Description of the NEOWISE Diameters and Albedos bundle V2.0 ============================================================ Bundle Generation Date: 2021-04-15 Peer Review: NEOWISE Review Discipline node: Small Bodies Node Content description for the NEOWISE Diameters and Albedos bundle ================================================================ Content description for the NEOWISE Diameters and Albedos bundle ================================================================ This data set is a compilation of the published physical properties for minor planets observed by the NEOWISE survey. Data are separated by orbital classification, with a separate file for objects with Main Belt orbits that have shown comet-like activity. These are listed by their cometary designations as well as their asteroidal designations, if available. Note that some objects in the Centaur list are also designated as comets (e.g. (2060) 95P/Chiron). The NEOWISE survey phases are divided by cryogenic state (for the prime mission) and survey year (for the reactivation mission). The Cryogenic survey, using all four infrared bands, was conducted from 14 January 2010 to 6 August 2010. The 3-band survey was conducted from 6 August 2010 to 29 September 2010. The Post-Cryo survey using the two shortest wavelengths was conducted from 29 September 2010 to 1 February 2011. The NEOWISE reactivation survey began 13 December 2013, and the survey is divided into annual data releases every 13 December. Each line of the data set provides effective spherical diameter at the given observing geometry (in km), visible geometric albedo (V band), near-infrared geometric albedo (at a wavelength of 3.4 microns) and thermal model beaming parameter. Thermal model fits were performed primarily using the Near-Earth Asteroid Thermal Model (NEATM; Harris 1998); in a few instances the Fast Rotating Model was used (Lebofsky & Spencer, 1989). Each line has a code identifying which parameters were allowed to vary during the least-squares fit. The number of parameters fit depended on the number of WISE bands available, whether each band was dominated by thermal emission or reflected sunlight, and the availability of a measured absolute magnitude (H). When measurements in all four WISE bands and an H magnitude were available, they were used as observations input to the thermal model which performed a least-squares minimization using diameter, albedo, infrared albedo and beaming parameter as free parameters to be fit. When fewer measurements were available, fewer parameters were fit. Parameters that could not be fit were set to an assumed value as described in the associated reference publications. Assumed values varied by population based on the typical value for that parameter for that population, as determined for objects where more bands were available. The majority of fits are based on single-frame detections. For the remainder, a flag of 'S' indicates that the fit is based on a co-moving stack of the predicted positions of the object in the NEOWISE data. For stacks, positions were computed using the IPAC Moving Object Search Tool (MOST; http://irsa.ipac.caltech.edu/applications/MOST/), and the resulting thumbnails were stacked using the Image Co-addition with Optional Resolution Enhancement routine (ICORE; Masci 2013). Extraction of photometry for each stack is described in the publication associated with the fit. As this is a different photometric measurement method than the standard PSF-fit photometry archived in the single-frame detection catalog, fits based on stacked data may include additional systematic uncertainties. The formal designation of each object (asteroid number, comet number, or satellite number) is also provided in each line of the tables. The tables include the provisional designation for an object where available, MPC packed format names (for comparison with the tables published in the referenced articles), absolute magnitude (H) and phase parameter (G) from the H-G photometric system (Bowell, et al., 1989), mean Julian Date of the observations used for the fit, number of detections in each band used for fitting, and a reference code that is described in the "references" table. The listed H and G are the measured values at the time of the original publication that were used as input to the thermal model. Objects that were detected at different epochs (and therefore different viewing geometries) will have multiple entries in a table. Fits for each epoch were computed independently; the individual publications describe the criteria for splitting observations into separate epochs. Fits from multiple epochs are included to give users an indication of whether an object is more or less likely to be round. All images obtained by the NEOWISE survey were processed using the standard WISE Scan-Frame Pipeline that includes photometric calibration and source extraction based on point spread function (PSF) fitting. The pipeline is described