Because I'm more sensitive to the situation now, I've been looking for some
indication of the impact of science fiction on "real" science. I've mentioned
before that in 40 years of attending scientific meetings, I've never once
heard of a science fiction author being quoted, other than Arthur C. Clarke's
communications satellites, HAL, and Carl Sagan's Ellie Arroway. I may have to
slightly revise that statement now.
I've included below an announcement that was released today by European Space
Organization and the Astrophysikalisches Institut Potsdam that actually
references a few science fiction stories. Although the article is long, the
reference of interest is Reference [6], which occurs near the middle of the
article and at the very end. However, at the risk of raising more ire, I am
unsure why they included this note. It certainly does nothing to raise their
credibility or provide any sort of additional factual information.
Wirt Atmar
=======================================
ESO Education and Public Relations Dept.
Contacts:
Ralf-Dieter Scholz
Astrophysikalisches Institut Potsdam
Germany
Tel.: +49 (0)331 749 9336
email: rdscholz at aip.de
Mark McCaughrean
Astrophysikalisches Institut Potsdam
Germany
Tel.: +49 (0)331 749 9525
Email: mjm at aip.de
----------------------------------------------------------------------------
Text with all links and the photo is available on the ESO Website at URL:
<A HREF="http://www.eso.org/outreach/press-rel/pr-2003/pr-01-03.html">
http://www.eso.org/outreach/press-rel/pr-2003/pr-01-03.html</A>
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For immediate release: 13 January 2003
ESO Press Release 01/03
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
deg C. 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 (circled). The upper image comes from one of the SuperCOSMOS
Sky Surveys (SSS) optical photographic 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.
At this point, the object was thought to be an isolated traveller. However,
a search through available online catalogues quickly revealed that just 7
arcminutes away was a well-known star, Epsilon Indi. The two share exactly
the same very large proper motion, and thus it was immediately clear the
two must be related, forming a wide binary system separated by more than
1500 times the distance between the Sun and the Earth.
Epsilon Indi is one of the 20 nearest stars to the Sun at just 11.8 light
years [5]. It is a dwarf star (of spectral type K5) and with a surface
temperature of about 4000 deg C, somewhat cooler than the Sun. As such,
it often appears in science fiction as the home of a habitable planetary
system [6]. That all remains firmly in the realm of speculation, but
nevertheless, we now know that it most certainly has a very interesting
companion.
This is a remarkable discovery: Epsilon Indi B is the nearest star-like
source to the Sun found in 15 years, the highest proper motion source
found in over 70 years, and with a total luminosity just 0.002% that of
the Sun, one of the intrinsically faintest sources ever seen outside the
Solar System!
After Proxima and Alpha Centauri, the Epsilon Indi system is also just
the second known wide binary system within 15 light years. However,
unlike Proxima Centauri, Epsilon Indi B is no ordinary star.
Brown dwarfs: cooling, cooling, cooling ...
ESO PR Photo 03b/03
Caption: PR Photo 03b/03 shows the near-infrared (0.9-2.5 micron)
spectrum of Epsilon Indi B, obtained on November 16-17, 2002, with the
SOFI multi-mode instrument on the ESO 3.5-m New Technology Telescope
(NTT) at the La Silla Observatory (Chile) The total integration time
is 360 sec. Regions of strong absorption in the Earth's atmosphere
have been removed for clarity. The locations of prominent molecular
absorption bands from water (H2O), methane (CH4) and carbon monoxide
(CO) in the atmosphere of Epsilon Indi B are indicated. Also labelled
are some spectral lines from potassium (KI, at 1.25 and 1.52 micron)
and sodium (NaI, at 2.33 micron) atoms. From these data, the spectral
type of Epsilon Indi B is determined as T2.5V, corresponding to an
effective temperature of 'just' 1000 +/- 60 deg C.
Within days of its discovery in the database, the astronomers managed to
secure an infrared spectrum of Epsilon Indi B using the SOFI instrument
on the ESO 3.5-m New Technology Telescope (NTT) at the La Silla
Observatory (Chile). The spectrum showed the broad absorption features
due to methane and water steam in its upper atmosphere, indicating a
temperature of 'only' 1000 deg C. Ordinary stars are never this cool --
Epsilon Indi B was confirmed as a brown dwarf.
