Radio Observing Possibilities for Deep Impact

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Radio Observing Possibilities for Deep Impact

• Deep Impact Workshop2004 Sep 6Paul JonesATNF

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• 1. To update the community on the status of
  the mission and the science goals.2. To
  discuss the key ground support observations that
  we will need at various wavelengths at the time
  of encounter.3. To discuss the unique
  capabilities of facilities in Australia to
  participate in the Deep Impact science.Summary
  partly based on science information from Karen
  Meech, Nicholas Biver, Laura Woodney etc.

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• Consider what radio observations already planned,
  and role of Australian radio facilities.
• Unique or complementary ?
• Collaborations

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1. Science Goals

• Radio (and sub-mm) spectral lines to study
  outgassing.
• Need observations at time of expected outburst
  due to impact.
• But outgassing varies with time - heliocentric
  distance- nucleus rotationso need baseline
  studies before/after impact

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2. Radio Observations

• see for example studies of
• Comet 19P/Borrelly Bokelee-Morvan D., et al.
  2004, The outgassing and composition of Comet
  19P/Borrelly from radio observations, Icarus,
  167, 113-128
• Comet C/1999 H1 (Lee)Biver N., et al. 2000,
  Spectroscopic observations of Comet C/1999 H1
  (Lee) with the SEST, JCMT, CSO, IRAM and Nancay
  radio telescopes, ApJ, 120, 1554-1570

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• OH - 1.665, 1667 MHz
• H2O - 110 - 101 557 GHz
• CO - J(2-1) 230.53 GHz
• CO2
• HCN - J(1-0) 88.63, J(3-2) 265.88, J(4-3) 354.51
  GHz
• ? CH3OH - several 145.09 - 145.13, 157.05 -
  157.28 GHz
• ? H2CO - 312 - 211 225.69 GHz
• ? CS - J(3-2) 146.96, J(5-4) 244.93 GHz
• ? H2S - 110 - 101 168.76 GHz

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• IRAM 30-m, 86 - 272 GHz
• IRAM PdBI 6 x 15 m, 86 - 115 and 205 - 250 GHz,
  but note (below) interferometry likely to be less
  efficient for detections than single dish
• JCMT 15-m and CSO 10-m 210 - 275, 300 - 365, 450
  - 510 GHz
• Apex 12-m ?, Kitt Peak 12-m ?, FCRAO 15-m ?,
  Nobeyama 45-m ?
• BIMA and OVRO inoperative while being moved to
  CARMA (2005 northern summer)
• SEST 15-m no longer operating

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• ODIN satellite 1-m (Swedish) for 557 GHz H2O line
• Nancay radio telescope for 1.66 GHz OH

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Molecular emission

• Nu N (gu/Q) exp(-Eu/kTex)
• where N total column density (cm-2)
• Nu column density of upper level, gu
  statistical weight,
• Eu energy of upper level, Tex excitation
  temperature,
• Q partition function ( S gi exp(-Ei/kTex) for
  all states)
• Nu (8 p u2/hc3Aul) ?Tb dv
• where ?Tb dv integral of brightness
  temperature of the emission line, Aul Einstein
  coefficient

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• so, the observed ?Tb dv depends on N
• but also temperature (Tex ) energy (Eu) and
  molecular parameters (Aul, gu Q)
• For these comet observations (compared to say
  Galactic molecular clouds) it looks like higher
  frequency (mm) transitions are easier to detect
  eg HCN (3-2) rather than (1-0)
• Also note the models include fractional
  production rates
• (relative to H2O), outlow velocity,
  photodissociation etc,
• in interpreting the column densities N

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OH maser

• OH (Hydroxyl) at 1667, 1665 (1612, 1720) MHz
  is observed from comets in emission or
  absorption depending on
• 1) The OH column density, in turn dependent on
  the outgassing of parent and daughter molecules
• 2) The distribution of energy levels, pumped by
  Solar UV. This depends on the spectrum seen by
  the comet and hence heliocentric velocity.
• 3) The background radio continuum, providing
  incident photons for absorption or stimulated
  emission (maser)

