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Characterizing Retired A Stars Luan Ghezzi Harvard-Smithsonian Center for Astrophysics Collaborators: John Johnson (CfA), Jessi Cisewski (Yale) August 7 th , 2015
Characterizing Retired A Stars
Luan Ghezzi
Harvard-Smithsonian Center for Astrophysics
Collaborators: John Johnson (CfA), Jessi Cisewski (Yale)
August 7th, 2015
Occurrence of giant planets appears to increase with stellar mass…
Johnson et al. (2010)
Johnson et al. (2010)
M Dwarfs f = 3.3%
Occurrence of giant planets appears to increase with stellar mass…
Johnson et al. (2010)
M Dwarfs f = 3.3%
FGK Dwarfs f = 8.5%
Occurrence of giant planets appears to increase with stellar mass…
Johnson et al. (2010)
M Dwarfs f = 3.3%
FGK Dwarfs f = 8.5%
Retired A Stars f = 14.0%
Occurrence of giant planets appears to increase with stellar mass…
Johnson et al. (2010)
M Dwarfs f = 3.3%
FGK Dwarfs f = 8.5%
Retired A Stars f = 14.0%
Occurrence of giant planets appears to increase with stellar mass…
…but masses could have been overestimated
Galactic Models Johnson, Morton & Wright (2013) Lloyd (2011,2013)
…but masses could have been overestimated
Schlaufman & Winn (2013)
Kinematics
Galactic Models Johnson, Morton & Wright (2013) Lloyd (2011,2013)
Scientific motivation
Johnson et al. (2010)
Were the masses of Retired A Stars overestimated?
Scientific motivation
Johnson et al. (2010)
Were the masses of Retired A Stars overestimated?
• Problems in the atmospheric parameters?
• Problems in the mass determination with the evolutionary tracks?
• Many implications: - Planetary formation - Stellar evolution - Galactic models
• Accurate measurements of masses of evolved stars.
Sample of 59 benchmark stars from the literature
Ghezzi & Johnson (2015) Submitted to ApJ
Stars in binary systems: 26 Field stars with asteroseismology: 33
PARSEC tracks from Bressan et al. (2012)
Masses are not overestimated by PARSEC tracks
∆𝑴 = −𝟎. 𝟏𝟎 ± 𝟎. 𝟎𝟓 𝑴
∆𝑴
𝑴𝑹𝒆𝒇.= −𝟏. 𝟑𝟎 ± 𝟐. 𝟒𝟐 %
Ghezzi & Johnson (2015)
Model-dependent masses calculated with PARAM
No trends in the residuals
Ghezzi & Johnson (2015)
Radii are slightly underestimated by PARSEC tracks
∆𝑹 = −𝟏. 𝟎𝟎 ± 𝟎. 𝟏𝟕 𝑹
∆𝑹
𝑹𝑹𝒆𝒇.= −𝟒. 𝟖𝟏 ± 𝟏. 𝟑𝟐 %
Ghezzi & Johnson (2015)
Model-dependent radii calculated with PARAM
Ages of stars in binary systems are consistent
Ghezzi & Johnson (2015)
• 10 systems with 2 evolved stars.
• Independent analysis for each member.
• Ages of components A and B agree within 15 ± 14% on average.
Masses of Retired A Stars proxies are not overestimated
Need more stars to confirm this result.
∆𝑴 = −𝟎. 𝟏𝟖 ± 𝟎. 𝟏𝟏 𝑴
∆𝑴
𝑴𝑹𝒆𝒇.= −𝟖. 𝟗𝟕 ± 𝟖. 𝟗𝟑 %
Ghezzi & Johnson (2015)
Revisiting the actual Retired A Stars
Ghezzi, Johnson & Cisewski (2016, in prep.)
Preliminary results
𝑉𝑡𝑜𝑡𝑎𝑙 = 𝑈2 + 𝑉2 + 𝑊2
Almost ready for the weekend?
To remember on the beach
• Evolutionary tracks (PARSEC + PARAM) provide reliable masses for evolved stars.
• Accuracy: -1.30 ± 2.42%
• Mass range: ≈0.7 – 4.5 M
• Heterogeneous data.
Ghezzi & Johnson (2015)
