Astro 20first 20lecture

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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