1. “The Dusty and Molecular Universe” ----- October 2004
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. Standard model of star formation
We need to find objects at different evolutionary stage to be able to study the star formation process.
Some Problems:
We need a clock for young stellar objects (YSOs).
Different star formation processes for stars with different masses.
The star formation process could depend on the molecular cloud initial conditions.
YSOs at different distances are sampled at different spatial scale.

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

5. Robust chemical diagnostics are required.
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.

6. Sample Selection Why NGC 7129 - FIRS 2 and LkHa234?
Both have similar luminosities (~ 500 Lsun). LkHa 234 is one of the youngest HBe star (Sp. type = B3). NGC FIRS 2 is a Class 0 object.
They are located in the same molecular cloud, minimizing the chemical differences because of different initial chemical conditions.
They are located at a distance of 1250 pc.

7. NGC 7129-FIRS 2 and LkHa234 LkHa 234 NGC7129-FIRS 2 Sp. type B5-7 Age
Continuum 1.3mm
Sp. type
B5-7
Age
0.1 Myr
Outflow No
NGC7129-FIRS 2
Lum
500 Lo
Age
>3000 yr
Outflow
Yes

8. Observational Strategy

9. 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.

10. Single-dish maps
NGC 7129-FIRS 2
LkHa 234

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

12. 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.

13. SiO NGC 7129-FIRS 2 NGC 7129-FIRS 2 LkHa 234 out 2
In NGC 7129-FIRS 2, the SiO emission is detected along the outlows axis. The peak emission is found towards the bullet R1 at a velocity of 7 km s-1.
out 1
In LkHa234, SiO is only detected towards the star position.

14. SiO
There is a correlation between the outflow ages and the SiO abundance, being the SiO abundance largest in the youngest outflow FIRS 2-out 1.
The SiO abundance in LkHa 234 is similar to that found in photodissociation regions (PDRS).

15. H2CO
In NGC 7129-FIRS 2, the H2CO emission arises in the jet (wide component) and the shocked gas of the molecular cloud.

16. CH3OH
NGC FIRS 2
Hot core?
The CH3OH column density is similar in both YSOs. In NGC 7129-FIRS 2 the emission arises in the outflow.Is there a hot core component?

17. CH3CN
A hot component in the CH3CN emission suggests the existence of a hot core in NGC FIRS 2.

18. 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 arcsec
Continuum 1mm
0.63x0.46 arcsec
CH3CN 5-4
N2D+ 3-2
D2CO
CH3OH 5-4 CD
1.51x1.42 arcsec

19. Continuum observations (PdBI)
Intense and compact continuum source
RA(2000)=21:43:01.68
Dec(2000)=66:03:23.62
The same spatial distribution at 3mm and 1mm, with a spectral index a=2.56 consistent with thermal dust emission.

20. 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
Flux=0.13 Jy

21. Molecular line observations (PdBI)
Hot core
Undetected

22. A chemistry rich in complex molecules(I)

23. A chemistry rich in complex molecules(II)

24. CH3CN observations (PdBI)
Hot core component
Cold envelope component
Size = 800 AU x 600 AU
Mass= 2 Mo
X(CH3CN) =
Size ~ 0.2 pc
Mass~ 16 Mo
X(CH3CN) =
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).

25. Conclusions
So far, two hot cores have been detected in low mass stars (IRAS : 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.

26. 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)