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Pan-STARRS will catalog 99% of the stars in
the northern hemisphere that have ever been observed by visible
light -- many billions of them. These individual stars will not
be confined to the Milky Way galaxy; stars in nearby galaxies
will routinely have their colors and positions noted, and will
be checked regularly for variablity. The stellar database that
results from Pan-STARRS will be a goldmine for statistical studies
of how different kinds of stars are distributed in their parent
galaxies. Selected regions of the sky, such as young star clusters,
will be searched in even greater depth. The ensemble
of positional information of stars observed with Pan-STARRS, whether
nearby or distant, will lead to what will become the de-facto astrometric
reference catalog for faint objects.
Most stars detected by Pan-STARRS will never
merit individual attention beyond an entry in a computer database,
but a minority of them will stand out from the crowd by moving
or varying. It is mainly these stars that will catch astronomers
interest. Among the variable stars that Pan-STARRS will
detect are eclipsing binaries, erupting stars,
microlensing events, and regular variables such as Cepheids and
RR Lyrae stars. These latter are particularly useful in that they
can be used for distance
measurements out to 10 Mpc, encompassing nearby galaxies as well
as the halo and most distant regions of our own Galaxy.
Exoplanet Searches
Pan-STARRS offers an excellent opportunity for detecting planets
around distant stars. When an extrasolar planet transits in front
its parent star, the slight dimming of that starlight may be detectable,
even if the planet is too faint to be seen. By measuring the brightness
of thousands of individual stars in a large star cluster like NGC 6791
every few weeks we can expect to see about 100 transits suitable
for follow-up studies. Pan-STARRS is also sensitive enough to detect
the passage of an Earth-size planet in front of a Brown Dwarf.
Solar Neighborhood
We know plenty about the large, luminous stars near the Sun, but
we know much less about the much more numerous cool, low luminosity
stars, since they are hard to pick out from the background of more
distant objects. Most stars that are within about 100 parsecs from
the Sun, however, have detectable parallaxes and/or proper motions
that mark them out as our neighbors. Since Pan-STARRS will survey
the whole sky to 24th magnitude every few days, it can generate
an unprecedented three-dimensional catalog of our immediate stellar
neighbors. This catalog will be a particularly rich resource for
the study of low-mass stars, brown dwarfs, and white dwarfs.
Evolution and Death of Stars
When stars die they usually become white dwarfs or neutron stars.
These compact objects tend to be difficult to observe directly, but
they readily draw attention to themselves when they are part of a
close binary pair with a brighter, larger companion star. Pan-STARRS
will be set up to search for the flares and other transient brightness
fluctuations that arise as matter is drawn off the larger star towards
the compact object. Among the interacting binary systems we expect
to discover will be precursor type Ia supernovae,
microquasars, millisecond pulsars, and cataclysmic variables. The
discovery and study of such systems provide the only laboratories
through which the extreme physical environments of high gravity,
high temperature, accretion and high magnetic field can be studied
in detail.
Young Stellar Objects
The youthful exuberance of young stars makes them among the most
variable of all astronomical phenomena, and essentially all known
young stars show photometric variability at some level. Brightness
and color changes arise from rotation, instinsic luminosity variations,
orbiting dust clouds, accretion processes, eruptions, and magnetic
and binary effects. THe ability of Pan-STARRS to search the whole of the
galactic plane for variable sources will provide a vast resource
for the study of star formation.
Next: The Active Universe
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