1. Methanol emission from low mass protostars
Sébastien Maret
University of Michigan, Department of Astronomy
Cecilia Ceccarelli, Xander Tielens

2. Introduction (1)
The formation of a star is accompanied with large physical and chemical changes
During the prestellar phase the gas is depleted on grain mantles
When the gravitational collapse starts, the protostar warms up the gas and grain mantles evaporate in a hot core region
The released molecules can trigger the formation of more complex molecules by hot gas phase chemistry (Charnley et al. 1992)

3. Introduction (2)
The existence of hot cores in low mass protostars has been established recently (Ceccarelli et al. 2000a,b; Schoier et al ; Maret et al. 2003; Cazaux et al. 2003; Bottinelli et al a,b; Kuan et al. 2004)
Methanol is well suited to study these regions because it is relatively abundant in grain mantles (Pontoppidan et al. 2003, Gibb et al. 2004a)
Measuring the methanol abundance inside hot cores can give constrains on the methanol abundances in grains mantles and therefore on its formation route

4. Observations (1)
Six Class 0 protostars have been observed with the JCMT and the IRAM-30m telescopes

5. Observations (2) Low energy transitions (50 -70 K) trace the outflow
Lines with higher upper energy (up to 250 K) are detected only on the sources
Emission of the envelope separated from the outflow by gaussian fitting

6. Model (1) 1D (spherical) radiative transfer model
Abundances assumed to follow a jump model

7. Model (2) Best fit abundances determined by a 2 analysis
Xout = 3-20 x 10-10
Abundance jumps in four sources ( Xin = 1-7 x 10-7)

8. Methanol formation (1)
Gas phase chemistry models predict abundances that are four order of magnitude lower than the abundances observed here

9. Methanol formation (2)
Relative abundances of CO, H2CO, CH3OH and well reproduced by a grain chemistry model (Keane & Tielens 2005)
Absolute abundances are difficult to reproduce
Adapted from Keane & Tielens (2005)

10. Conclusions
Methanol abundances in cold envelopes are 3-20 x 10-10, a comparable value with the one observed in dark clouds
Jump in the methanol abundance in the inner regions because of grain mantle evaporation
In sources where jumps are detected, abundances are 1-7 x 10-7, i.e. two orders of magnitude higher than dark clouds, but comparable to values observed for massive hot cores
Gas phase models fail to reproduce the observed abundances by orders of magnitude
Comparison with grain chemistry model gives a good agreement between relative abundances, but absolute abundances are difficult to reproduce