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ADINA FEINSTEIN — MAY 16, 2022 ASTR 28900 THE “HOW TO” ON FINDING & CONFIRMING EXOPLANETS 1

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THINGS YOU’LL LEARN BY THE END OF THIS TALK (HOPEFULLY) - What is an exoplanet? - What do transits and radial velocities tell us about exoplanets? - How does someone confirm an exoplanet? - What does the population of exoplanets look like? - What can young planets tell us that old planets can’t? 2

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WHAT IS AN EXOPLANET? 3

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WHAT IS AN EXOPLANET? 4

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WHAT IS AN EXOPLANET? 4

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-Is in orbit around the Sun -Has su ffi cient enough mass to become spherical (or nearly spherical) in shape -Has cleared its orbital path from other Solar System “stu ff ” WHAT IS AN EXOPLANET? 4

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-Is in orbit around the Sun -Has su ffi cient enough mass to become spherical (or nearly spherical) in shape -Has cleared its orbital path from other Solar System “stu ff ” WHAT IS AN EXOPLANET? 5 -“Exo” is short for “extrasolar” or… outside of the Sun

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THE FIRST EXOPLANETS 6

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THE FIRST EXOPLANETS 6

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THE TRANSIT METHOD 7

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THE CONCEPT 8 TOP DOWN VIEW EDGE ON VIEW

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THE CONCEPT 8 TOP DOWN VIEW EDGE ON VIEW

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THE CONCEPT 8 TOP DOWN VIEW EDGE ON VIEW

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PHOTOMETRY — MONITORING THE BROADBAND LIGHT FROM STARS 9

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PHOTOMETRY — MONITORING THE BROADBAND LIGHT FROM STARS 9 Ɣ Ɣ Ɣ Ɣ Ɣ

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PHOTOMETRY — MONITORING THE BROADBAND LIGHT FROM STARS 9 e e e e e

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PHOTOMETRY — MONITORING THE BROADBAND LIGHT FROM STARS 9 e e e e e

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BREAKING DOWN THE INFO IN A TRANSIT 10

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MOST IMPORTANTLY: TRANSIT DEPTH 11 TRANSIT DEPTH Observable: planet-to-star fl ux ratio Inferred parameter: planet radius

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12 TRANSIT DEPTH RSTAR RPLANET d = ( Rstar Rplanet ) 2 MOST IMPORTANTLY: TRANSIT DEPTH

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SECOND: TRANSIT PERIOD 13 PLANET PERIOD TOP DOWN VIEW

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THIRD: TRANSIT DURATION 14 TRANSIT DURATION t = P 2Rstar 2πa

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THIRD: TRANSIT DURATION 14 TRANSIT DURATION t = P 2Rstar 2πa

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THIRD: TRANSIT DURATION 15 TRANSIT DURATION t = P 2Rstar 2πa P2 = 4π2 G(Mstar + Mplanet ) a3 KEPLER’S THIRD LAW

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THIRD: TRANSIT DURATION 15 TRANSIT DURATION t = P 2Rstar 2πa P2 = 4π2 G(Mstar + Mplanet ) a3 KEPLER’S THIRD LAW

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ADDITIONAL ORBITAL PROPERTIES LEARNED 16 i INCLINATION how inclined the orbit is with respect to the stellar equator

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ADDITIONAL ORBITAL PROPERTIES LEARNED 17 INCLINATION how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER: what latitude the planet transits i a b b bR* = a cos i RSTAR

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ADDITIONAL ORBITAL PROPERTIES LEARNED 18 INCLINATION how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER: what latitude the planet transits b

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ADDITIONAL ORBITAL PROPERTIES LEARNED 18 INCLINATION how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER: what latitude the planet transits b

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ADDITIONAL ORBITAL PROPERTIES LEARNED 18 INCLINATION how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER: what latitude the planet transits b

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LIMB DARKENING 19 - At the edges of the star, we see the cooler, darker, outer layers of the atmosphere - At the center, we see the hotter brighter inner layers - At an intermediate distance, we see warm layers (hence the gradient)

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ADDITIONAL ORBITAL PROPERTIES LEARNED 20 INCLINATION ECCENTRICITY how circular the orbit is how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER what latitude the planet transits TOP DOWN VIEW

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ADDITIONAL ORBITAL PROPERTIES LEARNED 21 INCLINATION ECCENTRICITY how circular the orbit is how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER what latitude the planet transits TOP DOWN VIEW KEPLER’S FIRST LAW The orbits of planetary bodies are ellipses, with the star at one of the foci of the ellipse.

