Mark Willman

A spectroscopic comparison of HED meteorites and V-type asteroids in the inner Main Belt

V-type asteroids in the inner Main Belt (a < 2.5 AU) and the HED meteorites are thought to be genetically related to one another as collisional fragments from the surface of the large basaltic Asteroid 4 Vesta. We investigate this relationship by comparing the near-infrared (0.7–2.5 lm) spectra of 39 V-type asteroids to laboratory spectra of HED meteorites. The central wavelengths and areas spanned by the 1 and 2 lm pyroxene–olivine absorption bands that are characteristic of planetary basalts are measured for both the asteroidal and meteoritic data. The band centers are shown to be well correlated, however the ratio of areas spanned by the 1 and 2 lm absorption bands are much larger for the asteroids than for the meteorites. We argue that this offset in band area ratio is consistent with our currently limited understanding of the effects of space weathering, however we cannot rule out the possibility that this offset is due to compositional differences. Several other possible causes of this offset are discussed. Amongst these inner Main Belt asteroids we do not find evidence for non-Vestoid mineralogies. Instead, these asteroids seem to represent a continuum of compositions, consistent with an origin from a single differentiated parent body. In addition, our analysis shows that V-type asteroids with low inclinations (i <6 ) tend to have band centers slightly shifted towards long wavelengths. This may imply that more than one collision on Vesta’s surface was responsible for producing the observed population of inner belt V-type asteroids. Finally, we offer several predictions that can be tested when the Dawn spacecraft enters into orbit around Vesta in the summer of 2011.

The Distribution of Basaltic Asteroids in the Main Belt

Abstract We present the observational results of a survey designed to target and detect asteroids whose photometric colors are similar to those of Vesta family members and thus may be considered as candidates for having a basaltic composition. Fifty basaltic candidates were selected with orbital elements that lie outside of the Vesta dynamical family. Optical and near-infrared spectra were used to assign a taxonomic type to 11 of the 50 candidates. Ten of these were spectroscopically confirmed as V-type asteroids, suggesting that most of the candidates are basaltic and can be used to constrain the distribution of basaltic material in the Main Belt. Using our catalog of V-type candidates and the success rate of the survey, we calculate unbiased size-frequency and semi-major axis distributions of V-type asteroids. These distributions, in addition to an estimate for the total mass of basaltic material, suggest that Vesta was the predominant contributor to the basaltic asteroid inventory of the Main Belt, however scattered planetesimals from the inner Solar System ( a 2.0 AU ) and other partially/fully differentiated bodies likely contributed to this inventory. In particular, we infer the presence of basaltic fragments in the vicinity of Asteroid 15 Eunomia, which may be derived from a differentiated parent body in the middle Main Belt ( 2.5 a 2.8 ). We find no asteroidal evidence for a large number of previously undiscovered basaltic asteroids, which agrees with previous theories suggesting that basaltic fragments from the ∼100 differentiated parent bodies represented in meteorite collections have been “battered to bits” [Burbine, T.H., Meibom, A., Binzel, R.P., 1996. Meteorit. Planet. Sci. 31, 607–620].

Using the youngest asteroid clusters to constrain the space weathering and gardening rate on S-complex asteroids

We provide evidence of consistency between the dynamical evolution of main belt asteroids and their color evolution due to space weathering. The dynamical age of an asteroid’s surface (Bottke et al. 2005; Nesvorný et al. 2005) is the time since its last catastrophic disruption event which is a function of the object’s diameter. The age of an S-complex asteroid’s surface may also be determined from its color using a space weathering model (e.g. Willman et al. 2010; Jedicke et al. 2004; Willman et al. 2008; Marchi et al. 2006). We used a sample of 95 S-complex asteroids from SMASS and obtained their absolute magnitudes and u, g, r, i, z filter magnitudes from SDSS. The absolute magnitudes yield a size-derived age distribution. The u, g, r, i, z filter magnitudes lead to the principal component color which yields a color-derived age distribution by inverting our color-age relationship, an enhanced version of the ‘dual τ ’ space weathering model of Willman et al. (2010). We fit the size-age distribution to the enhanced dual τ model and found characteristic weathering and gardening times of τw = 2050± 80 Myr and τg = 4400 −500 Myr respectively. The fit also suggests an initial principal component color of −0.05 ± 0.01 for fresh asteroid surface with a maximum possible change of the probable color due to weathering of ∆PC = 1.34± 0.04. Our predicted color of fresh asteroid surface matches the color of fresh ordinary chondritic surface of PC1 = 0.17± 0.39.

