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Lecture program 1. Space Astrometry 1/3: History, rationale, and Hipparcos 2. Space Astrometry 2/3: Hipparcos scientific results 3. Space Astrometry 3/3: Gaia 4. Exoplanets: prospects for Gaia 5. Some aspects of optical photon detection Michael Perryman Friday, 15 November 13 1 Astrometry in the context of exoplanet detection/characterisation Star accretion (?) Exoplanet Detection November 2013 1030 exoplanets (784 systems, 170 multiple) Colliding planetesimals (1?) Miscellaneous Methods [numbers from exoplanet.eu] Radio emission Dynamical Microlensing Photometry Astrometry Astrometry Timing X-ray emission (1) Protoplanetary/ debris disks Imaging Rad velocity sub dwarfs decreasing planet mass 10MJ MJ optical 1 free-floating space 10M 5 M Friday, 15 November 13 photometric 15 planets (12 systems, 2 multiple) ground 24 projected (10–20 yr) 2 planets (2 systems, 0 multiple) 24 planets (22 systems, 2 multiple) n = planets known ground ground (adaptive optics) bound space 535 535 planets (403 systems, 93 multiple) space 39 1 reflected light Doppler variability 2 millisec existing capability radio astrometric 8 Discovered: Transits eclipsing binaries white dwarfs pulsars slow TTVs space (coronagraphy/ interferometry) 39 planets (36 systems, 1 multiple) discoveries 173 244 timing residuals (see TTVs) 417 planets (318 systems, 68 multiple) follow-up detections 2 Photometry Friday, 15 November 13 3 Hipparcos: a posteriori transit detection HD 209458 P=3.524739(14) days (Robichon & Arenou 2000; Söderhjelm et al 2000) 89 discrete observations around 1990, with 5 at transit epochs (P=3.5d and Δt = 0.1 d 3% transit probability) –4 Normalised residuals Hipparcos magnitude Hp 7.70 7.74 7.78 7.82 7800 8000 8200 8400 8600 8800 9000 Observation date (JD – 2440000) Normalised residuals –4 –2 0 2 4 –0.5 –0.4 –0.3 –0.2 –0.1 0.0 Phase Friday, 15 November 13 0.1 0.2 0.3 0.4 0.5 –2 0 HD 189733 also: P = 2.218574(8) days (Bouchy et al 2005; Hébrard & Lecavelier des Etangs 2006) 2 4 –0.5 –0.4 –0.3 –0.2 –0.1 0.0 0.1 0.2 Other studies set the scene for Gaia: Phase • Castellano et al 2000, 2001 • Laughlin 2000 • Koen & Lombard 2002 • Hoeg 2002 • Jenkins et al 2002 • Robichon 2002 • Hebrard et al 2006 • Gould & Morgan 2003 • Hatzes et al 2003, 2006 • Beatty & Gaudi 2008 0.3 0.4 0.5 4 Number of field of view transits Friday, 15 November 13 5 Gaia: estimates for (very) hot Jupiters (Dzigan & Zucker 2012) advantages: 1 mmag photometric accuracy disadvantages: n(measures), low cadence Simulations account for planet frequency, detection probability, stellar density, false detections, etc assumes 2-hr transit duration Conclusion: few hundred to a few thousand discoveries (with the need for high-precision RV follow-up) Friday, 15 November 13 6 Photometry: planetary accretion events? FH Leo (Dall et al. 2005): • • • • • suggestion: a planetary accretion event rapid magnitude rise suggests asteroid mass such as Pallas or Vesta decay over ~ 17 days abundances of α-elements and Li but may be a nova (Vogt 2006) 8.2 mag 8.3 8.4 8.5 8.6 BJD - 2440000 Friday, 15 November 13 7 Distances and space motions Friday, 15 November 13 8 Distances and motions Examples: • distances provide stellar parameters • e.g. transit planet diameters ∝ stellar diameters • verification of seismology models for M, R • proper motions characterise population(s) e.g. HIP 13044 low-metallicity Galactic halo stream (Helmi+1999, Setiawan+2010) • Galactic birthplace based on metallicity-age e.g. Wielen (1996) inferred that the Sun’s birthplace was at R=6.6 kpc Friday, 15 November 13 9 Asteroseismology Can hope to discriminate: • primordial or self-enriched metallicity (bulk/surface): μ Ara (Pepe 2007), ι Hor (Laymand 2007) • planet radii calibrated wrt stellar radii: HAT-P-7 (Christensen-Dalsgaard+ 2010) • mass estimates cf isochrone models: β Gem, HD13189 (Hatzes+ 2008) • etc For this, verification of the models by comparing parallax-based L with asteroseismology Asteroseismology of η Boo, Z=0.04. Left: M=1.70±0.005 M⊙ Right: with overshooting (Di Mauro et al 2003) Friday, 15 November 13 10 Galactic birthplace (cont.) 0.4 Sun 0.2 0 Ri (kpc) [Fe/H] –0.2 4.5 –0.4 6.5 –0.6 8.5 10.5 –0.8 12.5 –1.0 0 2 4 6 8 10 12 14 16 Age (Gyr) Friday, 15 November 13 11 Hipparcos distances to exoplanet host stars 100 brightest radial velocity host stars (end 2010) (versus RA, independent of dec) (a) (b) 50 pc ground-based: van Altena et al (1995) (unknown assigned π = 10±9 mas) Friday, 15 November 13 100 pc 50 pc 100 pc Hipparcos parallaxes (Perryman et al 1997) 12 Gaia distances to exoplanet host stars Transit host stars (~280, October 2013) Friday, 15 November 13 13 New astrometric detections Friday, 15 November 13 14 Discovery from ‘astrometric signature’ and provides M directly (not simply M sin i) Declination (mas) Unseen planets perturb the photocentre, which moves with respect to the barycentre (as for Doppler measures) 150 Parameters (x50): d = 50 pc μ = 50 mas/yr, over three years; orbited by a planet with Mp = 15 MJ, e = 0.2, a = 0.6 AU 100 2012.8 2011.6 50 2010.4 0 0 50 100 Right ascension (mas) Friday, 15 November 13 15 ∆δ (milli-arcsec) Astrometric analysis: principles 50 • as the satellite traces out a series of great circles on the sky, each star is (effectively) instantaneously stationary 0 • each star has a 2d position (abscissa and ordinate) projected onto that great circle • in principle one should solve for both coordinates –50 • in practice, only the projection along the great circle (abscissa) dominates the ‘greatcircle solution’ –100 • least-squares adjustment gives the alongscan position of each star at that epoch • all great circles over the entire mission are then ‘assembled’ –150 –200 –150 –100 –50 0 50 • a star’s position at any time t is represented by just five parameters: position (xy), proper motion components (μx, μy), parallax (π) ∆α cos δ (milli-arcsec) Friday, 15 November 13 16 Direct access to planet mass descending node orbiting body z r pericentre ν(t) ω ellipse focus ≡ centre of mass ϒ= reference direction i Ω= longitude of ascending node orbit plane apocentre reference plane ascending node ⇓ Keplerian orbit in 3d determined by 7 parameters: a, e: specify size and shape P: related to a and masses (Kepler’s 3rd law) tp: the position along orbit at some reference time i, Ω,ω: represent projections wrt observer to observer Radial velocity measures: • cannot determine Ω, • only determine the combination a sin i • only determine Mp sin i if M* can be estimated • cannot determine Δi for multiple planets All 7 parameters are determinable by astrometry (±180º on Ω). Conceptually: • xy(t) yields max and min angular rates, and hence the line of apsides (major axis) • then appeal to Kepler’s third law fixes the orbit inclination Friday, 15 November 13 17 The ‘tragic history’ of astrometric planet detection • Jacob (1855) 70 Oph: orbital anomalies made it ‘highly probable’ that there was a ‘planetary body’; supported by See (1895); orbit shown as unstable (Moulton 1899) • Holmberg (1938): from parallax residuals... `Proxima Centauri probably has a companion’ of a few Jupiter masses • • • • • • Reuyl & Holmberg (1943) 70 Oph: planetary companion of ~10 MJ • early discussions of space astrometry/Hipparcos exoplanet capabilities: Strand (1943) 61 Cyg: companion of ~16 MJ lengthy disputes about planets around Barnard’s star: van der Kamp (1963, 1982) similarly for Lalande 21185 (e.g. Lippincott 1960) Pravdo & Shaklan (2009) vB10 with Palomar-STEPS, later disproved (Bean 2010) Muterspaugh+ (2010) HD~176051, only current detection: ‘may represent either the first such companion detected, or the latest in the tragic history of this challenging approach.’ • Friday, 15 November 13 Couteau & Pecker (1964), Gliese (1982) 18 Astrometric signature Hipparcos astrometry is marginal for detection (and mass determination) Friday, 15 November 13 19 Gaia: number of astrometric detections • • Gaia was studied since 1997; accepted in 2000; launch: 20 December 2013 • more recent estimates (Castertano+ 2008): • early estimates of 10−30,000 detectable exoplanets were based on target accuracies at time of acceptance (Lattanzi et al 2000, Perryman et al 2001, Quist 2001, Sozzetti et al 2001), and are no longer applicable • • • • • single measurement error for bright stars σψ ~ 8 μas reliable detections for P<5 years and α > 3σψ at 2x this limit, errors