Faint Star Orbiting the Big Dipper's Alcor Discovered
0 views
Skip to first unread message
David
Dec 11, 2009, 2:01:09 PM12/11/09
to Dark Star Planet X
Even though this is a RD, it's still interesting that they're
discovering these "sub-stars" regularly. Click the link to view the
image.
http://www.sciencedaily.com/releases/2009/12/091210000851.htm
Faint Star Orbiting the Big Dipper's Alcor Discovered
ScienceDaily (Dec. 10, 2009) — Next time you spy the Big Dipper, keep
in mind that there is another star, invisible to the unaided eye,
contributing to this constellation. According to a new paper published
in The Astrophysical Journal, one of the stars that makes the bend in
the ladle's handle, Alcor, has a smaller red dwarf companion.
Newly discovered Alcor B orbits its larger sibling and was caught in
the act with an innovative technique called "common parallactic
motion" by members of Project 1640, an international collaborative
team that includes astrophysicists at the American Museum of Natural
History, the University of Cambridge's Institute of Astronomy, the
California Institute of Technology, and NASA's Jet Propulsion
Laboratory.
"We used a brand new technique for determining that an object orbits a
nearby star, a technique that's a nice nod to Galileo," says Ben R.
Oppenheimer, Curator and Professor in the Department of Astrophysics
at the Museum. "Galileo showed tremendous foresight. Four hundred
years ago, he realized that if Copernicus was right -- that the Earth
orbits the Sun -- they could show it by observing the "parallactic
motion" of the nearest stars. Incredibly, Galileo tried to use Alcor
to see it but didn't have the necessary precision." If Galileo had
been able to see change over time in Alcor's position, he would have
had conclusive evidence that Copernicus was right. Parallactic motion
is the way nearby stars appear to move in an annual, repeatable
pattern relative to much more distant stars, simply because the
observer on Earth is circling the Sun and sees these stars from
different places over the year.
Alcor is a relatively young star twice the mass of the Sun. Stars this
massive are relatively rare, short-lived, and bright. Alcor and its
cousins in the Big Dipper formed from the same cloud of matter about
500 million years ago, something unusual for a constellation since
most of these patterns in the sky are composed of unrelated stars.
Alcor shares a position in the Big Dipper with another star, Mizar. In
fact, both stars were used as a common test of eyesight -- being able
to distinguish "the rider from the horse" -- among ancient people. One
of Galileo's colleagues observed that Mizar itself is actually a
double, the first binary star system resolved by a telescope. Many
years later, the two components Mizar A and B were themselves
determined each to be tightly orbiting binaries, altogether forming a
quadruple system.
Now, Alcor, which is near the four stars of the Mizar system, also has
a companion. This March, members of Project 1640 attached their
coronagraph and adaptive optics to the 200-inch Hale Telescope at the
Palomar Observatory in California and pointed to Alcor. "Right away I
spotted a faint point of light next to the star," says Neil Zimmerman,
a graduate student at Columbia University who is doing his PhD
dissertation at the Museum. "No one had reported this object before,
and it was very close to Alcor, so we realized it was probably an
unknown companion star."
The team retuned a few months later and re-imaged the star, hoping to
prove that the two stars are companions by mapping the tiny movement
of both in relation to very distant background stars as the Earth
moves around the Sun, in other words, by mapping its parallactic
motion. If the proposed companion were just a background star, it
wouldn't move along with Alcor.
"We didn't have to wait a whole year to get the results," says
Oppenheimer. "We went back 103 days later and found the companion had
the same motion as Alcor. Our technique is powerful and much faster
than the usual way of confirming that objects in the sky are
physically related." The more typical method involves observing the
pair of objects over much longer periods of time, even years, to show
that the two are moving through space together.
Alcor and its newly found, smaller companion Alcor B are both about 80
light-years away and orbit each other every 90 years or more. Over one
year, the Alcor pair moves in an ellipse on the sky about 0.08 arc
seconds in width because of the Earth's orbit around the Sun. This
amount of motion, 0.08 arcsec, is about 1,000 times smaller than the
eye can discern, but a fraction of this motion was easily measured by
the Project 1640 scientists.
The team was also able to determine the color, brightness, and even
rough composition of Alcor B because the novel method of observation
that Project 1640 uses records images at many different colors
simultaneously. The team determined that Alcor B is a common type of M-
dwarf star or red dwarf that is about 250 times the mass of Jupiter,
or roughly a quarter of the mass of our Sun. The companion is much
smaller and cooler than Alcor A.
"Red dwarfs are not commonly reported around the brighter higher mass
type of star that Alcor is, but we have a hunch that they are actually
fairly common," says Oppenheimer. "This discovery shows that even the
brightest and most familiar stars in the sky hold secrets we have yet
to reveal."
The team plans to use parallactic motion again in the future. "We hope
to use the same technique to check that other objects we find like
exoplanets are truly bound to their host stars," says Zimmerman. "In
fact, we anticipate other research groups hunting for exoplanets will
also use this technique to speed up the discovery process."
In addition to Zimmerman and Oppenheimer, authors include Anand
Sivaramakrishnan, Sasha Hinkley, and Douglas Brenner of the
Astrophysics Department at the Museum; Lynne Hillenbrand, Charles
Beichman, Justin Crepp, Antonin Bouchez and Richard Dekany of the
California Institute of Technology; Ian Parry, David King, and
Stephanie Hunt of the Institute of Astronomy at Cambridge University;
Rémi Soummer of the Space Telescope Institute in Baltimore; and Gautam
Vasisht, Rick Burruss, Michael Shao, Lewis Roberts, and Jennifer
Roberts of the Jet Propulsion Laboratory at California Institute of
Technology. Project 1640 is funded by the National Science Foundation.
discovering these "sub-stars" regularly. Click the link to view the
image.
http://www.sciencedaily.com/releases/2009/12/091210000851.htm
Faint Star Orbiting the Big Dipper's Alcor Discovered
ScienceDaily (Dec. 10, 2009) — Next time you spy the Big Dipper, keep
in mind that there is another star, invisible to the unaided eye,
contributing to this constellation. According to a new paper published
in The Astrophysical Journal, one of the stars that makes the bend in
the ladle's handle, Alcor, has a smaller red dwarf companion.