in the Explanatory Supplement to each WISE and NEOWISE data release (Cutri, et al., 2012; 2015) that is hosted with the data at the NASA/IPAC Infrared Science Archive. Preliminary analysis of fitted physical properties was conducted by the NEOWISE team to describe and validate the data set. In addition to the analyses conducted in the papers presenting the fits, other analyses comparing the NEOWISE physical properties to external data sets include: -Discussion of the thermal modeling routine and comparison with radar and occultation data (Mainzer et al. 2011a) -Comparison of NEOWISE physical property fits to those from IRAS (Mainzer et al. 2011b) -Comparison of NEOWISE physical properties to spectral taxonomic classifications, including albedo distributions of each taxonomic class (Mainzer et al. 2011c) -Comparison of NEOWISE physical properties to taxonomic classifications based on Sloan Digital Sky Survey colors (Mainzer et al. 2012) -Comparison of NEOWISE-derived albedos with asteroid polarimetric properties (Masiero et al. 2012) -Analysis of the accuracy of asteroid diameter determinations using the albedo distributions of Main Belt families (Masiero et al. 2018) Examples of comparisons by external teams to other data sets or independent fits of the NEOWISE data include: -Comparison of B-type asteroid physical properties from an independent thermal model to the NEOWISE values (Ali-Lagoa et al., 2013) -Comparison of infrared-derived diameters from IRAS, AKARI, and NEOWISE (Usui et al. 2014) -Comparison of sizes found via detailed thermophysical models to NEATM-based sizes published by NEOWISE (Hanus et al., 2018) -Comparison of updated fits of the AKARI data to NEOWISE physical properties (Ali-Lagoa et al., 2018) References -------------- Ali-Lagoa, V., de Leon, J., Licandro, J., et al., 2013, "Physical properties of B-type asteroids from WISE data", A&A, 554, A71. Ali-Lagoa, V., Muller, T.G., Usui, F., Hasegawa, S., 2018, "The AKARI IRC asteroid flux catalogue: updated diameters and albedos ", A&A, 612, A85. Bowell, E., Hapke, B., Domingue, D., et al., 1989, "Application of photometric models to asteroids", Asteroids II, University of Arizona Press, 524. Cutri, R.M., Wright, E., Conrow, T., et al., 2012, "Explanatory Supplement to the WISE All-Sky Data Release Products". Cutri, R.M., Mainzer, A., Conrow, T., et al., 2015, "Explanatory Supplement to the NEOWISE Data Release Products". Hanus, J., Delbo, M., Durech, J., Ali-Lagoa, V., 2018, "Thermophysical modeling of main-belt asteroids from WISE thermal data", Icarus, 309, 297. Harris, A.W., 1998, "A Thermal Model for Near-Earth Asteroids", Icarus 131, 291. Lebofsky, L.A. & Spencer, J.R., 1989, "Radiometry and a thermal modeling of asteroids", Asteroids II, University of Arizona Press, 128. Mainzer, A., Grav, T., Masiero, J., et al., 2011a, "Thermal Model Calibration for Minor Planets Observed with Wide-field Infrared Survey Explorer/NEOWISE", ApJ, 736, 100. Mainzer, A., Grav, T., Masiero, J., et al., 2011b, "Thermal Model Calibration for Minor Planets Observed with WISE/NEOWISE: Comparison with Infrared Astronomical Satellite", ApJL, 737, 9. Mainzer, A., Grav, T., Masiero, J., et al., 2011c, "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results", ApJ, 741, 90. Mainzer, A., Masiero, J., Grav, T., et al., 2012, "NEOWISE Studies of Asteroids with Sloan Photometry: Preliminary Results", ApJ, 745, 7. Masci, F., 2013, "ICORE: Image Co-addition with Optional Resolution Enhancement", arXiv:1301.2718. Masiero, J., Mainzer, A., Grav, T., et al., 2012 "A Revised Asteroid Polarization-Albedo Relationship Using WISE/NEOWISE Data", ApJ, 749, 104. Masiero, J., Mainzer, A., Wright, E., 2018, "A Family-Based Method of Quantifying NEOWISE diameter errors", AJ, 156, 62. Usui, F., Hasegawa, S., Ishiguro, M., et al., 2014, "A comparative study of asteroid surveys: IRAS, AKARI, and WISE", PASJ, 66, 56. Caveats to the data user ======================== The quality of underlying photometric data is described in the WISE Explanatory Supplement documentation (Cutri et al., 2012; 2015). The quoted error bars for fitted physical properties represent statistical uncertainties propagated from the measured data and the assumed error bars on the absolute magnitudes (denoted H) and phase curve slope parameter (denoted G) drawn from the Minor Planet Center. As discussed in Mainzer et al. (2011b), there are additional minimum systematic errors on diameters computed from WISE observations that are ???10% 1-sigma for the ensemble of objects, subject to the assumption that spherical effective diameters can be computed for non-spherical shapes. This uncertainty propagates to a ~20% relative uncertainty in the albedos, subject to the assumption that the measurements of the H and G photometric parameters are accurate. These should be regarded as minimum errors in cases of good signal-to-noise detections when the beaming parameter and the infrared albedo can be fitted. It