ASTEROID LIGHTCURVE ANALYSIS AT CS3-PALMER DIVIDE STATION: 2015 OCTOBER-DECEMBER

Abstract

Lightcurves for 14 main-belt asteroids were obtained at the Center for Solar System Studies-Palmer Divide Station (CS3-PDS) from 2015 October-December.

CCD photometric observations of 14 main-belt asteroids were made at the Center for Solar System Studies-Palmer Divide Station (CS3-PDS) from 2015 October-December. Table I lists the telescope/CCD camera combinations used for the observations. All the cameras use CCD chips from the KAF blue-enhanced family and so have essentially the same response. The pixel scales for the combinations range from 1.24-1.60 arcsec/pixel.

Table I.

List of CS3-PDS telescope/CCD camera combinations.

Desig	Telescope	Camera
Squirt	0.30–m f/6.3 Schmidt–Cass	ML–1001E
Borealis	0.35–m f/9.1 Schmidt–Cass	STL–1001E
Eclipticalis	0.35–m f/9.1 Schmidt–Cass	ML–1001E
Australius	0.35–m f/9.1 Schmidt–Cass	STL–1001E
Zephyr	0.50–m f/8.1 R–C	FLI–1001E

All lightcurve observations were unfiltered since even a clear filter can result in a 0.1-0.3 magnitude loss. The exposure duration varied depending on the asteroid’s brightness and sky motion. Guiding on a field star sometimes resulted in a trailed image for the asteroid.

Measurements were made using MPO Canopus. If necessary, an elliptical aperture with the long axis parallel to the asteroid’s path was used. The Comp Star Selector utility in MPO Canopus found up to five comparison stars of near solar-color for differential photometry. Catalog magnitudes were usually taken from the MPOSC3 catalog, which is based on the 2MASS catalog (http://www.ipac.caltech.edu/2mass) but with magnitudes converted from J-K to BVRI using formulae developed by Warner (2007). The nightly zero points have been found to be consistent to about ± 0.05 mag or better, but on occasion are as large as 0.1 mag. This consistency is critical to analysis of long period and/or tumbling asteroids. Period analysis is also done using MPO Canopus, which implements the FALC algorithm developed by Harris (Harris et al., 1989).

In the plots below, the “Reduced Magnitude” is Johnson V as indicated in the Y-axis title. These are values that have been converted from sky magnitudes to unity distance by applying −5*log (rΔ) to the measured sky magnitudes with r and Δ being, respectively, the Sun-asteroid and Earth-asteroid distances in AU. The magnitudes were normalized to the given phase angle, e.g., alpha(6.5°), using G = 0.15, unless otherwise stated. The X-axis is the rotational phase ranging from −0.05 to 1.05.

If the plot includes an amplitude, e.g., “Amp: 0.65”, this is the amplitude of the Fourier model curve and not necessarily the adopted amplitude for the lightcurve. The value is meant only to be a quick guide.

For the sake of brevity, only some of the previously reported results may be referenced in the discussions on specific asteroids. For a more complete listing, the reader is directed to the asteroid lightcurve database (LCDB; Warner et al., 2009a). The on-line version at http://www.minorplanet.info/lightcurvedatabase.html allows direct queries that can be filtered a number of ways and the results saved to a text file. A set of text files of the main LCDB tables, including the references with bibcodes, is also available for download. Readers are strongly encouraged to obtain, when possible, the original references listed in the LCDB for their work.

16 Psyche.

This well-studied outer main-belt asteroid was observed to tie lightcurve features to those found, if any, with radar and thermal observations made about the same. The period agrees closely with previous results (see references in the LCDB).

4674 Pauling.

This is a known binary (Merline et al., 2004) that was discovered using adaptive optics. The satellite has an orbital period of about 1200 hours and is too faint to be observed by lightcurve photometry alone. The results agree with previous results by the author (Warner, 2006; 2011) and others.

5087 Emel’yanov.

The estimated diameter for this outer main-belt asteroid is 13.3 km, assuming an albedo of p_v = 0.057 and H = 13.1. It was in the same field as a planned NEA asteroid for two nights, but only the first night provided sufficient coverage of a bimodal lightcurve. A search of the half-periods of the likely full period solutions led to adopting a final result of P = 14.5 ± 1.0 h and amplitude A = 0.30 ± 0.03 mag. There were no previous entries in the LCDB for the asteroid.

9165 Raup.

A Hungaria asteroid of about 5 km effective diameter, Raup was observed for the second time by the author, the first time being in 2014 (Warner, 2014). At that time, the period was reported to be 560 h with the possibility of tumbling. The more extended data set in 2015 nearly doubled the period, P = 1320 ± 10 h, and found a slightly larger amplitude of A = 1.34 ± 0.03 mag. If the asteroid is tumbling, it would appear to be a very low level since there were no outward signs in the 2015 lightcurve.

17447 Heindl.

This is the first time that the author observed this Hungaria as part of the on-going project to study this intriguing group of asteroids (see Warner et al., 2009b). There were no previous entries in the LCDB for Heindl.

