Observational Astronomy

Slides:



Advertisements
Similar presentations
Astronomy Notes to Accompany the Text
Advertisements

1. absolute brightness - the brightness a star would have if it were 10 parsecs from Earth.
Oct. 18, Review: Telescopes – their primary purpose… Across the full EM spectrum (radio through very high energy gamma- rays) telescopes fundamentally.
WHY STUDY ASTROPHYSICS?  To gain an understanding of our universe and our role in it Learn about how the universe operates --> modern science  Observations.
Light and Telescopes Please pick up your assigned transmitter
Optical Astronomy Imaging Chain: Telescopes & CCDs.
Stellar Continua How do we measure stellar continua? How precisely can we measure them? What are the units? What can we learn from the continuum? –Temperature.
Many sources (hot, glowing, solid, liquid or high pressure gas) show a continuous spectra across wavebands. Emission spectra Elements in hot gases or.
The Origin of Modern Astronomy Chapter 4:. Isaac Newton 1689.
Telescopes (Chapter 6). Based on Chapter 6 This material will be useful for understanding Chapters 7 and 10 on “Our planetary system” and “Jovian planet.
ENERGY a proposal for a Multi-channel Cmos Camera F. Pedichini, A. Di Paola, R. Speziali INAF Oss. Astr. Roma h e-
Photometry. Measuring Energy Photometry measures the energy from a source using a narrow range of wavelengths. –Visual wavelengths from nm –Narrower.
Observational Astrophysics II: May-June, Observational Astrophysics II (L2)
Observational Astrophysics II: May-June, Observational Astrophysics II (L2) Getting our NIRF What do want to do? 1.Image a selected.
This Set of Slides This set of slides deals with telescopes. Units covered: 26, 27, 28, 29, and 30.
Astronomical Spectroscopy
Astronomical Instrumentation Often, astronomers use additional optics between the telescope optics and their detectors. This is called the instrumentation.
Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?
Naoyuki Tamura (University of Durham) Expected Performance of FMOS ~ Estimation with Spectrum Simulator ~ Introduction of simulators  Examples of calculations.
8 September Observational Astronomy TELESCOPES, Active and adaptive optics Kitchin pp
5 Components Common to All Optical Spectrometers Source Transparent Sample Holder Wavelength Selector Radiation Detector Signal Processor and Readout.
4. Telescopes Light gathering power and resolution Optical and radio telescopes Limitations of Earth’s atmosphere and satellite missions. Instruments (prism.
Chapter 6: The Tools of the Astronomer. Telescopes come in two general types Refractors use lenses to bend the light to a focus Reflectors use mirrors.
How do Astronomers know what they know? Almost everything we know about Astronomy was learned by gathering and studying light from distant sources Properties.
Announcements No lab this week due to observing night last night There will be a lab after class next week. If the skies are clear expect to stay out until.
Radiation Kirchoff’s Laws  Light emitted by a blackbody, a hot opaque body, or hot dense gas produces a continuous spectrum  A hot transparent gas produces.
Spectrophotometer Prof.Dr. Moustafa M. Mohamed Vice Dean Faculty of Allied Medical Science Pharos University in Alexandria, EGYPT.
14 October Observational Astronomy SPECTROSCOPY and spectrometers Kitchin, pp
天文觀測 I Optical Telescope. Telescope The main purposes of astronomical telescope: –To collect the weak light (photons) from sky. –To map the sky to image.
First results of the tests campaign in VISIBLE in VISIBLE for the demonstrator 12 October 2007 SNAP Collaboration Meeting Paris Marie-Hélène Aumeunier.
