Exoplanets & Exomoons

Characterizing Planetary Systems With SPIRou: M-dwarf Planet-search Survey And The Multiplanet Systems GJ 876 And GJ 1148

By Keith Cowing
Status Report
July 26, 2023
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Characterizing Planetary Systems With SPIRou: M-dwarf Planet-search Survey And The Multiplanet Systems GJ 876 And GJ 1148
Reconstructed maps of the large-scale field of GJ 876 in 2019 (top) and 2020 (bottom). The left, middle and right columns represent the radial, azimuthal, and meridional field components in spherical coordinates. The color bar is expressed in Gauss. The maps are shown in a flattened polar projection down to latitude –60◦ with the pole at the center and the equator depicted as a bold line. Outer ticks indicate phases of observations, assuming a rotation period of 83.7 d. — astro-ph.EP

SPIRou is a near-infrared spectropolarimeter and a high-precision velocimeter. The SPIRou Legacy Survey collected data from February 2019 to June 2022, half of the time devoted to a blind search for exoplanets around nearby cool stars.

The aim of this paper is to present this program and an overview of its properties, and to revisit the radial velocity (RV) data of two multiplanet systems, including new visits with SPIRou. From SPIRou data, we can extract precise RVs using efficient telluric correction and line-by-line measurement techniques, and we can reconstruct stellar magnetic fields from the collection of polarized spectra using the Zeeman-Doppler imaging method.

The stellar sample of our blind search in the solar neighborhood, the observing strategy, the RV noise estimates, chromatic behavior, and current limitations of SPIRou RV measurements on bright M dwarfs are described. In addition, SPIRou data over a 2.5-year time span allow us to revisit the known multiplanet systems GJ~876 and GJ~1148. For GJ~876, the new dynamical analysis including the four planets is consistent with previous models and confirms that this system is deep in the Laplace resonance and likely chaotic.

The large-scale magnetic map of GJ~876 over two consecutive observing seasons is obtained and shows a dominant dipolar field with a polar strength of 30~G, which defines the magnetic environment in which the inner planet with a period of 1.94~d is embedded. For GJ~1148, we refine the known two-planet model.

Chromatic behavior of the SPIRou data. Top: Relative S/N as a function of wavelength for the hottest and coolest stars in the sample. The S/N values have been normalized at 1650 nm. Middle: RV uncertainty for a selection of program stars with decreasing effective temperatures from top to bottom in the legend plotted along the spectrum. The yellow areas show the bands with maximum telluric absorption. The RV uncertainty has been normalized to an S/N of 150 at 1650 nm. Bottom: Ratio of the median RV error in a single band and the median RV error in the whole spectrum as a function of effective temperature for the whole data set. Larger symbols represent the few stars with a resolved projected rotational velocity. — astro-ph.EP

C. Moutou, X. Delfosse, A.C. Petit, J.-F. Donati, E. Artigau, P. Fouque, A. Carmona, M. Ould-Elhkim, L. Arnold, N.J. Cook, C. Cadieux, S. Bellotti, I. Boisse, F. Bouchy, P. Charpentier, P. Cortes-Zuleta, R. Doyon, G. Hebrard, E. Martioli, J. Morin, T. Vandal

Comments: accepted in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2307.11569 [astro-ph.EP] (or arXiv:2307.11569v1 [astro-ph.EP] for this version)
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Submission history
From: Claire Moutou
[v1] Fri, 21 Jul 2023 13:19:23 UTC (2,573 KB)

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