Arecibo Radar Astrometry of the Galilean Satellites from 1999 to 2016

Harmon et al. Arecibo radar observations from 1992 provided some of the most precise line-of-sight distance (ranging) measurements of Ganymede and Callisto to date. We report 18 new ranges obtained at Arecibo from 1999 to 2016, among which are the first measurements of Io and Europa. We also report accompanying line-of-sight velocity (Doppler frequency) measurements. In 2015, we detected Europa, Ganymede, and Callisto with time-delay (range) resolutions as fine as 10 mu s (1.5 km) while Io was detected with 70 mu s (10.5 km) resolution. We estimated residuals for the radar measurements with respect to the latest JPL satellite ephemeris JUP310 and planetary ephemeris DE438. We found that the rms of the time-delay residuals are 29 mu s for Io, 21 mu s for Europa, 58 mu s for Ganymede, and 275 mu s for Callisto. When normalized by the measurement uncertainties, these correspond to the rms of 0.82, 1.25, 2.17, and 3.17 respectively. As such, the orbit of Callisto has the largest residuals and may benefit from an orbital update that will use radar astrometry. All Doppler residuals were small and consistent with their 1 sigma uncertainties.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The Arecibo Legacy Fast ALFA survey I: science goals, survey design, and strategy

The recently initiated Arecibo Legacy Fast ALFA (ALFALFA) survey aims to map 7000 square degrees of the high galactic latitude sky visible from Arecibo, providing a HI line spectral database covering the redshift range between -1600 km/s and 18,000 km/s with 5 km/s resolution. Exploiting Arecibo's large collecting area and small beam size, ALFALFA is specifically designed to probe the faint end of the HI mass function in the local universe and will provide a census of HI in the surveyed sky area to faint flux limits, making it especially useful in synergy with wide area surveys conducted at other wavelengths. ALFALFA will also provide the basis for studies of the dynamics of galaxies within the Local and nearby superclusters, will allow measurement of the HI diameter function, and enable a first wide-area blind search for local HI tidal features, HI absorbers at z < 0.06 and OH megamasers in the redshift range 0.16 < z < 0.25. Although completion of the survey will require some five years, public access to the ALFALFA data and data products will be provided in a timely manner, thus allowing its application for studies beyond those targeted by the ALFALFA collaboration. ALFALFA adopts a two-pass, minimum intrusion, drift scan observing technique which samples the same region of sky at two separate epochs to aid in the discrimination of cosmic signals from noise and terrestrial interference. Survey simulations, which take into account large scale structure in the mass distribution and incorporate experience with the ALFA system gained from tests conducted during its commissioning phase, suggest that ALFALFA will detect on the order of 20,000 extragalactic HI line sources out to z=0.06, including several hundred with HI masses of less than 10^{7.5} msun