Telescopes and Instrumentation

October 24

Calendar

• Next class: Friday November 7• Field trips!– Visit the 61” on Mount Bigelow• Afternoon of Saturday November 1• Will need people willing to help drive/carpool up the

mountain

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

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

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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)

Looking for New Planets

Looking for New Planets

Looking for New Planets

Looking for New Planets

Looking for New Planets

Looking for New Planets

Looking for New Planets

Looking for New Planets

Looking for New Planets

Looking for New Planets

Transit Timing Variations(TTVs)

Looking for Exomoons

Looking for Exomoons

Measuring Exoplanetary Magnetic Fields

Measuring Exoplanetary Magnetic Fields

In the UV In the B

What is the 61”?

• REFLECTOR

• …and basically a giant bucket to collect light particles (photons)

Instrumentation

How do we record data?

• Back in the olden days, had to use your eyes and draw pictures– Eye has 100-200 ms integration time

New Revolution: Photography

• Use photographic plates to take images of the sky– 1840 photograph of the moon

• In use in astronomy until the 1990s• Many discoveries:– Pluto and Charon– Asteroids

• Clunky, fragile• Very low efficient (0.5%--4%)

Photomultiplier Tubes

CCD

• Charged Coupled Device• Invented in 1969 at AT&T Bell Labs (Boyle and

Smith)• Incoming photon hits silicon crystal lattice– Absorbed, causing some electrons to be liberated

from silicon– Induces a voltage– Voltage is directly

proportional to the photon count

61”/Mont4k• Device: Fairchild CCD486 4Kx4K CCD Backside Processed at ITL• Device Names: Mont4K SN3088• Device Size: 4096 x 4097 pixels (15 micron pixels)• Image Scale: 0.14 arcsec/pixel (7.1 pixels/arcsec)• Field of View: 580 x 580 arcsec^2 (9.7 x 9.7 arcmin^2)• Gain: 3.1 electrons/ADU• Readout Noise: 5.0 electrons• Dark Current: 16.6 electrons/pixel/hour• Full Well: 131,000 electrons unbinned (191 Ke for 2x2 binned)• Operating temperature: -130 C

Gain

• 3.1 electrons/ADU• ADU = Analog Digital Unit• 1 electron per photon• Gain “turns up” the signal over noise• What you measure with a CCD is actually the

ADU, commonly known as “counts”

Readout (“Read”) Noise

• As you read out an image, there can be some additional noise associated with moving the electrons

• Bias– 0 second integration– Read out the image– See how many electrons (noise) you get -> “read noise”

61”/Mont4k Bias

Dark Current

• Thermal variations in the system cause there to be an underlying “dark” current

• Can be minimized by cooling down– Hence the use of the dewar (liquid nitrogen)

61”/Mont4k Dark

Full Well

• 131,000 electrons unbinned (191 Ke for 2x2 binned)

• How many photons each pixel can hold before “saturating”– How much can each pixel “bucket” contain before

overflowing

Saturation!

Linearity

• 1 electron doesn’t always equal 1 photon

Hubble Wide Field Camera 3

Flat

• Measures FOV impurities– Telescope system• Maybe a moth got in the way

– Instrumentation system• Position-dependent impurities

• Flat field– Take an image of a white screen (or the dusk sky)

to see how efficiency changes across the image

61”/Mont4k Flat Field

Filters

• In the light path between the secondary mirror and the CCD

• Block light at some wavelengths, allow light through at others

• Can look at photometry(brightness) at multiplewavelengths

• Filter wheel– Allows filter change on

the fly– 61”: U, R, B, V, I

Mont4k Filter Efficiencies

Spectroscopy

Next time

• How do we reduce data?• IRAF!

• HOMEWORK!!!– Download and install IRAF• Directions will be on class website