Scientific Results in Press

The composition of ices in comet C/1995 O1 (Hale-Bopp) from radio spectroscopy. Further results and upper limits on undetected species

Crovisier J.$(^{1})$, Bockelée-Morvan D.$(^{1})$, Colom P.$(^{1})$, Biver N.$(^{1})$, Despois D.$(^{2})$, Lis D.C.$(^{3})$, the Team for target-of-opportunity radio observations of comets
$(^{1})$Observatoire de Paris, 92195 Meudon, France, $(^{2})$Observatoire de Bordeaux, BP 89, 33270 Floirac, France, $(^{3})$California Institute of Technology, MS 320-47, Pasadena, CA 91125, USA

Abstract:
From radio spectroscopic observations of comets, more than 22 molecules, radicals and ions, plus several isotopologues, were detected, the majority of them being recently revealed in comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp). Among them, 6 molecules were detected for the first time (Bockeée-Morvan et al. 2000) in the course of a spectral survey conducted at radio wavelengths in comet Hale-Bopp with the CSO, the IRAM 30-m telescope and Plateau de Bure interferometer. In addition, many species were searched for unsuccessfully, some of them with stringent upper limits. We present here a review of these observations and further analysis of their results. This include: (i) confirmed detection of acetaldehyde (CH$_3$CHO); (ii) limits on small molecules such as ketene (H$_2$CCO) or methanimine (CH$_2$NH); (iii) limits on the abundance ratios in homologous series such as HC$_5$N/HC$_3$N, ethanol/methanol, acetic acid/formic acid; (iv) searches for precursors of key cometary species such as atomic Na and HNC; (v) constraints on more exotic species ranging from water dimer (H$_2$O)$_2$ to glycine; (vi) detection of the H$_2^{34}$S isotopic species and independent observations of HDO and DCN; (vii) limits on several other deuterated species; (viii) limits on several radicals and ions and a tentative detection of the C$_2$H radical; (ix) the presence of unidentified lines. Typical abundance upper limits of $2-5 \times 10^{-4}$ relative to water are achieved for many species. Better upper limits are obtained for some linear molecules with high dipole moments. But more complex molecules such as dimethyl ether or glycine are poorly constrained. These results should give important clues to the chemical composition of cometary ices, to the formation mechanisms of cometary material, and to the chemical processes which occur in the inner coma.

Appeared in:Astronomy and Astrophysics, 418, 1141

The abundance of $^{36}$S in IRC+10216 and its production in the Galaxy

R. Mauersberger$(^{1})$, U. Ott$(^{2})$, C. Henkel$(^{3})$, J. Cernicharo$(^{4})$ and R. Gallino$(^{5,6})$
$(^{1})$Instituto de Radioastronomía Milimétrica, Avda. Divina Pastora 7, Local20, E-18012 Granada, Spain, $(^{2})$Max-Planck-Institut für Chemie, Becherweg 27, D-55128 Mainz, Germany, $(^{3})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany, $(^{4})$Instituto de la Estructura de la Materia, Dept. de Astronomía Molecular e Infrarroja, Serrano 113, E-28006 Madrid, Spain, $(^{5})$Dipartimento di Fisica Generale dell'Università di Torino, Via Pietro Giuria 1, I-10125 Torino, Italy $(^{6})$Centre for Stellar and Planetary Sciences, Monash University, Melbourne 3800, Australia

