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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
Disk evolution
betaPic_0.5µm
betaPic_10µm
A smooth decline of dust with time?
ISO view
The Spitzer sample
Age
3-10 Myr
N*/Ntot
50/
~140
10-30 Myr 50/
~110
30-100
50/
Myr
~130
100-300
50/
Myr
~100
0.3-1 Gyr 50/
~1000
1-3 Gyr
50/
~1000
Distance (pc)
80-160
Target
20-60
Tau, Oph, Cha,
Lup, Upper Sco
Tau, Oph, Cha,
Lup, Cen Crux
IC 2602 &
Alpha Per
Ursa Major,
Castor, Pleiades
Field stars, Hyades
20-60
Field stars
60-160
40-180
20-120
FEPS, only 15 stars with excess at 24 µm
Cold dust - little or plenty?
?
?
Disk evolution
Kuiper belt
The Sun+Kuiper belt at distance
Wavelength m
70
100
130
Flux (10pc) Jy
0.004
0.007
0.008
Flux (20pc) Jy
0.001
0.002
0.002
Contrast ratio Ldust/Lsun
Wavelength m
70
100
130
R (10pc)
0.04
0.14
0.27
R (20pc)
0.04
0.17
0.27
Planets, radial velocity
QuickTime och en
TIFF (LZW)-dekomprimerare
krävs för att kunna se bilden.
Orbits
QuickTime och en
TIFF (LZW)-dekomprimerare
krävs för att kunna se bilden.
Mass distribution
QuickTime och en
TIFF (LZW)-dekomprimerare
krävs för att kunna se bilden.
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
EMCCD
polarizer
NGC 7023
Image sharpening
Frame selection + MEM
Shift-and-add, 20%
PSF star
MEM, 33 iterations
Zoom
PSF star
betaPic
Gas component
TW Hya, 10 Myr
B Pic, 10-20 Myr