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Home , Star formation

Master course: Formation and Origin of Planetary Systems

Ewine F. van Dishoeck and Melissa McClure Leiden Observatory Spring 2020

Lecture 1: Introduction and overview

www.strw.leidenuniv.nl/~vgelder/SPF/ 1.1 Motivation

. Formation of and planetary systems is one of the most fundamental topics in but little material covered in bachelor curriculum . Many recent developments, both observationally and theoretically, including rapidly growing field of . ‘Star formation spans densities from 104 cm-3 to 1024 cm-3, involves all the known forces of , with observational diagnostics across the entire spectrum, and requires experimental access to relevant primitive materials that has no parallel in any other branch of astrophysics’ Shu et al. 1993 1.2 Outline course . Discuss systematically the various stages in the formation of (low-mass) stars, from collapse of interstellar cloud to formation of planetary systems (see schedule) . Level: advanced course . Basic concepts will be briefly recapitulated as needed (e.g., interstellar clouds, line + continuum radiation, ….) . Expect self-study (e.g., generally no step-by-step derivations done in lectures) . Focus is on broad picture, not on doing problem sets . One aim: follow and put in context colloquia in this field . You have to tell us what you learned! From clouds to disks to and back

Bill Saxton AUI/NRAO Organization . Lectures . Tuesday and Thursday Huygens 414 . Three afternoons for ‘werkcollege/problem sets’ . Tentamen . Oral exam on appointment . Short presentation to group as part of exam possible . If presentation on topic from first half of course, then exam on second part and vice versa . Required background . Radiation processes (Planck function, Einstein coeff.) . Statistical physics (Boltzmann, Maxwell distribution) . Quantum physics (H atom) . Assistants: Pooneh Nazari, Mantas Zilinskas, Martijn van Gelder Literature

. Exam based on content of lecture notes . Background reading useful for better understanding . Review chapters listed at start of each chapter and linked to course website where available; references to specialized literature provided Useful reference books . Origin of stars and planetary systems (Crete II), ed. C.J. Lada & N.D. Kylafis (Kluwer) (1999) . & Planets series (Univ. Arizona) . PPVI: eds. H. Beuther et al. 2014 . PPV: eds. B. Reipurth et al. 2007 . processes in star formation, L. Hartmann (Cambridge) (2008) . Formation of stars, S. Stahler & F. Palla (Wiley) (2004) . Astrophysics of formation, P. Armitage (Cambridge) (2010) . See list on website for other books 1.3 Scenario for low-mass star formation

Shu et al. 1987, 1993 The big picture: low-mass stars Shu et al. 1987 . Cores form within molecular clouds; gas and dust contract under their own gravitation and evolve toward centrally concentrated configuration such as a singular isothermal sphere (with 1/r2 density law)

. Cloud core collapses from inside-out; with surrounding disk forms at center; infalling envelope of gas and dust continues to rain down on growing star + disk, resulting in hundreds of magnitudes of

Figures: M. Hogerheijde Dense starless core B68

ESO-VLT Alves et al. 2001 Stars form in molecular clouds

Carina NASA/HST

- Need long wavelengths to peer into dark clouds - Clouds form stars with efficiency of only a few%: why? The big picture (cont’d)

. Stellar or disk wind breaks out along rotational axis of system, reversing infall and sweeping material into two outwardly expanding shells of gas and dust (‘jets, ’); infall still occurs in equatorial regions

. Outflow angle opens up with time, terminating infall and revealing a newly formed star optically with a circumstellar disk (‘T Tauri phase’) Long wavelengths

3.5, 4.6, 8 µm Spitzer Space Telescope

NASA/Spitzer Noriega-Crespo et al, 2004

- IR/Mm measures broadband thermal radiation from cold (10-50 K) and warm (50-300 K) dust particles and narrowband lines from molecules HH 30 disk + jet Optical image HST