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• The inversion
• i (nup - nlo)/(nup nlo)
• is positive for maser emission and negative
  for absorption.
• The model prediction is that i -0.2 to -0.3 for
  2005 Mar to May, but low at 0.02 at perihelion
  and impact in 2005 Jul.
• An order of magnitude increase would be required
  for OH to be detectable in early Jul(Galactic
  latitude 51.6 deg, so not high background)

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Observing parameters

• Impact date 2005 July 4, around 06 UTGeocentric
  distance 0.89 AUHeliocentric distance 1.5 AU
• Water molecule production rate 1028 molecules/sec
  before impact, near perihelion.
• From 2004 Oct to 2005 Sep, the declination of
  19P/Tempel 1 varies from 19 to -30 degrees, with
  the impact occuring at -10 degrees.
• This is well situated for observatories in both
  Northern and Southern Hemispheres (except
  Antarctica !)

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3. Australian Radio Facilities

• We don't have sub-mm (shorter than 3-mm band) in
  Australia
• However 3-mm and cm band observations may be
  complementary
• eg HCN (1-0) to combine with HCN (3-2)
• ATCA 6 (5) x 22-m, Parkes 64-m, Mopra 22-m

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Compact Array at 3-mm band ? eg HCN

• use a hybrid array to get good uv-coverage near
  equator
• Sensitivity 33 mJy/beam or 0.9 K (FULL_32_256,
  0.125 MHz or 0.4 km/s resolution) for 4 hours
  on-source integration (8 hour observation, with
  50 overheads for pointing, calibration etc)
  with 2.5 arcsec beam, H214 array

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HCN in NGC3576 ATCA, 3.9x2.7 arcsec2 1.7 km/s
RMS 26 mJy/beam
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• primary beam 36 arcsec (at 86 GHz), but the
  synthesized beam of a few arcsec could resolve
  out emission, 4 arcsec 2900 km at 1.5 AU.
• see, for example, Hogerheijde et al., 2004,
  Combined BIMA and OVRO observations of Comet
  C/1999 S4 (Linear), ApJ, 127, 2406-2412, where
  HCN was just detected in BIMA autocorrelation
  spectra, but not in BIMAOVRO cross-correlations
  with 12x9 arcsec2 beam.
• Warning for using interferometry - need to match
  to source scale !

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Same data cube as before position where Mopra
detects HCN easily - resolved out !
HCN in NGC3576 ATCA, 3.9x2.7 arcsec2 1.7 km/s
RMS 26 mJy/beam
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• It is possible to record autocorrelation
  ("single-dish") spectra on the ATCA(eg
  NO6AC_8_512_POL) to get 5 x 22 m dishes, but this
  requires a different observing mode of frequent
  on-off scans to get good spectral baselines
• Tests that I have done on autocorrelation data
  taken for Sgr B2 bonus' with cross-correlation
  observations do not give particularly good
  spectra

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Mopra at 3-mm band ? eg HCN

• Sensitivity 0.008 K assuming Tsys 250 K
  (including atmosphere) 0.06 MHz or 0.2 km/s
  resolution (AC_64_1024_2) for 4 hours integration
  on source (4 hours off source for bandpass, and
  overhead for pointing)
• primary beam around 34 arcsec at 85 GHz
• assuming 62 Jy/K, this is around 500 mJy/beam

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Mopra RMS 0.004 K 16 hours integration
?T Tsys (B t)-1/2
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Parkes 64-m for OH ?

• H-OH receiver for 1.66 GHz,
• Tsys 28 K, 1.5 Jy/K, 14 arcmin beam
• 7 mK for 0.4 km/s channels (4 hours on source)
• Compare Nancay Tsys 45 K, 1.1 Jy/K, 3.5 x 19
  arcmin2

ATCA for OH ?

• Resolution 2 arcmin, for H214 array, not too
  high ?
• 0.1 K line sensitivity for 0.7 km/s channels
• (10 hour integration), 5 mJy/beam

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Conclusion

• ATNF proposal deadline 2004 Dec 1 for 2005 Apr -
  Sep
• Austral Winter season, so expect ATCA
  oversubscribed, need strong science case
• Mopra likely to be more available
• Parkes for OH ? but OH not favourable around
  impact date