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외계 행성체의 검출
Giordano Bruno (1548-1600)
Christian Bartholméss, Jordano Bruno
(Paris: Libaririe Philosophique de Ladrange,
1846), frontispiece.
S.S.Hong
http://galileo.rice.edu/chr/bruno.html
SNU, 05-11-05
지구인의 정체는 자신의 우주적 이웃과의 만남에서
확인될 것입니다.
우주적 이웃을 찾으려는 지구인의 노력은 이미 그 첫
발을 내디뎠습니다. 달 표면에 찍힌 이 발자국들이
우리의 확고한 의지를 드러내고 있습니다.
우리의 이웃과 손을 맞잡고 만남의 기쁨을 나누기까
지, 앞으로 얼마나 더 긴 세월을 기다려야 할지 아직
은 모르겠습니다.
하지만 우리의 최우선 과제는, 인류의 우주적 피붙
이들이 거주할 지구형 고체 행성의 존재를 확인하는
일입니다.
S.S.Hong ; SNU 05-11-05
OBSERVATIONAL DETECTION
OF EXTRA-SOLAR PLANETS
1. HUNTING OF EXTRA-SOLAR PLANETS
2.
OCCULTATION OF CENTRAL STAR BY PLANET
3.
CORONAGRAPH: An Occultation Maker
4.
FRUITS OF DOPPLER SPECTROSCOPY
5. GRAVITATIONALLY REFRACTED RADIATION
6.
THERMAL EMISSION FROM DEBRIS
7.
PROSPECT OF THE IMMEDIATE FUTURE
8.
SUMMARY AND CONCLUSION
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REFERENCES :
Gilmour, I. 2004, in An Introduction to ASTROBIOLOGY, Chap. 6 The
Detection of Exoplanets, pp. 199 - 231.
Ulmschneider, P. 2003, in INTELLIGENT LIFE IN THE UNIVERSE, Chap.
3 The Search for Extrasolar Planets, pp. 51 - 78.
Lunine, J. I. 2005, ASTROBIOLOGY A Multidisciplinary Approach,
Chap. 15 Life Elsewhere II: The Discovery of Extrasolar Planetary
Systems and the Search for Habitable and Inhabited Worlds, pp.
474 - 508.
Morrison, D. and Owen, T. 2003, THE PLANETARY SYSTEM, 3rd Ed.
Chap. 18 Distant Worlds, pp. 471 – 502.
Im M. 2005, Why IR, a ppt file presented to an Astronomy Colloquium,
SEES, Seoul National University.
S.S.Hong ; SNU 05-11-05
1. HOW TO HUNT EXOPLANETS
1-1 WHY NOT JUST LOOK AT IT
The planet is going to be drowned in the flood of light from its
much brighter central star, even in space.
The Earth atmosphere makes things much worse for ground
based observations by blurring the images.
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Resolving Power of Telescope
Light is subject to diffraction due to its wave nature.
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The problem of diffraction is compounded by atmospheric blurring due to
air turbulence. Although stars are almost point like sources, but they look
like fuzzy disks through ground based optical telescopes.
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Under the most ideal situation the minimum angle diffraction of separation a
telescope can resolve is given by the ratio of wavelength  to diameter D of
the telescope aperture:
diffraction = 1.22   D = 0 .126 [   5,000 Å ]  [ 102 cm  D ]
In practice stellar images can not be sharper than the atmospheric seeing
disk, which is of the order of 0.1 even at world best observatory sites: The
atmospheric turbulence beats the diffraction limit of 1m telescope.
Human eye commands at best about
30 of resolving power.
For a hypothetical observer at 10 pc away
from us, the Sun-Jupiter distance extends
0 .52, which is four times the diffraction
limit of 1meter telescope.
The diffraction limit of only meter class
telescopes is good enough to resolve extrasolar Jovian planets and terrestrial ones
as well.