Abstract:
The $J=2-1$ and $3-2$ rotational lines of the rare isotopomer C$^{36}$S and the $J=5-4$ and $6-5$ transitions of Si$^{36}$S were detected in the carbon star IRC+10216 (CWLeo). These are the first detections of $^{36}$S bearing molecules in a star and the first spectroscopic detection of Si$^{36}$S. From a comparison of $^{34}$S and $^{36}$S bearing isotopomers, the $^{34}$S/$^{36}$S isotopic ratio is 107($\pm 15$). This value is comparable to values in the interstellar medium of the inner Galactic disk (115) but is smaller than the solar value of 288 (Ding et al. 2001). The increase of the $^{36}$S abundance relative to $^{34}$S only qualitatively follows model predictions of a low mass AGB star. Quantitative agreement of the observed $^{34}$S/$^{36}$S ratio with the stellar models can be reached if the age of IRC+10216 and Galactic chemical evolution are taken into account. Other less likely possibilities are the presence of considerable inhomogeneities in the interstellar medium and either IRC+10216 or the Sun started with a peculiar $^{36}$S abundance. Other production mechanisms potentially capable of enhancing the Galactic interstellar medium are discussed. From the observed line density toward IRC+10216 and toward Galactic star forming regions, we estimate the confusion limit toward those sources.


Accepted for publication in A&A

Molecular Clouds and their Structures in the Andromeda Galaxy

S. Muller$(^{1,2})$, M. Guélin$(^{2})$, H. Ungerechts$(^{3})$, N. Neininger$(^{4})$, R. Lucas$(^{2})$, R.Wielebinski$(^{5})$
$(^{1})$Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei, 106 Taiwan, $(^{2})$Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, F-38406 St Martin d Hères, France, $(^{3})$Instituto de Radioastronomia Millim´etrica, Avenida Divina Pastora 7, E 18012 Granada, Spain, $(^{4})$Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany, $(^{5})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Abstract:
We present the distribution and physical properties of the giant molecular clouds in the Andromeda galaxy (M31) as derived from observations of the CO molecule emission with the IRAM 30m telescope (Pico Veleta, Spain) and the Plateau de Bure Interferometer (PdBI, France). Not only is M31 the closest spiral galaxy, which allows to study the interstellar medium at molecular clouds scale with current mm interferometers (1 $^{\prime\prime}$corresponds to 4 pc), but its distance is also very accurately known ( $D = 780 \pm 17$ kpc, that is to say 5% uncertainty !) which allows reliable measurements of physical properties such as sizes and luminosities. Adding to this, and unlike in the case of Galactic molecular clouds, there are no distance ambiguities, and the line of sight is free from intervening material. We therefore have access to both global and local views, which is essential in interstellar medium studies from large scales (spiral pattern) down to the small scales of star formation sites (molecular clouds).


To appear in the Conference Proceedings of ``The Young Local Universe'', Rencontres de Moriond, held in La Thuile, Italy, March 21st-28th 2004

Disappearance of N$_2$H$^+$ from the Gas Phase in the Class 0 Protostar IRAM 04191

A. Belloche$(^{1,2})$ & P. André$(^{3})$
$(^{1})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany, $(^{2})$LERMA/LRA, Ecole Normale Supérieure, 24 rue Lhomond, F-75231 Paris Cedex 05, France, $(^{3})$Service d'Astrophysique, CEA/DSM/DAPNIA, C.E. Saclay, F-91191, Gif-sur-Yvette Cedex, France

Abstract:
We present a high-resolution millimeter study of the very young Class 0 protostar IRAM 04191+1522 in the Taurus molecular cloud. N$_2$H$^+$(1-0) observations with the IRAM Plateau de Bure Interferometer and 30m telescope demonstrate that the molecular ion N$_2$H$^+$ disappears from the gas phase in the inner part of the protostellar envelope ($r < 1600$ AU, $n_{\mbox{\tiny {H$_2$}}} > 5 \times 10^5$ cm$^{-3}$). This result departs from the predictions of current chemical models. It suggests either that N$_2$ is more depleted than the models predict, owing to a higher binding energy on polar ice or an enhanced grain chemistry transforming N$_2$ to less volatile species, or that strong deuterium fractionation enhances N$_2$D$^+$ to the detriment of N$_2$H$^+$.