Jet Green: [O III] White: broadband

Scattered stellar light

Edge-on Disk

Credit: C. Burrows/HST Characterizing stages of star formation with SED outflow

n~104-105 cm-3 T~10 K

infall Factor 1000 smaller Cloud collapse t=0 Protostar with disk t=105 yr Credit: M. McCaughrean

Class I Spitzer 70 µm

Spitzer 2MASS

6 7 Formation planets t=10 -10 yr t>108 yr

Spectral energy distributon Characterizing stages star- and planet formation outflow

6 7 Formation planets t=10 -10 yr Solar system t>108 yr

Cloud collapse t=0 Protostar with disk t=105 yr Disk

Class II Star Class III

6 7 Formation planets t=10 -10 yr Solar system t>108 yr

Note shiftSpitzer from probes long dust(far -atIR) temperatures to short (near between-IR) wavelengths 100 and 1500 with K. evolution Low-mass:

3,.8, 24 µm

Red: IR excess young stars Blue: mature stars The big picture (cont’d)

. Planets form in circumstellar disks; disks are dispersed by winds, UV radiation, planet formation, and/or gravitational interactions with nearby stars

. Mature and stable emerges Solar system view: Protosolar nebula

Lunine 1990, and in PPIII First images of exoplanets

Triple system Chauvin et al. 2005 Marois et al. 2008 ESO VLT Gemini statistics

More than 4000 exoplanets discovered to date (, Transit, Kepler!), some planetary systems (e.g., Trappist 1)

Exoplanet.org, exoplanet.eu What sets diversity in exoplanets?

Credit: Martin Vargic

Super , Mini , Giant Planets, ... Low vs. high-mass star formation . Above scenario holds for formation low mass stars (<2 MSun), or ‘loosely aggregated’ systems ⇒ occurs independently for individual small cores to form single stars or small multiples (binaries-quadruples) . High-mass star formation usually occurs in a ‘closely packed’ form, in which a large piece of a giant collapses to create a tight group of stars more or less simultaneously . Difference probably connected with initial mass of cloud, and strength of and level of turbulence, which help to support cloud . Even for low-mass stars, alternative scenarios of turbulent core formation and fragmentation of filaments to form cores exist (see Lectures 2 and 3) . -wide star formation relations (‘laws’) gaining increasing attention but not discussed here High-mass:

HST image Typical sizes

Linear Size size Angular Taurus 140 pc Orion 450 pc 5 AU 0.04’’ 0.01” Inner disk 100 AU 0.7’’ 0.2” Outer disk 1000 AU 7” 2” Protostar envelope 10000 AU=0.05 pc 74” 23” Cloud core

Note: debris disks found around nearby stars, ~10 pc => much bigger on the sky Typical spatial resolution mid/far IR/submm: 3-20”; only now ALMA → <0.1”

1.4 Some key historical developments (more details in individual chapters)

. 17th cent: Many speculations about planets around other stars and possibility of elsewhere . E.g. Huygens: Kosmotheoros 1698 . Dates back to Greeks, e.g. Ptolemy . ~1750: Swedenborg, Kant, Laplace postulate that solar system formed from ‘urnebel’ (‘solar nebula’) . 18th-20th cent: Observations of nebulae, dark clouds . E.g. W. Herschel: Orion 1789 . E. Barnard: catalogue of dark clouds 1919 . 1904-1930: Discovery of interstellar gas and dust . W. Hartmann: gas 1904 . Trumpler: dust 1930 Despite these observations/speculations, the prevailing view at the turn of the 20th century was that stars live forever and that origin of stars is part of cosmology History (cont’d)

. 1950’s: Theory of ⇒ stars do not live forever, i.p. massive OB stars must have been formed recently . Schwarzschild, Hoyle, … . 1947: OB stars are members of stellar groupings (‘OB associations’). Space density too low to prevent disruption by Galactic tidal forces ⇒ must be young ⇒ star formation still ongoing . Ambartsumian 1947-1949; Blaauw 1946 History (cont’d)

