Chapter 12 Flashcards
What are some properties of stars?
- Luminosity
- Surface Temperature
- Mass
What do stars form?
Stars form the gravitational collapse of clouds (nebula)
What are stars composed of?
~ 75% hydrogen
~ 25% helium
< 2% heavier elements
What is Luminosity?
Total amount of energy per second that a star radiates (emits into space)
- Luminosity of our sun is
3. 8x10^26 watts (joules/s)
What is Apparent Brightness?
Total amount of energy per second per area that reaches us from a star
Luminosity vs. Apparent Brightness
- Luminosity is a constant property of a star
- Apparent Brightness of a star depends on distance, the farther away the smaller the AB
What is the formula for Apparent Brightness?
AB= Luminosity/4(pie)d^2
d=distance between star and Earth
What are the Luminosity Range of Stars?
10^6 to 10^-4 (1,000,000 to 0.0001)
What is Parallax?
The shift in apparent position of an object in the sky when seen from different positions due to relative proximity
How can we measure distance through stellar parallax?
If the star is sufficiently close, we can measure its change of position with respect to distant stars as the Earth orbits the Sun. (Smaller the distance, larger parallax angle)
What is a parsec?
Distance of an object that presents a stellar parallax of 1 arc sec.
1 parsec=3.26 light years
What is the classification of Apparent Magnitude?
Used with whole numbers from 1-6.
1 being stars with largest AM and 6 being stars with smallest AM that is visible to the naked eye.
What is the formula for Apparent Magnitude?
m= -2.5*log10(ApparentBrightness)+K
K= -11.49 in CGS units [cm/g/s]
What is Absolute Magnitude?
Apparent Magnitude of a star if it were placed at a distance of 10 parsecs from Earth
What is the formula for Absolute Magnitude?
M= -2.5log10 (Luminosity/4(pie)10pc^2)+ K
What is Stellar Temperature?
Refers to the temperature of a star’s surface.
Sun’s Stellar Temperature= 5,800 K
How can we measure the Stellar Temperature of a Star?
Through the frequencies of light it emits. The hotter a star, the higher the light frequencies. “Cold Stars” will emit infrared and appear red. “Hot Stars” will emit ultraviolet and appear violet. We estimate a star’s stellar temperature by its color.
What is the Stellar Classification based on Stellar Spectra from hotter to cooler?
O-stars: >30,000 K B-stars: 30,000-10,000 K A-stars: 10,000-7,500 K F-stars: 7,500-6,000 K G-stars: 6,000-5,000 K (our sun) K-stars: 5,000-3,500 K M-stars: <3,500 K
What are Binary Stellar Systems?
Systems composed of 2 stars. Common in our galaxy (about 1/2 of stars in our galaxy are found in binary systems)
What are visual binary systems?
Systems where we can directly see both stars
What is Eclipsing Binary Systems?
Systems where we can detect a change in apparent brightness during eclipses
What is Spectroscopic Binary Systems?
Systems that are detected through Doppler Shifts of the spectral lines as the stars orbit each other.
- When spectral line increases frequency (blue shifted)
- When spectral line decreases frequency (red shift)
What is Stellar Mass?
Stellar Masses im binary systems can be determined through Newton’s Law of Gravitation if we can measure their period “P” and one of:
A) distance between the 2 stars or
B) orbital velocities
P^2=(4(pie)^2/G(M1+M2)a^3
What are some patterns in Stellar Parameters?
- Horizontal axis: Surface temperature
- Vertical axis: Stellar Luminosity
- Stars in the upper right are called “Supergiants” and “Giants” because their size is larger and more luminous
- Stars in the lower left are called “white dwarfs” because their size is smaller and less luminous
