The Value of Visual Observations of Variable Stars

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The Value of Visual Observations of Variable Stars

• Elizabeth O. Waagen
• AAVSO
• 25 Birch Street
• Cambridge, MA 02138
• eowaagen_at_aavso.org
• AAVSO Workshop for Visual Observing,
• 15 October 2005, Newton, MA

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What is a visual variable star observation?

• the estimation by an observer of the brightness
  of a variable star at a given date and time,
• using the eye by itself, or with binoculars or a
  telescope
• example
• 213843 SS CYG 2453289.7901 8.0 WEO
• Star identification date time mag
  observer

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How is a visual observation made?

• Compare the brightness of the variable star to
  the brightnesses of nearby stars of known
  brightness (comparison stars).

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Purpose of AAVSO

• Provide systematic observing program of variable
  stars to serious amateur astronomers worldwide
• Make the resulting observations useful and
  available to the professional astronomer,
  educator, and student

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Why is it important AMATEURS observe variables?

• Professionals cannot observe variables night
  after night
• do not have the time or equipment
• too many stars for them to monitor
• time better spent analyzing data, theorizing

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Why is it important AMATEURS observe variables?

• Amateurs can observe night after night
• They have the time and equipment
• They have the expertise
• They have the necessary enthusiasm and
  persistence
• Careful, longterm observing yields data the
  professional can use to correlate his/her special
  observations

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Visual observations are essential!

• What for?
• - Satellite observations schedule observing run,
  simultaneous monitoring, TOO trigger

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Visual observations are essential!

• What for?
• - Satellite observations schedule observing run,
  simultaneous monitoring, TOO trigger
• Correlation of multiwavelength space- and
  ground-based data

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Visual observations are essential!

• What for?
• - Satellite observations schedule observing run,
  simultaneous monitoring, TOO trigger
• Correlation of multiwavelength space- and
  ground-based data
• Analysis of long term behavior (stellar
  evolution)

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Visual observations are essential!

• What for?
• - Satellite observations schedule observing run,
  simultaneous monitoring, TOO trigger
• Correlation of multiwavelength space- and
  ground-based data
• Analysis of long term behavior (stellar
  evolution)
• Testing theoretical models

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Visual observations are essential!

• What for?
• - Satellite observations schedule observing run,
  simultaneous monitoring, TOO trigger
• Correlation of multiwavelength space- and
  ground-based data
• Analysis of long term behavior (stellar
  evolution)
• Testing theoretical models
• Furthering understanding of many/most subclasses
  of pulsating, eruptive, and extrinsic variables,
  esoteric high-energy objects

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Visual observations are essential!

• What for?
• - Satellite observations schedule observing run,
  simultaneous monitoring, TOO trigger
• Correlation of multiwavelength space- and
  ground-based data
• Analysis of long term behavior (stellar
  evolution)
• Testing theoretical models
• Furthering understanding of many/most subclasses
  of pulsating, eruptive, and extrinsic variables,
  esoteric high-energy objects
• Applications we havent even dreamed of yet!

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Examples of How Visual Observations Are Valuable
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Observing LPVs with HST

• AAVSO observations help astronomers schedule
  observations of pulsating stars with HST by
  providing the phase of variability and magnitude.
  
• Observations of Mira (omicron Ceti)
• 
  

AAVSO visual light curve of Mira 1994-1997 HST
observation made December 11, 1995, is marked.
Each dot is one observation.
HST images of Mira (left) and close companion VZ
Cet taken December 11, 1995 (M.
Karovska,Harvard-Smithsonian Center for
Astrophysics, and NASA).
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Modeling Pulsating Variables

• AAVSO data on hundreds of stars covering many
  decades are a treasure-trove for theoreticians!
• AAVSO observations provide astronomers with phase
  of variation and magnitude for correlating visual
  data with UV, optical (spectroscopic and
  photometric), IR, and radio data in theoretical
  research on
• ? Mechanism and mode of pulsation
• ? Composition and motion of atmosphere
• ? Radius, luminosity, mass, temperature,
• and other properties
• ? Correlations among parameters

Evolutionary models link stars in different
evolutionary states as well as relating stellar
properties and (occasionally) rates of change of
those properties. (L. A. Willson, 1997, JAAVSO,
25, 99, Figure 4)
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• AAVSO long term visual light curve
• Mira, 1835-2000

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• AAVSO long term visual light curve
• R Aquarii 1810-2000

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• AAVSO long term visual light curve
• V Hya 1884-2000

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• AAVSO longterm visual light curve
• V Hya 1913-2003

