S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Analysis of spectral features in TNO and asteroid spectra S. Erard, D. Despan, F. Merlin

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Spectral observation of TNOs 1998 Cruikshank et al. Dark objects (≥ 18th mag) Shallow spectral features (in the NIR) => Very long exposure times required to access compositional information  implication for observing strategy and for analysis methods

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Spectral observation of TNOs Methanol is the second most easily detected ice (after H 2 O) Detection requires SNR ≥ 70 for pure ice Ammonia detection requires SNR ≥ 125 Requirements are higher if only a fraction of the surface is covered, or mixture with other ices C. Trujillo, Catania 2006 meeting 8-10m telescope, mag 18: 1 h exposure SNR ~100 Only 2005 FY9 has been observed with SNR allowing detection of N 2, CO, CO 2, or ethane ice (only ethane is detected)

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Spectral observation of TNOs Trujillo’s conclusion, Catania 2006 meeting (excerpt) The Good News: - About 25 KBOs could be observed by an international team of collaborators using the world's largest telescopes. The Bad News: - Don't bother observing any of the brightest 15 KBOs unless you spend at least 4 hours of exposure time on a 8m – 10m telescope in good conditions. Tips for observers: -Don't repeat objects that are already done! -Observe in good conditions and at low airmass! -Take high (80-100) S/N spectra!

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Spectral detection /characterization methods Simulation + spectral fit, inversion: - The first step is to identify the components - Extra components just add noise to the fits - Continuum is always an issue Spectral ratios: - Historically important, but very crude MGM: - Adapted only to specific minerals (pyroxenes, olivines, feldpars…) Tetracorder, etc…: - Rely on a more or less complete data base, - Not really adapted to ices Geographic mixture Hapke modelShkuratov model H2Oa----6%5µm H2Oc1%5µm14%5µm5%5µm Carbo n 83%15µm50%15µm68%15µm Ice- Th 5%5µm7%31µm7%5µm Tit-Th5%5µm---- Tri-Th6%5µm29%12µm14%15µm Merlin & Barucci, Catania 2006 meeting

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Multiresolution spectral analysis Purpose: - Detection method adapted to low SNR situations Output: - Characteristics of absorptions features (center, depth, width) - Detection thresholds in terms of S/N and proximity to the edges Basis: - Wavelet decomposition + multiscale grouping (based on imaging algorithms) - Uses a dyadic algorithm to avoid band reconstruction Performances: - Separates bands within Rayleigh criterion (if slightly different) - Accuracy on band properties ~10% for Gaussians - Correctly identifies bands at SNR = 3 in I/F - Robust to asymmetrical band shapes - Separates continuum variations from resolved bands

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Orthopyroxene (laboratory spectrum) The two bands are correctly detected at all scales Grouping and identification of a dominant scale provides accurate band characteristics Simulations — High SNR

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Simulated spectrum + noise 3 wide bands and a narrow one, correctly detected Simulations — medium SNR

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Jarosite (lab. spectrum) Many narrow bands on varying structure, correctly detected Bands near the edge (uncomplete) are detected with a low statistical weight Simulations — very tilted continuum

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 VLT / Naco resolved observations Bright, extended object (mag ~8) Ice features? Clay features? Ceres, µm CH 3 OH CH 4 H2OH2O N2N2 NH 3

S. Erard et al. — Workshop 3e zone, Nantes, janvier structures detected, mainly small telluric (with atm. counterparts) and solar bands No ice absorption above 5  (disk centre or pole) Possible feature at 2.11 µm Improvement of telluric correction pending Ceres, µm Erard et al., EGU 2006

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Observations by Barucci et al 2005 (VLT), R~ structures detected, mostly telluric correction remants Positive detection at µm, corresponding to N 2 ice but significantly narrower Sedna, µm Erard et al., DPS 2005

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007 Multiscale analysis methods, coupled with noise filtering algorithm, are very efficient in low SNR situations TNO spectral studies require this kind of analysis The present one, based on a very redundant algorithm, may still be improved with band reconstruction Tests are still being performed on laboratory spectra + observations First article with full description and tests to be submitted in 2007 (hopefully) Conclusion

S. Erard et al. — Workshop 3e zone, Nantes, janvier 2007