Transcript FEPS_EPO_4public_July2005 - The Formation & Evolution of

Searching for extra-solar planets
in Infrared
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J. Serena Kim
Steward Observatory, Univ. of Arizona
In collaboration with FEPS Spitzer legacy team
(http://feps.as.arizona.edu/)
07/25/05
Wavelengths - There are other looks of the world!
Our eyes look at things in visible wavelength, but there are
other wavelengths!
Visible = 0.4 – 0.8 m
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Mid & Far-IR = 5 – 300 m
Near-IR = 1–2.5m
Lower energy
Higher energy
Infrared (IR) - the “heat” radiation you feel
• The near IR allows us to see through dusty regions
• The mid & far IR allows us to see the glowing dust
emission directly!
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Mid & Far-IR = 5 – 300 m
Near-IR = 1–2.5m
Visible = 0.4 – 0.8 m
Atmospheric windows for astronomical observations
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William Herschel
Discovers Infrared
Radiation
Properties of IR radiation
Any object that has a temperature over absolute zero
(-459.67 F, or -273.15 C, or 0 Kelvin) emits IR radiation.
Although we can’t see IR radiation, we can still feel it
as heat.
For example, camp fire heats your body, and you can
feel it (you see it
in visible).
Even objects like ice emit
IR radiation!
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What do infrared eyes see ?
- some examples…
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An infrared image of two burritos after they have been heated
in a microwave oven. Notice how the microwave cooks them
unevenly. The hottest areas are at the outside edges of the
burritos while the central areas are the coolest.
Infrared camera finds a victim of fire
through thick smoke.
(courtesy of Sierra Pacific Infrared)
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Visible/infrared images (left/right) taken
from the cockpit of an airplane preparing
to land in a dense fog.
Looking at the dusty
Universe in infrared…
Why do we use IR to
study the Universe?
… well… the Universe is
quite dusty!
So, how does the night sky look in visible and IR?
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Orion in visible and infrared
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Astronomers do not
want to have a
biased view of the
universe…
so we use multiwavelength data to
have more complete
look!
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Astronomers study circumstellar disk to study
planet formation.
why?
- Planets form in circumstellar disks orbiting young stars
- planets sweep debris and cause ring-like
structure in the disk
- we can test planet formation theories
Why use IR to detect planets and disks?
- The light from the parent star overwhelms the
light from planets and disks in shorter wavelengths
Formation of a Sun-like star
Stars form in a dense molecular
clouds.
The cloud contracts, and collapses
to create a protostar,
but dust still remains. Leftover gas
and dust begins to flatten.
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A significant amount of gas and
dust spirals into the star
(“accretion”).
The disk continues to flatten, and
gets denser. Dusts in the disk can
collide and also stick together.
Soon large body of asteroids form,
and attract other pebbles and dusts
gravitationally, and grow to be a
planet later.
Dusty young circumstellar disk
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Circumstellar disks - inner disk is hotter!
Shorter wavelengths detect hotter inner disk
Longer wavelengths detect colder outer disk!
Spitzer Space Telescope
explores the infrared
Universe
http://www.spitzer.caltech.edu/
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First results from Spitzer
What other things in the disk can be seen in IR?
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Now, in our Solar
System,
Two ring like structures:
Asteroid Belt and Kuiper Belt
Asteroid belt
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Kuiper belt
Zodi-like disks
Spitzer Space Telescope found evidence for
such a belt around the nearby star called HD
69830, when its infrared eyes spotted dust,
presumably from asteroids banging together.
The telescope did not find any evidence for a
planet in the system, but one or more may
be present.
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The zodiacal light in
the HD 69830 system
would be 1,000 times
brighter than our own,
outshining even the
Milky Way.
That system with bright zodi shows a spectrum similar to a comet!
FEPS (Formation and Evolution of Planetary Systems)
is a survey observing with all 3 Spitzer science
instruments (IRAC, IRS, MIPS) to sample sun-like stars
in different ages.
