Description of the NEOWISE Diameters and Albedos bundle V2.0
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Bundle Generation Date: 2021-04-15
Peer Review: NEOWISE Review
Discipline node: Small Bodies Node


Content description for the NEOWISE Diameters and Albedos bundle
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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.