Linking large-parallax Spitzer–CFHT–VLT astrometry of asteroids

Abstract

We show that the new ephemeris-space multiple-address-comparison (eMAC) method solves asteroid linking problems despite large parallaxes by applying the method to astrometric asteroid observation sets obtained nearly simultaneously with the Spitzer space telescope, the Canada-France-Hawaii Telescope (CFHT), and European Southern Observatory's Very Large Telescope (VLT). For main-belt asteroids, the parallax between Spitzer and the Earth-based telescopes is approximately one degree which is large as compared to a typical parallax for solely Earth-based telescopes in the arcseconds regime. In the eMAC method, we reduce the initially huge amount of possible linkages between observation sets by comparing samples of ephemerides that have been computed separately for all sets at, say, three common dates. If the non-zero ephemeris probability densities overlap at all common dates, we try to find an orbit solution for these so-called trial linkages. If there exists an orbit which reproduces all the astrometric observations assuming predefined observational errors, we call it a linkage. Known asteroids are independently identified among Spitzer, CFHT, and VLT astrometry, and comparing the identified observations to the linkages found shows that the method found all known correct linkages present in the data. In addition, we also found five previously unpublished linkages between Spitzer astrometry and Earth-based astrometry. Based on our simulations, we found virtually all Spitzer-related linkages between two single-night observation sets, and more than 99.4% of linkages between two single-night observation sets obtained by Earth-based observatories. Virtually all correct linkages consisting of at least three single-night sets were also detected. The results show that large-parallax discovery observations made from a spacecraft can be linked to Earth-based follow-up observations to ensure that the objects are not lost. Furthermore, we compute the heliocentric and Spitzer-centric distances as well as the corresponding solar phase angles at the dates of Spitzer observations. Based on comparisons to simulated geocentric observations, we also show that, for typical nearly-simultaneous observations, the parallax reduces the distance uncertainties by several orders of magnitude.

Mid-Infrared Photometric Analysis of Main Belt Asteroids: A Technique for Color-Color Differentiation From Background Astrophysical Sources

“…Since then, we have clearly linked all 8 μm asteroid detections to their counterparts at 24 μm. In Tables 2 and 3, we also include linkages to known objects, provided by Granvik et al (2007). These updated linkages between FLS-EPC sources and known asteroids are primarily based upon ground-based data taken from 2004 January to March in support of the FLS-EPC and reported to the Minor Planet Center.…”

“…Nine of these objects are well characterized and numbered. Seven have provisional designations, and five of these designations are based on the ground-based observations described by Granvik et al (2007). Only two of the objects are currently not linked with ground-based data, and these are labeled with a "0" in Table 2 to indicate their latitude and a letter that indicates the order in which they were identified in the initial analysis phase of this work in 2004.…”

“…We can improve results from the STM by applying empirically derived adjustments to H (Juric et al 2002;Romanishin & Tegler 2005;Parker et al 2008) and p v (Granvik et al 2007;Parker et al 2008;Ryan & Woodward 2009). Comparisons of observed and predicted magnitudes in the Sloan Digital Sky Survey (Juric et al 2002;Parker et al 2008) report an average offset of H ∼ H + 0.4, which we provide in Table 5.…”

Asteroid identification over apparitions

“…Whereas the eMAC method is, in principle, a general solution to any currently imaginable asteroid linking problem (see, for example, Granvik et al 2007), it is optimized to deal with short linking intervals. In the eMAC method, candidate linkages are sought by comparing ephemerides at a few common epochs.…”

“…Usually an improvement in the first leads to a degradation in the second, and vice versa. As comparison metrics, we use the sensitivity and the positive-predictive value as described by, e.g., Granvik et al (2007). The sensitivity Sens is a measure for how well a binary classifier correctly identifies a condition and it is defined as…”