Search Publications
Helioseismic Constraints on the Structure of the Solar Tachocline
Thompson, M. J.; Christensen-Dalsgaard, J.; Schou, J. +4 more
This paper presents a series of helioseismic inversions aimed at determining with the highest possible confidence and accuracy the structure of the rotational shear layer (the tachocline) located beneath the base of the solar convective envelope. We are particularly interested in identifying features of the inversions that are robust properties of…
The Age of β Pictoris
Barrado y Navascués, David; Stauffer, John R.; Song, Inseok +1 more
We have reanalyzed data for the proposed moving group associated with β Pictoris in order to determine if the group (or part of it) is real and, if so, to derive an improved age estimate for β Pic. By using new, more accurate proper motions from PPM and Hipparcos and a few new radial velocities, we conclude that on kinematic grounds, most of the p…
Plasma Properties in Coronal Holes Derived from Measurements of Minor Ion Spectral Lines and Polarized White Light Intensity
Fineschi, Silvano; Kohl, John L.; Raymond, John C. +5 more
Recent observations of the Lyα λ1216, Mg X λ625, and O VI λ1038 spectral lines carried out with the Ultraviolet Coronagraph Spectrometer (UVCS) on board SOHO at distances in the range 1.35-2.1 RS in the northern coronal hole are used to place limits on the turbulent wave motions of the background plasma and the thermal motions of the pr…
A Markov Stochastic Process Theory of Cosmic-Ray Modulation
Zhang, Ming
This paper introduces the use of Markov stochastic process theory to study heliospheric modulation of cosmic rays. The basic cosmic-ray transport equation is reformulated with a set of stochastic differential equations that describe the guiding center and momentum of individual charged particles randomly walking in the heliospheric magnetic field.…
SOHO EIT Observations of Extreme-Ultraviolet ``Dimming'' Associated with a Halo Coronal Mass Ejection
Sterling, Alphonse C.; Nitta, Nariaki; Thompson, Barbara J. +2 more
A solar flare was observed on 1997 April 7 with the Soft X-ray Telescope (SXT) on Yohkoh. The flare was associated with a ``halo'' coronal mass ejection (CME). The flaring region showed areas of reduced soft X-ray (SXR) brightness--``dimmings''--that developed prior to the CME observed in white light and persisted for several hours following the C…
The Optical Mass-Luminosity Relation at the End of the Main Sequence (0.08-0.20 Msolar)
Henry, Todd J.; Kirkpatrick, J. Davy; Wasserman, Lawrence H. +5 more
The empirical mass-luminosity relation at MV is presented for stars with masses 0.08-0.20 Msolar based upon new observations made with Fine Guidance Sensor 3 on the Hubble Space Telescope. The targets are nearby, red dwarf multiple systems in which the magnitude differences are typically measured to +/-0.1 mag or better. The …
Effects of Tidal Shocks on the Evolution of Globular Clusters
Ostriker, Jeremiah P.; Lee, Hyung Mok; Gnedin, Oleg Y.
We present new Fokker-Planck models of the evolution of globular clusters, including gravitational tidal shocks. We extend our calculations beyond the core collapse by adopting three-body binary heating. Effects of the shocks are included by adding the tidal shock diffusion coefficients to the ordinary Fokker-Planck equation: the first-order heati…
The η Chamaeleontis Cluster: A Remarkable New Nearby Young Open Cluster
Feigelson, Eric D.; Mamajek, Eric E.; Lawson, Warrick A.
A cluster of young, X-ray-emitting stars is found in the vicinity of η Chamaeleontis from a deep ROSAT high-resolution imager observation. The 12 X-ray sources have prominent (R=5-14) stellar counterparts, including two early-type stars (η Cha and RS Cha) and 10 Li-rich, Hα emission-line, late-type stars (K3-M5). Hipparcos astrometry reveals that …
Dust in the Local Interstellar Wind
Zank, Gary P.; Slavin, Jonathan D.; Geiss, Johannes +13 more
The gas-to-dust mass ratios found for interstellar dust within the solar system, versus values determined astronomically for the cloud around the solar system, suggest that large and small interstellar grains have separate histories and that large interstellar grains preferentially detected by spacecraft are not formed exclusively by mass exchange…
Observations of a Z = 1.44 Dusty, Ultraluminous Galaxy and Implications for Deep Submillimeter Surveys
Smail, Ian; Graham, James R.; Dey, Arjun +3 more
We present new near-infrared and optical spectroscopic observations that confirm the redshift of the z=1.44 extremely red object ERO J164502+4626.4 (object 10 of Hu & Ridgway, formerly known as HR 10 or [HR94] 10) and a Hubble Space Telescope image that reveals a reflected S-shaped morphology at (rest-frame) near-ultraviolet wavelengths. The c…