. 1960’s-1970’s: Mapping of interstellar clouds in H I (1960’s) and CO (1970’s)⇒ clouds contain much more mass than needed to form a single star or group of stars: abundant material available to form stars (e.g., Giant Molecular Clouds: up to 6 10 MSun) . 1960s-1970s: OB stars are near interstellar clouds with systematic (?) age variations ⇒ sequential/triggered star formation . Blaauw 1964, Elmegreen & Lada 1976 Sequential/triggered star formation

C. Lada 1999 Crete II History (cont’d)

. 1950’s-1960’s: Discovery of late-type stars with H emission lines ⇒ low-mass pre- main sequence stars: T Tauri, Herbig Ae/Be stars . e.g., Joy 1945, Walker 1956, Herbig 1960 . 1960’s-1970’s: Theories of pre-main sequence evolution and cloud collapse . e.g., Hayashi 1961, Larson 1969, Shu 1977 History (cont’d)

. 1970’s-1980’s: Discovery of Herbig-Haro objects with high proper motions (optical jets) and bipolar outflows (CO) . E.g., Luyten 1971, Cudworth & Herbig 1979, Snell et al. 1980, Lada 1985 . 1980’s: IRAS satellite maps clouds at 12, 25, 60, 100 µm ⇒ distribution of young stellar objects (YSOs) in clouds and evolutionary sequence . E.g., Beichman et al. 1983, Lada & Wilking 1984, Adams, Shu & Lada 1987 History (cont’d)

. Early 1980’s: Discovery of tenuous ‘debris’ disks around mature main-sequence A stars . Vega: Aumann et al. 1984, IRAS . β Pic: Smith & Terrile 1984: optical + coronagraph . Late 1980’s, early 90’s: Development of ground- based and submm observations ⇒ indirect evidence for massive disks around young T Tauri stars . Mid 1990’s: Definite proof for existence of disks around young stars through mm interferometry and HST imaging (‘’) Beta Pictoris disk

Disk warp ⇒ Planet?

Planet confirmed by direct imaging

Credit: ESO Lagrange et al. 2010 Protoplanetary disks

Size disks ~1010 km = 2xSun- Give me matter and I will make a world out of it Kant (1755) HST/C. O’Dell History (cont’d)

. 1970’s-1990’s: Development of theories for dust coagulation, planet formation, early solar nebula . E.g., Weidenschilling 1977, Safronov 1969, Cameron 1973, 1978; Lissauer 1987, … . 1995-1996: Detection of extrasolar planets by Mayor & Queloz (1995) and Marcy & Butler (1996) . >1996: Explosion of research on disks, planet formation and searches for extrasolar planets 1.5 Observational developments . IR array detectors: cover large areas ⇒ large surveys ⇒ census of young stellar objects in nearby clouds . IRAS, Spitzer, ground (2MASS, …), Herschel! . Space IR observatories: . cover entire IR-far-IR spectrum ⇒ spectroscopy of solid-state and gas- phase species . enhanced sensitivity ⇒ weak debris disks . ISO, Spitzer, Herschel . Submm single dish telescopes: array receivers to cover large areas ⇒ probe earliest deeply embedded phase when YSOs heavily extincted; disks around young and mature stars . JCMT (SCUBA), CSO, IRAM30m, APEX . Millimeter interferometers: high angular resolution over small field ⇒ study disks and envelopes on scales of ~100 AU in nearest star-forming regions (~scale of solar system) . IRAM PdBI (→NOEMA), CARMA, SMA, Nobeyama => ALMA! Exercise: google various facilities Examples of new IR facilities Far-infrared/THz

SOFIA 2010-

Various spectro- meters, incl. heterodyne Herschel May 2009 – April 2013 HIFI: heterodyne spectr 480- 1250; 1410-1910 GHz PACS: 60-200 µm SPIRE: 200-600 µm Herschel: techniques have come a long way

100μm map of the ρ-Oph star forming cloud: Fazio et al. 1976 Rosette molecular cloud PACS & SPIRE 70-350 µm Motte et al. 2010 Atacama Large Millimeter Array

. 54 x 12m + 12 x 7m antenna’s . Millimeter/submillimeter wavelengths . 7 – 0.35 mm (30-900 GHz)

Inauguration March 13, 2013

Credit: ALMA Disk evolution

Protoplanetary gas-rich disks Debris gas-poor disks

ALMA molecular lines HST (blue)/ALMA (red) image dust Keplerian

?

