The spine is not a straight line
passing through the star: the disc is bowed with a curvature to the NW direction. This is interpreted as
anisotropic scattering combined with a slight inclination (~86º) of the disc.
The warped and main components of the disc cannot be decomposed as done at Ks in Lagrange et al 2012 due to the lowest dynamical range at L’. The position angle of the disc measured between 3” and 3.8” is
30.8º / 211.0º confirming that our view is a superimposition of both components.
Deep imaging of
β
Pictoris at L’:
asymmetries in the disc and
constraints on planets
We demonstrate here the potential of VLT/NaCo at L’ (3.8µm) in Angular Differential Imaging (ADI). We detect
the β Pictoris disc above 5σ between 0.4’’ and 3.8’’, after
combining data from 7 epochs or 3.1 years. To avoid the smearing of the planet due to its orbital motion within this time span (green arrow), we subtracted the planet from the 7 datasets. We used a star subtraction technique based on PCA (Soummer et al. 2012) and corrected for ADI biases by iterating. We implemented a forward modeling approach to constrain the dust distribution.
1 Separation in arcsec 14 13 12 11 10
Disk brightness in mag/arcsec
2 NE SW NE uncertainty SW uncertainty 3σ noise −2 0 2 Separation in arcsec −4 −2 0 2 4 Deviation to mid − plane in AU NE side SW side
a) Single disc model
Julien Milli*, Dimitri Mawet, David Mouillet, Olivier Absil, Anne-Marie Lagrange, Julien Girard, Jean-Charles Augereau, Anthony Boccaletti, Justine Lannier, Miriam Keppler ESO/IPAG – Alonso de Cordova 3107 Vitacura, Santiago Chile * jmilli＠eso.org
Disk surface brightness
Spine position
No overall brightness
asymmetry within error bars One localized enhancement
at 2’’ on the SW side
Overall offset of the spine towards the NW
2σ departure of the spine at 0.8’’ on the NE side
Detection limits, corrected for ADI flux losses and small sample statistics, converted into masses using COND03 with an age of 20 Myrs. Potential planetary motion between the epochs is not taken into account here.
2. Two disc models to explain the observations
VLT/NaCo image of the disc at L’ (3.8µm) a:er subtrac>on of the planet β Pic b to reveal the innermost regions (Milli et al. 2014)
rwarp
1. The disc revealed in its innermost regions at the location of the planet
3. New constraints on additional planets using small sample statistics formalism
0 5 10 15
3
detection limit (MJup)
0.1 1.0
Angular separation in arcsec 1 Angular separation in a.u.10
Combination 26−12−09 28−09−10 17−11−10 12−10−11 11−12−11 31−01−13 16−12−12 10−7 10−6 10−5 10−4 10−3 10−2 3
small sample contrast
0.1 1.0
Angular separation in arcsec 1 Angular separation in a.u.10
Combination 26−12−09 28−09−10 17−11−10 12−10−11 11−12−11 31−01−13 16−12−12
Disc without planet subtrac>on (adjusted color scale)
Planet orbital mo>on
E N
Best model of the disc
Best model a:er ADI reduc>on (without noise)
Model-‐subtracted image of the disc
b) Disc with an inner warped component
To derive disc parameters free from biases introduced by ADI and constrain the density distribution, we built scattered light images using GRaTeR
(Augereau et al 1999) based on a grid of azimuthally symmetric surface density distributions compatible with the early modeling work of Augereau et al (2001) and the ALMA observations (Dent et al. 2014).
The best model has an inclination of 86º and an anisotropic
coefficient g=0.36.
The index of the inner power law inside 60 au is 1.5 and suggests
that dust lies within the inner 20AU as
suggested by previous observations (Pantin et al. 1997, Okamoto et al. 2004).
The model explains well the observa4ons beyond 0.8’’ but
underpredicts the disc luminosity inside 0.8’’ −2 0 2
Separation in arcsec −4 −2 0 2 4 6 Deviation to mid − plane in AU
Two−component discMain outer disc
Warped inner disc
In a second step, we keep the same radial distribution and dust properties but introduce a warp, as sketched below, and show that it can reproduce the position of the spine.
We used these deep multi-epoch observations to set constraints on planets. As we probe regions very close to the star, we
adopted the formalism of small sample statistics (Mawet et al. 2014) to preserve the confidence level.
The number of resolution elements (circles) is small at short separation and a classical 5σ threshold no
longer corresponds to a 1-3x10-7
false alarm probability (FAP).
Correction factor to apply to the classical 5σ/3σ threshold to
restore the equivalent gaussian FAP.
1 10
Threshold penalty factor
0 2 4 6 8 10
Angular separation (in /D)
0 200 Angular separation (in mas for =3.8 µ m)400 600 800
FAP=0.9987 (3 gaussian)
FAP=1−3× 10−7 (5 gaussian)
Poster by M. Keppler for an advanced modeling
Poster by J. Lannier to account for planetary mo4ons
