Observing the brightest stars

Tim WhiteStellar Astrophysics Centre, Aarhus University

Why bright stars?

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Why bright stars?

We want to characterize stars with the greatest possible precision:

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Why bright stars?

We want to characterize stars with the greatest possible precision:

• In order to provide the most stringent tests of stellar models

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Why bright stars?

We want to characterize stars with the greatest possible precision:

• In order to provide the most stringent tests of stellar models

• In order to achieve the best possible characterization of exoplanets

505/09/2017 PLATO Mission Conference 2017 – University of Warwick

Why bright stars?

We want to characterize stars with the greatest possible precision:

• In order to provide the most stringent tests of stellar models

• In order to achieve the best possible characterization of exoplanets

We need to use all of the tools at our disposal:

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Why bright stars?

We want to characterize stars with the greatest possible precision:

• In order to provide the most stringent tests of stellar models

• In order to achieve the best possible characterization of exoplanets

We need to use all of the tools at our disposal:• Asteroseismology

705/09/2017 PLATO Mission Conference 2017 – University of Warwick

Why bright stars?

We want to characterize stars with the greatest possible precision:

• In order to provide the most stringent tests of stellar models

• In order to achieve the best possible characterization of exoplanets

We need to use all of the tools at our disposal:• Asteroseismology

• Spectroscopy

805/09/2017 PLATO Mission Conference 2017 – University of Warwick

Why bright stars?

We want to characterize stars with the greatest possible precision:

• In order to provide the most stringent tests of stellar models

• In order to achieve the best possible characterization of exoplanets

We need to use all of the tools at our disposal:• Asteroseismology

• Spectroscopy

• Interferometry

905/09/2017 PLATO Mission Conference 2017 – University of Warwick

Why bright stars?

We want to characterize stars with the greatest possible precision:

• In order to provide the most stringent tests of stellar models

• In order to achieve the best possible characterization of exoplanets

We need to use all of the tools at our disposal:• Asteroseismology

• Spectroscopy

• Interferometry

• Polarimetry

1005/09/2017 PLATO Mission Conference 2017 – University of Warwick

Why bright stars?

We want to characterize stars with the greatest possible precision:

• In order to provide the most stringent tests of stellar models

• In order to achieve the best possible characterization of exoplanets

We need to use all of the tools at our disposal:• Asteroseismology

• Spectroscopy

• Interferometry

• Polarimetry

A long history of observations.1105/09/2017 PLATO Mission Conference 2017 – University of Warwick

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Why not bright stars?

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Why not bright stars?

SaturationOften our instruments are built to observe many faint stars.

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Why not bright stars?

SaturationOften our instruments are built to observe many faint stars.

1505/09/2017 PLATO Mission Conference 2017 – University of Warwick

Why not bright stars?

SaturationOften our instruments are built to observe many faint stars.

1605/09/2017 PLATO Mission Conference 2017 – University of Warwick

Arkūshanangarushash

ūtu

Why not bright stars?

SaturationOften our instruments are built to observe many faint stars.

Sometimes their names are hard to pronounce

1705/09/2017 PLATO Mission Conference 2017 – University of Warwick

Arkūshanangarushash

ūtu

Overcoming saturation

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Overcoming saturation

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Overcoming saturation

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Overcoming saturation

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Overcoming saturation

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HD 185351 – a ‘retired’ A star?

Problem: It’s difficult to conduct RV surveys around A-type stars. How can we find out about the population of planets aroundintermediate-mass stars?

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HD 185351 – a ‘retired’ A star?

Problem: It’s difficult to conduct RV surveys around A-type stars. How can we find out about the population of planets aroundintermediate-mass stars?

Solution: Wait until they evolve into cooler subgiants and giants.

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HD 185351 – a ‘retired’ A star?

Problem: It’s difficult to conduct RV surveys around A-type stars. How can we find out about the population of planets aroundintermediate-mass stars?

Solution: Wait until they evolve into cooler subgiants and giants.

Problem: How can you be sure these stars are evolved A stars?

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HD 185351 – a ‘retired’ A star?

Problem: It’s difficult to conduct RV surveys around A-type stars. How can we find out about the population of planets around intermediate-mass stars?

Solution: Wait until they evolve into cooler subgiants and giants.

Problem: How can you be sure these stars are evolved A stars?Solution: Characterize them with asteroseismology and

complementary techniques.

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HD 185351 – a ‘retired’ A star?

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Johnson et al. 2014, ApJ 794, 15

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HD 185351 – a ‘retired’ A star?

Hjørringgaard et al. 2017, MNRAS 464, 3713

1.5 Mʘ2.0 Mʘ

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Varying mixing length

1.5 Mʘ2.0 Mʘ1.5 Mʘ2.0 Mʘ

Hjørringgaard et al. 2017, MNRAS 464, 3713

αMLT= 2.00αMLT= 1.791

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Including convective coreovershooting

1.5 Mʘ2.0 Mʘ 1.5 Mʘ

2.0 Mʘ

Hjørringgaard et al. 2017, MNRAS 464, 3713

αMLT= 2.00, f = 0.030αMLT= 1.791, f = 0

The Pleiades

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‘Halo’ photometry

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White et al. 2017, MNRAS 471, 2882

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White et al. 2017, MNRAS 471, 2882

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White et al. 2017, MNRAS 471, 2882

‘Halo’ photometry

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𝑓𝑖 =

𝑗=1

𝑀

𝑤𝑗𝑝𝑖𝑗

https://github.com/hvidy/halophot

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White et al. 2017, MNRAS 471, 2882

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White et al. 2017, MNRAS 471, 2882

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Figure courtesy of JCD

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HypotheticalMaia Sequence

MAIA (4h?)

Figure courtesy of JCD Struve 1955, Sky & Telescope 14, 461

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R = 6.61 ± 0.11 Rʘ

i = 90 °

v sin i = 33 ± 5 km s-1

T = 10.34 ± 0.09 d

+0

−30

Summary

The brightest stars provide the best opportunities to characterize stars and test stellar models.

We have learnt from previous missions how to overcome the problems caused by saturation to achieve high precision photometry. We will apply these lessons to observe the brightest stars with PLATO.

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