Spitzer Infrared Spectrograph (IRS) Observations of Large Magellanic Cloud Planetary Nebula SMP 83 J. Bernard Salas, J. R. Houck, P. W. Morris, G. C. Sloan, S. R. Pottasch, & D. J. Barry ApJS, 154, 271 (2004) Presented by Shannon Guiles Astronomy 671 March 6, 2006 (This is actually an image of the PN NGC 6302, the Butterfly, Credit: ESO)
Dopita et al., ApJ, 418, 804 (1993) HST Observations of SMP 83
Why do we care? When measurements of planetary nebulae (PNe) in the infrared (IR) are combined with optical ones, many stages of ionization are observed, reducing abundance uncertainties Optical abundance measurements depend strongly on the adopted electron temperature (Te), while IR ones do not, again reducing abundance uncertainties Using both infrared & optical lines you can determine electron temperature for more ions than possible with optical lines alone
Why do we care? Before Spitzer it was impossible to do detailed infrared (IR) observations of extragalactic planetary nebulae (PNe) It is useful to study PNe in the Large and Small Magellanic Clouds (LMC and SMC) because they have known distances and also different metallicity than the Milky Way
Nature of the Central Star of SMP 83 Dopita et al. (1993) using HST images found that central star had ~ 6 M sun on the main sequence. The star now has 1 1.2 M sun.
Nature of the Central Star of SMP 83 Dopita et al. (1993) using HST images found that central star had ~ 6 M sun on the main sequence. The star now has 1 1.2 M sun. Studying PNe evolved from the most massive stars is important for determining the mass boundary between stars that evolve to Type I supernovae and those that evolve through the PNe stage Torres Peimbert et al. (1993) noticed sudden development of WR features (type WN)
Nature of the Central Star Hamann et. al. (2003) During 1994 the star experienced and increase in luminosity. The luminosity before and after the burst was 4.6 L sun and 5.4 L sun during the burst The effective temperature remained at ~ 112kK during the burst, so the luminosity increased because of a larger stellar effective radius Mass loss rate increased from 10 5.7 M sun /yr in the quiet state to 10 5.0 M sun /yr during the burst The chemical composition of the atmosphere is incompletely processed CNO material Several possibilities for the central star: low mass single star, high mass single star, binaries...
Observations These measurements of SMP 83 only took 15 minutes of Spitzer observation time The diameter of SMP 83 is less than 2'', so it was calibrated as a point source This is the first detection of mid infrared (MIR) fine structure lines in an extragalactic PN
Observations
Electron Density The electron density is too low to be measured by the available MIR lines The adopted electron density in this paper is 2350 cm 3 determined from optical lines This density is lower than the critical density of all the measured MIR lines except [S III] at 33.46 um and [Si II] at 34.84 um, and so does not affect the line intensities
Electron Temperature Determine the electron temperature (Te) from ratios of lines that originate from energy levels differing by several ev Use both infrared and optical lines to determine Te for more ions than possible with optical lines alone Find that Te increases with Ionization Potential (IP) This has been observed in several Galactic PN, but it is the first time for a PN in the LMC
Electron Temperature
Abundances Use the H flux along with MIR and optical fine structure lines to get ionic abundances Add the abundances for different ionization stages to derive the element abundance, get [S/H] = 4.8 x 10 6 & [Ne/H] = 8.6 x 10 5 Compare with the average LMC abundance of HII regions: [S/H] = 5.2 x 10 6 & [Ne/H] = 5.4 x 10 5
Abundances Sulfur Marigo et al. (2003) observed that the sulfur abundance of galactic PNe was less than solar. They suggested two possible causes: sulfur may be destroyed during evolution, but this is not predicted by evolution models solar sulfur abundance may be overestimated Pena et al. (1995) derived S/H in SMP 83 < S/H in LMC HII regions sulfur destroyed during evolution In this study S/H in SMP 83 ~ S/H in LMC HII regions solar sulfur abundance overestimated (but need to measure more LMC PNe to confirm)
Abundances Neon Using the MIR + optical lines to derive the neon abundance gives higher values than using the optical lines alone have more ionic stages to determine the total element abundance optical abundance measurements depend strongly on the adopted Te If Ne/H in SMP 83 > Ne/H in LMC HII regions, it may imply that neon enrichment took place during dredge up in the central star
Nature of the Central Star of SMP 83 If neon is enriched in the nebula, then the central star is probably not a massive star Neon enrichment in massive stars occurs along with carbon and oxygen enrichment. Since C and O are underabundant when compared to LMC HII regions (Pena et al. 1995), the progenitor star is probably not a massive WR star. Also, if neon is enriched, the reaction 22Ne(, n) 25 Mg expected to occur during thermal pulses is probably not very efficient
Summary and Conclusions The IRS MIR SED of PN SMP 83 in the LMC has high excitation fine structure lines, and negligible dust and continuum MIR and optical lines were used to determine e temperature for several ions e temp. correlates with ionization potential MIR derived Ne/H of SMP 83 ~ 2 x the optically derived Ne/H MIR derived S/H of SMP 83 agrees with the LMC HII region S/H
References Spitzer Infrared Spectrograph (IRS) Observations of Large Magellanic Cloud Planetary Nebula SMP 83, J. Bernard Salas, J. R. Houck, P. W. Morris, G. C. Sloan, S. R. Pottasch, & D. J. Barry, ApJS, 154, 271 (2004) Physics and Chemistry of Gas in Planetary Nebulae, thesis of Jeronimo Bernard Salas (2003) Dopita et al., ApJ, 418, 804 (1993) Hamann et al., A&A, 409, 969 (2003)