The Magellanic System: A History of Discovery

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The Magellanic System A History of Discovery

• Annie Hughes, Swinburne University of Technology

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Resumen

• Overview of The Magellanic System
• The MS in History (very abridged)
• Henrietta Leavitt and the SMC Cepheids
• WIMPs vs MACHOs
• Supernova 1987A
• Extended Stellar Populations in the MCs?
• Formation of the Magellanic Stream?

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Sky View
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The Local Group
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But galaxies are more than stars

• A galaxy is made of
• dark matter (gt90 of galaxy mass)
• stars
• interstellar medium (ISM, lt1 of mass)

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But galaxies are more than stars

• The ISM consists of gas
• mostly hydrogen, some helium and traces of
  heavier elements, which astronomers call metals

H2, cold
H, cool/warm
H, warm/hot
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Emu in the Sky
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Aboriginal Astronomy
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Al Sufi and The White Ox
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Cape Clouds
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John Herschel
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John Herschel
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Henrietta Leavitt

• Employed as computer at Harvard College
  Observatory in 1893 to catalogue the brighness of
  stars from Arequipa plates.

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Finding Cepheids in the SMC
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The Period-Luminosity Relation
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Hubble Discovers the Universe
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M100 Cepheids
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Zwicky Discovers Dark Matter
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Dark Matter Candidates

• MACHOs
• Massive Compact Halo Objects
• brown dwarfs, planets, black holes
• astronomers

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Gravitational Lensing
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MACHO Microlensing
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The MACHO Project

• Question What fraction of Milky Ways halo
  consists of MACHOs?
• Experiment Six years of photometric monitoring
  of 12 million stars in the LMC and 5 million
  stars in the SMC.

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MACHO Microlensing

• MACHO candidate
• LMC GPE 1
• (051444.5 -684800)

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Conclusions from MACHO

• Detected 13 to 17 events in LMC
• 9 x 1010 M? of MACHOs within 50 kpc of MW
• MACHOs are objects with mass 0.5 M?
• 20 of MWs halo is MACHOs
• MACHOs cannot be all the missing mass

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Flashback to 1987
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Flashback to 1987
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What is a supernova?
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Stellar Evolution
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Stellar Evolution
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Flashback to 1987
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Confirmation!
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Formation of the Stream

• Tidal interaction?
• Ram pressure stripping?
• Blow out from 30 Doradus?

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An extended stellar population

• RGB stars from LMC observed up to 23º from LMC
  optical centre
• What??!

Majewski et al 2009
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A conclusion (sort of)

• We still have a lot to learn about the Magellanic
  System!

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Cepheid Variables
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Pulsation

• Pulsation mechanism is the Eddington valve
• He is more opaque than He
• Radiation pushes outwards gravity pulls inwards

He
He
He
Dim
Bright
Dim
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Sky View