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Flooding of Light from Central Star
Cause of the 1010 - fold Decrease
(-16.5) – (- 6.8) = - 9.7
geometrical dilution
 R2  4  AU2  1.8 x 10-9
Earth albedo = 0.3
mean phase = 0.5
in total
1.8 x 10-9 x 0.3 x 0.5 = 2.7 x 10-10
Visible light detectors with dynamic range 1010 are hard to come by. Therefore, it is
impossible to detect the central starlight that is scattered or reflected by extra-solar
planets.
It may be possible to detect thermal emission from extra-solar planets, particularly
in far IR wavelengths, since Sun overpowers Jupiter by 105~6 in FIR emission.
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Why is IR So Important ?
in visible light
in infra - red
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Even cold stuff can be ‘hot’ in IR !
brown dwarf
Orion in visual and IR
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before bouncing the ball
after a few bouncings
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Infrared Excess in the SED
theoretical model simulations for the
spectral energy distribution of the
Solar system as observed by some
intelligent beings 10pc away from us
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Direct Hunting versus Indirect Guessing
Direct Methods : unambiguous recognition of those photons that left
extra-solar planet
• It is impossible to distinguish visible photons of planet origin from
ones of the central star. Direct method works only for the Solar system.
• It looks promising to distinguish origins of the IR photons.
Indirect Methods : seek for observable consequences of the existence of
planets orbiting around stars under consideration
What might then be the observable consequences?
1-2 INDIRECT DETECTION OF EXOPLANETS/ DEBRIS DISK
Natural Occultation : transit of planet in front of the central star
Coronagraph
: blocking off the starlight by occulting disk
Doppler Shift
: Kepler Motion, gravitational wobbling
Gravitational Lens
: gravitationally refracted light
Thermal Emission from Debris Disk : Dust is a better tracer than planet.
Nulling Interferometry in Space :
a promising future technology for direct detection
to be employed in NASA TPF or ESA Darwin project
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2. OCCULTATION OF CETRAL STAR BY PLANET
2-1 OCCULTATION PHOENOMENON
An accuracy better than 1% is
required in photometry.
If Doppler spectroscopy is done
simultaneously, size of the
planet, semi-major axis and
inclination angle of the orbit
can be fixed from the light and
velocity curves.
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2-2 AN EXAMPLE OF OCCULTATION OBSERVATIONS
HD209458
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2-3 DETERMINATION OF PLANET SIZE
The three lines correspond to the three different-sized planets; from top to
bottom : 1.15, 1.27, and 1.40 RJ .
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3. CORONAGRAPH: An Occultation Maker
3-1 DIRECT DETECTION OF BROWN DWARF
NASA IRTF on top of Mauna Kea,
Hawaii
IR image taken by a coronagraph
with specially designed soft edge
after heavy image processing with
specially developed SWs
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3-2 RECENT INNOVATIONS IN OCCULTATION THECHIQUE
Coronagraph + Adaptive Optics on 10m Class Telescopes
A brown dwarf of mass 60~80MJ orbits
around the central star at 20AU distance.
Occulting disk removes the central starlight; and a flexible secondary mirror
corrects for atmospheric distortion.
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4. FRUITS OF DOPPLER SPECTROSCOPY
4-1 PRINCIPLE BEHIND THE DOPPLER EFFECT
Letters written regularly by a traveling salesman ought arrive his wife at
ever increasing intervals as he moves away from home. However, the letters
written on his way back from the trip reach his wife at ever decreasing
intervals.
(obs - o)  o = vrad  c or
  o = vrad  c
Measurements of the Doppler shift  determine the relative velocity vrad
of the source with respect to the observer.
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4-2 DOPPLER SHIFT OF SPECTRAL LINE
In a star-planet system the star orbits the center of mass, as does the planet.
On the other hand the center of mass draws a straight line in the sky plane.
Although the planet can not be spotted by an Earth bound observer, the
orbital motion generates periodic change in the radial velocity of the star.
The Doppler shift measured by spectroscopic means may tell us the existence
of circum-stellar planet or planets.
