Searching for extra-solar planets in Infrared J. Serena Kim Steward Observatory, Univ. of Arizona In collaboration with FEPS Spitzer legacy team ( 07/25/05

Wavelengths - There are other looks of the world! Our eyes look at things in visible wavelength, but there are other wavelengths! Lower energy Higher energy Near-IR = 1–2.5  m Visible = 0.4 – 0.8  m Mid & Far-IR = 5 – 300  m

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! Near-IR = 1–2.5  m Visible = 0.4 – 0.8  m Mid & Far-IR = 5 – 300  m

Atmospheric windows for astronomical observations

William Herschel Discovers Infrared Radiation

Properties of IR radiation Any object that has a temperature over absolute zero (  F, or  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!

Infrared camera finds a victim of fire through thick smoke. (courtesy of Sierra Pacific Infrared) 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. Visible/infrared images (left/right) taken from the cockpit of an airplane preparing to land in a dense fog. What do infrared eyes see ? - some examples…

circum Looking at the dusty Universe in infrared… Why do we use IR to study the Universe? … well… the Universe is quite dusty!

Orion in visible and infrared So, how does the night sky look in visible and IR?

Astronomers do not want to have a biased view of the universe… so we use multi- wavelength data to have more complete look!

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. 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

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

First results from Spitzer

What other things in the disk can be seen in IR?

Now, in our Solar System, Asteroid belt Kuiper belt Two ring like structures: Asteroid Belt and 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. The zodiacal light in the HD 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 MIPS images - Meyer et al. (2004), Kim et al. (2005) HD HD 6963 HD ’ MIPS 70um images 160um 70um

Sample SEDs of new exo-KB disks HD 105, HD Meyer et al. (2004) HD 6963, HD 8907, HD , HD , HD ( 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 R in =42.5 AU log (L IR /L * ) =-3.6 M d = 0.02 M earth Debris Disk Model: Wolf & Hillenbrand (2003) star disk

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)!  ( 43AU) < Warm dust mass upper limit: M warm dust (R sub - 43AU) < M earth Gap < R in (43 AU)

There are other physical processes that can remove 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) AU~40 AU without planets Moro-Martin & Malhotra 2003 Why is there a gap in the disk?

Planetesimal collisions can create dusty ring…

Disk lifetime How long these disks survive? Disk Radius (AU) < Gyr-3Gyr Age (Myr)

Do we resolve these disks? Not with Spitzer for most of the time, but we can! ( e.g., HD ) 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= Gyr old, R in ~ 30 AU, Rout ~ 300 AU, M dust ~ M earth. 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 ? James Webb Space Telescope -launch planned in 2011 Planck (2007), TPF(2012), Darwin (>2015)

Other observational effort to detect planets Ground based AO - MMT, VLT, Gemini - LBT, GMT (future)

End of presentation!