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1 Astrophysical Information AS4100 Astrofisika Pengamatan Prodi Astronomi 2007/2008 B. Dermawan.

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Presentation on theme: "1 Astrophysical Information AS4100 Astrofisika Pengamatan Prodi Astronomi 2007/2008 B. Dermawan."— Presentation transcript:

1 1 Astrophysical Information AS4100 Astrofisika Pengamatan Prodi Astronomi 2007/2008 B. Dermawan

2 2 Introduction (1) The aim of astrophysics : to describe, to understand and to predict the physical phenomena that occur in the Universe information  signals The aim of observation : to work out a strategy for collecting this information, and to order the various variables or physical parameters measured to analyze this information in such a way that it is neither over-interpreted nor wasted to store if for later investigations, possibly by future generations carriers  energy

3 3 Introduction (2) Economic commodity: costly to acquire and to analyse, so decisions must often be made at the political level or, at least, on the level of the science research budget

4 4 Carriers of Information (1) Observation at a Distance: Electromagnetic Radiation Nick Strobel’s Astronomy

5 5 Carriers of Information (2) Matter: From Electrons and Nuclei to Meteorites Cosmic rays –Consist of electrons, atomic nuclei (proton to heavy nuclei) –Originate in the high-energy processes (supernova explosions) –Interact with the galactic magnetic field  highly isotropic spatial distribution Abundances in solar system Léna et al. 1996

6 6 Meteorites –Microscopic to a mass of several tons; rain upon the Earth –The abundance of the various elements at the time and place where it was produced: Present (solar wind), Past (meteorites) of the solar system, High-energy reactions on the surface of stars (explosive nucleosynthesis), The early Universe (helium abundance in cosmic rays)

7 7 Carriers of Information (3) Neutrino Weak interaction Strong interaction e  :electron, e + :positron n : neutron, p: proton e :neutrino electron e : anti neutrino electron  +,  ,  0 : pions/pi-mesons of charge +1,-1,0  +,  : muons/mu-mesons of charge +1,-1,  : neutrino muon  : anti-neutrino muon Léna et al. 1996

8 8 Carriers of Information (4) Gravitational Waves Sources: Periodic sources (binary stars, pulsars): freq. 10 -4 – 10 -1 Hz) Low-freq impulsive (or burst): the presence of black holes in massive objects (10 5 – 10 9 M  ) Higher freq impulsive (or burst): the gravitational collapse of 1 – 10 M  stars (during supernova event; freq. 10 – 10 4 Hz)

9 9 –As the black holes, stars, or galaxies orbit each other, they send out waves of "gravitational radiation" that reach the Earth –A more massive moving object will produce more powerful waves, and objects that move very quickly will produce more waves over a certain time period NASA

10 10 Carriers of Information (5) Observation in situ Allows local measurements To experiment in the same way as a physicist, a chemist, or a biologist

11 11 Collecting & Analysing Information Main Characteristics of Photons Photon PropertyObservational Strategy Energy, wavelength, frequency- Spectral coverage - Transmission through Earth ’ s atmosphere - Choice of appropriate detector Number of photons received (flux)Size of collecting area (telescope) Radiation intensity- Detector sensitivity - Photometry Time dependence (t  1/ ) Temporal coherence - Spectral analysis - Spectral resolution Time dependence (t >> 1/ ) - Time resolution - Rapid photometry (t  1 s) Spatial (angular) dependenceMapping, imaging, spatial (angular) resolution SpinPolarimetry

12 12 Observing Systems (1) The photon flux from the source is collected by a surface A (aperture) of the detector (generally a mirror: primary mirror) The photons are collected in a solid angle  (field of view, f.o.v) There may be parasitic sidelobes which take energy from directions other than the principal direction of observation Lena et al. 1996

13 13 Observing Systems (2) An optical system (a combination of mirrors/lenses) concentrates the received energy and forms an image in the image plane or focal plane The f.o.v  is thus decomposed into image elements (pixel), each one subtended by a solid angle  of the source A device for spectral selection isolates a particular frequency domain  in the incident radiation Imposed by: the physical characteristics of the optical system, or the detector itself, or from deliberate filtering of the radiation Lena et al. 1996