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S.S.Hong
SNU, 05-11-05
The amplitude of radial velocity curve depends on the star-to-planet mass
ratio, the semi-major axis, and the orbital inclination.
The radial velocity becomes zero  :
Maximum amplitude is obtained  :
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4-3 ESTIMATES OF THE DOPPLER SHIFT FOR SUN
BY EARTH
Vrad,E = 30 km s-1 x mE  (M⊙ + mE)
= 3 x106 cm s-1 x [6x1027g/ 2x1033g]
= 9 cm s-1
max,E
= 5000Å x 9 cm s-1  3 x1010 cm s-1
= 1.5 x 10-6 Å
BY JUPITER
Vrad,J = 1.4 x106 cm s-1 x mJ  (M ⊙ + mJ)
= 13 m s-1
max,J = 2 x 10-4 Å
In principle semi-major axis and eccentricity can be determined for the orbit, but only
lower limit can be given to the planet mass; since orbital inclination is unknown.
How to measure the wavelength change so accurately, even if one may monitor for
tens of years?
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4-4 WAVELENGTH CALIBRATION
Noble Idea + Pioneer’s Dedication
Michel Mayor on the right discovered
the first extra-solar planet around star
51 Peg, together with Geoff Marcy on
left who immediately confirmed it. Both
men have gone on to discover many
more wonderful new worlds.
The gas provides them with a fine ruler for precise measurement of wavelengths.
Extensive computing analysis is required for reducing large volume of data taken over
a decade, and will be so over coming many decades.
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4-5 EARLY DISCOVERIES
High Velocity resolution  High Spectral Resolution
• Large Telescope + High Quality Spectrograph + Decade Long Monitoring
• Extremely Accurate Calibration of Wavelengths  POISON GAS
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An Example of High Quality Data
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4-6 CURRENT STATUS OF THE ART
Discovery of terrestrial planets is still
challenge of the generations to come.
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4-7 SOME OF THE HIGHLIGHT FINDINGS
Hot Jupiters !
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Mass and Semi-major Axis of Extra-solar Planets
planetary system
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4-8 OBSERVATIONAL BIAS
massive planets ; short orbital periods ; small semi-major axis ;
single component systems ; edge-on orbits ; nearby systems
Is the Solar system an example of exceptional cases ?
Have only exceptional systems been detected so far ?
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5. GRAVITATIONALLY REFRACTED RADIATION
5-1 GRAVITATIONAL LENS
Einstein ring
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5-2 A SPLENDID FEAST OF GRAVIATIONAL MACRO-LENS
20세기 최고의 물리학자 앨버트 아인슈타인은 다음과 같이 말했습니다. "인생에는 두 가지 삶 밖에 없다. 한 가지는 기
적 같은 건 없다고 믿는 삶. 또 한 가지는 모든 것이 기적이라고 믿는 삶. 내가 생각하는 인생은 후자이다."
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5-3 PRINCIPLE BEHIND GRAVIATIONAL MICRO-LENS
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5-4 EXAMPLE OF GRAVIATIONAL MICRO-LENS
A micro-lensing event can be confirmed by monitoring photometry at two
wavelength bands, as the gravitational lensing affects all wavelengths in
the same way.
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6. THERMAL EMISSION FROM DEBRIS
Why We are So Much Interested in Debris:
Many small particles render much wider area than a single large
particle of the same total debris mass:
If a large mass body of radius
R is divided into N small
particles of size s, we expect an
enormous enhancement  in
the total cross-sectional area:
 = [N s2  R2]
= N [s  R]2
= [R  s]3 [s  R]2
= [R  s]
This can be an enormously
large number!
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This is the reason why it is easier to observe proto-planetary disk than planet,
and why Beta Pictoris demonstrates her charm and glory in IR emission and
scattered visible light as well.
This is the reason why we say “Small is better than Large!”
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7. PROSPECT OF THE IMMEDIATE FUTURE
Comparison of Planet Hunting Methods
as observed at 5 pc away from the Solar system
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Limitations and Promises
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8. SUMMARY AND CONCLUSION
1.
