NOTES: Cepheid Variable Stars: John Goodrick (1784) discovered Delta-Cephei. Henrietta Leavitt...
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Transcript of NOTES: Cepheid Variable Stars: John Goodrick (1784) discovered Delta-Cephei. Henrietta Leavitt...
NOTES:
Cepheid Variable Stars:John Goodrick (1784) discovered Delta-Cephei.Henrietta Leavitt (1908)--Period Luminosity Relation:(overlay). Stars varying in brightness with period 1-50 days have linear relation between period and luminosity. This gives luminosity and thus distance to stars even in other galaxies.
The Interstellar Medium:1. Dust--recycled star material. Light undergoes to changes ingoing through it (Trumpler 1930): A. reddening--preferential scattering-blue light (why sky is blue). B. absorption--this affects flux and measured distance.2. Molecular Clouds--H2 molecules--dense MC are star formation regions (stellar nurseries like Orion Nebula).
Cepheid Variable Stars:
John Goodrick (1764-1786), deaf person, discovered variable star Delta-Cephei at age 17. He died at age 22!
Henrietta Leavitt (1908)--Period Luminosity Relation:Stars varying in brightness with period 1-50 days have linear relation (in logarithmic plot) between period and luminosity. This gives luminosity and thus distance to stars, even in other galaxies.
1930: Trumpler observes open clusters. Finds dust is dimming and reddening spectrum.He is able to calculate influence of dust on apparent brightness. This changed distance to stars radically!
2. Dense Molecular Clouds--H2 molecules--star formation regions.
Possible origin: Monatomic H atoms meet in chat room (on dust grain)
to make H2
Proper Motion (angular movement of star)
The star with the largest proper motion is called Barnard's Star. It moves 10.3 seconds of arc per year
Comparison of two photographic plates taken 22 years apart shows evidence of it’s real space motion
(denoted by an arrow).
Proper motion gives transverse velocityDoppler shift gives radial velocityPythagorean theorem then yields space velocity.