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

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)

Far-IR to Visible Spectrometer IR microscope Bomem FTIR

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

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

Opaque spectral regions yield reliable data for thin samples, but

I 0 I 0 R I 0 R(1-R) 2 (1-  ) 2 I 0 (1-R) I 0 R(1-R)(1-  ) 2 d I meas I 0 (1-R)(1-  ) I 0 R(1-R)(1-  ) I 0 (1-R)(1-  )(1-R) = I meas back-reflections affect transparent spectral regions

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

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

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

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

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

Focus on far-IR because cold temperatures cut-off high frequency peaks:

Calcium aluminates provide the best match, Hibonite CaAl 12 O 19 is presolar but Ca, Mg, Al silicates match well, too:

The refractory end of the condensation sequence seems to be present in NGC 6302 C = corundum Al 2 O 3 D = diopside CaMgSi 2 O 6 E = enstatite MgSiO 3 F = forsterite Mg 2 SiO 4 G = grossite CaAl 4 O 7 H = hibonite CaAl 12 O 19 S = spinel MgAl 2 O 4 X = melilite Ca 2 MgSi 2 O 7 – CaAl 2 SiO 7

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

+ = =

Low frequency region best identifies dust

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.

Average band strengths (Hofmeister and Bowey in prep). typeν(cm ⁻ ¹)brucitetremolitelizarditetalc saponitemont. average O-H stretch Mg-O-H overtones Si-O stretch Si-O-Si bend ?1.0 O-Si-O bend Mg-O stretch Ca translation ? Mg translation 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.

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) Some minerals warrant detailed studies:

The “21  m” feature is SiC with excess C Ueta et al Speck and Hofmeister 2004

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

The 9  m 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)