Newly discovered Alcor B orbits its larger sibling and was caught in
the act with an innovative technique called "common parallactic
motion" by members of Project 1640, an international collaborative
team that includes astrophysicists at the American Museum of Natural
History, the University of Cambridge's Institute of Astronomy, the
California Institute of Technology, and NASA's Jet Propulsion
Laboratory.
"We used a brand new technique for determining that an object orbits a
nearby star, a technique that's a nice nod to Galileo," says Ben R.
Oppenheimer, Curator and Professor in the Department of Astrophysics
at the Museum. "Galileo showed tremendous foresight. Four hundred
years ago, he realized that if Copernicus was right -- that the Earth
orbits the Sun -- they could show it by observing the "parallactic
motion" of the nearest stars. Incredibly, Galileo tried to use Alcor
to see it but didn't have the necessary precision." If Galileo had
been able to see change over time in Alcor's position, he would have
had conclusive evidence that Copernicus was right. Parallactic motion
is the way nearby stars appear to move in an annual, repeatable
pattern relative to much more distant stars, simply because the
observer on Earth is circling the Sun and sees these stars from
different places over the year.
Alcor is a relatively young star twice the mass of the Sun. Stars this
massive are relatively rare, short-lived, and bright. Alcor and its
cousins in the Big Dipper formed from the same cloud of matter about
500 million years ago, something unusual for a constellation since
most of these patterns in the sky are composed of unrelated stars.
Alcor shares a position in the Big Dipper with another star, Mizar. In
fact, both stars were used as a common test of eyesight -- being able
to distinguish "the rider from the horse" -- among ancient people. One
of Galileo's colleagues observed that Mizar itself is actually a
double, the first binary star system resolved by a telescope. Many
years later, the two components Mizar A and B were themselves
determined each to be tightly orbiting binaries, altogether forming a
quadruple system.
Now, Alcor, which is near the four stars of the Mizar system, also has
a companion. This March, members of Project 1640 attached their
coronagraph and adaptive optics to the 200-inch Hale Telescope at the
Palomar Observatory in California and pointed to Alcor. "Right away I
spotted a faint point of light next to the star," says Neil Zimmerman,
a graduate student at Columbia University who is doing his PhD
dissertation at the Museum. "No one had reported this object before,
and it was very close to Alcor, so we realized it was probably an
unknown companion star."
The team retuned a few months later and re-imaged the star, hoping to
prove that the two stars are companions by mapping the tiny movement
of both in relation to very distant background stars as the Earth
moves around the Sun, in other words, by mapping its parallactic
motion. If the proposed companion were just a background star, it
wouldn't move along with Alcor.
"We didn't have to wait a whole year to get the results," says
Oppenheimer. "We went back 103 days later and found the companion had
the same motion as Alcor. Our technique is powerful and much faster
than the usual way of confirming that objects in the sky are
physically related." The more typical method involves observing the
pair of objects over much longer periods of time, even years, to show
that the two are moving through space together.
Alcor and its newly found, smaller companion Alcor B are both about 80
light-years away and orbit each other every 90 years or more. Over one
year, the Alcor pair moves in an ellipse on the sky about 0.08 arc
seconds in width because of the Earth's orbit around the Sun. This
amount of motion, 0.08 arcsec, is about 1,000 times smaller than the
eye can discern, but a fraction of this motion was easily measured by
the Project 1640 scientists.
The team was also able to determine the color, brightness, and even
rough composition of Alcor B because the novel method of observation
that Project 1640 uses records images at many different colors
simultaneously. The team determined that Alcor B is a common type of M-
dwarf star or red dwarf that is about 250 times the mass of Jupiter,
or roughly a quarter of the mass of our Sun. The companion is much
smaller and cooler than Alcor A.
"Red dwarfs are not commonly reported around the brighter higher mass
type of star that Alcor is, but we have a hunch that they are actually
fairly common," says Oppenheimer. "This discovery shows that even the
brightest and most familiar stars in the sky hold secrets we have yet
to reveal."
The team plans to use parallactic motion again in the future. "We hope
to use the same technique to check that other objects we find like
exoplanets are truly bound to their host stars," says Zimmerman. "In
fact, we anticipate other research groups hunting for exoplanets will
also use this technique to speed up the discovery process."
In addition to Zimmerman and Oppenheimer, authors include Anand
Sivaramakrishnan, Sasha Hinkley, and Douglas Brenner of the
Astrophysics Department at the Museum; Lynne Hillenbrand, Charles
Beichman, Justin Crepp, Antonin Bouchez and Richard Dekany of the
California Institute of Technology; Ian Parry, David King, and
Stephanie Hunt of the Institute of Astronomy at Cambridge University;
Rémi Soummer of the Space Telescope Institute in Baltimore; and Gautam
Vasisht, Rick Burruss, Michael Shao, Lewis Roberts, and Jennifer
Roberts of the Jet Propulsion Laboratory at California Institute of
Technology. Project 1640 is funded by the National Science Foundation.
tarkin
Dec 16, 2009, 2:29:42 PM12/16/09
to Dark Star Planet X
Reply all
Reply to author
Forward
0 new messages