Week 6

Review this spectral data for five stars. Which star is the hottest? Coolest? Most luminous? Least luminous? 1G, main sequence 2K, giant 3K, main sequence 4O, main sequence 5M, main sequence

4,5,4,5

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. Select one: A. Spin and radial velocities, chemical composition, and mass B. Spin and radial velocities, chemical composition, and radii/diameters C. Spin and transverse velocities, chemical composition, and radii/diameters D. Spin and radial velocities, mass, and radii/diameters

B

Who was the astronomer who is the "H" in H-R diagram?

Hertzsprung

The evolutionary track for a star of 1 solar mass remains nearly vertical in the H—R diagram for a while. How is its luminosity changing during this time? Its temperature? Its radius? Select one: A. Temprature is dropping along with radius while the luminosity remains constant. B. Luminosity is dropping along with radius while the surface temperature remains constant. C. Radius is dropping while the surface temperature remains and luminosity remain constant. D. Luminosity is dropping along with radius and surface temperature. Clear my choice

Luminosity is dropping along with radius while the surface temperature remains constant.

Stars have mass greater than _________ of the Sun's mass; __________ generally have between 1/100th and 1/12th the mass of our Sun; planets have masses ______ than that. Select one: A. 1/12th, brown dwarfs, less B. 1/12th, dwarfs, less C. 1/20th, brown dwarfs, more D. 1/5th, brown dwarfs, less Clear my choice

a

Tauri stars show a stellar wind, a flow of atomic particles away from the star. While the star is still surrounded by an __________ around its equator, the wind is stopped in that direction, and it emerges far more effectively in two ________, perpendicular to the accretion disk. As these jets plow into the surrounding material, they can occasionally collide with a somewhat-denser lump of gas nearby, transferring energy and exciting its atoms, causing them to emit light. These glowing regions are called ________ objects.

accretion disk, jets, Herbig-Haro (HH)

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life? Select one: a.forming from a reservoir of cosmic material b.fusing hydrogen into helium in their cores c.letting go of a huge outer layer d.dying e.you can't fool me; so many stars are on the main sequence that there is no special stage in a star's life that can be identified with it Clear my choice

b

In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)? Select one: a.along the right (vertical axis) b.along the bottom (the horizontal axis) c.only in the red giant region d.only on the main sequence e.H-R diagrams have nothing to say about spectral types

b

An H-R Diagram plots the luminosity of stars against their: Select one: a.mass b.diameter c.surface temperature d.age e.location in the sky

c

Measurements show a certain star has a very high luminosity (100,000 x the Sun's) while its temperature is quite cool (3500o K). How can this be? Select one: a.it must be a main sequence star b.it must be quite small in size c.it must be quite large in size d.it must be brown dwarf and not a regular star e.this must be an error in observations; no such star can exist

c

One of your good friends who is on a diet asks you to point out the stars with the smallest mass on an H-R diagram that you are studying. Where are you sure to find the stars with the lowest mass on any H-R diagram? Select one: a.among the white dwarfs b.among the stars at the top left of the main sequence c.among the stars at the bottom right of the main sequence d.among the supergiants e.stars with low mass can be located anywhere at all in the H-R diagram

c

The process of star formation. Generally, collapse leads to ________ heating, which eventually leads to __________ ignition temperatures. Specifically, when gravity exceeds pressure in the molecular cloud, material from the outer reaches of the cloud transfers ____________ into _____________ as it falls in towards the center of the cloud. When it reaches the center of the cloud, the kinetic energy is converted to ___________ as the material is either added to the central Protostar or spun out into the protoplanetary disk. The protostar increases in temperature and luminosity as more material is added. Its central pressure and temperature also increase until temperatures of _______million K are achieved and nuclear _________ begins. In the meantime, other processes related to conservation of angular momentum shape the material surrounding the collapsing core and limit the amount of material involved in the collapse.

central, hydrogen, gravitational potential energy, kinetic energy, thermal energy, 10-15, fusion

M stars are ___________ and emit very little energy per unit area (say per square meter), the only way that an M star can have a high luminosity is if it is very _______ (i.e., has a lot of square meters of surface area). This star is either a ______ or a ________.

cool, large, giant, supergiant cool, large, supergiant, giant

A star that is quite hot and has a very small radius compared to most stars is called Select one: a.a main-sequence star b.an O-type star c.a red giant d.a white dwarf e.an M-type star

d

A team of astronomers discovers one of the most massive stars ever founD. If this star is just settling down in that stage of its life where it will be peacefully converting hydrogen to helium in its core, where will we find it on the H-R diagram? Select one: a.among the supergiants, in the upper right b.a little bit below the Sun on the main sequence c.among the most brilliant of the white dwarfs, in the lower left d.near the very top of the main sequence, in the upper left e.it could be anywhere on the diagram; we would need more information to determine its place

d

Because of the period-luminosity relationship, intrinsically _________ cepheids have a shorter period, so it takes _________ time to confirm their identity.

