A new database of infrared mineral spectra for astrophysics

1. A new database of infrared mineral spectra for astrophysics by Anne M. Hofmeister Star sapphire Many thanks to Janet Bowey, Angela Speck, and Mike Barlow

2. Philosophy • Measure solids with diverse chemical compositions and structures • Study known astrominerals and condensates in copious detail • Obtain intrinsic, quantitative spectra (understand and eliminate sampling artifacts) • Use cryogenic temperatures (future work)

3. Far-IR to Visible Spectrometer IR microscope Bomem FTIR

4. Interpretation of observational data rests on the quality of laboratory IR measurements Control: Subject: Egg Nebula( R. Thompson et al. NASA site) Cell for thick films (t = 6 mm)

5. Reflectance is the best approach, but fairly large samples are needed: sample mirrors S-polarization FTIR microscope Specular reflection device Let’s look at reflectivity data – do artifacts exist?

6. Opaque spectral regions yield reliable data for thin samples, but

7. Imeas I0(1-R) I0R(1-R)(1-W)2 d I0(1-R)(1- W) I0R(1-R)(1- W) I0(1-R)(1- W)(1-R) = Imeas back-reflections affect transparent spectral regions I0 I0RI0R(1-R)2(1-W)2

8. A high-pressure device provides essentially quantitative absorption data from powdered, hard minerals Diamond anvil cell used to make thin films (t = 0.1 to 3 mm) Olivine-enstatite-diopside rock from Earth’s interior

9. Absorption/transmission spectra depend on Areal coverage Sample thickness Intensity of bands (absorption strength increases with reflectivity)

10. Various peaks “saturate” at different thicknesses, depending on individual band strengths TO modes saturate before LO, which rounds the profile, making spectra of crystalline material appear amorphous

11. Measurements at temperature are needed to provide relevant peak parameters Cryostat for dispersion or reflection (fixed points: 77, 200, 273 or 298 K) More work is needed: e.g. liquid helium temperatures with a variable T cryostat

12. Room temperature measurements provide a first-order model of cold dust in a nebula NGC 6302

13. Focus on far-IR because cold temperatures cut-offhigh frequency peaks:

14. Calcium aluminates provide the best match, but Ca, Mg, Al silicates match well, too: Hibonite CaAl12O19 is presolar

15. The refractory end of the condensation sequence seems to be present in NGC 6302 C = corundum Al2O3 D = diopside CaMgSi2O6 E = enstatite MgSiO3 F = forsterite Mg2SiO4 G = grossite CaAl4O7 H = hibonite CaAl12O19 S = spinel MgAl2O4 X = melilite Ca2MgSi2O7 – CaAl2SiO7

16. Could hydrosilicates be stable in space? Water + forsterite = lizardite Water + diopside = tremolite (and we can get band strengths, too)

17. = + =

18. Low frequency region best identifies dust

19. Lizardite and saponite (or their dehydroxylates) may be present in NGC 6302 Lizardite froms via alteration of forsterite below 700 K. Saponite via alteration of basalts.

20. Average band strengths (Hofmeister and Bowey in prep). type ν(cm⁻¹) brucite tremolite lizardite talc saponite mont. average O-H stretch 3500 1.4 0.40 0.95 0.45 0.11 0.21 0.6 Mg-O-H 1600 0.2 0.9 0.045 - 0.2 0.08 0.3 overtones 2000 0.01 0.05 0.045 0.025 0.1 0.014 0.04 Si-O stretch 1000 - 3.3 2.8 5.8 2.3 1.6 3.1 Si-O-Si bend 670 - 0.6 1.2 1.9 0.5 ? 1.0 O-Si-O bend 450 - 1.8 3.7 4.3 2.0 1.0 2.5 Mg-O stretch 300 2.4 0.3 0.67 - - 1.0 Ca translation 200 - 0.3 - ? 0.01 0.15 Mg translation 200 - 0.1 0.05 0.08 0.05 0.01 0.06 True absorption coefficients (in 1/μm) are given for the dominant band in the various spectral regions. allow estimation of concentrations even if mineral identification is unsure.

21. Some minerals warrant detailed studies: SiC has more features than the Si-C stretch expected for its simple structure due to • stacking disorder (polytypism) • impurities such as excess C or Si • crystallinity (bulk vs. nano vs. amorphous)

22. The “21 mm” feature is SiC with excess C Ueta et al. 2000 Speck and Hofmeister 2004

23. SiC in various forms has distinct spectra (Speck and Hofmeister in prep.)

24. The 9 mm features in AGBs are due to SiC with excess C (Speck and Hofmeister in prep.) This substance has the diamond structure and is nano-crystalline (Kimura and Kaito 2003)