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Circumstellar Disks: IRAS to ALMA (by way of HST) Dr. Karl Stapelfeldt JPL/Caltech Talk overview • History of space infrared astronomy • Disk energy distributions, spectra, and statistics • High resolution disk imaging • Disks and exoplanets • Future of Disk Studies 4/29/2016 Ay/Ge 198 Exoplanets 2 InfraRed Astronomical Satellite (IRAS) • First space infrared observatory • 0.5 cm cryogenic telescope • Operated in low Earth orbit for 10 months in 1983 • Primitive detectors limited spatial resolution to ~1 arcmin; mapping, not detailed imaging • All-sky survey at 12, 25, 60, and 100 m (corresponding to material at 270, 130, 60, and 30 K) 4/29/2016 Ay/Ge 198 Exoplanets 3 The Legacy of IRAS • Catalog of 500,000 sources seeded decades of high resolution imaging and spectroscopic work • High scientific impact: to date more than 6,400 refereed papers have “IRAS” in the abstract • At Caltech: IPAC and Morrisroe Astroscience building on S. Wilson Ave. • Major results included starburst and ultraluminous IR galaxies (URLIRGS), interstellar cirrus, zodiacal dust bands, asteroid sizes, protoplanetary and debris disks. • Major IRAS limitation was source confusion – often many objects blended together due to low spatial resolution 4/29/2016 Ay/Ge 198 Exoplanets 4 IRAS Revealed Stages of Disk Evolution IRAS was ideal for detecting the faint glow of cool circumstellar dust IRAS found dust around more than 50% of young stars in nearby molecular clouds (for stars > 1 Lsun) IRAS data allowed astronomers to classify young stellar objects according to IR spectral energy distribution Molecular gas discovered in Class 0, I, and II disks in the 1990s, confirming they could be hosting planet formation 4/29/2016 198 Exoplanets AndreAy/Ge et al. 1993 5 Extrasolar debris disks were discovered by IRAS measurement of stellar infrared excess: • Found around nearby main-sequence stars, mostly A type. The “Fabulous four” Vega, Fomalhaut, Eridani, and Pictoris • Optically thin, gas-poor particle disks but still 100- 10,000 times the dust of the Sun’s interplanetary dust cloud • Disk masses very small, < few lunar masses. NOT protoplanetary disks. • ~100 AU scales: Kuiper Belts • Re-emitting 10-6 to 10-3 of the stellar luminosity • The best evidence for extrasolar planetary systems prior to 1995 4/29/2016 Ay/Ge 198 Exoplanets 6 Smith & Terrile 1984 Debrisk disk dust must be constantly replenished, as small grains are readily lost 4/29/2016 Ay/Ge 198 Exoplanets 7 Disk Spectra and Statistics 4/29/2016 Ay/Ge 198 Exoplanets 8 Infrared Space Observatory (ISO) • European Space Agency Mission in low Earth orbit • 60 cm cryogenic telescope • Operated 1995-1998 • 2 spectrometers were very productive 4/29/2016 Ay/Ge 198 Exoplanets 9 ISO showed compositional link between comets & disks Tielens et al. 4/29/2016 Ay/Ge 198 Exoplanets 10 Spitzer Space Telescope • 85 cm beryllium telescope, 6.5 m diffraction limit • Operated cold 2003-2009, continues warm operation today • Two science cameras (IRAC and MIPS), plus a low/moderate resolution spectrograph (IRS); 3< < 180 m. Efficient mapping • Earth-trailing solar orbit • 10-1000x more sensitive than 1983 IRAS mission • Targeted observations, not a sky survey 4/29/2016 Ay/Ge 198 Exoplanets 11 Ophiuchus star-forming region (Padgett et al. 2008) Spitzer statistics of young disks disk formation typically complete after 0.9 Myrs; Evans et al. 2009 • Surveys of nearby star-forming regions find lifetimes of 0.5 Myrs for 4/29/2016 Ay/Ge 198 Exoplanets 13 Debris Disk Frequency from Spitzer Surveys (Trilling et al. 2008) 4/29/2016 Ay/Ge 198 Exoplanets 14 A star 24 m excesses vs. time: decay 1/t over ~200 Myr; but many stars of all ages have little or no excess. (Rieke et al. 2005) 4/29/2016 Ay/Ge 198 Exoplanets 15 Common warm dust temperatures (Morales et al. 2011) FGK stars A stars 4/29/2016 Ay/Ge 198 Exoplanets 16 Europe's Herschel Space Observatory • 3.5 meter primary mirror • Operated 2009-2013 • 70 m imaging resolution 4x sharper than Spitzer; resolving central holes & disk asymmetries • Sensitivity to lower levels of LIR/Lstar at 100 & 160 m • 600 nearby targets surveyed by DUNES and DEBRIS key programmes, plus ~200 others in small GO projects 4/29/2016 Ay/Ge 198 Exoplanets 17 • Herschel project to survey 200 nearby solar-type stars at 100 & 160 m • Excess detected in up to 20% of the targets, with examples seen down to a few times Kuiper Belt dust level • Many disks resolved in Herschel’s 6” beam 4/29/2016 Ay/Ge 198 Exoplanets Geoff, Karl, & Chas representing The DUNES Team 18 Resolved disks from Herschel DEBRIS survey (Booth et al. 2013) 4/29/2016 Ay/Ge 198 Exoplanets 19 Wide Field Infrared Survey Explorer • Mission similar to IRAS but with modern array detectors • Sensitivity ~100 times better and resolution 10x better than IRAS • 40 cm telescope, low Earth orbit • All-sky survey at 3.6, 4.5, 12, and 22 m • Launched late 2009, operated in all 4 bands to fall 2010. • Continues operation at two shortest wavelengths as NEOWISE 4/29/2016 Ay/Ge 198 Exoplanets 20 WISE all-sky survey finds field stars with warm debris disks ~400 Hipparcos main sequence stars within 120 pc show 22 um excess > 0.25 mag (Padgett et al. ) Warm excess sources are likely young – exoplanet imaging targets Below left: sky distribution of excess sources. Below right: 22 um excess frequency vs. spectral type 4/29/2016 Ay/Ge 198 Exoplanets 21 High Resolution Disk Imaging 4/29/2016 Ay/Ge 198 Exoplanets 22 Pictoris: A hard act to follow • 1984 coronagraphic detection in visible light of edge-on disk around a bright, nearby IRAS source • No other debris disks detected in scattered light for 15 years after IRAS • Beta Pic now recognized as exceptionally young (20 Myrs) and dusty • Imaging of other disks prevented by seeing-limited image quality: needed HST and adaptive optics to make progress in scattered light imaging 4/29/2016 Ay/Ge 198 Exoplanets Central 1600 AU of edge-on Pictoris disk; Kalas & Jewitt 1995 23 HST Imaging of Orion Silhouette Disks (Bally et al. 2000) 4/29/2016 Ay/Ge 198 Exoplanets 24 HST imaging of Edge-on protoplanetary disks 4/29/2016 Ay/Ge 198 Exoplanets 25 Bright debris disks now well-imaged using coronagraphy Left: HR 4976 A ring with GPI, Perrin et al. 2015 Right: HD 181327 ring, with HST, Schneider et al. 2014 Left: AU Mic edgeon disk with HST, Krist et al. 2005 Right: HD 32297 with HST, Schneider et al. 2014 4/29/2016 Ay/Ge 198 Exoplanets 26 HD 202628: G2 V star at 24 pc Broad ring with central clearing. Diameter of ~16 arcsec (400 AU). Mean surface brightness is V ~ 24 mag arcsec-2 : Faintest debris disk yet detected with HST. Clearly asymmetric: Inner edge is 139 AU from star in the NW, 161 AU in the SE. Star is offset from ring center by 0.8ˮ (20 AU) – Eccentric ring Krist et al. 2012 July 23, 2014 Sagan Summer School 2014 27 New Processing of Archival HST Debris Disk Images HD 181327 Soummer et al. 2014 Big improvements in NICMOS scattered light imagery 4/29/2016 Ay/Ge 198 Exoplanets 28 HST followup of WISE Disks New sample of bright debris disks; Padgett et al. 2015: 4/13 disks detected 1300 AU diameter Ld/L* = 2.5 *10-3 4/29/2016 Ay/Ge 198 Exoplanets 29 Adaptive optics disk images HD 115600 Currie et al. 2015 HD 106906 Kalas et al. 2015 4/29/2016 Ay/Ge 198 Exoplanets 30 Atacama Large Millimeter Array (ALMA) the penultimate disk observatory • 50 12-m antennas located at 16,000 ft plateau • Offers sensitive imaging and heterodyne spectroscopy • Operating over 0.3- 9 mm wavelength range • Most competitive observatory in the world today 4/29/2016 Ay/Ge 198 Exoplanets 31 Key ALMA disk imaging results I. Fomalhaut debris ring (Boley et al. 2012) • 870 m continuum image with 1 resolution • Shows narrower ring than in HST images: large particles trace parent bodies. Further evidence for shepherding planets • Unable to map at higher resolution due to low surface brightness 4/29/2016 Ay/Ge 198 Exoplanets 32 Key ALMA disk imaging results II. HL Tauri disk • 1 Myr old embedded young star. Long-known disk inclined 40° • 14 AU resolution image in submm continuum • Disk radius ~140 AU • Intricate structure of ring-like density contrasts • Regions of enhanced grain growth? • Gaps cleared in outer disk by planets ? 4/29/2016 Ay/Ge 198 Exoplanets 33 Key ALMA disk imaging results III. Asymmetric Transition disks (van der Marel et al. 2016) • Central holes seen both gas and dust distribution. Gas holes are smaller, suggesting planetesimal formation • Dust ring brightness is not uniform. Azimuthal peaks theorized to be dust traps where enhanced grain growth is taking place 4/29/2016 Ay/Ge 198 Exoplanets 34 Key ALMA disk imaging results IV. Highest resolution image of protoplanetary disk TW Hydrae (Andrews et al. 2016) • 8 Myr old face-on disk • Resolution of 30 mas surpasses Hubble • Radial gap structure reminiscent of HL Tauri • Central hole a few AU across: gap cleared by planets ? Prime ELT coronagraph target 4/29/2016 Ay/Ge 198 Exoplanets 35 Debris Disks and Exoplanets 4/29/2016 Ay/Ge 198 Exoplanets 36 Herschel results for Dust luminosity vs. presence of RV planets (Bryden et al. 2014) but see also Marshall et al. 2015 4/29/2016 Ay/Ge 198 Exoplanets 37 Systems known to have both planets and debris disks: In most cases they are well-separated Star Fomalhaut HR 8799 beta Pictoris HD 38529 Epsilon Eridani HD 216435 HD 202206 HD 50554 HD 10647 HD 19994 HD 128311 HD 82943 HD 52265 HD 38858 HD 142 HD 150706 HD 69830 70 Vir 61 Vir HD 178911 B Gl 581 HD 1461 HD 215152 HD 45184 4/29/2016 Planet orbital semi-major axes Outer Planet Eccentricity Disk inner radius Disk Resolved ? 115 15, 27, 43, 68 10 0.12, 3.70 3.4 2.56 0.83, 2.55 2.38 2.03 1.42 1.10, 1.76 0.75, 1.19 1.13 1.04 1 0.82 0.08, 0.19, 0.63 0.48 0.05, 0.22, 0.48 0.32 0.03, 0.04, 0.07, 0.22 0.11 0.09 0.06 0.11 ? ? ? 0.36 0.3-0.7 ? 