Exam 10: Characterizing Stars

For absorption lines in the Paschen series of hydrogen to be seen in the infrared spectrum of a star (see Section 3-17 of Comins,Discovering the Essential Universe,6th ed.),the temperature of its surface must be high enough to excite electrons by collision to the:

If the Sun were orbited by a star of 1.8 solar masses at Jupiter's distance of 5.2 AU (or,more precisely,the Sun and the other star were orbiting each other 5.2 AU apart),what would be the orbital period of the system? (You might want to compare your answer with the actual orbital period of Jupiter,11.9 years.)

Using Figures 10-8 and 10-9 of Comins,Discovering the Essential Universe,6th ed.,determine list is the CORRECT sequence of stars in order of increasing size or stellar radius.

The Hipparcos satellite was able to measure parallax for stars out to about 150 pc.This distance includes roughly 2.5 million stars.The new Gaia satellite should be able to measure the parallax of roughly a billion stars.Assuming the density of stars is approximately constant,what distance would this correspond to? (Hint: the volume of a sphere is proportional to the cube of the radius.)

Viewed from Earth,the Sun's absolute magnitude is M = 4.8 and its apparent magnitude is m = -26.7.Viewed from Neptune,30 AU from the Sun,the Sun's absolute magnitude is:

The star Algol in the constellation Perseus has the following unusual characteristics.Every 68.75 hours its brightness dims suddenly from apparent magnitude 2.3 to apparent magnitude 3.5 and remains there for a few hours before returning just as suddenly to 2.3.In addition,halfway through this 68.75 hour period,the apparent magnitude becomes slightly dimmer than 2.3 for a few hours and then returns to 2.3.From this information alone it is possible to classify Algol as a(n):

If the surface temperature of a star is very low,which atomic or molecular constituent will produce the most prominent absorption lines in its spectrum?

The star Regulus,in the constellation Leo,appears brighter through a blue filter than it does through a yellow filter.Suppose that a second star is found that has the same brightness as Regulus through the blue filter but is brighter than Regulus through the yellow filter.From this information,we can say conclusively that the second star has:

Name the spectral class of a star whose spectrum shows the following absorption lines: very strong Ca II lines; weak Fe I and Ca I lines; no He I,He II,or TiO lines.(Hint: Use the absorption line strengths shown in Figure 10-5 and Table 10-1 of Comins,Discovering the Essential Universe,6th ed.)

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

Why are Balmer absorption lines very weak in the spectra of stars with low surface temperatures-significantly below 10,000 K,for example?

The motion that is used to change the position of the observer in the most common parallax measurements of distances to relatively nearby stars is the:

For a pair of stars to be classified as a visual binary,which condition must be TRUE?

If you look out at the night sky,the number of stars with:

The spectrum of an ordinary main-sequence star is a:

The star Alderamin has an apparent magnitude of 2.4 and an absolute magnitude of 1.4.The star Merak has an apparent magnitude of 2.4 and absolute magnitude of 0.5.Assuming that neither star has been dimmed by interstellar clouds,we can say for sure that Merek is:

What is a star's luminosity?

Suppose the distance between an observer and a lightbulb is doubled.How does its final brightness compare with its initial brightness?

A star with a surface temperature of 5000 K and a luminosity greater than 10⁴ times that of the Sun is a member of which luminosity class? (See Figure 10-10,Comins,Discovering the Essential Universe,6th ed.)

A particular star appears brighter seen through a blue filter than seen through a yellow filter.Which surface temperature is possible for this star? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)