Sizes and albedos of Mars-crossing asteroids from WISE/NEOWISE data

Context. Mars-crossing asteroids (MCs) are a dynamically unstable group between the main belt and the near-Earth populations. Characterising the physical properties of a large sample of MCs can help to understand the original sources of many near-Earth asteroids, some of which may produce meteorites on Earth. Aims. Our aim is to provide diameters and albedos of MCs with available WISE/NEOWISE data. Methods. We used the near-Earth asteroid thermal model to find the best-fitting values of equivalent diameter and, whenever possible, the infrared beaming parameter. With the diameter and tabulated asteroid absolute magnitudes we also computed the visible geometric albedos. Results. We determined the diameters and beaming parameters of 404 objects observed during the fully cryogenic phase of the WISE mission, most of which have not been published elsewhere. We also obtained 1572 diameters from data from the 3-Band and posterior non-cryogenic phases using a default value of beaming parameter. The average beaming parameter is 1.2 +/- 0.2 for objects smaller than 10 km, which constitute most of our sample. This is higher than the typical value of 1.0 found for the whole main belt and is possibly related to the fact that WISE is able to observe many more small objects at shorter heliocentric distances, i.e. at higher phase angles. We argue that this is a better default value for modelling Mars-crossing asteroids from the WISE/NEOWISE catalogue and discuss the effects of this choice on the diameter and albedo distributions. We find a double-peaked distribution for the visible geometric albedos, which is expected since this population is compositionally diverse and includes objects in the major spectral complexes. However, the distribution of beaming parameters is homogeneous for both low- and high-albedo objects.Comment: 8 pages, 6 figures, accepted for publication in Astronomy & Astrophysic

Evidence of a metal-rich surface for the asteroid (16) Psyche from interferometric observations in the thermal infrared

We describe the first determination of thermal properties and size of the M-type asteroid (16) Psyche from interferometric observations obtained with the Mid-Infrared Interferometric Instrument (MIDI) of the Very Large Telescope Interferometer. We used a thermophysical model to interpret our interferometric data. Our analysis shows that Psyche has a low macroscopic surface roughness. Using a convex 3-D shape model obtained by Kaasalainen et al. (2002, Icarus 159, 369-395), we derived a volume-equivalent diameter for (16) Psyche of 247 +- 25 km or 238 +- 24 km, depending on the possible values of surface roughness. Our corresponding thermal inertia estimates are 133 or 114 J.m-2.s-0.5.K-1, with a total uncertainty estimated to 40 J.m-2.s-0.5.K-1. They are among the highest thermal inertia values ever measured for an asteroid of this size. We consider this as a new evidence of a metal-rich surface for the asteroid (16) Psyche.Comment: 45 pages (in referee and preprint format), 6 figure

Reconstructing the size distribution of the primordial Main Belt

In this work we aim to constrain the slope of the size distribution of main-belt asteroids, at their primordial state. To do so we turn out attention to the part of the main asteroid belt between 2.82 and 2.96~AU, the so-called "pristine zone", which has a low number density of asteroids and few, well separated asteroid families. Exploiting these unique characteristics, and using a modified version of the hierarchical clustering method we are able to remove the majority of asteroid family members from the region. The remaining, background asteroids should be of primordial origin, as the strong 5/2 and 7/3 mean-motion resonances with Jupiter inhibit transfer of asteroids to and from the neighboring regions. The size-frequency distribution of asteroids in the size range $17<D(\rm{km})<70$ has a slope $q\simeq-1$. Using Monte-Carlo methods, we are able to simulate, and compensate for the collisional and dynamical evolution of the asteroid population, and get an upper bound for its size distribution slope $q=-1.43$. In addition, applying the same 'family extraction' method to the neighboring regions, i.e. the middle and outer belts, and comparing the size distributions of the respective background populations, we find statistical evidence that no large asteroid families of primordial origin had formed in the middle or pristine zones

Determination of physical properties of the asteroid (41) Daphne from interferometric observations in the thermal infrared

