Period Changes in Delta Scuti stars

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Period Changes in Delta Scuti stars

• Matthew Templeton
• AAVSO
• March 25, 2005

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What are Delta Scuti stars?

• Pulsating variables on the lower instability
  strip
• 1.0-2.5 solar masses
• Periods of tens of minutes to 0.3 days
• From pre- to post-main sequence
• Radial and non-radial modes
• High and low amplitudes
• Single or multiple periods

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LADS and HADS
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The Instability Strip

• Pulsations driven by the H/He ionization region
• Cepheids, RR Lyrae, dSct

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Stellar Evolution
Delta Scuti stars can have multiple crossings (if
you include the main sequence!)
Cepheids undergo multiple crossings of the
instability strip
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Period Changes
Period changes have been observed in Cepheids, RR
Lyrae, and delta Scuti stars.
Evolution or not?
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Cepheids
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Cepheids
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RR Lyrae
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Period changes?
Percy et al. (1980), Rodriguez et al. (1995),
Breger Pamyatnykh (1998)
Its NOT evolution! Too fast, wrong direction.
Zhou (2001), Derekas et al. (2003)
It can be evolution! (Or binarity or light
curve variations or)
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Evolution? DY Her
(Derekas et al. 2003)
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Binarity SZ Lyn
(Derekas et al. 2003)
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Mode interaction? V1162 Ori
(Arentoft Sterken 2000)
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Nothing! AE UMa
The period change was a result of the light
curve variations from the secondary
mode. However, the period of the secondary mode
IS changing!
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No idea BE Lyn
(Derekas et al. 2003)
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What is going on?

• A few HADS appear to exhibit evolutionary period
  changes
• Some (especially LADS) have complex period
  changes that cant be evolutionary in origin
• Binarity. (SZ Lyn, definitely)
• Magnetic cycles?
• Non-linear mode interactions?
• Diffusion?
• Non-standard mass loss?

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Magnetic cycles
The effects of magnetic fields in stellar
structure are only beginning to be understood
Can local and global magnetic field variations
affect radial and non-radial modes, at least a
little?
Dont know for sure (but probably could)
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Mode interactions
Pulsations in stars are modeled as small
perturbations of eigenmodes, which interact
linearly (beating for example)
Can modes interact non-linearly? That is, can
they affect one another directly, or change the
structure of the star enough that mode periods
change on secular timescales?
Dont know yet
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Diffusion, mass loss
Diffusion of helium, heavy elements in stellar
interior can affect stellar structure, and hence
mode periods.
We dont think mass loss is very strong in these
stars, but what if it is sometimes?
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What to do now?
Keep observing!
Detection of period changes requires long-term
monitoring. Continued observations are
important. And there are lots of HADS that
havent been well studied (yet).
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dScts and AAVSO

• Similar behavior to RR Lyraes (already a few on
  the RR Lyrae Cmtes list!)
• Short periods, so you can see at least one full
  cycle in a few hours or less
• Diversity of behavior makes each star unique

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dScts and AAVSO

• dScts are important objects, lots still to be
  learned!
• AAVSO EB, RR, dCep dSct, too!
• Campaigns? Charts?
• Suggestions?