1. William H. Ryan1, Eileen V. Ryan1, and Lee K. Johnson2
Real-time Characterization of Near-Earth Objects: New Spectral Capabilities at the Magdalena Ridge Observatory 2.4-meter
William H. Ryan1, Eileen V. Ryan1, and Lee K. Johnson2
1New Mexico Institute of Mining and Technology, Magdalena Ridge Observatory 2NASA Jet Propulsion Laboratory/California Institute of Technology
Results
Figure 4 a,b compares the spectral signature of 2014 EC obtained via the slitless grating and the slit-based MOSS spectrometer. It is clear that the MOSS spectrometer provides a less noisy spectrum than the simple slitless grating system under similar conditions. However, Figure 4 shows that the Sq/Q nature of 2014 EC is still easily discernible using the simple grating mounted in the 2.4-meter telescope facility filter wheel. Therefore, this system can obtain rough classifications of objects as faint as V~17 when the MOSS spectrometer is unavailable. Figure 5 shows the lightcurve for 2014 EC obtained on the same night as the spectrum.
Abstract
Facility Description
The Magdalena Ridge Observatory’s (MRO) 2.4-meter telescope (Figure 1) is operated by the New Mexico Institute of Mining and Technology, and is located on Magdalena Ridge at an elevation of 10,600 feet. The telescope is used primarily to study solar system bodies and man-made satellites in low-Earth orbit. The telescope’s capabilities include slew speeds of 10 degrees per second, precise tracking, and the ability to look as far as 2 degrees below horizon. The telescope’s initial instrumentation included a CCD imager that was primarily used for Near-Earth Object (NEO) astrometry and photometry. However, the Magdalena Optical Spectroscopy System (MOSS) has become available enhancing the facility’s real-time NEO characterization resources.
Figure 1. The Magdalena Ridge Observatory 2.4-meter fast-tracking telescope (left) located outside of Socorro, NM . The MOSS is shown attached to one of the Nasmyth ports of the telescope (right) on a fork-mounted 3 x 4 foot optical bench .
Researchers at the Magdalena Ridge Observatory's (MRO) 2.4-meter telescope facility have been contributing to the Near-Earth Object (NEO) project by working in tandem with discovery survey programs since 2008 to provide real-time, rapid response astrometric and photometric characterization follow-up (i.e., lightcurves to deduce spin rates). We are now extending this to include rapid spectroscopic follow-up using the Magdalena Optical Spectroscopy System (MOSS). This R~300 visible wavelength spectrometer is permanently mounted at the Nasmyth port opposite the imager port (CCD camera) and is accessible in 30 seconds via repositioning of a tertiary mirror. A second spectroscopic capability is available via a simple filter wheel-mounted grating when MOSS is unavailable. By having these instruments mounted (CCD, spectrometer, and stand alone grating) while performing our normal astrometric follow-up tasks, determination of rotation rates and spectral classification are possible as soon as an interesting target is identified, even within minutes of discovery.
We report on the first spectral characterization results of NEOs utilizing this new capability at MRO. In particular, we present spectra for the Sq/Q-type asteroids 2010 XZ67 and 2000 DK79; and the more S-like 2012 HM. In addition, we will present the near simultaneous lightcurve and spectral observations of 2014 EC, 2014 UD57, and 2014 UN114. For 2014 EC, a simple grating spectrum was also obtained and was of sufficient quality to corroborate an Sq/Q classification. This demonstrates that the grating technique can be reliable for classification of targets-of-opportunity when it is the only instrumentation option.
Figure 4a, b. Spectra of 2014 EC obtained by the slitless grating system (left) and the slit-based MOSS spectrometer (right).
Figure 5. Lightcurve of EC obtained during close approach on 6 March 2014 showing a primary period of ~33 min. Analysis shows that the asteroid is likely to be tumbling.
Figure 6 a,b,c shows MOSS-obtained spectra for Sq/Q-type NEOs 2010 XZ67 and 2000 DK79; and the more S-like 2012 HM.
Real-time NEO Characterization
Researchers at MRO have been undertaking a program to derive physical characterization information concentrating on the smallest (less that 200 meters in diameter) objects in the NEO population. This is being pursued in conjunction with a program to provide astrometric follow-up of recently discovered NEO candidates. Since the smaller NEO’s are only detectable for a limited period of time after discovery, sometimes for a single night, engaging these projects simultaneously provides an opportunity to characterize small NEOs that would otherwise be missed.
Previous work included the determination of over 63 rotations rates for NEOs with H<22. The new spectroscopic capability utilizing MOSS as well as slitless spectroscopy via a simple grating should result in rough compositional information for ~20 NEOs per year.
Slitless Spectroscopy of Near-Earth Asteroids
In addition to MOSS, a prototype filter wheel-based, slitless grating system had previously been developed for observations of bright geosynchronous satellites (Dao et al., 2013). This set-up was also validated on a sample of bright, well-studied main belt asteroids. Figure 2 shows the extraction technique for a typical grating spectral source.
Figure 6a, b, c. MOSS spectra for Sq/Q-type NEOs 2010 XZ67 and 2000 DK79; and the more S-like 2012 HM.
The MRO 2.4-meter telescope can have multiple instruments mounted simultaneously. Therefore, a goal of this study is to attempt to characterize both spins and spectra in a single evening. Figure 7a, b shows the spectra and lightcurve obtained with MOSS on the same night for NEO 2014 UD57.
Figure 2a, b. Extraction fiducials for the grating spectrum of asteroid 79 Eurynome (left) and resulting extracted spectrum (right).
Figure 7a, b. Spectra (left) and lightcurve (right) of 2014 UD57 (V~19, H~26). The spin period is 5.75 minutes and it’s roughly C-type.
However, applying this to faint, fast-moving NEOs is a bit more challenging. On March 6, 2014, the near-Earth asteroid 2014 EC made a close approach to Earth, providing an opportunity to test the grating spectra technique for a real target-of-opportunity with scientific interest. A single 60 second exposure of this object is shown in Figure 3. There are field stars, fringe patterns and faint source signals to contend with. However, extracting and averaging 10 spectra results in the final spectra shown in Figure 4a.
Figure 8a, b shows the spectra and lightcurve obtained with MOSS on the same night for NEO 2014 UN114.
Magdalena Optical Spectroscopy System (MOSS)
The Magdalena Optical Spectroscopy System (MOSS) permits asteroid spectra to be obtained over the wavelength range nm and down to objects as faint as V~19. With the spectrometer’s current grating of 150 lines/mm, typical seeing (~1”) yields a usable spectrum sampled at a dispersion of ~1.4 nm/pixel. To acquire a spectrum over the range of nm requires two overlapping exposures to be made. A filter is used for the red component spectrum to avoid 2nd order grating effects. The dispersed light falls on a back-illuminated Princeton Instruments CCD detector. The raw spectral images obtained are usually software binned and resampled to a resolution of nm (R~ at 500 nm) and then divided by solar analog spectra to identify reflectivity.
Figure 8a, b. Spectra (left) and partial lightcurve (right) of 2014 UN114 (V~18.3, H~25). The spin rate is >>5 hours and it’s roughly C-type.
Figure 3. A single 60 second exposure of V~17 NEA 2014 EC is shown. The field stars are moving diagonally while the 2.4m telescope is tracking on the asteroid moving at ~30 arc-second per minute.
Summary
The MRO 2.4-meter telescope researchers are providing comprehensive characterization data (spins and composition) on newly discovered target-of-opportunity NEOs in real-time.
This research is funded through NASA’s NEOO program.