Scuti Variable Stars

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Scuti Variable Stars

• Kai Cai
• Feb.14, 2003

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? Scuti Variables

• Outline
• General Characteristics
• Positions on H-R diagram
• Statistics
• Observations
• Little Asteroseismology!

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Light curves
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Definition Characteristics

• Pulsating variables of spectral types A or F
• Period lt 0.3d
• Typical amplitudes 0.003 to 0.9 mag in V
• based on GCVS (General Catalogue of Variable
  Stars)
• Most belong to Population I
• SX Phe variables Population II ? Scutis

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? Scutis on H-R diagram

• Occupy the lower part of Instability Strip
• ½ of the stars show measurable variability
  (Breger 1990)
• Red edge of the Strip coupling between pulsation
  and convection (Xu et al.2002)

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Location of the ? Scuti stars (and related
variables) in the H-R-Diagram (Image from
www.deltascuti.net/ )
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How many ? Scutis ?

• Catalog (till Jan.2000) 636 variables
• 9 PMS ? Sct stars (?)
• 85 ? Scutis discovered in 21 open clusters (till
  Jan.2002)
• A few (86) in binary (or multiple) systems
• observational bias

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Some Statistics (from Rodríguez et al. 2000)

• Amplitude (visual) distribution
• Period distribution

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Period distribution

• Distribution of the variables in the catalogue
  (N) as function of the period (P)

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Observations of ? Scutis

• Large projects EROS, DUO, PLANET, MACHO, OGLE,
  STARE, etc.
• Hipparcos
• Small telescope monitoring
• Multi-site campaigns
• Examples STACC (Small Telescope Array with CCD
  Cameras), STEPHI (STEllar PHotometry
  International)

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Global observing campaigns
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History Resources

• Star ? Scuti Wright (1900), Colacevich (1935)
  Fath (1935)
• Other names "Dwarf Cepheids" , AI Velorum stars
• Delta Scuti Network www.deltascuti.net
• AAS Seattle meeting Session 117 (poster) Delta
  Scuti and Pulsating Friends

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A little bit of Asteroseismology

• Radial as well as nonradial pulsations
• Hundreds (or more) of nonradial pulsation modes
  are simultaneously excited
• Models (Dziembowski 1995) most of these excited
  modes are mixed modes with a p-mode character in
  the envelope and g-mode character in the core
• P-L relation exists

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