Is our solar system common or rare?
FEPS SAMPLE
~330 sun-like stars
0.8 to 1.5 Msun
3 Myr to 3 Gyr
10 < d < 150 pc
KB like disks
160um
MIPS images
- Meyer et al. (2004), Kim et al. (2005)
HD 13974
HD 6963
HD 105
70um
5.2’
MIPS 70um images
Sample SEDs of new exo-KB disks
HD 105, HD 150706 - Meyer et al. (2004)
HD 6963, HD 8907, HD 122652, HD 145229, HD 206374
(Kim et al. 2005, in press)
Sample SED of a new exo-KB disk
HD 8907 (Kim et al. 2005, in press)
a= 6um - 1mm
Astronomical silicate
Rin =42.5 AU
log (LIR/L*) =-3.6
Md = 0.02 Mearth
disk
star
Debris Disk Model: Wolf & Hillenbrand (2003)
Reminder: a SED of a system with a gap in its disk looks different
Now back to HD 8907:
Disk < 43 AU is cleared (a gap)!
Gap < Rin (43 AU)
(<43AU)/(>43AU) < 10-2
Warm dust mass upper limit:
Mwarm dust(Rsub- 43AU) < 10-7 Mearth
without planets
Why is there a gap in the disk?
There are other physical processes that can remove
Moro-Martin & Malhotra 2003
dusts in the system, but calculations showed that
these are difficult to explain this clean gap inside of the dusty ring.
A possible explanation: A planet like Neptune/Jupiter at ~10-30AU
stirring the planetesimal belt (Kim et al. 2005,
Moro-Martin and Malhotra 2003, 2005)
10 - 30 AU
~40 AU
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Planetesimal collisions
can create dusty ring…
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Planetesimal collisions
can create dusty ring…
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Disk lifetime
How long these disks survive?
Disk Radius (AU)
<0.1 0.3-1 1-10 30-100
3-10
Age (Myr)
10-30
100-300
1Gyr-3Gyr
Do we resolve these disks?
Not with Spitzer for most of the time, but we can!
(e.g., HD 107146)
Silverstone (2003): ISO detection of mid-IR excess
Williams et al. (2004): discovery of extended disk in sub-mm
Metchev et al. (2004): AO imaging
Ardila et al. (2005): HST/ACS coronagraphic imaging
Schneider et al. (2005): HST/NICMOS coronagraphic imaging
Sp. Type = G2, d = 29pc, age= 0.5 - 1.0 Gyr old,
Rin ~ 30 AU, Rout ~ 300 AU, Mdust ~ 0.1 - 0.4 Mearth.
Sub-mm
HST/NICMOS (preliminary)
HST/ACS
SUMMARY from Spitzer Results so far…
Disks dissipate inside of 1 A.U. in ≤ 30 Myr.
If planetesimals/planets form within 1 A.U., they must do so in less
than 30 Myr.
By the age of 1 Gyr, inner disks (≤ 30AU) seem to have been
cleared (by a planet?). About 20% of OLD (> 1 Gyr) systems have cold
outer disks in ~290 sun-like stars near the Sun.
Debris disks come in a wide variety, and their evolution is a
stochastic process. With Spitzer sensitive infrared vision, we are seeing
the steps toward terrestrial planet formation occurring around other
stars.
Can we detect our Sun at 30pc?
Toy Solar System Model:
- Solar system at 30 pc
- Trace back in time from Current
Solar System using our
knowledge about AB and KB
system evolution
(Backman et al. 2005, in prep.)
Future IR missions
HST (current)
-NICMOS
Herschel Space Telescope (far-IR and mm)
- scheduled launch date: 2007
SOFIA
- 2006?
James Webb Space Telescope
-launch planned in 2011
Planck (2007), TPF(2012), Darwin (>2015)
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Other observational effort to detect planets
Ground based AO
- MMT, VLT, Gemini
- LBT, GMT (future)
End of presentation!