Appeared in A&A, 419, L35 (May 2004)

Improvements 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$(^{1})$
$(^{1})$Institute de Radio Astronomie Millimétrique, 300 rue de la Piscine, F-38406 St. Martin d'Hères, France, $(^{2})$Instituto de Radioastronomía Milimétrica, Avda. Divina Pastora 7, Local20, E-18012 Granada, Spain, $(^{3})$Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei, 106 Taiwan

Abstract:
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 IRAM 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 actual 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.


To be published in IEEE Trans. on Ant. & Prop.

New light on the S235A-B star forming region

Felli M.$(^{1})$, Massi F.$(^{1})$, Navarrini A.$(^{2})$, Neri R.$(^{3})$, Cesaroni R.$(^{1})$ and Jenness T.$(^{4})$
$(^{1})$INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy, $(^{2})$Radio Astronomy Laboratory, University of California, Berkeley 601 Campbell Hall, Berkeley, CA 94720, USA, $(^{3})$IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 St. Martin d'Hères Cedex, France, $(^{4})$Joint Astronomy Centre, 660 N. A'ohoku Place, Hilo, HI 96720, USA

Abstract:
The S235A-B star forming region has been extensively observed in the past from the radio to the near IR, but what was happening in the immediate surroundings of the water maser, placed in between the two nebulosities, was still unclear because of insufficient resolution especially in the spectral range from the Far IR to the mm, even though there were sound indications that new young stellar objects (YSOs) are being formed there. We present here new high resolution maps at mm wavelengths in different molecules (HCO$^{+}$, C$^{34}$S, H$_2$CS, SO$_2$ and CH$_3$CN), as well as in the 1.2 and 3.3 mm continuum obtained with the Plateau de Bure interferometer, and JCMT observations at 450 $\mu$m and 850 $\mu$m that unambiguously reveal the presence of new YSOs placed in between the two HII regions S235A and S235B and associated with the water maser. A molecular core and an unresolved source in the mm and in the sub-mm are centred on the maser, with indication of mass infall onto the core. Two molecular bipolar outflows and a jet originate from the same position. Weak evidence is found for a molecular rotating disk perpendicular to the direction of the main bipolar outflow. The derived parameters indicate that one of the YSOs is an intermediate luminosity object ( $L \approx 10^3$ L$_\odot$) in a very early evolutionary phase, embedded in a molecular core of $\approx 100$ M$_\odot$, with a temperature of 30 K. The main source of energy for the YSO could come from gravitational infall, thus making of this YSO a rare example of intermediate luminosity protostar representing a link between the earliest evolutionary phases of massive stars and low mass protostars of class 0-I.


Appeared in A&A 420, 553 (2004)

Massive Molecular Outflows at High Spatial Resolution

Beuther H.$(^{1})$, Schilke P.$(^{2})$ and Gueth F.$(^{3})$
$(^{1})$Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA, $(^{2})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany, $(^{3})$Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d'Hères, France

Abstract:
We present high spatial resolution Plateau de Bure Interferometer CO(2-1) and SiO(2-1) observations of one intermediate-mass and one high-mass star-forming region. The intermediate-mass region IRAS 20293+3952 exhibits four molecular outflows, one being as collimated as the highly collimated jetlike outflows observed in low-mass star formation sources. Furthermore, comparing the data with additional infrared H$_2$ and centimeter observations, we see indications that the nearby ultracompact H II region triggers a shock wave interacting with the outflow. The high-mass region IRAS 19217+1651 exhibits a bipolar outflow as well, and the region is dominated by the central driving source. Adding two more sources from the literature, we compare position-velocity diagrams of the intermediate-to-high-mass sources with previous studies in the low-mass regime. We find similar kinematic signatures; some sources can be explained by jet-driven outflows, whereas others are better constrained by wind-driven models. The data also allow us to estimate accretion rates varying from a few times $10^{-5}$M$_\odot$yr$^{-1}$ for the intermediate-mass sources to a few times $10^{-4}$M$_\odot$yr$^{-1}$ for the high-mass source, consistent with models explaining star formation of all masses via accretion processes.


Appeared in: The Astrophysical Journal, 608, 330