Search Publications
Estimation of the total electron content of the Martian ionosphere using radar sounder surface echoes
Gim, Yonggyu; Kofman, Wlodek; Herique, Alain +5 more
The Martian ionosphere's local total electron content (TEC) and the neutral atmosphere scale height can be derived from radar echoes reflected from the surface of the planet. We report the global distribution of the TEC by analyzing more than 750,000 echoes of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). This is the fi…
A Morphological Study of Gamma-Ray Burst Host Galaxies
Berger, E.; Penprase, B. E.; Wainwright, C.
We present a comprehensive study of the morphological properties of 42 γ-ray burst (GRB) host galaxies imaged with the Hubble Space Telescope in the optical band. The purpose of this study is to understand the relation of GRBs to their macroenvironments and to compare the GRB-selected galaxies to other high-redshift samples. We perform both qualit…
The Coronal Heating Paradox
Peter, Hardi; Aschwanden, Markus J.; Winebarger, Amy +1 more
The ``coronal heating problem'' has been with us over 60 years, and hundreds of theoretical models have been proposed without an obvious solution in sight. In this paper we point out that observations show no evidence for local heating in the solar corona, but rather for heating below the corona in the transition region and upper chromosphere, wit…
Search for Polarization from the Prompt Gamma-Ray Emission of GRB 041219a with SPI on INTEGRAL
Kouveliotou, C.; Baring, M. G.; Boggs, S. E. +2 more
Measuring the polarization of the prompt γ-ray emission from gamma-ray bursts (GRBs) can significantly improve our understanding of both the GRB emission mechanisms as well as the underlying engine driving the explosion. We searched for polarization in the prompt γ-ray emission of GRB 041219a with the SPI instrument on INTEGRAL. Using multiple-det…
Super Star Cluster Velocity Dispersions and Virial Masses in the M82 Nuclear Starburst
Graham, James R.; McCrady, Nate
We use high-resolution near-infrared spectroscopy from Keck Observatory to measure the stellar velocity dispersions of 19 super star clusters (SSCs) in the nuclear starburst of M82. The clusters have ages on the order of 10 Myr, which is many times longer than the crossing times implied by their velocity dispersions and radii. We therefore apply t…
Hard X-ray emission from the Galactic ridge
Sunyaev, R.; Krivonos, R.; Revnivtsev, M. +3 more
We present results of a study of the Galactic ridge X-ray emission (GRXE) in hard X-rays performed with the IBIS telescope aboard INTEGRAL. The imaging capabilities of this coding aperture telescope make it possible to account for the flux from bright Galactic point sources whereas the wide field of view permits us to collect large flux from the u…
Principal Component Analysis of the Time- and Position-dependent Point-Spread Function of the Advanced Camera for Surveys
Ford, H. C.; Jee, M. J.; Blakeslee, J. P. +3 more
We describe the time- and position-dependent point-spread function (PSF) variation of the wide-field channel (WFC) of the Advanced Camera for Surveys (ACS) with the principal component analysis (PCA) technique. The time-dependent change is caused by the temporal variation of the HST focus, whereas the position-dependent PSF variation in ACS WFC at…
Why Haven't Loose Globular Clusters Collapsed Yet?
Paresce, Francesco; De Marchi, Guido; Pulone, Luigi
We report on the discovery of a surprising observed correlation between the slope of the low-mass stellar global mass function (GMF) of globular clusters (GCs) and their central concentration parameter c=log(rt/rc), i.e., the logarithmic ratio of tidal and core radii. This result is based on the analysis of a sample of 20 Gal…
Saturnian magnetospheric dynamics: Elucidation of a camshaft model
Southwood, D. J.; Kivelson, M. G.
Periodic modulation of magnetospheric phenomena at Earth and Jupiter results principally from the tilt of the dipole axis relative to the rotation axis. Saturn's nearly aligned dipole moment is tilted by less than 0.5° from the spin axis, yet the power of radio-frequency emissions, the orientation of the magnetic field, and many properties of the …
The ACS Fornax Cluster Survey. II. The Central Brightness Profiles of Early-Type Galaxies: A Characteristic Radius on Nuclear Scales and the Transition from Central Luminosity Deficit to Excess
Jordán, Andrés; Infante, Leopoldo; Tonry, John L. +9 more
We analyze brightness profiles for 143 early-type galaxies in the Virgo and Fornax Clusters, observed with the Advanced Camera for Surveys on the Hubble Space Telescope. Sérsic models are found to provide accurate representations of the global profiles with a notable exception: the observed profiles deviate systematically inside a characteristic `…