Variable Stars and the Stories They Tell

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Variable Stars and the Stories They Tell

• Mike Simonsen
• AAVSO
• C. E. Scovil Observatory

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Stars The Essential Building Blocks of the
Universe
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What is a Star?

• Massive object, typically comprised of mostly
  Hydrogen gas
• Balancing act between gravitys contraction and
  nuclear burnings expansion
• Mass is the most important quantity of a star
• Initial mass determines its life cycle

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Variable Stars

• Stars that vary in brightness
• Time scales of seconds, hours, days, years or
  centuries
• Understanding variable star behavior sheds light
  on other astronomical phenomena
• General classifications or types

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Pulsating variables

• Light changes are related to the expansion and
  contraction of the stars atmosphere
• Miras (LPVs)
• Cephieds (standard candles)

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Eruptive variables

• Novae
• Dwarf Novae
• Supernovae

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Eclipsing variables

• Eclipsing variables are not intrinsically
  variable
• The change in brightness is due to a line of
  sight effect

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Stellar EvolutionThe Life Cycle of Stars
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Star Birth

• In the beginning a star condenses from a cloud of
  dusty interstellar gases
• The life story of a star is the story of its
  perpetual attempt to contract

As the pillars themselves are slowly eroded away
by the ultraviolet light, small globules of even
denser gas buried within the pillars are
uncovered. These globules have been dubbed
"EGGs." EGGs is an acronym for "Evaporating
Gaseous Globules," but it is also a word that
describes what these objects are. Forming inside
at least some of the EGGs are embryonic stars
stars that abruptly stop growing when the EGGs
are uncovered and they are separated from the
larger reservoir of gas from whch they were
drawing mass. Eventually, the stars themselves
emerge from the EGGs as the EGGs themselves
succumb to photoevaporation.
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From A Cloud of Gas
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A Star is Born
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Orion NebulaNearby star forming region
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Variable stars within one degree of M42
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T Tauri type stars

• T Tauri stars are named for the prototype of the
  class, T Tauri. These objects are pre-main
  sequence stars and have recently emerged from the
  opaque envelope of stellar formation. Having
  recently coalesced from their dusty and gaseous
  surroundings, these stars now become visible at
  optical wavelengths.
• Our own Sun presumably passed through the T Tauri
  stage some 4 1/2 billion years ago. Therefore,
  these stars may be able to offer us a peak into
  the evolution of our own Sun, solar system, as
  well as other planetary systems.

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Middle Age

• As stars evolve to middle age, they, just like
  people, tend to swell at the waist.
• The instability strip on the H-R diagram
  represents stars in transition from one phase of
  their lives to another.
• Many M class stars are red giants. Pulsating
  variable stars, like Mira.

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Old AgePlanetary Nebulae

• Planetary nebulae are formed when a red giant
  star ejects its outer layers as clouds of
  luminescent gas, revealing the dense, hot, and
  tiny white dwarf star at its core.
• 95 of all stars that we see in our own galaxy
  will ultimately become "planetary nebulae". This
  includes the Sun.

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Our Future Sun
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V838 Mon

• Originally classified as a nova, V838 Mon may be
  an entirely new class of nova. Luminous Red Nova
  (LRN)
• Other potential explanations
• Thermal pulse of a dying star
• Thermonuclear event within a massive supergiant
• Mergeburst
• Planetary capture event

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Binary Star Systems

• Stars in close proximity to each other can
  influence the evolutionary development of their
  partner
• Symbiotic variable stars and cataclysmic variables

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Cataclysmic Variables
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Death and Destruction
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Seeding the Universe

• All the heavy elements in the universe were
  created inside the bowels of stars that have long
  since blown up or blown off their atmospheres.
• We are indeed stardust.
• We owe our very existence to variable stars.

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Modeling Larger Scale Phenomena

• Accretion disks
• Star formation
• Planetary formation
• Galaxy formation
• Active galactic nuclei
• Black holes

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The Search For Life

• Find extra terrestrial planets
• Exoplanet searches
• Exoplanet transit observations
• Serendipitous discoveries of variable stars

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Amateur Contributions to Science

• AAVSO American Association of Variable Star
  Observers
• Monitor pulsating variables
• Observing cataclysmic variables
• Timing eclipsing variables and RR Lyrae stars
• Chasing after GRB afterglows
• Observing exoplanet transits

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Be a Part of the Story
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Thank you!