Direct image detection of a rare brown dwarf companion taken at Keck Observatory
Credit: Crepp et al. 2014, ApJ
Justin Crepp, Freimann Assistant Professor of Physics at the University of Notre Dame
Credit: University of Notre Dame
MAUNA KEA, HAWAII – A team of researchers led by Justin R. Crepp,
the Freimann Assistant Professor of Physics at the University of Notre Dame, has
directly imaged a very rare type of brown dwarf that can serve as a benchmark
for studying objects with masses that lie between stars and planets. Their
paper on the discovery was published recently in Astrophysical Journal.
Initial data came from the TRENDS
(TaRgetting bENchmark-objects with Doppler Spectroscopy) high-contrast imaging
survey that uses adaptive optics and related technologies to target older,
faint objects orbiting nearby stars, and precise measurements were made at the W. M. Keck Observatory on the summit of
Mauna Kea, Hawaii. Brown dwarfs emit little light because they do not burn
hydrogen and cool rapidly. Crepp said they could provide a link between our understanding
of low-mass stars and smaller objects such as planets.
HD 19467 B, a T-dwarf, is a
very faint companion to a nearby Sun-like star, more than 100,000 times as dim
as its host. Its distance is known precisely, and the discovery also enables
researchers to place strong constraints on important factors such as its mass,
orbit, age, and chemical composition without reference to the spectrum of light
received from its surface.
Precise radial velocity
measurements were obtained using the HIRES instrument installed on Keck
Observatory's 10-meter, Keck I telescope. The
observations, which span 17 years starting from 1996, show a long-term
acceleration, indicating that a low-mass companion was "tugging" on
the parent star. Follow-up high-contrast imaging observations were then taken in
2012 using the NIRC2 instrument on the Keck II telescope with the adaptive
optics system revealing the companion as shown above. Observations were granted
through each of the Keck Observatory consortium members, including NASA, the
California Institute of Technology, and the University of California.
While scientists understand
the light received from stars relatively well, the spectra from planets is
complicated and little understood. Understanding brown dwarfs, such as HD 19467
B, could be a step towards a fuller understanding of exoplanets.
“This object is old and cold and will ultimately
garner much attention as one of the most well-studied and scrutinized brown
dwarfs detected to date,” Crepp said. “With continued follow-up observations,
we can use it as a laboratory to test theoretical atmospheric models.
Eventually we want to directly image and acquire the spectrum of Earth-like
planets. Then, from the spectrum, we should be able to tell what the planet is
made out of, what its mass is, radius, age, etc., basically all relevant
physical properties.”
HIRES (the High-Resolution
Echelle Spectrometer) produces spectra of single objects at very high spectral
resolution, yet covering a wide wavelength range. It does this by separating
the light into many "stripes" of spectra stacked across a mosaic of
three large CCD detectors. HIRES is famous for finding planets orbiting other
stars. Astronomers also use HIRES to study distant galaxies and quasars,
finding clues to the Big Bang.
NIRC2 (the Near-Infrared Camera,
second generation) works in combination with the Keck II adaptive optics
system to obtain very sharp images at near-infrared wavelengths,
achieving spatial resolutions comparable to or better than those
achieved by the Hubble Space Telescope at optical wavelengths. NIRC2 is
probably best known for helping to provide definitive proof of a central
massive black hole at the center of our galaxy. Astronomers also use
NIRC2 to map surface features of solar system bodies, detect planets
orbiting other stars, and study detailed morphology of distant galaxies.
The W. M. Keck Observatory
operates the largest, most scientifically productive telescopes on Earth. The
two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the
Island of Hawaii feature a suite of advanced instruments including imagers,
multi-object spectrographs, high-resolution spectrographs, integral-field
spectroscopy and world-leading laser guide star adaptive optics systems. The
Observatory is a private 501(c) 3 non-profit organization and a scientific
partnership of the California Institute of Technology, the University of
California and NASA.
Steve Jefferson
Communications Officer
W. M. Keck Observatory
(808)-881-3827
sjefferson@keck.hawaii.edu
Science Contact:
Justin Crepp
(574) 631-4092
jcrepp@nd.edu
Source: W.M. Keck Observatory
