ASTEROIDS OBSERVED FROM CS3: 2016 OCTOBER - DECEMBER

Abstract

CCD photometric observations of eight asteroids were obtained from the Center for Solar System Studies from 2016 October to December.

The Center for Solar System Studies “Trojan Station” (CS3, MPC U81) has two telescopes which are normally used in program asteroid family studies. When those targets are too dim to continue observations during bright moon times, brighter targets away from the Moon suitable for future shape modeling studies are selected to keep the telescopes operating. Eight asteroids, usually with known short rotational periods were selected for observations in the week nearest the Full Moon.

All images were made with a 0.4-m or a 0.35-m SCT using an FLI ML-Proline 1001E or FLI ML-Microline 1001E CCD camera. Images were unbinned with no filter and had master flats and darks applied. Image processing, measurement, and period analysis were done using MPO Canopus (Bdw Publishing), which incorporates the Fourier analysis algorithm (FALC) developed by Harris (Harris et al., 1989). Night-to-night calibration of the data (generally < ±0.05 mag) was done using field stars converted to approximate Johnson V magnitudes based on 2MASS J-K colors (Warner 2007). The Comp Star Selector feature in MPO Canopus was used to limit the comparison stars to near solar color.

In the lightcurve plots, the “Reduced Magnitude” is Johnson V corrected to a unity distance by applying −5*log (rΔ) to the measured sky magnitudes with r and Δ being, respectively, the Sun-asteroid and the Earth-asteroid distances in AU. The magnitudes were normalized to the phase angle given in parentheses using G = 0.15. The X-axis rotational phase ranges from −0.05 to 1.05.

The amplitude indicated in the plots is the amplitude of the Fourier model curve and not necessarily the adopted amplitude of the lightcurve.

2045 Peking

This Vestoid was selected because it is bright. With no previously reported results in the asteroid lightcurve database (LCDB; Warner et al., 2009), it was suspected there are observations residing in ‘dusty file cabinets’. Although this phrase is quickly becoming an anachronism. Suspicions were confirmed when after a few nights of observations, it became apparent that Peking has a long rotational period. Still, most of these long periods have been found for the brighter asteroids. The mystery has been partially solved when Peking started showing clear signs of tumbling. Specifically, observations on 12 and 14 November deviate dramatically from the best fit Fourier model curve. As is the case with most long period tumbling asteroids, sufficient observations could not be obtained to determine a secondary frequency.

2937 Gibbs

Behrend (2005) reported rotational periods of 3.06 and 3.06153 h. The former result is from a single night. The more precise period is a denser dataset but contains a number of noisy outliers which might skew the result. Our result is in good agreement with those observations from 2005.

5579 Uhlherr

We have studied this Hungaria in the past as part of a Hungaria family pole position study. Warner (2009b, 2012, 2015) previously found a period near of 4.5 h. Our result this year is in agreement with the earlier findings.

6618 Jimsimons

This asteroid has also been well studied in the past as part of the Hungaria family pole position study. Warner (2009a, 2012, 2014) observed it three times finding rotational periods near 4.14 h. Our period is in good agreement with those results.

7778 Markrobinson

Behrend (2008) and Warner (2009a) both observed this Mars Crosser in 2008 June, both finding a rotational period near 7.23 h. This result is in good agreement.

(16143) 1999 XK142

Using sparse data from the Palomar Transient Factory, Waszczak et al. (2015) and Chang et al. (2015) reported periods near 6.4 h. Our dense lightcurve this year confirms the results from these sparse data surveys.

(25320) 1999 CP15

There were no previously reported rotation periods of this long period Hungaria in the asteroid lightcurve database (LCDB; Warner et al., 2009).

(204517) 2005 WL21

Using sparse data from the Palomar Transient Factory, Waszczak et al. (2015) reported a rotational period of 3.1024 h. Our denser lightcurve confirms this result.

Table I.

Observing circumstances and results. Pts is the number of data points. The phase angle values are for the first and last date. LPAB and BPAB are the approximate phase angle bisector longitude and latitude at mid-date range (see Harris et al., 1984). Grp is the asteroid family/group (Warner et al., 2009c).

Number	Name	2016 mm/dd	Pts	Phase	LPAB	BPAB	Period(h)	P.E.	Amp.	A.E.	Grp
2045	Peking	11/10–11/25	615	17.8,12.8	89	8	82.4	1.0			V
2937	Gibbs	12/17–12/19	161	8.7,7.9	103	−7	3.189	0.003	0.26	0.03	MC
5579	Uhlherr	10/16–10/19	119	25.6,24.6	63	−17	4.48	0.01	0.42	0.03	H
6618	Jimsimons	11/17–11/18	90	32.1,32.0	109	27	4.171	0.012	0.12	0.02	H
7778	Markrobinson	11/11–11/14	156	15.2,14.1	79	−12	7.218	0.002	0.66	0.02	MC
16143	1999 XK142	12/17–12/19	235	5.1,4.7	89	9	6.400	0.001	1.02	0.02	MC
25320	1999 CP15	10/11–10/19	477	8.9,11.7	15	14	55.25	0.06	0.71	0.03	H
204517	2005 EL21	11/15–11/17	177	13.2,14.0	44	−12	3.108	0.002	0.22	0.03	MC