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