Brown dwarfs are thought to form in much the same way as stars, by the
gravitational collapse of clumps of cold gas and dust in dense molecular
clouds. However, for reasons not yet entirely clear, some clumps end up
with masses less than about 7.5% of that of our Sun, or 75 times the mass
of planet Jupiter. Below that boundary, there is not enough pressure in
the core to initiate nuclear hydrogen fusion, the long-lasting and stable
source of power for ordinary stars like the Sun. Except for a brief early
phase where some deuterium is burned, these low-mass objects simply
continue to cool and fade slowly away while releasing the heat left-over
from their birth.
Theoretical discussions of such objects began some 40 years ago. They
were first named 'black dwarfs' and later 'brown dwarfs', in recognition
of their predicted very cool temperatures. However, they were also
predicted to be very faint and very red, and it was only in 1995 that
such objects began to be detected.
The first were seen as faint companions to nearby stars, and then later,
some were found floating freely in the Solar neighbourhood. Most brown
dwarfs belong to the recently classified spectral types L and T, below
the long-known cool dwarfs of type M. These are very red to human eyes,
but L and T dwarfs are cooler still, so much so that they are almost
invisible at optical wavelengths, with most of their emission coming out
in the infrared. [7].
How massive is Epsilon Indi B?
The age of most brown dwarfs detected to date is unknown and thus it is
hard to estimate their masses. However, it may be assumed that the age
of Epsilon Indi B is the same as that of Epsilon Indi A, whose age is
estimated to be 1.3 billion years based on its rotational speed.
Combining this information with the measured temperature, brightness,
and distance, it is then possible to determine the mass of Epsilon Indi
B using theoretical models of brown dwarfs.
Two independent sets of models yield the same result: Epsilon Indi B must
have a mass somewhere between 4-6% of that of the Sun, or 40-60 Jupiter
masses. The most likely value is around 45 Jupiter masses, i.e. well below
the hydrogen fusion limit, and definitively confirming this new discovery
as a bona-fide brown dwarf.
The importance of Epsilon Indi B
ESO PR Photo 03c/03
Caption: PR Photo 03c/03 displays a 3D map of all known stellar systems
in the solar neighbourhood within a radius of 12.5 light-years. The Sun
is at the centre and the Epsilon Indi binary system with the newly
found brown dwarf Epsilon Indi B lies near the bottom. The colour is
indicative of the temperature and the spectral class -- white stars are
(main-sequence) A and F dwarfs; yellow stars like the Sun are G dwarfs;
orange stars are K dwarfs; and red stars are M dwarfs, by far the most
common type of star in the solar neighbourhood. The blue axes are
oriented along the galactic coordinate system, and the radii of the
rings are 5, 10, and 15 light-years, respectively. The Java Applet
conveniently provides detailed information about the stars in the
figure -- just move the cursor over the field. The figure is adapted
from a diagram by Richard Powell.
PR Photo 03c/03 shows the current census of the stars in the solar
neighbourhood. All these stars have been known for many years, including
GJ1061, which, however, only had its distance firmly established in
1997. The discovery of Epsilon Indi B, however, is an extreme case,
never before catalogued, and the first brown dwarf to be found within
the 12.5 light year horizon.
If current predictions are correct, there should be twice as many brown
dwarfs as main sequence stars. Consequently, Epsilon Indi B may be the
first of perhaps 100 brown dwarfs within this distance, still waiting
to be discovered!
Epsilon Indi B is an important catch well beyond the cataloguing the
Solar neighbourhood. As the nearest and brightest known brown dwarf and
with a very accurately measured distance, it can be subjected to a wide
variety of detailed observational studies. It may thus serve as a
template for more distant members of its class.
With the help of Epsilon Indi B, astronomers should now be able to see
further into the mysteries surrounding the formation and evolution of
the exotic objects known as brown dwarfs, halfway between stars and
giant planets, the physics of their inner cores, and the weather and
chemistry of their atmospheres.
An historical note -- the southern constellation Indus
ESO PR Photo 03d/03
Caption: PR Photo 03d/03 shows the southern constellation Indus (The
Indian) and its surroundings, as drawn in the famous Uranographia
published 1801 of German astronomer Johann Elert Bode. This
reproduction was made from original printing plates held by the
library of the Astrophysical Institute Potsdam (Germany). The binary
stellar system Epsilon Indi is associated with one of the arrows in
the Indian's hand. However, because of its proximity, only 12
light-years away, it is moving so fast across the sky that it is now
located someway below the arrows. In only a few thousand years, it
will have moved out of the Indus constellation and into the
neighbouring constellation Tucana (The Toucan).
