1 / 14

Analysis of spectral features in TNO and asteroid spectra

This workshop presentation discusses the analysis of spectral features in Trans-Neptunian Objects (TNOs) and asteroids. It covers topics such as the detection of specific ices, observation strategies, and characterization methods using multiresolution spectral analysis.

mhoyt
Download Presentation

Analysis of spectral features in TNO and asteroid spectra

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Analysis of spectral features in TNO and asteroid spectra S.Erard, D. Despan, F. Merlin S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  2. Spectral observation of TNOs • 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 1998 Cruikshank et al. S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  3. Spectral observation of TNOs Methanol is the second most easily detected ice (after H2O) 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 N2, CO, CO2, or ethane ice (only ethane is detected) S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  4. Spectral observation of TNOs 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! Trujillo’s conclusion, Catania 2006 meeting (excerpt) S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  5. 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 Merlin & Barucci, Catania 2006 meeting S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  6. 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, 11-12 janvier 2007

  7. Simulations — High SNR Orthopyroxene (laboratory spectrum) The two bands are correctly detected at all scales Grouping and identification of a dominant scale provides accurate band characteristics S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  8. Simulations — medium SNR Simulated spectrum + noise 3 wide bands and a narrow one, correctly detected S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  9. Simulations — very tilted continuum Jarosite (lab. spectrum) Many narrow bands on varying structure, correctly detected Bands near the edge (uncomplete) are detected with a low statistical weight S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  10. Ceres, 2.1-2.4 µm CH3OH VLT / Naco resolved observations Bright, extended object (mag ~8) • Ice features? • Clay features? CH4 H2O N2 NH3 S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  11. Ceres, 2.1-2.4 µm • 19 structures detected, mainly small telluric (with atm. counterparts) and solar bands • No ice absorption above 5 s (disk centre or pole) • Possible feature at 2.11 µm • Improvement of telluric correction pending Erard et al., EGU 2006 S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  12. Sedna, 1.9-2.5 µm Observations by Barucci et al 2005   (VLT), R~3000 • 6 structures detected, mostly telluric correction remants • Positive detection at 2.142 µm, corresponding to N2 ice but significantly narrower Erard et al., DPS 2005 S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  13. Conclusion • 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) S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

  14. S. Erard et al. — Workshop 3e zone, Nantes, 11-12 janvier 2007

More Related