# How Big is That Star?

## Measuring Binary Stars

Name: __________________________________

Date: ______

Class: _______________________

You are going to be measuring the sizes of stars in binary systems.

## Background

Look at the sample light curves below. They show the brightness of a binary system as a function of time.

• In a sentence, describe the relationship between t1 and d1. What does d1 represent?
• In a sentence, describe the relationship between t2 and d2. What does d2 represent?
• Using this information, data from real binary systems, and the equation d=v × t (distance equals velocity times time), you’ll calculate the sizes of a few stars.

## HT Cas

Work through this example along with your teacher.

• Using the graph above, determine and record the following (be sure to include units):
• t1: __________________
• t2: __________________
• The orbital velocity of HT Cas is known to be 390 km/sec.
• Using d=v × t, determine the size of each star in HT Cas. Show your work below, or on additional paper, if you need more room.
• Write the size of each star below (make sure to include units):
• d1: __________________
• d2: __________________

## X0748-676

• Using the graph above, determine and record the following (be sure to include units):
• t1: __________________
• t2: __________________
• The orbital velocity of X0748-676 is known to be 500 km/sec.
• Using d=v × t, determine the size of each star in X0748-676. Show your work below, or on additional paper, if you need more room.
• Write the size of each star in X0748-676 below (make sure to include units):
• d1: __________________
• d2: __________________

## Vela X-1

• Using the graph above, determine and record the following (be sure to include units):
• t1: __________________
• t2: __________________
• The orbital velocity of Vela X-1 is known to be 280 km/sec.
• Using d=v × t, determine the size of each star in Vela X-1. Show your work below, or on additional paper, if you need more room.
• Write the size of each star in Vela X-1 below (make sure to include units):
• d1: __________________
• d2: __________________

 A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC