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DEPARTMENT OF PHYSICS AND ASTRONOMY 3677 Life in the Universe: Extra-solar planets Dr. Matt Burleigh www.star.le.ac.uk/mrb1/lectures.html Course 3677 Life in Universe 2013/2014 Academic Year Course Given by Prof. Mark Sims and Dr. Matt Burleigh Topics: Life in Universe and Extra-Solar Planets Lecture Dates and Lecturer Actual Lecture Number 1 2 3 4 5 6 7 8 9 10 11 12 13 Lecture by Topic Locatio n Time Date Nominal Course Order 2013/14 M.R. Sims M. Burleigh M. Burleigh M. Burleigh M. Burleigh M.R. Sims M.R. Sims M.R. Sims M.R. Sims M.R. Sims M.R. Sims M. Burleigh Both Life in Universe Extra-Solar Planets Extra-Solar Planets Extra-Solar Planets Extra-Solar Planets Life In Universe Life In Universe Life In Universe Life In Universe Life In Universe Life In Universe Extra-Solar Planets Continuous Assessment Answers Revision Lectures Phys A KE LT2 Phys A Phys A KE LT2 Phys A Phys A KE LT2 Phys B KE LT2 Phys B KE LT2 Phys B 1300 1300 1300 0900 1300 1300 0900 1300 1100 1300 1100 1300 1100 5/11 8/11 12/11 13/11 15/11 19/11 20/11 22/11 27/11 29/11 4/12 6/12 11/12 1 8 9 10 11 2 3 4 5 6 7 12 13 R1 R2 M. Burleigh M.R. Sims Phys D Phys B 0900 0900 7/5/14 15/5/14 Please note course is not in nominal order due to availability of Lecturers Course has been extensively revised from previous years as Prof. Raine is no longer teaching part of the course, consequently exam format has changed to 4 questions two short (20 marks each), two long (30 marks each) all compulsory. Dr. Matt Burleigh 3677: Life in the Universe Course outline • Lecture 1 – – – – Definition of a planet A little history Pulsar planets Doppler “wobble” (radial velocity) technique • Lecture 2 – Transiting planets – Transit search projects – Detecting the atmospheres of transiting planets Dr. Matt Burleigh 3677: Life in the Universe Course outline • Lecture 3 – Microlensing – Direct Imaging – Planets around evolved stars • Lecture 4 – Statistics: mass and orbital distributions, incidence of solar systems, etc. – Hot Jupiters – Super-Earths – Planetary formation – The host stars Dr. Matt Burleigh 3677: Life in the Universe Course outline • Lecture 5 – The quest for an Earth-like planet – Results from the Kepler mission – Habitable zones – Biomarkers – Future telescopes and space missions Dr. Matt Burleigh 3677: Life in the Universe Useful numbers • • • • RSun = 6.995x108m Rjup = 6.9961x107m ~ 0.1RSun Rnep = 2.4622x107m ~ 4Rearth Rearth = 6.371x106m ~ 0.1Rjup ~ 0.01RSun • • • • MSun= 1.989x1030kg Mjup= 1.898x1027kg ~ 0.001MSun = 317.8Mearth Mnep= 1.02x1026kg ~ 5x10-5MSun ~ 0.05Mjup = 17.15Mearth Mearth= 5.97x1024kg = 3x10-6MSun = 3.14x10-3Mjup • 1AU = 1.496x1011m • 1 day = 86400s Dr. Matt Burleigh 3677: Life in the Universe Transits • Planets observed at inclinations near 90o will transit their host stars Dr. Matt Burleigh 3677: Life in the Universe Transits • Planets observed at inclinations near 90o will transit their host stars Dr. Matt Burleigh 3677: Life in the Universe Transits • Assuming – The whole planet passes in front of the star – And ignoring limb darkening as negligible • Then the depth of the eclipse is simply the ratio of the planetary and stellar disk areas: pR Df = f* pR 2 p 2 * æ Rp ö =ç ÷ è R* ø 2 • Where Δf is the change in the star’s flux (brightness), Rp is the planet radius and R* the star’s radius Dr. Matt Burleigh 3677: Life in the Universe Transits • RSun = 6.995x108m Rjup = 6.9961x107m Rearth = 6.371x106m (note: Rjup~ 0.1RSun & Rearth ~ 0.1Rjup ~ 0.01RSun) • Jupiter transit: depth = 0.01 = 1% • Earth transit: depth = 8.3x10-5 = 0.0083% (note: best photometry from ground ~0.1%) • 55 Cancri R* = 1.15RSun • Planet 55 Cancri e = 8.3Rearth • Transit depth = 0.004 = 0.4% Dr. Matt Burleigh 3677: Life in the Universe Transits • In practice: • We measure the change in magnitude Dm, and obtain the stellar radius from the spectral type – Hence by converting to flux we can measure the planet’s radius æ f ö – Rem. Dm = m - m = 2.5 log ç ÷ * transit – Thus * è ftransit ø æ f* ö 0.4Dm = 10 ç ÷ è ftransit ø • (rem in magnitude system a smaller number means brighter) Dr. Matt Burleigh 3677: Life in the Universe Discovery of first transiting planet: HD209458b • HD209458b was discovered originally via the radial velocity method – 3.5 day period • Astronomer Dave Charbonneau monitored it with a small telescope called STARE – Transit discovered in 1999 Dr. Matt Burleigh 3677: Life in the Universe Transits Example: first known transiting planet HD209458b – – – Dm = 0.017 mags So (f* / ftransit) = 1.0158, i.e. Df=1.58% From the spectral type (G0) R=1.15Rsun So using Df / f* = (Rp / R*)2 and setting f*=100% – Find Rp=0.145Rsun – Since Rsun=9.73RJ then – Rp = 1.41RJ Dr. Matt Burleigh 3677: Life in the Universe Transits • HD209458b more: – From Doppler wobble method know M sin i = 0.62MJ – Transiting, hence assume i=90o, so M=0.62MJ – Density = 0.29 g/cm3 • c.f. Saturn 0.69 g/cm3 – HD209458b is a gas giant! Dr. Matt Burleigh 3677: Life in the Universe The shape of the transit light curve • Ingress and egress affected by stellar limb darkening Dr. Matt Burleigh 3677: Life in the Universe Transits • For an edge-on orbit, transit duration is given by: æ PR* ö Dt= ç ÷ è πa ø • Where P=period, a=semi-major axis of orbit • Example: HD209458b –P=3.52475 days = 304538s –R*=1.15RSun = 1.15x6.955x108m –a=0.04747AU=7.1x109m –Δt=10920s=3.03hours –Note for Earth (a=1AU) Δt=46668s=12.96hours Dr. Matt Burleigh 3677: Life in the Universe Transits • Probability of transit (for random orbit) Ptransit R* = a – For Earth (a=1AU), Ptransit=0.5% – But for close, “hot” Jupiters, Ptransit=10% – Of course, relative probability of detecting Earths is lower since would have to observe continuously for up to 1 year • (See Kepler mission) Dr. Matt Burleigh 3677: Life in the Universe Transits: Advantages • Easy. Can be done with small, cheap telescopes • Possible to detect low mass planets, including “Earths”, especially from space (Kepler mission) Dr. Matt Burleigh 3677: Life in the Universe Transits: Disadvantages • Probability of seeing a transit is low • Need to observe many stars simultaneously for long periods of time • Mimics – Easy to confuse with starspots – Easy to confuse with grazing binary star eclipse – Blended eclipsing binary in a triple system, or merely in background • Low mass red dwarfs, brown dwarfs and gas giants have same radii – Needs radial velocity measurements for confirmation, masses Dr. Matt Burleigh 3677: Life in the Universe Super WASP • Wide Angle Search for Planets (by transit method) • First “telescope” located in La Palma, second in South Africa • “Telescopes” are 8 x 400mm camera lenses with a high grade CCD • Operations started May ‘04 • Data stored and processed at Leicester • ~100 new planets detected! • www.superwasp.org Dr. Matt Burleigh 3677: Life in the Universe Super WASP • SuperWASP monitors about 1/4 of the sky from each site • That means millions of stars, every night! Dr. Matt Burleigh 3677: Life in the Universe