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Supporting material for Lecture 1: Role of atmosphere in astronomical observations

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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. Telescopio Nazionale Galileo (3.5m). Hubble Space Telescope (2.4m). 2.5m Mount Wilson telescope.

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slide1

Supporting material for Lecture 1:

Role of atmosphere in astronomical observations

Definition of angular resolution

Optical, radio, X-ray telescopes

slide3

Telescopio

Nazionale

Galileo

(3.5m)

Hubble Space

Telescope

(2.4m)

2.5m Mount

Wilson telescope

slide4

Resolution or minimum resolvable distance is the minimum

distance between distinguishable objects in an image

Sources with angular size larger than the resolution are called

Extended, 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 the

Atmospheric 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)

slide5

Adaptive optics use wavefront sensors to adapt a deformable mirror to variations of the local seeing

Adaptive optics at

Gemini telescope

slide6

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”

slide7

INTERFEROMETRY

With an ARRAY of telescopes I can combine the wave trains

(aperture synthesis) and improve the resolution

Very Large Telescope:

Four 8.2m telescopes

Resolution = /B

B = Baseline

slide9

VLT NACO

Comparison of ground-based optical

and HST Images of the Homunculus

Nebula around Eta Carinae. The

Larger axis of the nebula is about 30

arcseconds

HST-WFPC2

slide11

Radiotelescopes

Natural concavities favour

Screening from human-related

Radio-interference

Resolution: ~10 arcmin

Parabola in

Medicina, Bologna

(32m)

Arecibo (100m)

slide12

Radiointerferometry:

Aperture synthesis

Croce del Nord (Medicina)

Angular resolution:

~1 arcsec

Very Large Array (New Mexico)

slide13

Very Long Baseline Interferometry (ang. Res.: milliarcsecond)

European VLBI Network (EVN)

Very Long Baseline Array (VLBA)

slide14

The VLBI Space

Observatory Program

(VSOP)

HALCA: Japanese 8m

Antenna orbiting the

Earth

Ang. Res: milli-to-microarcsec

30000 km

Halca

Relativistic jet

Of the active

galaxy Mkn501

(z = 0.033)

slide16

X-ray observations of Eta Carinae

Chandra XMM-Newton ASCA

slide17

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 astronomy

Reviews 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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