Cosmological Distance Ladder: Moving Clusters what more is there to say

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Cosmological Distance Ladder Moving
Clusters(what more is there to say?)

• Jeremy Maune

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Outline(As if you actually dont know what to
expect)

• The technique in all its glorious detail
• A very brief note on railroad tracks
• The Hyades and why this method actually mattered
  not too long ago
• Hipparcos and why this method no longer matters
  any more (or at least not as much)
• Wrapping up and going home

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Hey, Stars move! Who knew?(you know, besides
everyone in this room)
To find the distance to the star, we need to know
its velocity. Radial velocity can be measured
via doppler shift. Transverse velocity is more
difficult, since proper motion cannot directly
give it.
Credit the University of Washington and the
University of Victoria (Canada) for figures 1 3
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Because railroad tracks have everything to do
with astronomy
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Moving Clusters (Ta-da!)
Ditto for picture credit
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A different perspective
Note that This gives the relationship Where
µ is the proper motion If you care to see how
this equation is derived, feel free to go to the
following website since Im not wasting the time
here http//www.astro.washington.edu/labs/clearin
ghouse/labs/Hyades/derivation.html
Ditto the ditto
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Historical Importance the Hyades
The Hyades are a star cluster in the
constellation of Taurus 46 pc away. Lewis Boss
first applied the moving cluster method to the
Hyades in 1908 (Webb, 1999)
Historically, finding the distance to the Hyades
was of great importance to the distance ladder,
as there are several stars of different stellar
types within the cluster. Knowing the distance
to these stars allowed Main Sequence fitting of
similar types (ask Noel for details)
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Hipparcos

• Once Hipparcos got up into the sky, parallax
  measurements became much more accurate.
• Measurements of parallax could also be extended
  to greater distances, making the moving cluster
  method somewhat redundant.

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Wrapping Up

• Useful out to several hundred parsecs (still
  somewhat farther than parallax).
• Problem in that it must assume that all stars in
  a cluster are the same distance away. Parallax
  is now able to measure the distances to the stars
  in the Hyades, for example, making this method
  less accurate.

• One must also assume that all the stars in a
  moving cluseter have exactly the same velocity,
  and that all the stars you believe to be
  associated with the cluster actually are.

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Sources

• Binney Merrifield 1998 Extragalactic
  Astronomy (pgs 40-42)
• Webb, Steven 1999 Measuring the Universe The
  Cosmological Distance Ladder (pgs 122-124)
• http//www.astro.washington.edu/labs/clearinghouse
  /labs/Hyades/disthyad.html accessed Nov. 26th
  (source of pictures)