should also be noted that these error estimates apply only to objects as distant as Saturn. Objects observed by WISE at greater distances (and therefore lower temperatures) may be subject to additional errors. Most objects have ~10 detections spaced roughly evenly over 36 hours; thus, averaging over the rotational periods of many objects provides a robust measurement of the effective spherical diameter. However, the diameters could be less accurately constrained for objects with fewer detections, with spin axes near the line of sight, or with rotation periods related by a low integer ratio to the WISE satellite's orbital period (resulting in non-random, aliased samples of the light curve). Fits of objects at different epochs can mitigate some, but not all, of this uncertainty. Objects indicated with the 'S' stacked flag are based on fluxes derived from image co-adds that are co-moving with the object's predicted position and may have larger systematic uncertainties (e.g. Bauer et al., 2013). The objects presented here are moving objects with changing orbits. Orbit changes are both natural, due to perturbations, and caused by improved observational constraints, and thus can change dramatically in some cases. All fits were performed using the MPC-published orbit at the time the source papers were written; fits have not been updated based on changing orbits for this compilation. In 2011, a software bug was identified in the NEOWISE thermal modeling software; the net effect of this bug was to vary some of the diameters by a few percent on average. The magnitude of the shifts was small and below the quoted minimum systematic uncertainty in diameter that results from using the NEATM, and thus does not materially change the conclusions of the affected papers. The effect of the bug in general is smaller than the effects of other sources of uncertainty such as incomplete coverage of light curve amplitudes. This bug affects fits done before July 2011 when it was fixed. Reprocessing of the affected fits is currently being undertaken. Readers are advised to consult Wright et al. (2018) for details. For many Main Belt objects without optical followup, an artificial H magnitude is included in the MPC orbit catalog. These values originated with a request from the MPC that NEOWISE discoveries include a guess of the apparent visible magnitude to provide guidance for followup observers. While the majority of NEOs received later followup and this artificial magnitude was subsequently ignored by the MPC for calculations of the H absolute magnitude, for many MBAs this magnitude has persisted in the observation catalog, and thus has resulted in a published H magnitude that is not constrained by optical observation. As these objects tend to have short-arc orbits, and thus uncertain heliocentric and geocentric distances at the time of observation, diameter fits should be considered to be of lower confidence and albedo fits should not be used. These can be easily identified by users as they will only have observations from NEOWISE (observatory code C51) in the MPC observation database. See Masiero et al. (2011) and Grav et al. (2011) for further discussion of the impact of arc length on fit quality. References: Bauer, J.M., Grav, T., Blauvelt, E., et al., 2013, "Centaurs and Scattered Disk Objects in the Thermal Infrared: Analysis of WISE/NEOWISE Observations", ApJ, 773, 22. Cutri, R.M., Wright, E., Conrow, T., et al., 2012, "Explanatory Supplement to the WISE All-Sky Data Release Products". Cutri, R.M., Mainzer, A., Conrow, T., et al., 2015, "Explanatory Supplement to the NEOWISE Data Release Products". Grav, T., Mainzer, A., Bauer, J., et al., 2011, "WISE/NEOWISE Observations of Jovian Trojans: Preliminary Results", ApJ, 742, 40. Mainzer, A., Grav, T., Masiero, J., et al., 2011a, "Thermal Model Calibration for Minor Planets Observed with Wide-field Infrared Survey Explorer/NEOWISE", ApJ, 736, 100. Mainzer, A., Grav, T., Masiero, J., et al., 2011b, "Thermal Model Calibration for Minor Planets Observed with Wide-field Infrared Survey Explorer/NEOWISE", ApJ, 736, 100. Masiero, J., Mainzer, A., Grav, T., et al., 2011, "Main Belt Asteroids with WISE/NEOWISE. I. Preliminary Albedos and Diameters", ApJ, 741, 68. Wright, E., Mainzer A., Masiero, J., Grav, T., Cutri, R., Bauer, J., 2018, "Response to 'An empirical examination of WISE/NEOWISE asteroid analysis and results'", arXiv:1811.01454. Caveats to the data user ======================== The quality of underlying photometric data is described in the WISE Explanatory Supplement documentation (Cutri et al., 2012; 2015). The quoted error bars for fitted physical properties represent statistical uncertainties propagated from the measured data and the assumed error bars on the absolute magnitudes (denoted H) and phase curve slope parameter (denoted G) drawn from the Minor Planet Center. As discussed in Mainzer et al. (2011b), there are additional minimum systematic errors on