15 October Observational Astronomy Direct imaging Photometry Kitchin pp ,
18 October Observational Astronomy SPECTROSCOPY and spectrometers Kitchin, pp
Astronomical Spectroscopy Notes from Richard Gray, Appalachian State, and D. J. Schroeder 1974 in “Methods of Experimental Physics, Vol. 12-Part A Optical.
Multi-slit spectroscopy In sky-noise dominated conditions (most interesting!) the use of slits is essential: eg: Faint object, extra-galactic, surveys:
NORDFORSK Summer School, La Palma, June-July 2006 NOT: Telescope and Instrumentation Michal I. Andersen & Heidi Korhonen Astrophysikalisches Institut Potsdam.
10/26/20151 Observational Astrophysics I Astronomical detectors Kitchin pp
ASTR 3010 Lecture 18 Textbook N/A
Asteroids Image Calibration and Setup Making a Lightcurve What is a Lightcurve? Cole Cook  Physics and Astronomy  University of Wisconsin-Eau Claire.
Bear Elder Paul Lim LUMINOSITY, APPARENT BRIGHTNESS, AND STELLAR LUMINOSITY.
The Study of IFU for the Li Jiang 2.4m Telescope ZHANG Jujia 张居甲 Yun Nan Astronomical Observatory. CAS Sino-French IFU Workshop Nov Li Jiang.
1 Leonardo Pinheiro da Silva Corot-Brazil Workshop – October 31, 2004 Corot Instrument Characterization based on in-flight collected data Leonardo Pinheiro.
Class 4 : Basic properties of stars
PACS SVR 22/23 June 2006 Scientific/Performance Requirements1 PACS Science and Performance Requirements A. Poglitsch.
Newton’s Experiments with Light. Electomagnetic Waves.
Telescopes. Light Hitting a Telescope Mirror huge mirror near a star * * * small mirror far from 2 stars In the second case (reality), light rays from.
Astronomy Big Idea: The sun is one of billions of stars in one of billions of galaxies in the universe.
SNAP Calibration Program Steps to Spectrophotometric Calibration The SNAP (Supernova / Acceleration Probe) mission’s primary science.
1.Stable radiation source 2.Wavelength selector 3.Transparent sample holder: cells/curvettes made of suitable material (Table 7- 2) 4.Radiation detector.
Stellar Continua How do we measure stellar continua?
Looking for a Color-Luminosity Relationship for AGN July 16, 2012 prepared by Varoujan Gorjian NITARP Scientist.
Lecture 13 Light: the Cosmic Messenger Telescopes and Observational Astronomy.
Atmospheric extinction Suppose that Earth’s atmosphere has mass absorption coefficient  at wavelength. If f 0 is flux of incoming beam above atmosphere,
MPI Semiconductor Laboratory, The XEUS Instrument Working Group, PNSensor The X-ray Evolving-Universe Spectroscopy (XEUS) mission is under study by the.
July 25th, 2000WFC3 Critical Science Review1 Performance Summary in Key Science Areas Verify that WFC3 as designed is capable of carrying out the WFC3.
Astronomical Spectroscopic Techniques. Contents 1.Optics (1): Stops, Pupils, Field Optics and Cameras 2.Basic Electromagnetics –Math –Maxwell's equations.
 From the ground the atmosphere distorts images.  Light pollution from streetlights, city lights, car lights, and more hinders the seeing conditions.
CASE spectrograph Spectrograph Optical Specifications
Astronomical Spectroscopic Techniques
© 2017 Pearson Education, Inc.
© 2017 Pearson Education, Inc.
Single Object & Time Series Spectroscopy with JWST NIRCam
Chapter 5 Telescopes.
“It is important that students bring a certain ragamuffin, barefoot, irreverence to their studies; they are not here to worship what is know, but to question.
Intra-pixel Sensitivity Testing Preliminary Design Review
Observational Astronomy
Astronomical Photometry
4. Telescopes Light gathering power and resolution
The Study of Light Picture taken
Optics and Telescopes Chapter Six.
Modern Observational/Instrumentation Techniques Astronomy 500
Presentation transcript:

