Page numbers refer to the 1995 Edition of the Seeds textbook.
Our star from the last problem set is observed over the course of several years and found to have a parallax of p = 0.01 arcseconds. What is the distance d to the star in parsecs? What is this distance in light-years?
What is the distance modulus (the difference between the apparent and absolute visual magnitude m_v - M_v) for this star? (See p.157 of Seeds.)
Suppose that the apparent visual magnitude of this star were m_v = 0.825. What is the absolute visual magnitude M_v of this star? How many times more luminous is this star in the visual wave band than the Sun? (The absolute visual magnitude of the Sun is M_v = +4.83.)
Given the temperature deduced from last time (you should have got T = 20000 K), and this luminosity, locate this star on the H-R diagram (Fig 8-7) on page 160 of the Seeds text. What is the spectral type you would assign this star? (You did this in Problem Set 4 using the temperature alone - notice how these spectral classifications fit in with the bigger picture of the temperature, luminosity, radius and masses of stars.)
Locate the star on the H-R diagram (Fig 8-8) on page 161 of Seeds using the luminosity and temperature just found. What is the approximate radius for this star (in units of the solar radius)? Calculate the radius using the luminosity-radius-temperature formula on page 158. (The surface temperature of the Sun is T = 5800 K.) This should more or less agree with what you got from the chart.
Is this a main-sequence star or is it a giant or super-giant star, or is it a dwarf star? How do you tell the difference? We will see what these differences mean in the next chapter.
Using the Luminosity - Mass relation on page 171 of Seeds, what would you expect to find for the mass of the star (in units of the solar mass)?
What ways can we use to actually get a measurement of the mass of the star? How would you go about looking for this?
Be sure to visit the DRL rooftop Student's Observatory on a clear Monday or Thursday night, or the Flower & Cook observatory during one of the bi-weekly Wednesday field trips (next one scheduled Wed March 20).
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Steven T. Myers - Last revised 04Mar96