Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump

The Red Clump is an overdensity in luminosity on the HR diagram, caused by certain Core-Helium Burning stars with similar core masses, a product of their evolutionary physics. We identify the exact luminosity of the Red Clump using asteroseismology, and then separately using Gaia data, to see how our assumptions about one method lead to us drawing different inferences in the other.

We find that changing asteroseismic temperature scale and/or corrections to scaling relations change the position of the Red Clump significantly, and that the corresponding parallax zero-point offset required to find that same Red Clump luminosity similarly varies significantly. It should be noted that if we assume asteroseismology to be absolute, we do not recover a parallax zero-point offset that agrees with similar work done by Zinn et al. 2018.

Clearly, there is still much to be done!

Transcript

1. @asteronomer
   ojhall94
   Oliver J. Hall
   Guy Davies, Yvonne Elsworth,
   Thomas North, Rafael García, Saniya Khan
   TASC4/KASC11
   Aarhus University
   12/07/2018
   Testing asteroseismology with Gaia DR2:
   Luminosity of the Red Clump
   !1
   

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2. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
   @asteronomer
   ojhall94
   

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3. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
   @asteronomer
   ojhall94
   » Disagreement between
   asteroseismic & Gaia distances in
   DR1
   » Investigated using the Red Clump
   » ‘seismic parallax’: distance from
   luminosity from seismic radius
   Seismic parallax (mas)
   Apparent K-band mag
   Davies+17
   

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4. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
   @asteronomer
   ojhall94
   » Lindegren+ (Quasars):
   » Quasars in Kepler
   field:
   » Riess+ (Cepheids):
   » Zinn+ (seismo):
   ϖzp
   = − 29μas
   ϖzp
   = − 46μas
   ϖzp
   = − 53μas
   ϖzp
   = − 30μas
   Arenou +18
   

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5. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
   @asteronomer
   ojhall94
   » We aim to investigate the RC magnitude in:
   » Seismic absolute magnitude
   » Absolute magnitude from photometry
   + Gaia
   » We vary:
   » Temperature scale
   » Scaling corrections
   » Parallax zero-point
   Arenou +18
   

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6. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
   @asteronomer
   ojhall94
   » Data from Yu+ 2018
   » Reclassify with Elsworth+ 2017
   » K-band photometry from 2MASS
   » Extinction from Green+ 2018
   » BCs from Casagrande & Vandenberg
   2014 (& 2018, BCcodes)
   » And Gaia data via Megan Bedell @
   gaia-kepler.fun!
   

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7. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
   @asteronomer
   ojhall94
   μ σ Q σo ̂
   Mi
   σ ̂
   Mi
   

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8. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
   @asteronomer
   ojhall94
   μ σ Q σo Mi
   ̂
   Mi
   σ ̂
   Mi
   

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9. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
   @asteronomer
   ojhall94
   » Little more complicated for Gaia…
   » Two new parameters:
   » , length scale of distance prior
   » , parallax zero point
   » Input photometry, parallax, extinction
   Adapted from Hawkins+ 17
   μ σ Q σo
   ϖzp
   L
   ϖzp
   

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10. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
    @asteronomer
    ojhall94
    » Seismic luminosity of the RC
    is correlated with Teff scale
    » Choice of scaling-relation
    correction has non-negligible
    impact on RC luminosity
    

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11. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
    @asteronomer
    ojhall94
    » Used seismic RC
    magnitude to inform our
    Gaia model
    » For different RC
    magnitudes, the model
    requires a different
    zeropoint!
    μ = − 0.0068ϖzp
    − 1.952
    

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12. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
    @asteronomer
    ojhall94
    » If we trust a parallax zero-point,
    we can use the RC to calibrate
    asteroseismology
    OR
    » If we trust asteroseismic
    assumptions completely, we can
    use the RC to calibrate Gaia
    

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13. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
    @asteronomer
    ojhall94
    » If we trust a parallax zero-point,
    we can use the RC to calibrate
    asteroseismology
    OR
    » If we trust asteroseismic
    assumptions completely, we can
    use the RC to calibrate Gaia
    Slumstrup, P14
    

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14. Testing asteroseismology with Gaia DR2: Luminosity of the Red Clump
    @asteronomer
    ojhall94
    In summary…
    » Used hierarchical models to locate the RC in
    seismic & Gaia data
    » Choice of seismic temperature scale & scaling
    relations have strong impact on position of RC
    » Position of RC has strong correlation with
    parallax zero-point
    » To calibrate one, we’ll need a strong constraint
    on the other!
    

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