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Next: New IRAM Preprints Up: IRAM Newsletter 41(August 1999) Previous: Technical report


Scientific results in press

Proposed identification of Hubble Deep Field submillimeter source HDF850.1

D.Downes(1), R.Neri(1), A.Greve(1), S.Guilloteau(1), F.Casoli(2), D.Hughes(3,4), D.Lutz(5), K.M.Menten(6), D.J.Wilner(7), P.Andreani(8), F.Bertoldi(6), C.L.Carilli(9), J.Dunlop(3), R.Genzel(5), F.Gueth(6), R.J.Ivison(10), R.G. Mann(11), Y.Mellier(2,12), S.Oliver(11), J.Peacock(3), D.Rigopoulou(5), M.Rowan-Robinson(11), P.Schilke(6), S.Serjeant(11), L.J.Tacconi(5), M.Wright(13)
(1) Institut de Radio Astronomie Millimétrique, Domaine Universitaire, F-38406 St. Martin d'Hères, France (2) DEMIRM, Observatoire de Paris, 61 av. de l'Observatoire, F-75014 Paris, France, and UMR 8540 du CNRS (3) Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK (4) Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Apartado Postal 51 y 216, 72000 Puebla, Pue., Mexico (5) Max-Planck-Institut für extraterrestrische Physik, D-85748 Garching-bei-München, Germany (6) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany (7) Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA (8) Dipartimento di Astronomia, Università di Padova, vicolo dell'Osservatorio 5, I-35122 Padova, Italy (9) National Radio Astronomy Observatory, P.O. Box O, Socorro, N.M., 87801, USA (10) Dept. of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK (11) Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2BZ, UK (12) Institut d'Astrophysique, 98bis, Bd Arago, 75014, Paris, France (13) Radio Astronomy Laboratory, University of California, Berkeley, CA94720, USA


The IRAM Interferometer has been used to detect the submillimeter source HDF 850.1 found by Hughes et al. the Hubble Deep Field (1998, Nature, 394, 241). The 1.3mm (236GHz) map is shown in the Cover Picture of this issue; The flux density measured at 1.3mm is 2.2 $\pm 0.3 (1\sigma)$mJy, in agreement with the flux density measured at the JCMT. The flux densities and upper limits measured at 3.4, 2.8, 1.3, 0.85, and 0.45mm show that the emission comes from dust. We suggest that the 1.3mm dust source is associated with the optical arc-like feature, 3-593.0, that has a photometric redshift $z\approx 1.7$. If HDF 850.1 is at this redshift and unlensed, its spectral energy distribution, combined with that of 3-593.0, matches closely that of the ultraluminous galaxy VII Zw 31. Another possibility is that the dust source may be gravitationally lensed by the elliptical galaxy 3-586.0 at $z\approx 1$.

The position of the dust source agrees within the errors with that of the tentative VLA radio source 3651+1226.

Astronomy and Astrophysics, 347, p.809-820 1999

CO(4-3) and CO(3-2) studies of M51 and NGC6946

Ch. Nieten(1), M. Dumke(1,2), R. Beck(1), and R. Wielebinski(1)
(1) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
(2) Institut de Radio Astronomie Millimétrique, 300 Rue de la Piscine, F-38406 Saint Martin d'Hères, France

Abstract: We have mapped several nearby galaxies in the CO(4-3) line transition with the Heinrich-Hertz-Telescope on Mt. Graham, Arizona, during an excellent weather period in December 1998. In this Letter we report on our observations of M51 (Fig. 2) and NGC6946. The results suggest a concentration of highly excited CO gas to the nuclei of these galaxies. Moreover, in both objects CO(4-3) line emission was also detected for the first time in the spiral arms, several kiloparsecs away from the centre.

Astron. Astrophys. 347, L5 (1999)

Figure: 12CO(4-3) spectra in M51 at 17'' resolution, with positions relative to the central coordinates ${\rm R.A.[1950]} = 13^{\rm h}27^{\rm m}46^{\rm s}\!\!.1$, ${\rm Dec.[1950]} = 47^{\circ}27'14''$. In addition HHT observations of the CO(3-2) transition at 22'' resolution are plotted as dashed lines. In the box on the right the spectrum of a position on a dust lane of a spiral arm at an offset of ( -60''/30'') is shown.

