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Asteroid Models for PACS and SPIRE Calibration

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Asteroid models for PACS and SPIRE calibration Thomas M¨uller,MPE, Jan. 19, 2012 1. Asteroid calibration observations 2. Sample for flux calibration PACS & SPIRE results 3. Asteroids as prime calibrators 4. Cross-calibration aspects 5. Next steps and future plans 1 Why asteroid calibration observations? • absolute flux calibration better than 5% in the entire flux regime • characterisation of point-spread-function (PSF) • important sources for filter leak tests and colour-corrections • spatial calibration aspects via asteroid-planet-star encounters • sources for detector linearity tests (connecting stars & planets) • establishment of relative spectral response function (RSRF) • technical telescope aspects: tracking & pointing system • cross-calibration between instruments, observing modes, with other missions, over time, across different wavelength & flux regimes, ... • anything where bright, point-like sources of known fluxes and with featureless SEDs are needed 2 Overview PACS/SPIRE asteroid calibration PacsCal PacsRangeSpec PV 16.2 h PacsCal Phot PSF FieldDistort 3.4 h PacsCal Spec Chopped Raster 1.2 h PacsCal WaveCalChop 1.7 h PacsPhoto 33.7 h PacsRangeSpec 41.4 h SpirePacsParallel 2.5 h SpirePhoto 67.9 h SpireSpectrometer 46.7 h • Until Dec. 2011, Herschel has spent about 215 h on asteroids for calibration purposes (PACS & SPIRE) • In total, more than 900 individual calibration observations (OBSIDs) • Thermophysical model calculations have been provided on request, typ- ically per OBSID, SEDs with pre-defined resolution or monochromatic flux densities at given reference wavelengths • All models have the same version, i.e., based on a fixed set of model parameters per object (for consistency reasons) 3 Asteroid sample for absolute flux calibration 4 Asteroid sample for absolute flux calibration • About 25 main-belt asteroids have been observed for flux calibration purposes by PACS and SPIRE • The original list of 55 asteroids has been down-selected to 12 high-quality objects (May 2011): 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, 6 Hebe, 8 Flora, 10 Hygiea, 20 Massalia, 21 Lutetia, 52 Europa, 88 Thisbe, 704 Interamnia • based on Herschel (PACS/SPIRE) observations and including checks against other data from ground (mid-IR/submm/mm) and space (IRAS, ISO, MSX, Spitzer, Akari) • For these 12 targets the derived Herschel (PACS/SPIRE) monochromatic flux densities are typically within 5% of the model predictions (full thermo- physical models, including shape models, rotation properties, thermal surface properties, true size and albedo values, ....). • Some are still outside the 5% corridor, but have the potential to reach that zone via external information (new shape and/or size information) 5 SPIRE: asteroid flux calibration (1) Timeline of SPIRE asteroid observations 6 SPIRE: asteroid flux calibration (2) 7 SPIRE: asteroid flux calibration (3) 8 PACS: asteroid flux calibration (1) • On average, the mini scan-map observations of the 18 asteroids agree within 2% in all 3 bands with the corresponding model predictions (giving each asteroid the same weight; after colour-correction) • blue band, 53 independent high-quality observations: stdev = 0.036 • green band, 53 independent high-quality observations: stdev = 0.036 • red band, 119 independent high-quality observations: stdev = 0.042 • Numbers do change slightly (a few percent), depending on settings for specific reduction steps: deglitching, masking/HPFW, aperture size, ... 9 10 11 12 Individual asteroids as prime calibrators? 21 Lutetia (Rosetta) 4 Vesta (DAWN) 13 21 Lutetia Rosetta flyby target (shape model by Carry et al. 2010) 14 15 16 21 Lutetia O'Rourke, M¨ulleret al. 2012 17 18 SPIRE FTS and photometer data on Pallas and Vesta 19 Individual asteroids as prime calibrators (2) • Best candidates: 1 Ceres, 2 Pallas, 4 Vesta, 21 Lutetia • Ceres and Vesta have more than 10 independent observations with each instrument, Pallas just below 10, Lutetia only a few • Model predictions are based on pre-Herschel model parameters • Derived fluxes depend slightly on data reduction details • Completely different calibration schemes for PACS & SPIRE Ast. 70 100 160 250 350 500 µm 1 1.05±0.02 1.03±0.02 1.07±0.02 1.00±0.03 1.01±0.02 1.00±0.03 2 1.06±0.02 1.05±0.03 1.10±0.03 1.09±0.03 1.10±0.03 1.10±0.03 4 1.02±0.03 1.08±0.03 1.14±0.04 1.07±0.02 1.11±0.02 1.09±0.02 21 1.07±0.07 1.07±0.05 1.11±0.07 1.00±0.06 1.01±0.04 0.94±0.08 Excellent cross-calibration results! 20 Individual asteroids as prime calibrators (3) • Several asteroids are on a path to become truly prime flux calibrators: Absolute flux predictions <5% in FIR/submm/mm, at any given time • Availability of highly accurate shape models, spin-axis characterisation, surface properties for 1 Ceres, (2 Pallas), 4 Vesta, 21 Lutetia • Large database of thermal observations available, for fine-tuning relevant pa- rameters, like surface roughness and thermal inertia • The PACS and SPIRE fluxes will play a key role when converting them to prime calibrators (in Herschel post-mission phase) • 21 Lutetia: the Rosetta shape model is available and publications are submit- ted (O'Rourke et al.; Carry et al. 2012), but only ∼60% of the surface was seen, the rest is re-constructed via other techniques • 4 Vesta: DAWN Mission is still at Vesta (until July 2012), shape model will be available soon • 1 Ceres & 2 Pallas: new shape models by Carry et al. 2009/2010 • 1 Ceres: DAWN Mission will arrive at Ceres in Feb. 2015 21 Asteroid cross-calibration aspects • SOFIA/APEX/ALMA: use the same list of 12 asteroids based on the same models • All 3 projects have meanwhile observed a few of the asteroids • coordinated activities with Planck on many asteroids (and planets), but no feeback on Planck fluxes so far • current main cross-calibration tasks - PACS photometer vs. spectrometer - SPIRE photometer vs. spectrometer - PACS vs. SPIRE - Connecting a stellar based calibration scheme (PACS, gb-MIR) to a planet based calibration scheme (SPIRE, gb-submm/mm) 22 Outlook & Next Steps • continuation of asteroid model calculations on request • collaborations with Benoit Carry (ESAC) and Josef Durech (Prague Univer- sity) to establish better shape/spin-vector models for key asteroids • collection and identification of key thermal data per object • ISSI-project with a focus on thermal surface effects has started Oct. 2011 (funded for 2 years) • aspect for the near future and post-operations phase: - collect all Herschel observations of calibrators (planets, stars, asteroids) - combine with auxiliary data from ground (lightcurves, occultations) - combine with space data (Planck, Rosetta, Dawn, ...) - tune calibrators for future projects: SOFIA, ALMA, JWST, SPICA, .... - updated calibrator models, including new primary standards! ) An important legacy of Herschel! 23.
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  • Observer's Handbook 1981

