J/ApJ/874/107 HARPS-N solar radial velocities and activity (Milbourne+, 2019)
HARPS-N solar RVs are dominated by large, bright magnetic regions.
Milbourne T.W., Haywood R.D., Phillips D.F., Saar S.H., Cegla H.M.,
Cameron A.C., Costes J., Dumusque X., Langellier N., Latham D.W.,
Maldonado J., Malavolta L., Mortier A., III M.L.P., Thompson S.,
Watson C.A., Bouchy F., Buchschacher N., Cecconi M., Charbonneau D.,
Cosentino R., Ghedina A., Glenday A.G., Gonzalez M., Li C.-H., Lodi M.,
Lopez-Morales M., Lovis C., Mayor M., Micela G., Molinari E., Pepe F.,
Piotto G., Rice K., Sasselov D., Segransan D., Sozzetti A., Szentgyorgyi A.,
Udry S., Walsworth R.L.
<Astrophys. J., 874, 107 (2019)>
=2019ApJ...874..107M 2019ApJ...874..107M
ADC_Keywords: Sun; Radial velocities
Keywords: planets and satellites: detection ; Sun: activity ;
Sun: faculae, plages ; Sun: granulation ; sunspots ;
techniques: radial velocities
Abstract:
State-of-the-art radial-velocity (RV) exoplanet searches are currently
limited by RV signals arising from stellar magnetic activity. We
analyze solar observations acquired over a 3yr period during the
decline of Carrington Cycle 24 to test models of RV variation of
Sun-like stars. A purpose-built solar telescope at the High Accuracy
Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N)
provides disk-integrated solar spectra, from which we extract RVs and
logR'HK. The Solar Dynamics Observatory (SDO) provides disk-resolved
images of magnetic activity. The Solar Radiation and Climate
Experiment (SORCE) provides near-continuous solar photometry,
analogous to a Kepler light curve. We verify that the SORCE photometry
and HARPS-N logR'HK correlate strongly with the SDO-derived magnetic
filling factor, while the HARPS-N RV variations do not. To explain
this discrepancy, we test existing models of RV variations. We
estimate the contributions of the suppression of convective blueshift
and the rotational imbalance due to brightness inhomogeneities to the
observed HARPS-N RVs. We investigate the time variation of these
contributions over several rotation periods, and how these
contributions depend on the area of active regions. We find that
magnetic active regions smaller than 60Mm2 do not significantly
suppress convective blueshift. Our area-dependent model reduces the
amplitude of activity-induced RV variations by a factor of two. The
present study highlights the need to identify a proxy that correlates
specifically with large, bright magnetic regions on the surfaces of
exoplanet-hosting stars.
Description:
In this work, we analyze 3yr (Jul 2015-Sep 2017) of solar observations
during the decline of Carrington Cycle 24 to test models of
radial-velocity variations of Sun-like stars. We compare solar
telescope/HARPS-N measurements of the solar RVs and logR'HK, SDO/HMI
disk-resolved activity images, and SORCE/TIM measurements of the TSI.
The High Radial-velocity Planet Searcher for the Northern Hemisphere
(HARPS-N) spectrograph at the Telescopio Nazionale Galileo (TNG) on La
Palma is a cross-dispersed echelle spectrograph spanning the visible
range (383-690nm with resolving power R=115000). See Section 2.1.
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO) captures full-disk images of the Sun with near
single-granule resolution. We use six images each day, sampled evenly
over the 2.5yr operational period of the solar telescope at HARPS-N.
See Section 2.2.
The Total Irradiance Monitor (TIM) on board the SOlar Radiation and
Climate Experiment (SORCE) measures the Total Solar Irradiance (TSI)
using a set of four Electrical Substitution Radiometers. See Section 2.3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 67 613 The daily-averaged solar telescope and SDO/HMI
data products used in our analysis
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See also:
J/A+A/390/717 : Sun Solar Velocities in 1989-99 (IRIS++) (Salabert+, 2002)
J/AJ/138/312 : Activity of bright solar analogs (Hall+, 2009)
J/ApJ/725/875 : Chromospheric activity for CPS stars (Isaacson+, 2010)
J/A+A/544/A125 : Solar lines from Ceres spectra (Molaro+, 2012)
J/A+A/622/A85 : Starspot rotation rates vs. activity cycles (Nielsen+, 2019)
J/A+A/627/A118 : Optical activity indicators (Maldonado+, 2019)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 7 F7.3 d JD [1.4/790.6] Julian Date; JD-2457222.5
9- 15 F7.3 m/s RVel [98.4/113.2] Radial velocity
17- 21 F5.3 m/s e_RVel [0.39/0.6] Uncertainty in RVel
23- 28 F6.3 [-] logR'HK [-5.01/-4.95] Measured logR'HK value
30- 34 F5.3 --- fspot [0/2.31] Spot filling factor * 1000
36- 41 F6.3 --- fbright [15.38/59.11] Bright filling factor * 1000
43- 48 F6.3 m/s Delvp [-1.3/0.8] HMI-derived photometric
velocity shift
50- 55 F6.3 m/s Delvc [1.7/10.6] HMI-derived convective velocity shift
57- 61 F5.3 m/s Delvcs [0.02/6.8] Convective velocity shift (1)
63- 67 F5.3 m/s Delvcl [1.7/4.1] Convective velocity shift (2)
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Note (1): Due to active regions with area <20ppm.
Note (2): Due to active regions with area ≥20ppm.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Aug-2020