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INCLINATION ADDITIONAL ORBITAL PROPERTIES LEARNED 22 how circular the orbit is ECCENTRICITY how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER what latitude the planet transits

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INCLINATION ADDITIONAL ORBITAL PROPERTIES LEARNED 22 how circular the orbit is ECCENTRICITY how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER what latitude the planet transits

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INCLINATION ADDITIONAL ORBITAL PROPERTIES LEARNED 22 how circular the orbit is ECCENTRICITY how inclined the orbit is with respect to the stellar equator IMPACT PARAMETER what latitude the planet transits

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23 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Radius [REarth] Transit Depth around the Sun [%] Earth 1 0.08 Neptune 4 0.1 Jupiter 10 1

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23 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Radius [REarth] Transit Depth around the Sun [%] Earth 1 0.08 Neptune 4 0.1 Jupiter 10 1

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23 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Radius [REarth] Transit Depth around the Sun [%] Earth 1 0.08 Neptune 4 0.1 Jupiter 10 1

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23 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Radius [REarth] Transit Depth around the Sun [%] Earth 1 0.08 Neptune 4 0.1 Jupiter 10 1

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23 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Radius [REarth] Transit Depth around the Sun [%] Earth 1 0.08 Neptune 4 0.1 Jupiter 10 1

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23 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Radius [REarth] Transit Depth around the Sun [%] Earth 1 0.08 Neptune 4 0.1 Jupiter 10 1

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23 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Radius [REarth] Transit Depth around the Sun [%] Earth 1 0.08 Neptune 4 0.1 Jupiter 10 1

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THE RADIAL VELOCITY METHOD 24

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THE CONCEPT 25

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THE CONCEPT 25

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THE CONCEPT 25

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SPECTROSCOPY — MONITORING STELLAR ABSORPTION LINES 26

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SPECTROSCOPY — MONITORING STELLAR ABSORPTION LINES 26

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BREAKING DOWN THE INFO IN RADIAL VELOCITIES 27

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BREAKING DOWN THE INFO IN RADIAL VELOCITIES 28 PERIOD Observable: the motion of the star Inferred parameter: planet period

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BREAKING DOWN THE INFO IN RADIAL VELOCITIES 29 AMPLITUDE K = 203P−1/3 Mp sin i (M⋆ + wMp )2/3 1 1 − e2

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BREAKING DOWN THE INFO IN RADIAL VELOCITIES 29 AMPLITUDE K = 203P−1/3 Mp sin i (M⋆ + wMp )2/3 1 1 − e2

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30 K = 203P−1/3 Mp sin i (M⋆ + wMp )2/3 1 1 − e2 BREAKING DOWN THE INFO IN RADIAL VELOCITIES

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30 K = 203P−1/3 Mp sin i (M⋆ + wMp )2/3 1 1 − e2 BREAKING DOWN THE INFO IN RADIAL VELOCITIES

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31 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Mass [MEarth] Radial Velocity Signal [m/s] Earth 1 0.09 Neptune 16 1.5 Jupiter 320 28

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31 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Mass [MEarth] Radial Velocity Signal [m/s] Earth 1 0.09 Neptune 16 1.5 Jupiter 320 28

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31 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Mass [MEarth] Radial Velocity Signal [m/s] Earth 1 0.09 Neptune 16 1.5 Jupiter 320 28

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31 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Mass [MEarth] Radial Velocity Signal [m/s] Earth 1 0.09 Neptune 16 1.5 Jupiter 320 28

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31 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Mass [MEarth] Radial Velocity Signal [m/s] Earth 1 0.09 Neptune 16 1.5 Jupiter 320 28

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31 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Mass [MEarth] Radial Velocity Signal [m/s] Earth 1 0.09 Neptune 16 1.5 Jupiter 320 28

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31 GOOD REFERENCE NUMBERS TO REMEMBER Planetary Mass [MEarth] Radial Velocity Signal [m/s] Earth 1 0.09 Neptune 16 1.5 Jupiter 320 28

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WHAT CAN WE LEARN ABOUT EXOPLANETS IF WE HAVE BOTH THEIR RADII AND MASSES? 32 ρ = M 4 3 πR3 THE PLANET’S DENSITY!

