Download this ebook as PDF - E-Book Library

News Notes
Magnitude
Magnitude
Magnitude
12 May 2012 sky & telescope
To T get astronomy news as it breaks, visit
SkyandTelescope.com/newsblog.
S
Vast New Trove of Variable Stars
13.8
14.0
14.2
14.4
14.6
14.8
13.6
13.8
14.0
14.2
14.4
14.6
14.8
15.0
15.2
15.4
15.6
Algol type
W Ursae Majoris type
RR Lyrae type
15.8
0.0 0.5 1.0
Phase
1.5 2.0
These light curves of faint variable stars were plucked from
the tens of thousands now online courtesy of the Catalina
sky surveys. The thin vertical lines are the error bars for
each brightness measurement. Algol stars are eclipsing
binaries in which the two stars are separated; W Ursae
Majoris stars are contact binaries resembling fi gure 8s; RR
Lyraes are pulsators. These three variables have periods of
0.536934, 0.74429, and 0.331798 days, respectively.
S&T: LEAH TISCIONE, SOURCE: CATALINA SKY SURVEY / ANDREW DRAKE
We live in a golden age of automated sky surveys, and
it’s getting more golden all the time.
One way that massive sky surveys are changing
astronomy is by producing gigantic numbers of uniform,
high-quality light curves for new variable stars. Usually
these are merely the byproducts of surveys designed for
other purposes. But when some project measures the
brightnesses of millions of stars over and over, why not
save the data and mine it?
The largest such variable-star database yet has been
compiled by the Catalina Sky Survey and the Catalina
Real-Time Transient Survey. Their main jobs are looking
for near-Earth asteroids and watching for transient events
among the stars and galaxies. But along the way they
have collected 20 billion brightness measurements of 198
million stars and other objects since 2004. That’s an average
of 100 magnitude measurements for each one. The
objects range from magnitude 12.5 to 20 and span a little
more than half the celestial sphere.
The new light curves include more than 1,000 distant
supernovae, some of unusual or new varieties; about
3,000 other transient objects including fl are stars, dwarf
novae, and erupting galactic nuclei; and tens of thousands
of other new variable stars of every kind.
By comparison, the offi cial General Catalog of Variable
Stars, the bible of the fi eld since 1948, contains 43,675
named variables.
The Catalina light curves are uniform and consistent,
with measurements typically accurate to 0.06 or 0.08
magnitude. “This set is an order of magnitude larger than
the largest previously available data sets of the kind,” says
Andrew Drake (Caltech) of the Catalina project. He also
notes, “We discover transient events and publish them
electronically in real time, so that anyone can follow them
and make additional discoveries.”
In this way the program is a precursor to the much
bigger Large Synoptic Survey Telescope (LSST) project,
which should begin watching the sky with a unique,
wide-fi eld 8.4-meter scope around the end of this decade.
The LSST’s capabilities will be mind-boggling: it’s
designed to measure everything across half the celestial
sphere from magnitude 16 to 24.5 in six colors an average
of once every three or four days for at least 10 years.
Catalina’s observations so far come from the Univer-