1. PHOENIX spectra
microns region Epsilon Indi B. The former interval is dominated by
strong 12C16O(2-0) lines that are rotationally broadened.
Smith of the University of Texas El Paso led an international team of American, Canadian,
Brazilian and Japanese astronomers to a detailed study of the physical properties
of the recently discovered nearby brown dwarf companion to Epsilon Indi,
the fifth brightest star of the southern hemisphere constellation Indus.
star was discovered at Gemini South by Kevin Volk et al (2003) to be a close
optical double consisting of an early T dwarf (Epsilon Indi Ba) and a late
T dwarf (Epsilon Indi Bb) separated by 0.6 arcsec - see previous announcement,
"Gemini Detects Something "Cool" in Our Neighborhood". With an accurately
known distance of 3.626 +/- 0.009 pc, Epsilon Indi Ba and Bb are the nearest
known brown dwarfs.
infrared (IR) spectra were obtained on Epsilon Indi Ba using the Gemini
South Telescope and the NOAO PHOENIX spectrometer.
of Epsilon Indi Ba were explored by comparing the PHOENIX spectra to the
computer generated synthetic spectra from model atmospheres (Figure 1). These
models are so called "unified cloudy models" in which dust is allowed to
exist in the atmosphere of the brown dwarf over a limited range defined by
a condensation temperature and a critical temperature. This technique reproduces
the complex physical state of the atmospheres of brown dwarfs; they have
"weather" driven by dust condensation and a complex circulation pattern.
By matching the shape and the depth of the absorption lines of 12C16O
and H2O, the researchers derived an effective temperature of 1500K, a surface
gravity of log g = 5.2 (almost 6 times the surface gravity of the Sun).
From the luminosity derived by Scholz et al (2003) of log (L/Lsun)
= -4.71 (i.e. 30,000 times fainter than the Sun), Smith et al were able
to determine that the mass of Epsilon Indi Ba is M = 32 MJupiter.
fits to the line profiles (primarily the strong CO lines) yield the projected
rotational velocity of 28 km/s. This implies a maximum rotational period
for Epsilon Indi Ba of 3.0 hours, more than three times that of Jupiter (which
has the fastest rotation rate of any planet in our solar system with a period
of 9h 50m). Jupiter and Epsilon Indi Ba probably have similar diameters,
hence Epsilon Indi Ba must be significantly flattened by its fast rotation.
in described in details in the paper "High-Resolution Infrared Spectroscopy
of the Brown Dwarf e Indi Ba", by Verne V. Smith et al to appear in The
Astrophysical Journal Letters, December 20, 2003.
Interested readers should also be aware of the very thorough study by
the ESO team of McCaughrean, Close, Scholz et al., who discovered
Epsilon Indi B in December 2002 and independently discovered Eps Indi
Bb. They present near-IR adaptive optics imaging and spectroscopy
obtained with the NACO system at the VLT in "Epsilon Indi Ba/Bb: the
nearest binary brown dwarf", in press in Astronomy & Astrophysics and
available at http://xxx.lanl.gov/abs/astro-ph/0309256.
Interested readers should also be aware of the very thorough study by the ESO team of McCaughrean, Close, Scholz et al., who discovered Epsilon Indi B in December 2002 and independently discovered Eps Indi Bb. They present near-IR adaptive optics imaging and spectroscopy obtained with the NACO system at the VLT in "Epsilon Indi Ba/Bb: the nearest binary brown dwarf", in press in Astronomy & Astrophysics and available at http://xxx.lanl.gov/abs/astro-ph/0309256.
The Gemini Observatory
is an international collaboration that has built two identical 8-meter telescopes.
The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai`i
(Gemini North) and the Gemini South telescope is located on Cerro Pachón
in central Chile (Gemini South), and hence provide full coverage of both
hemispheres of the sky. Both telescopes incorporate new technologies that
allow large, relatively thin mirrors under active control to collect and
focus both optical and infrared radiation from space.
The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Particle Physics and Astronomy Research Council (PPARC), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). The Observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.