Astronomy from Space презентация

Содержание

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Skeleton

Why space astronomy? Atmospheric windows and distortion
Visible range. Atmospheric seeing and

Skeleton Why space astronomy? Atmospheric windows and distortion Visible range. Atmospheric seeing and
transmissivity. Objects and processes to be observed. Examples: HST, Gaia, Kepler, JWST. Asteroids for navigation in the solar system
UV. HST and IUE. Objects and processes.
IR. Effects of water vapour. Objects and processes. IRAS, SIRTF
Radio. Few examples. Big size, doable from the ground. COBE. Pulsars for attitude
X-rays. Atmosphere opaque. Chandra, ROSAT
Gamma rays. Atmosphere opaque. Objects and processes. Integral, Compton-GRO

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Why space astronomy?

The atmosphere filters and distorts the incoming light:
Some parts

Why space astronomy? The atmosphere filters and distorts the incoming light: Some parts
of the EM spectrum are completely blocked by the atmosphere
Others are only partially so
In the visible spectrum, the atmosphere severely distorts de wave fronts (seeing)
An analogue phenomenon happens at radio wavelengths due to the ionosphere

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Atmospheric windows

Atmospheric windows

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Atmospheric distortion due to turbulence. To a higher or lesser extent,

Atmospheric distortion due to turbulence. To a higher or lesser extent, this distortion
this distortion (seeing) is
always present.

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CCD cameras

Charge Coupled Devices are based on the photoelectric effect. Resulting

CCD cameras Charge Coupled Devices are based on the photoelectric effect. Resulting electrons
electrons are stored in capacitors
These capacitors are disposed in 2D, and are able to hand over their charge to the one in the neighbouring line
CCD chips have efficiencies of ~70%, and sport a linear behaviour
They have a noise due to finite temperature (dark current)
Ionizing particles generate similar signals as photons.

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CCD cameras. Pre-processing

 

CCD cameras. Pre-processing

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Flat field: Caused by inhomogeneity in the illumination
Sources: dust, defects on

Flat field: Caused by inhomogeneity in the illumination Sources: dust, defects on the CCD chip, contamination
the CCD chip, contamination

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Dark field: Caused by thermal noise. The longer the exposure,
the higher

Dark field: Caused by thermal noise. The longer the exposure, the higher the
the electron counts. Extra problem: hot pixels
Solution: low temperature

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Quantum efficiency: fraction of detected photons as a
function of wavelength

Quantum efficiency: fraction of detected photons as a function of wavelength

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Filters

CCD cameras are monochromatic.
To obtain colour information, there are sets of

Filters CCD cameras are monochromatic. To obtain colour information, there are sets of standard filters.
standard filters.

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Adaptive optics

Adaptive optics are a family of methods to improve the

Adaptive optics Adaptive optics are a family of methods to improve the resolution
resolution of ground based telescopes
The basis is to “deform” the main mirror of the telescope in order to keep the images of stars as point-like as possible
Sometimes, the observatory creates an “artificial star” by means of a laser. This artificial star is used as a reference for the adaptive optics system

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Adaptive optics allow
a significant reduction of
distortion at the cost

Adaptive optics allow a significant reduction of distortion at the cost of an increase in complexity
of an
increase in complexity

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Gaia – ESA cornerstone mission L1

Gaia is gathering information (position, parallax,

Gaia – ESA cornerstone mission L1 Gaia is gathering information (position, parallax, brightness,
brightness, and spectra) of 1.7 billion objects
It will generate 53 TB of data
The Payload Data Handling System pre-processes the information gathered on-board to reduce the amount of data relayed to the ground
The mission will last 5 years (up to 2019)
Launched with a Soyuz-Fregat from Kourou

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Map of the sky generated with Gaia’s DR2 (includes 1.7 billion

Map of the sky generated with Gaia’s DR2 (includes 1.7 billion objects) Gaia DR2
objects)

Gaia DR2

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Catalogues for Star Trackers

