47 research outputs found

    Nuclear Spectra of Comet 28P Neujmin 1

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    We present visible and near-IR spectra of the nucleus of comet 162P/Siding Spring (also known as 2004 TU12) obtained in 2004 December, while it had no detectable coma. This is the third object observed to have intermittent cometary activity even when relatively close to the Sun. The spectra show no strong features in this wavelength range. This paucity of deep absorptions is common among low-albedo asteroids and the few comet nuclei observed in this spectral region. Marginal spectral structure is observed in the visible spectrum, and beyond 2 μm the flux from the nucleus is dominated by thermal emission. We compare the spectrum of 162P with published spectra of other comet nuclei, primitive asteroids, and meteorites. Comet nuclei display a range of spectral shapes and slopes not unlike those observed among outer main-belt asteroids but closest to Trojan asteroids. No suitable spectral matches to comet 162P were found among primitive (chondritic) meteorites. We modeled our visible and near-IR spectra using the scattering theory described by Shkuratov et al. (1999), and our approach is similar to that used by Emery and Brown for modeling Trojan asteroids. Our best fits to the spectral shape and albedo include mixtures containing amorphous carbons, organics, and silicates. The absence of strong spectral features prevents the identification of specific minerals, and the resulting model compositions are not unique. The observations beyond 2 μm are interpreted in a companion publication by Fernández and coworkers

    Nuclear Spectra of Comet 162P/Siding Spring (2004 TU12)

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    We present visible and near-IR spectra of the nucleus of comet 162P/Siding Spring (also known as 2004 TU12) obtained in 2004 December, while it had no detectable coma. This is the third object observed to have intermittent cometary activity even when relatively close to the Sun. The spectra show no strong features in this wavelength range. This paucity of deep absorptions is common among low-albedo asteroids and the few comet nuclei observed in this spectral region. Marginal spectral structure is observed in the visible spectrum, and beyond 2 μm the flux from the nucleus is dominated by thermal emission. We compare the spectrum of 162P with published spectra of other comet nuclei, primitive asteroids, and meteorites. Comet nuclei display a range of spectral shapes and slopes not unlike those observed among outer main-belt asteroids but closest to Trojan asteroids. No suitable spectral matches to comet 162P were found among primitive (chondritic) meteorites. We modeled our visible and near-IR spectra using the scattering theory described by Shkuratov et al. (1999), and our approach is similar to that used by Emery and Brown for modeling Trojan asteroids. Our best fits to the spectral shape and albedo include mixtures containing amorphous carbons, organics, and silicates. The absence of strong spectral features prevents the identification of specific minerals, and the resulting model compositions are not unique. The observations beyond 2 μm are interpreted in a companion publication by Fernández and coworkers

    Thermophysical Characterization of Potential Spacecraft Target (101955) 1999 RQ36

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    We report on thermal emission measurements of 1999 RQ36 from Spitzer. The derived size is in agreement with radar measurements, and we find a moderately high thermal inertia and homogeneous surface properties

    A Comparative Study of the Themis and Veritas Asteroid Families

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    Our primary goal is to characterize the surface composition (and other properties such as radius, albedo and thermal inertia) of our sample of Themis-family and Veritas-family asteroids based on their 5 to 14 micron spectra. We chose these two families for several reasons. First, they are compositionally primitive (non-igneous) so they can yield information about their physical and chemical conditions of their formation environment. Second, their parent bodies formed in the same region, yet their disruption ages are sharply different: 2.5 Gy and 8.3 My, respectively. This gives us a remarkable opportunity to understand the evolutionary processes that have affected the asteroids fragments. For example, Nesvorny et al. (2005) found clear evidence of color variations between young and old asteroids families. They identified a well defined trend among primitive asteroids, with the Themis and Veritas families at opposite ends of this color variation, which they attribute to space weathering. Finally, both families formed beyond the \u27frost line\u27 and some fragments appear to have retained water-ice reservoirs for the age of the solar system; more specifically Rivkin (2007) reported the first (preliminary) detection of water ice on 24 Themis. If confirmed, this detection of water-ice opens up interesting possibilities that could transform of our understanding of these asteroids. For example, since water ice is not stable on the surface of 24 Themis over the age of the solar system what is its source? What does this imply about the interior of this asteroid and of the other members of these two families. Why does 24 Themis not show cometary activity? These are some of the questions this proposed study will address. Understanding the abundance of water-ice and hydrated minerals in this area of the solar system is particularly important, as it may be linked to the origin of Earth\u27s water. Our total time request is 6.4 hours

