the devil’s in the details
DESCRIPTION
The Devil’s in the Details. Transits in detail Telescopes. 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 - PowerPoint PPT PresentationTRANSCRIPT
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The Devil’s in the Details
Transits in detailTelescopes
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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
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Transit
• What is it measuring?
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Transit
• The atmosphere + the planet’s disk
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Transit
• The atmosphere + the planet’s optically-thick disk
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Transit
• The atmosphere + the planet’s optically-thick disk
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Transit
• Amount of atmospheric absorption will change with wavelength
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Transit
• Amount of atmospheric absorption will change with wavelength
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Transit
• So a planet’s radius will change with wavelength due to absorption by different molecules in its atmosphere
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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
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Example!
• Detection of H2 scattering
Zellem et al. (in prep.)
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Example!
• Detection of H2 scattering
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Another Example!
• Detection of water, methane, and carbon dioxide in a hot Jupiter’s atmosphere
Swain et al. (2009)
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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)
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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
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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
=
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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
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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
≠
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Rob does spectroscopy magic
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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)
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Telescopes
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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
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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
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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
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What is the 61”?
• Reflector or refractor?
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What is the 61”?
• Light comes in the dome, hits primary mirror
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What is the 61”?
• Reflected off of primary mirror and focused on secondary mirror
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What is the 61”?
• Light reflects off of secondary mirror and is focused on detector
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What is the 61”?
• REFLECTOR
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Next time….
• Learn about instrumentation used to collect data– CCDs– Spectrographs
• Start learning how we will reduce telescopic data
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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