Jack Baldwin’s work on

Chemical Abundances in Planetary Nebulae

Planetary Nebulae (PNe):

• Gas shells blown off stars that have run out of nuclear fuel.

  • The remaining central star is becoming a "white dwarf".

  • Light from central star ionizes the shell, causing it to glow.

• Geometry is often bi-conical, rather than a simple shell.

  • Flow is often channeled by a circumstellar disk.

Emission Lines as diagnostic tools for measuring chemical abundances:

• Emission line strengths easily measured in very distant objects.

• Relative strengths of lines of different chemical elements ==> ratio of chemical abundances.

  • Classical analysis uses collisionally excited forbidden lines.

  • Deep spectra with high wavelength resolution now allows abundance determination also with permitted recombination lines.

  • The two techniques often give very discrepant results.

    • Up to factor 20 different.

  • What is going on???

    • Permitted lines excited by means other than recombination?

    • Using wrong density or temperature to determine abundances from strengths of collisionally excited lines?

• Brian Sharpee's PhD thesis

  • Picked a PN with roughly spherical geometry.

    • IC 418

  • Expanding shell ==> faster moving gas is farther from ionizing star

    • Causes ionization-velocity correlation.

    • Used this correlation to study which permitted lines are really formed by recombinations.

  • Developed EMILI, a computer-aided EMIssion Line Identifier.

    • Publicly available at http://www.pa.msu.edu/astro/software/emili/

• Comparing emission and absorption lines from same object.

  • Absorption lines ==> column density of gas in form of a particular ion.

    • Measure in UV with HST.

  • Find density needed to produce observed forbidden emission line surface brightness from that ion.

    • This should be ~same as density found for that ion from standard forbidden line analysis.

    • If not ==> problem with analysis of collisionally excited lines.

Measuring r- and s-process abundances in PNe:

• PNe spectra include weak collisionally excited lines from heavy r- and s-process elements.

  • s-process elements might be enhanced by processes in star that has formed PN. .

  • However, the r-process elements must be left over from the interstellar gas that originally formed the central star.

  • We are using very deep echelle spectra to measure abundances of r- and s-process elements.

    • 4m Mayall Telescope at KPNO

    • 6.5m Magellan Telescope at Las Campanas.

SOAR Telescope image of NGC 2440

My collaborators:

• Bob Williams (Space Telescope Science Institute)

• Brian Sharpee (Stanford Research Institute)

• Ed Jenkins (Princeton University)

• Mark Phillips (Las Campanas Observatory)

• Peter Van Hoof (Queen's University Belfast)

• Eric Pellegrini (MSU grad student)

• Ken Cavagnolo (MSU grad student)

Some of our relevant papers:

• Williams, R., Jenkins, E.B., Baldwin, J.A., Zhang, Y., Sharpee, B., Pellegrini, E. & Phillips, M. 2008, ApJ (in press) “Independent Emission and Absorption Abundances for Planetary Nebulae” http://xxx.lanl.gov/abs/0801.2147

• Sharpee, B., Zhang, Y., Williams, R., Pellegrini, E., Cavagnolo, K., Baldwin, J., Phillips, M. & Liu, X.-W. 2007, ApJ, 659, 1265,  “s-Process Abundances in Planetary Nebulae” http://xxx.lanl.gov/abs/astro-ph/0612101

• Sharpee, B., Baldwin, J.A. & Williams, R. 2004, ApJ, 615, 323 “Identification and Characterization of Faint Emission Lines in the Spectrum of the Planetary Nebula IC 418”  http://arxiv.org/abs/astro-ph/0407186

• Sharpee, B., Williams, R., Baldwin, J.A. & van Hoof, P.A.M. 2003, ApJS, 149, 157, “Introducing EMILI: Computer-aided Emission Line Identification” http://arxiv.org/abs/astro-ph/0307053

• Williams, R, Jenkins, E.B., Baldwin, J.A. & Sharpee, B. 2003, PASP, 115, 178 “Comparative Absorption and Emission Analyses of Nebulae: Ion Emission Densities for IC 418”    http://arxiv.org/abs/astro-ph/0210551