Radial-velocity variability of the Sun as a star with HARPS and - - PowerPoint PPT Presentation

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Radial-velocity variability of the Sun as a star with HARPS and - - PowerPoint PPT Presentation

Mar 07, 2024 49 likes •191 views

Radial-velocity variability of the Sun as a star with HARPS and HARPS-N Raphalle D. Haywood (Harvard Observatory) D. Charbonneau, A. Collier Cameron, X. Dumusque, A. Glenday, D. W. Latham, C. Lovis, J. Maldonado, G. Micela, E. Molinari, A.

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SLIDE 1

Raphaëlle D. Haywood (Harvard Observatory)

  • D. Charbonneau, A. Collier Cameron, X. Dumusque, A. Glenday, D. W. Latham, C. Lovis,
  • J. Maldonado, G. Micela, E. Molinari, A. Mortier, F. Pepe, D. F. Phillips, S. Udry

Radial-velocity variability of the Sun as a star

with HARPS and HARPS-N

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SLIDE 2

Motivation

Stellar activity is the main limitation in exoplanet radial-velocity (RV) searches

  • Can we observe the Sun as a star with a stellar

spectrograph?

  • Can we reconstruct the disc-averaged RV of the Sun using

high spatial resolution solar images? Two experiments:

  • 1. HARPS observations of sunlight reflected from asteroid

Vesta

  • 2. HARPS-N observations of disc-integrated sunlight through

the solar telescope

SDO 3.6m/HARPS solar/HARPS-N

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SLIDE 3

Experiment 1: sunlight scattered off Vesta

Sun as-a-star Earth

Observations span ~2 solar rotations taken during Sept. — Dec. 2011

Haywood et al. (2016)

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SLIDE 4

Sun as-a-star Earth

Observations span ~2 solar rotations taken during Sept. — Dec. 2011

Haywood et al. (2016)

Experiment 1: sunlight scattered off Vesta

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SLIDE 5

Reconstruct solar activity RV with SDO images

Technique developed by Meunier et al. (2010)

Doppler image Continuum intensity Magnetic flux Thresholded image

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SLIDE 6

How do active regions induce radial-velocity variations?

Rotational imbalance due to brightness inhomogeneities (~0.1 m/s)

Star rotates Doppler shifts balanced More redshift More blueshift Doppler shifts balanced

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SLIDE 7

How do active regions induce radial-velocity variations?

Rotational imbalance due to brightness inhomogeneities (~0.1 m/s)

Star rotates Doppler shifts balanced More redshift More blueshift Doppler shifts balanced

Suppression of convective blueshift by magnetic regions (~few m/s)

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SLIDE 8

How do active regions induce radial-velocity variations?

Rotational imbalance due to brightness inhomogeneities (~0.1 m/s)

Star rotates Doppler shifts balanced More redshift More blueshift Doppler shifts balanced

Suppression of convective blueshift by magnetic regions (~few m/s)

Earth orbit around Sun: 0.09 m/s!

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SLIDE 9

Can we reconstruct the radial velocity of the Sun?

(a) (b) (c) (d) (e)

Time [days]

ΔRVphot

HARPS Sun as-a-star RVs

Model Residuals

[m/s]

ΔRVconv

Haywood et al. (2016)

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SLIDE 10

Faculae are the main source of suppression of convective blueshift

Faculae pixels Sunspot pixels

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SLIDE 11

Optical lightcurves can only give incomplete prediction of RV variations Because sunspots and faculae are not completely co-spatial

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SLIDE 12

Experiment 2: solar telescope at HARPS-N

Full dataset since July 2015, 5-min cadence

See X. Dumusque’s plenary talk on Thursday

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SLIDE 13

velocity time

Time-series of spectral line profile distortions seen by HARPS-N

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SLIDE 14
  • We measured the disc-averaged radial-velocity

variations of the Sun with two exoplanet-hunting spectrographs

Summary

  • The dominant contribution to activity-induced

radial-velocity variations is suppression of convective blueshift via faculae, not spots

(Meunier et al. 2010a, b, Haywood et al. 2016)

  • Studying distortions in the spectral line profiles

will give us the proxies we need to correct the radial velocities of other stars