J/AJ/150/75 Asteroid light curves from PTF survey (Waszczak+, 2015)
Asteroid light curves from the Palomar transient factory survey: rotation
periods and phase functions from sparse photometry.
Waszczak A., Chang C.-K., Ofek E.O., Laher R., Masci F., Levitan D.,
Surace J., Cheng Y.-C., Ip W.-H., Kinoshita D., Helou G., Prince T.A.,
Kulkarni S.
<Astron. J., 150, 75 (2015)>
=2015AJ....150...75W 2015AJ....150...75W (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Minor planets ; Magnitudes ; Magnitudes, absolute
Keywords: minor planets, asteroids: general - surveys
Abstract:
We fit 54296 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
∼53000 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 ∼2g/cm3,
while C types have a lower limit of between 1 and 2g/cm3. These
results are in agreement with previous density estimates. For 5-20km
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.
Description:
The Palomar Transient Factory (PTF) is a synoptic survey designed
primarily to discover extragalactic transients (Law et al.,
2009PASP..121.1395L 2009PASP..121.1395L; Rau et al., 2009PASP..121.1334R 2009PASP..121.1334R).
The PTF camera, mounted on Palomar Observatory's 1.2m Oschin Schmidt
Telescope, uses 11 CCDs (each 2K*4K) to image 7.3deg2 of sky at a
time at 1.0''/pixel resolution. Most exposures (∼85%) use a Mould-R
filter (very similar to the SDSS-r filter; see Ofek et al.
2012PASP..124...62O 2012PASP..124...62O for its transmission curve). The remaining
broadband images acquired use a Gunn g-band filter.
Science operations began in 2009 March. Median seeing is 2'' with a
limiting magnitude R∼20.5 (for 5σ point-source detections),
while dark conditions routinely yield R∼21.0 (Law et al.,
2010SPIE.7735E..0ZL).
The PTF survey is ongoing and expected to continue through mid-2016.
In January 2013 the PTF project formally entered a second phase called
the intermediate PTF ("iPTF"; Kulkarni, 2013ATel.4807....1K 2013ATel.4807....1K). In this
paper we simply use "PTF" to mean the entire survey, from 2009 through
the present (2015).
In terms of content, we search all PTF (R and g-band) data from 2009
March 01 through 2014 July 18 for all numbered asteroids as of 2014
July 12 (401810 objects). We exclude unnumbered objects as the
positional uncertainty of these objects can be very large, and as they
tend to be very faint, their light curves will not in general be of
high quality.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table4.dat 241 9663 Parameters describing Palomar Transient Factory
(PTF) light curves with a reliable period or
phase function
table5.dat 89 496933 Individual Palomar Transient Factory (PTF)
photometric observations in each light curve
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See also:
B/astorb : Orbits of Minor Planets (Bowell+ 2014)
J/ApJ/759/49 : Jovian Trojan asteroids with WISE/NEOWISE: taxonomy
(Grav+, 2012)
J/ApJ/741/68 : Main Belt asteroids with WISE/NEOWISE. I. (Masiero+, 2011)
J/ApJ/740/65 : VLA search for 5GHz radio transients (Ofek+, 2011)
J/AJ/142/60 : Palomar Transient Factory Orion Project (Van Eyken+, 2011)
http://ptf.caltech.edu/ : Palomar Transient Factory survey
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- LCNum [1/9663] Light-curve identification number (1)
6- 11 I6 --- Ast [99/400878] Asteroid number (IAU designation)
13- 14 I2 yr Year [9/14] Last two digits of opposition year
16 I1 --- Flt [1/2] Photometric band (1=Gunn-g, 2=Mould-R)
18- 20 I3 --- Nobs [20/499] Number of observations in the
light-curve
22- 26 F5.2 mag mag [13.2/20.4] Median apparent magnitude (2)
28- 37 F10.5 d MJD0 Modified Julian Date (MJD) time of first
observation
39- 48 F10.5 d MJD1 MJD time of final observation
50- 54 F5.2 deg amin [0/32] Minimum-observed phase angle
(αmin)
56- 60 F5.2 deg amax [0.50/55.3] Maximum-observed phase angle
(αmax)
62- 63 I2 --- Nbin [1/13] Number of sampled phase-angle bins of
3-deg width
65- 68 F4.2 --- Q1 [0/1] Reliability score from machine
classifier (from 0=bad to 1=good)
70 I1 --- Q2 [0/1] Manually-assigned reliability flag
(0=bad, 1=good)
72 I1 --- Q3 [0/1] Period reliability flag (0=bad, 1=good)
74- 79 F6.3 mag HMag [7.6/18.9] Absolute magnitude from G12 fit
81- 85 F5.3 mag e_HMag [0/0.05] Uncertainty in HMag
87- 91 F5.3 --- G12 [0/1] Phase-function parameter G12 (3)
93- 98 F6.3 --- e_G12 [-1/1] Uncertainty in G12 (4)
100-105 F6.3 --- G [-0.3/0.7]? Phase-function parameter G (5)
107-113 F7.4 mag/deg beta [-1.2/5]? Phase-function parameter β (6)
115-119 F5.3 mag C [0/0.8]? Phase-function parameter C (amplitude of
