PEERING INTO THE PROTOSTELLAR SHOCK L1157-b1

PEERING INTO THE PROTOSTELLAR SHOCK

L1157-B1

M. Benedettini, A. Lorenzani, B. Nisini, M. Vasta (Italy)S. Cabrit, E. Caux, C. Ceccarelli, P. Hily-Blant, B. Lefloch, L. Pagani, S. Pacheco, M. Salez (France) F. Gueth, K. Schuster (IRAM), J. Cernicharo (Spain)A. Boogert, G. Melnick, D. Neufeld (USA)P. Caselli, S. Viti (UK), B. Parise (Germany)

C. Codella (OAA, Firenze, Italy)

on behalf of the CHESS team

Outline

1. The CHESS Herschel KP2. The L1157-B1 outflow shock region 3. L1157-B1: what we learned from ground4. L1157-B1: the Herschel lesson

ULTIMATE GOAL: chemical surveys during the early phases of low-, intermediate-, and high-mass star formation;

IMMEDIATE GOAL: to guide successive Herschel observations and provide a legacy database for the general community;

METHOD: HIFI (and PACS) spectral surveys in representative SFRs;

TARGETS: from low- to high-mass protostars, from pre- to post-collapse, from the source to the surroundings;

OUTFLOWS: to study the effects of shocks on the cloud hosting the protostar. Shocks trigger endothermic chemical reactions, ice grain

mantle sublimation or sputtering.

The CHESS KP in a nutshell(PI: C. Ceccarelli, LAOG, France)

The L1157-mm chemical active outflow

Spitzer 8 μm: grey CO: contours

Bachiller et al. (2001), Looney et al. (2007), Neufeld et al. (2009)

Distance: 250 pc (440 pc);Driven source: Class 0 protostar (IRAS20386+6751), L= 4-11 L;Most chemically rich outflow known so far;Ideal laboratory to observe the effects of shocks on the gas chemistry;Precessing molecular outflow associated with several bow shocks seen in CO and in H2.


H2: grey CO: blue and red

Several red- and blue-bow shocks seen in CO and in H2;

The brightest blue-shifted bow-shock has been mapped with the PdB and VLA arrays 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. 1996, 1998, Benedettini et al. 2007, Codella et al. 2009);

Well traced by molecules released by dust mantles such as H2CO, CH3OH, and NH3 as well as typical tracers of high-speed shocks such as SiO.

B1

B2

B0

R

R0

R2

Several red- and blue-bow shocks seen in CO and in H2;

The brightest blue-shifted bow-shock has been mapped with the PdB and VLA arrays 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. 1996, 1998, Benedettini et al. 2007, Codella et al. 2009);

Well traced by molecules released by dust mantles such as H2CO, CH3OH, and NH3 as well as typical tracers of high-speed shocks such as SiO.


B1

B2

B0

R

R0

R2

STAR B1

SiO(3-2)

CH3OH(3k-2k)


Different gas components:Slow and cold (10-20 K) swept-up material (low-J CO lines);Hot gas (2000 K) usually traced by H2.

The link between cold and hot components (i.e. the warm component) is crucial to understand how the protostellar wind transfers energy back to the ambient medium.

So far, temperatures between 60-200 K has been measured using NH3, CH3CN, and SiO (Tafalla & Bachiller 1995, Nisini et al. 2007, Codella et al. 2009).

However, a detailed study of the excitation conditions of the B1 structure is still missing due to the limited range of excitation covered by the cm- and mm-observations performed so far. Observations of lines with high excitation (Eu > 50-100 K) are required.

First results: the unbiased spectral survey of HIFI-Band 1b (555-636 GHz)

First results: the unbiased spectral survey of HIFI-Band 1b (555-636 GHz)

A total of 27 lines are identified in Band 1b, down to

an average 3-sigma level of 30 mK (Ta scale) . Besides CO and H2O (Lefloch et

al. 2010) we identify lines from NH3, H2CO, CH3OH, CS, HCN, and HCO+

(Codella et al. 2010)

Origin of the Molecular EmissionBright broad emission in CO and H2O up to v ≈ - 30 km/s (Vsys = +2.6 km/s)

Two Velocity Components in CO : HVC : v < -7 km/sLVC : v > -7 km/s

HVC !

LVC

CO(6-5) @ CSO (12”) CO(6-5) averaged over 40”

Lefloch et al. (2010)

The Low- and High-Velocity Components:filling factors

LVC: Extended: From CO(6-5)@CSO and , SiO(2-1)@PdBI we infer ff 1/3

Gueth et al. (1998), Lefloch et al. (2010), Nisini et al. (2010)

SiO HVC SiO LVC

HVC: Compact: SiO(2-1)/H2O intensity ratio is constant for v < -7 km/s; both emissions arise from the same region : ff ≈ 0.03

Physical Conditions in the CO Gas

Derived from LVG analysis of CO 5-4 using complementary CO 3-2, 6-5 line (CSO observations), and assuming ff= 0.03 (HVC) and 0.3 (LVC).

