Variable Stars in the Old Dwarf Spheroidal Galaxies, SDSS dSph

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Variable Stars in the Old Dwarf Spheroidal
Galaxies, SDSS dSphs, and Globular Clusters

• Charles Kuehn
• Michigan State University

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Galaxy formation mechanisms

• Cloud collapse

• Merging

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Pulsating Variable Stars
Class Periods (days) MV Pop Evo. Phase
? Cephei 1 100 -7 ? -2 I Blue Loop
? Scuti lt 0.5 2 ? 3 I MS
? Cephei lt 0.3 -4.5 ? -3.5 I MS
RV Tauri 30 100 -2 ? -1 I,II post-AGB
Mira gt 100 -2 ? 1 I,II AGB
Semiregulars gt 50 -3 ? 1 I,II AGB
RR Lyrae 0.3 1 0.0 ? 1.0 II HB
W Virginis 10 50 -3 ? -1 II post-HB
BL Herculis lt 10 -1 ? 0 II post-HB
SX Phoenicis lt 0.1 2 ? 3 II MS
A.C. 0.3 - 2.5 -2 ? 0 ? HB
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RR Lyrae

• Old Stars (gt 10 Gyr)
• Horizontal branch stars that lie in the
  instability strip
• Radially pulsate
• Mv 0.6

(Smith 1995)
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Bailey Types

• Based on shape of light curve
• RRab pulsate in the fundamental mode
• RRc pulsate in the first overtone

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Oosterhoff Groups

• In 1939 Oosterhoff noticed a division in the
  properties of globular cluster RR Lyraes
• OOI OOII
• ltPabgt .55d .65d
• ltPcgt .32d .37d
• NRRc/Ntotal .17 .44
• Fe/H gt-1.7 lt-1.7

(Oosterhoff 1939)
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Galaxy formation mechanisms
Oosterhoff plane
RR Lyrae stars
In the MW, most of the GCs with an RR Lyrae
population divide into two distinct groups,
based on ltPabgt Oo I ltPabgt 0.55 d OoII ltPabgt
0.65 d (Oosterhoff 1939)
Oo II
Gap
Oo I
And outside the Milky Way?
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Outside the Milky Way the old dSphs
Oo II
Gap
Oo I
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Field Stars in the Milky Way Halo

• The majority of the RRab stars fall along the
  Oosterhoff I line.
• Different from the stars seen in most dSphs which
  were Oosterhoff intermediate.

(Courtesy of N. DeLee)
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• Bootes
• Canes Venatici I
• Canes Venatici II
• Coma
• UMa II

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Building blocks of the MW halo?
dSph
GGCs
Luminosity --gt
LeoT
SDSS dSph
BooII
Dimensions --gt
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Cycles of Discovery Stellar Pulsation
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Oosterhoff II !!!!
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Variable Stars in CVn-I
RRab
RRc
AC
WIRO -Prime -2.3 m Wyoming Infrared
Observatory DOLORES - TNG 3.5 m Italian National
Telescope La Palma WHT - 4.2 m William Herschel
Telescope La Palma
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23 RR Lyrae stars 18 RRabs, 5 RRcs 3
ACs 61 candidate variables
ltPabgt 0.60 d
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Oosterhoff Intermediate!!!!
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ltPabgt 0.66 d
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Variables in the SDSS dSphs
Oosterhoff II !!!!
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Summary