Variability

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Variability
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Learning outcomes

• Variability classes of long period variables
• Various time scales of variability phenomena
• Spectroscopic variability
• Connection between variability and atmospheric
  structure

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Mira the wonderful star
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Historical Background

• Catalog der rothen, isolirten Sterne, welche bis
  zum Jahre 1866 bekannt gevorden sind. Von Herrn
  Professor, Dr. Schjellerup
• 1782 observation of semiregular variability of µ
  Cep by Sir William Herschel

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Variability class Mira

• Mira (Omicron) Ceti-type variables. These are
  long-period variable giants with characteristic
  late-type emission spectra (Me, Ce, Se) and light
  amplitudes from 2.5 to 11 mag in V. Their
  periodicity is well pronounced, and the periods
  lie in the range between 80 and 1000 days.
  Infrared amplitudes are usually less than in the
  visible and may be lt2.5 mag. For example, in the
  K band they usually do not exceed 0.9 mag. If the
  amplitudes exceed 1 - 1.5 mag , but it is not
  certain that the true light amplitude exceeds 2.5
  mag, the symbol "M" is followed by a colon, or
  the star is attributed to the semiregular class
  with a colon following the symbol for that type
  (SR).

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Variability class SRV

• SRA Semiregular late-type (M, C, S or Me, Ce, Se)
  giants displaying persistent periodicity and
  usually small (lt2.5 mag in V) light amplitudes (Z
  Aqr). Amplitudes and light-curve shapes generally
  vary and periods are in the range of 35-1200
  days. Many of these stars differ from Miras only
  by showing smaller light amplitudes
• SRB Semiregular late-type (M, C, S or Me, Ce, Se)
  giants with poorly defined periodicity (mean
  cycles in the range of 20 to 2300 days) or with
  alternating intervals of periodic and slow
  irregular changes, and even with light constancy
  intervals (RR CrB, AF Cyg). Every star of this
  type may usually be assigned a certain mean
  period (cycle), which is the value given in the
  Catalogue. In a number of cases, the simultaneous
  presence of two or more periods of light
  variation is observed

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SRV lightcurves
Kerschbaum et al. 2003
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Variability class SRV

• SRC Semiregular late-type (M, C, S or Me, Ce, Se)
  supergiants (Mu Cep) with amplitudes of about 1
  mag and periods of light variation from 30 days
  to several thousand days
• SRD Semiregular variable giants and supergiants
  of F, G, or K spectral types, sometimes with
  emission lines in their spectra. Amplitudes of
  light variation are in the range from 0.1 to 4
  mag, and the range of periods is from 30 to 1100
  days (SX Her, SV UMa).

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Variability class L

• LB Slow irregular variables of late spectral
  types (K, M, C, S) as a rule, they are giants
  (CO Cyg). This type is also ascribed, in the
  GCVS, to slow red irregular variables in the case
  of unknown spectral types and luminosities.
• LC Irregular variable supergiants of late
  spectral types having amplitudes of about 1 mag
  in V (TZ Cas).
• stars are often attributed to this type
• because of being insufficiently studied

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Variability on various time scales

• Short time variations
• Humps
• Long secondary periods
• Period changes

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Outbursts in miras
de Laverny et al. 1998
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Long secondary periods
Lebzelter Hinkle 2002
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L2 Pup
Bedding et al. 2002
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Secular evolution
Tempelton et al. 2005
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Colour variations 1
Le Bertre 1992
Le Bertre 1993
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Colour variations 2
Whitelock et al. 2000
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Colour variations 3
Bouchet 1984
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Spectral variability

• Strong changes in the shape of visual spectra
  with pulsation phase
• TiO-bands dominant feature sensitive to
  temperature changes
• IR-spectrum mainly changes due to H2O
• Occurrence of emission lines
• Radial velocity variations

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Max
Max
Min
H2O
CO2
Min
Aringer et al. 2002
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Emission lines

• in miras and some semiregular variables
• present over 2/3 of the light cycle (not present
  after minimum)
• typically brightest after maximum
• first H lines, later Fe II, Fe I, Mg I, Si I, Mn
  II, Cr II, Ca II, Sr II, ...
• in some stars He I 10830 Å

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Fox et al. 1984
multiple emission or self-absorption?
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Joy 1954
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Near-IR absorption lines
Hinkle, Hall Ridgway 1982
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Hinkle, Lebzelter Scharlach 1997
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Nowotny et al. 2005
Alvarez et al. 2000
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Lebzelter et al. 2005
Lebzelter et al. 2001
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Lebzelter et al. 2001
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CO lines Dv1 Dv1 low exc. Dv2 mod.exc.
Dv2 high exc. Dv2 Dv3 high exc.
Dv2 Dv3
Na I, K I Cr I, Mn I TiO? 400 nm 800
nm 800 nm
Wallerstein 1985
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Variability and Parallax
Bastian Hefele 2005
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Filin 1952
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Microlensing surveys and LPVs

• MACHO http//wwwmacho.mcmaster.ca/
• OGLE http//www.astrouw.edu.pl/ogle/
• EROS http//eros.in2p3.fr/
• MOA http//www.phys.canterbury.ac.nz/moa/