Cosmic Distances

Cosmic Distances
DISTANCE MODULUS
● For this lab, we will focus on two techniques that can be used to measure the distance modulus of objects in deep space – supernovas and Cepheid variable stars. Before we begin, though, we must understand what “distance modulus” means.
● Read through the background material on distance modulus.
● Use the distance modulus page to complete the following table:

Object Apparent Magnitude
(m) Absolute Magnitude
(M) Distance Modulus
(m – M) Distance
(pc)
Star A 2.4 10
Star B 5 16
Star C 10 25
Star D 8.5 0.5

● Could one of the stars listed in the table above be an RR Lyrae star?
Explain why or why not.

[Insert answer here]

CEPHEIDS
● Next, read through the background information on Cepheid Variable Stars.

● Suppose that a Type II Cepheid has an apparent magnitude (m) of 12 and a pulsation period of 3 days. Use the chart at right along with the period to find the absolute magnitude (M). Then use the interactive tool on the distance modulus page to determine the distance to the Cepheid variable star. What is the distance?

[Insert answer here]

SUPERNOVAE
● Begin by reading the background information on supernovae.
● Open the Supernova Light Curve Fitting Explorer. (Trouble viewing the simulation? Click here. If you still can’t get the simulation to work, then use this video screen capture of the simulation, which shows the necessary data to complete the lab.)
● The red line illustrates the expected profile for a Type I supernovae in terms of Absolute Magnitude. Data from various supernovae can be graphed (in blue) in terms of apparent magnitude.
● If the data represents a Type I supernovae it should be possible to fit the data to the Type I profile with the appropriate shifts in time and magnitude. Once the data fit the profile, then the difference between apparent and absolute magnitude again gives the distance modulus.
● As an example load the data for 1995D. Grab and drag the data until it best matches the Type I profile as shown.
● With the “show horizontal bar” option turned on, you can see that the distance modulus (m – M) for this supernova is approximately 33.

1. Load the data for Supernova 1998aq. What is the distance modulus of this supernova?

[Insert answer here]

Completing the Lab
● Submit your completed lab document to Canvas.

● Return to the course and complete the lab quiz to demonstrate your understanding.