We describe interferometric observations of the asteroid (41) Daphne in the thermal infrared obtained with the Mid-Infrared Interferometric Instrument (MIDI) of the Very Large Telescope Interferometer (VLTI). We derived the size and the surface thermal properties of (41) Daphne by means of a thermophysical model (TPM), which is used for the interpretation of interferometric data for the first time. From our TPM analysis, we derived a volume equivalent diameter for (41) Daphne of 189 km, using a non-convex 3-D shape model derived from optical lightcurves and adaptive optics images (B. Carry, private communication). On the other hand, when using the convex shape of Kaasalainen et al. (2002. Icarus 159, 369-395) in our TPM analysis, the resulting volume equivalent diameter of (41) Daphne is between 194 and 209 km, depending on the surface roughness. The shape of the asteroid is used as an a priori information in our TPM analysis. No attempt is made to adjust the shape to the data. Only the size of the asteroid and its thermal parameters (albedo, thermal inertia and roughness) are adjusted to the data. We estimated our model systematic uncertainty to be of 4% and of 7% on the determination of the asteroid volume equivalent diameter depending on whether the non-convex or the convex shape is used, respectively. In terms of thermal properties, we derived a value of the surface thermal inertia smaller than 50 J m-2 s-0.5 K-1 and preferably in the range between 0 and 30 J m-2 s-0.5 K-1. Our TPM analysis also shows that Daphne has a moderate macroscopic surface roughness.Comment: 44 pages, 8 figures, 3 table

Die Natur von erdnahen Asteroiden abgeleitet aus dem Studium ihrer thermischen Infrarot-Emissionen