dim, less

Imagine that powerful telescopes in the future give us a truly representative sampling of all the stars in the Sun's cosmic neighborhooD. Where on the H-R diagram would most of the stars in our immediate vicinity lie? Select one: a.in the upper right, among the supergiants b.in the upper left, among the bright main sequence stars c.in the middle of the main sequence, roughly where the Sun is d.in the lower left, among the white dwarfs e.in the lower right, among the least luminous main sequence stars

e

The best part of measuring a parallax to a star is that there are no assumptions made about the star itself. The parallax distance only depends on __________ and thus can result in a very _________ distance estimate. There is also no need to examine the star's spectra with this method.

geometry, precise

Stars can form when _________ exceeds the local _______. Pressure is ______ in hot material and _________ in cold material, so colder clouds put up less resistance to gravitaional forces and can collapse more readily. Also, at lower temperatures, molecules form. Because molecules are __________ than individual atoms, they move around more slowly and can congregate in a small volume of space, increasing the local matter density and thereby the local gravity.

gravity, pressure, higher, lower, heavier

Sirius is more massive than Alpha Centauri; both are main-sequence stars, and main-sequence stars with ______temperatures have _______ masses. According to their spectral types, Sirius is _______ than Alpha Centauri. Regulus is a main-sequence star and is ________ in radius than Rigel, which is a supergiant. Betelgeuse, with a spectral type of M2 is ________ than Rigel, which has a spectral type of B8.

higher, larger, hotter, smaller, cooler

We now understand that planets can migrate in the protoplanetary disk through gravitational friction or drag. For example, Jupiters can migrate ________ and be quite close to their _________. We now understand that planet formation is more ________ than we imagined.

inward, stars, chaotic

Consider the following data on four stars:Star Luminosity (in LSun) 1 100B, main sequence 2 1/100B, white dwarf 3 1/100M, main sequence 4 100M, giant Star 4 has the ________ radius, with a ____ temperature, yet a high luminosity. Star 2 has the smallest radius, with a ______ temperature and a ______ luminosity. Star 3 is the most common, since main-sequence stars are the most common, and _____-luminosity, main-sequence stars are more common than high-luminosity, ________ stars. Star 4 is the least common, since _________ are among the rarest populations

largest, low, high, small, low, main-sequence, giants

Stars that lie in different places on the main sequence of the H-R diagram differ from each other mainly by having different:

masses

The Doppler technique measures the __________ of the star caused by the pull of one or more planets around it. The gravitational force is proportional to the _______ of the planet and inversely proportional to the ______________. So the easiest planets to detect with this method are massive and close to the star. That's why the hot Jupiters were found first. The size of the planet must be big enough to give a measureable decrease in the brightness of the star. Since astronomers need to wait for three transits before they feel comfortable confirming their observation, that means that the _________ the planet takes to orbit its star, the longer it will take to confirm the existence of a transiting planet. So this method works best for planets of larger size, orbiting ______ to their stars

motion, mass, square of the separation, longer, close

Where on the H-R Diagram would we find stars that look red when seen through a telescope?

only on the right side of the diagram and never on the left

The advantage of measuring the parallaxes of stars relative to galaxies or ____________ is that we know the reference objects are very much more ________ than the stars and therefore will show no parallax of their own. Quasars make better reference markers than ordinary galaxies because they are smaller (they look like stars and so appear to be mere points of light); thus, their positions can be measured more precisely.

quasars, distant

A white dwarf, compared to a main sequence star with the same mass, would always bE.

smaller in diameter

Explain how you would use the spectrum of a star to estimate its distance. Begin by examining the detailed spectrum to estimate the star's__________ and __________. Use this information to find the place where the star belongs on the H—R diagram, and then read off the star's __________ from the diagram. Finally, measure the distance by comparing the ___________ to the luminosity.

spectral type, luminosity class, luminosity, apparent brightness

Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call:

the main sequence

Two ways of determining the diameter of a star. In one method, the _____ for an object like the Moon to pass in front of a star can be measured to determine the diameter of a star. Since we know the _________ of the Moon in its orbit, we can calculate the size of the star. For an eclipsing binary star, the time for one star to pass in front of another is dependent upon the relative ________ of each star. When the eclipses are aligned in such a way that they eclipse each other, we can measure the _______ for each star to eclipse the other. We can measure the _______ of the stars from the Doppler shift in the spectrum. From knowing the time of eclipse and the speed, the ______ of each star can be determined.

time, speed, diameters,time, speed, size