478 research outputs found
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 "jay walk" 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 "cool" they are. Vehicles also flee the terrorist and will drive on sidewalks and over pedestrians to save themselves
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