LVCT < 100 Kn(H2)= (1-3)x105 cm-3

N(CO)= 8x1016 cm-2

Consistent with: LVC: warm, dense gas; HVC: warmer, less dense gas

HVC T= > 300 Kn(H2)= (1-3) x 104 cm-3 N(CO)= 5x1016 cm-2


Water Emission in L1157-B1

LVG analysis (slab geometry) of each component assuming the same physical conditions (T, n, ff) as for CO.

If we assume OPR=3, T(LVC)=100 K, and T(HVC)=400 K (from CO):

LVC: X(H2O) < 10-6 HVC: X(H2O) < 10-4

Higher H2O abundance in the HVC: high-T reactions favored and more efficient removal from grain mantles. In this model, the bulk of the PACS-WISH 179 µm line arises from the (unresolved) HVC


Preliminary analysis in agreement with steady-state C-shock models for HVC: Vshock 15-20 km/s in pre-shock gas n(H2)= 5 x 104 cm-3 (Gusdorf et al. 2008)

Different tracers at different velocities

Codella et al. (2010)

All the spectra (but CO and H2O) show blue-shifted wings peaking near 0 km/s, and with a terminal velocity equal to -8,-6 km/s.

Lack of HV possibly due to S/N (PdBI spectra: HV emission weaker than the peak emission by a factor 5-10). HV emission is more diluted: HIFI data at higher frequencies will be instructive.

A secondary peak occurs between -3.0 and -4.0 km/s (here defined medium velocity, MV) and well outlined by e.g. HCN(7-6). The MV peak is visible also in NH3 and in some lines of CH3OH and H2CO.

PdBI spectra show that the MV secondary peak is observed in a couple of lines of CH3OH at 3mm and only towards the western B1b clump. This finding suggests the existence of a velocity component mainly coming from the western side of B1, while the HV gas is emitted from the eastern one.



NH3/H2O vs. Velocity:It could reflect different pre-shock ice

compositions in the MV gas.Alternatively, this behavior is consistent

with the SPECULATION thatNH3 is released by grain mantles, whereas water is released by grain mantles and, in addition, copiously formed in the warm

shocked gas byendothermic reactions, which convert all

gaseous atomic oxygen into water.Codella et al. (2010)

Gas-grain shock model(Viti et al. 2004; Jiménez-Serra et al. 2008)

- Gas grain chemical model + C-shock model + pre-existing clump at 105 cm-3;- Clear difference in the trend of the water abundance w.r.t to other species;

- All species are enhanced by mantle sputtering; - During the shock period water and, to a lesser extent, ammonia are also enhanced but

water is the only species that is maintained high even after the shock has passed.

Viti et al. (2010) Log(age/yr)

H2O

H2CO

NH3

CH3OH

Different gas components….

In agreement with the old 30-m results

Two components at different temperatures or non-LTE effects and line opacity?

The present observations provide a link between the gas at Tkin 60--200 K (NH3, CH3CN, SiO) previously observed from ground and the warmer gas

probed by the H2 lines.




Two components at different temperatures or non-LTE effects and line opacity?

The present observations provide a link between the gas at Tkin 60--200 K (NH3, CH3CN, SiO) previously observed from ground and the warmer gas

probed by the H2 lines.

Codella et al. (2010)Flower et al. (2010)

Fit of H2 mid- and NIR-data using a temperature stratification model (from 300 to 4000 K)

H2 S(1) 17 m

L1157-mm

dN T-

B1 position

Nisini et al. (2010)


What about other outflows?


REDTrot = 14 K

BLUETrot = 13 KNGC1333-IRAS 2

(Bachiller et al. (1998)

Physical properties along the B1 bow shock

LVG: CS(12-11), HIFI, and CS(2-1), (3--2), PdBI: we derive a kinetic temperature definitely above 300 K.

Caution: we could trace differentgas components, as suggested by methanol, the gas at higher excitation

being traced by CS(12-11). Densities around 104 cm-3.LV gas denser than the MV one?


PACS-CHESS spectral survey (55-210 m) of L1157-B1

Preliminary PACS results:

AT LEAST: CO lines: from J = 14-13 to 22-21

7 H2O lines, OI @ 63 m, OH @ 119 m

Excitation vs. position & Filling Factor

OI 63 m o-H2O

o-H2O

o-H218O

p-H2OCO(14-13)o-H2OCO(15-14)

PACS

In addition: other HIFI-CHESS spectra so far observed:

CO: from 6-5 to 10-9, 14-13, 16-15 + 13CO: 8-7 H2O: 111-000, 312-303, 312-221, 212-101, 221-212

HCl: 1-0 + C+ @ 157 μm

PEERING INTO A PROTOSTELLAR SHOCK: CONCLUSIONS

The molecular emission arises from 2 physically distinct regions:

LVC : warm, extended, chemically rich dense gas, with internal structure revealed from specific tracers : high-velocities from

the eastern side, high-densities on the western side.

