Monitoring All Sky for Variability

A few percent of all stars are variable, yet over 90% of variables brighter than 12 magnitude have not been discovered yet. There is a need for an all sky search and for the early detection of any unexpected events: optical flashes from gamma-ray bursts, novae, dwarf novae, supernovae, `killer asteroids'. The ongoing projects like ROTSE, ASAS, TASS, and others, using instruments with just 4 inch aperture, have already discovered thousands of new variable stars, a flash from an explosion at a cosmological distance, and the first partial eclipse of a nearby star by its Jupiter like planet. About one million variables may be discovered with such small instruments, and many more with larger telescopes. The critical elements are software and full automation of the hardware. A complete census of the brightest eclipsing binaries is needed to select objects for a robust empirical calibration of the the accurate distance determination to the Magellanic Clouds, the first step towards the Hubble constant. An archive to be generated by a large number of small instruments will be very valuable for data mining projects. The real time alerts will provide great targets of opportunity for the follow-up observations with the largest telescopes.Comment: 6 pages, latex, minor changes, published in the Publications of the Astronomical Society of the Pacific as one of Millennium Essays: 2000, PASP, 112, 1281-128

The ESO-Sculptor Faint Galaxy Redshift Survey: The Photometric Sample

We present the photometric sample of a faint galaxy survey carried out in the southern hemisphere, using CCDs on the 3.60m and NTT-3.5m telescopes at La Silla (ESO). The survey area is a continuous strip of 0.2 deg x 1.53 deg located at high galactic latitude (-83 deg) in the Sculptor constellation. The photometric survey provides total magnitudes in the bands B, V (Johnson) and R (Cousins) to limiting magnitudes of 24.5, 24.0, 23.5 respectively. To these limits, the catalog contains about 9500, 12150, 13000 galaxies in B, V, R bands respectively and is the first large digital multi-colour photometric catalog at this depth. This photometric survey also provides the entry catalog for a fully-sampled redshift survey of ~ 700 galaxies with R < 20.5 (Bellanger et al. 1995). In this paper, we describe the photometric observations and the steps used in the data reduction. The analysis of objects and the star-galaxy separation with a neural network are performed using SExtractor, a new photometric software developed by E. Bertin (1996). The photometric accuracy of the resulting catalog is ~ 0.05 mag for R < 22. The differential galaxy number counts in B, V, R are in good agreement with previously published CCD studies and confirm the evidence for significant evolution at faint magnitudes as compared to a standard non evolving model (by factors 3.6, 2.6, 2.1). The galaxy colour distributions B-R, B-V of our sample show a blueing trend of ~ 0.5 mag between 21 < R < 23.5 in contrast to the V-R colour distribution where no significant evolution is observed.Comment: LATEX, 18 Postscript figures, 20 pages. To appear July 1997. Modified version of article. Abstract corrected for missing lin

Diffraction-limited near-IR imaging at Keck reveals asymmetric, time-variable nebula around carbon star CIT 6

We present multi-epoch, diffraction-limited images of the nebula around the carbon star CIT 6 at 2.2 microns and 3.1 microns from aperture masking on the Keck-I telescope. The near-IR nebula is resolved into two main components, an elongated, bright feature showing time-variable asymmetry and a fainter component about 60 milliarcseconds away with a cooler color temperature. These images were precisely registered (~35 milliarcseconds) with respect to recent visible images from the Hubble Space Telescope (Trammell et al. 2000), which showed a bipolar structure in scattered light. The dominant near-IR feature is associated with the northern lobe of this scattering nebula, and the multi-wavelength dataset can be understood in terms of a bipolar dust shell around CIT 6. Variability of the near-IR morphology is qualitatively consistent with previously observed changes in red polarization, caused by varying illumination geometry due to non-uniform dust production. The blue emission morphology and polarization properties can not be explained by the above model alone, but require the presence of a wide binary companion in the vicinity of the southern polar lobe. The physical mechanisms responsible for the breaking of spherical symmetry around extreme carbon stars, such as CIT 6 and IRC+10216, remain uncertain.Comment: 18 pages, 5 figures (one in color), to appear in the Astrophysical Journa