Title page, Table of Contents, List of Figures Abstract and Acknowledgments Deutsche Zusammenfassung viii 1\. Introduction 1 1.1 Asteroids 1 1.2 Main Belt Asteroids 2 1.3 Physical characteristics of Near Earth Asteroids and Near Earth Objects 5 1.4 The need of physical characterization of NEOs: statement of the problem 10 1.5 Scope of this work 2 2\. Sizes and albedos of asteroids: the radiometric method and asteroid thermal models 13 2.1 Foreword 13 2.2 Introduction 13 2.3 Asteroid surface temperatures 15 2.4 Calculation of the emitted thermal infrared flux 18 2.5 Constraints on diameter and albedo from the visible absolute magnitude 19 2.6 Radiometric diameters and albedos 19 2.7 Thermal models of asteroids 20 2.7.1 The Standard Thermal Model (STM) 20 2.7.2 The Fast Rotating Model (FRM) 22 2.7.3 The near-Earth asteroid thermal model (NEATM) 23 2.8 Uncertainties 26 2.8.1 Rotational variability effects and lightcurve correction of infrared fluxes 26 2.8.2 The actual temperature distribution differs from the modeled one 26 2.8.3 Accuracy of the H values 27 2.9 Thermophysical models 27 2.10 Summary 28 3\. Thermal infrared observations of near-Earth asteroids and data reduction 31 3.1 Foreword 31 3.2 Introduction 31 3.3 Thermal infrared ground based observations 33 3.4 Thermal IR photometry 36 3.5 Aperture photometry and photometric uncertainties 38 3.6 Data reduction of thermal IR data 39 3.7 Thermal infrared observations of NEAs: a method for accurate nod-set registering 42 3.8 Color correction 44 3.9 Thermal IR spectroscopy at the TIMMI2 45 3.10 Visible CCD observations at ESO: data reduction 49 3.11 The data set 50 3.11.1 Near-Earth asteroids observed at KECK 51 3.11.2 Near-Earth asteroids observed at ESO 52 3.11.3 Near-Earth asteroids observed at NASA-IRTF 53 3.12 Summary 54 4\. Thermal model fits to thermal infrared data and derivation of albedos and diameters 57 4.1 Foreword 57 4.2 Introduction 57 4.2.1 Diameters, albedos and eta-values derived from observations at Keck 58 4.2.2 Diameters, albedos and eta-values derived from observations at ESO 59 4.2.3 Diameters, albedos and eta-values derived from observations at NASA- IRTF 60 4.3 Comments on individual asteroids 60 4.3.1 15817 Lucianotesi (1994 QC) 61 4.3.2 2000 EV70 62 4.3.3 2001 HW15 62 4.3.4 25143 Itokawa (formerly known as 1998 SF36) 62 4.3.5 2001 LF 65 4.3.6 5381 Sekmeth 67 4.3.7 25330 (1999 KV4) 69 4.3.8 2002 AV4 70 4.3.9 5587 (1990 SB) 71 4.3.10 19356 (1997 GH3) 75 4.3.11 5604 (1992 FE) 75 4.3.12 37314 (2001QP) 76 4.3.13 33342 (1998WT24) 76 4.3.14 35396 (1997 XF11) 79 4.3.15 1580 Betulia 83 4.4 Physical characterization of NEAs: summary of results 85 5\. Analysis of results from thermal models: the observed albedo distribution of NEAs and the correlation of eta with the phase angle 91 5.1 Foreword 91 5.2 The observed albedo distribution of NEAs 91 5.3 Phase angle dependence of the observed color temperature 95 5.3.1 NEAs with anomalous thermal properties (eta>2) 96 5.3.2 NEAs with "common" thermal properties 97 5.4 The infrared phase curve of NEAs with �common� thermal properties 98 5.5 Comparison of radiometric diameters with radar 100 5.6 On the recalibration of the STM for NEAs 105 5.7 Correlation of radiometric albedos with solar phase angle 108 5.8 Conclusions 109 6\. Estimate of the thermal inertia of NEAs and assessment of the accuracy of thermal models 113 6.1 Foreword 113 6.2 Introduction 113 6.3 Thermophysical model components 116 6.4 Thermal Inertia and the heat diffusion within spherical craters 117 6.5 Numerical simulations 120 6.6 Results of the simulations 124 6.6.1 Effects of thermal inertia and rotation rate on the theoretical dependence of the NEATM eta-value as a function of the phase angle 124 6.6.2 Effects of surface roughness on the theoretical dependence of the NEATM eta-value as a function of the phase angle 126 6.6.3 Combined effects of thermal inertia, rotation rate and surface roughness on the theoretical dependence of the NEATM eta-value as a function of the phase angle 127 6.7 The thermal inertia of NEAs 132 6.8 Implications for the Yarkovsky effect on kilometer and sub-kilometer size asteroids 138 6.9 Effects of surface roughness, thermal inertia and rotation rate on the accuracy of NEA radiometric diameters and albedos 139 6.10 Conclusions 146 7\. Conclusions and future works 149 7.1 Conclusions 149 7.1.1 This work increases the number of NEAs with measured sizes and albedos by 54% 149 7.1.2 The observed NEAs are on average brighter than main belt asteroids 149 7.1.3 There is a trend of increasing albedo with decreasing size for observed S-type NEAs 150 7.1.4 The ambiguous taxonomic classifications of six asteroids have been clarified in the light of the new albedo values. 