on orbits and masses are ~ 15−20% > 70% of 2-planet systems with 0.2 < P < 9 yr and e < 0.6 are identified typical uncertainties on Δi for favourable systems are <10o bottom line: • • Friday, 15 November 13 discover/measure several thousand giant planets with a =3−4 AU and d < 200pc characterise hundreds of multiple systems with meaningful tests of coplanarity 20 For multiple planet systems... Drawing on extensive radial velocity work, multiple systems can be fit by (e.g.) recursive decomposition Non-linearity of the fitting for Gaia/SIM: considered by Casertano et al (2008), Wright & Howard (2009), Traub et al (2010) 5-planet system 55 Cnc (Fischer et al 2008) Friday, 15 November 13 Periodograms wrt: (i) 2-planet model (ii) 3-planet model (iii) 4-planet model Periodicity of the fifth planet in the Keck data 21 Astrometric motion for multiple planets... (assuming orbits are co-planar) 4 planets, 60 yr (a) Sun 2020 4 planets, 3 (b) µ Ara The sun’s motion guides us: • Newton: ‘since that centre of gravity 2010 1990 is continually at rest, the Sun, according to the various positions of the planets, must continuously move every way, but will never recede far from that centre’ (Cajori 1934) 1970 2030 • barycentre frequently extends 1980 2000 beyond the solar disk • periods when the Sun’s motion is ‘retrograde’ with respect to the barycentre (~1990, 1811,1632) –0.008 –0.004 0 0.004 Displacement (AU) Friday, 15 November 13 0.008 –0.01 0 0.01 Displacement (AU) 22 Motion of host star around barycentre for multiple exoplanets (assuming coplanarity) 2 yr HD 69830 –4e–05 3 planets, 2 yr 0 Displacement (AU) Friday, 15 November 13 4e–05 HD 155358 –0.001 2 planets, 10 yr 0 0.001 Displacement (AU) 23 Motion for multiple planets (cont.) HIP 14810 –0.001 3 planets, 2 yr 0 0.001 Displacement (AU) Friday, 15 November 13 0.002 HD 40307 –4e–06 3 planets, 2 yr 0 4e–06 HD 69 –4e Displacement (AU) 24 Astronomia Nova (1609) includes Kepler’s hand drawing of the orbit of Mars viewed from Earth ...designated as ‘mandala’ (Sanskrit for circle) by Wolfram (2010) Friday, 15 November 13 25 Exoplanets and the solar dynamo Friday, 15 November 13 26 Now for something contentious... • solar axial rotation is invoked in models of the solar cycle (e.g. turbulent dynamo operating in or below the convection envelope) • precise nature of the dynamo, and details of associated solar activity (sun spot cycles, and the prolonged Maunder-type solar minima) are unexplained • empirical investigations have long pointed to a link between the Sun’s barycentric motion and various solar variability indices (e.g. Wolf, 1859; Brown, 1900; Schuster, 1911; Jose, 1965; Ferris, 1969), specifically: • • • • • • • • • • Friday, 15 November 13 the Wolf sun spot number counts (Wood & Wood, 1965) climatic changes (Mörth & Schlamminger, 1979; Scafetta, 2010) the 80-90-yr secular Gleissberg cycles (Landscheidt, 1981, 1999) prolonged Maunder-type minima (Fairbridge & Shirley, 1987; Charvátová, 1990, 2000) short-term variations in solar luminosity (Sperber et al., 1990) sun spot extrema (Landscheidt, 1999) the 2400-yr cycle seen in 14C tree-ring proxies (Charvátová, 2000) hemispheric sun spot asymmetry (Juckett, 2000) torsional oscillations in long-term sun spot clustering (Juckett, 2003) violations of the Gnevishev–Ohl sun spot rule (Javaraiah, 2005) 27 Just one example... Abreu et al (2012), A&A 548, 88 (ETH Zürich) Gleissberg Amplitude 120 88 de Vries 104 150 solar modulation potential over 9400 yr from 10Be and 14C 208 506 80 solar activity 40 Amplitude 0 torque modulus 0.015 0.01 0.005 0 50 100 150 200 250 300 350 Period (years) 400 450 500 550 600 Proposed coupling mechanisms between the solar axial rotation and orbital revolution: • Zaqarashvili (1997), Juckett (2000), contested by Shirley (2006) • Abreu (2012): time-dependent torque exerted by the planets on a non-spherical tachocline • Callebaut & de Jager (2012): effect considered as negligible Friday, 15 November 13 28 Exoplanets can arbitrate (Perryman & Schulze-Hartung 2011) • behaviour cited as correlated with the Sun’s activity includes • • changes in orbital angular momentum, dL/dt intervals of negative orbital angular momentum • • these are common (but more extreme) in exoplanet systems • activity monitoring should therefore offer an independent test of the hypothetical link between: HD 168443 and HD 74156 have dL/dt exceeding that of the Sun by more than 105 • • Friday, 15 November 13 the Sun’s barycentric motion and the many manifestations of solar activity 29 HD 168433 Lz (Msun AU2 d-1) dLz/dt (Msun AU2 d-2) • • • Friday, 15 November 13 two massive planets (8−18MJ) at 0.3−3 AU, e1~0.5 most extreme negative Lz and largest dL/dt periodicity of ~58 days 30 Coplanarity of orbits and transit geometry Friday, 15 November 13 31 Exoplanet detection with HST−FGS quite a long history, starting with Benedict et al (1993) [HST−FGS yields relative parallaxes based on assumed luminosities of reference stars] 4 ν And d 1.0 ν And c 0.5 ν And b 0.0 0 8 16 24 Inclination (˚) 32 40 (b) 2 2 0 (c) 2004 1 –2 y (mas) 1.5 X residuals (mas) (a) Y residuals (mas) Astrometric signature, α (mas) 2.0 4 2 0 2002 2005 2003 2006 –1 0 ν And –2 –2 400 800 1200 1600 JD – 2 452 000 (d) • radial velocity observations determine only Mp sin i • astrometric measurements determine Mp directly • and hence relative inclinations (van der Kamp 1981): –2 –1 0 1 2 x (mas) For ν And, McArthur et al (2010) found: • Mp (ν And c) = 14.0 MJ • Mp (ν And d) = 10.2 MJ • Δi = 29.9°±1° the first direct determination of relative orbit inclinations Friday, 15 November 13 32 Importance of Δi • Δi ~ 0 in the solar system • various evidence that this is not necessarily the rule in exoplanets: (2) Rossiter-McLaughlin effect used to measure the (sky projection) of the orbital and stellar rotation axes indicates that many orbits are misaligned wrt stellar equator (some retrograde) Rad velocity (m s−1) (1) long-term dynamical stability (via numerical integrations) b = – 0.5, λ = 0˚ some cannot be coplanar b = – 0.5, λ = 30˚ b = – 0.5, λ = 60˚ + 60 0 – 60 –2 –1 0 Time (h) 1 2 –2 –1 0 Time (h) 1 2 –2 –1 0 1 2 Time (h) (3) models of formation and evolution admit the possibilities of: (a) asymmetric protoplanetary infall; (b) gravitational scattering during the giant impact stage of protoplanetary collisions; (c) Kozai resonance/migration in which Lz is conserved, and hence i and e can be ‘traded’ (explains high e in triple systems, and hot Jupiters when combined with tidal friction) Friday, 15 November 13 33 Baluev 2008 optimal strategies of radial velocity observations in search surveys 20 J12 15 (inefficient) preceding observations observation particularly efficient HD 208487 observations not possible 10 5 0 2005 2006 2007 2008 Year example: • how to decide between two orbit solutions from 35 measurements (Butler 2006) • Wright (2007) identified a second planet at P=28.6d or 900d • J12 estimates the maximum information from the two predictions • maxima give the most promising times for new observations • here: • predictions differed by 20m/s • actual observations during 2005 were all at epochs of low information content • one observation in 2005 would have resolved the degeneracy, those in 2006 could not Friday, 15 November 13 34 Transit geometry HD 189733 • R* = 370 normally, there is no information on the position angle of a transiting planet’s orbit plane 181 95 120 • valuable for higher-order light curve effects? provided by Gaia if the astrometric signature of the transiting planet is high E1S1 Visibility • provided (in principle) by 2d interferometry: due to asymmetry in the source brightness introduced by the planet Closure phase (˚) • Rp = 64 W1E1 S1W1 0.008 0.000 –0.008 0.2 0.1 0.0 –0.1 –0.2 0.04 0.08 Time (d) 0.12 0.04 0.08 0.12 Time (d) (CHARA) V = 7.7, K1, d = 19pc Friday, 15 November 13 35 Summary • • • • accurate distances: calibration of host star parameters, including R for transiting calibration of asteroseismology models accurate proper motions: Galactic dynamics and population multi-epoch high-accuracy photometry: new transiting systems (several hundred?) calibration of photometric jitter vs spectral type multi-epoch astrometry: discovery of new (massive, long-period) planets (3000?) co-planarity of systems: evolutionary models position angle of planet transits (some multiple?) • • • • • • • Friday, 15 November 13 36 End Friday, 15 November 13 37