Transits: Planet Detection and False Signals
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Transits: planet detection and false signals Raphaëlle D. Haywood Sagan Fellow, Harvard College Observatory Outline • Transit method basics • Transit discoveries so far • From transit detection to planet confirmation • Astrophysical false positives • Factors that can affect derived planet parameters: • stellar activity • stellar parameter estimations What is the transit method? Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the transit method? Transit depth δ ≈ Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the transit method? Assuming circular orbit and i = 90°: Jupiter δ = 1% Transit depth δ ≈ Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the transit method? Assuming circular orbit and i = 90°: Jupiter Earth δ = 1% δ = 84 ppm Transit depth δ ≈ Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the transit method? Assuming circular orbit and i = 90°: Jupiter Earth δ = 1% δ = 84 ppm Transit depth δ ≈ ⇒ It is easier to find small planets around small stars. Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the transit method? Assuming circular orbit and i = 90°: Jupiter Earth δ = 1% δ = 84 ppm Transit duration T ~ Transit depth δ ≈ ⇒ It is easier to find small planets around small stars. Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the transit method? Assuming circular orbit and i = 90°: Jupiter Earth δ = 1% δ = 84 ppm T ≈ 30h Transit duration T ~ Transit depth δ ≈ ⇒ It is easier to find small planets around small stars. Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the transit method? Assuming circular orbit and i = 90°: Jupiter Earth δ = 1% δ = 84 ppm T ≈ 30h T ≈ 3h Transit duration T ~ Transit depth δ ≈ ⇒ It is easier to find small planets around small stars. Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the transit method? Assuming circular orbit and i = 90°: Jupiter Earth δ = 1% δ = 84 ppm T ≈ 30h T ≈ 3h Hot Jupiter T ≈ 2.5h Transit duration T ~ Transit depth δ ≈ ⇒ It is easier to find small planets around small stars. Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Image credits: NASA Winn 2010. Exoplanets edited by S. Seager What is the probability of a planet transiting its star? Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Winn 2010. Exoplanets edited by S. Seager What is the probability of a planet transiting its star? sphere i Celestial To observer Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Winn 2010. Exoplanets edited by S. Seager What is the probability of a planet transiting its star? sphere a i Celestial To observer Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Winn 2010. Exoplanets edited by S. Seager What is the probability of a planet transiting its star? sphere a i Celestial To observer For transits we need: acosi ≤ R* − Rp Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Winn 2010. Exoplanets edited by S. Seager What is the probability of a planet transiting its star? sphere a i Celestial To observer For transits we need: acosi ≤ R* − Rp " R* + Rp % R* + Rp R Prob$ cos i < The probability' = is ≈ * # a & a a € Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Winn 2010. Exoplanets edited by S. Seager What is the probability of a planet transiting its star? sphere a i Celestial To observer For transits we need: acosi ≤ R* − Rp " R* + Rp % R* + Rp R Prob$ cos i < The probability' = is ≈ * # a & a a 10% 0.5% 0.1% 0.05AU € 1AU 5AU Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Winn 2010. Exoplanets edited by S. Seager What is the probability of a planet transiting its star? sphere a i Celestial To observer For transits we need: acosi ≤ R* − Rp " R* + Rp % R* + Rp R Prob$ cos i < The probability' = is ≈ * # a & a a 10% 0.5% 0.1% 0.05AU € 1AU 5AU ⇒ Transit surveys must monitor thousands of stars at a time. They find planets in small orbits around large parent stars. Collier Cameron, A., 2016. Methods of Detecting Exoplanets Seager & Mallén-Ornelas 2003, ApJ 585, 1038 Winn 2010. Exoplanets edited by S. Seager >2920 transiting planets confirmed since 1999 2 HD209458 1 55 Cnc e CoRoT-7b 0.1 0.03 Kepler-37b 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 >2920 transiting planets confirmed since 1999 2 HD209458 1 “sub-Neptunes” 55 Cnc e CoRoT-7b 0.1 0.03 Kepler-37b 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 >2920 transiting planets confirmed since 1999 2 HD209458 1 “sub-Neptunes” 55 Cnc