3677 Life in the Universe: Extra-solar planets

1. 3677 Life in the Universe:Extra-solar planets Dr. Matt Burleigh www.star.le.ac.uk/mrb1/lectures.html

3. 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

4. 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

5. Course outline • Lecture 5 • The quest for an Earth-like planet • Results from the Kepler mission • Habitable zones • Biomarkers • Future telescopes and space missions

6. 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

7. Transits • Planets observed at inclinations near 90o will transit their host stars

8. Transits • Planets observed at inclinations near 90o will transit their host stars

9. 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: • Where Δf is the change in the star’s flux (brightness), Rp is the planet radius and R* the star’s radius

10. 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%

11. 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 • Rem. • Thus • (rem in magnitude system a smaller number means brighter)

12. 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

13. 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

14. 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!

15. The shape of the transit light curve • Ingress and egress affected by stellar limb darkening

16. Transits • For an edge-on orbit, transit duration is given by: • 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

17. Transits • Probability of transit (for random orbit) • 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)

18. Transits: Advantages • Easy. Can be done with small, cheap telescopes • Possible to detect low mass planets, including “Earths”, especially from space (Kepler mission)

19. 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 binarystar 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

20. 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

21. Super WASP • SuperWASP monitors about 1/4 of the sky from each site • That means millions of stars, every night!

22. www.ngtransits.org Belfast, DLR Berlin, Geneva, Leicester, Warwick, Cambridge

23. WASP planets in green

24. NGTS Prototype La Palma 2010

25. Early NGTS v SuperWASP

26. NGTS sensitivity (planet periods)

27. NGTS Site: ESO Paranal observatory, Chile VLT Astronomers’ hotel / baddies’ lair in “Quantum of Solace” VISTA Construction 2014 Operations 2014-2019 NGTS

29. 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

30. Transmission spectroscopy

31. 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

32. Secondary eclipses • Note that the secondary eclipse depth increases with wavelength • Bcse planets are cooler than stars, their emission is stronger at longer wavelengths

33. Madhusudhan … Wheatley ... Pollacco & West 2010, Nature Carbon rich atmosphere in WASP-12b Secondary eclipses

34. 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?

35. 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

36. Transit timing variations • The maximum TTV for an inner planet, due to influence of a more distant second planet, is given by: • 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 a1=0.05AU with a period of 4 days, and the outer planet has a mass half that of Jupiter (i.e. 0.5x10-3MSun) and a period of 100 days for an eccentric orbit with a2=0.42AU and e2=0.5? A: 3.6 seconds