The problem of atmospheric blurring can be handled comfortably
by adaptive optics even on ground and of course on space platform.
2.
Light flooding is a target for coronagraph.
3.
With two decades of dedicated struggle the Doppler spectroscopy
has revealed a glimpse of the Promised Land, I mean, Gardens of
Eden for extra-solar intelligent beings.
4.
Yet, extra-solar counterparts of the terrestrial planets defy all our
hunting effort with contemporary innovations.
5.
Nulling interferometry in space and monitoring of micro-lensing
events on the Earth and from the space as well promise us to
witness extra-solar terrestrial planets in a coming decade.
6.
Large millimeter radio telescope arrays being built, like ALMA
some 5,000m above the sea level in Northern Chile, will be
available for us within a decade to probe fine details in dense
molecular cores, proplyds, and debris disks.
7.
The sub-millimeter radio interferometry will eventually detect
biological signs, if intelligent beings enjoy civilizations that are
advanced at least as ours.
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In Conclusion :
I may proclaim you are the blessed generation of human beings; after
so many millions of years we humans are soon to hear about news from
our cosmic neighbors. You are the first members of the species to
receive such a good news. Let us think about Fr. Giordano Bruno of the
16th century. And let us pay a special tribute to our beloved poet Ji Yong
Chung, who wrote in 1937 :
별 똥 떨어진 곳
마음에 두었다
다음날 가보려
벼르다 벼르다
이 젠 다 자 랐 소.
It is not Ji Yong but Seungsoo who has ‘grown up’ too early. This is
the very reason why I envy you so much. I, therefore, ask each one of
you to live a cosmopolitan life in its fuller and truer sense.
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Appendix: Kepler’s Third Law
P
4 2
a3
G ( M  m)
2 a
P

2

V
 G ( M  m) 


a
1/ 2
 V

 AU   M  m 
 30 km s 
 a   M 
1/ 2
 AU   M  m 
 30 km s 
 a   M 
1/ 2

1/ 2
Vstar
 AU 
 30 km s 1 
 a 
1/ 2
 AU 
 30 km s 1 
 a 
V
1
star
1/ 2
1
1/ 2
 m 

 M  m 
1/ 2
m 1 
 M   M  m 
 m 
 M 3 / 2 
spectroscopic observations  maximum radial velocity  orbital velocity
spectral type of the central star  mass M of the star  mass m of the planet
orbital period P, star mass M sin i , planet mass m  semi-major axis a
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Giordano Bruno (1548-1600)
Filippo Bruno was born in Nola, near Naples, the son of Giovanni Bruno, a soldier, and
Fraulissa Savolino. He took the name Giordano upon entering the Dominican order. In the
great Dominican monastery in Naples (where Thomas Aquinas had taught), Bruno was
instructed in Aristotelian philosophy. His exceptional expertise in the art of memory
brought him to the attention of patrons, and he was brought to Rome to demonstrate his
abilities to the Pope. During this period he may also have come under the influence of
Giovanni Battista Della Porta, a Neapolitan polymath who published an important book on
natural magic. Bruno was attracted to new streams of thought, among which were the
works of Plato and Hermes Trismegistus, both resurrected in Florence by Marsilio Ficino
in the late fifteenth century. Hermes Trismegistus was thought to be a gentile prophet who
was a contemporary of Moses. The works attributed to him in fact date from the turn of the
Christian era.
Because of his heterodox tendencies, Bruno came to the attention of the Inquisition in
Naples and in 1576 he left the city to escape prosecution. When the same happened in
Rome, he fled again, this time abandoning his Dominican habit. For the next seven years
he lived in France, lecturing on various subjects and attracting the attention of powerful
patrons. From 1583 to 1585 he lived at the house of the French ambassador in London.
