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A&A
Volume 518, July-August 2010
Herschel: the first science highlights
Article Number L112
Number of page(s) 5
Section Letters
DOI https://doi.org/10.1051/0004-6361/201014582
Published online 16 July 2010
A&A 518, L112 (2010)

Herschel: the first science highlights

LETTER TO THE EDITOR

The CHESS spectral survey of star forming regions: Peering into the protostellar shock L1157-B1

I. Shock chemical complexity[*],[*]

C. Codella1 - B. Lefloch2 - C. Ceccarelli2 - J. Cernicharo3 - E. Caux4 - A. Lorenzani1 - S. Viti5,6 - P. Hily-Blant2 - B. Parise7 - S. Maret2 - B. Nisini8 - P. Caselli9,1 - S. Cabrit10 - L. Pagani10 - M. Benedettini6 - A. Boogert11 - F. Gueth12 - G. Melnick13 - D. Neufeld14 - S. Pacheco2 - M. Salez10 - K. Schuster12 - A. Bacmann2,15 - A. Baudry15 - T. Bell16 - E. A. Bergin17 - G. Blake16 - S. Bottinelli4 - A. Castets2 - C. Comito7 - A. Coutens4 - N. Crimier2,3 - C. Dominik18,19 - K. Demyk4 - P. Encrenaz10 - E. Falgarone10 - A. Fuente20 - M. Gerin10 - P. Goldsmith21 - F. Helmich22 - P. Hennebelle10 - Th. Henning23 - E. Herbst24 - T. Jacq15 - C. Kahane2 - M. Kama18 - A. Klotz2 - W. Langer21 - D. Lis16 - S. Lord16 - J. Pearson21 - T. Phillips16 - P. Saraceno6 - P. Schilke7,25 - X. Tielens26 - F. van der Tak22 - M. van der Wiel27,22 - C. Vastel4 - V. Wakelam15 - A. Walters4 - F. Wyrowski7 - H. Yorke21 - C. Borys16 - Y. Delorme10 - C. Kramer28 - B. Larsson29 - I. Mehdi21 - V. Ossenkopf25 - J. Stutzki25

1 - INAF, Osservatorio Astrofisico di Arcetri, Firenze, Italy
2 - Laboratoire d'Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France
3 - Centro de Astrobiologìa, CSIC-INTA, Madrid, Spain
4 - CESR, Université Toulouse 3 and CNRS, Toulouse, France
5 - Department of Physics and Astronomy, University College London, London, UK
6 - INAF, Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
7 - Max-Planck-Institut für Radioastronomie, Bonn, Germany
8 - INAF, Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy
9 - School of Physics and Astronomy, University of Leeds, Leeds, UK
10 - Observatoire de Paris-Meudon, LERMA UMR CNRS 8112. Meudon, France
11 - Infared Processing and Analysis Center, Caltech, Pasadena, USA
12 - Institut de RadioAstronomie Millimétrique, Grenoble, France
13 - Center for Astrophysics, Cambridge MA, USA
14 - Johns Hopkins University, Baltimore MD, USA
15 - CNRS/INSU, Laboratoire d'Astrophysique de Bordeaux, Floirac, France
16 - California Institute of Technology, Pasadena CA, USA
17 - University of Michigan, Ann Arbor, MI 48109, USA
18 - Astronomical Institute Anton Pannekoek, University of Amsterdam, Amsterdam, The Netherlands
19 - Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands
20 - IGN Observatorio Astronómico Nacional, Alcalá de Henares, Spain
21 - Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
22 - SRON, Institute for Space Research, Groningen, The Netherlands
23 - Max-Planck-Institut für Astronomie, Heidelberg, Germany
24 - Ohio State University, Columbus OH, USA
25 - Physikalisches Institut, Universität zu Köln, Köln, Germany
26 - Leiden Observatory, Leiden University, Leiden, The Netherlands
27 - Kapteyn Astronomical Institute, Groningen, The Netherlands
28 - Institut de RadioAstronomie Millimétrique, Granada, Spain
29 - Department of Astronomy, Stockholm University, Stockholm, Sweden