150 7.1.5 The apparent color temperature of the observed NEAs is phase angle dependent 150 7.1.6 The variation of the color temperature with phase angle depends on the albedo 151 7.1.7 The observed distribution of the color temperature with the phase angle can be explained in terms of thermal inertia and surface roughness 151 7.1.8 The best-fit thermal inertia of the observed NEAs is 550±100J m^(-2) s^(-0.5) K^(-1) or about 11 times that of the Moon 151 7.1.9 There are asteroids with anomalously low color temperature 152 7.1.10 The observed distribution of color temperature allows a calibration of thermal models for applications to NEAs 152 7.1.11 We have derived a quantitative assessment of the accuracy of thermal models and a correction function for the nominal results of the NEATM and the STM 153 7.2 Future works 153 7.2.1 Application of thermophysical models to NEAs 153 7.2.2 Study of the contribution of a selection bias in the observed trend of increasing albedo with decreasing size 154 7.2.3 Study the range of thermal and surface properties of NEAs by means of thermal infrared 154 Appendix A 165 Observed thermal Infrared Fluxes of near-Earth asteroids 165 Appendix B 173 Colour correction factors for LWS, TIMMI2, MIRSI and MIRLIN filters 173 B.1 LWS at Keck 1 filters and color correction factors 173 B.2 TIMMI2 filters and color correction factors 176 B.3 MIRLIN filters and color correction factors 177 B.4 MIRSI filters and color correction factors 178 Appendix C 179 Thermal Infrared photometry: NOTES 179 LEBENSLAUF 181The topic of this dissertation is the investigation of physical properties of near-Earth Asteroids (NEAs) to improve our understanding of their nature, origin and their relation to main-belt asteroid (MBAs) and comets. A major aspect of the research is the use and the improvement of models of the thermal infrared emission of asteroids (the so-called thermal models) to facilitate the determination of sizes, albedos and other physical properties of NEAs. A major development within this study is the discussion of the results from new observing programs with the 10m - Keck 1 telescope, the NASA- Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii and the 3.6m telescope at the European Southern Observatory (ESO), La Silla, Chile. In the framework of these observing programs, thermal emission continua of thirty-two NEAs have been obtained in the medium infrared (MidIR) (5-20 microns). By fitting thermal models to the observational data, we have derived the sizes and the albedos of a significant sample of the near-Earth asteroid population. This work increments the number of NEAs with measured sizes and albedos by 54%. If we include objects for which the diameter and the albedo have been refined, this increment increases up to almost 70%. The uniqueness of our project was the possibility of studying smaller and fainter objects which are only accessible with the most up-to-date Mid-IR instrumentations and the largest telescopes on the ground. There were very few thermal infrared observations of asteroids in the 1-kilometer size range, and we have more than doubled the number of subkilometer-NEAs with measured size and albedos. The good quality data that we have obtained constitute the largest database of NEAs radiometric diameters and albedos. An accurate determination of sizes for a significant sample of NEAs, besides providing crucial input for the assessment of the impact hazard these objects pose for our planet, gives important clues about their surface characteristics. Although we confirm that the spread of NEA albedos is very large (pV = 0.02 - 0.55), consistent with their being supplied from more than one source region, we have found that observed NEAs are on average brighter than MBAs. The average value of radiometrically determined albedo is 0.27, which is much higher than the mean albedo of observed MBAs (~0.11). In several cases the albedos are in the ranges expected for their taxonomic types, although some exceptions are evident. Overall, we find that observed S-type NEAs are on average 20% brighter than S-type MBAs, whereas observed C-type NEAs have on average albedos 57% higher than C-type MBAs. Such dichotomy between the albedo statistics of large and small asteroids implies a fundamental difference in surface properties of small asteroids with respect to the larger ones. We show, moreover, that a variation of surface properties with size exists within the NEA population itself. A trend of increasing albedo with decreasing diameter for S-type NEAs has