March 2001 arXiv papers — page 28

Paul J. Wiita

Extragalactic radio sources, including quasars, are now typically understood as being produced by a pair of nearly symmetric, oppositely directed relativistic jets. While some these sources span megaparsecs, and are thus the largest physically connected structures in the universe, emitting regions identified as jets have now been found on all scales down to

Bo Reipurth, Cathie Clarke

We conjecture that brown dwarfs are substellar objects because they have been ejected from small newborn multiple systems which have decayed in dynamical interactions. In this view, brown dwarfs are stellar embryos for which the star formation process was aborted before the hydrostatic cores could build up enough mass to eventually start hydrogen burning. Th

Peter Coles

I review the standard paradigm for understanding the formation and evolution of cosmic structure, based on the gravitational instability of dark matter, but many variations on this basic theme are viable. Despite the great progress that has undoubtedly been made, steps are difficult because of uncertainties in the cosmological parameters, in the modelling of

A. A. Suchkov

Binary F stars exhibit large brightness anomaly, which is defined here as the difference between the absolute magnitude from the uvby photometry and the actual absolute magnitude of the star. We have found that the anomaly inversely correlates with the binary components separation. There is evidence that the correlation reflects actual population differences

H. -Th. Janka, K. Kifonidis, M. Rampp

The current picture of the collapse and explosion of massive stars and the formation of neutron stars is reviewed. According to the favored scenario, however by no means proven and undisputed, neutrinos deposit the energy of the explosion in the stellar medium which surrounds the nascent neutron star. Observations, in particular of Supernova~1987A, suggest t

Nicolas Grosso

I analyze unpublished or partially published archival ROSAT data of the rho Ophiuchi dark cloud. This set of seven overlapping ROSAT HRI pointings, composed of eight ~one-hour exposures, detects mainly the X-ray brightest T Tauri stars of this star-forming region. Only two HRI sources are new X-ray sources, and their optical counterparts are proposed as new

A. Sivaramakrishnan, C. D. Koresko, R. B. Makidon, T. Berkefeld

We summarize the theory of coronagraphic optics, and identify a dimensionless fine-tuning parameter, F, which we use to describe the Lyot stop size in the natural units of the coronagraphic optical train and the observing wavelength. We then present simulations of coronagraphs matched to adaptive optics (AO) systems on the Calypso 1.2m, Palomar Hale 5m and G

E. Nakar, T. Piran

We analyze the temporal structure of long ((T_{90}>2sec)) and short ((T_{90}<2sec)) BATSE bursts. We find that: (i) In many short bursts (δt_{min}/T\ll 1) (where (δt_{min}) is the shortest pulse). This indicates that short bursts arise, like long ones, in internal shocks. (ii) In long bursts there is an excess of long intervals between pulses (relative to a

Andreas Reisenegger

Observations indicate that magnetic fields on neutron stars span at least the range $10^{8-15}$ G, corresponding to a range of magnetic fluxes similar to that found in white dwarfs and main sequence stars. The observational evidence is discussed, as well as the possible origin of the field, and the associated phenomenology (``classical&#39;&#39;, millisecond

J. A. Munoz, C. S. Kochanek, C. R. Keeton

Recent observations of galaxy luminosity profiles and dark matter simulations find luminosity and mass distributions characterized by central cusps rather than finite core radii. We introduce and implement a set of cusped ellipsoidal lens models which include limits similar to the Jaffe, Hernquist, ηand NFW models and apply them to the gravitational lenses A

Moshe Carmeli

The early stage of the Universe is discussed and the time lengths of its first days are given. If we denote the Hubble time in the zero-gravity limit by T (approximately 12.16 billion years), and T(n) denotes the length of the n-th day, then we have the very simple relation T(n)=T/(2n-1). Hence we obtain for the first days the following lenghts of time: T(1)

J. Sánchez Almeida, A. Asensio Ramos, J. Trujillo Bueno, J. Cernicharo

Narrow band imaging in the G-band is commonly used to trace the small magnetic field concentrations of the Sun, although the mechanism that makes them bright has remained unclear. We carry out LTE syntheses of the G-band in an assorted set of semi-empirical model magnetic concentrations. The syntheses include all CH lines as well as the main atomic lines wit

M. Landgraf, R. Jehn

The zodiacal foreground for a highly sensitive space infrared interferometer is predicted for various observing locations. For the predictions we use a model that was derived from measurements of the Cosmic Background Explorer (COBE). We find that at a wavelength of $10{\rm μm}$ 96% of the sky is darker than $1{MJy}{\rm sr}^{-1}$ for observations in the ecli

Falk Herwig

I discuss recent new models of post-Asymptotic Giant Branch stellar evolution. These models aim to clarify the evolutionary origin and status of a variety of hydrogen-deficient post-AGB stars such as central stars of planetary nebulae of Wolf-Rayet spectral type, PG1159 stars or Sakurai&#39;s object. Starting with AGB models with overshoot such stars can evo

Falk Herwig

Sakurai&#39;s object is a born again AGB star of the very late thermal pulse flavor. In this contribution I will discuss new models of stellar evolution and nucleosynthesis models of this phase. Two most intriguing properties of Sakurai&#39;s objects have so far not been understood theoretically: the peculiar chemical appearance, in particular the high lithi

Frederic A. Rasio, John M. Fregeau, Kriten J. Joshi

We summarize the results of recent theoretical work on the dynamical evolution of globular clusters containing primordial binaries. Even a very small initial binary fraction (e.g., 10%) can play a key role in supporting a cluster against gravothermal collapse for many relaxation times. Inelastic encounters between binaries and single stars or other binaries

Frederique Motte, Philippe Andre

Recent (sub)millimeter continuum surveys of nearby star-forming regions have revealed a wealth of new, cold cloud fragments. Those which are small-scale (diameter < 10000 AU), starless, and gravitationally bound are good candidates for being the direct progenitors of protostars, i.e., the structures within which individual protostellar collapse is initiated.