Received 30 March 2010 / Accepted 5 May 2010

Abstract
We present the first results of the unbiased survey of the L1157-B1 bow shock, obtained with HIFI in the framework of the key program Chemical HErschel Survey of Star forming regions (CHESS). The L1157 outflow is driven by a low-mass Class 0 protostar and is considered the prototype of the so-called chemically active outflows. The bright blue-shifted bow shock B1 is the ideal laboratory for studying the link between the hot ($\sim$1000-2000 K) component traced by H2 IR-emission and the cold ($\sim$10-20 K) swept-up material. The main aim is to trace the warm gas chemically enriched by the passage of a shock and to infer the excitation conditions in L1157-B1. A total of 27 lines are identified in the 555-636 GHz region, down to an average 3$\sigma$level of 30 mK. The emission is dominated by CO(5-4) and H2O(1$_{\rm 10}$-1$_{\rm01}$) transitions, as discussed by Lefloch et al. in this volume. Here we report on the identification of lines from NH3, H2CO, CH3OH, CS, HCN, and HCO+. The comparison between the profiles produced by molecules released from dust mantles (NH3, H2CO, CH3OH) and that of H2O is consistent with a scenario in which water is also formed in the gas-phase in high-temperature regions where sputtering or grain-grain collisions are not efficient. The high excitation range of the observed tracers allows us to infer, for the first time for these species, the existence of a warm ($\ge$200 K) gas component coexisting in the B1 bow structure with the cold and hot gas detected from ground.

Key words: ISM: individual objects: L1157 - ISM: molecules - stars: formation

1 Introduction

A newborn protostar generates a fast and well collimated jet, possibly surrounded by a wider angle wind. In turn, the ejected material drives (bow-)shocks travelling through the surrounding high-density medium and traced by H2 ro-vibrational lines at excitation temperatures of around 2000 K. As a consequence, slower and cold (10-20 K) molecular outflows are formed by swept-up material, usually traced by CO. Shocks heat the gas and trigger several processes such as endothermic chemical reactions and ice grain mantle sublimation or sputtering. Several molecular species undergo significant enhancements in their abundances (see e.g., van Dishoeck & Blake 1998), as observed by observations at millimeter wavelengths towards a number of outflows (Garay et al. 1998; Bachiller & Pérez Gutiérrez 1997, BP97 hereafter; Jørgensen et al. 2007). The link between the gas components at $\sim$10 K and the hot 2000 K shocked component is crucial to understanding how the protostellar wind transfers momentum and energy back to the ambient medium. In this context, the understanding of the chemical composition of a typical molecular bow-shock is essential bevause it represents a very powerful diagnostic tool for probing its physical conditions.

The L1157 outflow, located at a distance estimated to be between 250 pc (Looney et al. 2007) and 440 pc (Viotti 1969) may be regarded as the ideal laboratory for observing the effects of shocks on the gas chemistry, being the archetype of the so-called chemically rich outflows (Bachiller et al. 2001). The low-luminosity (4-11 $L_{\rm\hbox{$\odot$ }}$) Class 0 protostar IRAS20386+6751 drives a precessing powerful molecular outflow associated with several bow shocks seen in CO (Gueth et al. 1996) and in IR H2images (Davis & Eislöffel 1995; Neufeld et al. 2009). In particular, the brightest blue-shifted bow-shock, called B1 (Fig. 1), has been extensively mapped with the PdB and VLA interferometers at mm- and cm-observations revealing a rich and clumpy structure, the clumps being located at the wall of the cavity with an arch-shape (Tafalla & Bachiller 1995; Gueth et al. 1998; Benedettini et al. 2007, hereafter BVC07; Codella et al. 2009). L1157-B1 is well traced by molecules thought to be released by dust mantles such as H2CO, CH3OH, and NH3 as well as typical tracers of high-speed shocks such as SiO (e.g., Gusdorf et al. 2008). Temperatures $\simeq$60-200 K (from NH3, CH3CN, and SiO) as well as around 1000 K (from H2) have been derived (Tafalla & Bachiller 1995; Codella et al. 2009; Nisini et al. 2007, in prep.). However, a detailed study of the excitation conditions of the B1 structure has yet to be completed because of the limited range of excitation covered by the observations performed so far at cm- and mm-wavelengths. Observations of sub-mm lines with high excitation ($\ge$50-100 K above the ground state) are thus required.

As part of the Herschel key program CHESS[*] (Chemical HErschel Surveys of Star forming regions), L1157-B1 is currently being investigated with an unbiased spectral survey using the HIFI instrument (de Graauw et al. 2010). In this Letter, we report the first results based on HIFI observations in the 555-636 GHz spectral window, confirming the chemical richness and revealing different molecular components at different excitation conditions coexisting in the B1 bow structure.

