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Exam 12: Characterizing Stars

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Question 61

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A star shows weak hydrogen Balmer lines but strong lines of neutral sodium. What is a likely explanation for this?

A) This particular star contains no hydrogen.
B) The hydrogen has been ionized.
C) The hydrogen is not receiving enough energy to populate the n = 2 level required for Balmer transitions.
D) The sodium lines are masking the hydrogen lines because these occur at the same wavelengths.

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Question 62

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The luminosity of a star is

A) its brightness as seen by people on Earth.
B) its brightness if it were at a distance of 10 pc (32.6 ly) from Earth.
C) its total energy output into all space.
D) another name for its color or surface temperature.

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Question 63

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How do two unequal-mass stars in a binary star system move around each other, in general?

Two stars in a binary system orbit around a common point that is

In the spectral classification scheme, what designation is given to a star just a little cooler than a K5 star?

The light curve made of a pair of eclipsing binaries will exhibit dips in intensity. The bottoms of these dips can have different shapes. How do astronomers interpret this?

A star of apparent magnitude +5 appears _____ than a star of apparent magnitude +3.

White dwarfs are NOT included in the luminosity classification because they are

The MOST accurate stellar parallax measurements for distances to the majority of stars in Earth's neighborhood in the universe have been made by

Suppose astronomers want to measure the distance to a star in astronomical units. They would use the equation d (au) = x/parallax angle (arcsec) . What is x?

Vega is often used as the star to define an apparent magnitude of 0. Actually, the standard for 0 magnitude is the average of a group of stars including Vega. But the averaging must be done with care. If one takes the combined brightness of one 0.1-magnitude star and one -0.1-magnitude star and divides this brightness by two, the equivalent brightness is

In a particular binary star system, only one star is visible because the other star is too faint to see at that distance. An astronomer measures the size (semimajor axis) and period of the orbit of the visible star. From this information, the astronomer

What is the intensity of sunlight per square meter reaching Venus compared with this intensity at Earth's orbital distance? (Venus's orbit has a semimajor axis of about 0.7 au.)

The sequence of letters that is used to classify star surface temperatures, as determined by relative spectral absorption line strengths, in order of DECREASING temperature, is

Some stars are variable, with many properties that change over time. The statement that the apparent magnitude of a variable star has INCREASED indicates that its

Two stars are found to have the same luminosity. However, one star has twice the surface temperature of the other. From this information, what can one determine about their radii?

A simple relationship exists between mass and luminosity for

Compared with a star in the middle of the Hertzsprung-Russell diagram, a star in the lower left of the diagram is

Where on the Hertzsprung-Russell diagram do MOST stars near the Sun congregate?

How many times brighter does the Sun appear from Earth than it does from Neptune, which has an orbital radius of approximately 30 au?