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Next: New IRAM Preprints Up: IRAM Newsletter 38 (January Previous: Scientific contribution

Scientific results in press

Low and high velocity SiO emission around young stellar objects

C. Codella tex2html_wrap_inline2257 , R. Bachiller tex2html_wrap_inline2257 , B. Reipurth tex2html_wrap_inline2261
tex2html_wrap_inline2257 Observatorio Astronomico Nacional (IGN), Apartado 1143, E-28800 Alcalá de Henares (Madrid), Spain
tex2html_wrap_inline2261 CASA, University of Colorado, Campus Box 389, Boulder, CO 80309, USA
Abstract: We present a multiline mm-wave survey of SiO emission towards a sample of star-forming regions associated with molecular and Herbig-Haro outflows. The sample includes sources in the northern and southern hemispheres. We extensively mapped some particularly interesting objects (IRAS00338+6312, HH7-11 and CepA). The high detection rate in the sample (52%) confirms that the SiO emission is closely associated with outflows. There exists a trend so that the more intense SiO sources are associated with higher luminosities, with an average tex2html_wrap_inline2579 / tex2html_wrap_inline2581 ratio of 1.8 10 tex2html_wrap_inline2583 .

The SiO lines exhibit a variety of profiles, ranging from narrow lines (1-3 km s tex2html_wrap_inline2051 width) at ambient velocities to broad profiles (10-20 km s tex2html_wrap_inline2051 ), with complex profiles consisting of a blend of low and high velocity components as intermediate stages. In the regions where SiO was mapped, the low velocity SiO emission comes from regions definitely offset from the position where the high velocity emission is present, indicating that the low and high velocity SiO emissions trace two distinct regimes. The SiO abundances are different in those two regimes: we estimate that typical SiO abundances are tex2html_wrap_inline2589 10 tex2html_wrap_inline2591 -10 tex2html_wrap_inline2593 in the high velocity components, but they decrease by two orders of magnitude (10 tex2html_wrap_inline2595 -10 tex2html_wrap_inline2583 ) when SiO is detected at low velocities.

The hydrogen volume densities estimated from the multiline SiO observations are in the range 10 tex2html_wrap_inline2599 to fews 10 tex2html_wrap_inline2601 cm tex2html_wrap_inline2603 , in both the low and the high velocity regimes, indicating that all the SiO emission arises in shock-compressed regions. We argue that the different observed SiO profiles could be caused by an evolutionary effect: the SiO molecules produced at high velocities could be slowed down because of their interaction with the surrounding gas before they stick onto the dust grains. However, the possibility that the low velocity SiO emission is due to slow shocks cannot be ruled out, but this would require the presence of a small amount of silicon compounds on the dust grain mantles.Astronomy & Astrophysics, in press

Carbon-chain molecules as tracers of time-dependent chemistry

M. Guélin tex2html_wrap_inline2257 , N. Neininger tex2html_wrap_inline2261 , R. Lucas tex2html_wrap_inline2257 and J. Cernicharo tex2html_wrap_inline2267
tex2html_wrap_inline2257 IRAM, 300 rue de la piscine, F-38406 St Martin d'Hères, France
tex2html_wrap_inline2261 Radioastron. Institut der Universität Bonn, Germany
tex2html_wrap_inline2267 Instituto de Estructura de la Materia, Madrid, Spain
Abstract: Gas-phase chemical models seem able to reproduce the abundances of organic interstellar molecules, provided the clouds are relatively young (Figure gif). Age, however, is not observationally constrained in most astronomical sources. An exception is IRC+10216, an expanding circumstellar envelope, where the distance to the central star is also a measure of age. An analysis of the spatial distribution of carbon chains in that source shows that the agreement between predicted and observed abundances is fortuitous.

Figure 13: Observed (filled symbols) and predicted (open symbols) column densities of the carbon-chain radicals in IRC+10216 (after Guélin et al. 1997&98). The predicted column densities are taken from Millar & Herbst (1994) and correspond to the peak abundances of the different species.

The current chemical models predict that C tex2html_wrap_inline2027 H forms from C tex2html_wrap_inline2025 H and C tex2html_wrap_inline2025 H from C tex2html_wrap_inline2023 H. C tex2html_wrap_inline2023 H itself results from the photodissociation of acetylene. A lower limit to the formation times of C tex2html_wrap_inline2025 H and C tex2html_wrap_inline2027 H can be derived by using the largest possible reaction rates, gas density and acetylene abundance. It takes tex2html_wrap_inline2633 yr to form C tex2html_wrap_inline2025 H from C tex2html_wrap_inline2023 H and C tex2html_wrap_inline2027 H from C tex2html_wrap_inline2025 H, which means, considering the envelope expansion velocity (14 kms tex2html_wrap_inline2051 ) and its distance (simeq 200 pc), that the abundances of these species should peak respectively tex2html_wrap_inline2647 and tex2html_wrap_inline2649 further out than tex2html_wrap_inline2651 H. In contrast, Figure 14 shows that the 3 species coexist spatially within tex2html_wrap_inline2653 and should form quasi-simultaneously (i.e. within 120 yr).

