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遨遊天際 Wondering around the Sky
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Transcript of 遨遊天際 Wondering around the Sky
遨遊天際Wondering around the Sky
江瑛貴國立清華大學
Are Planetary Systems Quantized ?
江瑛貴(Ing-Guey Jiang)國立清華大學
Outline
1. The discoveries2 The data3. The mass & period function 4. Cluster Analysis5. Our results6. The discussions & implications
The Discoveries
• 188 extra-solar planets (10 May 2006)• Methods: Doppler effect, transit, micro-len
sing, imaging• 176 exoplanets by Doppler effect• About 7 confirmed by both transit & Doppl
er effect• Wide range of mass & period & eccentricity
The Data
The (Statistical) Trend
• A deficit of high mass planets at separations smaller than 0.3 AU
• Implies a mass-period correlation• Not an observational bias (Jiang et al. 2003,
Gu et al. 2004)• Another deficit of sub-Jupiter mass planets
at separations larger than 0.5 AU ?
The Mass & Period Function
(Tabachnik & Tremaine 2002) (maximum-likelihood method) • Only 72 planets were used• Assuming a simple power-law distribution• 4 percent of solar-type stars have planets
Questions
• Is single-power law a good approximation ?• How about broken double-power law ? • There are about 176 exoplanets now.• Would the result change a lot if much more
planets are included ?• We decided to group the data first• Then, determine the mass distributions etc. f
or each group
Cluster Analysis
• To find groups in data by an algorithm• An important field in statistics• Used in a few astronomy papers• Zappala et al. (1995) identified the dynamical fami
lies from 12487 asteroids• Baggaley & Galligan 1997, Galligan 2003 used Cl
uster Analysis in meteoroid stream searches• Only Single Linkage Algorithm was used in astro.
Single Linkage Algorithm
Dendrogram
Similarity-Based Clustering Method (SCM)
• Assume there are c clusters, with c cluster centers z_i
• Define a dis-similarity function J
• Find maximums, i.e. peaks, of J by setting dJ/dz_i=0 & form a iteration algorithm
• z_i will change positions at each iteration
The Example
Our Results
• A collaboration with statistics experts: Prof. Hung, Wen-Liang & Prof. Yang, Miin-Shen
• We use the data of April 2005 of the Extrasolar Planets Catalog
• We consider those planets which projected mass, period, orbital eccentricity and semi-major axis are all available
• 143 exoplanets are in our data set
The Mass
The Period
The Mass & Period
The Period & Eccentricity
Main Results
• The mass distribution is continuous, i.e. there is no particular gap, in which planets cannot be formed
• There are two clusters in terms of period• Planetary migration did happen• Likely to have more than one migration
mechanisms: tidal & disc interactions• Eccentricity-period correlation is strong
Discussions• Our method, SCM, can determine the number and centers
of groups reasonably• It is not good to simply assume a cluster number• It can be used in other astronomical data set• To fit the data with a distribution function (as the
astronomers usually do), it would be good to do clustering analysis first
• We then can try to fit the data in each group with functions
• These functions can be more meaningfully explained by physical mechanisms
Implications on Protoplanetary Discs/Debris Discs
• In the gas-rich environment , the disc influences the planet (Trilling et al. 2002, Jiang & Yeh 2004)
• The existence of planets might also affect the disc structure
• Even after the gas is depleted, the planet might influence the structure of debris disk, the dynamics of dust grains.
• We are working on structures of debris discs etc.• It will be great to have images on gas, dust grains
etc. all together to have a complete story