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MASS - RADIUS DIAGRAM 33 (Zeng et al 2019)

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CONFIRMING A TRANSITING PLANET IS REAL 34

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STEPS IN THE CONFIRMATION PROCESS (FOR TRANSITING PLANETS) 35 STEP 1: FIND A TRANSIT SIGNAL (IDEALLY 3)

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STEPS IN THE CONFIRMATION PROCESS (FOR TRANSITING PLANETS) 35 STEP 1: FIND A TRANSIT SIGNAL (IDEALLY 3) STEP 2: OBSERVE ANOTHER TRANSIT FROM THE GROUND

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STEPS IN THE CONFIRMATION PROCESS (FOR TRANSITING PLANETS) 35 STEP 1: FIND A TRANSIT SIGNAL (IDEALLY 3) STEP 2: OBSERVE ANOTHER TRANSIT FROM THE GROUND STEP 3: CHARACTERIZE THE HOST STAR

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STEPS IN THE CONFIRMATION PROCESS (FOR TRANSITING PLANETS) 35 STEP 1: FIND A TRANSIT SIGNAL (IDEALLY 3) STEP 2: OBSERVE ANOTHER TRANSIT FROM THE GROUND STEP 3: CHARACTERIZE THE HOST STAR STELLAR PROPERTIES SEARCH FOR BINARY COMPANIONS

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STEPS IN THE CONFIRMATION PROCESS (FOR TRANSITING PLANETS) 35 STEP 1: FIND A TRANSIT SIGNAL (IDEALLY 3) STEP 2: OBSERVE ANOTHER TRANSIT FROM THE GROUND STEP 3: CHARACTERIZE THE HOST STAR STEP 4: THEORIZE SOME STUFF ABOUT THE PLANET STELLAR PROPERTIES SEARCH FOR BINARY COMPANIONS

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STEP 1: IDENTIFYING TRANSITS IN A LIGHT CURVE 36 KEPLER/K2 TRANSITING EXOPLANET SURVEY SATELLITE (TESS)

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- Want to make sure the transit signal / period are real and not instrumental systematics STEP 2: GROUND-BASED TRANSIT 37 Next Generation Transit Survey (NGTS) Mearth

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- From transit — planet-to-star radius ratio - From radial velocities — planet-to-star mass ratio STEP 3A: STELLAR PROPERTIES 38

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- This uses a technique called “adaptive optics imaging” which searches for binary star companions, which may also cause transit events (these are called eclipsing binaries). STEP 3B: IDENTIFYING BINARY COMPANIONS 39

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- This uses a technique called “adaptive optics imaging” which searches for binary star companions, which may also cause transit events (these are called eclipsing binaries). STEP 3B: IDENTIFYING BINARY COMPANIONS 39

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- This uses a technique called “adaptive optics imaging” which searches for binary star companions, which may also cause transit events (these are called eclipsing binaries). STEP 3B: IDENTIFYING BINARY COMPANIONS 39

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- Dynamical arguments: looking into the longterm stability of the system - For multi-planet systems: looking for transit timing variations as another means to measure the planetary masses - Modeling transmission spectra: what absorption features you would see from the planetary atmospheres - Only for transiting exoplanets - Dependent on planet radius, mass, orbital period/equilibrium temperature STEP 4: DISCUSS & PROPOSE 40

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WHAT DOES THE CURRENT POPULATION OF EXOPLANETS LOOK LIKE? 41

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~4500 PLANETS HAVE MEASURED RADII 42 Jupiter Earth

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~4500 PLANETS HAVE MEASURED RADII 42 Jupiter Earth

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~4500 PLANETS HAVE MEASURED RADII 42 Jupiter Earth

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WHERE ARE ALL THE ~1.8REARTH PLANETS? 43 (Fulton et al 2017)

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WHAT DO WE THINK CAUSES THIS GAP? 44

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WHAT DO WE THINK CAUSES THIS GAP? 44 Have gaseous 
 envelopes No atmospheres

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GAP THEORY: PHOTOEVAPORATION 45 Have gaseous 
 envelopes No atmospheres

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GAP THEORY: PHOTOEVAPORATION 45 Have gaseous 
 envelopes No atmospheres

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< 1000 PLANETS HAVE MEASURED MASSES 46 Jupiter Earth

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YOUNG PLANETS & WHAT THEY TEACH US 47

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THERE ARE <100 TRANSITING PLANETS YOUNGER THAN 300 MYR 48 Jupiter Earth

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TRANSITS — TOO EASY TO BE TRUE 49 Implies a well- behaved star

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WELL-BEHAVED = STELLAR SURFACE IS BORING 50

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WELL-BEHAVED = STELLAR SURFACE IS BORING 50

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THIS IS NOT A RADIAL VELOCITY CURVE! 51

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THIS IS NOT A RADIAL VELOCITY CURVE! 52