2 Observations

\begin{figure} \par\includegraphics[angle=-90,width=5cm,clip]{14582fg1.ps}\vspace{-1mm} \vspace*{-3mm} \end{figure} Figure 1:

The B1 clump. PdBI emission of CH3OH(2$_{\rm 1}$-1$_{\rm 1}$)A- (grey) on the CS(2-1) one (contours), from BVC07. The maps are centred on the coordinates used for the present HIFI observations $\alpha _{\rm J2000}$ = 20$^{\rm h}$39$^{\rm m}$10 $\hbox{$.\!\!^{\rm s}$ }$2, $\delta_{\rm J2000} = +68\hbox{$^\circ$ }01\hbox{$^\prime$ }10\hbox{$.\!\!^{\prime\prime}$ }5$, i.e. at $\Delta\alpha = +25\hbox{$.\!\!^{\prime\prime}$ }6$ and $\Delta\delta = -63\hbox{$.\!\!^{\prime\prime}$ }5$from the driving protostar. The labels indicate the main B1 clumps detected in different tracers. Circles are for the HPBWs of the HIFI data presented here (39 $\hbox {$^{\prime \prime }$ }$) and of Band 7 (11 $\hbox {$^{\prime \prime }$ }$), i.e., at the highest frequencies of the CHESS surveys.

Open with DEXTER

\begin{figure} \par\includegraphics[width=12cm,clip]{14582fg2New.eps} % \end{figure} Figure 2:

Molecular line profiles observed towards L1157-B1: species and transitions are reported in the panels. The vertical solid line indicates the ambient LSR velocity (+2.6 km s-1 from C18O emission; BP97), while the dashed one is for the secondary peak at -4.0 km s-1.

Open with DEXTER

The observations were performed on 2009, August 1, during the Performance Verification phase of the HIFI heterodyne instrument (de Graauw et al. 2010) on board of the Herschel Space Observatory (Pilbratt et al. 2010). The band called 1b (555.4-636.2 GHz) was covered in double-sideband (DSB) with a total integration time of 140 min. The wide band spectrometer was used with a frequency resolution of 1 MHz. The typical HPBW is 39 $\hbox {$^{\prime \prime }$ }$. The data were processed with the ESA-supported package HIPE[*] (Herschel interactive processing environment) for baseline subtraction and sideband deconvolution and then analysed with the GILDAS[*] software. All the spectra (here in units of antenna $T_{\rm a}$) were smoothed to a velocity resolution of 1 km s-1, except those showing the weakest emission, which were smoothed to lower spectral resolutions (up to 4 km s-1). At a velocity resolution of 1 km s-1, the rms noise is 6-13 mK ($T_{\rm a}$ scale), depending on the line frequency. The main-beam efficiency ( $\eta_{\rm mb}$) has not yet been reliably determined. When needed, we adopted an average $\eta_{\rm mb}$ of 0.72.

3 Different tracers at different velocities

A total of 27 emission lines were detected, with a wide range of upper level energies, from a few tens to a few hundreds of Kelvin. Table 1 lists the spectroscopic and observational parameters of all the transitions. For the first time, high excitation (up to $\simeq$200 K) emission lines related to species whose abundance is largely enhanced in shocked regions were detected. The CO(5-4) and H2O(1$_{\rm 10}$-1$_{\rm01}$) lines are analysed in Lefloch et al. (2010). Figure 2 presents representative examples of line profiles observed towards L1157-B1. All the spectra contain lines with blue-shifted wings peaking near 0 km s-1, which have a terminal velocity equal to $\sim$-8,-6 km s-1. Previous PdBI observations showed that L1157-B1 is associated with very high velocities (HVs) of as low as $\simeq$-20 km s-1 ( $v_{\rm LSR} = +2.6$ km s-1, BP97). We cannot exclude the lack of detected emission in the HV regime in the present HIFI spectra being caused by their relatively low signal-to-noise (S/N) ratio. The PdBI images indicate that the brightness of the emission lines in the HV regime is indeed weaker than the emission at low velocities by a factor of 5-10. The spectra in Fig. 2 clearly show that this weak emission would lie below the noise. On the other hand, the HV gas is detected in the very bright lines of CO and H2O (Lefloch et al. 2010). We note that the HV emission is mostly confined to within the eastern B1a clump (Fig. 1), within an emitting region of size $\le$10 $\hbox {$^{\prime \prime }$ }$ (Gueth et al. 1998; BVC07), whereas low velocity lines originate in both the bow-structure and the walls of the outflow cavity (e.g., the B0e and B0d in Fig. 1), of typical size 15 $\hbox {$^{\prime \prime }$ }$-18 $\hbox {$^{\prime \prime }$ }$. Therefore, the forthcoming HIFI-CHESS observations at higher frequencies and higher spatial resolution (see the dashed circle in Fig. 1) should allow us to study the HV wings in species other than CO and H2O.

