatial resolution observations of HCO⁺ (J=1-0), SO (J=22-11), H¹³CN (J=1-0), SiO (v=1, J=2-1), and the continuum at 3mm from OH231.8+4.2, taken with the IRAM interferometer at Plateau de Bure. We also report the first detection of NS in circumstellar envelopes. The overall distribution of the emission of all molecules (except for HCO⁺ and the SiO maser) is similar to that of CO. The most intense emission arises from a compact, slowly-expanding component around the central star. The rest of the emission comes from gas distributed in a narrow region along the symmetry axis, that flows outwards following a velocity gradient also similar to that found in CO. Our observations show with high accuracy the distribution of the HCO⁺ intensity, that is found to be very clumpy and strongly enhanced in the shock-accelerated lobes. We argue that such a distribution is due to the efficient formation of this molecule by shock-induced reactions. An expanding disk or ring around the central star is detected from the SO emission. The characteristic radius and expansion velocity of this structure are 210¹⁶cm and 6-7kms^-1, respectively. The SiO maser emission could arise from the innermost parts of such a disk. The 3mm continuum emission seems to be due to cold dust ($\sim 20$K) distributed in the lobes of object OH231.8+4.2 as well as from warmer ($\sim 55$K) dust located in a compact region surrounding the central star.

Appeared in: A&A 357, 651

A ridge of recent massive star formation between Sgr B2M and Sgr B2N

de Vicente, P.(¹); Martín-Pintado, J.(¹); Neri, R.(²) and Colom, P.(³)
(¹)Observatorio Astronomico Nacional, Ap. 1143, 28080 Alcala de Henares, Spain, (²)IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, (³)Observatoire de Meudon, Meudon, Paris, France

Abstract:
We present single dish and interferometric maps of several rotational transitions of HC₃N vibrationally excited levels towards SgrB2. HC₃N is a very suitable molecule to probe hot and dense regions (hot cores) affected by high extinction since its vibrational levels are mainly excited by mid-IR radiation. The single dish maps show, for the first time, that the HC₃N vibrationally excited emission (HC₃N$^\star$) is not restricted to SgrB2M and N but extended over an area $40'' \times 20''$ in extent. We distinguish four bright clumps (SgrB2R1 to B2R4) in the ridge connecting the main cores SgrB2M and SgrB2N, and a low brightness extended region to the west of the ridge (SgrB2W). The physical properties and the kinematics of all hot cores have been derived from the HC₃N$^\star$lines. Our high angular resolution images show that the SgrB2N hot core breaks in two different hot cores, SgrB2N1 and N2, with different radial velocities and separated by $\sim 2''$ in declination. We find that the excitation of the HC₃N$^\star$emission in all hot cores can be represented by a single temperature and that the linewidth of the HC₃N$^\star$ rotational lines arising from different vibrational levels systematically decreases as the energy of the vibrational level increases. The systematic trend in the linewidth is likely related to the increase of the velocity as the distance to the exciting source increases. We have developed a simple model to study the excitation of the HC₃N vibrational levels by IR radiation. We find that the single excitation temperature can be explained by high luminosities of embedded stars ($\sim 10^7$L$_\odot$) and small source sizes ( $\sim 2-3''$). The estimated clump masses are 500 M$_\odot$ for SgrB2M, 800M$_\odot$ for SgrB2N and 10-30M$_\odot$ for SgrB2R1 to B2R4. Luminosities are $1-2\,10^6$ L$_\odot$ for SgrB2R1-B2R4 and SgrB2M and 10⁷L$_\odot$ for SgrB2N. We estimate HC₃N abundances of $5\,10^{-9}$ for SgrB2M and SgrB2N2 and 10^-7 for the rest of the hot cores. The different HC₃N abundances in the hot cores reflect different stages of evolution due to time dependent chemistry and/or photo-dissociation by UV radiation from nearby HII regions. According to the mass and the luminosity of the different hot cores, we propose that SgrB2M and B2N contain a cluster of 20-30 hot cores, each like that in OrionA, a number similar to the UC HII regions already detected in the region. The SgrB2R1-B2R4 hot cores represent isolated formation of massive stars.

Appeared in: A&A 361, 1058