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AMAGAZING
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Nuovo
Pianeta Abitabile (Italian)
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New
Habitable Planet
(English)
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Gliese
581
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INDEX
NASA --
larger
image
Gliese 581 is a dim red
dwarf star, like Gliese
623 A (M2.5V) and B (M5.8Ve)
at lower right.
(See a Digitized Sky
Survey
field image
around
Gliese 581 at the
NStars Database.)
- System Summary
Also known as HO Librae,
this dim star lies
around 20.4 light-years
from Sol. It is located
in the northeast part
(15:19:26.8-07:43:20.2,
ICRS 2000.0) of
Constellation
Libra,
the Scales -- northeast
of Delta Librae, north
of Gamma Librae and
Graffias
(Beta Scorpii), and
southwest of Epsilon (Yed
Posterior)
and Delta (Yed
Prior)
Ophiuchi, and Mu,
Epsilon, and Alpha (Unukalhai)
Serpentis. Like other
red dwarf stars, however,
it is not visible to the
naked eye. On November
30, 2005, a team of
French and Swiss
astronomers announced
the discovery of a
Neptune-class
planet in a very close "torch"
orbit around Gliese 581
(ESO
press release
and
Bonfils et al, 2005,
in
pdf
-- details below). (See
an animation of the
planetary and
potentially habitable
zone orbits
of this system, with a
table of basic orbital
and physical
characteristics.)
This
star was probably first
designated as BD-07 4003
and added to a catalogue
that was originally
published in 1863 by
Friedrich Wilhelm August
Argelander
(1799-1875) on the
position and brightness
of 324,198 stars between
+90° and -2° declination
that were measured over
11 years from Bonn,
Germany with his
assistants Eduard
Schönfeld (1828-1891)
and Aldalbert Krüger
(1832-1896). This
catalogue became famous
as the
Bonner Durchmusterung
("Bonn Survey") and is
typically abbreviated as
BD. It was later
expanded and extended
during the early 20th
Century with the
Cordoba
(observed from
Argentina) then the
Cape Photographic
Durchmusterung
(observed from South
Africa).
Its
high proper motion was
probably discovered
photographically, and it
was designated as Wolf
562 by
Max (Maximilian Franz
Joseph Cornelius) Wolf
(1863-1932). Wolf was a
pioneer of
astrophotography who
discovered hundreds of
variable stars and
asteroids, and about
5,000 nebulae by
analyzing photographic
plates and developing
the "dry plate" in 1880
and the "blink
comparator" in 1900 with
the Carl Zeiss optics
company in Jena, Germany.
Today, many astronomers
refer to this star by
its earliest designation
as Gl 581 in the first
Gliese Catalogue of
Nearby Stars (CNS, now
ARICNS database)
of
Wilhelm Gliese
(1915-93), who was a
longtime astronomer at
the
Astronomiches
Rechen-Institut at
Heidelberg
(even when it was at
Berlin).
The Star
Gliese 581 is a cool and
dim, main sequence red
dwarf (M2.5 V). The star
has almost a third (31
+/- 2 percent) of Sol's
mass, possibly 29
percent of its diameter,
and a bit more than one
percent (around 0.013)
of its visual luminosity
(Bonfils
et al, 2005,
in
pdf).
The star appears to be
only around 47 to 56
percent as enriched as
Sol in elements heavier
than hydrogen ("metals")
((Bean
et al, 2006;
Ken Crosswell, 2006;
and
Bonfils, et al, 2005).
Its kinematic
characterisitcs,
magnetic activity, and
sub-Solar metallicity
indicate that that
Gliese 581 is at least
two billion years old.
Gliese 851 is a variable
star with the
designation "HO Librae"
and NSV 7023. Some other
useful star catalogue
designations include: HO
Lib, Gl 581, Hip 74995,
BD-07 4003, G 151-46, G
152-9, LHS 394, LTT
6112, LPM 564, LFT 1195,
Vys/MCC 159, and Wolf
562.
Planet b
JPL,
NASA
Larger
image.
It is not yet known
whether
planetary candidate "b"
is
rocky or gaseous -- like
Neptune.
On November 30, 2005, a team of French and Swiss
astronomers announced
the discovery of a
Neptune-class
planet in a very close "torch"
orbit around this star
using the
HARPS spectrograph
on the
European Southern
Observatory's
3.6-meter telescope at
La Silla,
Chile (ESO
press release)
and
Bonfils et al, 2005,
in
pdf).
Planet "b" has around
16.6 times the Earth's
mass. with a semi-major
axis of 0.041 AUs (around
6 million kilometers),
it orbits so close to
its host star that its
orbital period last only
only 5.366 days. As a
result, the planet must
be very hot, about 147
degrees Celsius (420°
Kelvin), and its
presence would have
disturbed the
development and orbit of
a nearby earth-type in
the habitable zone
(center around 0.05 AUs).
Other measurements of
the star suggest that no
Jupiter-mass planet
orbits Gliese 581 with a
period of around 10
years or less. (See an
animation of the
planetary and
potentially habitable
zone orbits
of this system, with a
table of basic orbital
and physical
characteristics.)
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