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THIS IS NOT A RADIAL VELOCITY CURVE! 52

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53 YOUR TURN TO FIND THE PLANET

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53 YOUR TURN TO FIND THE PLANET

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V1298 TAU — 4 PLANETS AROUND A 30 MYR STAR 54 (David et al 2019)

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V1298 TAU — 4 PLANETS AROUND A 30 MYR STAR 54 (David et al 2019)

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V1298 TAU — STELLAR CHARACTERIZATION 55 (David et al 2019) - Placing membership with a nearby young moving group - Kinematics argument - HR diagram argument - Rotation period

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V1298 TAU — STELLAR CHARACTERIZATION 55 (David et al 2019) - Placing membership with a nearby young moving group - Kinematics argument - HR diagram argument - Rotation period

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V1298 TAU — STELLAR CHARACTERIZATION 55 (David et al 2019) - Placing membership with a nearby young moving group - Kinematics argument - HR diagram argument - Rotation period

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V1298 TAU — STELLAR CHARACTERIZATION 55 (David et al 2019) - Placing membership with a nearby young moving group - Kinematics argument - HR diagram argument - Rotation period

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V1298 TAU — “WATCHING” RADIUS EVOLUTION 56 (David et al 2019)

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V1298 TAU — AN EXAMPLE OF HOW CHALLENGING YOUNG PLANETS ARE 57 (Suarez Mascareño et al 2021)

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V1298 TAU — AN EXAMPLE OF HOW CHALLENGING YOUNG PLANETS ARE 57 (Suarez Mascareño et al 2021) No known 
 orbital period 
 from transits 
 (claim ~40 days from RVs) Well constrained 
 orbital period 
 of ~24 days

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V1298 TAU — WHAT’S UP WITH THEIR DENSITIES? 58 Density (g/cm3) Jupiter 1.33 Saturn 0.69 V1298 Tau b 1.2 ± 0.45 V1298 Tau e 3.6 ± 1.6

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V1298 TAU — THE WRONG PERIOD FOR PLANET E 59 (Feinstein et al 2022) 😬 New TESS data gave 
 lower period of V1298 Tau e 
 of >= 42.7 days

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V1298 TAU — SO WHAT HAPPENED? 60 - Young stars are variable, active, and this manifests in their own intrinsic radial velocities - Speci fi cally, young stellar RVs are dominated by magnetic activity - Young stars have strong stellar winds - Eventually, they will lose angular momentum via winds & spin down (decreases magnetic activity) - This period could be intrinsic to the star, not the planet - Timescales of stellar activity RVs are dependent on the star

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THINGS YOU’VE LEARNED TODAY (HOPEFULLY) - What is an exoplanet? - What do transits tell us about exoplanets? - What do radial velocities tell us about exoplanets? - How does someone confirm an exoplanet? - What does the population of exoplanets look like? - What can young planets tell us that old planets can’t? 61 [email protected]

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THINGS YOU’VE LEARNED TODAY (HOPEFULLY) - What is an exoplanet? - What do transits tell us about exoplanets? - What do radial velocities tell us about exoplanets? - How does someone confirm an exoplanet? - What does the population of exoplanets look like? - What can young planets tell us that old planets can’t? 61 [email protected]

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THINGS YOU’VE LEARNED TODAY (HOPEFULLY) - What is an exoplanet? - What do transits tell us about exoplanets? - What do radial velocities tell us about exoplanets? - How does someone confirm an exoplanet? - What does the population of exoplanets look like? - What can young planets tell us that old planets can’t? 61 [email protected]

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THINGS YOU’VE LEARNED TODAY (HOPEFULLY) - What is an exoplanet? - What do transits tell us about exoplanets? - What do radial velocities tell us about exoplanets? - How does someone confirm an exoplanet? - What does the population of exoplanets look like? - What can young planets tell us that old planets can’t? 61 [email protected]

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THINGS YOU’VE LEARNED TODAY (HOPEFULLY) - What is an exoplanet? - What do transits tell us about exoplanets? - What do radial velocities tell us about exoplanets? - How does someone confirm an exoplanet? - What does the population of exoplanets look like? - What can young planets tell us that old planets can’t? 61 [email protected]

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THINGS YOU’VE LEARNED TODAY (HOPEFULLY) - What is an exoplanet? - What do transits tell us about exoplanets? - What do radial velocities tell us about exoplanets? - How does someone confirm an exoplanet? - What does the population of exoplanets look like? - What can young planets tell us that old planets can’t? 61 [email protected]