[Paper Review] Comparison of Asteroids Observed in the SDSS with a Catalog of Known Asteroids

Mario Jurić, Željko Ivezić+3 more|arXiv (Cornell University)|Feb 25, 2002

Astro and Planetary Science60 citations

TL;DR

This paper cross-matches 18,000 asteroids detected by the Sloan Digital Sky Survey (SDSS) with known asteroid catalogs, identifying 2,641 unique matches with accurate multi-color photometry and orbital elements. It reveals a 0.4 mag systematic offset in SDSS-derived V magnitudes compared to catalog predictions—worse for red asteroids—leading to a 1.7× overestimate of bright asteroid counts, and confirms strong color segregation in asteroid families, with extreme i*-z* colors reliably identifying Vesta family members.

ABSTRACT

We positionally correlate asteroids from existing catalogs with a sample of $\about$18,000 asteroids detected by the Sloan Digital Sky Survey (SDSS, Ivezić {\em et al.} 2001). We find 2641 unique matches, which represent the largest sample of asteroids with both accurate multi-color photometry and known orbital parameters. The matched objects are predominantly bright, and demonstrate that the SDSS photometric pipeline recovers \about90% of the known asteroids in the observed region. For the recovered asteroids we find a large offset (\about 0.4 mag) between Johnson V magnitudes derived from SDSS photometry and the predicted catalog-based visual magnitudes. This offset varies with the asteroid color from 0.34 mag for blue asteroids to 0.44 mag for red asteroids, and is probably caused by the use of unfiltered CCD observations in the majority of recent asteroid surveys. This systematic photometric error leads to an overestimate of the number of asteroids brighter than a given absolute magnitude limit by a factor of \about 1.7. The distribution of the matched asteroids in orbital parameter space indicates strong color segregation. We confirm that some families are dominated by a single asteroid type (e.g. the Koronis family by red asteroids and the Themis family by blue asteroids), while others appear to be a mixture of blue and red objects (e.g. the Nysa/Polana family). Asteroids with the bluest \iz colors, which can be associated with the Vesta family, show particularly striking localization in orbital parameter space.

Motivation & Objective

• To assess the completeness and accuracy of asteroid detection in the SDSS imaging survey by cross-matching with known asteroid catalogs.
• To quantify systematic photometric offsets between SDSS-derived magnitudes and catalog-based visual magnitudes.
• To investigate color segregation in asteroid families using SDSS five-band photometry.
• To evaluate the reliability of SDSS photometric pipeline in identifying moving objects and its implications for asteroid population studies.

Proposed method

• Positionally cross-correlated SDSS-detected moving objects with the ASTORB catalog of known asteroids using astrometric positions.
• Calculated SDSS-based Johnson V magnitudes from five-band photometry (u*, g*, r*, i*, z*) using standard transformations.
• Compared SDSS-derived V magnitudes with catalog-based visual magnitudes to identify systematic offsets.
• Analyzed orbital parameter space (a', e', sin(i')) for asteroids with extreme i*-z* colors to test for clustering in the Vesta family region.
• Used statistical analysis to assess completeness of asteroid detection and contamination levels in the SDSS moving object pipeline.
• Applied taxonomic classification (J/V types) to high-redshift objects based on i*-z* color to validate Vesta family membership.

Experimental results

Research questions

• RQ1 What fraction of known asteroids in the observed SDSS region are recovered by the SDSS photometric pipeline, and what is the contamination rate?
• RQ2 Why does the SDSS magnitude scale systematically differ from catalog-based visual magnitudes, and how does this vary with asteroid color?
• RQ3 Can i*-z* color in SDSS photometry reliably identify members of the Vesta family in orbital element space?
• RQ4 How do asteroid families differ in their color composition, and is there a strong segregation between blue and red asteroids?
• RQ5 To what extent does the photometric offset affect the normalization of asteroid population counts in surveys like SDSS?

Key findings

• The SDSS photometric pipeline recovers approximately 90% of known asteroids in the observed region, with a contamination level of only a few percent.
• A systematic offset of ~0.4 mag exists between SDSS-derived V magnitudes and catalog-based visual magnitudes, increasing from 0.34 mag for blue asteroids to 0.44 mag for red asteroids.
• This photometric offset leads to an overestimation of the number of asteroids brighter than a given absolute magnitude limit by a factor of ~1.7.
• The distribution of matched asteroids in orbital parameter space shows strong color segregation: the Koronis family is dominated by red asteroids, the Themis family by blue ones, and the Nysa/Polana family is a mix.
• A high fraction (99 out of 131) of asteroids with i*-z* < -0.25 are clustered in the core and tail regions of the Vesta family orbital space, confirming that this color index reliably identifies Vesta family members.
• The SDSS five-band photometry enables robust identification of Vesta family asteroids via i*-z* color, providing a powerful tool for compositional and dynamical studies of asteroid families.