Using Fe II Emission Lines to Determine Dust Properties in Jets

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Using Fe II Emission Lines to Determine Dust
Properties in Jets

• Adam Ginsburg
• Advisor Pat Hartigan

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Outline

• Background on Herbig Haro objects, dust, and
  forbidden line emission
• Data extraction, calibration, and measurement
• Results and early analysis
• Shock model
• Javascript code

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Herbig Haro objects

• Form from T-Tauri stars, young solar systems
• Accretion disk consists of dust and gas and is
  presumed to be the source of the HH jets
• Jets are ejected from the stars poles (or
  mag-netic poles) and impact the sur-rounding
  medium, causing a shock to form
• Knots in the jet are emitted at variable
  velocities, causing many smaller shocks to form

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Why is dust important?

• A recent article from Harvards CfA showed
  pebbles in the protoplanetary disk around TW
  Hydrae
• Dust forms into larger bodies (pebbles) which
  then form into planets
• By studying dust in other systems, we can better
  understand the formation of our own

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Dust Formation and Destruction

• In cool post-shock regions, iron atoms may
  condense into dust, depleting Fe II emission
  relative to S II emission
• Dust particles could be broken apart in the
  shock, splitting (or sputtering) back into
  ionizable gas particles, enhancing Fe II
  relative to S II
• If we witness neither formation nor destruction,
  we could determine abundances, which could then
  be compared between star forming regions

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Diagram vs. Image
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Dust Detection

• Fe II l8617 and S II ll(6717 6731) are good
  comparison lines
• source upper state has similar energy
• Therefore have similar temperature dependence
• similar ionization energies
• difficult to doubly ionize
• Dust particles will not emit significantly in
  optical wavelengths, and do not show emission
  lines

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The Data

• Reduced spectra using standard IRAF tasks
• Fluxes are measured relative to H-alpha
• Some lines are too small to measure if they are
  present at all
• Measurement uncertainty /- 5 for good S/N
• Because of multiple steps of background
  subtraction, the continuum (zero flux) level was
  the dominant source of measurement error
• Reddening correction C.34 derived from Balmer
  decrement (Ha/Hb 3)

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Standard Star Calibration

• Clouds were a problem for some nights
• Standard star sensitivity functions had the right
  shape but wrong level
• Matched levels to give correct line ratios

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Tables
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(No Transcript)
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The Shock Code
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Knot interaction in the jets
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Javascript Model Analyzer

• Accepts input of tab separated ratios to H-alpha
• Can reddening correct line ratios
• Once we have multiple data sets, will be able to
  show best fits in different star forming regions

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HH34 Aperture Selection
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Analysis
Calculated best-fit models without (left) and
with (right) iron lines included for the E shock.
With iron, the fit is about the same While
reddening correction improved the fit, it did not
change the result
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Shock Velocity
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Fe II/S II and Data
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Conclusion

• The null hypothesis, i.e. that there is no change
  in dust, is probably correct
• Still need to work out some kinks in chi-squared
  fitting program
• Data is in good agreement with Hartigan et al.
  1994, which gives shock speed 25-33 km/s and
  partial ionization of 1

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Future Work

• Same work for HH 111
• Expand the database of shock models
• Since there is no change in the dust, we can
  calculate abundances using a modification to the
  best fit code and the larger shock model database
• Publish

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HH111 Aperture Selection
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References

• Hartigan, P., Raymond, J., Pierson, R. 2004, ApJ,
  614, L69-71
• Hartigan, P., Morse, J., Tumlinson, J., Raymond,
  J., Heathcote, S. 1999, ApJ, 512, 901-915
• Brown, Korgsen, Evenson 1998, ApJ, 509927-930
• Morse et al., 1993, AJ vol 106 no 3 p 1139
• Hartigan, P., Morse, J., Raymond, J., 1994, ApJ,
  436, 125-143
• Wilner et al., 2005, ApJ, 626, L109-112