The Devil’s in the Details

Transits in detailTelescopes

Last time….

• Radial velocity– Measures Doppler shift– Planet’s mass– Must be in line-of-sight of observer– Need a large telescope for high-precision measurements

• 1 m/s ~ 1 Earth-sized planet, need 6 m class telescope

• Transit– Measures drop in light as planet moves in front of or behind host

star– Planet’s radius– Must be in line-of-sight of observer– Can do with a relatively small telescope

Transit

• What is it measuring?

Transit

• The atmosphere + the planet’s disk

Transit

• The atmosphere + the planet’s optically-thick disk

Transit

• The atmosphere + the planet’s optically-thick disk

Transit

• Amount of atmospheric absorption will change with wavelength

Transit

• Amount of atmospheric absorption will change with wavelength

Transit

• So a planet’s radius will change with wavelength due to absorption by different molecules in its atmosphere

So….

• If we measure the transit of an exoplanet at different wavelengths…– We can measure how its radius varies with

wavelength– Indicates its atmospheric structure and content• Atmospheric structure = how temperature varies with

altitude• Atmospheric content = what molecules are present

Example!

• Detection of H2 scattering

Zellem et al. (in prep.)

Example!

• Detection of H2 scattering

Another Example!

• Detection of water, methane, and carbon dioxide in a hot Jupiter’s atmosphere

Swain et al. (2009)

Measuring radii at the 61”

• Planet has same signature in the infrared (IR) despite differing atmospheric contents

• Signal very different in the optical

Benneke & Seager (2013)

Why are the IR signatures the same?

• In the IR, a small planet with a thick atmosphere can block as much light as a large planet with a small atmosphere– Hot Jupiter atmospheres are opaque in the IR

Why are the IR signatures the same?

• In the IR, a small planet with a thick atmosphere can block as much light as a large planet with a small atmosphere– Hot Jupiter atmospheres are opaque in the IR

=

However, not the same in the visible

• In the visible, the planet’s atmosphere is now transparent, so a small planet will look different than a large one

However, not the same in the visible

• In the visible, the planet’s atmosphere is now transparent, so a small planet will look different than a large one

≠

Rob does spectroscopy magic

Measuring radii at the 61”

• Planet has same signature in the infrared (IR) despite differing atmospheric contents

• Signal very different in the optical

Benneke & Seager (2013)

Telescopes

History

• First telescopes were refractors in the Netherlands in 1608

• Galileo heard about them in 1609 and built his own– First person to point

towards the heavens– Discovered craters on

Moon, moons of Jupiter, Saturn’s rings

Refractors vs. Reflectors

• Refractor: objective lens on front refracts (focuses) light at the back end of the telescope– Lens can obscure

image– Very long focal

length, so telescope itself is long

Refractors vs. Reflectors

• Reflector: primary mirror reflects light to a focal point– No more lens– Can reflect the image

back on itself, makes shorter focal length and telescope

– Developed by Newton in 1680

• Most professional telescopes today are reflectors

Schmidt-Cassegrain design

What is the 61”?

• Reflector or refractor?

What is the 61”?

• Light comes in the dome, hits primary mirror

What is the 61”?

• Reflected off of primary mirror and focused on secondary mirror

What is the 61”?

• Light reflects off of secondary mirror and is focused on detector

What is the 61”?

• REFLECTOR

Next time….

• Learn about instrumentation used to collect data– CCDs– Spectrographs

• Start learning how we will reduce telescopic data

Calendar

• Next class: Friday October 24• Field trips!– Visit the 61” on Mount Bigelow• Afternoon of Saturday November 1• Limited space for those who want to stick around

through the night to help observe• Will need people willing to help drive/carpool up the

mountain

– Mirror Lab Tour• Friday November 14 from 4-5 PM