ASTR Ch. 10

Which star is more distant? Two stars - A and B, with luminosities 1.2 and 3.8 times the luminosity of the Sun, respectively - are observed to have the same apparent brightness.

B

Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

cooler and larger in radius

Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

hotter and smaller in radius

Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.

less luminous, cooler, smaller, and less massive

How far away is the star Spica, whose parallax is 0.012"?

83 pc

Which star is more distant? Two stars - A and B, with absolute magnitudes 3 and 10, respectively - are observed to have the same apparent magnitude.

A

The following figure shows how four identical stars appear in the night sky as seen from earth. The shading is used to indicate how bright (white) or dim (dark gray) the star would appear in the sky from Earth.

Brightest is closest, dimmest (or darkest) is most distant

Red giants are very bright because they are extremely hot.

F

Listed following are several fictitious stars with their luminosities given in terms of the Sun's luminosity (LSun) and their distances from Earth given in light-years (ly). Rank the stars based on how bright each would appear in the sky as seen from Earth, from brightest to dimmest. If two (or more) stars have the same brightness in the sky, show this equality by dragging one star on top of the other(s).

Nismo: 100LSun, 8 ly Ferdinand: 400LSun, 20 ly Shelby: 100LSun, 10 ly Enzo: 200LSun, 20 ly Lotus: 400LSun, 40 ly

Listed following is the same set of fictitious stars given in Part A. Rank the stars based on how bright each would appear in the sky as seen from Jupiter, from brightest to dimmest.

Nismo: 100LSun, 8 ly Ferdinand: 400LSun, 20 ly Shelby: 100LSun, 10 ly Enzo: 200LSun, 20 ly Lotus: 400LSun, 40 ly

Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.

Red giant or supergiant stars found in the upperright of the H-R diagram very cool butvery luminous Main-sequence stars the Sun, forexample the majority of starsin our galaxy the hottest andmost luminous stars White dwarfs not much larger inradius than Earth very hot but very dim

A star radiates light across the electromagnetic spectrum in what is known as a spectral intensity distribution. Because each star's surface has a characteristic temperature, the resulting spectral intensity distribution approximates that of an ideal blackbody. In the figure, the theoretical blackbody curves for three stars of differing surface temperatures are plotted. Here, the sizes of the idealized stars can be assumed to be equal.

Star A: 30,000 K the star appearing bluest the star with maximum intensity at ultraviolet wavelengths the star appearing brightest Star B: 10,000 K the star whose equal intensities measured through yellow (V) and blue (B) filters Star C: 3,000 K the star appearing reddest the star with maximum intensity at infrared wavelengths

An astronomer measures the light coming from two stars, star A and star B. They appear to be equally bright. From other measurements, she knows that star B is actually twice as far away as star A. What can she conclude?

Star B is actually four times as bright as star A.

There are no billion-year-old main-sequence O- or B-type stars.

T

Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest.

blue white dwarf star sun orange main sequence star red supergiant

In Part A, you considered the spectral intensity distributions emitted by stars of differing surface temperatures. The stellar spectra, when examined in greater detail, contain a wealth of information that can be used to describe various physical properties of the star (see figure). Most stellar spectra contain absorption lines that are produced by certain atoms and molecules in the stellar atmospheres, such as helium, hydrogen, heavy elements, and molecules. The width of a spectral line indicates the relative prominence of a given atom or molecule. A thin line is a "weak" line, meaning a relatively small presence, and a thick line is a "strong" line, meaning a relatively big presence.

very few lines of hydrogen and helium mostly the bluest colors metal lines but no molecular lines strong hydrogen lines lots of metal and molecular lines the reddest colors