An analysis of the peculiar A star HD 204411

Spectrum analysis of cool Ap star HD 20441

RELBET 4.0 user's guide

This manual describes the operation and use of RELBET 4.0 implemented on the Hewlett Packard model 9000. The RELBET System is an integrated collection of computer programs which support the analysis and post-flight reconstruction of vehicle to vehicle relative trajectories of two on-orbit free-flying vehicles: the Space Shuttle Orbiter and some other free-flyer. The manual serves both as a reference and as a training guide. Appendices provide experienced users with details and full explanations of program usage. The body of the manual introduces new users to the system by leading them through a step by step example of a typical production. This should equip the new user both to execute a typical production process and to understand the most significant variables in that process

Rotation In Young Stars

The smallest molecular cores observed to date have at least ∼6 orders of magnitude greater angular momentum per unit mass than the Sun, suggesting that they would greatly exceed the breakup velocity if no angular momentum was lost during the star formation process. Therefore, an angular momentum regulation mechanism must be at work in the pre-main-sequence phase, and disks are often invoked as the solution to the angular momentum problem. Thanks to large-format CCDs, more than 1000 periods for young stars are now known (with more being presented at this conference), and with the Spitzer Space Telescope, we have the ability to get reliable circumstellar disk indicators for many 1000s of stars at once. Now, for the first time, we may have enough stars to start to constrain the angular momentum loss mechanism in a meaningful fashion. In this contribution, we review the observations made to date of rotation in pre-main-sequence low-mass stars

The Early Angular Momentum History of Low Mass Stars: Evidence for a Regulation Mechanism

We examine the early angular momentum history of stars in young clusters via 197 photometric periods in fields flanking the Orion Nebula Cluster (ONC), 81 photometric periods in NGC 2264, and 202 measurements of v sin i in the ONC itself. We show that PMS stars spanning an age range from 0.1 to 3 Myr do not appear to conserve stellar angular momentum as they evolve down their convective tracks, but instead preserve the same range of periods even though they have contracted by about a factor of three. This result seems to require a mechanism that regulates the angular velocities of young stars. We discuss several candidate mechanisms. The most plausible appears to be disk-locking, though most of our stars do not have (I-K) excesses suggestive of disks. However, a decisive test of this hypothesis requires a more sensitive diagnostic than the (I-K) excesses used here.Comment: 32 pages, 11 figures, accepted to A

Self-Generated Magnetic Fields in Galactic Cooling Flows

Interstellar magnetic fields in elliptical galaxies are assumed to have their origin in stellar fields that accompany normal mass loss from an evolving population of old stars. The seed fields are amplified by interstellar turbulence driven by stellar mass loss and supernova events. These disordered fields are further amplified by time-dependent compression in the inward moving galactic cooling flow and are expected to dominate near the galactic core. Under favorable circumstances, fields similar in strength to those observed $B \sim 1-10~(r/10~kpc)^{-1.2}\mu$G can be generated solely from these natural galactic processes. In general the interstellar field throughout elliptical galaxies is determined by the outermost regions in the interstellar gas where the turbulent dynamo process can occur. Because of the long hydrodynamic flow times in galactic cooling flows, currently observed magnetic fields may result from periods of intense turbulent field amplification that occurred in the outer galaxy in the distant past. Particularly strong fields in ellipticals may result from ancient galactic mergers or shear turbulence introduced at the boundary between the interstellar gas and ambient cluster gas.Comment: 21 pages in AASTEX LaTeX with 2 figures; accepted by Astrophysical Journa

No Fossil Disk in the T Tauri Multiple System V773 Tau

We present new multi-epoch near-infrared and optical high-angular images of the V773 Tau pre-main sequence triple system, a weak-line T Tauri (WTTS) system in which the presence of an evolved, ``fossil'' protoplanetary disk has been inferred on the basis of a significant infrared excess. Our images reveal a fourth object bound to the system, V773 Tau D. While it is much fainter than all other components at 2 micron, it is the brightest source in the system at 4.7 micron. We also present medium-resolution K band adaptive optics spectroscopy of this object, which is featureless with the exception of a weak Br gamma emission line. Based on this spectrum and on the spectral energy distribution of the system, we show that V773 Tau D is another member of the small class of ``infrared companions'' (IRCs) to T Tauri stars. It is the least luminous, and probably the least massive, component of the system, as opposed to most other IRCs, which suggests that numerous low-luminosity IRCs such as V773 Tau D may still remain to be discovered. Furthermore, it is the source of the strong IR excess in the system. We therefore reject the interpretation of this excess as the signature of a fossil (or ``passive'') disk and further suggest that these systems may be much less frequent than previously thought. We further show that V773 Tau C is a variable classical T Tauri star (CTTS) and that its motion provides a well constrained orbital model. We show that V773 Tau D can be dynamically stable within this quadruple system if its orbit is highly inclined. Finally, V773 Tau is the first multiple system to display such a variety of evolutionary states (WTTS, CTTS, IRC), which may be the consequence of the strong star-star interactions in this compact quadruple system.Comment: Accepted for publication in Astrophysical Journal, 29 pages, 2 tables, 5 figure