been identified. We argue that this trend is indicative of recently exposed, relatively unweathered surfaces. Although a selection effect in favor of the discovery of the brightest asteroids would give rise to such trend, this result is also consistent with the trend to ordinary-chondrite-type reflection spectra with decreasing size observed in the NEA population. This last effect is also attributed to a lack of space weathering of relatively young surfaces. NEAs do not only have higher albedos than larger MBAs, but they differ also in surface thermal properties. Our work confirms the hypothesis that these asteroids have higher thermal inertias than large MBAs. We have derived a best-fit estimate for the thermal inertia of the observed near-Earth asteroids of 550±100 J m^(-2) s^(-0.5) K^(-1). This value is about eleven times higher that of the Moon and more than 30 times larger that of the largest asteroids 1 Ceres and 2 Pallas. This result has important implications for our understanding of the nature and the origin of these bodies. For instance, the higher thermal inertia is an indication that these asteroids have surfaces covered with a regolith courser than the lunar one and, very likely, different surface fractional rock coverage than large MBAs. This result was obtained by studying the correlation of the observed distribution of surface color temperatures that NEAs display as a function of the phase angle in the light of a thermophysical model. The thermophysical model that we have developed in this work, takes account of the effects of rotation rate, thermal inertia and surface roughness on the thermal emission of airless bodies. In particular, we have demonstrated that the observed distribution of the color temperature with the phase angle can be used to constrain the thermal inertia (and partially the surface roughness) of the observed asteroids in the hypothesis that their spin vectors were randomly oriented. By means of our thermophysical model, we have also obtained a quantitative assessment of the uncertainties in the NEAs albedos and diameters derived by using the Standard Thermal Model (STM and the near-Earth asteroids thermal (NEATM) model, which both make assumption about the surface temperature distribution and the thermal inertia of NEAs. We have numerically estimated a correction function for NEAs radiometric diameters and albedos derived by means of the STM and of the NEATM, provided that spin status and thermal parameter of the asteroid are known. When such information is not available, the accuracy of NEATM results can be still estimated on the basis of the derived color temperature of the objects. Our intriguing new results suggest that, by analyzing thermal infrared observations of NEAs of different sizes and classes by means of thermophysical modelling, it is possible to study the range of thermal properties and surface structure present in the NEA population.Das Thema dieser Dissertation ist die Untersuchung der physikalischen Eigenschaften von erdnahen Asteroiden (NEAs), um unser Verstaendnis ihrer Natur, ihren Ursprungs und ihre Beziehung zu Hauptgürtelasteroiden (MBAs) zu verbessern. Ein Hauptaspekt dieser Forschungsarbeit ist der Einsatz verbesserter thermischer Modelle zur Beschreibung der Infrarot-Emissionen von Asteroiden. Ziel der Modellierung ist die Bestimmung von Groesse, Albedo und anderen Eigenschaften von NEAs aus Beobachtungsdaten. Einen Kernpunkt dieser Arbeit stellt die Diskussion der Ergebnisse von drei neuen Beobachtungsprogrammen, mit dem 10m Keck 1 Teleskop, dem NASA-Infrared Telescope F. (IRTF) auf dem Mauna Kea, Hawaii, und dem 3,6m Teleskop auf der Europaeischen Suedsternwarte (ESO) in La Silla, Chile, dar. Diese Beobachtungsprogramme umfassten die Messung der thermalen Emission von 32 NEAs im mittleren Infrarot (Mid-IR) von 5-20 microns. Durch einen Fit der thermischen Modelle an die Beobachtungsdaten konnten wir Groesse sowie Albedo einer beachtlichen Anzahl von erdnahen Asteroiden bestimmen. Diese Arbeit erhoeht die Anzahl von NEAs mit bekannten Groessen und Albedos um 54%. Nimmt man Objekte hinzu, deren Durchmesser und Albedo korrigiert wurden, so erhöht sich diese Zahl sogar auf 70%. Die Besonderheit unseres Projektes besteht in der Moeglichkeit, kleinere und lichtschwächere Objekte zu studieren, die sonst nur mit neuesten Mid-IR Instrumenten und den groessten erdgebundenen Teleskopen zugaenglich waren. Bisher gab es nur sehr wenige Beobachtungen von Asteroiden der Groessenordnung von einem Kilometer und wir konnten die Anzahl von Sub-Kilometer NEAs mit bekannter Groesse und Albedo mehr als verdoppeln. Die von uns erhaltenen