Welcome to http://www.handsonuniverse.org/activities/Explorations/BinaryStars

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Binary & Multiple Stars

Many stars are binary or multiple stars systems
.... bound by gravity & orbiting each other! 

Measure separation, compare brightness counts or calculate magnitudes, compare star colors, and more.... 

In the Handle of the Big Dipper

alcor_mizar_show.jpg (7568 bytes)The pair of stars, Mizar and Alcor, is easy to see in the Big Dipper of the constellation, Ursa Major. Their separation is 11'48" (11 arcminutes, 48 arcseconds).

mizar.jpg (6315 bytes) Mizar itself is a double star.  Mizar was the first star to be discovered as a telescopic binary (Herschel, 1650).  We took this image of Mizar at Yerkes Observatory using the 24 inch telescope.  Image:  mizar_r.fts

HOU Image Processing Investigation: 
The separation of the two components of Mizar is about 14".    
How many pixels separate the stars on the image?  ________
How many arcseconds are represented by each pixel in this image?  ________

Magnitudes of the two components are  2.27 v? (suspected variable) and 3.95.
Compare the brightness counts for each star using the aperture tool. 
What is the (x,y) position of the star which has a magnitude of 2.27v? ________
What is the (x,y) position of the star which has a magnitude of 3.95?  _________

Brighter stars have a magnitude value which is a lower number than dimmer stars.   Did you identify the above stars correctly?

Orion's Belt Stars
Which of Orion's Belt Stars is this one?  beltdbl.jpg (5895 bytes)

The three belt stars of Orion, Mintaka, Alnilam and Alnitak, were imaged (with the ISIS ccd camera , B filter, 0.55 seconds) through a small finder scope (80 mm Celestron refractor attached to the side of  the Yerkes 24 inch telescope). The stars shown in this image have a separation of about 53"; their magnitudes in B are about 2.02 for the brighter star and about 6.71 for the dimmer star.  

The other two stars belt_abv.jpg (5240 bytes) and belt_lw.jpg (5323 bytes) do not show any companions in these images.  Open up the three star images to discover which star shows a dim companion!   Images: alnitak5.fts, alnilam5.fts, and mintaka5.fts.  

The Beak of the Swan

albireo.jpg (7235 bytes) Albireo is the star at the tail of Cygnus the Swan (or the foot of the Northern Cross).  It is a beautiful telescopic binary with stars of two different colors.  One star looks amber, the other star looks bluish.  HOU teachers taking a summer course at Aurora University in Williams Bay, WI, took many images of Albireo with a ten inch reflector in the South Building at Yerkes Observatory.   Download this image of Albireo.  Download other images of Albireo

RA & Dec:   North is up and East is left in the picture of Albireo above. 
The East / West position (Right Ascension or RA for short) of the two stars are almost the same, with the dimmer star slightly east of the brighter one.  The coordinates for the dimmer star are right ascension, 19h 30m 45.3s and the declination,  +27degrees 57arcmin 55arcsec.
The North / South position is called Declination (Dec).  The brighter star is south of the dimmer star.    The coordinates for the brighter star are right ascension, 19h 30m 43.3s and declination,  +27degrees 57arcmin 35arcsec. 

Magnitudes:   The brighter star's magnitude is 3.08 and the dimmer star's magnitude is 5.15. Use auto aperture to compare the brightness counts for each star. 

Castor in Gemini
castor.jpg (8111 bytes)
is a multiple star system in Gemini with six components, three of which you can see in this image.  The pair at the top of the image are the A and B components; each has a spectroscopic companion.  The star at the bottom is component C.  There is also one other star, D, which is part of the system, further away and not shown here. 

pollux.jpg (5903 bytes)Pollux is Castor's 'brother' in Gemini.  Pollux is not a binary star.

Colors of Castor and Pollux.  These images of Castor and Pollux were taken in red, green and blue filters.  (However to compare the star colors, divide the red images by 3, and the green images by 1.5 before comparing brightness counts to get a sense of the color of the stars.  Reason: CCD chip is most sensitive in red and all the images were taken for .11 seconds.  So you have to divide the counts on the red and green images to make them comparable to the blue image. )

Download the Yerkes 24 inch telescope images of Castor and Pollux.
Go to another webpage,  Right Ascension & Declination, to learn about the coordinate system for the sky, illustrated with  images of Castor and Pollux.  

Alcyone, the Brightest Star of the Pleiades
alcyone.jpg (7072 bytes)
Alcyone is a multiple star system; Alcyone is the brightest star of the Pleiades Star Cluster in Taurus.   This picture is part of the image, pleiades.fts.

Calculate Apparent Magnitude.
eta_tau.jpg (4185 bytes)
This image includes Alcyone and its three neighbors clearly.  It was taken with the '41inch' reflector at Yerkes Observatory.  Using this image, etatau3.fts, you can calculate the apparent magnitude of the three neighboring stars to Alcyone using Auto aperture and comparing their brightness counts to the brightness counts and the magnitude of Alcyone.  (Refer to the Apparent Magnitude Word document, or HOU Measuring Brightness manual, Supplementary Activity # 14.)

Find Star Colors
This next image shows the three companion stars to Alcyone.   The stars were imaged in b and v filters.  B is a filter which lets through mostly blue light.   V is a filter referred to as 'visual' and lets through light which is mostly green. 
by_alcy_sm.jpg (2466 bytes) 
This image was taken with the Yerkes 24 inch reflector.  The images are named, by_alcy_bi.fts and by_alcy_gi.fts.   Compare the brightness counts of these stars using Auto aperture.  Refer to the HOU manual: Color of stars to calculate the B-V index for these stars.  (Exposures are comparable as presented in the images because the green or V exposure is half as long as the blue exposure, approximately matching the sensitivity of the CCD chip.  You do not need to divide counts to compare filtered images.) The brightest of these stars (24 Tau) has a B-V index of 0.01.  Its V magnitude is 6.29.

Download all these .fts  images
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