J/ApJ/920/21 HARPS-N time series of solar observations (Milbourne+, 2021)
Estimating Magnetic Filling Factors from Simultaneous Spectroscopy and
Photometry; Disentangling Spots, Plage, and Network.
Milbourne T.W., Phillips D.F., Langellier N., Mortier A., Haywood R.D.,
Saar S.H., Cegla H.M., Collier Cameron A., Dumusque X., Latham D.W.,
Malavolta L., Maldonado J., Thompson S., Vanderburg A., Watson C.A.,
Buchhave L.A., Cecconi M., Cosentino R., Ghedina A., Gonzalez M., Lodi M.,
Lopez-Morales M.,Sozzetti A.,Walsworth R.L.
<Astrophys. J., 920, 21 (2021)>
=2021ApJ...920...21M 2021ApJ...920...21M
ADC_Keywords: Solar system; Sun; Photometry, K-line
Keywords: Exoplanets ; Radial velocity ; Exoplanet detection methods ;
Solar activity ; Solar active regions
Abstract:
State-of-the-art radial velocity (RV) exoplanet searches are limited
by the effects of stellar magnetic activity. Magnetically active
spots, plage, and network regions each have different impacts on the
observed spectral lines and therefore on the apparent stellar RV.
Differentiating the relative coverage, or filling factors, of these
active regions is thus necessary to differentiate between
activity-driven RV signatures and Doppler shifts due to planetary
orbits. In this work, we develop a technique to estimate
feature-specific magnetic filling factors on stellar targets using
only spectroscopic and photometric observations. We demonstrate linear
and neural network implementations of our technique using observations
from the solar telescope at HARPS-N, the HK Project at the Mt. Wilson
Observatory, and the Total Irradiance Monitor onboard SORCE. We then
compare the results of each technique to direct observations by the
Solar Dynamics Observatory. Both implementations yield filling factor
estimates that are highly correlated with the observed values.
Modeling the solar RVs using these filling factors reproduces the
expected contributions of the suppression of convective blueshift and
rotational imbalance due to brightness inhomogeneities. Both
implementations of this technique reduce the overall activity-driven
rms RVs from 1.64 to 1.02m/s, corresponding to a 1.28m/s reduction in
the rms variation. The technique provides an additional 0.41m/s
reduction in the rms variation compared to traditional activity
indicators.
Description:
We use the HARPS-N solar telescope measurements of the S-index, as
described in Milbourne+, 2019, J/ApJ/874/107 (MH19) and Collier
Cameron+, 2019MNRAS.487.1082C 2019MNRAS.487.1082C. The S-index quantitatively represents
activity-driven chromospheric re-emission in the CaII H and K lines.
The presence of spots, plage, and network all increase the S-index.
The solar telescope takes exposures every five minutes while the Sun
is visible. Each measurement of the S-index has an average precision
of 2.5x10-4 or a fractional uncertainty of 0.0016.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig2.dat 61 1377 Time series of solar observations used in this work
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See also:
J/other/Nat/486.375 : Stellar parameters of KOI stars (Buchhave+, 2012)
J/ApJ/835/25 : Calibrated solar S-index time series (Egeland+, 2017)
J/ApJ/874/107 : HARPS-N solar radial velocities & activity (Milbourne+, 2019)
J/A+A/648/A103 : Thorium line list (Dumusque+, 2021)
Byte-by-byte Description of file: fig2.dat
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Bytes Format Units Label Explanations
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1- 11 F11.3 d JD [2455294/2458045] Julian Date
13- 18 F6.4 --- SI [0.15/0.18] Calcium S-Index from Mt. Wilson &
HARPS-N
20- 28 F9.4 W/m2 TSI [1359/1363] Total Solar Irradiance from SORCE/TIM
30- 39 F10.8 --- Plage [0.0002/0.05] SDO/HMI plage filling factor
41- 48 F8.6 --- Network [0.01/0.03] SDO/HMI network filling factor
50- 61 E12.5 --- Spot [-7.87/0.009] SDO/HMI spot filling factor
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 06-Feb-2023