astro 20first 20lecture
DESCRIPTION
Astrophysics lectureTRANSCRIPT
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COURSE 251- NOTES FOR FIRST LECTURE ON ASTROPHYSICS (from various sources including wikipedia)
1. Equatorial coordinates
2. Galactic coordinates
(0,0) galactic longitude l
galactic latitude b
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3. Basic stellar parameters
Direction or co-ordinates Right Acension RA, declination Energy flux L/4d2 Apparent magnitude
m = -2.5log10(L/4d2) + constant Distance d light years or parsecs (1 ly = 3.26 pc)
Luminosity L Absolute Magnitude M = -2.5log10(L/410pc2) + constant
Colour index B V = mB mV = -2.5log10(Lblue/Lvisual) Distance modulus m-M = -2.5log10(10pc2/d2)
Temperature From colour
4. Stellar distances
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5. Famous stars Bright stars
Constellation Name Type mV distance RA hr min
Dec deg min
- Sun G2 V -26.74 1 AU - - Eri Achenar B3 V 0.51 36 pc 1 37.0 -57 20 UMi Polaris F8 I 1.99 208 pc 2 12.5 +89 11 Pir Mirfak F5 I 0.86 175 pc 3 22.9 +49 47 Tau Aldebaran K5 III 0.86 21 pc 4 34.8 +16 28 Ori Rigel B8 I 0.14 276 pc 5 13.6 -08 13 Aur Capella G8 III 0.05 14 pc 5 15.2 +45 59 Ori Bellatrix B2 III 1.64 144 pc 5 24.0 +6 20 Tau Elnath B7 III 1.65 92 pc 5 25.0 +28 36
Nearby stars
Con Name Type mV Distance RA Dec - Sun G2 V -26.74 1 AU - -
Cen Cen A G2 V -0.1 1.3 pc 14.38.4 -60 46 Cen Cen B K4 V 1.40 1.3 pc 14.38.4 -60 46 CMa Sirius A1 V -1.47 2.7 pc 6 44.2 -16 42 CMi Procyon F5 V 0.37 3.5 pc 7 38.2 +5 17 Lyr Vega A0 V 0.04 8 pc 18 36.2 +38 46 PsA Foralhaut A3 V 1.15 7 pc 22 56.5 -29 44 Aql Altair A7 IV-V 0.77 5 pc 19 49.8 +8 49
6. Colour-Magnitude (Hertzsprung-Russell) diagram
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7. Stellar evolution and stellar ages
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8. Main sequence stars
Class Temp Color Mass (solar
masses)
Radius (solar radii)
Luminosity(bolometric
solar luminosity)
H lines
Fraction of all main sequence
stars O 33,000 K blue 16 6.6 30,000 Weak ~0.00003%
B 10,00033,000 K blue to blue white 2.116 1.86.6 2530,000 Medium 0.13%
A 7,50010,000 K white 1.42.1 1.41.8 525 Strong 0.6%
F 6,0007,500 K yellowish white 1.041.4 1.151.4 1.55 Medium 3%
G 5,2006,000 K yellow 0.81.04 0.961.15 0.61.5 Weak 7.6%
K 3,7005,200 K orange 0.450.8 0.70.96 0.080.6 Very weak 12.1%
M 3,700 K red 0.45 0.7 0.08 Very weak 76.45%
NOTE: The spectral classes O through M are subdivided by numerals 0 to 9. For example, A0 denotes the hottest stars in the A class and A9 denotes the coolest ones. The Sun is classified as G2.
9. Stellar Spectra
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Spectrum of a K5V star:-
10. Stellar temperature
Colour B-V Temperature K Type Sub-type -.35 40,000 O O0O9 -.16 15,500 B B0B9 +.13 9,900 A A0A9 +.42 6,580 F F0F9 +.70 5,520 G G0G9 +1.18 4,130 K K0K9 +1.63 2,800 M M0M9
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11. Stellar masses and sizes from binaries
12. Stellar radii from luminosity
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13. Stellar composition from spectra
14. Type I, II and III stars
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15. External galaxies
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16. Extra-solar planets