making a color-magnitude diagram for globular cluster omega centauri
DESCRIPTION
Making a Color-Magnitude Diagram for Globular Cluster Omega Centauri. Jay Anderson, STScI. 1. This is the Early-Release Image of Omega Centauri, taken by WFC3/UVIS on board the Hubble Space Telescope (HST). http://hubblesite.org/gallery/wallpaper/pr2009025q/. 2. - PowerPoint PPT PresentationTRANSCRIPT
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Making a Color-MagnitudeDiagram for Globular Cluster
Omega Centauri
Jay Anderson, STScI
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This is the Early-Release Image of Omega Centauri, taken by WFC3/UVIS on board the
Hubble Space Telescope (HST)
http://hubblesite.org/gallery/wallpaper/pr2009025q/
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A close up of the central region.
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This image was made by combining
separate red, green, and blue images. 4
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The red image is from filter F814W, which sees only very red light.
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The green image is from filter F336W, which sees only blue light.
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The blue image is from filter F225W, which sees only ultra-violet light.
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The combined image again.
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The colors are so extreme because…
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… the red stars have almost no blue light, and the blue stars have almost no red light.
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The composite image again.
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Astronomers like to study the colors of stars in a quantitative way.
12
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13a
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13b
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13c
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13d
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13e
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13f
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13g
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13h
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13i
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13j
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They like to sort the stars by color, putting the blue stars on the left and the red stars on the right.
13k
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Note that there are very few extreme stars; most stars are white, meaning
they have a balanced spectrum.14
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Astronomers also like to characterize the stars in terms of brightness.
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15a
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15b
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15c
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15d
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15e
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15f
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15g
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15h
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They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15i
![Page 35: Making a Color-Magnitude Diagram for Globular Cluster Omega Centauri](https://reader034.vdocuments.us/reader034/viewer/2022052701/56812db2550346895d92ded4/html5/thumbnails/35.jpg)
They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15j
![Page 36: Making a Color-Magnitude Diagram for Globular Cluster Omega Centauri](https://reader034.vdocuments.us/reader034/viewer/2022052701/56812db2550346895d92ded4/html5/thumbnails/36.jpg)
They like to sort the stars, putting the bright stars on top,
and the faint stars on the bottom.15k
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This is called a Color-Magnitude Diagram
(CMD).16
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When Astronomers first plotted stars this way, they realized that stars don’t
fall just anywhere in the diagram.17
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Stars tend to lie along a few well-defined sequences.
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The unmistakable order in diagrams like this led astronomers to develop theories
to explain stellar evolution.19
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The vast majority of stars lie along the Main Sequence (MS).
20a
MS
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Stars don’t move along this sequence; rather they sit at the same place for a long
time fusing their hydrogen into helium.20b
MS
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This is a sequence in mass. Stars at the bright end are massive, and those at the
faint, red end have very low masses.20c
MS
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The more massive stars consume their hydrogen fuel much faster than the
lower-mass stars.20d
MS
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When fuel becomes sparse in the stellar core, stars readjust their internal structure and move red-ward along the Sub-Giant Branch (SGB).
21
MS
SGB
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They start to burn the hydrogen in a shell around the core and become big and bloated as they move up the Red Giant Branch (RGB).
22a
MS
SGB
RGB
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As the shell-burning continues, more and more helium gets deposited onto the core.
22b
MS
SGB
RGB
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When the core has enough mass, it is finally able to ignite helium into carbon.
22c
MS
SGB
RGB
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The star readjusts its structure again and finds itself on the Horizontal Branch (HB).
23a
MS
SGB
RGBHB
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The helium fuel is not as potent as the hydrogen, so it runs out quickly.
23b
MS
SGB
RGBHB
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That is why there are so few stars on the HB compared to the MS. Stars do not
spend much time on the HB.23c
MS
SGB
RGBHB
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When the helium is gone, the star has no more fuel. With nothing left to burn, it fades away into
blue darkness as a White Dwarf (WD).24
MS
SGB
RGBHB
WD
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Since a star’s color and brightness tell us
its evolutionary phase, we can easily
identify stars by phase in the image.
25
MS
SGB
RGBHB
WD