Observational Astronomy Direct imaging Photometry Kitchin pp. 329-340, 357-366 5 May 2019

Astronomical Imaging Deep Wide or Specific goal: As many objects as possible (e.g. clusters, star-forming regions) As large range of surface brightness as possible (e.g. galaxies)

Wide Field Imager: VST The VST is a 2.6m f/5.5 Cassegrain telescope Corrected FoV is 1.5º square with angular resolution of 0.5” Focal plane is equipped with a 16kx16k CCD mosaic camera with a 15 pixel

VST Optics Optical layout including ADC, field corrector etc. Plate scale: focal length=2.6m5.5=14.3m 1”=  /180º/3600≈510-6 rad Resolution element: 0.5”  0.5  510-6 rad  14.3m ≈ 35 ≈ 2.3 CCD pixel (nearly perfect Nyquist sampling)

Sampling Theorem (Whittaker-Nyquist-Kotelnikov-Shannon sampling theorem) The sampling frequency must be at least twice the highest frequency of the signal. For Gaussian PSF where  is standard deviation and  is HWHM. What is the shortest period  one can detect? FWHM= Different samplings: -Once per period -Twice per period -Nyquist sampling

A general purpose telescope VLT UT (8.2m f/13.4): focal length=8.2m13.4=108.8m Plate scale in Cassegrain: 510-6 rad  108.8m ≈ 530/arcsec VLT+FORS FOcal Reducer/low dispersion Spectrograph

Focal Reducers Purpose: adjusting plate scale Side benefits: collimated beam is good for filters

NOT workhorse: ALFOSC

Unconventional instrument: FORS Two resolutions: 0.2” and 0.1” by changing collimators and CCD binning

Filters Broad band filters (UBV system, Johnson H.L. & Morgan W.W.: 1953, ApJ, 117, 313)

Broad-Band Filter Technology Color absorption glasses: blocking (high absorption shorter than certain wavelength while highly transparent at longer wavelengths) or bell-curve (sharp cut-off at shorter wavelength and gradual drop towards longer wavelength) Transmission is high, up to 75-90%

Narrow-Band Filter Technology Interference coatings: Multiple (up to 20) dielectric layers producing interference between internal reflections Create multiple transparency windows at different wavelengths Must be combined with broad-band filters Transmission is low, around 20-30%

Chromatism and other problems Filters are best used in parallel beam, otherwise they introduce chromatism They also shift focal plane (transparent glass plates) Slight tilt is used to avoid ghosts (shift of optical axis) and fringing Transmitted light Reflected light

Transmission Function

Photometry Classical one-channel photometer:

What do we measure and how? Magnitudes: Filters: a and b are selected such that Vega will be 0 magnitude in all colors Interstellar extinction: objects with the same SED located in different direction and distances will have different magnitudes (The main source of extinction is the scattering and absorption-heating of the dust particles and their main effect is to "redden" the energy distribution). Color excess:

More What and How (II) The variation of extinction with wavelength is similar in different directions: we measure color excess in one band then scale it to other bands. Knowing scaling parameters (in principle) allows to convert apparent magnitudes m to absolute magnitudes M. Absolute magnitude is the apparent magnitude of the same object at a distance of 10 parsecs: d is the distance and A is the interstellar extinction, which can be estimated from the color excess in B-V and scaled:

More What and How (III) Absolute magnitude M does not a measure the total irradiance. Bolometric magnitude M(bol) is defined as the absolute magnitude that would be measured by an ideal bolometer exposed to all of the radiation from the star. The relation between bolometric magnitude and the absolute magnitude MV requires the knowledge of the bolometric correction B.C.: Traditionally B.C. for solar type stars is set to -0.07 and it grows for hotter and cooler objects.

Absolute and differential photometry Radiation in a given band is affected by the atmosphere, telescope, photometer and detector. All of these must be calibrated. Absolute photometry is done either from space or with absolute calibration e.g. against a black body standard source.

Absolute and differential photometry (cont’d) Once absolute measurements are done for a few objects they can be used as standards. Differential photometry measures flux difference in a given band between a target and a standard. Observations should be close on the sky and in time. Classical sequence: <selecting band>:<standard> - <target> - <standard>

CCD Photometry Many objects at once (standards and targets) Large dynamic range PSF is spread over several pixels Pixels have different sensitivity and color sensitivity Photometry of extended sources

Next time… Astronomical detectors