So far, the catalogues used for star trackers

Catalogues for Star Trackers So far, the catalogues used for star trackers have
have included a few million stars with different errors both in astrometric coordinates as well as in brightness
With the advent of data from Gaia, both sources of errors can be considered negligible
Errors in coordinates ≈ 0.05 mas
Error in brightness ≈ 1 – 20 millimag
The catalogue can be made as large as required with even sky distribution

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Often, there is a prior on the pointing that allows a

Often, there is a prior on the pointing that allows a very significant
very significant
reduction on the amount of calculations

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The James Webb Space Telescope

It is the successor of the Hubble

The James Webb Space Telescope It is the successor of the Hubble Space
Space Telescope
The diameter of its main (segmented) mirror is 6.5 m
Its development has been plagued with difficulties, and it is behind schedule, as well as above budget
Launch is expected in 2020 with an Ariane 5 from Kourou

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Silly ideas also have an effect on Astronomy

Silly ideas also have an effect on Astronomy

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Ultraviolet

Ultraviolet

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Infrared telescopes

 

Infrared telescopes

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There are several windows in the IR, and so observations can

There are several windows in the IR, and so observations can be made
be
made from the ground provided the atmospheric water vapour
content is low

Near IR

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IRAS all-sky map

IRAS all-sky map

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ISO (2.5 – 240 μm)

ISO (2.5 – 240 μm)

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Infrared detectors

The CCDs we have analysed for visible range have a

Infrared detectors The CCDs we have analysed for visible range have a fair
fair QE in the NIR
Other detectors are the bolometers, temperature-sensitive resistance materials can be used to determine the amount of electromagnetic radiation falling on them

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The Crab Nebula as imaged by ROSAT (left) and Chandra (right).

The Crab Nebula as imaged by ROSAT (left) and Chandra (right). Credit: S.
Credit: S. L. Snowden USRA, NASA/GSFC (ROSAT), NASA/CXC/SAO/F. Seward et al. (Chandra)

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The Cygnus Loop Supernova Remnant in X-rays as imaged by three different

The Cygnus Loop Supernova Remnant in X-rays as imaged by three different X-ray
X-ray telescopes.
From the left: image by early X-ray telescopes mounted on sounding rockets, image by the
ROSAT's High Resolution Imager (HRI) instrument, image by the ROSAT's Position Sensitive
Proportional Counter (PSPC) instrument.
Credits: rocket image: Rappaport et al, ApJ (1979) 227, 285;
ROSAT images: N. Levenson (Johns Hopkins), S. Snowden (USRA/GSFC)

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X-ray telescopes

X rays are capable of penetrating matter, and thus are

X-ray telescopes X rays are capable of penetrating matter, and thus are not
not efficiently reflected by mirrors at large incidence angle.
Giacconi and Rossi developed X-ray telescopes out of a set of designs for X-ray microscopes devised by Wolter
These designs improved the sensitivity by a factor of a 1000 between HEAO-1 and 2 (Einstein), as well as their spatial resolution
Typical metallic materials for XRTs are Au, Ni, and Ir, among others
In the case of multilayer coatings, materials can be Ni/C, W/Si, Ro/Be, among others
Surface roughness is a significant problem

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X-ray reflectance

 

X-ray reflectance

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X-ray reflectance

 

X-ray reflectance

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This system generates an annular aperture.
In the case of Chandra, the

This system generates an annular aperture. In the case of Chandra, the external
external paraboloid had a total
surface of 3.2 m2, but the entrance aperture is just 0.047 m2

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Solution: co-aligned, confocal, nested mirrors

Solution: co-aligned, confocal, nested mirrors

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XMM Newton

XMM Newton

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Wolter type I telescope (NASA)

Einstein
ROSAT
Chandra
XMM

Wolter type I telescope (NASA) Einstein ROSAT Chandra XMM

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Wolter type II telescope (NASA)

EUVE

Wolter type II telescope (NASA) EUVE

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Wolter type III telescope (NASA)

Wolter type III telescope (NASA)

