Polarizing Coronagraph for Circumstellar Dust Observations by Göran Olofsson, Astronomy, SU Thursday the 16th of November 10.00 o'clock at FA32 Abstract The idea that there exists planetary systems other than that of the Sun is old, but it has until recently been beyond the technical feasibility to get any observational evidence for external planetary systems. By the IRAS discovery of far-IR dust emission around nearby stars, like Vega, it was realized that the dust replenishment required larger colliding or evaporating bodies, i.e. processes similar to those that provide the zodiacal dust. In addition, a steadily increasing number of planets are being found by detecting the minimal cyclic radial velocity variations of the central star caused by an orbiting planet. Obviously this (indirect) detection method works bests for heavy planets, orbiting close to their central stars, and there is an ongoing discussion what technical means it may take to do direct detection of planetary systems similar to our own. It has been argued that a new generation of extremely large ground-based telescopes (ELTs) may provide the tool for such observations (actually this is one of the main scientific drivers for the large investments required to build ELTs). But probably we have to wait for space interferometers, like Darwin, for the first detection of an Earth like planet orbiting an nearby star. Until then, much closer in time, we can explore the properties of circumstellar dust disks, and I will describe our own plans in that direction, both using Herschel Space Observatory and a 'home-made' polarizing coronagraph.

Vega (IRAS)

Disk evolution

Silhouette disks

silh2

silh3

Silh4

Disk evolution

betaPic_0.5µm

betaPic_10µm

A smooth decline of dust with time?

ISO view

Age N*/Ntot Distance (pc) Target Spitzer sample The Spitzer sample Age N*/Ntot Distance (pc) Target

FEPS, only 15 stars with excess at 24 µm Spitzer_FEPS FEPS, only 15 stars with excess at 24 µm

Herschel will see cold dust Cold dust - little or plenty? ? ?

Disk evolution

The Sun+Kuiper belt at distance Contrast ratio Ldust/Lsun

Planets, radial velocity

Orbits

Mass distribution

PSF

Lyot Coronagraph Focal plane Relay lens Pupil stop EMCCD

Seeing 0.7”, disk 1” diam Pupil image

Seeing 0.7” disk =1”

Seeing 0.7”, disk 3” diam Pupil image

Seeing 0.7” disk 3”

PSF, coronagraph

Observed PSF

Lyot Coronagraph Focal plane Relay lens Pupil stop polarizer EMCCD

NGC 7023

Image sharpening

Frame selection + MEM Shift-and-add, 20% MEM, 33 iterations PSF star

Zoom PSF star

betaPic

Gas component Gas component TW Hya, 10 Myr B Pic, 10-20 Myr