TRACING ABUNDANCES IN GALAXIES WITH THE SPITZER ...

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Mendez et al. (1992) use their determinations of IC 2448’s stellar gravity (log g = 4.8) and effective temperature (Teff = 65000 K) to derive the current mass of IC 2448’s star as 0.58 M⊙. This current stellar mass corresponds to an initial stellar mass of Mi ≈ 1 M⊙ at a metallicity of Z = 0.5-1.0 Z⊙ (Vassiliadis & Wood, 1993). This low stellar mass, along with the low metallicity of IC 2448’s progenitor star, imply that the first and perhaps the third dredge-up occurred. First dredge-up would have increased the abundances of 4 He, 14 N, and 13 C, decreased the abundance of 12 C, and left the 16 O abundance the same (Marigo et al., 2003). Second dredge-up (which increases 4 He and 14 N but decreases 12 C, 13 C, and 16 O) is only expected to occur if the initial mass of the progenitor star is between 3 and 5 M⊙ (Marigo et al., 2003), and so it is not expected to occur here. Third dredge-up, which significantly increases 4 He and 12 C and slightly increases the amounts of some other elements (Marigo et al., 2003), might have occurred. It is expected to occur in stars that have Mi � 1.5 M⊙ at Z = Z⊙, but this limit is at lower masses for lower Z (Marigo et al., 1999). Third dredge-up enriches the amount of carbon relative to oxygen, and thus a C/O ratio greater than one would indicate that third dredge-up occurred (Iben & Renzini, 1983). The C/O ratio in IC 2448 derived here is 1.1, but the carbon abundance of IC 2448 is very uncertain as discussed above. Thus we cannot determine if the C/O ratio is really greater or less than one. The IR spectrum of IC 2448 (Figure 2.1) does not show PAHs which are often observed in PNe with C/O > 1, nor does it show silicates which are often observed in PNe with C/O < 1 (Zuckerman & Aller, 1986; Bernard-Salas & Tielens, 2005). The uncertainty in our carbon abundance and the lack of PAHs and silicates in the IR spectrum do not allow us to determine if IC 2448 is carbon-rich or oxygen-rich. The abundances of IC 2448 are close to the abundances of PN IC 2165 which 49
is a spherical nebula with a low mass (� 3 M⊙) progenitor star (Pottasch et al., 2004). IC 2165 probably experienced third dredge-up (in addition to first dredge- up) because it has C/O ∼ 2 (Pottasch et al., 2004). The elements not much affected by the various dredge-up episodes (Ar, Ne, S, and O) all have subsolar values in IC 2448 and IC 2165, which implies that the progenitor stars of these nebula were created from metal deficient gas. The IR continuum of IC 2448 gives a cool dust temperature of ∼ 100 K, support- ing previous studies that show IC 2448 to be an old, evolved nebula. Additionally, IR lines that would come from the photodissociation region such as [Ar II] and [Si II] are not observed. Perhaps this indicates that most of the photodissociation region has been destroyed, which fits the picture of IC 2448 being an old PN where the ionization front has gobbled up most of the photodissociation region. 2.7 Conclusions This is the first mid-IR spectral study of IC 2448. The abundance of helium is slightly above solar, indicating that some chemical enrichment has occurred. The high uncertainties in the nitrogen and carbon abundances (due to their reliance on abundances determined from UV lines which depend strongly on the electron temperature and to a lesser extent on the extinction) make it difficult to determine how much chemical enrichment occurred. The elements not affected much by stellar evolution (Ar, Ne, S, and O) all have subsolar values in IC 2448, indicating that the progenitor star formed out of somewhat metal deficient material. Our use of infrared ionic lines which are less sensitive to extinction and temperature, and some of which arise from ions with no observable lines in the optical or UV, leads to a more accurate determination of abundances for Ar, Ne, S, and O than previously possible. The abundances determined fit with the picture of IC 2448 having a low 50
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TRACING ABUNDANCES IN GALAXIES WITH
