On the Metal Richness of M Dwarfs With Planets

Context. GJ 436b is one of the few transiting warm Neptunes for which a detailed characterisation of the atmosphere is possible, whereas its non-negligible orbital eccentricity calls for further investigation. Independent analyses of several individual datasets obtained with Spitzer have led to contradicting results attributed to the different techniques used to treat the instrumental effects. Aims. We aim at investigating these previous controversial results and developing our knowledge of the system based on the full Spitzer photometry dataset combined with new Doppler measurements obtained with the HARPS spectrograph. We also want to search for additional planets. Methods. We optimise aperture photometry techniques and the photometric deconvolution algorithm DECPHOT to improve the data reduction of the Spitzer photometry spanning wavelengths from 3-24 µm. Adding the high-precision HARPS radial velocity data, we undertake a Bayesian global analysis of the system considering both instrumental and stellar effects on the flux variation.Results. We present a refined radius estimate of R P = 4.10 ± 0.16 R ⊕ , mass M P = 25.4 ± 2.1 M ⊕ , and eccentricity e = 0.162 ± 0.004 for GJ 436b. Our measured transit depths remain constant in time and wavelength, in disagreement with the results of previous studies. In addition, we find that the post-occultation flare-like structure at 3.6 µm that led to divergent results on the occultation depth measurement is spurious. We obtain occultation depths at 3.6, 5.8, and 8.0 µm that are shallower than in previous works, in particular at 3.6 µm. However, these depths still appear consistent with a metal-rich atmosphere depleted in methane and enhanced in CO/CO 2 , although perhaps less than previously thought. We could not detect a significant orbital modulation in the 8 µm phase curve. We find no evidence of a potential planetary companion, stellar activity, or a stellar spin-orbit misalignment. Conclusions. Recent theoretical models invoking high-metallicity atmospheres for warm Neptunes are a reasonable match to our results, but we encourage new modelling efforts based on our revised data. Future observations covering a wide wavelength range of GJ 436b and other Neptune-class exoplanets will further illuminate their atmosphere properties, whilst future accurate radial velocity measurements might explain the eccentricity.

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“…26) as supported by our derived metallicity, and by e.g. Johnson & Apps (2009) and Neves et al (2013) with [Fe/H] = +0.25 and +0.02 respectively.…”

Section: On the Host Starsupporting

confidence: 76%

A global analysis ofSpitzerand new HARPS data confirms the loneliness and metal-richness of GJ 436 b

Lanotte

Gillon

Demory

et al. 2014

A&A

128

133

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“…Owing to the difficulty in deriving precise values for the effective temperature and metallicity based on spectral fitting procedures (e.g. Valenti et al 1998;Woolf & Wallerstein 2005;Bean et al 2006;Önehag et al 2012), most determinations of their values are based on calibrations using colors (Bonfils et al 2005a;Johnson & Apps 2009;Casagrande et al 2008;Schlaufman & Laughlin 2010;Neves et al 2012) or spectroscopic indices (e.g. Terrien et al 2012;Rojas-Ayala et al 2012;Mann et al 2013;Neves et al 2013).…”

Section: M-dwarfs Starsmentioning

confidence: 99%

SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs

Santos

Sousa

Mortier

et al. 2013

A&A

274

255

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Context. Thanks to the importance that the star-planet relation has to our understanding of the planet formation process, the precise determination of stellar parameters for the ever increasing number of discovered extra-solar planets is of great relevance. Furthermore, precise stellar parameters are needed to fully characterize the planet properties. It is thus important to continue the efforts to determine, in the most uniform way possible, the parameters for stars with planets as new discoveries are announced. Aims. In this paper we present new precise atmospheric parameters for a sample of 48 stars with planets. We then take the opportunity to present a new catalogue of stellar parameters for FGK and M stars with planets detected by radial velocity, transit, and astrometry programs. Methods. Stellar atmospheric parameters and masses for the 48 stars were derived assuming local thermodynamic equilibrium (LTE) and using high-resolution and high signal-to-noise spectra. The methodology used is based on the measurement of equivalent widths for a list of iron lines and making use of iron ionization and excitation equilibrium principles. For the catalogue, and whenever possible, we used parameters derived in previous works published by our team, using well-defined methodologies for the derivation of stellar atmospheric parameters. This set of parameters amounts to over 65% of all planet host stars known, including more than 90% of all stars with planets discovered through radial velocity surveys. For the remaining targets, stellar parameters were collected from the literature. Results. The stellar parameters for the 48 stars are presented and compared with previously determined literature values. For the catalogue, we compile values for the effective temperature, surface gravity, metallicity, and stellar mass for almost all the planet host stars listed in the Extrasolar Planets Encyclopaedia. This data will be updated on a continuous basis. The compiled catalogue is available online. The data can be used for statistical studies of the star-planet correlation, as well as for the derivation of consistent properties for known planets.

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“…We tested the metallicity calibration of Bonfils et al (2005) (hereafter B05), as well as the calibrations of Johnson & Apps (2009) (hereafter JA09) and Schlaufman & Laughlin (2010) (hereafter SL10), with a sample of 17 M dwarf secondaries with a wide (> 5 arcsec separation) physical FGK companion.…”

Section: Preliminary Resultsmentioning

confidence: 99%

Metallicity of M dwarfs: The link to exoplanets

Neves

Bonfils²,

Santos³

2010

Proc. IAU

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Abstract. The determination of the stellar parameters of M dwarfs is of prime importance in the fields of galactic, stellar and planetary astronomy. M stars are the least studied galactic component regarding their fundamental parameters. Yet, they are the most numerous stars in the galaxy and contribute to most of its total (baryonic) mass. In particular, we are interested in their metallicity in order to study the star-planet connection and to refine the planetary parameters. As a preliminary result we present a test of the metallicity calibrations of Bonfils et al. Following B05, three papers with different calibrations were published: JA09, SL10, and Rojas-Ayala et al. (2010) (hereafter RA10). Each work claims a calibration with a better precision than the previous ones, and in general, poor V photometry is identified as a serious limitation. In order to address the photometric limitation, only M stars with precise V photometry ( σ < 0.04 mag) were selected. Most stars have V magnitude uncertainties of 0.01 or 0.02 mag. Note that the RA10 calibration was not tested because it requires IR indices that we do not have. This test will be done in the near future.We found that the metallicity values of our stars (obtained from the FGK primary component) are in reasonable agreement with the [Fe/H] values obtained with all calibrations, as can be seen in Fig. 1. However, our calibrators are found to be more metal poor (on average) than both JA09 and SL10 calibrations.A better photometry did not improve the dispersion measured around the different calibrations. This means that precision on V photometry may not be the main limitation in the derivation of the [Fe/H] calibration. Table 1. shows a quantitative comparison between the calibrations. We note that the rms, RM S P and the R 2 ap values were offset-corrected. In general, the calibrations have similar offsets, rms, RM S P , and correlation coefficients. 443at https://www.cambridge.org/core/terms. https://doi

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On the Metal Richness of M Dwarfs With Planets

Cited by 201 publications

References 33 publications

A global analysis ofSpitzerand new HARPS data confirms the loneliness and metal-richness of GJ 436 b

A global analysis ofSpitzerand new HARPS data confirms the loneliness and metal-richness of GJ 436 b

SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs

Metallicity of M dwarfs: The link to exoplanets

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