The constellation Indus lies deep in the southern sky, nestled between
three birds, Grus (The Crane), Tucana (The Toucan) and Pavo (The Peacock),
cf. PR Photo 03d/03.
First catalogued in 1595-1597 by the Dutch navigators Pieter Dirkszoon
Keyser and Frederick de Houtman, this constellation was added to the
southern sky by Johann Bayer in his book 'Uranometria' (1603) to honour
the Native Americans that European explorers had encountered on their
travels.
In particular, it has been suggested that it is specifically the native
peoples of Tierra del Fuego and Patagonia that are represented in Indus,
just over two thousand kilometres south of La Silla where the first
spectroscopic observations of Epsilon Indi B were made some 400 years
later.
In the later drawing by Bode shown here, Epsilon Indi, the fifth brightest
star in Indus, is associated with one of the arrows in the Indian's hand.
More information
The information in this press release is based on a paper ("Epsilon Indi
B: a new benchmark T dwarf" by Ralf-Dieter Scholz and co-authors), soon
to be published in the European journal Astronomy & Astrophysics (Letters).
It is available on the web in preprint form at
<A HREF="http://babbage.sissa.it/abs/astro-ph/0212487">
http://babbage.sissa.it/abs/astro-ph/0212487</A>
Notes
[1]: This is a joint press release of the European Southern Observatory
(ESO) and the Astrophysical Institute Potsdam (Germany). A German version
of this press release is also available.
[2]: The team consists of Ralf-Dieter Scholz, Mark McCaughrean, Nicolas
Lodieu (Astrophysical Institute Potsdam, Germany) and Bjoern Kuhlbrodt
(Hamburg Observatory, Germany).
[3]: The SuperCOSMOS Sky Surveys (SSS) at the Wide-Field Astronomy Unit
of the Institute for Astronomy at the University of Edinburgh include
digitised data of UKST Schmidt plates in the BJ-, R- and I-passbands,
with additional scans of ESO and POSS1 Schmidt plates in the R-band.
A dedicated compilation of all photographic plates obtained for
astronomical studies during the past century is carried out by the
Wide-Field Plate Database project, based at the Institute of Astronomy
of the Bulgarian Academy of Sciences in Sofia.
[4]: 1 arcsec (arcsecond) is 1/60th of 1 arcmin (arcminute), which in
turn is 1/60th of 1 degree. A proper motion of 1 arcsec/year corresponds
to a position change of 1 degree (two full lunar diameters) in 3600
years.
[5]: Distances for relatively nearby objects can be measured accurately
via the technique of "trigonometric parallax". As the Earth orbits the
Sun, nearby objects appear to move slightly against the relatively fixed
background of distant, faint stars. By measuring the shift of the nearby
star over a six month period, its distance from the Earth can be
calculated via standard trigonometry, knowing the distance of the Earth
from the Sun. The ESA Hipparcos satellite, orbiting the Earth in the
1990s, measured a distance to Epsilon Indi of 3.626 parsecs or 11.82
light years (112 million million kilometres), with an error of just
0.3%.
[6]: Epsilon Indi has been suggested to have a planetary system in many
works of science fiction, including the "Known Space" novels of Larry
Niven, the award-winning short story "Sleeping Dogs" by Harlan Ellison,
episodes of both the original Star Trek and the more recent Next
Generation series, and in many role-playing and fan fiction sites on
the Internet.
[7]: Definitions of the new L and T spectral classes, along with detailed
information on their photometric and spectroscopic characteristics can be
found at these websites:
<A HREF="http://spider.ipac.caltech.edu/staff/davy/ARCHIVE/">
http://spider.ipac.caltech.edu/staff/davy/ARCHIVE/</A>
and
<A HREF="http://www.astro.ucla.edu/~adam/homepage/research/tdwarf/">
http://www.astro.ucla.edu/~adam/homepage/research/tdwarf/</A>
Other ESO Press Releases about brown dwarf objects include PR 07/97, PR
16/00, PR 14/01, and PR 14/02.
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