20936 Nemrut Dagi.

The author first worked this Hungaria as (20936) 4835 T-1 (Warner, 2008). The period was reported to be P = 5.697 h. Observations in 2011 (Warner, 2011b) changed that to P = 3.321 h but with an alternate solution of P = 6.643 h. Skiff (2011) found a similar pair of ambiguous solutions. The results from the 2015 data seem to establish the shorter period with P = 3.2754 h since a fit to the longer period is not reasonable. The 2007 data were re-examined and found to fit P = 3.233 ± 0.002 h, A = 0.05 mag.

(36496) 2000 QK49.

This appears to be the first reported period for 2000 QK49, an inner main-belt asteroid of about 2.8 km effective diameter, assuming p_v = 0.2, H = 15.1. It was in the same field as a planned target on two successive nights. Fortunately, each observing run covered more than a full cycle of the adopted period, which resulted in a secure solution. There were no previous entries in the LCDB.

(49669) 1999 RZ30.

This asteroid was observed as part of the Hungaria observing project (now more than 10 years old). This appears to be the first reported period.

(53115) 1999 AM14.

This middle main-belt asteroid was another target of opportunity, meaning that it was in the same field as a planned target. Only one night’s data were obtained, but the proposed period of P = 4.0 ± 0.1 h seems a reasonable estimate. There were no previous entries in the LCDB.

(135885) 2002 TX49.

Another target of opportunity (in the same field as 9165 Raup), 2002 TX49 is a middle main-belt asteroid of about 2.6 km effective diameter, assuming p_v = 0.1, H = 16.0. Despite data from only one night, the amplitude and phase angle make the period of P ~ 5.29 h more likely correct than not.

(139515) 2001 PD53.

The Hungaria 9165 Raup was a target of opportunity magnet in October. This was one of no less than four such targets in the same field on one or more nights. 2001 PD53 is an outer main-belt asteroid of about 4 km diameter. Given the apparent coverage of more than half a cycle and amplitude, the period of P = 8.3 ± 0.5 h seems to be reliable, though not fully secure. There were no previous entries in the LCDB.

(241339) 2007 VL269.

Another one of 9165 Raup’s entourage in October was this 1.2 km inner main-belt asteroid. There were no previous entries in the LCDB.

(241804) 2001 QW282.

This is a 3 km outer main-belt asteroid with no previous entries in the LCDB.

The period shown in the lightcurve (7.0 ± 0.82 h) is just one of many that fit the data. Assuming a bimodal lightcurve, the best solution is an indefinite one of P ≥ 12 h and A ≥ 0.2 mag.

(249590) 1996 UG2.

This was another target of opportunity. There were no previous entries in the LCDB for the 3.5 km outer main-belt asteroid. With data from two nights, the period is considered mostly, but not completely, secure.

Table II.

Observing circumstances.

Number	Name		2015 mm/dd	Pts	Phase	LPAB	BPAB	Period	P.E.	Amp	A.E.	Group
16	Psyche		11/30–12/26	540	4.5, 4.1, 7.5	77	−4	4.1963	0.0005	0.13	0.01	MB–O
4674	Pauling		11/26–12/01	126	31.5, 31.7	356	15	2.532	0.002	0.13	0.02	H
5087	Emel’yanov		11/01–11/02	128	11.8, 12.1	67	−5	14.5	1	0.3	0.03	MB–O
9165	Raup		08/30–10/19	2907	23.2, 3.3, 11.8	8	−7	1320	10	1.34	0.03	H
17447	Heindl		10/21–10/23	181	3.6, 3.2	29	−5	2.569	0.005	0.18	0.01	H
20936	4835	T–1	0711/06–11/15	161	27.4, 30.2	6	−3	3.233	0.002	0.05	0.01	H
20936	Nemrut Dagi		11/26–12/13	467	27.2, 22.6	107	24	3.2754	0.0005	0.08	0.01	H
36496	2000	QK49	10/09–10/10	146	13.1, 12.5	35	2	5.31	0.01	0.35	0.02	MB–I
49669	1999	RZ30	10/22–10/26	132	15.7, 17.2	10	18	3.119	0.005	0.26	0.03	H
53115	1999	AM14	12/16–12/16	62	4.0	76	2	4.04	0.1	0.16	0.02	MB–M
135885	2002	TX49	10/09–10/09	49	3.9	8	−3	5.3	0.5	0.33		MB–M
139515	2001	PD53	10/09–10/09	77	3.3	8	−3	8.3	0.5	0.63	0.05	MB–O
241339	2007	VL269	10/09–10/09	74	4.6	9	−3	7.7	0.5	0.85	0.05	MB–I
241804	2001	QW282	10/09–10/09	71	15.6	265	−9	>12.		>0.2		MB–O
249590	1996	UG2	10/09–10/10	87	11.1, 10.6	36	2	4.45	0.05	0.23	0.03	MB–O

⁰⁷Observations in 2007.

The phase angle (α) is given at the start and end of each date range, unless it reached a minimum, which is then the second of three values. If a single value is given, the phase angle did not change significantly and the average value is given. L_PAB and B_PAB are each the average phase angle bisector longitude and latitude, unless two values are given (first/last date in range). The Group column gives the orbital group to which the asteroid belongs. The definitions and values are those used in the LCDB (Warner et al., 2009a). H = Hungaria; MB-I/M/O = Main-belt inner/middle/outer.