polarizing coronagraph for circumstellar dust observations

Polarizing Coronagraph for Circumstellar Dust Observations

Polarizing Coronagraph for Circumstellar Dust Observationsby 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

Spitzer sample

The Spitzer sample

3-10 Myr 50/~140

80-160 Tau, Oph, Cha,Lup, Upper Sco

10-30 Myr 50/~110

60-160 Tau, Oph, Cha,Lup, Cen Crux

30-100Myr

50/~130

40-180 IC 2602 &Alpha Per

100-300Myr

50/~100

20-120 Ursa Major,Castor, Pleiades

0.3-1 Gyr 50/~1000

20-60 Field stars, Hyades

1-3 Gyr 50/~1000

20-60 Field stars

Age N*/Ntot Distance (pc) Target

Spitzer_FEPSFEPS, only 15 stars with excess at 24 µm

Herschel will see cold dustCold dust - little or plenty?

?

?

Disk evolution

Kuiper belt

Wavelength m Flux (10pc) Jy Flux (20pc) Jy70 0.004 0.001100 0.007 0.002130 0.008 0.002

Wavelength m R (10pc) R (20pc)70 0.04 0.04100 0.14 0.17130 0.27 0.27

Contrast ratio Ldust/Lsun

The Sun+Kuiper belt at distance

Planets, radial velocity

QuickTime och enTIFF (LZW)-dekomprimerare

krävs för att kunna se bilden.

Orbits

QuickTime och enTIFF (LZW)-dekomprimerare

krävs för att kunna se bilden.

Mass distribution

QuickTime och enTIFF (LZW)-dekomprimerare

krävs för att kunna se bilden.

PSF

Focal plane

Relay lens

Pupil stop

EMCCD

Lyot Coronagraph

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

Focal plane

Relay lens

Pupil stop

EMCCD

Lyot Coronagraph

polarizer

NGC 7023

Image sharpening

Frame selection + MEM

PSF star

Shift-and-add, 20% MEM, 33 iterations

ZoomPSF star

betaPic

Gas componentTW Hya, 10 Myr

Pic, 10-20 Myr

Gas component