Main belt structure and the orbit of Fomalhaut b Paul Kalas (UCB) | James Graham (UCB) | Michael Fitzgerald (UCLA) | Mark Clampin (GSFC)

Extended halo of dust Fomalhaut’s main belt is much wider than previously thought. Gap

Posterior distribuons of periapse and apoapse.

Fomalhaut b Four epochs over eight years reveal a highly eccentric orbit.

Sample of 30 orbits drawn from the Markov chains, represenng orbits in the face-on and edge-on views that are consistent with astrometric data.

Sketch of the Fomalhaut system based on observaonal evidence.

Introducon Observaons Orbit of Fomalhaut b Take Home Points

• Re-analysis of astrometry and error • We use an MCMC method to sample the • Fomalhaut b is confirmed in four opcal sources for 2004, 2006 ACS data, and 2010 posterior probability distribuon for the coronagraphic observaons with HST spread STIS data. orbital elements based on 4 epochs of over eight years, and in independent analyses of astrometry. the 2004, 2006, & 2010 data sets performed by • New Observaons with HST/STIS obtained Kalas et al. (2008), Currie et al. (2012), and May 2012: • Our new esmates for Fomalhaut b orbital Kalas et al. 2008 Acke et al. 2012 Boley et al. 2012 elements are: Galicher et al. (2013). 12 orbits, 12 roll angles • Fomalhaut at d = 7.7 pc, age= 440 Myr, and a = 177 ± 68 AU [Main Belt ~ 140 AU] STIS coronagraphic wedge, blocks 2.5 arcsec • The 2012 epoch presented here yields the SpT=A3V has a dusty debris disk discovered e = 0.8 ± 0.1 [Main Belt ~ 0.1] with IRAS in 1984 (Backman & Paresce 1993). 0.05077”/pix, no filters, 0.2-1.0 micron surprising result that Fomalhaut b’s orbit is q = 32 ± 24 AU, Q = 322 ± 119 AU highly eccentric (Kalas et al. 2013). Use self-subtracon at mulple rolls, no PSF • JCMT observaons revealed a belt of material star I = 17˚ ± 12˚ [mutual inclinaon w.r.t. belt] • Also detected are the main belt outer dust in thermal emission (Holland et al. 1998),  = 152˚ ± 13˚ [Main Belt 156.2˚ ± 0.1˚] confirmed with Spitzer (Stapelfeldt et al. 2004). halo to >209 AU radius, and an azimuthal gap in Core Results  = 26˚ ± 25˚ [Main Belt 30˚ ± 1˚] the main belt located at PA ~ 331˚. P ~ 1700 yr [Main Belt 1100-1400 yr] • The first opcal images of Fomalhaut, • Fomalhaut b is detected again in 2010 and obtained with HST in 2004, show a narrow dust 2012 using HST / STIS in the opcal. • The Fomalhaut system is dynamically complex belt seen in scaered light, which is offset from and may represent a brief, chaoc period of • The high eccentricity makes the orbit of dynamical instability in a planetary system. Key the star by 15 AU, and with a sharp inner edge • Also confirmed in 2010 and 2012 are two Fomalhaut b appear belt crossing in the sky open quesons are: (Kalas et al. 2005). These findings are new main belt features: (1) an extended halo plane projecon, but it is not known if the consistent with dynamical perturbaons from a of dust that shows the belt is much wider two orbital planes are coplanar due to the planet on an eccentric orbit (Wya et al. 1999). than previously known, and (2) an azimuthal uncertaines. (1) Why is Fomalhaut b on a highly eccentric gap in the belt located northward of orbit while at the same me showing apsidal Fomalhaut b’s posion. • Fomalhaut b and the belt show apsidal alignment with belt? • A common proper moon companion, alignment. Fomalhaut b, was discovered at two epochs • The periastron distance for Fomalhaut b is with HST opcal coronagraphy, but it was not • Photometric variability for Fomalhaut b (2) What is the dynamical stability of the system, now known to be significantly closer to the detected in the infrared, suggesng that we cannot be confirmed due to the effects of parcularly if other hypothecal planets are star, suggesng that it could have been may be detecng stellar light reflected from speckle noise on the photometry. required to account for the known features? circumplanetary dust (Kalas et al. 2008). The scaered outward due to a dynamical Where is a hypothecal Fomalhaut c? model-dependent mass for Fomalhaut b is less instability involving interior planets yet to be than about a Jupiter mass (Janson et al. 2012). • Fomalhaut b itself appears extended with detected. an ellipcal morphology, but we can aribute (3) Is Fomalhaut b a scaered planet in a mul- • Fomalhaut b had periastron 125 years ago this to speckle noise. Future observaons are planet system, or is it analogous to a short and will appear to cross the belt beginning • The present work represents a major advance required to confirm any extended period comet or Centaur in our solar system? two decades from now. in esmang Fomalhaut b’s orbital parameters. morphology. Kalas et al. 2013, submied to ApJ; hp://lanl.arxiv.org/abs/1305.2222