the opposition surge) (6)
121-124 F4.2 mag Amp [0.02/1.31] Amplitude from G12 fit
126-134 F9.4 h Per1 [2/1918] Period from G12 fit
136-144 F9.4 h e_Per1 [0/2717] Uncertainty in Per1
146-152 F7.4 mag A11 [-0.2/0.2] Fourier coefficient A1,1 from G12 fit
154-160 F7.4 mag A12 [-0.3/0.2] Fourier coefficient A1,2 from G12 fit
162-168 F7.4 mag A21 [-0.6/0.6] Fourier coefficient A2,1 from G12 fit
170-176 F7.4 mag A22 [-0.6/0.6] Fourier coefficient A2,2 from G12 fit
178-181 F4.2 --- Rpeak [0/1] Ratio of two peak heights in folded
rotation curve (7)
183-186 F4.2 --- chi2 [0.34/3] Reduced chi-squared of the fit
(χ2red)
188-192 F5.3 mag cosmic [0/0.077] The "cosmic error" (8)
194-198 F5.3 mag rms [0/0.09] Root-mean-square residual of
observations with respect to the fit
200-206 F7.3 h Per2 [1/380]? Reference period (9)
208-213 F6.2 km Diam [0.9/133]? Diameter derived from thermal
infrared (IR) data (10)
215-218 F4.2 km e_Diam [0/4.25]? Uncertainty in Diam
220-224 F5.3 --- Alb [0/0.2]? Bond albedo (11)
226-231 F6.4 --- e_Alb [0/0.0363]? Uncertainty in bond albedo
233-236 F4.2 --- CI [0/1]? Color-based taxonomic index
(0=C-type asteroid, 1=S-type asteroid; See
Section 6 for details)
238-241 F4.2 --- PI [0/1]? Photometry-based taxonomic index
(0=C-type, 1=S-type; See Section 6.3.1 for
details)
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Note (1): Identification number labels individual observations in Table5.
Note (2): In this work we model an asteroid's apparent visual magnitude V (log
flux) as: V=H+δ+5log10(rΔ)-2.5log10[Φ(α)],
(Eq.(1) in the paper), where H is the absolute magnitude (a constant),
δ is a periodic variability term due to rotation (e.g., if the object
is spinning and has some asymmetry in shape or albedo), r and Δ are
the heliocentric and geocentric distances (in AU), and Φ=Φ(α)
is the phase function, which varies with the solar phase angle α
(the Sun-asteroid-Earth angle). We obtain three separate fits for each
light curve, each using a different phase function (Φ) and allowing for
unique solutions for H and δ in Equation (1). The three
phase-function models are:
1. The two-parameter model of Shevchenko (1997SoSyR..31..219S 1997SoSyR..31..219S);
2. The one-parameter G model (Bowell et al., 1989aste.conf..524B);
3. The one-parameter G12 model (Muinonen et al., 2010Icar..209..542M 2010Icar..209..542M).
Note (3): We use the single-parameter G12 form of the Muinonen et al.
(2010Icar..209..542M 2010Icar..209..542M) model (see Section 3.2.3 in the paper).
Note (4): Set to -1 if larger than the interval tested in grid search.
Note (5): Use of the Lumme-Bowell phase function Φ (Bowell et al.,
1989aste.conf..524B) in our light-curve model (Equation (1))
introduces a second nonlinear parameter (G) into the model, the period P
being the other nonlinear parameter (see Section 3.2.2).
Note (6): Shevchenko (1997SoSyR..31..219S 1997SoSyR..31..219S) introduced a phase function dependent
on two parameters; in terms of Equation (1) the model is:
-2.5log10[Φ(α)]=βα-C(α/1+α) (Eq.(7) in
the paper).
Note (7): Set to 0 if there is only one maximum in the folded light-curve.
Note (8): So-named because it encompasses contamination from possible errors (in
all the "cosmos"). See Section 4.1 for details.
Note (9): From http://sbn.psi.edu/pds/.
Note (10): References for the IR diameters are given in the text (Appendix A.2).
Note (11): Bond albedo only computed for objects with reliable G12 and available
diameter.
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- LCNum [1/9663] Light-curve identification number (1)
6- 15 F10.5 d tau [4907/6764] Light-time-corrected observation
epoch (τ)
17- 26 F10.7 AU HDist [1/13.7] Heliocentric distance
28- 37 F10.7 AU GDist [0.2/14.1] Geocentric distance (Δ)
39- 43 F5.2 deg alpha [0/56] Solar phase angle (α)
45- 50 F6.3 mag mag1 [6/26] Apparent magnitude (2)
52- 56 F5.3 mag e_mag1 [0/0.9] Uncertainty in mag1
58- 62 F5.3 mag emag1 [0/0.9] Uncertainty in mag1 with cosmic-error
64- 69 F6.3 mag mag2 [1.6/19.4] Magnitude corrected for distance and
G12 phase function
71- 76 F6.3 mag mag3 [2.4/20.1] Magnitude corrected for distance
and rotation (G12 fit)
78- 83 F6.3 mag Res [-1/1.3] Residual with respect to the G12 fit
85- 89 F5.3 --- Phase [0/1] Rotational phase from 0 to 1 (G12 fit)
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Note (1): Identification number also corresponds to the line number in Table4.
Note (2): Filter/band is specified in Table4.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 14-Oct-2015