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TRACING ABUNDANCES IN GALAXIES WITH
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BIOGRAPHICAL SKETCH Shannon was bor
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ACKNOWLEDGEMENTS First and foremost
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thank my husband Ryan. The rest of
Page 11 and 12: 3 Chemical Abundances and Dust in P
Page 13 and 14: LIST OF FIGURES 1.1 Diagram of the
Page 15 and 16: ditionally we find that these nebul
Page 17 and 18: seed nuclei relative to the β deca
Page 19 and 20: shape (Carollo et al., 2007). These
Page 21 and 22: Boltzmann velocity distribution cha
Page 23 and 24: etween recapture and photoionizatio
Page 25 and 26: a whole. Additionally, abundances f
Page 27 and 28: at the appropriate temperature and
Page 29 and 30: (a) 3.37 eV 1.40 eV 0.10 eV 0.04 eV
Page 31 and 32: (Iion), the radiative transition ra
Page 33 and 34: lines. For example, changing the ad
Page 35 and 36: Figure 1.4 Starburst99 synthetic sp
Page 37 and 38: Figure 1.5 Example of crystalline s
Page 39 and 40: H H H H H H H H H Anthanthrene C H
Page 41 and 42: year lifetime. Spitzer is in an Ear
Page 43 and 44: CHAPTER 2 THE SPITZER IRS INFRARED
Page 45 and 46: these elements than previous studie
Page 47 and 48: dust is seen in the spectrum. We se
Page 49 and 50: Figure 2.2 Close-ups of emission li
Page 51 and 52: 2.4 Optical and UV Data We compleme
Page 53 and 54: 2.5 Data Analysis Our goal is to ca
Page 55 and 56: 2.5.2 Electron Density We assume an
Page 57 and 58: Table 2.6 Electron temperatures ass
Page 59 and 60: O, N, and C. The helium ionic abund
Page 61: Barlow (1994) use UV lines for impo
Page 65 and 66: CHAPTER 3 CHEMICAL ABUNDANCES AND D
Page 67 and 68: essential data on important ionizat
Page 69 and 70: are members of the Bulge, (Acker et
Page 71 and 72: Table 3.2 Properties of observed GB
Page 73 and 74: nod-averaged line fluxes. Uncertain
Page 75 and 76: Table 3.3 Multiplicative scaling fa
Page 77 and 78: Table 3.4 Observed infrared line fl
Page 79 and 80: 3.5 Data Analysis 3.5.1 Abundances
Page 81 and 82: Table 3.6 Comparison of the derived
Page 83 and 84: from the most reliable line(s), and
Page 85 and 86: Table 3.7 Electron temperatures and
Page 87 and 88: Table 3.9 Ionic abundances Ion x a
Page 89 and 90: 3.5.2 Crystalline Silicates Crystal
Page 91 and 92: argon, neon, and sulfur tend to be
Page 93 and 94: Figure 3.2 Continuum subtracted spe
Page 95 and 96: Figure 3.3 Profiles of PAH features
Page 97 and 98: mean argon and sulfur abundances ar
Page 99 and 100: of two smaller than that of Simpson
Page 101 and 102: towards the Galactic Center. On the
Page 103 and 104: Table 3.14 Parameters of linear fit
Page 105 and 106: models that show how a binary compa
Page 107 and 108: y an outer dense O-rich torus, indi
Page 109 and 110: CHAPTER 4 ABUNDANCES IN H II REGION
Page 111 and 112: expect their abundance ratio to rem
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We extract spectra processed throug
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Figure 4.2 IRS spectra of H II regi
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IRS slits from these WIRC observati
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S IV) we employ is equal to Te(O +2
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Figure 4.3 M51 H II region Ne III/N
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Figure 4.4 shows a plot of the (Ne
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James Webb Space Telescope (JWST);
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Bernard-Salas, J. & Tielens, A. G.
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Edgar, R. G., Nordhaus, J., Blackma
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Hummer, D. G., Berrington, K. A., E
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Matsuura, M., Zijlstra, A. A., Mols
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Pradhan, A. K., Montenegro, M., Nah
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Vassiliadis, E. & Wood, P. R. 1993,
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