Michael Cretignier

Abstract:

Abstract Many areas of astrophysics, including exoplanetary studies, rely on precise and accurate stellar parameters. This demands that uncertainties on these parameters truly reflect all biases and systematics. Within this second work of the gr8stars collaboration, we take a set of 585 bright FGK dwarfs with high resolution, high signal-to-noise ratio spectra from the SOPHIE spectrograph. We determine stellar effective temperature, surface gravity, and metallicity using five different spectroscopic methods for each star, with an additional method used for comparisons. We find a typical scatter of 76 K in Teff, 0.14 dex in log g, and 0.07 dex in $\rm [Fe/H]$. These deviations are significantly larger than the average precision error on these parameters. We furthermore use isochrone fitting to determine mass, radius, and age for all 585 stars, using input from all results. We use the radii determined by SED fitting in the first gr8stars paper as a comparison to our isochronal radii from this work, in addition to comparing the isochronal log g to spectroscopic log g. The scatter in mass and radius from the use of different spectroscopic methods is investigated and propagated to exoplanetary parameters. The induced fractional uncertainties in planetary radius (≲ 3 %) and mass (≲ 5 %) are found to be below those typically found in the literature. We estimate a lower limit on planetary equilibrium temperature fractional uncertainty of ≈ 4 %, a noise floor that is currently not sufficiently represented in the literature.

Abstract:

-1 to be investigated. Long-term RV surveys allow the detection of Earth-like and super-Earth-like planets in the habitable zones of Sun-like stars, prime targets for future missions for the atmospheric characterization of exoplanets. We present the analysis of the nearby G8,V-type star HD 161098 (V = 7.68,mag, d =,29.75 pc). We searched for terrestrial planets in the habitable zone. We combined historical datasets with new data collected in an ongoing blind search program with HARPS, HARPS-N, and ESPRESSO. We utilized recently developed tools to extract RVs and to deal with the analysis of stellar activity. We performed a joint analysis of RVs and activity indicators to separate the planetary signals from those related to activity. -1 $ signals that we claim as candidate planets. We are not able to confirm their nature with certainty. Candidate HD 161098 b has an orbital period of 72.578_ -0.060 ^ +0.059 , and a minimum mass of 3.63 ± 0.59,M_⊕. HD 161098 c has an orbital period of 682.5_ -9.9 ^ +9.5 , and a minimum mass of 7.8_ -1.4 ^ +1.5 ,M$_⊕.If confirmed, candidate HD 161098 c would reside in the optimistic habitable zone of the star. We find a magnetic cycle of 4090_ -130 ^ +140 , period and a rotation period of 28.22_ -0.35 ^ +0.30 , . Our analysis sets the stage for future observing campaigns of the star, finalized for the confirmation of our results. -1 era at long orbital periods with a combination of stellar activity treatment and long-term campaigns.

Abstract:

Context . Stellar activity remains one of the main limitations in the detection of Earth-like planets using radial velocity (RV) measurements. The Sun, as the only star for which surface features can be spatially resolved, offers a unique testbed for studying the impact of active regions on RV and photometric variability. Aims . Using SOAPv4 (Spot Oscillation And Planet), we modelled solar RV and photometric variability induced by spots and faculae over long timescales. Our goal is to verify whether present-day, state-of-the-art models of the cross-correlation function correctly reproduce the observed variability. Moreover, we aim to assess how the choice of input data and identification technique influences the agreement between simulated and observed signals. Methods . To simulate solar RV and photometric time series, we first identified active regions in SDO images. This was done using mathematical morphological transforms applied to SDO/HMI and AIA images. Mathematical morphological identification was validated against other state-of-the-art identification methods. Using these inputs, we ran SOAPv4 to simulate solar RVs and photometry, and we validated the results with HARPS-N RV observations, as well as with VIRGO/SPM photometric measurements. Results . The simulations that use mathematical morphological identification achieved the best match with the observed RV time series, yielding residuals with a measured standard deviation of ~0.91 m/s. Other state-of-the-art methods produced higher filling factors and, consequently, larger discrepancies. The photometric simulations reproduced the overall variability trends. Conclusions . We demonstrate that mathematical morphological transforms accurately identify solar active regions. Using these inputs, SOAPv4 reproduces the observed solar RV variability with a measured standard deviation of the residuals of ~0.91 m/s. Photometric simulations capture the overall variability trends, confirming that SOAP can reliably model the impact of both spots and faculae on solar RVs and photometry.

