arXiv subjects

Elisa Delgado Mena

Publications and source records attributed to Elisa Delgado Mena.

At least 19 recordsLinked to original sources

arXiv2025

The TOI-1117 Multi-planetary System: 3 sub-Neptunes, 1 in both the Neptunian Desert and Radius Valley

We present the discovery of three sub-Neptune planets around TOI-1117, a Sun-like star with mass $0.97\pm0.02M_{\odot}$, radius $1.05\pm0.03R_{\odot}$, age $4.42\pm1.50$ Gyr and effective temperature $5635\pm62$ K. Light curves from TESS and LCOGT show a transiting sub-Neptune with a $2.23$ day period, mass $M_b=8.90_{-0.96}^{+0.95}M_{\oplus}$ and radius $R_b=2.46_{-0.12}^{+0.13}R_{\oplus}$. This is a rare 'hot Neptune' that falls within the parameter spaces known as the 'Neptunian Desert' and the 'Radius Valley'. Two more planetary signals are detected in HARPS radial velocities, revealing two non-transiting planets with minimum masses $M_c=7.46_{-1.62}^{+1.43}M_{\oplus}$ and $M_d=9.06_{-1.78}^{+2.07}M_{\oplus}$, and periods of $4.579\pm0.004$ and $8.67\pm0.01$ days. The eccentricities were poorly constrained by the HARPS data, with upper limits $e_b=0.11$, $e_c=0.29$, and $e_d=0.24$. However, dynamical simulations of the TOI-1117 system, suggest that the orbits must be nearly circular to be stable. The simulations also show that TOI-1117b and c are likely to be in a near 2:1 resonance. The multi-planet nature of TOI-1117 makes it a more complex case for formation theories of the Neptunian Desert and Radius Valley, as current theories such as high-eccentricity migration are too turbulent to produce a stable, non-eccentric, multi-planet system. Moreover, analysis of TOI-1117b's photoevaporation history found rocky core and H/He atmosphere models to be inconsistent with observations, whilst water-rich scenarios were favoured.

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arXiv2025

The NCORES Program: Precise planetary masses, null results, and insight into the planet mass distribution near the radius gap

NCORES was a large observing program on the ESO HARPS spectrograph, dedicated to measuring the masses of Neptune-like and smaller transiting planets discovered by the TESS satellite using the radial velocity technique. This paper presents an overview of the programme, its scientific goals and published results, covering 35 planets in 18 planetary systems. We present spectrally derived stellar characterisation and mass constraints for five additional TOIs where radial velocity observations found only marginally significant signals (TOI-510.01, $M_p=1.08^{+0.58}_{-0.55}M_\oplus$), or found no signal (TOIs 271.01, 641.01, 697.01 and 745.01). A newly detected non-transiting radial velocity candidate is presented orbiting TOI-510 on a 10.0d orbit, with a minimum mass of $4.82^{+1.29}_{-1.26}M_\oplus$, although uncertainties on the system architecture and true orbital period remain. Combining the NCORES sample with archival known planets we investigate the distribution of planet masses and compositions around and below the radius gap, finding that the population of planets below the gap is consistent with a rocky composition and ranges up to a sharp cut-off at $10M_\oplus$. We compare the observed distribution to models of pebble- and planetesimal-driven formation and evolution, finding good broad agreement with both models while highlighting interesting areas of potential discrepancy. Increased numbers of precisely measured planet masses in this parameter space are required to distinguish between pebble and planetesimal accretion.

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arXiv2024

The enigma of Li-rich giants and its relation with temporal variations observed in radial velocity and stellar activity signals

Despite the large number of studies focused on the characterisation of Li-rich stars and understanding the mechanisms leading to such enrichment, their origin remains a mystery. Magnetic activity, particularly the phenomena usually associated with it, and the Li abundance (A(Li)) of stars, are in general thought to be connected. As of today, however, just how they are connected is unclear. In this work, we study a sample of young but evolved intermediate-mass red giants that are inhabitants of open clusters where planets have been searched for. Our aim is to use radial velocity (RV) and stellar activity indicator signals to look for relations between Li abundances and stellar activity or variability. We explored how the standard deviation (STD), peak-to-peak amplitude (PTP), mean, and median of typical stellar activity indicators (BIS, FWHM, $T_\textrm{eff}$, and H$α$ index) change as a function of the Li content of 82 red giants. Furthermore, we computed weighted Pearson correlation coefficients ($ρ_w$) between time series of RV measurements and the stellar activity indicators for the stars in our sample. To aid our results, we also studied generalized Lomb-Scargle periodograms (GLSP) to capture possible significant periodic temporal variations in our data. Our analysis indicates that the STD and PTP of BIS and FWHM, the mean and median of the H$α$ index, and $v\sin(i)$ increase exponentially with A(Li) in our sample of red giants. Significant temporal variations and correlations between RVs and activity indicators also tend to be found preferentially for stars where high A(Li) is observed. Most of the Li-rich stars in our sample either show strong correlations of RV with at least one of the stellar activity indicators or reveal significant periodic temporal variations in their GLSPs of stellar activity indicators that are consistent with those found for RV.