qualitativ guten Daten bilden die groesste Datenbank von radiometrischen Durchmessern und Albedos von NEAs. Die genaue Groessenbestimmung einer grossen Anzahl von NEAs ermoeglicht uns, neben der Beurteilung der Auswirkungen eines moeglichen Einschlages auf unserem Planeten, wichtige Rueckschuesse auf deren Oberflaecheneigenschaften. Wir konnten bestaetigen, dass die Verteilung der NEA-Albedos sehr breit ist (pV = 0.02 � 0.55), was im Einklang zu der Tatsache steht, dass sie aus mehr als einer Ursprungsregion gespeist werden. Allerdings erwiesen sich die beobachteten NEAs im Allgemeinen als heller als MBAs. Der durchschnittliche Wert der radiometrisch bestimmten Albedos kann mit 0.27 angegeben werden und liegt damit viel hoerher als die durchschnittliche Albedo von beobachteten MBAs (~0.11). In den meisten Fällen bewegen sich die Albedos in den aufgrund ihrer taxonomischen Art erwarteten Bereichen, obwohl einige Ausnahmen evident wurden. Im Allgemeinen fanden wir, dass beobachtete S-type NEAs im Durchschnitt 20% heller als S-type MBAs sind, wobei beobachtete C-type NEAs im Durchschnitt 57% hoehere Albedos als C-type MBAs haben. Solch eine Diskrepanz in der Albedo Statistik zwischen grossen und kleinen Asteroiden impliziert einen fundamentalen Unterschied in den Oberflaecheneigenschaften von kleinen Asteroiden im Vergleich zu den groesseren. Wir zeigen weiterhin, dass es eine Variation der Oberflaecheneigenschaften mit der Groesse innerhalb der NEAs selbst gibt. In diesem Zusammenhang konnte ein Trend von steigender Albedo mit sinkendem Durchmesser von S-type NEAs identifiziert werden. Wir argumentieren weiter, dass dieser Trend ein Anzeichen von erst letztlich freigelegten und dem "space-weathering" ausgesetzten Oberflaechen ist. Dieses Ergebnis ist konsistent mit dem Trend zu Reflexionsspektren von gewoehnlichen Chondriten bei kleineren NEAs, der auch auf das verringerte space weathering an jungen Oberflaechen zurueck gefuehrt wird. NEAs weisen nicht nur eine hoehere Albedo als die groessten MBAs auf, sie differieren auch in ihren thermalen Oberflaecheneigenschaften. Unsere Arbeit bestaetigt die Hypothese, dass diese Asteroiden eine groessere thermische Traegheit als grosse MBAs haben und wir leiten im Zuge dessen einen best-fit Wert von 550±100 J m^(-2) s^(-0.5) K^(-1) fuer die thermische Traegheit der beobachteten NEAs ab. Dieser Wert ist ungefaehr 11-mal höher als der des Mondes und 30-mal hoeher als der der größten Asteroiden 1 Ceres und 2 Pallas. Dieses Resultat hat wichtige Implikationen für unser Verständnis von Natur und Ursprung dieser Objekte. Zum Beispiel weist eine hoehere thermische Traegheit auf groeberes Regolith auf der Oberflaeche dieser Asteroiden im Vergleich zu der des Mondes und, sehr wahrscheinlich, auf eine andere Oberflaechen- Felsverteilung in Bezug auf grosse MBAs hin. Dieses Resultat ergab sich aus dem Studium der Korrelation von beobachteter Verteilung der Oberflaechen-Farbtemperatur von NEAs als Funktion des Phasenwinkels im Lichte eines thermophysikalischen Modells. Das in dieser Arbeit entwickelte Modell bezieht Effekte wie Rotationsrate, thermische Trägheit und Oberflächen-Rauhigkeit für die Berechnung der thermischen Emission von Körpern ohne Atmosphäre ein. Im Speziellen konnten wir demonstrieren, dass die beobachtete Verteilung der Farbtemperatur in Abhaengigkeit vom Phasenwinkel als Mittel zur Bestimmung der thermischen Traegheit (und zum Teil der Oberflaechen-Rauhigkeit) der beobachteten Asteroiden unter der Annahme von zufällig verteilten Spin-Vektoren benutzt werden kann. Mit Hilfe unseres thermophysikalischen Modells konnten wir eine quantitative Bestimmung der Unsicherheiten in Albedo und Durchmesser der NEAs, abgeleitet mit dem Standard Thermal Model (STM) und dem Near Earth Asteroid Thermal Model (NEATM), die beide Annahmen ueber die Oberflaechentemperaturverteilung und thermische Traegheit von NEAs machen, gewinnen. Weiterhin haben wir numerisch eine Korrekturfunktion fuer die radiometrischen Durchmesser und Albedos, die aus dem STM bzw. aus NEATM ermittelt werden, bestimmt, vorausgesetzt Spin Status und thermische Parameter des Asteroiden sind bekannt. Sind solche Informationen nicht verfuegbar, kann die Genauigkeit der NEATM Ergebnisse immer noch auf Basis der abgeleiteten Farbtemperatur der Objekte abgeschätzt werden. Unsere aufregenden neuen Ergebnisse legen nahe, dass die Analyse von thermischen Infrarot- Beobachtungen von NEAs unterschiedlicher Groesse und Klasse mit Hilfe von thermophysikalischen Modellen ein Studium der in der NEA Population vorkommenden thermischen Eigenschaften und Oberflaechenstrukturen möglich macht

