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The Solar System and other Planetary Systems or failed stars:
Brown Dwarfs
Solar system
Planets
Exo-planets
Brown Dwarfs (back to top)
 | The Search for Very Cold Brown Dwarfs at the
Canada-France-Hawaii Telescope (from the colloquium talk by Dr. Loic
Albert at ASIAA on Nov. 16, 2007) A definition of brown
dwarf (BD) is: its core temperature T is higher than D burning
temperature but lower than H burning temperature. Li burning temperature is
also in this range.
 | 1985: the first brown dwarf (BD), the prototype BD
Gl299B was found. |
| 1995: a BD of spectral type M8 with Li line was found -- Teide 1. |
| 1997: the first isolated field BD found -- KELU-1
(in a binary system) |
| 1998: the first L-type BD found -- GD 165B. |
| 1999: 4 field T-type BD found. |
|
Solar system (back to top)
| Solar physics facts:
| CME: Coronal Mass Ejection (CME) is
thought to be produced by magnetic reconnection in the solar corona. CME
has important effects to the space climate around the earth and so is
very interesting to many solar physicists. Here is a list of all CME white light records
recorded since 1996 by Large Angle and Spectrometric Coronagraph (LASCO)
on board the Solar and Heliospheric Observatory (SOHO) mission. |
| Flare is also a phenominon caused mainly
by magnetic reconnection, but on the photosphere. Flare usually arises
near boundary of magnetical distribution regions. |
| Prominence is ejection of material from
the solar surface that is observable on the edge of the white light sun.
It's also known as filaments when it moves to the surface of the sun. |
| Sunspots are strong foot points of the
magnetic flow ropes on the photosphere. |
| Voyager2 Exploration Results:
 | A review on the solar system recently revealed by Voyager 2
satelite. (from Jokippi, 2008,
Nature, 454, 38) |
| Electron plasma frequency fp = 8980 sqrt(ne) Hz with electron density ne in cm^-3.
They discussed the intense plasma waves at
or near the solar wind termination shock.
Voyager 2 passed heliospheric termination shock at
a distance of 83.4 AU. Voyager 1 speed: 3.6 AU/yr,
Voyager 2 speed: 3.2 AU/yr. (Gurnett & Kurth, 2008,
Nature, 454, 78) |
| Mesurement of magnetic fields at the solar wind termination shock.
(from Burlaga et al., 2008,
Nature, 454, 75) |
|
|
Planets (back to top)
| Compressible convection in fast rotating spherical
shells: anelastic model (from Dr. Kirill Kuzanyan's talk in YNAO on
Nov. 6, 2008). Taylor-Proudman theorem (see wiki page)
states that the gas motion in the Jovian atmosphere is cylinderic due
to the steady rotation of the planet itself. His anelastic
model demonstrates that turbulent jets
occurs from the root of the H2-He surface layer (above the metallic H-He
layer) and develop upwards and bend in the same
direction of the planet rotation to surface layer. Thus the cylinderically
aligned turbulent jet layers intersect with the spherical surface of the
atmosphere to produce the observed layer flows
on the Jupiter suface. |
| A
systemic study of final masss of gas giant panets. (from Dr. Tanigawa Takayuki's lunch box talk in ASIAA on Apr. 17,
2007)
| Hydrodynamical simulation of planet accretion shows that the final
masses of the gas giant planets are controlled by two factors: viscosity
time scale and disk dissipation time scale.
Here the disk is the gas disk around the young star. |
| Gravitational interaction between the planet and surrounding
differentially rotating gas may open a circular
gap in the orbiting gas disk near the radius of the planet. The
reason is that the local gravational force of the planet will produce a
shock wave in the differentially rotating (around central star, not
around the planet) gas on both side of it. The local interaction results
in angular momentum transfer from inner gas to the planet and from the
planet to outer gas. The inner gas loses angular momentum and so thrinks
its orbital radius, while the outer gas gains angular momentum and
enlarge it's orbital radius. Therefore, a circular gap form around the
radius of the planet. |
| According to Takayuki's semi-analytical simulations, (1) the final
mass of a planet within 1 AU distance from the cetral star is mainly controlled
by gap formation, because the disk diffusion timescale is
longer than the gap formation timescale and so the planet is left hungry
in the empty gap; (2) the final mass of a planet within 1-100 AU is
mainly controlled by circumstellar disk
dissipation, because the disk dissipation timescale is smaller
than the gap formation timescale; (3) the final mass of a planet beyond
100 AU is not affected by accretion,
because the viscosity is too small and so accretion is not important for
planet growth. |
|
| Formation of stony planets. (from discussions with Dr. Pingao,
Gu)
| The formation mechanism of stony planets
is still unclear. These solid planets, such as Mars and Earth, are
usually too small to form by accreting gas. One of the possible way is
the merge of smaller solid planetesimals. |
| The actual physical processes in the formation of the small
planetesimals are also unclear yet. |
| Planets formed by accreting gas are almost always gaseous giant
planets. |
|
| Fine-structure patterns in Saturn's ring as
disturbed spirals. (from Dr. Uri Griv's colloquium talk given in
ASIAA on Apr. 27, 2007)
| It's well known that the Saturn's ring is composed of many big and
small sub-rings. With the even higher resolution observations by Cassini
satellite, some irregular density patterns appear on the fine-structure
scale. Hydrodynamic simulations that take account collision can
reproduce these patterns as disturbed spiral patterns formed through
density wave mechanism. |
|
Exo-planets (back to top)
| Extrasolar planets (from lunch talk by Dr.
France Allard at ASIAA on Oct. 31, 2007)
| Several example of well known extrasolar planets: GQ Lupi, Gliese 876
(the 1st super-earth), G 1581 (the 1st
terrestrial planet), TrES-1 (an eclipsing
planet observed by Spitzer IRAC at 8um), HD
209458b (a metal rich eclipsing planet observed by Spitzer MIPS
at 24um). |
| Habitable zone: a range of radius within
which planets get a reasonable amount of radiation from its host star to
allow the habitation of human-like life. For the solar system, the
habitable zone is from about 0.75-1.75 earth orbit radius. |
| During the formation and evolution of planets, the formation of molecule weight gradient with counteract with
heat gradient and so stop the convection motion and stabilize the stratification of materials inside the planets. |
|
| A massive planet with M=9.8+-3.3 MJupiter
is found around TW Hydrae, a young star with protoplanetary disk. The age of TW Hya is only
8-10 Myr, which demonstrate that planet can form in the circumstellar disks within 10 Myr before the dissipation of the disk by radiation and pressure.
(from Setiawan et al., 2008Nat..451L...38S) |
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