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Unformatted text preview: Celestial Census Distances d = 1 / p" (pc)
d = 206,265 / p" (AU)
1 pc = 3.26 LY Radial Velocity
/ = v / c = (obs – ) / v = c / Proper Motion & Tangential Velocity T = 4.74 d = 4.74 / p" (km/s) where is in arcsec/year, d is in parsecs, and p" is in arcsec. Space Velocity The total space velocity is
V2 = VR2 + VT2 Flux-Distance-Luminosity
Brightness = Flux = Luminosity / 4 d2
b = F = L / d2
---------F2 d22 L1
= ----L2 Apparent Magnitudes
F2 / F1 = 100(m1 – m2)/5
log (xn) = n log (x)
log (F2 / F1) = (m1 – m2) / 5 log (100) = 2 (m1 – m2) / 5
m1 – m2 = 2.5 log ( F2 / F1 ) Absolute Magnitudes
m1 – m2 = 2.5 log ( F2 / F1 )
F = L / 4 d2
F(10) / F(d) = ( d / 10 )2
m – M = 5 log ( d / 10 ) Spectral Types Ionization via Temperature Diameters of Stars
L = 4 R2 T4
L R2 T4 Masses of Stars
Kepler’s 3rd Law
(M1 + M2) P2 = a3
M is in solar masses
P is in years, and
a is in Astronomical Units
(1 AU = mean Earth-Sun distance) Spectroscopic Binaries
Conservation of Angular Momentum
M1 / M2 = v 2 / v 1
v 2 / v 1 = r 1 / r2
Doppler Shift = v / c Mass-Luminosity Relationship L M 4.0
0.08 solar < M < 50 solar How Can We Visualize It All?
E. Hertzsprung (1911) and Norris Russell (1913) independently produced
plots to investigate stellar properties.
Today, those graphs are called H-R Diagrams. Hertzsprung-Russell Diagram PRS Question
1. The HR Diagram is a statistical plot of which two stellar parameters?
a. Luminosity and Surface Temperature
b. Radius and Mass
c. Mass and Surface Temperature
d. Luminosity and Mass
e. Radius and Luminosity Hertzsprung-Russell Diagram
The most significant feature of the
HR diagram is that the stars are not
distributed over it at random.
Rather they cluster into certain
parts of the diagram.
L R2 T4 Radii Relationships The Brightest Stars Of the 20 brightest, only 6 are within
10 pc of the Sun. The vast majority
of nearby stars, those less luminous
than the Sun, do not send enough
light across interstellar distances to
be seen without optical aid. The Nearest Stars
Only 3 of the 43 nearest stars
(other than the Sun) are among the
20 brightest stars: Sirius, Alpha
Centauri, and Procyon. The nearby
stars also tend to have large proper
motions. Also interesting is that 13
of the 44 stars are really binary- or
multiple-star systems. Total of 59
stars within 5 pc. The Nearest Stars
The most important datum is that most nearby stars are intrinsically faint.
Only 10 of the 50 nearest stars are visible to the unaided eye.
Only 3 are as intrinsically luminous as the Sun.
43 have luminosities less than 0.01 solar.
If the stars in our immediate stellar neighborhood are representative of the
stellar population in general, we must conclude that the most numerous stars
are those of low luminosity. In this sample, only about 1 star in 20 is as
luminous as the Sun. (90% are main sequence; 10% are white dwarfs) Hipparcos Distances to 20 pc Hipparcos Distances to 50 pc Hipparcos Distances to 100 pc Hipparcos Distances to 200 pc Main Sequence Masses Luminosity, Temp, Radius, & Mass Main Sequence Extremes
Most Luminous Least Luminous L = 50,000 solar L = 0.005 solar M = 60 solar M = 0.08 solar R = 400 solar R = 0.1 solar T = 45,000 K T = 3000 K O5 M5 PRS Question
2. Where do we find the most massive stars on the Main Sequence in the
a. Evenly distributed across the Main Sequence
b. No correlation of mass on the Main Sequence
c. Lower right end
d. Upper left end
e. Middle Section Further Distances
4. Take the Spectrum of the star.
Classify the Spectrum.
Use the HR Diagram to assign an Absolute Magnitude (M).
Measure the Apparent Magnitude (m).
m – M = 5 log ( d / 10 )
Spectroscopic Parallax The White Dwarfs Mass of the Sun but the Size of the Earth = 1.6 x 105 g/cm3
(one spoonful = 50 tons) ...
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- Spring '10