The uniqueness of HIFI lies in its high spectral profile resolution for many high excitation transitions of a large number of molecular species. The analysis of the present HIFI spectra reveals a secondary peak occuring between -3.0 and -4.0 km s-1 (here defined medium velocity, MV) and well outlined by e.g., HCN(7-6). The MV peak is also visible in NH3(10-00) and in some lines of CH3OH and H2CO (see Fig. 3), but its occurrence does not show any clear trend with the choice of tracer of line excitation. No single-dish spectra had previously detected this spectral feature (BP97; Bachiller et al. 2001). An inspection of the spectra observed at PdBI shows that the MV secondary peak is observed in a couple of lines of the CH3OH(2$_{\rm K}$-1$_{\rm K}$) series (see Fig. 3 of BVC07) and only towards the western B1b clump (size $\sim$5 $\hbox {$^{\prime \prime }$ }$). This finding implies that there is a velocity component originating mainly in the western side of B1, while the HV gas is emitted from the eastern one (see above).

\begin{figure} \par\includegraphics[angle=-90,width=7.3cm,clip]{14582fg3.ps}\vspace{-5mm} \end{figure} Figure 3:

Top and middle panels: Comparison between the profiles of NH3(10-00), multiplied by a factor 7.4, H2CO(8$_{\rm 17}$-7$_{\rm 16}$), multipled by a factor 22.5, HCN(7-6), multipled by a factor 9.0, and H2O( $1_{\rm 10}{-}1_{\rm01}$), the latter from Lefloch et al. (2010). The vertical solid line indicates the ambient LSR velocity (+2.6 km s-1). The velocity ranges arbitrarily defined as HV (-20,-6 km s-1; traced by H2O), MV (-6, -1.5 km s-1; outlined by the HCN and H2CO secondary peak), and LV (-1.5,+2.6 km s-1; the rest of the blue wing) are drawn (see text). Bottom panel: Intensity NH3/H2O line ratio as a function of velocity.

Open with DEXTER

\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{14582fg4.ps}\vspace{-1mm} \vspace{-3mm} \end{figure} Figure 4:

Rotation diagrams for the CH3OH transitions measured with HIFI (triangles) and from ground (PdBI; squares). Black and blue points are for A- and E-form, respectively. The parameters $N_{\rm u}$, $g_{\rm u}$, and $E_{\rm u}$ are, respectively, the column density, the degeneracy and the energy (with respect to the ground state of each symmetry) of the upper level. The derived values of the rotational temperature are reported: (i) 106 K, for the HIFI lines covering the $E_{\rm u}$ = 32-211 K excitation range and (ii) 12 K (as Bachiller et al. 1995), for the PdBI lines, at lower excitation.

Open with DEXTER

Figure 3 compares the profiles of the NH3(10-00) and H2CO(8$_{\rm 17}$-7$_{\rm 16}$) lines with the H2O(1$_{\rm 10}$-1$_{\rm01}$) profile, where the S/N allows such an analysis (MV and LV ranges). By assuming that the emission in the MV range is optically thin (including the H2O line) and originates in the same region, we obtained from the comparison of their profiles a straightforward estimate of the relative abundance ratios of the gas at different velocities. As a notable example, the NH3/H2O intensity ratio decreases by a factor $\sim$5 moving towards higher velocities (Fig. 3), implying that a similar decrease in the abundance ratios occurs. This may reflect different pre-shock ice compositions in the gas emitting the MV emission. Alternatively, this behavior is consistent with NH3 being released by grain mantles, but water both being released by grain mantles and, in addition, copiously forming in the warm shocked gas from endothermic reactions, which convert all gaseous atomic oxygen into water (Kaufman & Neufeld 1997; Jiménez-Serra et al. 2008, and references therein). The water abundance may be enhanced with respect to ammonia in the fast and warm ($\geq$220 K) gas, which might explain why the H2O wings are larger than those of NH3, CH3OH, and H2CO, all species being directly evaporated from dust grain mantles.

