Search Publications
Subsurface Meridional Circulation in the Active Belts
Howe, R.; Komm, R.; Hill, F. +2 more
Temporal variations of the subsurface meridional flow with the solar cycle have been reported by several authors. The measurements are typically averaged over periods of time during which surface magnetic activity existed in the regions where the velocities are calculated. The present work examines the possible contamination of these measurements …
Titan's hydrodynamically escaping atmosphere
Strobel, Darrell F.
The upper atmosphere of Titan is currently losing mass at a rate ∼(4-5)×10 amus, by hydrodynamic escape as a high density, slow outward expansion driven principally by solar UV heating by CH 4 absorption. The hydrodynamic mass loss is essentially CH 4 and H 2 escape. Their combined escape rates are restricted by po…
Ionospheric photoelectrons at Venus: Initial observations by ASPERA-4 ELS
Coates, A. J.; Kallio, E.; Fedorov, A. +46 more
We report the detection of electrons due to photo-ionization of atomic oxygen and carbon dioxide in the Venus atmosphere by solar helium 30.4 nm photons. The detection was by the Analyzer of Space Plasma and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) on the Venus Express (VEx) European Space Agency (ESA) mission. Characteristic peaks i…
X-Ray Properties of Protostars in the Orion Nebula
Robberto, M.; Grosso, N.; Micela, G. +8 more
The origin and evolution of the X-ray emission in very young stellar objects (YSOs) are not yet well understood because it is very hard to observe YSOs in the protostellar phase. Using COUP data, we study the X-ray properties of stars in the ONC in different evolutionary classes: luminosities, hydrogen column densities NH, effective pla…
Transverse Oscillations of Flowing Prominence Threads Observed with Hinode
Oliver, R.; Ballester, J. L.; Terradas, J. +1 more
Recent observations with the Hinode Solar Optical Telescope display an active region prominence whose fine threads oscillate in the vertical direction as they move along a path parallel to the photosphere. A seismological analysis of this event is carried out by taking advantage of the small radius of these structures compared to the total length …
X-ray emission from dense plasma in classical T Tauri stars: hydrodynamic modeling of the accretion shock
Orlando, S.; Peres, G.; Reale, F. +3 more
Context: High spectral resolution X-ray observations of classical T Tauri stars (CTTSs) demonstrate the presence of plasma at temperature T∼ 2-3× 106 K and density n_e∼ 1011-1013 cm-3, which are unobserved in non-accreting stars. Stationary models suggest that this emission is due to shock-heated accreti…
The Nascent Red Sequence at z ~ 2
Demarco, R.; Pentericci, L.; Rosati, P. +12 more
We present new constraints on the evolution of the early-type galaxy color-magnitude relation (CMR) based on deep near-infrared imaging of a galaxy protocluster at z = 2.16 obtained using NICMOS on board the Hubble Space Telescope. This field contains a spectroscopically confirmed space overdensity of Lyα- and Hα-emitting galaxies that surrounds t…
Mass and gas profiles in A1689: joint X-ray and lensing analysis
Lemze, Doron; Rephaeli, Yoel; Barkana, Rennan +1 more
We carry out a comprehensive joint analysis of high-quality HST/ACS and Chandra measurements of A1689, from which we derive mass, temperature, X-ray emission and abundance profiles. The X-ray emission is smooth and symmetric, and the lensing mass is centrally concentrated indicating a relaxed cluster. Assuming hydrostatic equilibrium we deduce a 3…
Realistic Numerical Simulations of Solar Convection and Oscillations in Magnetic Regions
Kosovichev, A. G.; Mansour, N. N.; Jacoutot, L. +1 more
We have used 3D, compressible, nonlinear radiative magnetohydrodynamics simulation to study the influence of magnetic fields of various strengths on convective cells and on the excitation mechanisms of acoustic oscillations by calculating the spectral properties of the convective motions and oscillations. The results reveal substantial changes of …
Main-Sequence Fitting Distance to the σ Ori Cluster
Walter, F. M.; Wolk, S. J.; Sherry, W. H. +1 more
The σ Ori cluster is an unbound aggregate of a few hundred young, low-mass stars centered on the multiple system σ Ori. This cluster is of great interest because it is at an age when roughly half of the stars have lost their protoplanetary disks, and the cluster has a very large population of brown dwarfs. One of the largest sources of uncertainty…