Exam 2 review Flashcards
What is Luminosity?
The total amount of energy at all wavelengths that a star emits per second. Also could be referred to as apparent brightness.
What is Apparent Brightness?
The amount of a stars energy that reaches a given area each second here on Earth. What we see in the sky.
For two stars of the same apparent brightness, the star closer to the Sun will generally have what?
A lower luminosity.
Magnitude Scale
According to the naked eye, the brightest stars were of magnitude 1, and the dimmest of magnitude 6. Now we know stars that have negative magnitude and large positive magnitudes.
How many times brighter is a magnitude 6 star compared to a magnitude 1 star.
100 times brighter
Which sign leads to larger magnitudes, +, or -?
Negative apparent magnitudes are brighter.
What do you need in order to calculate a star’s luminosity?
Apparent Brightness and Distance to the Star
Color spectrum (ranking) of stars
(blue) O B A F G K M (red)
(hot) (cool)
What can analyzing the spectrum of a star tell us?
Star size, composition, Radial Velocity, Rotation
What do narrow spectral lines from a star imply?
Lower density of gasses in photosphere
What can the doppler effect tell us about the motion of the star?
Translational or rotational velocity
Are there more low luminosity stars or more high luminosity stars?
Low luminosity, this implies that the stars have a relatively low mass as well.
What is a binary star system? What are the different types of binary star systems?
A solar system with two stars. A visual binary is when you can see both stars using a telescope. A spectroscopic binary is one that which looks like one star but is revealed to be two when using spectroscopy.
Mass luminosity relation
Luminosity is proportional to the square of the mass
A binary star system has what qualities?
composed of two stars
is held together by gravity
is useful to find the mass of he component stars
is not always visually detectable
What are some techniques for measuring the diameter of stars?
F = σT^4 (stephan boltzman)
or using a moon passing infront to compare diameter to luminosity decrease
The H-R diagram plots what?
plots luminosity versus surface temperature
Are stars bright because of luminosity or proximity?
Brightness is more typically due to luminosity then proximity
What are the two most important intrinsic properties for classifying stars?
Luminosity and Surface Temperature
What is parallax?
apparent motion of objects against distant background from two vantage points.
What is the “distance ladder”
It depicts methods to measure distance depending on how far away the object is.
What is an arc minute?
1/60 of a degree
relationship to distance in parsecs to angle in arcseconds
d(parsec) = 1/θ(arcseconds)
spectroscopic parallax
1) measure apparent magnitude
2) assume star lays on the main sequence ( this gives absolute magnitude ( luminosity))
3) apply inverse square law to determine distance
What happens to absorption lines when atmospheric pressure increases
absorption lines get broader as pressure increases
What makes a star a Variable star?
Stars that are seen to vary in brightness
What do you call a graph that shows how the brightness of a variable star changes with time?
a light curve
RR Lyrae stars
such stars have essentially the same luminosity curve, with periods from 0.5 to 1 day, all have the same luminosity
Cepheid variable stars
Cepheid periods range from about 1 to 100 days, have a luminosity that is strongly correlated with the period of their oscillations
What is interstellar matter?
The interstellar medium consists of gas and dust.
Gas is atoms and small molecules, dust is larger clumps of particles
How dense is interstellar gas?
one atom of gas per cubic centimeter
Interstellar gas is composed primarily by…
90% hydrogen, 9% helium, and 1% heavier elements
What is ionized hydrogen?
Gas that is found in Emission nebulae
What are Emission nebulae?
hot, glowing area associated with the formation of large stars usually part of a larger dust cloud
Where is Atomic Hydrogen found?
Found in cold regions without stars between dust clouds
Where is Molecular hydrogen found?
Found in cold dark dust clouds
What are HII regions?
Emission Nebulae, they are composed of atomic hydrogen gas that is ionized by near-by stars
What is the spin flip of an electron?
When an electron switches its spin direction, it is a way to emit energy without changing atomic orbital
How do we see Interstellar Matter
Dust clouds absorb blue light, interstellar matter exists in dark regions
What is a nebula?
