next up previous
Next: New Preprints Up: IRAM Newsletter 62 (February 2005) Previous: Call for Observing Proposals


Scientific Results in Press

Repetitive Radio Reflector Surface Deformations

A. Greve$(^{1})$ and D. Morris$(^{1})$
$(^{1})$IRAM, 300 rue de la Piscine, F-38406 St. Martin d'Hères, France

Holography measurements of radio reflector surfaces have revealed temperature induced panel buckling. This buckling is a typical example of repetitive deformations which are not covered by the theory of systematic wavefront deformations, for instance of Zernike polynomial type. We present examples of repetitive surface deformations, and explain the corresponding beam patterns. The loss in main beam (on-axis) efficiency from repetitive deformations can be derived from the associated effective rms-value used in the Ruze relation; the full beam pattern can be derived from an exact diffraction calculation. We provide an example which shows that panel buckling affects the beam pattern of the IRAM 30-m telescope, at the shortest wavelength of observation.

Accepted for publication in IEEE Trans. Antennas Propagation, 2005

Molecular hydrogen beyond the optical edge of an isolated spiral galaxy

Jonathan Braine$(^{1})$ and Fabrice Herpin$(^{1})$
$(^{1})$Observatoire de Bordeaux, UMR 5804, CNRS/INSU, B.P. 89, F-33270 Floirac, France

Knowledge about the outermost portions of galaxies is limited owing to the small amount of light coming from them. It is known that in many cases atomic hydrogen (H I) extends well beyond the optical radius. In the centres of galaxies, however, molecular hydrogen (H$_2$) usually dominates by a large factor, raising the question of whether H$_2$ is also abundant in the outer regions. Here we report the detection of emission from carbon monoxide (CO), the most abundant tracer of H$_2$, beyond the optical radius of the nearby galaxy NGC 4414. The host molecular clouds probably formed in the regions of relatively high H I column density and in the absence of spiral density waves. The relative strength of the lines from the two lowest rotational levels indicates that both the temperature and density of the H$_2$ are quite low compared to conditions closer to the centre. The inferred surface density of the molecular material continues the monotonic decrease from the inner regions. We conclude that although molecular clouds can form in the outer region of this galaxy, there is little mass associated with them.

Appeared in NATURE 3054, 20/10/2004

Detection of the SiNC radical in IRC+10216

Guélin M.$(^{1})$, Muller$(^{1,2})$ S., Cernicharo J.$(^{3})$, McCarthy M. C.$(^{4})$, Thaddeus, P.$(^{4})$
$(^{1})$IRAM, 300 rue de la Piscine, 38406 Saint-Martin-d'Hères, France, $(^{2})$Institute of Astronomy and Astrophysics, Academia Sinica, 128 Section 2, PO Box 1-87, Nankang, Taipei 115, Taiwan, $(^{3})$Instituto de Estructura de la Materia, C/Serrano 121, 28006 Madrid, Spain, $(^{4})$Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Following discovery of the free radical SiCN in the C-star envelope IRC+10216, we report the detection in the same source of its isomer SiNC (Fig. 1).
Figure 1: Spectra of 4 rotational transitions of SiNC observed with the IRAM 30-m telescope. Most lines are cusped in shape and have 29 km/s widths. The rest frequencies of the SiNC Lambda-doublet components are indicated by short vertical lines and the line edges by vertical arrows. The insert shows the average of the two 10.5-9.5 doublet components. The bottom spectrum has an r.m.s. noise of 0.5 mK/1-MHz channel and is one of the most sensitive spectra ever taken with the 30-m telescope.
The microwave spectra of SiNC and SiCN were studied in the laboratory and their rotational transition frequencies are accurately known. The ground fine structure state of SiNC, $^2\Pi_{1/2}$, gives rise to a series of rotational transitions, spaced by 12.8 GHz, each with $\Lambda$-doubling. Five weak lines are detected with the IRAM 30-m telescope at the frequencies of the $J=6.5 \rightarrow 5.5$ (e), $7.5 \rightarrow 6.5$ (f), $8.5\rightarrow 7.5$ (f) and $10.5\rightarrow 9.5$ (e) and (f) rotational transitions. Other SiNC lines from these or adjacent rotational transitions are found to be blended with stronger lines from known molecules. The lines assigned to SiNC have a cusped shape, characteristic of species confined to a hollow shell in the outer circumstellar envelope. They are twice weaker than their SiCN counterparts, which have the same shape, and presumably arise in the same region of the envelope. SiNC and SiCN have about the same abundance in IRC+10216, $\approx 4 \times 10^{-9}$ with respect to H$_2$. This contrasts with HCN, HC$_3$N and HC$_5$N, for which the cyanide to isocyanide abundance ratio is >100.

