Methyl Formate as a probe of temperature ���and structure of Orion-KL

N. Brouillet (LAB), D. Despois (LAB), A. Baudry (LAB), A. Wootten (NRAO), F. Combes (LERMA), M. Guélin (IRAM) ���

& G. Wlodarczak (PhLAM)

Spectroscopy2011 - Extending the Limits of Astrophysical Spectroscopy���17th of January 2011 (Victoria, British Columbia)

© ESO

Cécile Favre

Århus University - Institut for Fysik og Astronomy (IFA)

An explosive event : ���500 years ago !

Gómez et al. 2008���Rodríguez et al. 2005

Level step : 150 µJy/beam First contour : 300 µJy/beam

The Orion Kleinmann-Low ���nebula

Hot Core

Compact ���Ridge

VLA beam ���0.26’’x0.22”

21.6 km/s

26 km/s

14.6 km/s

ν = 8.46 GHz

  A very rich source of molecules   Provides unique conditions for the study in interstellar chemistry : the release of molecules from grain mantles

Compact ���Ridge

Hot Core

See Laurent Loinard (P34) & Luis Zapata (P67) posters

R. Y. Shuping, UCLA,��� W. M. Keck Observatory.

(’’)���

~ 5000 AU���

U-101470 MHz U-101500 MHz H2CS

CH3CH2CN CH3OCH3

A ���

C���D ���

A ���B���

D ���

A ���B���

D ���

A ���B���

A ���B���

C���D ���

IRc2

The Orion-KL nebula :���a very rich source of molecules

M. Guélin, Nobel Symposium 2006 « Cosmic Chemistry » - A, B, C and D : hot core (or corinos)

O-bearing and N-bearing species tend to peak at different locations

CH3CH2OH D ��� C��� C���

C���

(’’)��� (’’)��� (’’)���

Data sets from the IRAM ���Plateau de Bure Interferometer

Frequency (GHz)

Spatial resolution (’’ x ’’)

Spectral resolution ���(km/s)

101 3.79 x 1.99 1.85

203 2.94 x 1.44 0.92

223 1.79 x 0.79 0.84

225 3.63 x 2.26 0.42

  Methyl formate HCOOCH3 o  An abundant O-bearing molecule toward Orion-KL o  Probe of the temperature and structure of Orion-KL

o  Results obtained with the PdBI at very high angular resolution (1.8’’x0.8’’)

  Other [C2H4O2] isomers o  Acetic acid: NCH3COOH ≤ 1.8x1015 cm-2

o  Glycolaldehyde: NCH2OHCHO ≤ 2.4x1014 cm-2

  Strong emission in the Compact Ridge : an external heating   Two major velocity components along a N-S structure   Methyl formate is probably released from the ice mantle

Methyl Formate HCOOCH3

  On grain surfaces   And/or in gas phase from precursor methanol (CH3OH)

Structure

Methyl Formate formation ? (Garrod & Herbst 2006)

Theoretical spectrum (JPL& Ilyushin et al. 2009)

  64 transitions up to Eu ≤ 650 K 37 in fundamental state vt = 0��� 27 in the first torsionally excited state vt =1

Methyl Formate HCOOCH3 ���A “clumpy” structure

Integrated intensity map obtained with PdBI Synthesized beam 1.79”x0.79” PA:14°

( 223465 MHz, 223500 MHz and 223534 MHz) Level step : 3.2 K.km/s (3σ)

PdBI uv coverage @223 GHz

Compact ���Ridge

Hot Core

Favre et al. 2011 submitted to A&A

The Compact Ridge ���an unusual region ?

The combination of high angular and spectral resolution

yields kinematic ( ALMA !)

Frequency���(GHz)

Beam���(’’X’’)

Spectral resolution ���(GHz) (km.s-1)

203 2.9 X 1.4 0.625 0.92

223 1.8 X 0.8 0.625 0.84

225 3.6 X 2.3 0.3125 0.42

203435.554 MHz (Ix2K) 223465.340 MHz 225855.505 MHz (Ix5K)

Favre et al. 2011 submitted to A&A

The Compact Ridge ��� an unusual region ?

Beam��� (’’x’’)

Trot ���(K)

NHCOOCH3 ���(cm-2)

1.79’’ X 0.79’’ 79±2 1.6x1017

3.6’’ X 2.2’’ 119±10 3.0x1016

1.79’’ X 0.79’’

3.6’’ X 2.2’’

7.6 km/s component

7.6 km/s component

T = 79 K

T = 119 K

An external heating Shocks ?

Favre et al. 2011 submitted to A&A

The Compact Ridge ��� an unusual region ?

An external heating Shocks ?

Beam��� (’’x’’)

Trot ���(K)

NHCOOCH3 ���(cm-2)

1.79’’ X 0.79’’ 112±50 6.8x1016

3.6’’ X 2.2’’ 168±29 1.6x1016

1.79’’ X 0.79’’ 9.3 km/s component

3.6’’ X 2.2’’

9.3 km/s component

T = 112 K

T = 168 K Favre et al. 2011 submitted to A&A

Relation to vibrationally excited H2

A close correlation between the distributions of HCOOCH3 and H2

at several places

Favre et al. 2011 submitted to A&A

Methyl Formate 8.7 km/s channel map ���overlaid over 2.12 μm excited H2 emission (ESO-VLT) Lacombe et al. (2004)

Shocks destroy ice grain mantles

Release of HCOOCH3 (or a precursor) by shocks ?

