comets with ALMA

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Comets with ALMA N. Biver, LESIA, Paris
Observatory
I Comets composition Chemical investigation and
taxonomy Monitoring of comet outgassing II
Mapping of cometary atmospheres 3-D Gas and dust
jets Physical properties of the coma and
extended sources
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• ALMA and the composition of comets
• Observing all types of comets (Kuiper Belt ones),
  new molecules

Biver et al. 2002, E.M.P. 90, 323
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Measuring isotopic ratios in comets with ALMA
D/H HDO/H2O 2 terrestrial in 3 comets, DCN/HCN
7 higher in Hale-Bopp HDO with ALMA in bright
comets (Herschel more sensitive) D/H in other
molecules with ALMA (DCN, CH2DOH, HDCO, NH2D,)
13C/12C terrestrial in gt 6 comets ALMA H13CN,
13CS, 13CO, 13CH3OH, 34S/32S terrestrial
in 2 comets ALMA C34S, H234S 18O/16O
terrestrial in 4 comets (H2O) 15N/14N terrestri
al in HCN Hale-Bopp but twice higher in CN in gt 4
comets? ALMA HC15N, H15NC?
Hersant et al. 2001, ApJ 554, 391
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Cumulative number of molecules detected in comets
as a function of abundance relative to water
RADIO
Crovisier et al. 2004, AA 418, L35
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Detection of ethylene glycol in comet C/1995 O1
(Hale-Bopp) together with 3 other new species
(HC3N, HCOOCH3 and NH2CHO)
Crovisier et al. 2004, AA 418, L35
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Comparison of comets chemical composition with
interstellar medium
Bockelée-Morvan et al. 2000, AA 353, 1101
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Progressive release of 9 molecules by comet
C/1995 O1 (Hale-Bopp) - As it approached the
Sun (left 1995-1997) - As it receded from the
Sun (right1997-2001)

• ALMA
• Similar monitoring in less active comets
  (especially investigating transition between H2O
  and CO sublimation dominated regimes)
• Distant activity of comets detection of CO
  outgassing in comets active at 5-15 AU
• (mag. 16-17 ? QCO51026molec./s)

Biver et al. 2002, E.M.P. 90, 5
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ALMA and the origins (composition) of comets
(from line or dust integrated fluxes)

• I.1 Relative abundance of 6-8 molecules in a wide
  diversity of comets
• Chemical difference between Oort clouds
  comets and Kuiper Belt (Jupiter Family) ones?
• I.2 Measuring molecular isotopic ratio
• 34S/32S, 13C/12C, 15N/14N (issue with
  C15N and HC15N?) in moderately bright comets,
• D/H in several molecules (H2O, HCN,
  H2CO, NH3, CH3OH) differs between molecules due
  to different enrichment process
• Place of formation of nuclei and proto-planetary
  nebula properties
• I.3 Searching for complex molecules
• 15 only observed before in Hale-Bopp
  and new molecules
• Origin of solar system material
• I.4 Monitoring molecular and dust production
  rates with heliocentric distance
• Retrieving nucleus composition from
  abundances in the coma
• Structure of cometary ices

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II Interferometric maps of cometary
atmospheres ALMA will enable high resolution
(50-100km) 3-D imaging of gas jets with
simultaneous dust jets imaging and good time
sampling thanks to its extensive u-v plane
coverage (large number of baselines)
Strong gas and dust jets in Hale-Bopp (most of
nuclear CO) determines the rotation period of
11h21m
Dust jets 75 of the near nucleus coma signal in
1P/Halley (Giotto)
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Rotation of a CO jet in comet Hale-Bopp 3-D
information ALMA HCN(3-2) or HCN(4-3) in
several comets
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Cometary  jets  with ALMA Investigating the
coupling between dust and gas, and different
gaseous species Difference between night and
day-time activity? Dust features predicted
different from gas ones close to the
nucleus? Variation of dust properties (opacity
index, size distribution) with distance to the
nucleus Measurement of gas (e.g. CH3OH)
temperature and velocity field
Interferometric maps at 90 GHz and 220 GHz comet
Hale-Bopp with IRAM Plateau de Bure 9, 11, 13
and 16 March 1997 continuum of dust and nucleus
Altenhoff et al. 1999, AA 348, 1020
v
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Molecules coming from a distributed source in the
cometary atmospheres ALMA will be used to
measure the scalelengths (100-10000 km)
H2CO 80 extended thermo-degradation of
polymers? CO 50 extended in Hale-Bopp HNC,
OCS extended in Hale-Bopp? CS, SO, NS? daughter
molecules Molecules released by grain sublimation
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ALMA and the cometary atmospheres
(interferometric mapping of physical properties)

• II.1 Measuring rotation from molecular lines
  (e.g. HCN(3-2), strongest)
• 3-D measurements thanks to the spectral
  resolution rotation of several comets per year
• II.2 Comparing gaseous molecular jets and dust
  jets close to the nucleus
• Coupling of gas and dust in the near nucleus coma
  (sensitive to the nucleus shape), difference in
  day/night side activity e.g. molecules only
  subliming on day side, difference in dust lifted
  by the gas,
• Cometary nuclei surface and gross properties (in
  addition to size)
• II.3 Gas temperature and velocity field in the
  inner coma (50-1000km)
• Measuring adiabatic cooling and photolytic
  heating, T(r), v(r)
• II.4 Molecular density profiles n(r) extended
  sources
• Characterizing the parents (grains, other
  molecules, chemical reaction) of such daughter
  molecules CO, H2CO, CS, SO, HNC, NS
• New parent molecules, better characterization of
  productions

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Example of observable comets for ALMA
comet date QH2O s-1 D AU Molecules detectable isotopes Moni-toring Jets imaging
22P/Kopff 07/2009 1028 0.8 6 - - Low res.
81P/Wild 2 03/2010 1028 0.7 6 H13CN - Low res.
103P/Hartley2 10/2010 2.1028 0.13 15 new ones 13C, 34S, D, 15N, (7 molec.) - High res., Dust, 6 molec.
45P/H.-M.-P. 08/2011 2.1027 0.07 10 13C,34S - Med. res.
2P/Encke 10/2013 6.1027 0.5 8 - - Low res.
New Comet Every year 1.1029 0.6 15 13C, 34S, D, 15N, in 7 molec. Up to 5 AU High res., Dust, 6 molec
Great Comet Every 5 years 5.1029 0.6 15 new ones 13C, 34S, D, 15N, gt10molec. Up to 10AU High res., Dust, 10 molec