Interacting Binaries with Eccentric Orbits. Secular Orbital Evolution Due To Conservative Mass Transfer

We investigate the secular evolution of the orbital semi-major axis and eccentricity due to mass transfer in eccentric binaries, assuming conservation of total system mass and orbital angular momentum. Assuming a delta function mass transfer rate centered at periastron, we find rates of secular change of the orbital semi-major axis and eccentricity which are linearly proportional to the magnitude of the mass transfer rate at periastron. The rates can be positive as well as negative, so that the semi-major axis and eccentricity can increase as well as decrease in time. Adopting a delta-function mass-transfer rate of 10^{-9} M_\sun {\rm yr}^{-1} at periastron yields orbital evolution timescales ranging from a few Myr to a Hubble time or more, depending on the binary mass ratio and orbital eccentricity. Comparison with orbital evolution timescales due to dissipative tides furthermore shows that tides cannot, in all cases, circularize the orbit rapidly enough to justify the often adopted assumption of instantaneous circularization at the onset of mass transfer. The formalism presented can be incorporated in binary evolution and population synthesis codes to create a self-consistent treatment of mass transfer in eccentric binaries.Comment: 16 pages, 8 figures, Accepted by The Astrophysical Journa

`Similar' coordinate systems and the Roche geometry. Application

A new equivalence relation, named relation of 'similarity' is defined and applied in the restricted three-body problem. Using this relation, a new class of trajectories (named 'similar' trajectories) are obtained; they have the theoretical role to give us new details in the restricted three-body problem. The 'similar' coordinate systems allow us in addition to obtain a unitary and an elegant demonstration of some analytical relations in the Roche geometry. As an example, some analytical relations published in Astrophysical Journal by Seidov in 2004 are demonstrated.Comment: 9 pages (preprint format), 9 figures, published in Astrophysics and Space Scienc

Navigation Challenges in Massively Destructible Worlds

Abstract The creation of life-like believable characters is emerging as the central focus of next-generation game development and is viewed as critical to obtaining true mass-market appeal. Visually-realistic movement in complex physics driven worlds is an increasingly critical component in creating believable characters. The demo is based on our extension to the Unreal 3 engine (UE3) and runs on advanced PCs, the Xbox 360 and PlayStation 3 (PS3) and shows advance navigation behaviors such as dynamic obstacle avoidance, local dynamic path finding and advanced obstacle traversal such as vaulting. A typical first-person shooter (FPS) game level (an underground subway system) is constructed out of physics-simulated objects; the benches and garbage cans can be displaced by gun fire and the pillars and railings can be destroyed by grenades. This allows the player to quickly and significantly disrupt the world making it extremely difficult for the non-player characters (NPCs) to navigate towards the player. NPCs can be given specific movement abilities so that some NPCs can avoid obstacles by circumventing them while more advanced NPCs can vault over them. Upon discovery of blocked passageways such as staircases, NPCs can take alternative routes

Believable and Reactive Crowds in Next Generation Games

Abstract The creation of life-like believable characters is emerging as the central focus of next-generation game development and is viewed as critical to obtaining true mass-market appeal. Reactive crowd simulation is a critical component in creating believable character. The demo runs on a Xbox 360 and shows the following crowd behaviors. A typical downtown is populated with pedestrians and vehicles. The pedestrians mill about the town staying on the sidewalk and cross only at street corners (although some decide will &quot;jay walk&quot; from time to time). Occasionally, they will stop to talk with one another. Cars drive around the city and obey the traffic lights. The ambient behaviour is interrupted by traumatic event; in this case a terrorist pulls out a run and starts firing at the crowd who now move into a panic behaviour. Some crowd members run away immediately from the terrorist while others first cower in fear before running away. Crowd members who do not hear the weapon fire but see a panicking pedestrian may also panic or continue about their business depending on how &quot;cool&quot; they are. Vehicles also flee the terrorist and will drive on sidewalks and over pedestrians to save themselves