Velocity structure: ���a North-South component at 9.3 km/s

  Most signal at 8 km/s   No emission at 4-5 km/s ���

(even toward the Hot Core)   North-South Structure :

HCOOCH3 channel maps @223465.340 MHz Synthesized PdBI beam: 1.79”x0.79” PA:14°

Level step : 50 mJy/beam

223.465 GHz 203.435 GHz (Ix2K) 225.855 GHz (Ix1.5K)

Compact Ridge emission peak

T (K

)

Velocity (km/s)

Favre et al. 2011 submitted to A&A

Hot Core Compact���

Ridge

N-S Structure BN

4.52 5.36 6.19

11.22 10.38 9.54

8.71 7.87 7.03   9-10 km/s   two spectral components

  ALMA and molecular observations towards Orion-KL

CH2OHCHO Glycolaldehyde

CH3COOH Acetic Acid

HCOOCH3 Methyl formate

HOCH2-CH2OH Ethylene Glycol

Spectral confusion in Orion-KL: a major problem

Tercero, B. et al. 2010 2 mm molecular survey (IRAM-30m)

  Many lines (almost all peaks are real lines)   Many unidentified   Many with a low intensity

such molecules have relatively low abundances

49% of real detected lines

Detected: 20 Blended : 33 Part. Blended : 2 Not detected : 9 HCOOCH3 Integrated intensity map obtained with PdBI

(223465 MHz, 223500 MHz et 223534MHz) Level step (3σ): 3.2 K.km/s

40% of real detected lines

Detected: 14 Blended : 40 Part. Blended : 3 Not detected : 7

30% of real detected lines

Detected: 8 Blended : 28 Part. Blended : 5 Not detected : 23

Hot Core

Compact Ridge

Spectral Confusion a major problem toward Orion-KL !

ALMA should allow the reduction of spectral confusion …

N = 1.6x1017 cm-2 @79 K

N = 1.6x1017 cm-2 @130 K

N = 4.5x1016 cm-2 @108 K

Line identification / Remove lines blends

IRAM 30m telescope���(11’’)

Frequency (MHz) Beam of 30 m

Ethylene glycol ?

Beam of���PdBI

T

Ethy

lene

gly

col ?

T

Frequency (MHz)

Plateau de Bure���Interferometer ���

(2.52’’ x 1.64’’)

Ethy

lene

gly

col ?

SO2

SO2

Form

amid

e Fo

rmam

ide

PdBI

Importance of spatial resolution

30m

ALMA may reduce���the confusion problem ���

U-li

ne

Importance of spectral resolution

Frequency���(MHz)

Beam���(’’X’’)

Spectral Resolution���(MHz) (km.s-1)

101414 3.8 X 2.0 0.625 1.85

225855 3.6 X 2.3 0.313 0.42

Δv = 3.6 km/s

Δv = 1.1 km/s

ALMA may reduce���the confusion problem

Reveal new molecules

Present PdBI data :���2 GHz of bandwidth in total !

Detection ratio : o  Methyl formate HCOOCH3 : 49%

What ALMA will make easier  Multi-molecule / line studies

  Needed several observing run   Inhomogeneous data

PdBI

ALMA Bandwidth 2 GHz or more in one run

Summary   Orion-KL nebula is a very molecular rich source high line confusion

  HCOOCH3 is a probe of the temperature and structure of Orion-KL o  Temperatures cover the range 80 to 170 K o  28 emission peaks o  Compact Ridge: an external heating o  Two velocity components and a velocity gradient o  MF production involves the release of molecules from ice mantles

  Detection of low abundance molecules is difficult …

  High angular and spectral resolutions of ALMA : lower the spectral confusion limit

  Bandwidth vs spectral resolution multi molecular lines

Thank you for your attention

Compromise between ���resolution / bandwidth

Frequency (GHz)

Beam (’’X’’)

PdBI Spectral Resolution (GHz) (km.s-1)

ALMA Bandwidth 8 GHz

ALMA Bandwidth 125 MHz

101 3.8 X 2.0 0.625 1.85 1.48 km/s 0.02 km/s

225 3.6 X 2.3 0.3125 0.42 0.66 km/s 0.01 km/s

€

0.5km.s−1 × 300ν (GHz)

125 MHz of bandwidth

€

0.008km.s−1 × 300ν (GHz)

8 GHz of bandwidth

Bandwidth 2 GHz : 0.35 km/s @3mm 0.17 km/s @1mm

Methyl Formate HCOOCH3: ���data analysis

  Lines are optically thin��� τ << 0.05 in general   At most 20% of flux is missing   Lines are thermalized��� nH2 ~ 3-7x108 cm-3 >> ncr ~ 102-107 cm-3 ���

Tex = Tkin = Trot

Compact ���Ridge

Hot Core

Source I

HCOOCH3 Integrated intensity map obtained with PdBI Synthesized beam 1.79”x0.79” PA:14°

( 223465 MHz, 223500 MHz and 223534 MHz) Level step : 3.2 K.km/s (3σ)

LTE is reached

Favre et al. 2011 submitted to A&A