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arXiv2023

HRMOS White Paper: Science Motivation

The High-Resolution Multi-Object Spectrograph (HRMOS) is a facility instrument that we plan to propose for the Very Large Telescope (VLT) of the European Southern Observatory (ESO), following the initial presentation at the VLT 2030 workshop held at ESO in June 2019. HRMOS provides a combination of capabilities that are essential to carry out breakthrough science across a broad range of active research areas from stellar astrophysics and exoplanet studies to Galactic and Local Group archaeology. HRMOS fills a gap in capabilities amongst the landscape of future instrumentation planned for the next decade. The key characteristics of HRMOS will be high spectral resolution (R = 60000 - 80000) combined with multi-object (20-100) capabilities and long term stability that will provide excellent radial velocity precision and accuracy (10m/s). Initial designs predict that a SNR~100 will be achievable in about one hour for a star with mag(AB) = 15, while with the same exposure time a SNR~ 30 will be reached for a star with mag(AB) = 17. The combination of high resolution and multiplexing with wavelength coverage extending to relatively blue wavelengths (down to 380\,nm), makes HRMOS a spectrograph that will push the boundaries of our knowledge and that is envisioned as a workhorse instrument in the future. The science cases presented in this White Paper include topics and ideas developed by the Core Science Team with the contributions from the astronomical community, also through the wide participation in the first HRMOS Workshop (https://indico.ict.inaf.it/event/1547/) that took place in Firenze (Italy) in October 2021.

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arXiv2023

TOI-908: a planet at the edge of the Neptune desert transiting a G-type star

We present the discovery of an exoplanet transiting TOI-908 (TIC-350153977) using data from TESS sectors 1, 12, 13, 27, 28 and 39. TOI-908 is a T = 10.7 mag G-dwarf ($T_{eff}$ = 5626 $\pm$ 61 K) solar-like star with a mass of 0.950 $\pm$ 0.010 $M_{\odot}$ and a radius of 1.028 $\pm$ 0.030 $R_{\odot}$. The planet, TOI-908 b, is a 3.18 $\pm$ 0.16 $R_{\oplus}$ planet in a 3.18 day orbit. Radial velocity measurements from HARPS reveal TOI-908 b has a mass of approximately 16.1 $\pm$ 4.1 $M_{\oplus}$ , resulting in a bulk planetary density of 2.7+0.2-0.4 g cm-3. TOI-908 b lies in a sparsely-populated region of parameter space known as the Neptune desert. The planet likely began its life as a sub-Saturn planet before it experienced significant photoevaporation due to X-rays and extreme ultraviolet radiation from its host star, and is likely to continue evaporating, losing a significant fraction of its residual envelope mass.

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arXiv2023

TOI-2498 b: A hot bloated super-Neptune within the Neptune desert

We present the discovery and confirmation of a transiting hot, bloated Super-Neptune using photometry from TESS and LCOGT and radial velocity measurements from HARPS. The host star TOI-2498 is a V = 11.2, G-type (T$_{eff}$ = 5905 $\pm$ 12K) solar-like star with a mass of 1.12 $\pm$ 0.02 M$_{\odot}$ and a radius of 1.26 $\pm$ 0.04 R$_{\odot}$. The planet, TOI-2498 b, orbits the star with a period of 3.7 days, has a radius of 6.1 $\pm$ 0.3 R$_{\oplus}$, and a mass of 35 $\pm$ 4 M$_{\oplus}$. This results in a density of 0.86 $\pm$ 0.25 g cm$^{-3}$. TOI-2498 b resides on the edge of the Neptune desert; a region of mass-period parameter space in which there appears to be a dearth of planets. Therefore TOI-2498 b is an interesting case to study to further understand the origins and boundaries of the Neptune desert. Through modelling the evaporation history, we determine that over its $\sim$3.6 Gyr lifespan, TOI-2498 b has likely reduced from a Saturn sized planet to its current radius through photoevaporation. Moreover, TOI-2498 b is a potential candidate for future atmospheric studies searching for species like water or sodium in the optical using high-resolution, and for carbon based molecules in the infra-red using JWST.