    Observer's Handbook 1981

    OBSERVER’S HANDBOOK 1 9 8 1 EDITOR: JOHN R. PERCY ROYAL ASTRONOMICAL SOCIETY OF CANADA CONTRIBUTORS AND ADVISORS A l a n H. B a t t e n , Dominion Astrophysical Observatory, Victoria, B.C., Canada V8X 3X3 (The Nearest Stars). Terence Dickinson, Editor, Star and Sky, 44 Church Lane, Westport, Conn. 06880 (The Planets). Alan Dyer, Queen Elizabeth Planetarium, 10004-104 Ave., Edmonton, Alta. T5J 0K 1 (Messier Catalogue, Deep-Sky Objects). M arie Fidler, Royal Astronomical Society of Canada, 124 Merton St., Toronto, Ont., Canada M4S 2Z2 (Observatories and Planetariums). V ictor Gaizauskas, Herzberg Institute of Astrophysics, National Research Council, Ottawa, Ont., Canada K1A 0R6 (Sunspots). J o h n A. G a l t , Dominion Radio Astrophysical Observatory, Penticton, B.C., Canada V2A 6K3 (Radio Sources). Ian H alliday, Herzberg Institute of Astrophysics, National Research Council, Ottawa, Ont., Canada K1A 0R6 (Miscellaneous Astronomical Data). H e l e n S. H o g g , David Dunlap Observatory, University of Toronto, Richmond Hill, Ont., Canada L4C 4Y6 (Foreword). D o n a l d A. M a c R a e , David Dunlap Observatory, University of Toronto, Richmond Hill, Ont., Canada L4C 4Y6 (The Brightest Stars). B r i a n G. M a r s d e n , Smithsonian Astrophysical Observatory, Cambridge, Mass., U.S.A. 02138 (Comets, Minor Planets). J a n e t A. M a t t e i , American Association of Variable Star Observers, 187 Concord Ave., Cambridge, Mass. U.S.A. 02138 (Variable Stars). P e t e r M. M i l l m a n , Herzberg Institute of Astrophysics, National Research Council, Ottawa, Ont., Canada K1A 0R6 (Meteors, Fireballs and Meteorites).