arXiv subjects

E. Costa-Almeida

Publications and source records attributed to E. Costa-Almeida.

3 recordsLinked to original sources

arXiv2026

Chemical Abundances of the Bioessential Elements C, O and S, and the Refractory Elements Fe and Ni, in Solar-type Exoplanet-hosting Stars from HARPS North and South

We determined atmospheric and evolutionary parameters, along with chemical abundances of C, O, S, Fe, and Ni for 290 solar-type exoplanet hosting stars using high-resolution HARPS-North and HARPS-South spectra, and radii for 373 exoplanets using literature transit depths. We find that stars hosting giant exoplanets (R$_{\text{pl}}>4\ \text{R}_{\oplus}$) show enhanced [X/H] abundances compared to small exoplanet hosts for all elements analyzed. When considering only exoplanets with $P_{\text{orb}}\leq30$ days, there is a statistically significant anti-correlation between host star [Fe/H] and $P_{\text{orb}}$. However, [Fe/H] does not continue to decline as the orbital period increases, but rather rises again for exoplanets with larger orbital periods. Stars hosting only small exoplanets or hosting at least one sub-Saturn show significant differences between the populations of hot and warm exoplanets for all elements. In contrast, stars hosting at least one Jupiter-sized planet show no abundance differences. The host star C/O ratios obtained vary from 0.17 to 0.95, with giant exoplanet hosts exhibiting the lowest median C/O ratios (0.43$^{+0.02}_{-0.03}$), while the 3 -- 4 R$_\oplus$ sub-Neptune hosts in our sample exhibit the highest median C/O ratios (0.55$^{+0.05}_{-0.01}$). Our sample has 199 exoplanets with estimated masses and we find correlations between host star [O/H] and [S/H] and $\log(M_{\text{pl}}/\text{M}_\oplus)$. When segregating the sample into hot and warm exoplanet hosts, these trends are only found for warm exoplanets. Dividing the sample between low- (91 exoplanets) and high-[$α$/Fe] (20 exoplanets) stars, there are trends between host star [O/H], [S/H], [Fe/H] and [Ni/H] and $\log(M_{\text{pl}}/\text{M}_\oplus)$ only for the low-[$α$/Fe] sample.

astro-ph.EP↗

arXiv2026

The SOL $\textit{(Solar Origin and Life)}$ Project: Detailed characterization of candidates for the ZAMS and Subgiant stages

The context of the Sun in the galactic neighborhood is not well understood, especially when we compare its physical properties to those of nearby stars. Thereby, we still cannot fully comprehend whether or not the Sun is a typical star. This work aims to identify and characterize stars aligned with the solar evolutionary track that could represent it at the ZAMS and subgiant stages. We performed a spectroscopic analysis of 18 photometrically selected candidates using high-resolution and high-SNR spectra as well as the classical spectroscopic method, based on the excitation and ionization equilibria of Fe I and Fe II lines. Additionally, we derived evolutionary parameters using isochrones, and kinematic parameters. We also estimated chromospheric activity levels and performed age estimates through 3 additional independent methods: activity-age relations using the Ca II H $\&$ K and H$α$ lines, and rotation periods estimated from TESS light curves. We identified three candidates that provide a good match to the Sun at $\approx$ 0.5 Gyr (HD 13531 and HD 61033) and subgiant (HD 148577) stages. Moreover, HD 197210 could be of interest when studying the Sun at $\approx$ 2 Gyr, when the Earth's atmosphere started having a significant amount of oxygen. Our selection method was successful and we were able to identify stars similar to the Sun at different evolutionary stages, which is essential for future research in the search of exoplanets and understand habitability, especially with the advent of the next generation of exoplanet-hunting instruments.

astro-ph.SR↗

arXiv2021

M dwarf spectral indices at moderate resolution: accurate $T_{\mathrm{eff}}$ and [Fe/H] for 178 southern stars

We present a spectroscopic and photometric calibration to derive effective temperatures $T_{\mathrm{eff}}$ and metallicities [Fe/H] for M dwarfs, based on a Principal Component Analysis of 147 spectral indices measured off moderate resolution $R \sim 11\,000$), high S/N ($>100$) spectra in the $λλ$ 8390-8834 region, plus the J$-$H color. Internal uncertainties, estimated by the residuals, are 81 K and 0.12 dex, respectively, for $T_{\mathrm{eff}}$ and [Fe/H], the calibrations being valid for 3050 K $< T_{\mathrm{eff}} <$ 4100 K and $-$0.45 $<$ [Fe/H] $<$ $+$0.50 dex. The PCA calibration is a competitive model-independent method to derive $T_{\mathrm{eff}}$ and [Fe/H] for large samples of M dwarfs, well suited to the available database of far-red spectra. The median uncertainties are 105 K and 0.23 dex for $T_{\mathrm{eff}}$ and [Fe/H], respectively, estimated by Monte Carlo simulations. We compare our values to other works based on photometric and spectroscopic techniques and find median differences 75 $\pm$ 273 K and 0.02 $\pm$ 0.31 dex for $T_{\mathrm{eff}}$ and [Fe/H], respectively, achieving good accuracy but relatively low precision. We find considerable disagreement in the literature between atmospheric parameters for stars in common. We use the new calibration to derive $T_{\mathrm{eff}}$ and [Fe/H] for 178 K7-M5 dwarfs, many previously unstudied. Our metallicity distribution function for nearby M dwarfs peaks at [Fe/H]$\sim$-0.10 dex, in good agreement with the RAVE distribution for GK dwarfs. We present radial velocities (internal precision 1.4 km/s) for 99 objects without previous measurements. The kinematics of the sample shows it to be fully dominated by thin/thick disk stars, excepting the well-known high-velocity Kapteyn's star.

astro-ph.SR↗