Jorge Meléndez

We present an implementation of the well-known and broadly used Generalized Lomb–Scargle Periodogram (GLS) which simultaneously takes into account individual offsets introduced in the data by different instruments: a “multi-instrument” GLS periodogram. While the algorithm itself is not new, the simple closed form implementation we provide, to our knowledge, is. We showcase an application of our multi-instrument GLS on radial-velocity (RV) data of the hot Jupiter TOI-481 b, whose period is recovered with a higher significance compared to the standard GLS approach. The code is available on GitHub.

Beatriz Barbuy has made fundamental contributions to the study of stellar populations, from calibrating atomic and molecular line lists to establishing elemental abundances and isotopic ratios in different stellar populations of the Milky Way, particularly of the Galactic Bulge, providing thus important clues on how the Galaxy formed and how it was enriched over time. Furthermore, she has had a significant impact on the scientific community through organizing conferences and contributing through leading international roles, such as the vice-presidency of the International Astronomical Union. Her contribution to training young researches in stellar populations is also noteworthy, having supervised more than 20 PhD theses. Finally, her involvement in instrumentation projects, such as ESO’s VLT and ELT, is helping pave the way for new exciting discoveries.

The chemistry, kinematics, and low Li abundance of the star HD 65907 suggest that despite its isochronal age of ∼5 Gyr, it is a merger of two old Pop. II stars. To further investigate this star, we determine its Li and Be abundances and evaluate its radial velocity time series and activity cycle. Li and Be abundances were determined via spectral synthesis of their resonance lines using HARPS and UVES spectra. HARPS data were also used to study variations in the star’s radial velocity and activity levels. Our analysis reveals that HD 65908 is severely Li- and Be-depleted. Its radial velocity is nearly constant, with a small modulation likely associated with stellar activity, which points to the lack of an undetected close companion. These results are strong pieces of evidence in favor of the stellar merger scenario.

Carbon, nitrogen and oxygen in stars bring valuable information for Galactic chemical evolution (GCE) modelling, stellar evolution and exoplanet studies. We have measured the ¹² C abundance, the isotopic ratio ¹² C/ ¹³ C and the ¹⁴ N abundance for 27 solar analogue stars and 55 solar twin stars, having both samples a wide range in isochrone age. ¹⁴ N and ¹⁴ N/ ¹⁵ N have been measured for 59 metal-rich solar twin stars that have a wide age coverture too. The three samples contain solar-type dwarfs belonging to the Galactic thin disc up to around 106 pc in distance. All samples stars are identified as stars hosting gaseous giant planets and stars without detected gaseous giant planets. Both isotopic ratios have been derived for ‘solar twins’ for the first time. In this work, we compile our main results on several abundance ratios involving C and N isotopes as a function of the isochrone age and metallicity.

: We obtained [X/Fe] ratios of 20 elements with high precision (0.01 - 0.02 dex) for a sample of 100 solar twins using Neural Networks (NN) and high quality spectra from HARPS. The abundances were corrected by the Galactic Chemical Evolution (GCE) and studied along with the condensation temperature (T _cond ) of the elements, to verify how distinct the Sun is compared to the solar twins. We concluded that the Sun is peculiar, being more depleted in refractories than 89% of the solar twins, with a significance of ∼9σ, which may be a signature of planetary systems like ours. The results presented here are part of Martos et al., (2025).

Stellar ages are an important parameter for studying the chemical evolution of the Galaxy. To improve age estimates, various complementary methods to the conventional isochrone-fitting method have been implemented in the last decade. The [Y/Mg] ratio has been proposed as a chemical clock for solar-metallicity stars, due to its strong dependence on stellar age. In this work, we study the behaviour of the abundance ratio [Y/Mg] in metal-poor stars, along with other solar-type disk stars, as a function of stellar age determined through isochrones. The analysis is based on the line-by-line differential technique, applied to a sample covering a wide metallicity range (−0.70 ≤ [Fe/H] <+0.34), using high-resolution (R = 115,000) and high S/N spectra (= 270 - 1000) taken with the HARPS spectrograph at the ESO La Silla Observatory. We find that the stellar sample follows a metallicity-dependent [Y/Mg]-Age relation.