e “super-Earths” CoRoT-7b 0.1 0.03 Kepler-37b 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 Radius distribution of small planets Fulton et al. (2017) See also Zeng et al. (2017), Van Eylen et al. (2017), Schlichting (2018) Radius distribution of small planets Fulton et al. (2017) See also Zeng et al. (2017), Van Eylen et al. (2017), Schlichting (2018) Radius distribution of small planets Fulton et al. (2017) See also Zeng et al. (2017), Van Eylen et al. (2017), Schlichting (2018) Radius distribution of small planets Fulton et al. (2017) sub-Neptunes super-Earths See also Zeng et al. (2017), Van Eylen et al. (2017), Schlichting (2018) Radius distribution of small planets Fulton et al. (2017) evaporation “valley” Owen & Wu (2017) Jin & Mordasini (2017) sub-Neptunes super-Earths See also Zeng et al. (2017), Van Eylen et al. (2017), Schlichting (2018) Radius distribution of small planets Fulton et al. (2017) evaporation “valley” Owen & Wu (2017) evaporation Jin & Mordasini (2017) “desert” Sanchez-Ojeda et al. (2014) sub-Neptunes Lundkvist et al. (2016) Lopez (2016) super-Earths See also Zeng et al. (2017), Van Eylen et al. (2017), Schlichting (2018) From initial detection of a transit to confirmation or validation of a planet Pipeline identifies planet candidates (TCE) Robo vetting (KOI) Photometric Data processing pipeline monitoring From initial detection Human Statistical Confirmed of a transit vetting validation planet to confirmation or validation of a planet Follow-up observations 1: (astrophysical) Validated Follow-up observations 1I: Reconnaissance spectroscopy, false positive ground-based photometry, planet Radial-velocity monitoring for speckle interferometry, lucky independent confirmation imaging, AO imaging Pipeline identifies planet candidates (TCE) Robo vetting (KOI) Photometric Data processing pipeline monitoring From initial detection Human Statistical Confirmed of a transit vetting validation planet to confirmation or validation of a planet See Tim Morton and Andrew Vanderburg’s talks after lunch Follow-up observations 1: (astrophysical) Validated Follow-up observations 1I: Reconnaissance spectroscopy, false positive ground-based photometry, planet Radial-velocity monitoring for speckle interferometry, lucky independent confirmation imaging, AO imaging Pipeline identifies planet candidates (TCE) Robo vetting (KOI) Photometric Data processing pipeline monitoring From initial detection Human Statistical Confirmed of a transit vetting validation planet to confirmation or validation of a planet See Tim Morton and Andrew Vanderburg’s talks after lunch Follow-up observations 1: (astrophysical) Validated Follow-up observations 1I: Reconnaissance spectroscopy, false positive ground-based photometry, planet Radial-velocity monitoring for speckle interferometry, lucky independent confirmation imaging, AO imaging See tomorrow’s talks! Pipeline identifies planet candidates (TCE) Robo vetting (KOI) Photometric Data processing pipeline monitoring From initial detection Human Statistical Confirmed of a transit vetting validation planet to confirmation or validation of a planet See Tim Morton and Andrew Vanderburg’s talks after lunch Follow-up observations 1: (astrophysical) Validated Follow-up observations 1I: Reconnaissance spectroscopy, false positive ground-based photometry, planet Radial-velocity monitoring for speckle interferometry, lucky independent confirmation imaging, AO imaging See tomorrow’s talks! Detecting transits: the Box-fitting Least Squares technique (BLS) Kovács, Zucker & Mazeh (2002) See also Aigrain & Irwin (2004), Collier Cameron et al. (2006) and others Detecting transits: the Box-fitting Least Squares technique (BLS) Kovács, Zucker & Mazeh (2002) F₀, u1, u2 ,٭Rp/R ,٭parameters: P, t₀, ω, e, i, a/R 10 Flux Time See also Aigrain & Irwin (2004), Collier Cameron et al. (2006) and others Detecting transits: the Box-fitting Least Squares technique (BLS) Kovács, Zucker & Mazeh (2002) F₀, u1, u2 ,٭Rp/R ,٭parameters: P, t₀, ω, e, i, a/R 10 3 non-linear parameters: P, t₀, width and 2 linear parameters: F₀, depth Flux Time See also Aigrain & Irwin (2004), Collier Cameron et al. (2006) and others Detecting transits: the Box-fitting Least Squares technique (BLS) Kovács, Zucker & Mazeh (2002) F₀, u1, u2 ,٭Rp/R ,٭parameters: P, t₀, ω, e, i, a/R 10 3 non-linear parameters: P, t₀, width and 2 linear parameters: F₀, depth Flux Step through a Time grid of P, t₀, width.