Follow this link to skip to the main content

How Big is That Star?

Binary stars

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.

Diagram showing how t1 and d1 relate to the light curve for a binary system Diagram showing how t1 and d1 relate to the light curve for a binary system

Illustration of the relationship between the dips in the light curve and the stars in a binary. The large red circle represents the larger star in the binary system and the smaller circles represent the smaller star as it moves through its orbit.

  • 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.

Light curve for HT Cas

Light curve for binary system HT Cas.

  • 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

Light curve for X0748-676

Light curve for binary system 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

Light curve for Vela X-1

Light curve for binary system 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

NASA Logo, National Aeronautics and Space Administration
Goddard