Gianni Cataldi The eccentric dust ring of Fomalhaut: Reminder: debris disks planetary perturbations or gas-dust The Fomalhaut system and its interactions? eccentric dust ring Planetary perturbations: Gianni Cataldi 1 , 2 , Alexis Brandeker 1 , 2 , G¨ oran Olofsson 1 , 2 Fomalhaut b The eccentric dust ring revisited: 1 Department of Astronomy, Stockholm University gas-dust 2 Stockholm University Astrobiology Centre interactions 2014-02-11 1 / 16
Outline Gianni Cataldi Reminder: debris disks 1 Reminder: debris disks The Fomalhaut system and its 2 The Fomalhaut system and its eccentric dust ring eccentric dust ring Planetary perturbations: 3 Planetary perturbations: Fomalhaut b Fomalhaut b The eccentric dust ring 4 The eccentric dust ring revisited: gas-dust interactions revisited: gas-dust interactions 2 / 16
What are debris disks? • circumstellar, gas-poor disks consisting of dust, comets Gianni Cataldi and leftover planetesimals Reminder: • Kuiper belt / asteroid belt analogues debris disks The • size: from a few AU to > 1000 AU Fomalhaut system and its • dust continuously replenished by collisions eccentric dust ring • several hundred examples known today Planetary perturbations: Fomalhaut b The eccentric dust ring revisited: gas-dust interactions Image credit: NASA 3 / 16
The Fomalhaut system • spectral type: A-star Gianni Cataldi • distance: 8 pc Reminder: debris disks • age: 400 Myr The • eccentric dust ring with semi-major axis of ∼ 150 AU Fomalhaut system and its eccentric dust ring Planetary perturbations: Fomalhaut b The eccentric dust ring revisited: gas-dust interactions Image credit: Acke et al. 2013 4 / 16
The Fomalhaut dust ring Gianni Cataldi Reminder: debris disks The Fomalhaut system and its eccentric dust ring Planetary perturbations: Fomalhaut b The eccentric dust ring revisited: gas-dust interactions Herschel PACS 70 µ m Image credit: Acke et al. 2013 5 / 16
Is a planet shaping the dust ring? Gianni Cataldi Reminder: debris disks • Indications for a planet The Fomalhaut shaping the dust ring system and its eccentric dust (Kalas et al. 2005) : ring • centre of dust ring Planetary perturbations: offset by ∼ 15 AU from Fomalhaut b star The eccentric • sharp inner edge dust ring revisited: gas-dust • ⇒ search for planetary interactions candidates Optical HST image. Image credit: Kalas et al. 2005 6 / 16
Detection of Fomalhaut b • detection of Fomalhaut b with HST (Kalas et al. 2008, 2011, Gianni Cataldi 2013) Reminder: debris disks The Fomalhaut system and its eccentric dust ring Planetary perturbations: Fomalhaut b The eccentric dust ring revisited: gas-dust interactions Image credit: NASA and ESA 7 / 16
The nature of Fomalhaut b • puzzling spectral properties: Gianni Cataldi • detected in optical (e.g. Kalas et al. 2013) Reminder: • . . . but non-detection in mid-IR (e.g. Janson et al. 2012) debris disks • ⇒ inconsistent with models of planetary spectra The Fomalhaut system and its • ⇒ detection in reflected starlight eccentric dust ring • ⇒ need additional reflecting surface Planetary perturbations: Fomalhaut b The eccentric dust ring revisited: gas-dust interactions Image credit: Paul Kalas (UC Berkeley) 8 / 16
The nature of Fomalhaut b • proposed models: Gianni Cataldi • circumplanetary dust disk (Kalas et al. 2008) Reminder: • transient dust cloud (Kalas et al. 2008) debris disks • swarm of irregular satellites around 2–10 M ⊕ planet The Fomalhaut (Kennedy & Wyatt 2011) system and its eccentric dust ring Planetary perturbations: Fomalhaut b The eccentric dust ring revisited: gas-dust interactions Image credit: ESA, NASA, and L. Calcada (ESO for STScI) 9 / 16
Fomalhaut b and the eccentric dust ring revisited Gianni Cataldi Reminder: debris disks • orbit of The Fomalhaut Fomalhaut b system and its eccentric dust highly eccentric ring ⇒ unlikely to be Planetary perturbations: responsible for Fomalhaut b eccentricity / The eccentric dust ring morphology of revisited: gas-dust the disk! interactions • Fomalhaut c ? Kalas et al. 2013 10 / 16
