Introduction to Astronomy 2019-2020 STISTK-10 Rijksuniversititet Groningen / Kapteyn Astronomical Institute. Lecture 3b (Images and Spectra)

2. IMAGES AND
SPECTRA
• Measuring Brightness
(usually in different
wavelength bands)
Photometry
• Measuring features in an
object's spectrum
Spectroscopy

3. IS THAT WHAT IT REALLY LOOKS LIKE?
GOAL IS TO SEE WHAT YOU CAN’T SEE!!

4. CCD + FILTER WHEEL

5. COLOURS BY
COMBINING
OBSERVATIONS IN
DIFFERENT FILTERS
(BROAD AND NARROW BAND)

6. HUBBLE SPACE TELESCOPE FILTERS (WF3/ACS)

7. ImageProcessingisKing

8. Image in multiple wavelengths
Identify objects and measure
Learn

9. THIS OBJECT IS A…

10. HOT AND COOL STARS IN RED AND BLUE FILTERS

11. THE COOL STAR
MUST BE…

12. SPECTRA CAN EXTEND OUR UNDERSTANDING
Why not always take spectra then?
• Harder to obtain, map, and analyse
• Light is dispersed so you need more and
more light as you increase spectral resolution
• To add exposures need to keep alignment
very steady, as fewer references between
images
• Need images to understand structures
Information about
Composition
Information about
velocity
(red/blue shift)
Information about
physical processes
and parameters

14. Hot
Black
Body
Cloud of Gas
Absorption Spectrum
Emission SpectrumContinuum Spectrum
STAR
Absorption Spectrum
Structure of a Star

15. Spectral lines (Absorption or Emission) provide a “Chemical Fingerprint”

17. LINES ARE FROM
TRANSITIONS
(HERE HYDROGEN)
• Balmer lines to the n=2 state
are in the visible spectrum
• Cooler stars have insufficient
n=2 population for
absorption
• Hotter stars have also
insufficient n=2 population
for absorption
(nanometers)
 =
ℎ𝑐
∆𝐸

18. LINES DEPEND ON
TEMPERATURE AND DEFINE
SPECTRAL TYPE
Spectral types are alphabetical in the
strength of Hydrogen absorption lines;
before they realized that HI absorption
would get lower in stars that are too hot.
O B A F G K M

19. Wavelength (nm)

20. Rest Frame
Blue Shifted
Red Shifted
VELOCITY INFORMATION (RED SHIFT / BLUE SHIFT)
Redshift: z =
∆

=
1+ 𝑣 𝑐
1−𝑣/𝑐
− 1 ≈
𝑣
𝑐
(for v ≪ c)

21. SINGLE POINTING
SPECTROGRAPH:
SLOW AS YOU HAVE TO
POINT EVERYWHERE!
(BUT… FIRST “DISCOVERY” OF A BLACK HOLE)

22. PRISM SPECTRA: NOT BRILLIANT AS ALL OVERLAPPING
HERE – AN OPEN STAR CLUSTER

23. LONG SLIT SPECTRA: INFORMATION ALONG ONE IMAGE AXIS
HERE – EMISSION FROM GAS IN THE CENTRE OF A GALAXY

24. INTEGRAL FIELD SPECTRA: A ‘3D’ VIEW
HERE – VELOCITY OF STARS IN A GALAXY
VELOCITY: BLUE MOVES TOWARDS US AND RED MOVES AWAY
DISPERSION: RANDOM MOTIONS OF THE STARS (LIKE TEMPERATURE OF
GAS)

25. FROM MY PHD!!
LONG SLIT SPECTRUM BLACK HOLE HUNTING

26. IF AN OBJECT IS
MOVING AWAY
FROM US IT IS…

27. A STAR IS LIKE A
HOT BLACK
BODY, WITH A
COOLER
ATMOSPHERE…
IT WILL HAVE:

28. A STAR
FORMING
NEBULA IS A
LARGE CLOUD
OF GAS… IT
WILL HAVE:

29. A DARK NEBULA
IS A LARGE
CLOUD OF DUST
OR GAS IN
FRONT OF
OTHER
SOURCES… IT
WILL HAVE:

30. A REFLECTION
NEBULA IS A
GAS CLOUD
WHICH
ABSORBS AND
RE-EMITS LIGHT
FROM NEARBY
STARS… IT WILL
HAVE:

31. QUESTIONS?

32. DON’T FORGET – START
CREATING YOUR A5 NOTEBOOK!!

33. CONCEPT BANK
Images Spectra Filters Types of Spectra Doppler Effect
Composition
Continuum
Spectrum
Absorption
Spectrum
Emission
Spectrum
Colours
Emission and
Absorption Lines
Hydrogen Lines
Types of Spectra
from different
objects

34. IN THE BOOK THIS WEEK
More Depth
3.1 Observing Through the Atmosphere
Chapter 4: Photometric Concepts and
Magnitudes
5.2 The Hydrogen Atom
5.6, 5.7, 5.8 Spectra, Black Body Radiation,
Temperature
9.5 The H-R Diagram
Mega Depth
3.3 Detectors and Instruments
Chapter 5: Radiation Mechanisms
Chapter 9: Stellar Spectra