Context . Binary systems composed of stars with similar parameters are expected to have identical chemical composition. However, many chemically anomalous pairs have been found in the literature, such as the binary HD 129171/HD 129209. It is still unclear whether these anomalies originate from inhomogeneities of protostellar clouds, with important implications for chemical tagging and theories of star formation, or if they are caused by a planet engulfment event suffered by one binary component. Aims . In this work, we measured precise differential abundances for the system HD 129171/HD 129209 to explore the planet engulfment hypothesis proposed in the literature. We focused on the Be abundance in particular, showing that this element can serve as a diagnostic of engulfment events for solar-type stars. Methods . Atmospheric parameters were determined imposing spectroscopic equilibrium of iron lines. Masses and ages were estimated with the isochronal method. The Li, Be, N, and O abundances were determined via spectral synthesis. Other elemental abundances (up to Zn) were determined by equivalent width measurements. The spectra adopted in the analysis was gathered using UVES/ESO. Results . We confirm the large difference in [Fe/H] (0.120 ± 0.004 dex) and A(Li) (−1.00 ± 0.02 dex) among the members of the pair, as well as the trend between differential abundances and condensation temperature of the elements. The binary system also shows detectable differences in Be abundances (−0.20 ± 0.04 dex). The abundance pattern of the pair is reasonably reproduced by an engulfment model of 11.2 M _⊕ of rocky material. Conclusions . The difference in chemical abundances of the HD 129171/HD 129209 pair provides strong evidence in favor of the planet engulfment scenario. In this context, the detection of a Be difference among chemically inhomogeneous binary systems can be used as a diagnostic of rocky material ingestion experienced by a member of the pair.

We report the detection of rotation in the old (∼7 Gyr) solar twin HIP 73815. This result provides new insight into the validity of gyrochronology beyond the solar age, a subject of intense debate in recent years. Previous claims in the literature often relied on merged or fragmented time series or on model-dependent proxies, leading to ambiguous interpretations. Thanks to ESPRESSO’s service mode, we obtained an unprecedented, single, coherent data set spanning over 80 days and covering more than two full rotation cycles of this old solar twin. We measure a rotation period of P GP = 31 . 1 − 1.1 + 1.3 days, consistent with predictions from gyrochronology, in contrast with recent studies suggesting that these relations break down past the solar age. Our result demonstrates that gyrochronology remains a reliable method for estimating stellar ages for Sun-like stars at least up to ∼7 Gyr, beyond the solar age, where its validity has been under debate. Moreover, we show that with a carefully designed ground-based observational strategy, precise and accurate rotation periods can be measured even in old stars, enabling robust age determinations for Sun-like stars and providing critical calibration for independent dating methods.

Determining stellar ages is challenging, particularly for cooler main-sequence (MS) stars. Magnetic evolution offers an observational alternative for age estimation via the age–chromospheric activity (AC) relation. We evaluate the impact of metallicity on this relation using near one-solar-mass stars across a wide metallicity range. We analyze a sample of 358 solar-type stars with precise spectroscopic parameters determined through a line-by-line differential technique and with ages derived using Yonsei–Yale isochrones. We measured chromospheric activity (S-index) using high-quality High Accuracy Radial Velocity Planet Searcher spectra, calibrated to the Mount Wilson system and converted to the R HK ′ ( T eff ) index with a temperature-based photospheric correction. Our findings show that the AC relation for R HK ′ ( T eff ) is strongly influenced by metallicity. We propose a new age–activity–metallicity relation for solar-type MS stars ( log g ≳ 4.2 ) with temperatures 5370 ≲ T _eff ≲ 6530 K and metallicities from −0.7 to +0.3 dex. We show that taking metallicity into account significantly enhances chromospheric ages’ reliability, reducing the residuals’ rms relative to isochronal ages from 2.6 to 0.92 Gyr. This reflects a considerable improvement in the errors of chromospheric ages, from 53% to 15%. The precision level achieved in this work is also consistent with previous age–activity calibration from our group using solar twins.

Context. The chemistry and Galactic velocity components of the star HD 65907 suggest that despite its young isochronal age of ∼5 Gyr, it is in fact a merger of two old Population II stars. Its low Li abundance is also consistent with a mass accretion episode. Aims. We determine Li and Be abundances for this star and evaluate its radial velocity time series, activity cycle, and spectral energy distribution in search of clues regarding the origin of this enigmatic star. Methods. Li and Be abundances were determined via spectral synthesis of their resonance lines using HARPS and UVES spectra, respectively. HARPS data were also used to study variations in the star’s radial velocity and activity levels. Photometric data were adopted to evaluate the stellar spectral energy distribution. Results. HD 65908 is severely Li- and Be-depleted. Its radial velocity is nearly constant (σ = 2 m/s), with a small modulation likely associated with stellar activity, and the star shows no further signs of an undetected close companion. The excess infrared emission is consistent with a 30 K blackbody, which is interpreted as a debris disk surrounding the star. The post-merger mass, rotation rate, and evolution of this star are discussed. Conclusions. The low Li and Be abundances, in addition to the lack of evidence for a companion, are strong pieces of evidence in favor of the stellar merger scenario. In this context, Be can be used to confirm other blue stragglers among field solar-type stars, as proposed in the literature.