100 AU 100 AU Boley et al. Mathews et al. 2013 2012 Fantastic new images of disks

ALMA 20 mas (few AU resolution) HL Tau young disk Age ~few x 105 yr

Orbit of

ALMA partnership Brogan et al. 2015 New era of observational planet formation

Not yet clear what is causing these rings, cavities, dust traps...

1 AU gap= scale

Orbit of Neptune

HL Tau young disk ALMA: Pinilla et al. 2017 ALMA TW Hya ALMA partnership Andrews et al. 2016 et al. 2015 HD 135344B HD 169142

VLT-Sphere, Gemini-GPI Stolker et al. 2016 ALMA: Subaru-SEEDS ALMA: van der Marel et al. 2013, 2016 Fedele et al. 2017 e.g. Muto et al. 2012 First detection young planet in disk

PDS 70 VLT-Sphere

Keppler et al. 2018 Large samples of disks

ALMA 2’’x2’’ 1 mm Dust cont Sz111 J1608

1-2 min Each

20 AU resolution

Ansdell et al. 2018 van Terwisga et al. 2018

Lupus survey pre-main sequence stars Observations of debris disks

HD 207129 G0V, d=15.6 pc

Star M=0.01 MEarth

ISO: HD 141569 IR scattered disk

Fomalhaut 450 µm

Jourdain de Muizon et al. 1999

Weinberger et al. 1999

Holland et al. 2003 Observations (cont’d)

. Optical/near-IR imaging: . high angular resolution ⇒ disks, jets . high sensitivity ⇒ brown dwarfs, Objects, … . HST, ground 8m . Solar system spacecrafts: exploration outer planets and (Titan, Triton, Charon) and (Halley, Wild-2, 67P) . Voyager I, II; Galileo, Giotto, Cassini-Huygens, Stardust . Rosetta mission: landing on a ! . The great comet crashes: Shoemaker-Levy collisions with 1994; Deep Impact mission 2006 . The great comet year 1996: Hyakutake, Hale Bopp: first bright comets to be studied with new generation telescopes . New facilities ALMA (ramping up), JWST (>2021) Future: James Webb Space Telescope

Launch 2021 ~6 m

NASA

0.6-28 µm Extremely Large Telescope

Spectral surveys

ESO ~2026

39m diameter → Extremely high spatial resolution + sensitivity Comets

Hale Bopp

67 P/C-G

Messengers of our own solar nebula Experimental developments

. Improvements sensitivity of measurements of structure and composition primitive solar system material (, interplanetary dust particles) . Development of non-destructive micropobe techniques down to µm scale Million dollar question: how were ‘we’ formed 4.5 billion years ago?

Comet

Rosetta

Meteorites

Credit: NASA/ESA Importance of lab astrophysics

Cavity Ringdown Spectroscopy Ultra-L MS NanoSIMS 2

UHV surface science UV plasma Theoretical developments

. Complete scenario and analytical description of formation low mass stars . Increase computer speed ⇒ more realistic numerical models of various phases (cloud collapse, evolution disk, outflow + jets, …) The Big Picture Astronomical Units

. pc = parsec = 206,265 AU = 3.086 × 1018 cm 33 . M = = 1.99 × 10 g 33 -1 . L = solar = 3.90 × 10 erg s . eV = 1.602 × 10-12 erg . Å = 10-8 cm . Jansky = 10-23 erg s-1 cm-2 Hz-1 . Raleigh = 106 photons s-1 cm-2 (4π sr)-1 . Debye = 10-18 esu cm