    Albedos of Small Jovian Trojans

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    We present thermal observations of 44 Jovian Trojan asteroids with diameters D ranging from 5 to 24 km. All objects were observed at a wavelength of 24 μm with the Spitzer Space Telescope. Measurements of the thermal emission and of scattered optical light, mostly from the University of Hawaii 2.2 m Telescope, together allow us to constrain the diameter and geometric albedo of each body. We find that the median R-band albedo of these small Jovian Trojans is about 0.12, much higher than that of large Trojans with D\u3e57 km (0.04). Also the range of albedos among the small Trojans is wider. The small Trojans\u27 higher albedos are also glaringly different from those of cometary nuclei, which match our sample Trojans in diameter, however, they roughly match the spread of albedos among (much larger) Centaurs and trans-Neptunian objects. We attribute the Trojan albedos to an evolutionary effect: the small Trojans are more likely to be collisional fragments and so their surfaces would be younger. A younger surface means less cumulative exposure to the space environment, which suggests that their surfaces would not be as dark as those of the large, primordial Trojans. In support of this hypothesis is a statistically significant correlation of higher albedo with smaller diameter in our sample alone and in a sample that includes the larger Trojans. This correlation of albedo and radius implies that the true size distribution of small Trojans is shallower than the visible magnitude distribution alone would suggest, and that there are approximately half the Trojans with D\u3e1 km than previously estimated

    Albedos of Small Jovian Trojans

    No full text
    We present thermal observations of 44 Jovian Trojan asteroids with diameters D ranging from 5 to 24 km. All objects were observed at a wavelength of 24 μm with the Spitzer Space Telescope. Measurements of the thermal emission and of scattered optical light, mostly from the University of Hawaii 2.2 m Telescope, together allow us to constrain the diameter and geometric albedo of each body. We find that the median R-band albedo of these small Jovian Trojans is about 0.12, much higher than that of large Trojans with D\u3e57 km (0.04). Also the range of albedos among the small Trojans is wider. The small Trojans\u27 higher albedos are also glaringly different from those of cometary nuclei, which match our sample Trojans in diameter, however, they roughly match the spread of albedos among (much larger) Centaurs and trans-Neptunian objects. We attribute the Trojan albedos to an evolutionary effect: the small Trojans are more likely to be collisional fragments and so their surfaces would be younger. A younger surface means less cumulative exposure to the space environment, which suggests that their surfaces would not be as dark as those of the large, primordial Trojans. In support of this hypothesis is a statistically significant correlation of higher albedo with smaller diameter in our sample alone and in a sample that includes the larger Trojans. This correlation of albedo and radius implies that the true size distribution of small Trojans is shallower than the visible magnitude distribution alone would suggest, and that there are approximately half the Trojans with D\u3e1 km than previously estimated

    APIRP: The Automated Photometric Data Reduction Package

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    For decades the Image Reduction and Analysis Facility (IRAF) has been the standard for processing CCD-based image datasets. During that time, technology has advanced and the astronomical record greatly expanded. However, the discovery process is often bogged down by the time consuming procedures of image reduction. To keep up with demand and shorten reduction steps programmers have developed a series of command languages (CL) for IRAF and most recently, within only the past five years, the Python-based language, Pyraf. Python is a robust and powerful language that combines syntactical simplicity with versatile and dynamic file management, database access and software development capabilities, to name just a few features. Pyraf, by extension, incorporates all of the qualities of IRAF CL, with all of the power and flexibility provided by Python. Pyraf scripts may be written to automate file processing at the same time that reduction tasks are called from IRAF. Thus, the potential to write fully automated reduction procedures is here; tightening the gaps of scientific advancement. We have created such a tool for CCD Photometry. Our Automated Photometric Image Reduction Package (APIRP) uses a range of graphical user interfaces (GUI\u27s) to form an interactive yet non-overbearing user environment. A combination of built-in file management and procedural variability makes APIRP a perfect choice for both amateur and professional astronomers. Due to the programs design, it can be run from anywhere on your computer and users can specify exactly what steps of reduction they wish to execute. Thus, setup is easy with no need for cumbersome documentation and tasks may be preformed piecewise or in blocks, depending on the users needs

    Characterization of Surface Heterogeneity among Asteroid Taxonomic Classes according to Sloan Digital Sky Survey Observations

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    This research characterizes the extent of surface heterogeneity among asteroid classes by the extent of Sloan Digital Sky Survey (SDSS) color variance within multiple observations of the same asteroid. The SDSS MOC4 database includes data from 220,101 observations of 104,449 unique objects. The amount of multiple observations of one target makes it ideal for statistically analyzing the surface inhomogeneity of asteroid surfaces. Information from the SDSS MOC4 database (below an error threshold determined from standard error propagation techniques and the interquartile range) is combined with information from the classification in Carvano et al. (2010) to analyze asteroid surface heterogeneity based on taxonomic class. Individual observations are grouped by asteroid, and asteroids are grouped by class. The standard deviation of each normalized SDSS color (i.e. u-r, g-r, r-i, r-z) for each asteroid with multiple observations is calculated. The mean of the standard deviations is then computed for a given class. Comparison of the size of the average standard deviation to the size of the error determines the extent of true variance within a normalized color in a class. The effect of phase angles on SDSS data, as discussed in Carvano et al. (2015), are considered. Additionally, implications for space weathering and evolutionary relationships between taxonomic classes are explored
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