“The Dusty and Molecular Universe” ----- October 2004

Chemical evolution of the envelopes of intermediate-mass young stellar objects (YSOs): NGC 7129-FIRS 2 and LkH 234

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

“The Dusty and Molecular Universe” ---- October 2004

Standard model of star formation

1. Formation of pre-stellar clumps in molecular clouds.

2. The pre-stellar clump collapses

3. Protostar (infall and outflow coexists) 4. Formation of a planetary systemFig. from McCaughrean

“The Dusty and Molecular Universe” ---- October 2004

Chemistry as a clock for YSOs

13COC18O

C17O

H13CO+

N2H+

NH3

CH3OH

H2CO

HCOOH

CH3CN

SiO SO

CH3OH

CN HCN

C2H3CN

C2H5CN

“The Dusty and Molecular Universe” ---- October 2004

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.

“The Dusty and Molecular Universe” ---- October 2004

NGC 7129-FIRS 2 and LkH234

Sp. type B5-7

Age 0.1 Myr

Outflow No

LkH 234

NGC7129-FIRS 2Lum 500 Lo

Age >3000 yr

Outflow Yes

Continuum 1.3mm

“The Dusty and Molecular Universe” ---- October 2004

Observational Strategy

“The Dusty and Molecular Universe” ---- October 2004

Physical conditions

Two gas components in NGC 7129-FIRS 2 and LkH234: -Cold component: v~1 kms-1, Tk<30 K-Warm component: v>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 LkH234, while the mean kinetic temperature increases from 13 K to 28 K.

“The Dusty and Molecular Universe” ---- October 2004

Chemical evolution

–Cold envelope:

–Warm envelope:

–Outflow:

–PDR:

“The Dusty and Molecular Universe” ---- October 2004

Chemical clocks

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.

Complexbehavior

“The Dusty and Molecular Universe” ---- October 2004

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.

Continuum 3mm A 1.56x1.2 arcsecContinuum 1mm A 0.63x0.46 arcsecCH3CN 5-4 A 1.56x1.2 arcsecN2D+ 3-2 A 0.63x0.46 arcsecD2CO 404-303 A 0.63x0.46 arcsecCH3OH 5-4 CD 1.51x1.42 arcsec

“The Dusty and Molecular Universe” ---- October 2004

Continuum observations (PdBI)

Elliptical GaussianRA=21:43:01.7Dec=66:03:23.7Major=0.72(0.01) arcsecondsMinor=0.52(0.01) arcsecondsFlux= 0.43 Jy

Point sourceRA=21:43:01.7Dec=66:03:23.7Flux=0.13 Jy

“The Dusty and Molecular Universe” ---- October 2004

Molecular line observations (PdBI)

Undetected

Hot core

“The Dusty and Molecular Universe” ---- October 2004

A chemistry rich in complex molecules(I)

“The Dusty and Molecular Universe” ---- October 2004

A chemistry rich in complex molecules(II)

“The Dusty and Molecular Universe” ---- October 2004

CH3CN observations (PdBI)

Hot core component

Size = 800 AU x 600 AUMass= 2 Mo

X(CH3CN) = 2.3 10-8

Cold envelope component

Size ~ 0.2 pcMass~ 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,H2

13CS?), and deuterated molecules (D2CO,c-C3D,c-C3HD).

“The Dusty and Molecular Universe” ---- October 2004

Conclusions

–NGC 7129-FIRS 2 is the first hot core detected in an intermediate mass YSOs with a size ~600 AU.

–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.

–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.

“The Dusty and Molecular Universe” ---- October 2004

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)