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arXiv2022

TESS Hunt for Young and Maturing Exoplanets (THYME) IX: a 27 Myr extended population of Lower-Centaurus Crux with a transiting two-planet system

We report the discovery and characterization of a nearby (~ 85 pc), older (27 +/- 3 Myr), distributed stellar population near Lower-Centaurus-Crux (LCC), initially identified by searching for stars co-moving with a candidate transiting planet from TESS (HD 109833; TOI 1097). We determine the association membership using Gaia kinematics, color-magnitude information, and rotation periods of candidate members. We measure it's age using isochrones, gyrochronology, and Li depletion. While the association is near known populations of LCC, we find that it is older than any previously found LCC sub-group (10-16 Myr), and distinct in both position and velocity. In addition to the candidate planets around HD 109833 the association contains four directly-imaged planetary-mass companions around 3 stars, YSES-1, YSES-2, and HD 95086, all of which were previously assigned membership in the younger LCC. Using the Notch pipeline, we identify a second candidate transiting planet around HD 109833. We use a suite of ground-based follow-up observations to validate the two transit signals as planetary in nature. HD 109833 b and c join the small but growing population of <100 Myr transiting planets from TESS. HD 109833 has a rotation period and Li abundance indicative of a young age (< 100 Myr), but a position and velocity on the outskirts of the new population, lower Li levels than similar members, and a CMD position below model predictions for 27 Myr. So, we cannot reject the possibility that HD 109833 is a young field star coincidentally nearby the population.

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arXiv2021

A compositional link between rocky exoplanets and their host stars

Stars and planets both form by accreting material from a surrounding disk. Because they grow from the same material, theory predicts that there should be a relationship between their compositions. In this study, we search for a compositional link between rocky exoplanets and their host stars. We estimate the iron-mass fraction of rocky exoplanets from their masses and radii and compare it with the compositions of their host stars, which we assume reflect the compositions of the protoplanetary disks. We find a correlation (but not a 1:1 relationship) between these two quantities, with a slope of >4, which we interpret as being attributable to planet formation processes. Super-Earths and super-Mercuries appear to be distinct populations with differing compositions, implying differences in their formation processes.

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arXiv2021

Determination of spectroscopic parameters for 313 M dwarf stars from their APOGEE Data Release 16 H-band spectra

The scientific community's interest on the stellar parameters of M dwarfs has been increasing over the last few years, with potential applications ranging from galactic characterization to exoplanet detection. The main motivation for this work is to develop an alternative and objective method to derive stellar parameters for M dwarfs using the H-band spectra provided by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Synthetic spectra generated with \textit{iSpec}, \textit{Turbospectrum}, \textit{MARCS} models atmospheres and a custom made line list including over 1 000 000 water lines, are compared to APOGEE observations, and parameters are determined through $χ^2$ minimization. Spectroscopic parameters ($T_\mathrm{eff}$, $[M/H]$, $\log g$, $v_{mic}$) are presented for a sample of 313 M dwarfs, obtained from their APOGEE H-band spectra. The generated synthetic spectra reproduce observed spectra to a high accuracy level. The impact of the spectra normalization on the results are analyzed as well. Our output parameters are compared with the ones obtained with APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) for the same stellar spectrum, and we find that the values agree within the expected uncertainties. Comparisons with other previous near-infrared and optical literature are also available, with median differences within our estimated uncertainties found in most cases. Possible reasons for these differences are explored. The full H-band line list, the line selection for the synthesis, and the synthesized spectra are available for download, as are the calculated stellar parameters.

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arXiv2020

A remnant planetary core in the hot-Neptune desert

The interiors of giant planets remain poorly understood. Even for the planets in the Solar System, difficulties in observation lead to large uncertainties in the properties of planetary cores. Exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. Planets found in and near the typically barren hot-Neptune 'desert' (a region in mass-radius space that contains few planets) have proved to be particularly valuable in this regard. These planets include HD149026b, which is thought to have an unusually massive core, and recent discoveries such as LTT9779b and NGTS-4b, on which photoevaporation has removed a substantial part of their outer atmospheres. Here we report observations of the planet TOI-849b, which has a radius smaller than Neptune's but an anomalously large mass of $39.1^{+2.7}_{-2.6}$ Earth masses and a density of $5.2^{+0.7}_{-0.8}$ grams per cubic centimetre, similar to Earth's. Interior structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than $3.9^{+0.8}_{-0.9}$ per cent of the total planetary mass. The planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation. Although photoevaporation rates cannot account for the mass loss required to reduce a Jupiter-like gas giant, they can remove a small (a few Earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on TOI-849b is likely to be enriched by water or other volatiles from the planetary interior. We conclude that TOI-849b is the remnant core of a giant planet.