The very good agreement of Figure 13 is thus fortuitous and a new formation mechanism must be sought. This mechanism could be the desorption from dust grains of weakly attached carbon-chains, under the influence of interstellar UV and/or shocks.

Figure 14: Brightness temperature distribution of the tex2html_wrap_inline2021 3-mm lines of C tex2html_wrap_inline2023 H, C tex2html_wrap_inline2025 H and C tex2html_wrap_inline2027 H, observed in IRC+10216 with the IRAM interferometer. The intensities (multiplied by 1,1.3, and 7, respectively) have been integrated over a narrow band centred on the star velocity and represent roughly the species' abundance distribution in a meridian plane. Except for the larger noise in C tex2html_wrap_inline2027 H, the 3 maps look very similar; their brightest spots lie all along a circle of radius 16''. Note that the emission from the central star has been removed.

Proc. 3rd Cologne-Zermatt Symposium The Physics and Chemistry of the Interstellar Medium, ed V. Ossenkopf.


The jet-driven molecular outflow of HH211

F. Gueth tex2html_wrap_inline2671 and S. Guilloteau tex2html_wrap_inline2257
tex2html_wrap_inline2257 Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d'Hères, France
tex2html_wrap_inline2261 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Figure: CO  tex2html_wrap_inline2033 emission (thin contours) integrated in two different velocity intervals and superimposed on the H tex2html_wrap_inline2023  v=1-0 S(1) emission (greyscale; from McCaughrean et al.  1994) and the 230 GHz continuum emission (thick contours; contours are 10, 30, 50 and 70 mJy/beam). The angular resolutions are tex2html_wrap_inline2037 for the H tex2html_wrap_inline2023 , tex2html_wrap_inline2041 at PA  tex2html_wrap_inline2043 for the CO, and tex2html_wrap_inline2045 at PA  tex2html_wrap_inline2047 for the continuum observations. Upper panel: CO  tex2html_wrap_inline2033 emission integrated between LSR velocities 2.2 and 18.2kms tex2html_wrap_inline2051 (the systemic velocity is 9.2kms tex2html_wrap_inline2051 ); contours are 1.6 Jykms tex2html_wrap_inline2051 /beam. Lower panel: CO  tex2html_wrap_inline2033 emission integrated for velocities lower than 2.2kms tex2html_wrap_inline2051 and larger than 18.2kms tex2html_wrap_inline2051 ; first contour is 1 Jykms tex2html_wrap_inline2051 /beam and contour step is 1.5 Jykms tex2html_wrap_inline2051 /beam.

We present high angular resolution (down to tex2html_wrap_inline2713 ) interferometric maps of the CO  tex2html_wrap_inline2715 and tex2html_wrap_inline2717 emission in the molecular outflow associated with the extremely young HH211 jet, which is located in the IC348 molecular complex. At velocities close to the systemic velocity, the CO emission traces the outflow cavities, while an extremely collimated, continuous jet-like structure is observed at high CO velocities. The continuum emission reveals a tex2html_wrap_inline2719 dust condensation surrounding the central exciting (Class 0) protostar, clearly resolved and elongated perpendicular to the jet axis. The strong (bow-)shocks observed in vibrationally excited H tex2html_wrap_inline2023 emission are located at the terminal ends of the jet and the low-velocity CO cavities are precisely situated in their wake. Hence, the overall structure of HH211 perfectly fits into the picture of a jet-driven flow and strongly supports shock-entrainment models as the formation mechanisms of young, embedded molecular outflows. The shape of the cavities traced by the low-velocity CO emission can actually be (surprisingly well) reproduced by a simple, semi-analytical toy-model of a jet-driven flow, in which prompt entrainment occurs at the head of a travelling bow-shock. The estimated jet mass and mass loss rate yield a timescale of order one thousand years, in agreement with the kinematical age. Finally, we discuss the physical properties of the different parts of the outflow, and especially the actual nature of the high-velocity CO jet.
Astronomy & Astrophysics, in press
e-mail: Preprints:

A Strong Magnetic Field in the Disk of MWC349

C. Thum tex2html_wrap_inline2257 and D. Morris tex2html_wrap_inline2257 ,
tex2html_wrap_inline2257 Institut de Radioastronomie Millimétrique, Grenoble, France

Figure 16: Zeeman observations of the H tex2html_wrap_inline2067 transition in MWC349 obtained with an autocorrelator backend and smoothed to a resolution of 0.7 kms tex2html_wrap_inline2051 . All data obtained during 23-28 June 1996 have been averaged, representing 245 min of polarization-switched spectra. The three subframes show: (a) the total power spectrum (Stokes I), (b) the V-spectrum (RHC-LHC), corrected for instrumental polarization, (c) same as (b), but observed with the filter bank at a spectral resolution 1.3 kms tex2html_wrap_inline2051 . Vertical dotted lines mark the maxima of the total power maser spikes.

