High resolution ALMA observation of the 12CO(3-2) and 350 GHz continuum emissions of the debris disc of 49 Ceti P.T. Nhung on behalf of the Department of Astrophysics Vietnam National Satellite Center (VNSC/VAST) NTHU, Hsinchu, March 2017 49 Ceti, a debris disc 49 Ceti, a bright debris disc, seen close to edge on, surrounding a single A1V star at a distance of 59 pc Age: in 40 Myr range (member of the Argus association) Dust mass: ~ 0.3 Earth masses (SED) CO mass: > 2×10−4 Earth masses SMA: rotating ring + central hole (UV dissociation) (Hughes 2008) HST (far-UV) a long l.o.s.: presence of atomic species (C, O) and absence of CO absorption lines (Roberge 2014) Dust CO(3-2) 2 ALMA Observations Archived data. Project: 2012.1.00195.S, PI: M. Hughes 350 GHz continuum (15MHz width) and 12CO(3-2) emissions observed on 14/11/2013, during 39 min 0.56×0.43 arcsec2 28 antennas, maximal baseline of 1284 m, minimal baseline of 17.3 m, beam size ~ 0.5'' spectral resolution: ~ 0.1 kms−1 0.50×0.38 arcsec2 frame rotated clockwise by 17.5o 3 Continuum and 12CO(3-2): main features frame rotated clockwise by 17.5o Continuum CO(3-2) 0.3” wide intervals of x • emission of the dust disc extends farther out in y than the gas disc; • smooth regularity of the gas emission, lumpy emission of the dust 4 Continuum and 12CO(3-2): main features Distribution of observed intensity CO(3-2) (red) / Continuum (x620, black) Dust: a broad and shallow central depression , as expected from an azimuthally symmetric disc, Gas: a narrower and deeper central dip 5 Gas kinematics Velocity spectrum Velocity map • double-horn structure – rotating disc • central depression significantly deeper than for typical rotating discs, the valley is deep and narrow over a range of ~2 kms−1 6 Evidence for central attenuation of the CO(3-2) emission No optically thin model assuming rotation invariance about the disc axis can reproduce the narrow central dip observed in x distribution of intensity The emission observed at large values of |x| (large disc radii) contributes more than what is observed along lines of sight pointing to x = 0. → effective emissivity intensity in a pixel F∗ & ρ∗ : the integrals over y of F & ρ -> significant attenuation of the detected emission near x =0 (covering ∼1'' FWHM, ∼60 au, in x) 7 A simple model of CO(3-2) emission Morphology: rotation invariance about the disc axis, symmetry about the disc mid-plane, flaring disc, flat disc mid-plane (no warping) Important: along the l.o.s to the central star, column density [CO] ≤ 5×1012 cm−2 Parameters: position angle (PA), inclination (i), flaring angle and radial distribution including ad hoc attenuation. radial distribution: obtained from the solution of integral equation, using a one-parameter family of functions central attenuation using two different forms: 8 A simple model of CO(3-2) emission Morphology: Flaring disc: dependence on the distance h to the disc mid-plane radius in disc plane n Kinematics: V=V0 r Parameters to be adjusted: i , k , ηh , V0 , nh , λx ,Δx (λV ,ΔV ) To make best possible use of available sensitivity, three sets of data are jointly used in the evaluation of χ2 : - map of the velocity integrated intensity, - map of the mean velocity, - the global velocity spectrum. 9 CO(3-2) emission : fit results data model data (colour) & model (contours) 10 CO(3-2) emission : fit results data model velocity map velocity distribution 11 data (colour) & model (contours) Continuum emission (Common PA was fit jointly to line and continuum) Radial dependence No need for attenuation Two parameters to be adjusted: inclination i flaring angle Δh= ηh R 12 Summary: fit results (common PA = 17.5o) CO(3-2) (5.5o FWHM) Dust emission i = 11.1o±1.4o and η = 0.10±0.06 (13.5o FWHM) h 13 Line width effects observed line profiles (back) vs modelled profiles (red) • Line widths are completely dominated by Keplerian shear, leaving little room for other contributions. • Upper limits to the intrinsic line widths of ~ 1 kms−1 FWHM. 14 Summary - both CO and dust discs share a same position angle and a same inclination but the gas disc is more homogeneous, more central and thinner than the dust disc - evidence for a significant deficit of observed CO(3-2) emission at Doppler velocities differing from the star systemic velocity by < 1 km s−1 −4 - measured brightness corresponds to a CO mass of 2.7×10 MEarth, continuum flux density is in good agreement with current SED estimates - gas velocities are accurately measured and found Keplerian over a broad range of disc radii; - the observed CO(3-2) line width is dominated by Keplerian shear and upper limits are obtained to the intrinsic line width - simple phenomenological models of both CO(3-2) and 350 GHz continuum emissions are presented using only very few parameters 15 We are making extensive use of the open data policy of the ALMA collaboration, who make their observations publicly available one year after collection. The data are reduced by the ALMA staff who provide adequate support to check them and handle them properly. This generous policy is an invaluable asset to teams such as ours, working in developing countries having otherwise no direct access to frontier astrophysics. We are immensely indebted and grateful to the ALMA partnership. List of publications using ALMA archival data arXiv Journal Source Type 1503.00858 RAA Red Rectangle Planetary Nebula 1601.04834 RAA Pi Gru AGB star 1601.01439 RAA W Aql AGB star 1603.00148 MNRAS Mira Ceti AGB star 1603.02405 MNRAS Various Methodology 1604.03801 MNRAS L1527 Young protostar 1609.03271 MNRAS RX J0911 High z galaxy 1701.02131 MNRAS(subm.) 49 Ceti Debris disc 16 16.