The Distance to the Coma Cluster from Surface Brightness Fluctuations

We report on the first determination of the distance to the Coma Cluster based on surface brightness fluctuation (SBF) measurements obtained from Hubble Space Telescope WFPC2 observations of the bright E0 galaxy NGC 4881 in the Coma Cluster and ground-based observations of the standard E1 galaxy NGC 3379 in the Leo-I group. Relative distances based on the I-band fluctuation magnitude, I(SBF), are strongly dependent on metallicity and age of the stellar population. However, the radial changes in the stellar populations of the two giant ellipticals, NGC 3379 and NGC 4881, are well described by published Mg_2 gradients, and the ground-based measurements of I(SBF) at several radial points in NGC 3379 are used to calibrate I(SBF) in terms of the Mg_2 index. The distance to NGC 3379, assumed to be identical to the average SBF distance of the Leo-I group, is combined with the new SBF measurements of NGC 4881 to obtain a Coma Cluster distance of 102+-14 Mpc. Combining this distance with the cosmic recession velocity of Coma (7186+-428 km/s), we find the Hubble constant to be H_0 = 71+-11 km/s/Mpc.Comment: 12 pages, LaTex, includes aaspp4.sty and 3 eps figures. To appear in ApJ Letter

AVAST Survey 0.4-1.0 {\mu}m Spectroscopy of Igneous Asteroids in the Inner and Middle Main Belt

We present the spectra of 60 asteroids, including 47 V-types observed during the first phase of the Adler V-Type Asteroid (AVAST) Survey. SDSS photometry was used to select candidate V-type asteroids for follow up by nature of their very blue $i-z$ color. 47 of the 61 observed candidates were positively classified as V-type asteroids, while an additional six show indications of a 0.9 $\mu$m feature consistent with V-type spectra, but not sufficient for formal classification. Four asteroids were found to be S-type, all of which had $i-z$ values very near the adopted AVAST selection criteria of $i-z \le -0.2$, including one candidate observed well outside the cut (at a mean $i-z$ of -0.11). Three A-type asteroids were also identified. Six V-type asteroids were observed beyond the 3:1 mean motion resonance with Jupiter, including the identification of two new V-type asteroids (63085 and 105041) at this distance. Six V-type asteroids were observed with low ($<5\deg$) orbital inclination, outside of the normal dynamical range of classic Vestoids, and are suggestive of a non-Vesta origin for at least some of the population.Comment: 1 table, 3 figures, To appear to Icaru

Moon Zoo: citizen science in lunar exploration

The Moon Zoo Team describe how citizen scientists can get involved and explore the Moon online

Solar System Objects Observed in the SDSS Commissioning Data

We discuss measurements of the properties of about 10,000 asteroids detected in 500 deg2 of sky in the Sloan Digital Sky Survey (SDSS) commissioning data. The moving objects are detected in the magnitude range 14 < r < 21.5, with a baseline of 5 minutes. Extensive tests show that the sample is at least 98% complete, with the contamination rate of less than 3%. We find that the size distribution of asteroids resembles a broken power-law, independent of the heliocentric distance: D^{-2.3} for 0.4 km < D < 5 km, and D^{-4} for 5 km < D < 40 km. As a consequence of this break, the number of asteroids with r < 21.5 is ten times smaller than predicted by extrapolating the power-law relation observed for brighter asteroids (r < 18). The observed counts imply that there are about 530,000 objects with D>1 km in the asteroid belt, or about four times less than previous estimates. The distribution of main belt asteroids in the 4-dimensional SDSS color space is bimodal, and the two groups can be associated with S (rocky) and C (carbonaceous) asteroids. A strong bimodality is also seen in the heliocentric distribution of asteroids and suggests the existence of two distinct belts: the inner rocky belt, about 1 AU wide (FWHM) and centered at R~2.8 AU, and the outer carbonaceous belt, about 0.5 AU wide and centered at R~3.2 AU. The colors of Hungarias, Mars crossers, and near-Earth objects are more similar to the C-type than to S-type asteroids, suggesting that they originate in the outer belt. (abridged).Comment: 89 pages, 31 figures, submitted to A

The composition of near-earth objects

Thesis (Ph. D.)--University of Washington, 1998I present reflectance spectra of 34 near-Earth objects (NEOs), 6 main-belt asteroids, and four non-NEO cometary candidates, all obtained with the Apache Point Observatory 3.5m telescope + Double Imaging Spectrograph. The spectra cover the wavelength range 3800-10,000 A, encompassing regions of mineralogically important absorption features. Nearly all of the NEOs observed display ultraviolet and near-infrared absorptions characteristic of rock-forming silicate minerals. Of the 27 NEOs belonging to the S or Q taxonomic classes observed in this study, 15 are spectrally indistinguishable from ordinary chondrite meteorites. I perform extensive Monte Carlo simulations of the NEO and main belt populations aimed at quantifying the severe biases affecting observed taxonomic distributions. The bias-corrected NEO population in the 1-10 km diameter range is composed of 67 $\pm$ 13% S- or Q-type, objects, and 30 $\pm$ 7% C-types objects, with the remainder being primarily of the spectrally degenerate X-Class. The NEO population resembles most closely that of the inner main belt near the 3:1 mean motion resonance, and is consistent with that region being the sole source for NEOs. If extinct comet nuclei resemble the primitive taxonomic classes C, P, or D, the cometary component of the NEOs is constrained at \sbsp{\sim}{<}30%. I investigate trends of S-type spectral characteristics with size. The strength of the 1 $\mu$m absorption increases with decreasing size. There is a possible trend towards shorter-wavelength band centers with decreasing size, possibly reflecting a decreasing olivine abundance in the optically active surface fraction. For sizes below about 6 km, the spectral continuum reddens with increasing size. Above 6 km, this trend reverses, and larger objects have on average bluer continua. For the smaller objects, these trends are all consistent with predictions of the "space weathering" hypothesis. The bluer continua of the larger objects remains unexplained. All of these trends appear to be systematically dependent on size; specifically, no distinct separation exists between the larger S-type objects and the smaller ordinary chondrite-like bodies

Astro-Science Workshop: Education and Public Outreach at the Adler Planetarium

Astro-Science Workshop, a 43-year-old program, is a unique opportunity for research astronomers at the Adler Planetarium in Chicago to work with gifted area high school students on project-based learning. In its current form, ASW is funded by a fellowship from the NSF and run by a graduate student from the University of Chicago. The immersion program is as much a learning experience for the graduate student as for the high school students who attend the 3-4 week course. Because the graduate student tailors the program to his/her interests, the program varies greatly from year to year. Recent topics include impacts in the solar system and solar astronomy. Last year the course included an extended weekend at the Yerkes Observatory. The students took images of asteroids with the telescopes on site, analyzed the data themselves, and submitted their measurements of the asteroids' positions to the Minor Planet Center, some of which have already been published on the ADS. The plan for Summer 2007 is a 3-week course on the formation of the Solar System, in which students will explore the near-space environment with high-altitude balloon-born instruments that they build themselves. ASW provides a unique opportunity for an informal learning instituion to connect high school students with astronomers and institutions of higher learning. It has provided over a thousand students with college-level instruction and exposure to the cutting edge of astronomical research