diameters computed from WISE observations that are [INVALID_PDS_CHARACTER]10% 1-sigma for the ensemble of objects, subject to the assumption that spherical effective diameters can be computed for non-spherical shapes. This uncertainty propagates to a ~20% relative uncertainty in the albedos, subject to the assumption that the measurements of the H and G photometric parameters are accurate. These should be regarded as minimum errors in cases of good signal-to-noise detections when the beaming parameter and the infrared albedo can be fitted. It should also be noted that these error estimates apply only to objects as distant as Saturn. Objects observed by WISE at greater distances (and therefore lower temperatures) may be subject to additional errors. Most objects have ~10 detections spaced roughly evenly over 36 hours; thus, averaging over the rotational periods of many objects provides a robust measurement of the effective spherical diameter. However, the diameters could be less accurately constrained for objects with fewer detections, with spin axes near the line of sight, or with rotation periods related by a low integer ratio to the WISE satellite's orbital period (resulting in non-random, aliased samples of the light curve). Fits of objects at different epochs can mitigate some, but not all, of this uncertainty. Objects indicated with the 'S' stacked flag are based on fluxes derived from image co-adds that are co-moving with the object's predicted position and may have larger systematic uncertainties (e.g. Bauer et al., 2013). The objects presented here are moving objects with changing orbits. Orbit changes are both natural, due to perturbations, and caused by improved observational constraints, and thus can change dramatically in some cases. All fits were performed using the MPC-published orbit at the time the source papers were written; fits have not been updated based on changing orbits for this compilation. In 2011, a software bug was identified in the NEOWISE thermal modeling software; the net effect of this bug was to vary some of the diameters by a few percent on average. The magnitude of the shifts was small and below the quoted minimum systematic uncertainty in diameter that results from using the NEATM, and thus does not materially change the conclusions of the affected papers. The effect of the bug in general is smaller than the effects of other sources of uncertainty such as incomplete coverage of light curve amplitudes. This bug affects fits done before July 2011 when it was fixed. Reprocessing of the affected fits is currently being undertaken. Readers are advised to consult Wright et al. (2018) for details. For many Main Belt objects without optical followup, an artificial H magnitude is included in the MPC orbit catalog. These values originated with a request from the MPC that NEOWISE discoveries include a guess of the apparent visible magnitude to provide guidance for followup observers. While the majority of NEOs received later followup and this artificial magnitude was subsequently ignored by the MPC for calculations of the H absolute magnitude, for many MBAs this magnitude has persisted in the observation catalog, and thus has resulted in a published H magnitude that is not constrained by optical observation. As these objects tend to have short-arc orbits, and thus uncertain heliocentric and geocentric distances at the time of observation, diameter fits should be considered to be of lower confidence and albedo fits should not be used. These can be easily identified by users as they will only have observations from NEOWISE (observatory code C51) in the MPC observation database. See Masiero et al. (2011) and Grav et al. (2011) for further discussion of the impact of arc length on fit quality. References: Bauer, J.M., Grav, T., Blauvelt, E., et al., 2013, "Centaurs and Scattered Disk Objects in the Thermal Infrared: Analysis of WISE/NEOWISE Observations", ApJ, 773, 22. Cutri, R.M., Wright, E., Conrow, T., et al., 2012, "Explanatory Supplement to the WISE All-Sky Data Release Products". Cutri, R.M., Mainzer, A., Conrow, T., et al., 2015, "Explanatory Supplement to the NEOWISE Data Release Products". Grav, T., Mainzer, A., Bauer, J., et al., 2011, "WISE/NEOWISE Observations of Jovian Trojans: Preliminary Results", ApJ, 742, 40. Mainzer, A., Grav, T., Masiero, J., et al., 2011a, "Thermal Model Calibration for Minor Planets Observed with Wide-field Infrared Survey Explorer/NEOWISE", ApJ, 736, 100. Mainzer, A., Grav, T., Masiero, J., et al., 2011b, "Thermal Model Calibration for Minor Planets Observed with Wide-field Infrared Survey Explorer/NEOWISE", ApJ, 736, 100. Masiero, J., Mainzer, A., Grav, T., et al., 2011, "Main Belt Asteroids with WISE/NEOWISE. I. Preliminary Albedos and Diameters", ApJ, 741, 68. Wright, E., Mainzer A., Masiero, J., Grav, T., Cutri, R., Bauer, J., 2018, "Response to 'An empirical examination of WISE/NEOWISE asteroid analysis and results'", arXiv:1811.01454.