4 Physical properties along the B1 bow shock

We detected several lines from CH3OH (17 lines with upper level energies up to 211 K). We can derive a first estimate of the emitting gas temperature by means of the standard analysis of the rotational diagram. We show the case of methanol (A- and E-forms) in Fig. 4. The derived rotational temperature ( $T_{\rm rot}$) is 106 K (with an uncertainty of $\sim$20 K), which represents a lower limit to the kinetic temperature ( $T_{\rm kin}$). In the same figure, we report the methanol lines (2$_{\rm K}$-1$_{\rm K}$) observed with PdBI and whose intensity is integrated in the HIFI 39 $\hbox {$^{\prime \prime }$ }$ beam. The $T_{\rm rot}$ derived from the ground-based data (based only on lines with $E_{\rm u}$ $\le$ 50 K; BVC07) is definitely lower, $\sim$12 K, in perfect agreement with that found with the 30-m spectra in the same excitation range by Bachiller et al. (1995). As discussed by Goldsmith & Langer (1999), this behavior may be caused by either two components at different temperatures or both non-LTE effects and line opacity. These two possibilities cannot be distinguished based only on the rotational diagram. However, given that a range of $T_{\rm kin}$ and $n_{\rm H_2}$ is naturally expected in a shock, if we were to assume that two gas components provide an explanation, they would not only have different temperatures but also a different column densities. Taking the filling factor ${\it ff} = 0.13$, derived by the CH3OH maps obtained at the PdBI, the low temperature component column density is $8 \times 10^{14}$ cm-2 (in agreement with Bachiller et al. 1995), whereas the high temperature component has a column density of around 1014 cm-2. We note that the rotation diagrams obtained for the MV and LV CH3OH emission separately do not allow us to infer any clear difference.

It is possible to more tightly constrain the emitting gas temperature and $n_{\rm H_2}$ density for the species where the collisional rate coefficients are known, by performing of a non-LTE analysis. To this end, we used the non-LTE excitation code RADEX with an escape probability formalism for the radiative transfer (Van der Tak et al. 2007) coupled with the LAMDA database (Schöier et al. 2005). Methanol is the species detected in the largest number of lines. The full non-LTE study will be reported in a forthcoming paper. Here we analysed only the E-form, for which the collisional rate coefficients are available (Pottage et al. 2004). The major result of this analysis is that for a range of densities of 103-107 cm-3, the gas temperature exceeds 200 K. A similar result is obtained by considering H2CO emission.

Finally, by combining the HIFI CS(12-11) line with CS(2-1) and (3-2) lines observed with ground-based telescopes, we also derive a kinetic temperature that is definitely above 300 K for the outflowing gas. In this case, caution should be taken since we are abl eto trace different gas components, as suggested by CH3OH, the gas at higher excitation being traced by CS(12-11). If we analyse only the (2-1)/(3-2) intensity ratio, the non-LTE approach does not allow us to constrain the temperature in this way, but we are able to infer $n_{\rm H_2}$ of around $4 \times 10^4$ cm-3. Interestingly, when we check for a possible dependence of $n_{\rm H_2}$ on velocity, the LV range is found to be indicative of a denser medium ( ${\sim}10^5$ cm-3) by an order of magnitude with respect to the MV gas.

5 Conclusions

We have presented the HIFI unbiased spectral survey in the 555-636 GHz band towards the bright bow-shock B1 of the L1157 protostellar outflow. For the first time, we have detected high-excitation (up to $\simeq$200 K) emission lines of species whose abundance is largely enhanced in shocked regions (e.g., H2O, NH3, H2CO, CH3OH). This has allowed us to trace with these species the existence of a high excitation component with $T_{\rm kin}$$\ge$200-300 K. Temperature components from $\sim$300 K to $\sim$1400 K have been inferred from the analysis of the H2 pure rotational lines (Nisini et al., in prep.). Therefore the present observations provide a link between the gas at $T_{\rm kin}$ 60-200 K previously observed from the ground and the warmer gas probed by the H2 lines. We plan to perform additional HIFI observations in the THz region towards L1157-B1 to observe more species and transitions, thus to be able to derive reliable abundances and study of the different gas components associated with the bow structure.