A cluster of young stellar objects in L 1211

M. Tafalla(1), P.C. Myers(2), D. Mardones(3), R. Bachiller(1)
(1)Observatorio Astronómico Nacional, Apartado 1143, E-28800 Alcala de Henares, Spain
(2)Harvard-Smithsonian Center for Astrophysics, MS 42, 60 Garden St, Cambridge, MA 02138, USA
(3) Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

Abstract: We present millimeter continuum and line observations of a dense core in L1211, a member of the Cepheus cloud complex. We find a small cluster of at least 4 millimeter (mm) sources with no optical counterpart, but each associated with near infrared (NIR) diffuse emission. The strongest mm source has no NIR point-like counterpart, and constitutes a good candidate for a Class 0 object. The other mm objects seem associated with NIR sources and most likely belong to Class I, as also suggested by the spectral energy distributions derived from combining our mm data with IRAS HIRES fluxes. As evidenced by our line data, the mm sources are embedded in an elongated, turbulent core of about 150 M$_\odot$ of mass and 0.6 pc length. Two of the millimeter sources power bipolar molecular outflows, another signature of their extreme youth. The outflows are well resolved by our observations and seem to have unrelated orientations.

The combination of millimeter sources and bipolar outflow emission indicates that multiple star formation in L1211 has occurred during a short period of time (a few 105 yr). The lack of a noticeable enhancement in the number of NIR sources suggests that the core has not had enough time to form a cluster, so we infer that L1211 is undergoing a first episode of star formation.

Astron.& Astrophys. in press. Preprints available at:

Unveiling the disk-jet system in the massive (proto)star IRAS 20126+4104

Cesaroni R.(1), Felli M.(1), Jenness T.(2), Neri R.(3), Olmi L.(4), Robberto M.(5,6), Testi L.(1,7), Walmsley C.M.(1)
(1) Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5, I-50125 Firenze, Italy
(2) Joint Astronomy Centre, 660 N. A`ohoku Place, Hilo, HI 96720, USA
(3) IRAM, 300 Rue de la Piscine, Domaine Universitaire, F-38406 St. Martin d'Hères Cedex, France
(4) LMT Project and FCRAO, University of Massachusetts, 630 L.G.R.C., Amherst, MA 01003, USA
(5) Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
(6) Osservatorio Astronomico di Torino, Str. Osservatorio 20, I-10025 Pino Torinese, Italy
(7) Division of Mathematics, Physics and Astronomy, MS105-24, Pasadena, CA 91125, USA

Abstract: We present the results of line and continuum observations towards the source IRAS 20126+4104, performed at 1.3mm and 3.5 mm with the Plateau de Bure interferometer, from 350$\mu $m to 2mm with the James Clerk Maxwell telescope, and at 10 and 20$\mu $m with the United Kingdom infrared telescope. The results fully confirm the findings of Cesaroni et al. (1997), namely that IRAS 20126+4104 is a very young stellar object embedded in a dense, hot core and lying at the centre of a rotating disk. The bipolar jet imaged by Cesaroni et al. (1997) in the 2.122$\mu $m H2 line is seen also in the SiO(2-1) transition, which allows to study the velocity field in the jet. A simple model is developed to obtain the inclination angle of the jet (and hence of the disk axis), which turns out to be almost perpendicular to the line of sight. By studying the diameter of the disk in different transitions and the corresponding line widths and peak velocities, one can demonstrate that the disk is Keplerian and collapsing, and thus compute the mass of the central object and the accretion luminosity. We show that if all the mass inducing the Keplerian rotation is concentrated in a single star, then this cannot be a ZAMS star, but more likely a massive protostar which derives its luminosity from accretion.