Sharp (eccentric) rings through gas-dust interactions Gianni Cataldi • alternative without invoking planets: gas-dust interactions Reminder: • dust affects gas temperature - gas affects dust dynamics debris disks • operates for stars with spectral type as late as K The Fomalhaut system and its • works for a wide range of dust and gas masses eccentric dust ring � d / � 0 at t = 100 T orb < � d >/ � 0 Planetary 0 0.2 0.4 0.6 0.8 0 0.1 0.2 perturbations: a b c Fomalhaut b 0.3 100 0.4 0.2 80 The eccentric 0.2 dust ring 0.1 60 revisited: t / T orb z / H y / H 0 0 gas-dust 40 interactions –0.1 –0.2 20 –0.2 –0.4 0 –0.3 –0.4 –0.2 0 0.2 0.4 –0.4 –0.2 0 0.2 0.4 –0.4 –0.2 0 0.2 0.4 x / H x / H x / H )/ � 0 d 1 � Lyra & Kuchner 2013 � 11 / 16 � � � � � � � � � �
The photoelectric instability Gianni Cataldi • start with generic dust enhancement (e.g. from Reminder: debris disks collision) The • gas is primarily heated by Fomalhaut system and its eccentric dust photoelectrons from the ring dust Planetary perturbations: • photoelectric instability: Fomalhaut b • dust heats gas by The eccentric dust ring photoelectric effect revisited: gas-dust • ⇒ gas temperature rises Besla & Wu 2007 interactions • ⇒ gas pressure rises • dust concentrates where gas pressure is maximum • . . . 12 / 16
Gianni Cataldi system and its perturbations: eccentric dust The eccentric 12 / 16 Fomalhaut b debris disks interactions Fomalhaut Reminder: Planetary dust ring revisited: gas-dust The ring Besla & Wu 2007 The photoelectric instability • ⇒ gas temperature rises • dust concentrates where • gas is primarily heated by enhancement (e.g. from photoelectrons from the • photoelectric instability: • ⇒ gas pressure rises • start with generic dust photoelectric effect • dust heats gas by gas pressure is maximum collision) • . . . dust
Search for gas in the Fomalhaut dust ring Gianni Cataldi Reminder: • search for gas emission within the Fomalhaut dust ring: debris disks • C II 158 µ m and O I 63 µ m: Herschel PACS The Fomalhaut (non-detections) system and its • CO 867 µ m: ALMA (non-detection) eccentric dust ring • known dust ring structure allows ”forward modelling” Planetary perturbations: approach Fomalhaut b • general strategy: The eccentric dust ring 1 derive upper limits on O I / C II / CO gas luminosity revisited: gas-dust 2 convert into total gas mass using the gas ionisation / interactions thermal balance code ontario 13 / 16
PACS observations Gianni Cataldi Reminder: debris disks The Fomalhaut system and its eccentric dust ring Planetary perturbations: Fomalhaut b The eccentric dust ring revisited: gas-dust interactions 14 / 16
preliminary result for C II • rough first analysis indicates that PACS data can give Gianni Cataldi stringent upper limits Reminder: debris disks • 5 σ upper limits: • solar abundances: � 1 . 8 · 10 − 3 M ⊕ of gas ( ⇒ ǫ � 10) The Fomalhaut • C overabundant 300 × : � 4 . 0 · 10 − 5 M ⊕ of gas system and its eccentric dust ( ⇒ ǫ � 400) ring Planetary perturbations: Fomalhaut b The eccentric dust ring revisited: gas-dust interactions 15 / 16
Summary Gianni Cataldi 1 The Fomalhaut system appears as an increasingly complex Reminder: debris disks planetary system The 2 The exact nature of Fomalhaut b is unclear Fomalhaut system and its eccentric dust 3 Current constraints on the orbital elements of Fomalhaut b ring suggest a different origin of the ring morphology: Planetary • Fomalhaut c perturbations: Fomalhaut b • gas-dust interactions The eccentric • (interactions with other stars) dust ring revisited: 4 We use Herschel PACS and ALMA to search for gas in the gas-dust interactions Fomalhaut dust ring to test whether gas-dust interactions could be at work 16 / 16
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