Acknowledgements
HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France and the US. Consortium members are: Canada: CSA, U.Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiología (CSIC-INTA). Sweden: Chalmers University of Technology - MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University - Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. We thank many funding agencies for financial support.

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Online Material

Table 1:   List of molecular species and transitions observed with HIFI (Band 1b).

Footnotes

... complexity[*]
Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA.
...[*]
Table 1 is only available in electronic form at http://www.aanda.org
... CHESS[*]
http://www-laog.obs.ujf-grenoble.fr/heberges/chess/
... HIPE[*]
HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS and SPIRE consortia.
... GILDAS[*]
http://www.iram.fr/IRAMFR/GILDAS

All Tables

Table 1:   List of molecular species and transitions observed with HIFI (Band 1b).

All Figures

  \begin{figure} \par\includegraphics[angle=-90,width=5cm,clip]{14582fg1.ps}\vspace{-1mm} \vspace*{-3mm} \end{figure} Figure 1:

The B1 clump. PdBI emission of CH3OH(2$_{\rm 1}$-1$_{\rm 1}$)A- (grey) on the CS(2-1) one (contours), from BVC07. The maps are centred on the coordinates used for the present HIFI observations $\alpha _{\rm J2000}$ = 20$^{\rm h}$39$^{\rm m}$10 $\hbox{$.\!\!^{\rm s}$ }$2, $\delta_{\rm J2000} = +68\hbox{$^\circ$ }01\hbox{$^\prime$ }10\hbox{$.\!\!^{\prime\prime}$ }5$, i.e. at $\Delta\alpha = +25\hbox{$.\!\!^{\prime\prime}$ }6$ and $\Delta\delta = -63\hbox{$.\!\!^{\prime\prime}$ }5$from the driving protostar. The labels indicate the main B1 clumps detected in different tracers. Circles are for the HPBWs of the HIFI data presented here (39 $\hbox {$^{\prime \prime }$ }$) and of Band 7 (11 $\hbox {$^{\prime \prime }$ }$), i.e., at the highest frequencies of the CHESS surveys.

Open with DEXTER
In the text

  \begin{figure} \par\includegraphics[width=12cm,clip]{14582fg2New.eps} % \end{figure} Figure 2:

Molecular line profiles observed towards L1157-B1: species and transitions are reported in the panels. The vertical solid line indicates the ambient LSR velocity (+2.6 km s-1 from C18O emission; BP97), while the dashed one is for the secondary peak at -4.0 km s-1.

Open with DEXTER
In the text

  \begin{figure} \par\includegraphics[angle=-90,width=7.3cm,clip]{14582fg3.ps}\vspace{-5mm} \end{figure} Figure 3:

Top and middle panels: Comparison between the profiles of NH3(10-00), multiplied by a factor 7.4, H2CO(8$_{\rm 17}$-7$_{\rm 16}$), multipled by a factor 22.5, HCN(7-6), multipled by a factor 9.0, and H2O( $1_{\rm 10}{-}1_{\rm01}$), the latter from Lefloch et al. (2010). The vertical solid line indicates the ambient LSR velocity (+2.6 km s-1). The velocity ranges arbitrarily defined as HV (-20,-6 km s-1; traced by H2O), MV (-6, -1.5 km s-1; outlined by the HCN and H2CO secondary peak), and LV (-1.5,+2.6 km s-1; the rest of the blue wing) are drawn (see text). Bottom panel: Intensity NH3/H2O line ratio as a function of velocity.

Open with DEXTER
In the text

  \begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{14582fg4.ps}\vspace{-1mm} \vspace{-3mm} \end{figure} Figure 4:

Rotation diagrams for the CH3OH transitions measured with HIFI (triangles) and from ground (PdBI; squares). Black and blue points are for A- and E-form, respectively. The parameters $N_{\rm u}$, $g_{\rm u}$, and $E_{\rm u}$ are, respectively, the column density, the degeneracy and the energy (with respect to the ground state of each symmetry) of the upper level. The derived values of the rotational temperature are reported: (i) 106 K, for the HIFI lines covering the $E_{\rm u}$ = 32-211 K excitation range and (ii) 12 K (as Bachiller et al. 1995), for the PdBI lines, at lower excitation.

Open with DEXTER
In the text

Copyright ESO 2010

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