Abstract:

The young TOI-451 planetary system, aged 125 Myr, provides a unique opportunity to test theories of planetary internal structures and atmospheric mass-loss through examination of its three transiting planets. We present an exhaustive photometric and spectroscopic follow-up to determine the orbital and physical properties of the system. We perform multidimensional Gaussian Process regression with the code pyaneti on spectroscopic time-series and NGTS/LCO light curves to disentangle the stellar and planetary signal in ESPRESSO radial velocities. We show how contemporaneous photometry serves as an activity indicator to inform RV modelling within a multidimensional Gaussian Processes framework. We argue that this can be exploited when spectroscopic observations are adversely affected by low signal-to-noise and/or poor sampling. We estimate the Doppler semi-amplitudes of , , and . This translates in 2 mass estimates for TOI-451 b and d of and ; as well as a mass upper limit for TOI-451 c of . The derived planetary properties suggest that planets c and d contain significant hydrogen-rich envelopes. The inferred parameters of TOI-451 b are consistent with either a rocky world that still retains a small hydrogen envelope or a water world. These insights make the TOI-451 system an ideal laboratory for future follow-up studies aimed at measuring atmospheric compositions, detecting atmospheric mass-loss signatures, and further exploring planetary formation and evolution processes.

Abstract:

The HARPS-N solar telescope has been observing the Sun every possible day since the summer of 2015. We have recently released 10 years of these data, which are available online. The goal of this paper is to present the different optimisations made to the ESPRESSO data reduction software used to extract the published HARPS-N solar spectra, describe the data curation, and perform some analyses that demonstrate the extreme radial velocity (RV) precision of those data. By analysing all of the HARPS-N wavelength solutions over 13 years, we brought to light instrumental systematics at the 1 level. We mitigated those systematics by curating the thorium line list used to derive the wavelength solution and applying a correction to the drift of thorium lines induced by the aging of thorium-argon hollow cathode lamps. After optimisation, we demonstrated a peak-to-peak precision on the HARPS-N wavelength solution better than 0.75 or well-understood instrumental systematics. Finally, we corrected the curated data for spurious sub-meter-per-second RV effects caused by erroneous instrumental drift measurements and by changes in the spectral blaze function over time. over 13 years. We then carefully curated the decade of HARPS-N re-reduced solar observations by rejecting 30% of the data affected either by clouds, bad atmospheric conditions After curation and correction, a total of 109,466 HARPS-N solar spectra and respective RVs over a decade were made available. The median photon-noise precision of the RV data is 0.28 and on daily timescales, the median RV rms is 0.49 which is similar to the level imposed by stellar granulation signals. On 10 year timescales, the large RV rms of 2.95 results from the RV signature of the Sun's magnetic cycle. Through modelling of this long-term effect using the Bremen composite magnesium II activity index, we demonstrate a long-term RV precision of 0.41 We also analysed contemporaneous HARPS-N and NEID solar RVs and found the data from both instruments to be of similar quality and precision. However, an analysis of the RV difference between these two RV datasets over the three available years gave a surprisingly large RV rms of 1.3 This variation is dominated by an unexplained trend that could be caused by a different sensitivity to stellar activity of the two datasets. Once this trend was modelled, the overall RV rms for three years reached 0.79 and the RV rms during the low-activity phase decreased to 0.6 compatible with what is expected from supergranulation. This decade of high-cadence HARPS-N solar observations with short- and long-term precision below one represents a crucial dataset in the pursuit of further understanding the stellar activity signals in solar-type stars and advancing other science cases requiring such extreme precision.