Image (72 dpi,
103 KB) |
Object Name: A Young Brown Dwarf
Companion to DH Tauri
Telescope: Subaru Telescope (Effective
Aperture 8.2m), Cassegrain Focus
Instrument:
Coronagraphic Imager with Adaptive Optics (CIAO) +
Subaru Adaptive Optics System (AO)
Filter: K (2.2μm)
Observation Date: January 9 , 2004
(UT)
Exposure Time: 12 min
Filed of View: 10 arcsec x 10 arcsec
Image Orientation:
North is up, East is left.
Position: R.A. 4h29m42.5s?Dec. +26°32'56"
(J2000)
Constellation: Taurus |
Astronomers have weighed DH Tauri's companion and have
found that it is a brown dwarf with only 40 times the
mass of Jupiter. DH Tauri is a young star only one million
years old in the constellation Taurus. It is so young
it will not begin nuclear fusion for another one hundred
million years. It is 460 light years away and two thirds
as massive as the Sun. It's companion is among the coolest
and lightest of known brown dwarfs orbiting young stars.
If the companion had been less massive it probably would
have been a planet. A team from the National Astronomical
Observatory of Japan, Kobe University, the University
of Tokyo, and the Graduate University for Advanced Studies
conducted this research.
The search for planets outside our solar
system (extrasolar planets) motivates much of modern astronomy.
Subaru Telescope is contributing to this search by observing
many nearby young stars in the constellation Taurus with
its Coronagraphic imager with Adaptive
Optics (CIAO). (See our April
2004 press release for more information on this program
and an image of a protoplanetary disk.)
CIAO's speciality is observing faint
objects near bright objects. CIAO sharpens an image using
a technique called adaptive
optics, and blocks the light from a bright object
using a mask called a coronagraph.
The research team targeted young stars
since planets and brown dwarfs are brighter when they
are young. Planets weigh less than 13 times the mass of
Jupiter. Brown dwarfs are 13 to 80 times more massive
than Jupiter. Unlike stars like the Sun, brown dwarfs
don't have enough mass to generate energy through nuclear
fusion.
So far, extrasolar planets orbiting around
normal stars have been detected only by indirect means,
such as observing the wobble in the main star caused by
the gravitational tug and pull with the orbiting planet.
No direct image of an extrasolar planet around a normal
star exists to date. If astronomers could get a direct
image of an extrasolar planet, they can begin to study
physical properties such as temperature and composition.
When the research team took an image
of the star DH Tauri (abbreviated as DH Tau), they noticed
an object 250 times fainter 2.3 arcseconds away. At the
distance of DH Tauri (460 light years), this separation
is equivalent to 330 times the distance between Earth
and the Sun. Although the object was in older images of
DH Tauri, its location in the new image revealed that
it was not an unrelated background object, but a companion
that orbits DH Tauri.
To understand the physical nature of
this companion, the team made followup observations using
a spectrograph on Subaru (the
Cooled Infrared Spectrograph and Camera; CISCO), The
companion's spectrum in the 1 to 2.5 μm region shows
signatures of water and potassium. From these, the research
team can infer that the surface temperature of the companion
is about 2700 to 2800 degrees Kelvin, its surface gravity
is 4 times that of Jupiter and its mass is only 40 times
larger than Jupiter. This puts the companion in the brown
dwarf category.
Yoichi Itoh from the Kobe University
says "this discovery gives substance to our hope
that we can find a planet with a mass comparable to Jupiter
using our technique and strategy." "We are getting
ever closer to our goal of getting an image of an extrasolar
planet," he says
These results were published in the February
20, 2005, edition of the Astrophysical Journal (ApJ 620,
984-993).