Appeared in Astron. and Astrophys. 345, 949

Spectroscopic monitoring of comet C/1996 B2 (Hyakutake) with the JCMT and IRAM radio telescopes

N. Biver(1,2), D. Bockelée-Morvan(1), J. Crovisier(1), J.K. Davies(3), H.E. Matthews(3), J.E. Wink(4), H. Rauer(1,5), P. Colom(1), W.R.F. Dent(3,6), D. Despois(7), R. Moreno (8,1,4), G. Paubert(8), D. Jewitt(2), and M. Senay(2,9)
(1) Observatoire de Paris-Meudon, 5, place J. Janssen, F-92195 Meudon, France
(2)Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
(3)Joint Astronomy Centre, 660 N. A'ohoku Place, Hilo, HI 96720, USA
(4) IRAM, 300 rue de la Piscine, F-38406 St Martin d'Hères, France
(5) DLR, Institut für Planetenerkundung, Rudower Chaussee, 5 , D-12484 Berlin, Germany
(6) Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, United Kingdom
(7) Observatoire de Bordeaux, BP 89, Avenue Pierre Sémirot, F-33270 Floirac, France
(8)IRAM, Avenida Divina Pastora, 7, E-18012 Granada, Spain
(9)FCRAO, 619 LGRC, University of Massachusetts, Amherst, MA 01003, USA

Abstract: Molecular radio lines were monitored in comet C/1996 B2 (Hyakutake) from February 10 to June 23, 1996, using the James Clerk Maxwell Telescope, and the 30-m telescope and the Plateau-de-Bure interferometer of the Institut de Radio Astronomie Millimétrique. We report on observations of HCN, CH3OH, CO, H2CO, CS and H2S and on the evolution of their production rates with heliocentric distance (rh), from 1.86 down to 0.24 AU at perihelion. Most production rates increased roughly as rh-2.2 down to 0.6 AU pre-perihelion. Closer to the Sun, they stalled before decreasing beyond 0.6 AU post-perihelion when observations resumed. The CS/HCN ratio varied as rh-0.8 from 1.2 to 0.24 AU. A rapid increase of the mean gas temperature in the coma is measured, and the gas expansion velocity increased from 0.55 to 1.6 km s-1, as the comet approached the Sun from 1.6 to 0.3 AU. Molecular abundances of the minor species around 1 AU are similar to those observed in other comets whilst the CO abundance relative to water is high ( $\approx
22$%). Coarse mapping was used to check the comet's position and to investigate the density distribution of the molecules within the coma. It provides constrains on the size of the extended source of formaldehyde, found to be between 1.2 and 2 times the scale-length of H2CO itself. The density distribution of CS is compatible with its production from the photodissociation of a short lived molecule such as CS2. The density distribution observed for CO can be mostly explained by a nuclear source.

Astron. J. in press.

A 2 mm molecular line survey of the C-star envelope IRC+10216

J. Cernicharo(1), M. Guélin(2), and C. Kahane(3)
(1)CSIC. Instituto de Estructura de la Materia. C.Serrano 121. 28006 Madrid. Spain
(2)IRAM. Domaine Universitaire de Grenoble. 300 rue de la Piscine. 38406 St Martin d'Hères, France
(3)Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex, France

Abstract: The mm-wave spectrum of the C-star envelope IRC+10216 has been continuously surveyed between 129.0 and 172.5 GHz with the IRAM 30-m telescope. This spectrum (see Fig. 3 and Fig. 4) can be inspected on the IRAM WEB page.

Figure 3: Overview of the 2mm spectrum of IRC+10216, smoothed to a resolution of 3 MHz (10 kms-1).

380 lines are detected, of which 317 have been identified. The identified lines arise from 30 different molecules and radicals which, in their vast majority, are not observed in hot and dense interstellar clouds such as Orion A or W3(OH). Actually, half of the molecular species identified in the mm-wave spectrum of IRC+10216 were first observed in the course of this spectral survey.

The new species include several carbon-chain molecules and radicals, as well as silicon and metallic compounds. They also include molecules containing rare isotopes of C, Mg, Si, S and Cl, whose elemental abundance ratios in the envelope are redetermined.

Figure 4: Portion of the 2mm spectrum of IRC+10216 at full resolution. The rest frequencies of the identified lines are marked by vertical arrows.

We observe, in particular, four 13C isotopomers of C4H, three of C3N and HC3N, and four doubly-substituted isotopomers of SiS and CS .

63 lines remain unidentified. Probably, a large fraction of those are rotational transitions inside the excited bending states of the abundant species NaCN, C5H, and C6H. We can also expect some lines to be ground state transitions of poorly known silicon and metal compounds, such as the slightly asymmetrical top molecule SiCSi.

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Next: New IRAM Preprints Up: IRAM Newsletter 41(August 1999) Previous: Technical report