A region of space that is clearly distinguishable through a telescope, but is not sharply defined like a planet or a star
Compare nebula size and density
Nebula’s are MASSIVE with low density
What are cosmic rays?
a third class of particle in interstellar space, high-speed atomic nuclei and electrons
Where do cosmic rays come from
supernova explosions, difficult to tell because of direction change due to magnetic fields
Describe stage 1 in star formation
Interstellar cloud starts to contract, usually triggered by shock or pressure wave from nearby star. As it contracts, cloud fragments into smaller pieces. Takes a couple million years.
Describe stage 2 of star formation
individual cloud fragments begin to collapse, once the density is high enough there is no further fragmentation. this contraction produces energy.
Describe stage 3 of star formation
Spherical gas ball about the size of our solar system,. density is massive, radiation cannot escape. interior is about 10,000 K
Describe stage 4 or star formation
The core of the cloud is now a protostar, and makes its first appearance on the H-R diagram
describe stage 5 of star formation
The protostar is still not in equilibrium – outward pressure is becoming a force, but all heating still comes from the gravitational collapse. gets nebular disk, possibly planets.
Describe T-Tauri phase of star formation
violent surface activity, extremely strong protostellar winds, interaction of winds and disk cause bipolar “jets” emitting energy
Describe stage 6 of star formation
The core reaches 10 million K, and nuclear fusion begins, PROTOSTAR HAS BECOME A STAR, star continues to contract and increase in temperature, lasts 30,000,000 yr or so
Describe stage 7 of star formation
The star is in equilibrium, it has reached the main sequence and will remain there as long as it has hydrogen to fuse in its core
compare a protostars luminosity to its temperature
luminosity increases drastically as temperature rises (stephan boltzman)
What is a Brown Dwarf
if the mass of the original nebular fragment is too small, nuclear fusion will never begin, failed star, jupiter
What is an open cluster
loose irregular cluster, found mainly in the plane of the Milky Way, contains few hundred to a thousand stars
Globular clusters are…
spherical clusters of stars with the absence of massive main-sequence stars, and the heavily populated red giant region, found away from the galactic plane, at least 10 billion years
what is an exoplanet
planet outside the solarsystem
What is a planetary nebula
an old star that is shedding its outer layers
Describe stage 8 of stellar evolution
subgiant status, 100 mill yrs. when the fuel in the core depletes, the core contracts, hydrogen fuses in a shell outside the core
–> energy production increases and star gets brighter
Describe stage 9 of stellar evolution
red giant status
its luminosity increases enormously due to its large size. He core is tiny, but has 25% of the stellar mass.
Describe stage 10 of stellar evolution
helium fusion
the helium flash- when helium fuses rapidly, luminosity spikes huge for a short period of time
Describe stage 11 of star evolution
giant branch, asymptotically
helium in cor fuses to carbon and oxygen
now there are two shells, outward pressure swells the star
evolution of star clusters
turn off point lowers the older the star cluster gets
do all stars undergo the helium flash
NO, stars between 4M and 10M do NOT undergo helium flashes
Star cores from out to in
Hydrogen, Helium, Carbon, Oxygen, Neon, Magnesium, Silicon, Iron
Relate a stars mass to its life span
higher mass, lower lifespan
Describe stage 13 of stellar evolution
Fusion ceases, the envelope blows off, leaving a white dwarf to slowly cool
Describe stage 14 of stellar evolution
White dwarf continues to cool, no more contraction due to electron pressure remains the size of Earth, temperature approaches 0 k, 1 trillion years –> star is dead.
What is a neutron star
A star that is so dense that electrons are squeezed into the atomic nucleus. They then combine with protons to form neutrons and neutrinos
What is a supernova
one time violent explosion, once it happens, there is little or nothing left of the progenitor star
What is a Type II supernova
Fusion of iron core ceases, temperature is 10 bill k
protons and electrons are crushed together, creates shock wave
Type Ia supernova
Type Ib supernova
Type Ic supernova
Type Ia - posses Si lines in the spectra
Type Ib - Posses He lines in the spectra
Type Ic - anything else
What is a black hole
post supernova, so dense even electromagnetic radiation cannot escape
What is a Novae
a star that flares up very suddenly and then returns slowly to its former luminosity
What is the Chandrasekhar limit
A maximum mass that a white dwarf can have before it collapses and supernovas
