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Asunción Fuente, Ricardo Rizzo, Roberto Neri, Paola Caselli, Rafael Bachiller

Chemical evolution of the envelopes of intermediate-mass young stellar objects (YSOs): NGC 7129-FIRS 2 and LkH a 234. Asunción Fuente, Ricardo Rizzo, Roberto Neri, Paola Caselli, Rafael Bachiller. Standard model of star formation. 1. Formation of pre-stellar clumps in molecular clouds.

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Asunción Fuente, Ricardo Rizzo, Roberto Neri, Paola Caselli, Rafael Bachiller

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  1. Chemical evolution of the envelopes of intermediate-mass young stellar objects (YSOs): NGC 7129-FIRS 2 and LkHa 234 Asunción Fuente, Ricardo Rizzo, Roberto Neri, Paola Caselli, Rafael Bachiller “The Dusty and Molecular Universe” ----- October 2004

  2. Standard model of star formation 1. Formation of pre-stellar clumps in molecular clouds. 2. The pre-stellar clump collapses 4. Formation of a planetary system 3. Protostar (infall and outflow coexists) Fig. from McCaughrean

  3. Chemistry as a clock for YSOs H13CO+ CH3CN H2CO 13CO CH3OH C2H3CN C18O N2H+ C17O HCOOH NH3 C2H5CN SiO SO CN HCN CH3OH

  4. Some problems In addition to the evolutionary stage of the protostar, chemical changes also depend on the final stellar mass. Thus, the chemical composition of the hot core is dependent on the kinetic temperature of the gas (see e.g. Rodgers & Charnley 2003). High mass star creates a PDR or HII region around them. Chemical changes also depend on the initial chemical conditions of the molecular cloud, i.e., the chemical composition of the gas and icy mantles(see e.g. Maret et al. 2004, Wakelam et al. 2004) Robust chemical diagnostics are required.

  5. NGC 7129-FIRS 2 and LkHa234 LkHa 234 Continuum 1.3mm NGC7129-FIRS 2

  6. Observational Strategy

  7. Physical conditions Two gas components in NGC 7129-FIRS 2 and LkHa234: -Cold component: Dv~1 kms-1, Tk<30 K -Warm component: Dv>3 kms-1, Tk>50 K. The column density of the cold component decreases by an order of magnitude between NGC 7129-FIRS 2 and LkHa234, while the mean kinetic temperature increases from 13 K to 28 K.

  8. Chemical evolution Cold envelope: Outflow: Warm envelope: PDR:

  9. Chemical clocks Complex behavior These abundance ratios are averaged values in the protostellar envelopes. Thus, they do not correspond to values of the molecular abundances any part of the envelope. In general, they reveal the relative importance of the different envelope components.

  10. Interferometric observations (PdBI) in NGC 7129-FIRS 2 Single-dish observations provide information on the physical and chemical of the cold protostellar envelope. Interferometric observations are required to study the physical and chemical structure of the warm inner protostellar envelope.

  11. Continuum observations (PdBI) Elliptical Gaussian RA=21:43:01.7 Dec=66:03:23.7 Major=0.72(0.01) arcseconds Minor=0.52(0.01) arcseconds Flux= 0.43 Jy Point source RA=21:43:01.7 Dec=66:03:23.7 Flux=0.13 Jy

  12. Molecular line observations (PdBI) Hot core Undetected

  13. A chemistry rich in complex molecules(I)

  14. A chemistry rich in complex molecules(II)

  15. CH3CN observations (PdBI) Hot core component Cold envelope component Size = 800 AU x 600 AU Mass= 2 Mo X(CH3CN) = 2.3 10-8 Size ~ 0.2 pc Mass~ 16 Mo X(CH3CN) = 1.4 10-11 Our interferometric observartions unambiguously show the existence of a hot core in the IM protostar NGC 7129-FIRS 2. The chemistry of the hot core is enriched in complex oxygenated compounds (CH3OH, HCOOH, CH3OCHO-A and CH3OCHO-E), nitrogen-bearing molecules (CH3CN,C2H5CN,HOONO2?), sulphur-bearing species (S18O,OCS,13CS,H213CS?), and deuterated molecules (D2CO,c-C3D,c-C3HD).

  16. Conclusions So far, two hot cores have been detected in low mass stars (IRAS 16293-2422: Cazaux et al. 2003; NGC 1333-FIRS 4A. Bottinelli et al. 2004) with sizes ~150 AU. NGC 7129-FIRS 2 is the first hot core detected in an intermediate mass YSOs with a size ~600 AU. The size and chemical complexity detected in NGC 7129-FIRS 2 suggest that this is an intermediate object between the low-mass stars and high-mass hot cores. There are morphological and kinematic evidences of an internal structure of the hot core. But the high angular resoludion provided by ALMA is required to study it.

  17. The HIFI intermediate-mass team Asunción FUENTE, Observatorio Astronómico Nacional (Spain) Cecilia CECCARELLI, Observatoire de Grenoble (France) Paola CASELLI, Osservatorio Astrofisico di Arcetri (Italy) Doug JOHNSTONE, NRC (Canada) Ewine VAN DISHOECK, Leiden Observatory (Netherlands) René PLUME, University of Calgary (Canada) Bertrand LEFLOCH, Observatoire de Grenoble (France) Friedrich WYROWSKI, MPIfR (Germany) Mario TAFALLA, Observatorio Astronómico Nacional (Spain) Brunela NISINI, Italy Main goals: • Preparatory observations for the HIFI core programme (SCUBA, JCMT, IRAM, Effelsberg) • Preparatory observations for ALMA (PdBI)

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