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Supporting material for Lecture 1:
Role of atmosphere in astronomical observations
Definition of angular resolution
Optical, radio, X-ray telescopes
Atmospheric absorption
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2.5m MountWilson telescope
Telescopio NazionaleGalileo(3.5m)
Hubble SpaceTelescope(2.4m)
Resolution or minimum resolvable distance is the minimum distance between distinguishable objects in an image
Sources with angular size larger than the resolution are calledExtended, otherwise their are point-like, i.e., their angular Extent does not exceed the point spread function
The resolution of ground-based optical images is limited by theAtmospheric seeing (about 1-2 arcseconds on average).
How can one overcome the atmospheric limitation in optical?• By using adaptive optics • By using interferometry • By putting a telescope in space (HST)
Adaptive optics use wavefront sensors to adapt a deformable mirror to variations of the local seeing
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Adaptive optics atGemini telescope
Luminous infrared galaxy IRAS 18293-3413 (79 Mpc)
Comparison of NTT/SOFI and VLT/NACO images
Angular size of each image: 16.5” x 11.5”
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Four 8.2m telescopes
Resolution = /B
B = Baseline
With an ARRAY of telescopes I can combine the wave trains(aperture synthesis) and improve the resolution
INTERFEROMETRY
VLTI/AMBER discovers a companion to HD 87643By image synthesis
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Comparison of ground-based opticaland HST Images of the HomunculusNebula around Eta Carinae. TheLarger axis of the nebula is about 30 arcseconds HST-WFPC2
VLT NACO
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Radiotelescopes
Natural concavities favourScreening from human-relatedRadio-interference
Resolution: ~10 arcmin
Arecibo (100m)
Parabola inMedicina, Bologna (32m)
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Radiointerferometry:Aperture synthesis
Very Large Array (New Mexico)
Croce del Nord (Medicina)
Angular resolution:~1 arcsec
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Very Long Baseline Array (VLBA)
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European VLBI Network (EVN)
Very Long Baseline Interferometry (ang. Res.: milliarcsecond)
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The VLBI SpaceObservatory Program(VSOP)
HALCA: Japanese 8m Antenna orbiting the Earth
Ang. Res: milli-to-microarcsec
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Relativistic jetOf the active galaxy Mkn501(z = 0.033)
30000 kmHalca
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X-ray telescopes: grazing incidence
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X-ray observations of Eta Carinae
Chandra XMM-Newton ASCA
X-ray: 0.1 - 100 keV
The history of X-ray astronomy started in the 1960s:
R. Giacconi 2003:Nobel Lecture: The dawn of x-ray astronomyReviews of Modern Physics 75, 995
In 40 years the X-ray flux sensitivity has improved by 10 orders of magnitudes, comparable to the improvement in optical instruments sensitivity in the last 400 years!
First high-energy baloon experiments: about e-08 erg/s/cm2
Chandra (launched 1999): e-18 erg/s/cm2
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