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CCDs for X-rays

Semiconductors release electrons when an X-ray photon impacts on

CCDs for X-rays Semiconductors release electrons when an X-ray photon impacts on them
them
The number of released electrons range from a few dozens for low energy photons (~0.1 keV) to a few thousands for 10 keV photons
There is a good correlation between the number of electrons released and the energy of the incoming X-ray photon, thus allowing spectroscopic observations (as well as imaging)

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Gas proportional counters

In this kind of detectors, a gas is ionized

Gas proportional counters In this kind of detectors, a gas is ionized by
by incoming X-ray photons (but also by high energy particles!). The ion-electron pairs are separated by a weak electric field
The avalanche of electrons from an ionization event is detected (and measured) in the anode
The gas is a combination of inert gas and quenching gas to ensure that the ionization current terminates
Typical mix: 90% Ar, 10% CH4
Usable for X-rays under 20 keV

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If the geometry of the detector and the radius of the

If the geometry of the detector and the radius of the wire are
wire are adequate, the
number of electrons detected are proportional to the energy of the X-ray photon

ion drift region

avalanche region

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Scintillators

When an X-ray photon is absorbed by the matter of the

Scintillators When an X-ray photon is absorbed by the matter of the detector,
detector, produces a visible photon that can be registered
Timescales for scintillation range from ns to several hours (the last case is called afterglow)
Charged particles and X-rays have different pulse profiles, thus allowing a discrimination between both

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Microcalorimeters

These devices measure the heat deposited by a single X-ray photon

Microcalorimeters These devices measure the heat deposited by a single X-ray photon on
on the detector
To avoid thermal noise, the detector must be cooled to a fraction of a kelvin
The temperature detector uses to be a Si thermistor, whose resistance experiences a dramatic changes even for small increases in temperature, a very low heat capacity, and works at less than 0.1 K
Used in Suzaku and Astro-H, among others

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Gamma rays

Gamma rays

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Fermi LAT gamma ray sky at 1 GeV

Fermi LAT gamma ray sky at 1 GeV

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Physical processes and detectors

Gamma rays are produced in nuclear processes (X-rays

Physical processes and detectors Gamma rays are produced in nuclear processes (X-rays are
are generated in electronic transition processes)
Scintillators and solid-state detectors work in the same manner than in the case of X-rays
For imaging, gamma ray telescopes rely on Compton effect and pair production

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Compton effect detectors

Compton effect accounts for the scattering of high energy

Compton effect detectors Compton effect accounts for the scattering of high energy photons
photons by charged particles. Work properly at 1 – 30 MeV

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Compton effect detectors

Compton effect telescopes scatter the incoming photon on a

Compton effect detectors Compton effect telescopes scatter the incoming photon on a scintillator,
scintillator, and absorb it on the second layer

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Pair telescopes

Useful for gamma ray imaging at energies over 30 MeV

Pair telescopes Useful for gamma ray imaging at energies over 30 MeV

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Gravitational wave astronomy

Gravitational wave astronomy

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Wrinkles in space time

Violent events involving large masses generate gravitational waves

Wrinkles in space time Violent events involving large masses generate gravitational waves that
that are within our detection capabilities
Black hole mergers
Neutron star mergers
Very nearby core collapse supernovae
The required accuracy (for LIGO, a ground-based GW observatory) involves determining a longitude of less than 10–3 times the radius of a proton

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LISA – Pathfinder

LISA is one of ESA’s cornerstone mission
LISA – Pathfinder

LISA – Pathfinder LISA is one of ESA’s cornerstone mission LISA – Pathfinder
is a technological demonstrator to analyse the feasibility of the full mission
In its core, there are two identical masses (2 kg of Au-Pt alloy, with a cubic shape of 46 mm in side) in free fall just subjected to their mutual gravitational fields
The mission was to determine the residual forces acting on the cubes at different frequencies

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One of the sources of noise was the residual gas impacting

One of the sources of noise was the residual gas impacting on the cubes
on the cubes

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Just something to keep in mind

Just something to keep in mind

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Asteroid 2015 bz509: an interstellar object in solar orbit

Asteroid 2015 bz509: an interstellar object in solar orbit
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