arXiv subjects

Alix Violet Freckelton

Publications and source records attributed to Alix Violet Freckelton.

4 recordsLinked to original sources

arXiv2026

gr8stars II : judgement day for spectroscopic parameter model systematics

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 \texttt{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 \logg, and 0.07 dex in \feh. 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 \texttt{gr8stars} paper as a comparison to our isochronal radii from this work, in addition to comparing the isochronal \logg to spectroscopic \logg. 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 ($\lesssim$ 3 \%) and mass ($\lesssim$ 5\%) are found to be below those typically found in the literature. We estimate a lower limit on planetary equilibrium temperature fractional uncertainty of $\approx$ 4\%, a noise floor that is currently not sufficiently represented in the literature.

astro-ph.SR↗

arXiv2025

The mass of the exo-Venus Gliese 12 b, as revealed by HARPS-N, ESPRESSO, and CARMENES

Small temperate planets are prime targets for exoplanet studies due to their possible similarities with the rocky planets in the Solar System. M dwarfs are promising hosts since the planetary signals are within our current detection capabilities. Gliese 12 b is a Venus-sized temperate planet orbiting a quiet M dwarf. We present here the first precise mass measurement of this small exoplanet. We performed a detailed analysis using HARPS-N, ESPRESSO, and CARMENES radial velocities, along with new and archival \tess, \cheops, and MuSCAT2/3 photometry data. From fitting the available data, we find that the planet has a radius of $R_\mathrm{p} = 0.93\pm0.06 \,\mathrm{R_\oplus}$ and a mass of $M_\mathrm{p} = 0.95^{+0.29}_{-0.30} \,\mathrm{M_\oplus}$ (a $3.2σ$ measurement of the semi-amplitude $K=0.67\pm0.21\,\mathrm{m\,s^{-1}}$), and is on an orbit with a period of $12.761418^{+0.000060}_{-0.000055}\,\mathrm{d}$. A variety of techniques were utilised to attenuate stellar activity signals. Gliese 12 b has an equilibrium temperature of $T_\mathrm{eq}=317 \pm 8\,\mathrm{K}$, assuming an albedo of zero, and a density consistent with that of Earth and Venus ($ρ_\mathrm{p}=6.4\pm2.4\,\mathrm{g\,cm^{-3}}$). We find that Gliese 12 b has a predominantly rocky interior and simulations indicate that it is unlikely to have retained any of its primordial gaseous envelope. The bulk properties of Gliese 12 b place it in an extremely sparsely populated region of both mass--radius and density--$T_\mathrm{eq}$ parameter space, making it a prime target for follow-up observations, including Lyman-$α$ studies.

astro-ph.EP↗

arXiv2025

gr8stars I: A homogeneous spectroscopic study of bright FGKM dwarfs and a public library of their high-resolution spectra

As the fields of stellar and exoplanetary study grow and revolutionary new detection instruments are created, it is imperative that a homogeneous, precise source of stellar parameters is available. This first work of the gr8stars collaboration presents the all-sky magnitude limited sample of 5645 bright FGKM dwarfs, along with homogeneously derived spectroscopic parameters of a subset of 1716 targets visible from the Northern hemisphere. We have collected high-resolution archival and new spectra from several instruments. Spectrosocpic parameters are determined using the PAWS pipeline, employing both the curve-of-growth equivalent width method, and the spectral synthesis method. We achieve median uncertainties of 106K in stellar effective temperature, 0.08 dex in surface gravity, and 0.03 dex in metallicity. This paper also presents photometric stellar parameters for these dwarfs, determined using SED fitting. The full gr8stars sample selection, including derived spectroscopic and photometric parameters, is made available through an interactive online database. We also perform a kinematic analysis to classify these stars according to their Galactic component.

astro-ph.SR↗

arXiv2024

TOI-837b is a Young Saturn-sized Exoplanet with a Massive 70 $M_{\oplus}$ Core

We present an exhaustive photometric and spectroscopic analysis of TOI-837, a F9/G0 35 Myr young star, hosting a transiting exoplanet, TOI-837b, with an orbital period of 8.32d. Utilising data from TESS and ground-based observations, we determine a planetary radius of 0.82 R_J for TOI-837b. Through detailed HARPS spectroscopic time series analysis, we derive a Doppler semi-amplitude of 35 m/s, corresponding to a planetary mass of 0.39 M_J. The derived planetary properties suggest a substantial core of approximately 70 M_E, constituting about 60% of the planet's total mass. This finding poses a significant challenge to existing theoretical models of core formation. We propose that future atmospheric observations with JWST could provide insights into resolving ambiguities of TOI-837b, offering new perspectives on its composition, formation, and evolution.

astro-ph.EP↗