www.ngtransits.org Belfast, DLR Berlin, Geneva, Leicester, Warwick, Cambridge Dr. Matt Burleigh 3677: Life in the Universe WASP planets in green Dr. Matt Burleigh 3677: Life in the Universe NGTS Prototype La Palma 2010 Dr. Matt Burleigh 3677: Life in the Universe Early NGTS v SuperWASP Dr. Matt Burleigh 3677: Life in the Universe NGTS sensitivity (planet periods) Dr. Matt Burleigh 3677: Life in the Universe NGTS Site: ESO Paranal observatory, Chile VLT Astronomers’ hotel / baddies’ lair in “Quantum of Solace” VISTA Construction 2014 Operations 2014-2019 NGTS Dr. Matt Burleigh 3677: Life in the Universe Dr. Matt Burleigh 3677: Life in the Universe Transmission spectroscopy • • • • • Transiting planets allow us to make measurements of the chemical composition and physical properties of their atmospheres Previously we assumed the planet was an opaque disk with a sharp edge In reality, it has an atmosphere & the opacity diminishes with height By observing a transit at a specific wavelength (eg Na, H) can measure the extra absorption from that element in the planet’s atmosphere Very challenging observations: HST, Spitzer, 8m telescopes Dr. Matt Burleigh 3677: Life in the Universe Transmission spectroscopy Dr. Matt Burleigh 3677: Life in the Universe Secondary eclipses • In secondary eclipse the planet passes behind the star • The drop in combined light is tiny, but measurable with careful observations • Gives thermal emission and temperature of “day” side of planet Dr. Matt Burleigh 3677: Life in the Universe Secondary eclipses • Note that the secondary eclipse depth increases with wavelength – Bcse planets are cooler than stars, their emission is stronger at longer wavelengths Dr. Matt Burleigh 3677: Life in the Universe Carbon rich atmosphere in WASP-12b Secondary eclipses Dr. Matt Burleigh 3677: Life in the Universe Madhusudhan … Wheatley ... Pollacco & West 2010, Nature Phase curve & map of HD189733b • Equisite observations of the transiting planet HD189733b at 8 microns with Spitzer reveal the changing brightness of the planet as it rotates • The hottest point on the “day” side is offset slightly from the expected position – Extreme weather? Dr. Matt Burleigh 3677: Life in the Universe Transit timing variations • The transits of a planet in a Keplarian orbit around its host star are exactly periodic. • However, if a third body is present in the system, the orbits are not Keplarian, and the time between consecutive transits varies • This offers the possibility of detecting non-transiting planets via photometry. • It is even possible to determine the maximum mass of the planets Dr. Matt Burleigh 3677: Life in the Universe Transit timing variations • The maximum TTV for an inner planet, due to influence of a more distant second planet, is given by: æ M 2 ö æ a1 ö Dt1 » ç ÷ e2 ç ÷ P2 è M * ø è a2 ø 3 • • where M2 and P2 are the mass and period of the second planet, M* the mass of the star, a1 and a2 are the semi-major axis of the planets’ orbits, and e2 is the eccentricity of the 2nd planet’s orbit. Note that there is no TTV in this instance if the second planet’s orbit is perfectly circular! – Q: What is the maximum TTV in the orbit of the inner planet in a system around a solar type star, where an inner, Jovian mass planet orbits at a 1=0.05AU with a period of 4 days, and the outer planet has a mass half that of Jupiter (i.e. 0.5x10 3M Sun) and a period of 100 days for an eccentric orbit with a 2=0.42AU and e2=0.5? A: 3.6 seconds Dr. Matt Burleigh 3677: Life in the Universe