This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1\13 ESO - Nearest Brown Dwarf- AVO Press Conference- Teachers' Summer School
Part 1 of 3

           Information from the European Southern Observatory

 ESO Press Release 01/03
 13 January 2003                                           [ESO Logo]
 For immediate release
 --------------------------------------------------------------------

Discovery of Nearest Known Brown Dwarf

Bright Southern Star Epsilon Indi Has Cool, Substellar Companion [1]

Summary
-------
A team of European astronomers [2] has discovered a Brown Dwarf object 
(a 'failed' star) less than 12 light-years from the Sun. It is the 
nearest yet known.

Now designated Epsilon Indi B, it is a companion to a well-known 
bright star in the southern sky, Epsilon Indi (now "Epsilon Indi A"), 
previously thought to be single. The binary system is one of the 
twenty nearest stellar systems to the Sun.

The brown dwarf was discovered from the comparatively rapid motion 
across the sky which it shares with its brighter companion : the pair 
move a full lunar diameter in less than 400 years. It was first 
identified using digitised archival photographic plates from the 
SuperCOSMOS Sky Surveys (SSS) and confirmed using data from the Two 
Micron All Sky Survey (2MASS).  Follow-up observations with the 
near-infrared sensitive SOFI instrument on the ESO 3.5-m New 
Technology Telescope (NTT) at the La Silla Observatory confirmed its 
nature and has allowed measurements of its physical properties.

Epsilon Indi B has a mass just 45 times that of Jupiter, the largest
planet in the Solar System, and a surface temperature of only 1000 
degC. It belongs to the so-called 'T dwarf' category of objects which 
straddle the domain between stars and giant planets.

Epsilon Indi B is the nearest and brightest T dwarf known. Future 
studies of the new object promise to provide astronomers with 
important new clues as to the formation and evolution of these exotic 
celestial bodies, at the same time yielding interesting insights into 
the border zone between planets and stars.

PR Photo 03a/03: Epsilon Indi B, the nearest known Brown Dwarf.
PR Photo 03b/03: Near-infrared spectrum of Epsilon Indi B.
PR Photo 03c/03: The nearest stars (incl. Java Applet).
PR Photo 03d/03: The southern constellation Indus.
 --------------------------------------------------------------------

Tiny moving needles in giant haystacks
--------------------------------------
ESO PR Photo 03a/03              Caption: PR Photo 03a/03 shows
                                 Epsilon Indi A (the bright star at
                                 far right) and its newly discovered
                                 brown dwarf companion Epsilon Indi B
[Preview - JPEG: 400 x 605 pix - (circled). The upper image comes
92k]                             from one of the SuperCOSMOS Sky
[Normal - JPEG: 1200 x 1015 pix -Surveys (SSS) optical photographic
1.0m]                            plates (I-band, centred at
                                 wavelength 0.7 micron) on which this
                                 very high proper motion object was
                                 discovered. The lower image is the
                                 'Quicklook atlas' infrared image
                                 (Ks-band, 2.1 micron) from the Two
                                 Micron All Sky Survey (2MASS).
                                 Epsilon Indi B is much brighter in
                                 the near-infrared than at optical
                                 wavelengths, indicating that it is a
                                 very cool object. Both images cover
                                 roughly 7 x 5 arcmin.

Imagine you are a professional ornithologist, recently returned home 
from an expedition to the jungles of South America, where you spent 
long weeks using your high-powered telephoto lenses searching for rare 
species of birds.  Relaxing, you take a couple of wide-angle snapshots 
of the blooming flowers in your back garden, undistracted by the 
common blackbird flying across your viewfinder. Only later, when 
carefully comparing those snaps, you notice something tiny and 
unusually coloured, flittering close behind the blackbird: you've 
discovered an exotic, rare bird, right there at home.

In much the same way, a team of astronomers [2] has just found one of 
the closest neighbours to the Sun, an exotic 'failed star' known as a 
'brown dwarf', moving rapidly across the sky in the southern 
constellation Indus (The Indian). Interestingly, at a time when 
telescopes are growing larger and are equipped with ever more 
sophisticated electronic detectors, there is still much to be learned 
by combining old photographic plates with this modern technology.

Photographic plates taken by wide-field ("Schmidt") telescopes over 
the past decades have been given a new lease on life through being 
digitised by automated measuring machines, allowing computers to trawl 
effectively through huge and invaluable data archives that are by far 
not yet fully exploited [3]. For the Southern Sky, the Institute for 
Astronomy in Edinburgh (Scotland, UK) has recently released scans made 
by the SuperCOSMOS machine of plates spanning several decades in three 
optical passbands. These data are perfectly suited to the search for 
objects with large proper motions and extreme colours, such as brown 
dwarfs in the Solar vicinity.

Everything is moving - a question of perspective
------------------------------------------------
In astronomy, the `proper motion' of a star signifies its apparent 
motion on the celestial sphere; it is usually expressed in arcseconds 
per year [4].  The corresponding, real velocity of a star (in 
kilometres per second) can only be estimated if the distance is known.

A star with a large proper motion may indicate a real large velocity 
or simply that the star is close to us. By analogy, an airplane just 
after takeoff has a much lower true speed than when it's cruising at 
high altitude, but to an observer watching near an airport, the 
departing airplane seems to be moving much more quickly across the 
sky.

Proxima Centauri, our nearest stellar neighbour, is just 4.2 
light-years away (cf. ESO PR 22/02) and has a proper motion of 3.8 
arcsec/year (corresponding to 23 km/sec relative to the Sun, in the 
direction perpendicular to the line-of-sight). The highest known 
proper motion star is Barnard's Star at 6 light-years distance and 
moving 10 arcsec/year (87 km/sec relative to the Sun). All known stars 
within 30 light-years are high-proper-motion objects and move at least 
0.2 arcsec/year.

Trawling for fast moving objects
--------------------------------
For some time, astronomers at the Astrophysical Institute in Potsdam 
have been making a systematic computerised search for 
high-proper-motion objects which appear on red photographic sky 
plates, but not on the equivalent blue plates. Their goal is to 
identify hitherto unknown cool objects in the Solar neighbourhood.

They had previously found a handful of new objects within 30 
light-years in this way, but nothing as red or moving remotely as fast 
as the one they have now snared in the constellation of Indus in the 
southern sky. This object was only seen on the very longest-wavelength 
plates in the SuperCOSMOS Sky Survey database. It was moving so 
quickly that on plates taken just two years apart in the 1990s, it had 
moved almost 10 arcseconds on the sky, giving a proper motion of 4.7 
arcsec/year. It was also very faint at optical wavelengths, the reason 
why it had never been spotted before. However, when confirmed in data 
from the digital Two Micron All Sky Survey (2MASS), it was seen to be 
much brighter in the infrared, with the typical colour signature of a 
cool brown dwarf.

(continued)

---