Chap 17 and 18 Flashcards
What two factors determine how bright a star appears to be in the sky?
Luminosity of a star and itβs distance
Explain why color is a measure of a starβs temperature.
The spectrum of colors, from red to blue correlate with the stars temperature. The more blue side of spectrum, the hotter, and the more red side of spectrum, the cooler.
What elements are stars mostly made of? How do we know this?
Stars are primarily made up of hydrogen and helium. We know this from measuring the stars spectral lines.
Name five characteristics of a star that can be determined by measuring its spectrum. Explain how you would use a spectrum to determine these characteristics.
1.) πΉππ
ππππ ππππππππ, find the Doppler shift (red-shift, blue-shift)
2.) πͺππππππππππ, use spectral lines
3.) πΊπππ, the smaller the star the more compact and higher pressure it is, so it has broader spectral lines, and vise versa for larger stars
4.) π»ππππππππππ, use Wienβs law and color of star
5.) πΉπππππππ, Doppler broadening of spectral lines for faster rotations
How do objects of spectral types L, T, and Y differ from those of the other spectral types?
They are known as brown dwarfs because they arenβt hot enough to fuse hydrogen, but can fuse deuterium.
The star Antares has an apparent magnitude of 1.0, whereas the star Procyon has an apparent magnitude of 0.4. Which star appears brighter in the sky?
Procyon, because the smaller the magnitude the more bright.
Order the seven basic spectral types from hottest to coldest.
OBAFGYKM
Oh boy, another freaking giraffe kicked mom
Brown dwarfs: LTY
How would two stars of equal luminosityβone blue and the other redβappear in an image taken through a filter that passes mainly blue light? How would their appearance change in an image taken through a filter that transmits mainly red light?
Blue filter: The blue star would appear brighter then red star
Red filter: The star star would appear brighter then blue star.
Two stars have proper motions of one arcsecond per year. Star A is 20 light-years from Earth, and Star B is 10 light-years away from Earth. Which one has the faster velocity in space?
The further star A is moving faster as it has a larger distance to produce the same arcsecond.
Suppose there are three stars in space, each moving at 100 km/s. Star A is moving across (i.e., perpendicular to) our line of sight, Star B is moving directly away from Earth, and Star C is moving away from Earth, but at a 30Β° angle to the line of sight. From which star will you observe the greatest Doppler shift? From which star will you observe the smallest Doppler shift?
Star B, which is moving away, will have the biggest doppler effect.
Star A, moving perpendicular, will have the smallest doppler effect.
Star A and Star B have different apparent brightnessβs but identical luminosities. If Star A is 20 light-years away from Earth and Star B is 40 light-years away from Earth, which star appears brighter and by what factor?
Star A is closer, and will be brighter by a factor of 1/4, so 4x times brighter
2x times away from Star A, inverse square law: 1/d ^2
1/2^2= 1/4
As seen from Earth, the Sun has an apparent magnitude of about β26.7. What is the apparent magnitude of the Sun as seen from Saturn, about 10 AU away? (Remember that one AU is the distance from Earth to the Sun and that the brightness decreases as the inverse square of the distance.) Would the Sun still be the brightest star in the sky?
1/10^2 = 1/100 = 0.01
2.512^x = 0.01
log 2.512^x = log 0.01
x (log 2.512) = log 0.01
x= log 0.0/ log 2.512 = -4.99
-26.7 - (-4.99) = -21.71
The star Sirius A has an apparent magnitude of β1.5. Sirius A has a dim companion, Sirius B, which is 10,000 times less bright than Sirius A. What is the apparent magnitude of Sirius B? Can Sirius B be seen with the naked eye?
2.512^x = 10^-4
x= log 10^-4/ log 2.512 = 9.99
-1.5 -(9.99) = -11.49
How does the mass of the Sun compare with that of other stars in our local neighborhood?
Itβs a lot bigger, only few are more massive, majority are smaller.
Name and describe the three types of binary systems.
π½πππππ ππππππ: two stars can be resolved by a telescope
πΊπππππππππππππ: spectral lines are doppler shifted showing orbital motion
π¬ππππππππ ππππππ: we observe a light curve as stars ecliptic one another
Describe two ways of determining the diameter of a star.
Stefan Boltzmann law and lunar eclipse of the star
You are able to take spectra of both stars in an eclipsing binary system. List all properties of the stars that can be measured from their spectra and light curves.
Radical velocity, size, composition, temperature, and rotation
How do we distinguish stars from brown dwarfs? How do we distinguish brown dwarfs from planets?
Brown dwarfs are on the infrared spectrum, they can fuse deuterium.
They have a lot more mass then planets as they are massive.
Describe how the mass, luminosity, surface temperature, and radius of main-sequence stars change in value going from the βbottomβ to the βtopβ of the main sequence.
Radius, temperature, and luminosity all increase in top main sequence stars.
Why do most known visual binaries have relatively long periods and most spectroscopic binaries have relatively short periods?
Visual binaries are further apart so they have a longer period based on keplerβs third law. Spectroscopic binaries are shorter apart so they have a shorter period.
There are fewer eclipsing binaries than spectroscopic binaries. Explain why.
Our perspective on Earth can change whether or not they are eclipsing based on their angle.
Suppose you want to search for brown dwarfs using a space telescope. Will you design your telescope to detect light in the ultraviolet or the infrared part of the spectrum? Why?
Infrared because brown dwarfs have lower luminosity and energy, making them only visible in infrared light
An astronomer discovers a type-M star with a large luminosity. How is this possible? What kind of star is it?
This type of star is called a red giant, itβs possible because itβs large surface, an example would be Betelgeuse
If two stars are in a binary system with a combined mass of 5.5 solar masses and an orbital period of 12 years, what is the average distance between the two stars?
D^3= (m1+ m2) P^2
m1+m2= 5.5 M
p= 12
D= 9.25 AU
The lowest mass for a true star is 1/12 the mass of the Sun. What is the luminosity of such a star based upon the mass-luminosity relationship?
L= M ^3.5
M= 1/12
L= 1/12 ^3.5 = 1.67 x 10^-4 solar lum
The star Betelgeuse has a temperature of 3400 K and a luminosity of 13,200 LSun. Calculate the radius of Betelgeuse relative to the Sun.
Lb / Ls β>
4pi (Rb^2 delta Tb^4) / 4pi (Rs^2 delta Ts^4)
13200 ls/ ls = Rb^2 (3400)^4/ Rs^2
(5800)^4
Rb^2/ Rs^2 = 13200 (5800)^4/ 3400 ^4
Rb= sqaure root(111,782) = 334
Rb= 334 Rs