Asteroid Bennu Temperature Maps for OSIRIS-REx Spacecraft and Instrument Thermal Analyses

A thermophysical model has been developed to generate asteroid Bennu surface temperature maps for OSIRIS-REx spacecraft and instrument thermal design and analyses at the Critical Design Review (CDR). Two-dimensional temperature maps for worst hot and worst cold cases are used in Thermal Desktop to assure adequate thermal design margins. To minimize the complexity of the Bennu geometry in Thermal Desktop, it is modeled as a sphere instead of the radar shape. The post-CDR updated thermal inertia and a modified approach show that the new surface temperature predictions are more benign. Therefore the CDR Bennu surface temperature predictions are conservative

Physical Characterization of Warm Spitzer-observed Near-Earth Objects

Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic spectral features to specific surface mineralogies. The combination of spectroscopy with albedos and diameters derived from thermal infrared observations can increase the scientific return beyond that of the individual datasets. To that end, we have completed a spectroscopic observing campaign to complement the ExploreNEOs Warm Spitzer program that obtained albedos and diameters of nearly 600 NEOs (Trilling et al. 2010). Here we present the results of observations using the low-resolution prism mode (~0.7-2.5 microns) of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also include near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our survey and 213 observations of 154 objects from the MIT survey). We identify a taxonomic class for each spectrum and use band parameter analysis to investigate the mineralogies for the S-, Q-, and V-complex objects. Our analysis suggests that for spectra that contain near-infrared data but lack the visible wavelength region, the Bus-DeMeo system misidentifies some S-types as Q-types. We find no correlation between spectral band parameters and ExploreNEOs albedos and diameters. We find slightly negative Band Area Ratio (BAR) correlations with phase angle for Eros and Ivar, but a positive BAR correlation with phase angle for Ganymed. We find evidence for spectral phase reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary chondrite type analog for a subset of our sample. Our resulting proportions of H, L, and LL ordinary chondrites differ from those calculated for meteorite falls and in previous studies of ordinary chondrite-like NEOs.Comment: 6 Tables, 9 Figure

Extending Lunar Impact Flash Observations into the Daytime with Short-Wave Infrared

Lunar impact flash (LIF) observations typically occur in R, I, or unfiltered light, and are only possible during night, targeting the night side of a 10-60% illumination Moon, while >10{\deg} above the observers horizon. This severely limits the potential to observe, and therefore the number of lower occurrence, high energy impacts observed is reduced. By shifting from the typically used wavelengths to the J-Band Short-Wave Infrared, the greater spectral radiance for the most common temperature (2750 K) of LIFs and darker skies at these wavelengths enables LIF monitoring to occur during the daytime, and at greater lunar illumination phases than currently possible. Using a 40.0 cm f/4.5 Newtonian reflector with Ninox 640SU camera and J-band filter, we observed several stars and lunar nightside at various times to assess the theoretical limits of the system. We then performed LIF observations during both day and night to maximise the chances of observing a confirmed LIF to verify the methods. We detected 61 >5{\sigma} events, from which 33 candidate LIF events could not be discounted as false positives. One event was confirmed by multi-frame detection, and by independent observers observing in visible light. While this LIF was observed during the night, the observed signal can be used to calculate the equivalent Signal-to-Noise ratio for a similar daytime event. The threshold for daylight LIF detection was found to be between Jmag=+3.4+-0.18 and Jmag=+5.6+-0.18 (Vmag=+4.5 and Vmag=+6.7 respectively at 2750 K). This represents an increase in opportunity to observe LIFs by almost 500%