14 14 Observing Systems (3) The polarisation of the radiation can be determined by means of a polarising filter, which selects a particular polarisation (linear or circular) in the incident radiation The incident EM signal is transformed by the detector or receiver into a physical quantity which can be measured and stored (ex: current, voltage, chemical transformation) The detector is generally followed by a set of electronic devices which make up the acquisition system for analysing and recording the signal Lena et al. 1996

15 Spectral Coverage M81: Spiral Galaxy UltravioletVisibleInfraredRadio Emission of hot region Stellar emissionDust emission Emission of cold region Ultraviolet VisibleInfraredRadio Saturn

16 16 Measurement of Intensity –The number of photons received per unit time depends on the collecting area used –The telescope has double function of collecting the radiation and of forming an image Thermal and mechanical effects limit the collecting power of telescopes –The performance of the detector determines both the precision and the ultimate sensitivity which can be attained Depends on the technology available and on fundamental physical limitations Photometry: the measurement of received radiation intensity, not relative of reference objects, but in an absolute sense Require the techniques of absolute calibration

17 17 Spectral Analysis (1) Astrophysics is built upon the achievements of spectroscopy, given the results made possible using spectral analysis  chemical and isotopic composition, velocity fields, turbulence, temperature, pressure, magnetic fields, gravity, etc The spectral resolving power ( /  ): its ability to independently measure two emissions of distinct frequency  depend on the spectrograph, the collecting area, the measurement time, and the sensitivity of the detectors

18 18 Spectral Analysis (2) Rapid spectroscopy and photometry (< 1 ms) Solar flares, eruptive variable stars, accretion phenomena, X-ray sources Spectroscopy and Imaging (images at different wavelengths are obtained simultaneously) Spectroheliogram, X-ray mapping of solar corona, maps of the hydrogen velocity distribution in a galaxy (the 21 cm line) Lena et al. 1996

19 19 Time Variability Variable stars slow: Mira Ceti (ancient times) rapid: Pulsar, of period 1.377 ms (1968) Sensitivity  1959 1979 1989 Lena et al. 1996

20 20 Imaging To distinguish between rays coming from different directions in space The capacity of a given observation device to do this: spatial resolving power  angular resolution (the size of the instrument, the wavelength of the radiation, the effects of atmospheric turbulence) ResolutionNumber of pixels to cover 4  sr Information available on this scale (1985) Spectral region 11 4  10 4 Background radiation chart Sky survey millimeter  -ray 11.5  10 8 Sky survey IR (10-100  m) 11 5.4  10 11 Sky survey Specific objects (restricted fields) Visible mm, IR, UV, X-ray 0.01  5.4  10 15 Specific objectsIR, visible 10 -3  5.4  10 17 Specific objectsRadio [cm] 10 -6  5.4  10 21 Specific objectsRadio [cm,mm]

21 21 Polarisation Usually very characteristic both of the physical conditions: Its emission: scattering, presence of magnetic fields, bremsstrahlung Physical condition on its path: the presence of a macroscopically oriented anisotropic medium (interstellar grains) Space-Time Reference Frames Refer astronomical events (able to use correctly the information transported by photons) Know the location of objects in some well-defined spatial frame The FK5 catalogue: global accuracy of 0.02  (stellar positions), an accuracy of 1.5 x 10 -3  /yr (stellar proper motions) Essential to:

22 Processing and Storage of Information Astrophysical information  data gathered across the whole range of observed sources –Always being susceptible to improvement as regards accuracy –Has great historical value (any variation in the course of time) The increase in volume of data gathered is enormous –Around 10 7 stars has been catalogued (position, magnitude, color) –1990 ’ s  10 10 to 10 13 bits per year

23 Source signal Observing system Raw data Data archive Preliminary reduction Quick-look data Commands, optimization Interactive analysis Full analysis Data bank Images, spectra … Publication Images,spectra … Statistical analysis, modelling Malasan, priv. com. Acquisition and treatment of astronomical information

