Abstract
Independent CCD photometry observations by the authors of the near-Earth asteroid 2015 HM10 were made in 2015 July. Analysis of both data sets found a synodic rotation period of approximately 0.376 h and amplitude of 1.47 ± 0.05 mag.
CCD photometric observations of the near-Earth asteroid 2015 HM10 were made in early 2015 July at the Magdalena Ridge Observatory (MRO) and the Center for Solar System Studies – Palmer Divide Station (CS3). Both sets of observations were made in support of radar observations by providing rotation periods and astrometry and, more generally, as part of on-going programs to determine physical characteristics of near-Earth asteroids (see, e.g., Ryan and Ryan, 2015). The MRO data were collected early in the asteroid’s apparition under less than ideal conditions to provide the critical spin rate information necessary to optimize radar observations.
Observations at MRO were made using the 2.4-m f/8.8 telescope, located in the Magdalena Mountains of New Mexico, using a VR filter (V and R). Exposures were 45 seconds. Approximately 1.4 hours of data were obtained at air masses X = 2.5 to 3.8 with thin cirrus clouds and a full moon. The images were bias-subtracted and flat-fielded, and on-chip differential photometry was performed using IRAF (Tody, 1993). The V magnitudes were calibrated using magnitudes from the MPOSC catalog, which converts 2MASS J-K magnitudes to BVRI using formulae developed by Warner (2007). These were checked for consistency using SDSS transformations (Jester et al., 2005). The data were corrected to unit geocentric and heliocentric distances and then analyzed using the techniques described by Harris et al. (1989).
Observations at CS3 were made using a 0.30-m Schmidt-Cassegrain telescope (SCT) and Finger Lakes ML-1001E CCD camera. The images were dark-subtracted and flat-fielded using MPO Canopus (Warner, 2015). The 60-second unfiltered images were converted to V magnitudes using comparison star magnitudes from the MPOSC catalog and differential photometry. Period analysis was also done in MPO Canopus, which implements the FALC Fourier analysis algorithm (Harris et al., 1989).
Analysis
Figure 1 shows the lightcurve derived from the data obtained at MRO. While the absolute calibration errors are on the order of 0.05 mag, the low photon statistics and high background levels resulted in differential errors on the order of 0.1-0.3 mag. Even so, these were relatively small in comparison to the amplitude of the lightcurve and so allowed finding a reliable synodic period of P = 0.376 ± 0.002 h.
Figure 1.
The lightcurve for 2015 HM10 based on data from Magdalena Ridge Observatory.
Figure 2 shows the lightcurve derived from two nights of observations at CS3. Analysis found a period of 0.3761 ± 0.0001 h. The formal error was about 5x less (0.00002 h), but the span of the observations called for a less precise solution. The CS3 data had photon statistical errors on the order of 0.1 mag. Even though the CS3 scope was about 8x smaller in diameter, it had the advantages of the asteroid being about 2.3 magnitudes brighter, observations were at air masses X = 1.1-1.9, and the moon was almost new.
Figure 2.
The lightcurve of 2015 HM10 based on data from CS3. Note the significant change in the shape from that in Figure 1 due to changing phase and viewing aspect.
While the amplitudes of the two lightcurves were similar, ~1.47 ± 0.05 mag, the shape changed significantly over the 10-day interval between the two data sets. These differences will be helpful when modeling the asteroid’s shape and spin in combination with radar data.
Table 1.
Observation details. The last three columns give, respectively, the solar phase angle and the phase angle bisector longitude and latitude.
| Date 2015/mm/dd | Obs | α | LPAB | BPAB |
|---|---|---|---|---|
| 07/01 | MRO | 100.0 | 227 | −4 |
|
| ||||
| 07/10 | CS3 | 85.4 | 331 | +7 |
| 07/11 | CS3 | 80.8 | 330 | +6 |
Acknowledgements
Funding for PDS observations, analysis and publication was provided by NASA grant NNX13AP56G. Funding for work at MRO was provided by the Arecibo/MRO cooperative agreement under NASA grant NNX13AQ46G. This research was made possible in part based on data from CMC15 Data Access Service at CAB (INTA-CSIC) and the AAVSO Photometric All-Sky Survey (APASS), funded by the Robert Martin Ayers Sciences Fund.
Contributor Information
Brian D. Warner, Center for Solar System Studies – Palmer Divide Station, 446 Sycamore Ave., Eaton, CO USA 80615
William H. Ryan, Magdalena Ridge Observatory, New Mexico Institute of Mining and Technology, Socorro, NM USA 87801
References
- Harris AW, Young JW, Bowell E, Martin LJ, Millis RL, Poutanen M, Scaltriti F, Zappala V, Schober HJ, Debehogne H, Zeigler KW (1989). “Photoelectric Observations of Asteroids 3, 24, 60, 261, and 863.” Icarus 77, 171–186. [Google Scholar]
- Jester S, Schneider DP, Richards GT, Green RF, Schmidt M, Hall PB, Strauss MA, Vanden Berk DE, Stoughton C, Gunn JE, Brinkmann J, Kent SM, Smith JA, Tucker DL, Yanny B (2005). “The Sloan Digital Sky Survey View of the Palomar-Green Bright Quasar Survey.” Astron. J 130, 873–895. [Google Scholar]
- Ryan WH, Ryan EV (2015). “Target-of-Opportunity characterization of sub-200 meter Near-Earth Asteroids.” Proceedings of the 4th IAA Planetary Defense Conference, in press. [Google Scholar]
- Tody D (1993). “IRAF in the Nineties.” in Astronomical Data Analysis Software and Systems II, A.S.P Conference Ser. 52, eds. Hanisch RJ, Brissenden RJV, Barnes J, p. 173 ff [Google Scholar]
- Warner BD (2007). “Initial Results of a Dedicated H-G Program.” Minor Planet Bul. 34, 113–119. [Google Scholar]
- Warner BD (2015). MPO Canopus v10.7.0.