HVC : hot, compact, lower density gas.

Less dense medium towards B1b (MV peak)?

H2O abundance increases by 2 orders of magnitude between LVC and HVC.

SiO HVC SiO LVC

Codella et al. (2009, 2010)

132 K

55 K

92 K

67 K

73 K

Origin of the Molecular Emission



Bachiller et al. (2001)

H2O localized on the CO peaks of the precessing jet

Correlation between H2O and H2 warm gas at T ~ 300 K

H2O follows SiO --> tracer of high density shocks with V > ~ 20 km/s

H2 17µm Neufeld et al. (2009), H2O 179 µm Nisini et al. (2010)CO(2-1), SiO(3-2) Bachiller et al. (2001)

PACS-WISH KP map of 179 µm line in L1157

SiO(2-1) @ PdBI Gueth et al. (1998)

PACS map of 179 µm line in L1157

L1157 mm

Spitzer IRAC Herschel PACS

H2O

179 m

104 AU

Strong water emission from the embedded protostar

Emission peaks trace the shock interaction regions

PACS observations:

9.4”/pixel, 6’x2’ raster map

R(179 µm) ~ 1500

H2: grey CO: blue and red

The Low-Velocity Component

Extended: From CO(6-5)@CSO and , SiO(2-1)@PdBI we infer ff 1/3

Gueth et al. (1998), Lefloch et al. (2010)

SiO HVC SiO LVC

The High-Velocity Component

SiO(2-1)/H2O intensity ratio is constant for v < -7 km/s Both emissions arise from the same region : ff ≈ 0.03 (4” x 12”, PdBI) Emission is optically thick

SiO HVC SiO LVC

Gueth et al. (1996, 1998), Lefloch et al. (2010)


LVG analysis (slab geometry) of each component assuming the same physical conditions (T, n, ff) as for CO and taking into account the total 179 µm line flux (PACS-WISH, Nisini et al. 2010).


LVC: N(H2O)= (4.0-5.0) x 1014 cm-2 X= (0.7-0.8) x 10-6

HVC: N(H2O)= (2.5-3.0) x 1016 cm-2 X= (0.6-0.8) x 10-4

Higher H2O abundance in the HVC: high-T reactions favored and more efficient removal from grain mantles.

In this model, the bulk of the 179 µm line arises from the (unresolved) HVC



LVG analysis (slab geometry) of each component assuming the same physical conditions (T, n, ff) as for CO and taking into account the total 179 µm line flux (PACS-WISH, Nisini et al. 2010).


LVC: N(H2O)= (4.0-5.0) x 1014 cm-2 X= (0.7-0.8) x 10-6

HVC: N(H2O)= (2.5-3.0) x 1016 cm-2 X= (0.6-0.8) x 10-4

Higher H2O abundance in the HVC: high-T reactions favored and more efficient removal from grain mantles.

In this model, the bulk of the 179 µm line arises from the (unresolved) HVC


Preliminary analysis in agreement with steady-state C-shock models for HVC: Vshock 15-20 km/s in pre-shock gas n(H2)= 5 x 104 cm-3 (Gusdorf et al. 2008)

Gas-grain shock model(Viti et al. 2004; Jiménez-Serra et al. 2008)

- Gas grain chemical model + C-shock model + pre-existing clump at 105 cm-3;- Clear difference in the trend of the water abundance w.r.t to other species;

- All species are enhanced by mantle sputtering; - During the shock period water and, to a lesser extent, ammonia are also enhanced but

water is the only species that is maintained high even after the shock has passed.

Viti et al. (2010)

N(H2)

Tkin

Log(age/yr)

H2O

H2CO

NH3

CH3OH

Forthcoming analysis:PACS-CHESS spectral survey (55-210 m) of L1157-B1

Preliminary results: AT LEAST: CO lines: from J = 14-13 to

22-217 H2O lines, OI @ 63 m, OH @ 119 m

Excitation vs. position

Filling factors

OI 63 m

o-H2O

o-H2O

o-H218O

p-H2OCO(14-13)o-H2OCO(15-14)

PACS

PACS-CHESS spectral survey (55-210 m) of L1157-B1

Preliminary results: AT LEAST: CO lines: from J = 14-13 to

22-217 H2O lines, OI @ 63 m, OH @ 119 m

Excitation vs. position

Filling factor

OI 63 m

o-H2O

o-H2O

o-H218O

p-H2OCO(14-13)o-H2OCO(15-14)

PACS

Other HIFI-CHESS spectra so far observed:

CO: from 6-5 to 10-9, 14-13, 16-15 13CO: 8-7 H2O: 111-000, 312-303, 312-221, 212-101, 221-212

HCl: 1-0 C+ @ 157 μm

PEERING INTO THE PROTOSTELLAR SHOCK L1157-b1

Documents

Transcript of PEERING INTO THE PROTOSTELLAR SHOCK L1157-b1