0.07 0.27 0.42 0.1 0.3 0.25 0.22 0.29 0.27 0.37 0.38 0.07 0.4 0.35 0.12 0.38 0 0.38 0.3 133 AU 95 AU 30 AU > 103 AU 2 AU, 35 AU > 13 AU > 50 AU > 58 AU ~10 AU > 7 AU > 11 AU > 65 AU > 40 AU ~120 AU > 28 AU 110 AU 1.0 AU > 5 AU ~30 AU > 28 AU 4 AU > 49 AU > 25 AU > 70 AU HST, IR, submm IR HST, IR, submm Ay/Ge 198 Exoplanets IR, submm IR HST, IR, submm IR IR IR IR 38 Disks constrain planets • Presence of IR excess indicates small colliding small bodies in a planetary system • Imaged disk provides system inclination and localizes where planets may be seen • Sharpness of disk edge constrains planet mass, if planet is also imaged • Disks Azimuthal variations also trace planet mass [Right: cases of 1 Me and 5 Me planet gravitational effects on warm dust distribution, Stark et al. 2009] • Perturbed outer disks are only means to detect low-mass outer planets (evidenced again by proposed Planet IX in our system) Ay/Ge 198 Exoplanets 3 HD 69830 triple Neptune System Old K0 star, d= 13 pc Unusual population of small/warm dust particles; major recent collision ? (Beichman et al. (Lisse et al. 2007) 2005) Planets at 0.08, 0.19, 0.63 AU (Lovis et al. 2006) Detailed dust size/composition analysis & radiative balance places the dust belt at ~1 AU, exterior to planets. Parent bodies would be dynamically stable there. 4/29/2016 Ay/Ge 198 Exoplanets 40 Four planets orbiting HR 8799 Marois et al. 2008, 2010 A0 star at 40 pc distance Young system age ~60 Myrs Spectra of outer 3 below 4/29/2016 Ay/Ge 198 Exoplanets 41 The HR 8799 Debris Disk Infrared excess shows two blackbody-like components Simple blackbody grains would produce this if located in belts at 9 AU (T= 150 K) 95 AU (T= 45 K) Dynamically viable: This places the dust interior and exterior to the planets imaged at 15, 27, 43, 68 AU 4/29/2016 (Su et al. 2009) see also Chen et al. 2009, Reidemeister et al. 2009 Ay/Ge 198 Exoplanets 42 Disk/planet arrangement in the HR 8799 system Planet e wasfound in the gap between inner belt and planet d Suggestion that belt edges may be located at major resonances Planet orbits still being defined Marois et al. 2010 4/29/2016 Ay/Ge 198 Exoplanets 43 The state of disk science • Protoplanetary and debris disks appear to be common; consistent with Kepler results for planet frequency • Protoplanetary disks dissipate by 10 Myrs, and debris disk brightness decays quickly over a few hundred Myrs • Disk sizes are comparable to the Kuiper Belt, radii of ~100 AU. Central holes are apparent by ages of a few Myrs • Debris disks often have 2 planetesimal belts. Their structures include gaps, warps, and asymmetries indicative of planetary perturbations, but number of imaged systems showing this is still small • There at least as many known disks as stars hosting exoplanets 4/29/2016 Ay/Ge 198 Exoplanets 44 Future of Disk Studies • Comprehensive ALMA studies of disk structure, chemistry, and evolution • Resolve more examples of small disks with SPHERE, GPI, and future ELTs. Directly image protoplanets in disks and observe interactions • Assess exozodiacal dust as noise source for future direct imaging of habitable exoplanets • High contrast imaging on optical space telescopes will provide best sensitivity to tenuous debris disks and mature planets 4/29/2016 Ay/Ge 198 Exoplanets 45 Large Binocular Telescope Interferometer Twin 8.4m telescopes at Univ. of Arizona NASA-funded 10 µm nulling interferometer instrument Survey of habitable zone dust around nearby stars Expected sensitivity down to 10 “zodis” Results will drive design of future planet finders Progress slowed by telescope issues 4/29/2016 Ay/Ge 198 Exoplanets 46 Future large planetfinding telescope ? Planet imagers will get disk observations for free Community studies now beginning for two flagship mission concepts “HabEx” and “LUVOIR“. To be completed in 2019. 4/29/2016 Ay/Ge 198 Exoplanets 47 Circumstellardisks.org 4/29/2016 Ay/Ge 198 Exoplanets 48