Appeared in A&A, 426, p.L49-L52

Detection of two massive CO systems in 4C 41.17 at z = 3.8

De Breuck C.$(^{1})$ Downes D.$(^{2})$, Neri R.$(^{2})$, van Breugel W.$(^{3})$, Reuland M.$(^{3,4})$; Omont A.$(^{5})$, Ivison, R.$(^{6,7})$
$(^{1})$European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany, $(^{2})$IRAM, 300 rue de la Piscine, F-38406 St. Martin-d'Hères, France, $(^{3})$IGPP/LLNL, L-413, 7000 East Ave, Livermore, CA 94550, USA, $(^{4})$Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands, $(^{5})$Institut d'Astrophysique de Paris, CNRS & Université Paris 6, 98bis Boulevard Arago, 75014 Paris, France, $(^{6})$Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK, $(^{7})$Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

We have detected CO(4-3) in the z=3.8 radio galaxy 4C 41.17 with the IRAM Interferometer. The CO is in two massive ( $M_{dyn} \approx 6\times 10^{10} \mbox{M$_\odot$}$) systems separated by 1. $^{\prime\prime}$8 (13 kpc), and by 400 km s$^{-1}$ in velocity, which coincide with two different dark lanes in a deep Lya image. One CO component coincides with the cm-radio core of the radio galaxy, and its redshift is close to that of the He II AGN line. The second CO component is near the base of a cone-shaped region southwest of the nucleus, which resembles the emission-line cones seen in nearby AGN and starburst galaxies. The characteristics of the CO sources and their mm/submm dust continuum are similar to those found in ultraluminous IR galaxies and in some high-z radio galaxies and quasars. The fact that 4C 41.17 contains two CO systems is further evidence for the role of mergers in the evolution of galaxies at high redshift.

Appeared in: A&A 430, L1-L4

Improvement of the IRAM 30-m Telescope from temperature measurements and finite element calculations

A. Greve$(^{1})$, M. Bremer$(^{1})$, J. Peñalver$(^{2})$, P. Raffin$(^{3})$ and D. Morris$(^{1})$
$(^{1})$IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{2})$IRAM, Avenida Divina Pastora 7, Local 20 E-18012 Granada, Spain, $(^{3})$Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan

Millimeter wavelength radio telescopes built in a conventional way from steel and aluminum require elaborate thermal control to guarantee small structural deformations and good observing performance. We describe the temperature monitoring system of the Institut de Radioastronomie Millimétrique 30-m telescope and the use of temperature measurements in finite-element calculations of structural deformations. These calculations reproduce with good precision the measured thermal deformations of the telescope and allow the investigation and localization of thermally important elements in the telescope structure. The data are used for calculation of temperature induced main reflector surface deformations and of the associated beam pattern, and for prediction and real-time correction of the focus. The pointing cannot be fully predicted since the available finite-element model does not include the Nasmyth focus cabin (and the concrete pedestal). The long-term investigation of the telescope's thermal behaviour led to an improvement of the thermal control system and to a better performance of the telescope.

Accepted for publication in IEEE Trans. on Antennas and Propagation

next up previous
Next: New Preprints Up: IRAM Newsletter 62 (February 2005) Previous: Call for Observing Proposals