Stellar masks and bisector’s shape for M-type stars observed in the GAPS programme with HARPS-N at TNG

Rainer, M.; Borsa, F.; Affer, L.

doi:10.1007/s10686-020-09654-z

Cited by 15 publications

(10 citation statements)

References 27 publications

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“…However the M2 line-mask has been found to heavily distort the CCFs (see e.g. Rainer et al 2020). Moreover, we also found that the values of the FWHM obtained for stars where a M2 line-mask was used were systematically (and significantly) lower than for the stars where other line-masks were employed.…”

Section: Observations and Data Reductionsupporting

confidence: 53%

Long-term stellar activity variations and their effect on radial-velocity measurements

Costes,

Watson,

de Mooij

et al. 2021

Preprint

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Long-term stellar activity variations can affect the detectability of long-period and Earthanalogue extrasolar planets. We have, for 54 stars, analysed the long-term trend of five activity indicators: log 𝑅 HK , the cross-correlation function (CCF) bisector span, CCF full-width-athalf-maximum, CCF contrast, and the area of the Gaussian fit to the CCF; and studied their correlation with the RVs. The sign of the correlations appears to vary as a function of stellar spectral type, and the transition in sign signals a noteworthy change in the stellar activity properties where earlier type stars appear more plage dominated. These transitions become more clearly defined when considered as a function of the convective zone depth. Therefore, it is the convective zone depth (which can be altered by stellar metallicity) that appears to be the underlying fundamental parameter driving the observed activity correlations. In addition, for most of the stars, we find that the RVs become increasingly red-shifted as activity levels increase, which can be explained by the increase in the suppression of convective blue-shift. However, we also find a minority of stars where the RVs become increasingly blue-shifted as activity levels increase. Finally, using the correlation found between activity indicators and RVs, we removed RV signals generated by long-term changes in stellar activity. We find that performing simple cleaning of such long-term signals enables improved planet detection at longer orbital periods.

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Section: Observations and Data Reductionsupporting

confidence: 53%

Long-term stellar activity variations and their effect on radial-velocity measurements

Costes,

Watson,

de Mooij

et al. 2021

Preprint

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“…The FAP levels are computed using the analytical relation also described in Zechmeister & Kürster (2009) for this normalization. We display the GLSP of the BIS for completness and comparison with C19, but we caution that the reliability of BIS measurements from CCFs for M dwarfs is uncertain (Rainer et al 2020).…”

Section: Lc Analysismentioning

confidence: 99%

Warm terrestrial planet with half the mass of Venus transiting a nearby star

Demangeon

Osorio

Alibert

et al. 2021

A&A

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In recent years, the advent of a new generation of radial velocity instruments has allowed us to detect planets with increasingly lower mass and to break the one Earth-mass barrier. Here we report a new milestone in this context by announcing the detection of the lowest-mass planet measured so far using radial velocities: L 98-59 b, a rocky planet with half the mass of Venus. It is part of a system composed of three known transiting terrestrial planets (planets b–d). We announce the discovery of a fourth nontransiting planet with a minimum mass of 3.06−0.37+0.33 M⊕ and an orbital period of 12.796−0.019+0.020 days and report indications for the presence of a fifth nontransiting terrestrial planet. With a minimum mass of 2.46−0.82+0.66 M⊕ and an orbital period 23.15−0.17+0.60 days, this planet, if confirmed, would sit in the middle of the habitable zone of the L 98-59 system. L 98-59 is a bright M dwarf located 10.6ṗc away. Positioned at the border of the continuous viewing zone of the James Webb Space Telescope, this system is destined to become a corner stone for comparative exoplanetology of terrestrial planets. The three transiting planets have transmission spectrum metrics ranging from 49 to 255, which undoubtedly makes them prime targets for an atmospheric characterization with the James Webb Space Telescope, the Hubble Space Telescope, Ariel, or ground-based facilities such as NIRPS or ESPRESSO. With an equilibrium temperature ranging from 416 to 627 K, they offer a unique opportunity to study the diversity of warm terrestrial planets without the unknowns associated with different host stars. L 98-59 b and c have densities of 3.6−1.5+1.4 and 4.57−0.85+0.77 g cm−3, respectively, and have very similar bulk compositions with a small iron core that represents only 12 to 14% of the total mass, and a small amount of water. However, with a density of 2.95−0.51+0.79 g cm−3 and despite a similar core mass fraction, up to 30% of the mass of L 98-59 d might be water.

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“…Masks optimized for G2-, K5-, and M2-type stars are readily available and have been widely used, though more recently, bespoke masks for other stellar types have also been developed (e.g. Rainer, Borsa & Affer 2020). The DRS uses the resulting CCF both for RV extraction and for building stellar activity indicators, since e.g.…”

Section: Drs Rv Extraction and Activity Indicatorsmentioning

confidence: 99%

A HARPS-N mass for the elusive Kepler-37d: a case study in disentangling stellar activity and planetary signals

Rajpaul

Buchhave

Lacedelli

et al. 2021

Monthly Notices of the Royal Astronomical Society

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To date, only 18 exoplanets with radial velocity (RV) semi-amplitude <2 m s−1 have had their masses directly constrained. The biggest obstacle to RV detection of such exoplanets is variability intrinsic to stars themselves, e.g. nuisance signals arising from surface magnetic activity such as rotating spots and plages, which can drown out or even mimic planetary RV signals. We use Kepler-37 – known to host three transiting planets, one of which, Kepler-37d, should be on the cusp of RV detectability with modern spectrographs – as a case study in disentangling planetary and stellar activity signals. We show how two different statistical techniques – one seeking to identify activity signals in stellar spectra, and another to model activity signals in extracted RVs and activity indicators – can each enable a detection of the hitherto elusive Kepler-37d. Moreover, we show that these two approaches can be complementary, and in combination, facilitate a definitive detection and precise characterisation of Kepler-37d. Its RV semi-amplitude of 1.22 ± 0.31 m s−1 (mass 5.4 ± 1.4 M⊕) is formally consistent with TOI-178b’s $1.05^{+0.25}_{-0.30}$ m s−1, the latter being the smallest detected RV signal of any transiting planet to date, though dynamical simulations suggest Kepler-37d’s mass may be on the lower end of our 1σ credible interval. Its consequent density is consistent with either a water-world or that of a gaseous envelope ($\sim 0.4\%$ by mass) surrounding a rocky core. Based on RV modelling and a re-analysis of Kepler-37 TTVs, we also suggest that the putative (non-transiting) planet Kepler-37e should be stripped of its ‘confirmed’ status.

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Stellar masks and bisector’s shape for M-type stars observed in the GAPS programme with HARPS-N at TNG

Cited by 15 publications

References 27 publications

Long-term stellar activity variations and their effect on radial-velocity measurements

Long-term stellar activity variations and their effect on radial-velocity measurements

Warm terrestrial planet with half the mass of Venus transiting a nearby star

A HARPS-N mass for the elusive Kepler-37d: a case study in disentangling stellar activity and planetary signals

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