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 optical 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 ≠

Measuring radii at the 61” Planet has same signature in the infrared (IR) despite differing atmospheric contents optical Signal very different in the optical Benneke & Seager (2013)

Looking for New Planets

Transit Timing Variations (TTVs)

Looking for Exomoons

Measuring Exoplanetary Magnetic Fields

In the UVIn 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 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 ITLITL 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 multiple wavelengths Filter wheel – Allows filter change on the fly – 61”: U, R, B, V, I

Mont4k Filter Efficiencies

Next time How do we reduce data? IRAF! HOMEWORK!!! – Download and install IRAF Directions will be on class website