Using Zeeman observations of the H tex2html_wrap_inline2067 recombination line maser transition at 1.3 mm we have detected a magnetic field which is associated with the corona of the circumstellar disk of MWC349A. At a radial distance of 40 a.u.,where the H tex2html_wrap_inline2067 maser is located, the line-of-sight component of the field is approximately parallel to the plane of this edge-on disk, and its average strength is 22 mG. The corresponding magnetic energy density is tex2html_wrap_inline2741 % of the thermal energy density of the plasma where the maser emission originates, very likely making the detected field dynamically important. Spectral fine structure of the detected Zeeman pattern suggests that the field may have a strong radial component, although other models for the field configurations are possible. The strength of the field at such a large distance from the star makes it unlikely that the field is of stellar origin. We suggest that it is generated by a local disk dynamo.%

Detection of CO(4-3), CO(9-8) and dust emission in the BAL quasar APM08279+5255 at a redshift of 3.9

D. Downes tex2html_wrap_inline2257 , R. Neri tex2html_wrap_inline2257 , T. Wiklind tex2html_wrap_inline2261 , Wilner tex2html_wrap_inline2267 and Shaver tex2html_wrap_inline2753
tex2html_wrap_inline2257 IRAM, 300 rue de la piscine, F-38406 St Martin d'Hères, France
tex2html_wrap_inline2261 Onsala Space Observatory, S-43992 Onsala, Sweden
tex2html_wrap_inline2267 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
tex2html_wrap_inline2753 European Southern Observatory, D-85648 Garching bei München, Germany
Abstract: We detected with the IRAM interferometer the lines of CO(4-3) and CO(9-8) from the recently-discovered broad absorption line quasar APM 08279+5255. The molecular lines are at a redshift of 3.911, which we take to be the true cosmological redshift of the quasar's host galaxy. This means the quasar emission lines at z=3.87 are blueshifted by a kinematic component of -2500 kms tex2html_wrap_inline2051 , and, along with the broad absorption lines, are probably emitted in the quasar's wind or jet, moving toward us. The CO line ratios suggest the molecular gas is at a temperature of about 200 K, at a density of about 4000 cm tex2html_wrap_inline2603 . We also detected the dust emission at 94 and 214 GHz (emitted wavelengths 650 and 290 tex2html_wrap_inline2533 m). The spectral index of the mm/submm continuum is +3.2, indicating the dust emission is optically thin in this part of the spectrum. The extremely high CO and dust luminosities suggest magnification by gravitational lensing. Using the optical extent and our limit on the size of the CO region, we estimate a magnification of 7 to 30 for the CO lines and the far-IR continuum, and 14 to 60 for the optical/UV. In this interpretation, the molecular gas and dust is in a nuclear disk of radius 90 to 270 pc around the quasar. The quasar is 25 to 100 times stronger than, but otherwise resembles, the nucleus of Mrk 231.

Astron. & Astrophys., in press

Interferometric tex2html_wrap_inline2073 CO observations of the box-shaped bulge spiral NGC4013

S. Garcia-Burillo tex2html_wrap_inline2257 , F. Combes tex2html_wrap_inline2261 and R. Neri tex2html_wrap_inline2267 ,
tex2html_wrap_inline2257 Observatorio Astronomico Nacional (IGN), Apartado 1143, E-28800 Alcalá de Henares (Madrid), Spain
tex2html_wrap_inline2261 Observatoire de Paris, 61 av. de l'Observatoire, 75014 Paris, France
tex2html_wrap_inline2267 IRAM, 300 rue de la piscine, 38406 St Martin d'Hères, France
Abstract: The nucleus of the box-shaped galaxy NGC4013 has been observed with the IRAM interferometer in the J=1-0 and J=2-1 lines of tex2html_wrap_inline2073 CO. Our maps show the existence of a fast-rotating (130 km/s) molecular gas disk of radius r=110 pc. Several arguments support the existence of a bar potential in NGC 4013. The figure-of-eight pattern of the major axis p-v plot, the ring-like distribution of gas, and the existence of gas emission at non-circular velocities are best accounted by a bar. We have also detected gas at high z distances from the plane (z=200-300 pc). The latter component is related to a system of 4 Halpha filaments of diffuse ionized gas that come out from the nucleus. The galactic fountain model seems the best to account for the Halpha and CO filaments. Although the peanut distortion can be spontaneously formed by a stellar bar in the disk, gas at high z might have been ejected after a nuclear starburst. The Halpha filaments start in the plane of the disk at r=200 pc, and reach several Kpc height at r=600 pc, coinciding with the maximum peanut distortion. Although a link between the bar and the box-shaped bulge in NGC4013 is suggested we find noticeable differences between the results of previous numerical simulations and the present observations. The discrepancy concerns the parameters of the bar generating the peanut. We see in NGC 4013 the existence of a strong ILR region. The inclusion of a dissipative component, which remains to be thoroughly studied, may change the evolution of the stellar peanut: although in simulations the peanut appears initially near a marginal ILR, the inflow of gas driven by the bar, can make two ILRs appear.
Astron. & Astrophys., in press
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Next: New IRAM Preprints Up: IRAM Newsletter 38 (January Previous: Scientific contribution