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Amateurs Assist Hipparcos

• AAVSO data were crucial to success of
  observations of Long Period Variables with the
  ESA High-Precision Parallax Collecting Satellite
  (1989-1997)
• Pre-launch
• ? 1 million AAVSO observations provided
  before satellite launch to determine and test
  methods of predicting long period variable (LPV)
  behavior during mission (illustration below,
  left)
• During mission
• ? Real-time observations (70,000 per year)
  provided monthly to
• ? refine LPV predictions
  (illustration below, left)
• ? calibrate aging satellite optics
  (esp. for observing red stars)
• ? 245 LPVs successfully observed through
  this collaboration

AAVSO light curve with successive fittings of
Hipparcos prediction algorithm to data dashed
line is final fit
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Light curves from Hipparcos and Tycho Catalogues,
Vol. 12 (ESA 1997) Smoothed curves fitted to
AAVSO observations (left) Hipparcos photometry
on transformed-AAVSO smoothed curves (right)

• Amateurs Assist Hipparcos

Post-mission ? Hipparcos precision
photometry superimposed on AAVSO light curves for
optimal interpretation of photometry
(illustration below, middle) ? Combined
light curves published in The Hipparcos and Tycho
Catalogues, Vol. 12 - Hipparcos Variability
Annex Light Curves (illustration below,
right) Good agreement of fit between Hipparcos
and AAVSO data shows the high quality of AAVSO
data
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Visual Observations Contribute to High-Energy
Cataclysmic Variable Research

• Amateur astronomers worldwide have helped
• ? to obtain the first detection of X-ray emission
  from several members of each cataclysmic variable
  category
• ? to obtain the first detection of soft X-ray
  pulsations from astrophysical sources such as
  dwarf novae
• ? to obtain the first multi-wavelength spectra of
  dwarf novae
• ? in the discovery that 70 of cataclysmic
  variables emit X-rays (information that is vital
  in testing theories for high-energy emission in
  compact systems)
• ? in the discovery of stellar winds during the
  outburst of some dwarf novae
• ? in the discovery of a delay during outburst
  between optical, ultraviolet, far ultraviolet,
  extreme ultraviolet, and X-ray emission in some
  dwarf novae
• ? in discovering that the EUV soft X-ray flux
  initially tracks the optical flux, but then falls
  quickly during the decline from outburst in some
  dwarf novae

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• ? in discovering that during the rise to optical
  outburst, the hard X-ray flux rises, followed by
  a fast decline, with a subsequent rise in the EUV
  flux? in discovering that the hard X-ray flux
  remains suppressed throughout the outburst but
  recover suddenly at the end of the optical
  outburst
• ? in discovering novae and supernovae? in
  triggering multi-wavelength observations at the
  onset of an outburst, which is crucial in
  understanding the nature and origin of
  outbursts? in providing a continuous record of
  the behavior of cataclysmic variables to
  correlate multi-wavelength observations and
  theories? in furthering our understanding of
  compact binaries, the nature of the white dwarf
  and the secondary component, accretion disks, and
  the nature and origin of outbursts.

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Amateurs Keep Astronauts Pointing with Astro-1
and Astro-2

• In 1990 and 1995, AAVSO observers assisted in
  space shuttle-based observing programs
• Astro-1 (1990, 9-day mission)
• AAVSO observers monitored 19 cataclysmic
  variables
• and active galactic nuclei for outbursts,
  reporting activity to Headquarters
• Unique, excellent far-UV spectra on Z Cam
  obtained using Hopkins Ultraviolet Telescope on
  Astro-1 less than 48 hours after first detection
  of outburst by amateur astronomer
• Astro-2 (1995, 16-day mission)
• Satellite observations were scheduled based on
  information provided by AAVSO (often every 8
  hours, around the clock) thanks to dedicated
  AAVSO observers worldwide
• ? Results Excellent data obtained on 17
  cataclysmic variables

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• AAVSO longterm data on RX And part 1

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AAVSO longterm data on RX And part 2
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AAVSO longterm data on GK Per 1904-2003
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AAVSO longterm data on Z And 1913-2003
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AAVSO longterm data on R CrB 1905 - 2003
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Z Cha(P. Wheatley C. Mauche)10/13/05
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U Gem (Smak Waagen 2004)AAVSO light curve and
residuals
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AAVSO visual observations continue to helpbreak
new ground in variable star astronomy!
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• Visual observations
• Are enormously valuable

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• Visual observations
• are enormously valuable
• and
• They always will be!

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