A SPECTROSCOPICALLY UNIQUE MAIN-BELT ASTEROID: 10537 (1991 RY16)

We present visible and near-infrared reflectance spectra and interpreted surface mineralogy for asteroid 10537 (1991 RY16). The spectrum of this object is without precedent among the main-belt asteroids. A unique absorption band centered at 0.63 mm could be attributed to one of several mineralogies. Pronounced 1 and 2 mm absorption bands suggest that the composition of 10537 is a mixture of pyroxenes and olivine and that it originated from a parent body that was partially or fully differentiated. The closest available analog is the large main-belt asteroid 349 Dembowska, but 10537 may be an isolated fragment from a completely eroded parent body. Subject headings: minor planets, asteroids — solar system: formation

Supernovae 2016bdu and 2005gl, and their link with SN 2009ip-like transients: another piece of the puzzle

PRIN-INAF; MIUR PRIN; Royal Society - Science Foundation Ireland University Research Fellowship; European Union through ERC [320360]; US National Science Foundation (NSF) [AST-1515876, AST-1515927]; NSFC [11573003]; Chinese Academy of Sciences [XDB09000000]; National Aeronautics and Space Administration (NASA) - Space Telescope Science Institute (STScI) [HST-HF-51348.001]; NASA [NAS 5-26555, NN12AR55G, NNX08AR22G, NNX12AR65G, NNX14AM74G]; NSF [AST-1515927, AST-1211916, PHY-1607611, AST-1313422, AST-1413600]; TABASGO Foundation; Christopher R. Redlich Fund; Miller Institute for Basic Research in Science (U.C. Berkeley); STScI [HST-AR-14295]; DOE [DE-FG02-97ER25308]; FONDECYT [1151445]; Ministry of Economy, Development, and Tourisms Millennium Science Initiative [IC120009]; ERCgrant [291222]; Emil Aaltonen Foundation; Finnish Cultural Foundation; Vilho, Yrjo and Kalle Vaisala Foundation of the Finnish Academy of Science and Letters; EU via ERCgrant [307260]; Quantum Universe I-Core program by Israeli Committee for Planning and Budgeting; ISF; Kimmel award; Israel Science Foundation, Minerva; I-CORE Program of the Planning and Budgeting Committee; Israel Science Foundation; Danish Agency for Science and Technology and Innovation through Sapere Aude; Villum foundation; Instrument Center for Danish Astrophysics (IDA); Gordon and Betty Moore Foundation [GBMF5490]; Center for Cosmology and Astro-Particle Physics (CCAPP) at OSU; Chinese Academy of Sciences South America Center for Astronomy (CASSACA); Mt Cuba Astronomical Foundation; US NSF [AST-1238877]; UK Science and Technology Facilities Council; NASA; NSF

The Foundation Supernova Survey Motivation, design, implementation, and first data release

© 2017 The Author(s). The Foundation Supernova Survey aims to provide a large, high-fidelity, homogeneous, and precisely calibrated low-redshift Type Ia supernova (SN Ia) sample for cosmology. The calibration of the current low-redshift SN sample is the largest component of systematic uncertainties for SN cosmology, and new data are necessary to make progress. We present the motivation, survey design, observation strategy, implementation, and first results for the Foundation Supernova Survey. We are using the Pan-STARRS telescope to obtain photometry for up to 800 SNe Ia at z>~0.1. This strategy has several unique advantages: (1) the Pan-STARRS system is a superbly calibrated telescopic system, (2) Pan-STARRS has observed 3/4 of the sky in grizyP1 making future template observations unnecessary, (3) we have a well-tested data-reduction pipeline, and (4) we have observed ~3000 high-redshift SNe Ia on this system. Here, we present our initial sample of 225 SN Ia grizP1light curves, of which 180 pass all criteria for inclusion in a cosmological sample. The Foundation Supernova Survey already contains more cosmologically useful SNe Ia than all other published low-redshift SN Ia samples combined. We expect that the systematic uncertainties for the Foundation Supernova Sample will be two to three times smaller than other low-redshift samples.We find that our cosmologically useful sample has an intrinsic scatter of 0.111 mag, smaller than other low-redshift samples. We perform detailed simulations showing that simply replacing the current low-redshift SN Ia sample with an equally sized Foundation sample will improve the precision on the dark energy equation-of-state parameter by 35 per cent, and the dark energy figure of merit by 72 per cent.

A transient search using combined human and machine classifications

Large modern surveys require efficient review of data in order to find transient sources such as supernovae, and to distinguish such sources from artefacts and noise. Much effort has been put into the development of automatic algorithms, but surveys still rely on human review of targets. This paper presents an integrated system for the identification of supernovae in data from Pan-STARRS1, combining classifications from volunteers participating in a citizen science project with those from a convolutional neural network. The unique aspect of this work is the deployment, in combination, of both human and machine classifications for near real-time discovery in an astronomical project. We show that the combination of the two methods outperforms either one used individually. This result has important implications for the future development of transient searches, especially in the era of Large Synoptic Survey Telescope and other large-throughput surveys.