ASTEROID LIGHT CURVES from the PALOMAR TRANSIENT FACTORY SURVEY: ROTATION PERIODS and PHASE FUNCTIONS from SPARSE PHOTOMETRY

Adam Waszczak, Chan Kao Chang, Eran O. Ofek, Russ Laher, Frank Masci, David Levitan, Jason Surace, Yu Chi Cheng, Wing Huen Ip, Daisuke Kinoshita, George Helou, Thomas A. Prince, Shrinivas Kulkarni

Research output: Contribution to journalArticlepeer-review

40 Scopus citations

Abstract

We fit 54,296 sparsely sampled asteroid light curves in the Palomar Transient Factory survey to a combined rotation plus phase-function 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 light-curve attributes. Using the 805-asteroid ground-truth 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 light-curve fits indicates a 4% contamination in these "reliable" periods. For 3902 light curves with sufficient phase-angle coverage and either a reliable fit period or low amplitude, we examine the distribution of several phase-function parameters, none of which are bimodal though all correlate with the bond albedo and with visible-band colors. Comparing the theoretical maximal spin rate of a fluid body with our amplitude versus spin-rate distribution suggests that, if held together only by self-gravity, 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 5-20 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 apparent-magnitude residuals) to those of the Minor Planet Center's nominal (G = 0.15, rotation-neglecting) model; our phase-function plus Fourier-series fitting reduces asteroid photometric rms scatter by a factor of ∼3.

Original languageEnglish
Article number75
JournalAstronomical Journal
Volume150
Issue number3
DOIs
StatePublished - 1 Sep 2015

Keywords

  • asteroids: general-surveys
  • minor planets

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