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During this period he published the books that are most important for our purposes, Cena
de le Ceneri ("The Ash Wednesday Supper") and De l'Infinito, Universo e Mondi ("On the
Infinite Universe and Worlds"), both published in 1584. In Cena de le Ceneri, Bruno
defended the heliocentric theory of Copernicus . It appears that he did not understand
astronomy very well, for his theory is confused on several points. In De l'Infinito ,
Universo e Mondi, he argued that the universe was infinite, that it contained an infinite
number of worlds, and that these are all inhabited by intelligent beings.
Wherever he went, Bruno's passionate utterings led to opposition. During his English
period he outraged the Oxford faculty in a lecture at the university; upon his return to
France, in 1585, he got into a violent quarrel about a scientific instrument. He fled Paris
for Germany in 1586, where he lived in Wittenberg, Prague, Helmstedt, and Frankfurt. As
he had in France and England, he lived off the munificence of patrons, whom after some
time he invariably outraged. In 1591 he accepted an invitation to live in Venice. Here he
was arrested by the Inquisition and tried. After he had recanted, Bruno was sent to Rome,
in 1592, for another trial. For eight years he was kept imprisoned and interrogated
periodically. When, in the end, he refused to recant, he was declared a heretic and burned
at the stake.
It is often maintained that Bruno was executed because of his Copernicanism and his belief
in the infinity of inhabited worlds. In fact, we do not know the exact grounds on which he
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was declared a heretic because his file is missing from the records. Scientists such as
Galileo and Johannes Kepler were not sympathetic to Bruno in their writings.
Sources: A convenient introduction to Bruno is the article by Frances Yates in the
Dictionary of Scientific Biography. Several of Bruno's works have been translated into
English. See The Ash Wednesday Supper, tr. Stanley L. Jaki (The Hague: Mouton, 1975);
Sidney Greenberg, The Infinite in Giordano Bruno, with a Translation of his Dialogue
Concerning the Cause, Principle, and One (New York: King's Crown Press, 1950); Jack
Lindsay, Cause, Principle, and Unity; Five Dialogues (New York: International Publishers,
1964); Dorothea Waley Singer Giordano Bruno, his Life and Thought. With Annotated
Translation of his Work, On the Infinite Universe and Worlds (New York: Schuman).
The crucial work on Bruno's thought is Frances Yates, Giordano Bruno and the Hermetic
Tradition (Chicago: University of Chicago Press, 1964). See also Walter Pagel, "Giordano
Bruno: The Philosophy of Circles and the Circular Movement of the Blood," Journal of
the History of Medicine and Allied Sciences 6 (1951)): 116-125; Angus Armitage, "The
Cosmology of Giordano Bruno, Annals of Science 6 (1948): 24-31.
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별똥이 떨어진 곳
정 지용
밤뒤1 를 보며 쪼그리고 앉았으려면, 앞집 감나무 위에 까치 둥우리가
무섭고, 제 그림자가 움직여도 무섭다. 퍽 추운 밤이었다. 할머니만 자꾸
부르고, 할머니가 자꾸 대답하셔야 하였고, 할머니가 딴 데를 보지나
아니하시나 하고, 걱정이었다.
아이들 밤뒤 보는 데는 닭 보고 묶은 세배를 하면 낫는다고, 닭 보고 절을
하라고 하셨다. 그렇게 괴로운 일도 아니었고, 부끄러워 참기 어려운 일도
아니었다. 둥우리 안에 닭도 절을 받고, 꼬르르 꼬르르 소리를 하였다.
별똥을 먹으면 오래 산다는 것이었다. 별똥을 주워 왔다는 사람이 있었다.
그날 밤에도 별똥이 찌익 화살처럼 떨어졌다. 아저씨가 한번 메추라기를
산 채로 훔켜잡아 온, 뒷산 솔 포대기2 속으로 분명 바로 떨어졌다.
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별똥 떨어진 곳
마음에 두었다
다음날 가보려
벼르다 벼르다
이젠 다 자랐소.
『소년』, 1937. 12.
─『정지용전집』, 민음사, 1988 에서 재수록
─『모던 수필』, 향연, 2003 에서 재재수록 ssh
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