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ASTR 1346:Chapter 11
How to measure Stars
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- distance
- luminosity/brightness
- temperature
- size
- evolutionary stage (H-R diagram)
- mass
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A full circle contains __ degrees
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360o
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1o = __ arc min
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60'
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1' = ___ arcsec
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60"
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Ways to measure apparent size and position of the objects
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degree, arc min, arc sec
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The family of distance-measurement techniques used by astronomers to chart the universe
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cosmic distance scale
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For nearby stars, we use __ method
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Stellar Parallax method
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The apparent displacement of foreground object relative to a distant background as the observer's position changes
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parallax
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Inversely proportional to distance
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parallax
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Formula for Distance (pc)
Unit of distance; defined as a distance at which parallax angle (the shift) is 1 arcsec (1")
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parsec
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1 Parsec = __ light years
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3.3 light years
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1 Parsec = ___ AU
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206,265
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For measuring the distances of the planets of our Solar System, we use ___ as a baseline
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earth's diameter
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For measuring the distance of nearby stars we use ___ as a baseline
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earth's orbit
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According to the spectrum, stars are classified into following categories (temperature sequence)
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O, B, A, F, G, K, M, L, T
temp decreasing ->
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Scientists used to classify stars based on their hydrogen line intensities, but now they classify stellar spectra based on ___
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temperature
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Temperature of "O" stars
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30,000 K
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Temperature of "B" stars
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20,000 K
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Temperature of "A" stars
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10,000 K
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Temperature of "F" stars
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7,000 K
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Temperature of "G" stars
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6,000 K
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Temperature of "K" stars
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4,000 K
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Temperature of "M" stars
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3,000 K
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Temperature of "L" stars
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1,300 - 2,500 K
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Temperature of "T" stars
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< 1300 K
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Failed Star
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"T" type star
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Sun is __ star
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G2
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Barnard star is a ___ star
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M5
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Astronomers further subdivide each spectral classification into __ subdivisions
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10
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Which is hotter & cooler star - G0 G1 G2 G3 G4 G5 G6 G7 G8 G9
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G0 = hotter star
G9 = cooler star
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Which type of stars are smallest in size?
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"M" stars
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Which type of star is the largest star?
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"O" stars
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We can estimate a star's effective temperature from its ___ or ___
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spectral type or black body curve
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We can estimate a stars luminosity from its ___ and ____
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apparent brightness and distance
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We can estimate a stars radius from ____
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radius-luminosity-temperature relationship
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Differences in Stellar Spectra are only due to ___
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different temperatures
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Is there a correlation between temperature and luminosity?
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Yes
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(1912) Danish astronomer Eljnar Hertzsprung and American astronomer Henry Norris Russell studied nearby stars to determine what?
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correlation between temperature and luminosity
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Plot of temperature and luminosity
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HR Diagram
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On HR Diagram, what is on the horizontal axis?
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temperature; hottest to coolest
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On HR Diagram, what is on the vertical axis?
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luminosity; faintest to brightest
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HR Diagram is also called __
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color-magnitude diagram
1. supergiants
2. giants
3. main sequence
4. white dwarfs
5. luminosity (Lsun)
6. temperature (K)
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Majority of stars that lie along a diagonal band in the HR-Diagram
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main sequence stars
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What percent of stars are Main Sequence Stars?
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90%
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Most of the stars on Main Sequence of HR-Diagram are __
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red dwarfs
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K and M stars with low luminosity
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red dwarfs
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A few of the stars on Main Sequence of HR-Diagram are __
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blue giants
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Hot, luminous stars
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blue giants
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Very few of the stars on Main Sequence of HR-Diagram are __
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blue supergiants
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Very hot and very luminous stars
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blue supergiants
1. blue giants
2. red dwarfs
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Very hot but very faint
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white dwarfs
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Stars on lower left of HR diagram
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white dwarfs
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Stars that must have smaller radius
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white dwarfs
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Stars that are much fainter and smaller than Main Sequence stars of the same temperature
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white dwarfs
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Cool but very luminous
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red giants
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Stars on upper right of HR-Diagram
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red giants
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Stars that must have much larger radius
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red gaints
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Stars that are much brighter and bigger than MS stars of the same temperature
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red giants
1. blue giants
2. luminosity
3. main sequence
4. white dwarfs
5. temperature
6. main sequence
7. red giants
8. red supergiants
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Indicate stellar radii (HR-Diagram)
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dashed diagonal lines
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For stars of the same radius (size), hotter stars are ___
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more luminous than cooler stars
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Radius-Luminosity- Temperature Relationship Formula
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luminosity is directly proportional to radius square and temperature to the power four
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____ gives us the information about the density of stars
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width of the lines in the spectrum
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By studying ___ we can distinguish the main sequence stars from other types of stars like gaints, dwarfs etc.
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width of lines
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Categorization of Stars
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luminosity class
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Tells us the approximate location of star on HR-Diagram
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full spectral classification
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The Sun's classification
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G2V (G2 main-sequence star)
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Betelguese's classification
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M2Ib (M2 supergiant star)
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Rigel's classification
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B8Ia (B8 bright supergiant star)
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Sirius's classification
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A1V (A1 main-sequence star)
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Alebaran's classification
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K5III (K5 giant star)
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Bright supergiants
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Ia
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Supergiants
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Ib
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Bright giants
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II
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Giants
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III
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Subgiants
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IV
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Dwarfs (MS stars)
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V
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This diagram is called
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luminosity class
1. luminous supergiant; 2. Ia
3. less luminous supergaint; 4. Ib
5. bright giants; 6. II
7. giants; 8. III
9. subgiants; 10. IV
11. main sequence; 12. V; 13. sun
14. surface temperature
15. luminosity
16. absolute magnitude
17. spectral type
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From O-K temperature ___ (decreases/increases)
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decreases
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The hotter the star, the ___
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brighter it is
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The cooler the star, the ___
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fainter it is
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__% of stars are main sequence stars
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99%
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Extremely hot, dim stars
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white dwarfs
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Extremely bright, low temperature stars
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red giant
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Difference between white dwarf and red giant is due to ___
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size
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___ relationship in Paralax
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inverse
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Shift in parallax becomes lesser and lesser as we __
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move away
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To increase shift in parallax, you need to __
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increase baseline
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Largest baseline we can get on Earth
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poles (any diagonally opposite points)
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__" = 1o
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3600"
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1" = width of a ___
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dime; 1 1/4 miles away
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Distance were parallax angle (the shift) is 1 arcsec (1")
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1 parsec (pc)
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If a Star A has more distance than Star B - Star A would have ___ parallax angle than Star B
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smaller
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Star X has a parallax angle of 5" and Star Y has an parallax angle of 10"
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Star X is twice as far as Star Y
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The smaller the angle, the ___ the star
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further
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(T/F) The closer the distance, the smaller the angle
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FALSE
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Star A is 3 parsecs away; Star B is 9.9 light years away. Which star is closer?
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Both stars are same distance
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Star A has a parallax of 3 arcsec. How far away is it in parsecs?
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Star is 1/3 (0.33) parsecs away
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Star X has parallax of 0.2 arcsec; Star Y has 2 arcsec. Which star is closest to Earth?
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Star Y
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Stars that are blue
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O, B, A type stars
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Stars that are red
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M type stars
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Stars that are yellow
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K, G, F type stars
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