Search Publications
HE 1113-0641: The Smallest-Separation Quadruple Lens Identified by a Ground-Based Optical Telescope
Wisotzki, Lutz; Schechter, Paul L.; Blackburne, Jeffrey A.
The Hamburg/ESO quasar HE 1113-0641 is found to be a quadruple gravitational lens, based on observations with the twin 6.5 m Magellan telescopes at the Las Campanas Observatory, and subsequently with the Hubble Space Telescope. The zS = 1.235 quasar appears in a cross configuration, with i' band magnitudes ranging from 18.0 to 18.8. Wit…
The central region of M83
Houghton, R. C. W.; Thatte, N.
We combine VLT/ISAAC near-infrared (NIR) spectroscopy with archival HST/WFPC2 and HST/NICMOS imaging to study the central 20 × 20arcsec2 of M83. Our NIR indices for clusters in the circumnuclear starburst region are inconsistent with simple instantaneous burst models. However, models of a single burst dispersed over a duration of 6 Myr …
The lower exosphere of Titan: Energetic neutral atoms absorption and imaging
Krupp, N.; Dandouras, I.; Garnier, P. +8 more
The Saturn magnetosphere interacts with the Titan atmosphere through various mechanisms. One of them leads, by charge exchange reactions between the energetic Saturnian ions and the exospheric neutrals of Titan, to the production of energetic neutral atoms (ENAs). The Ion and Neutral Camera (INCA), one of the three sensors that comprise the Magnet…
Using Resolved Galaxies in Hubble Space Telescope Images to Measure Absolute Proper Motions
Anderson, Jay; Mahmud, Naved
We explore the possibility of using resolved background galaxies to measure accurate absolute proper motions with the Hubble Space Telescope. Because galaxies are not point sources, we cannot use stellar point-spread functions (PSFs) to measure their positions. Rather, we must develop a template for each galaxy that can be used to measure a consis…
New astrometric observations of Phobos with the SRC on Mars Express
Jaumann, R.; Oberst, J.; Matz, K. -D. +5 more
Aims: New astrometric measurements for Phobos are reported on the basis of 69 SRC (Super Resolution Channel) images obtained during 28 Mars Express Phobos flybys executed between 2004 and 2007.
Methods: The measurements have been made using a newly developed technique that involves positional measurements of surface control points and verifica…
GALS - Gradient Analysis by Least Squares
Hamrin, M.; Vaivads, A.; Rönnmark, K. +2 more
We present a method, GALS (Gradient Analysis by Least Squares) for estimating the gradient of a physical field from multi-spacecraft observations. To obtain the best possible spatial resolution, the gradient is estimated in the frame of reference where structures in the field are essentially locally stationary. The estimates are refined iterativel…
On the properties of O + and O 2+ ions in a hybrid model and in Mars Express IMA/ASPERA-3 data: A case study
Kallio, E.; Fedorov, A.; Budnik, E. +3 more
We have performed a numerical simulation to analyze the energy spectra of escaping planetary O + and O 2+ ions at Mars. The simulated time-energy spectrograms were generated along orbit no. 555 (June 27, 2004) of Mars Express when its Ion Mass Analyzer (IMA)/ASPERA-3 ion instrument detected escaping planetary ions.…
Foreshock density holes in the context of known upstream plasma structures
Parks, G. K.; Mazelle, C.; Harris, A. +4 more
We present case examples of foreshock density holes and results from a statistical survey, which provide additional characterizations of these recently-described structures. Specific effort is made to place these objects into context with well-studied foreshock phenomena, such as hot flow anomalies (HFAs) and large-amplitude magnetic pulsations (S…
A Comparison of Weak-Lensing Measurements from Ground- and Space-Based Facilities
Ellis, Richard S.; Massey, Richard; Rhodes, Jason +2 more
We assess the relative merits of weak-lensing surveys, using overlapping imaging data from the ground-based Subaru telescope and the Hubble Space Telescope (HST). Our tests complement similar studies undertaken with simulated data. From observations of 230,000 matched objects in the 2 deg2 COSMOS field, we identify the limit at which fa…
The solar wind disappearance event of 11 May 1999: source region evolution
Mason, H. E.; Janardhan, P.; Tripathi, D.
Context: A recent, detailed study of the well-known “solar wind disappearance event” of 11 May 1999 traced its origin to a coronal hole (CH) lying adjacent to a large active region (AR), AR8525 in Carrington rotation 1949. The AR was located at central meridian on 05 May 1999 when the flows responsible for this event began. We examine the evolutio…