24 Stages in the Processing of Astronomical Data & the Role Played by Computer Systems (1) The acquisition of information in real time The so-called quick look optimises an observation The rate of acquisition can vary widely: from the detection of individual photons from a weak source (1 or 2 per hr or per day), to the production of instantaneous images using the speckle interferometry in the visible (10 8  10 9 bits per sec) Real-time data handling (data compression and filtering): reducing the volume of the raw data and facilitating permanent storage Subsequent analysis is generally interactive (scientist-computer-data) –Selection of the best data, optimal filtering of noise, various corrections for properties of observing systems (variations in sensitivity, atmospheric effects, pointing drift, etc), calibration by comparison with the standard sources –A set of algorithm for thematic extraction and analysis of information, a set of programs (calibration programs), viewing programs to simplify the interface between calculation tools and the user

25 25 Stages in the Processing of Astronomical Data & the Role Played by Computer Systems (2) Processed data includes error estimates The signal-to-noise (S/N) ratio Can be relayed to the scientific community  Publication  As a part of data bank (standardising) The detailed treatment  A large volume of data or properties of sources is extracted from the data bank to be handled by powerful machines (statistical features, sophisticated physical modelling)

26 26 Strategies and Costs (1) Astronomical research programs are financed by public funding or (private) foundations Choices have to be made to determine priorities in the research budget of a country Research activities require personnel in a wide range of skills and know-how (researchers, engineers, technicians, administrators) The ratio of supporting staff to researchers: 1 or 2 in lab., 10 in operational observatory

27 27 The financing of astronomical research FranceEuropeUnited States GDP Gross Domestic Spending on RD 1320 G$ (1992) 25 G$ (1991): 49% public funding, 42.5% industry 7504 G$ (1992) 116 G$ (1991) 5920 G$ (1992) 154 G$ (1991) Civilian RD budget7.8 G$ (1992)28 G$ (1992) Civilian space science funds (all disciplines) 110 M$ (1992)290 M$ (1992) (ESA)14 G$ (1992) Astronomy: Equipment Operation Personnel Ground 47.3 M$ (1992) Space 62.3 M$ (1992) 730 researchers, 1440 engineers & technicians, 220 postdoc & doctoral Ground 112 M$ (1992) Space 1427 M$ (1992) 4200 researchers with PhD (1992) Very large scale scientific projects 329.1 M$ (1992)

28 28 Strategies and Costs (2) Observational astrophysics requires: Observing apparatus, telescopes, on the ground or in space Space probes, exploring solar system in situ and sometimes bringing samples back to Earth Sophisticated instrumentation working in relation with these telescopes and probes (cameras, detectors, spectrographs) The means of processing the data (computers, data bases) Various tools require a whole range of technology, including optoelectronics, mechanics, robotics, system theory, AI, etc. Theoretical astrophysics uses: Tools of mathematics, physics, chemistry Large-scale numerical calculation (computers of the highest level of performance in speed and storage capacity)

29 29 Strategies and Costs (3) The cost per unit of equipment and projects rise steadily with increasing size and complexity The cost of traditional ground-based optical telescopes (1980): 0.45 D 2.6 M$ Keck telescope (1995): 100 M$ The cost of radio telescopes (1980): 3.8 x 10 -2 D 2.6 M$ The cost of space missions are an order of magnitude larger HST (1995): 4 G$ ESA (1995): minor missions (215 M$), major missions (645 M$), missions for exploration and/or return of samples (1-2 G$)

30 30 Strategies and Costs (4) The progress in productivity has been spectacular Factors contributing to a higher yield of information per hour from the instruments used: a careful choice of sites or orbits, improvements in detectors, better analysis of available photons, optimised image processing, expert systems improving real-time decision capability, optimising the use of available observation time There still does not exist any reasonably sure way of quantifying the yield in terms of discovery of a research instrument; neither volume of publications, nor the number of citations of those publications, would be sufficient in themselves for this purpose Unable to evaluate the intrinsic worth of a discovery or an observation


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