Asteroid Light Curves from the Palomar Transient Factory Survey: Rotation Periods and Phase Functions from Sparse Photometry
Abstract
We fit 54,296 sparsely sampled asteroid light curves in the Palomar Transient Factory survey to a combined rotation plus phasefunction model. Each light curve consists of 20 or more observations acquired in a single opposition. Using 805 asteroids in our sample that have reference periods in the literature, we find that the reliability of our fitted periods is a complicated function of the period, amplitude, apparent magnitude, and other lightcurve attributes. Using the 805asteroid groundtruth sample, we train an automated classifier to estimate (along with manual inspection) the validity of the remaining ̃53,000 fitted periods. By this method we find that 9033 of our light curves (of ̃8300 unique asteroids) have “reliable” periods. Subsequent consideration of asteroids with multiple lightcurve fits indicates a 4% contamination in these “reliable” periods. For 3902 light curves with sufficient phaseangle coverage and either a reliable fit period or low amplitude, we examine the distribution of several phasefunction parameters, none of which are bimodal though all correlate with the bond albedo and with visibleband colors. Comparing the theoretical maximal spin rate of a fluid body with our amplitude versus spinrate distribution suggests that, if held together only by selfgravity, most asteroids are in general less dense than ̃2 g cm^{3}, while C types have a lower limit of between 1 and 2 g cm^{3}. These results are in agreement with previous density estimates. For 520 km diameters, S types rotate faster and have lower amplitudes than C types. If both populations share the same angular momentum, this may indicate the two types’ differing ability to deform under rotational stress. Lastly, we compare our absolute magnitudes (and apparentmagnitude residuals) to those of the Minor Planet Center’s nominal (G = 0.15, rotationneglecting) model; our phasefunction plus Fourierseries fitting reduces asteroid photometric rms scatter by a factor of ̃3.
 Publication:

The Astronomical Journal
 Pub Date:
 September 2015
 DOI:
 10.1088/00046256/150/3/75
 arXiv:
 arXiv:1504.04041
 Bibcode:
 2015AJ....150...75W
 Keywords:

 minor planets;
 asteroids: general;
 surveys;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 35 pages, 29 figures. Accepted 15Apr2015 to The Astronomical Journal (AJ). Supplementary material including ASCII data tables will be available through the publishing journal's website