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arXiv2020

Derivation of parameters for 3748 FGK stars using H-band spectra from APOGEE Data Release 14

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed the H-band spectra of over 200 000 stars with $R\sim22 000$. The main motivation for this work is to test an alternative method to the standard APOGEE pipeline (APOGEE Stellar Parameter and Chemical Abundances Pipeline, ASPCAP) to derive parameters in the Near-InfraRed (NIR) for FGK dwarfs. \textit{iSpec} and \textit{Turbospectrum} are used to generate synthetic spectra matching APOGEE observations and to determine the parameters through $χ^2$ minimization. We present spectroscopic parameters ($T_\mathrm{eff}$, $[M/H]$, $\log g$, $v_{mic}$) for a sample of 3748 main-sequence and subgiant FGK stars, obtained from their APOGEE H-band spectra We compare our output parameters with the ones obtained with ASPCAP for the same stellar spectra, and find that the values agree within the expected uncertainties. A comparison with the optical samples California Planet Survey, HARPS-GTO (High Accuracy Radial Velocity Planet Searcher - Guaranteed Time Observations), and PASTEL, is also available, and median differences below 10 K for $T_\mathrm{eff}$ and 0.2 dex for $[M/H]$ are found. Reasons for these differences are explored. The full H-band line-list, the line selection for the synthesis and the synthesized spectra are available for download, as well as the calculated parameters and their estimated uncertainties.

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arXiv2019

Chemical abundances of 1111 FGK stars from the HARPS-GTO planet search sample. III. Sulfur

Context. Elemental abundances are of prime importance to help us reconstruct the origin and evolution of stars and galaxies in our Universe. Sulfur abundances have not been as heavily studied as other elements, so some details regarding its behaviour are still unclear. Aims. We aim to investigate [S/Fe] ratios in stars of the solar neighbourhood in order to analyse the chemical evolution of sulfur and probe for possible differences in abundances of planet host and non-planet host stars. Methods. We use the code MOOG to perform spectral synthesis and derive v*sin(i) values and [S/Fe] ratios for 719 FGK stars with high-resolution (R~115000) and high-quality spectra from the HARPS-GTO program. We find the best fit and corresponding parameter values by performing chi-square minimisation of the deviation between synthetic profiles and observational spectra. Results. Our results reveal that sulfur behaves as a typical alpha-element, with low abundances in young thin disk stars and high abundances in old thick disk stars, following what was expected from our understanding of the Galactic chemical evolution (GCE). Nevertheless, further studies into the abundances of sulfur in very metal-poor stars are required as our sample only derived sulfur abundances to stars with metallicity as low as [Fe/H]=-1.13 dex. High-alpha metal rich stars are more enhanced in sulfur compared to their thin disk counterparts at the same metallicity. We compare our results to GCE models from other authors in the [S/Fe] vs. [Fe/H] plane. The [S/Fe]-age relationship is a good proxy for time, just like it is the case with other alpha-elements. We report no differences in the abundances of sulfur between stars with and without planetary companions in the metallicity range [Fe/H] >= -0.3 dex.

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arXiv2019

The Gaia-ESO Survey: Carbon abundance in the Galactic thin and thick disks

This paper focuses on carbon that is one of the most abundant elements in the Universe and is of high importance in the field of nucleosynthesis and galactic and stellar evolution. Even nowadays, the origin of carbon and the relative importance of massive and low- to intermediate-mass stars in producing it is still a matter of debate. In this paper we aim at better understanding the origin of carbon by studying the trends of [C/H], [C/Fe],and [C/Mg] versus [Fe/H], and [Mg/H] for 2133 FGK dwarf stars from the fifth Gaia-ESO Survey internal data release (GES iDR5). The availability of accurate parallaxes and proper motions from Gaia DR2 and radial velocities from GES iDR5 allows us to compute Galactic velocities, orbits and absolute magnitudes and, for 1751 stars, ages via a Bayesian approach. Three different selection methodologies have been adopted to discriminate between thin and thick disk stars. In all the cases, the two stellar groups show different abundance ratios, [C/H], [C/Fe], and [C/Mg], and span different age intervals, with the thick disk stars being, on average, older than those in the thin disk. The behaviours of [C/H], [C/Fe], and [C/Mg] versus [Fe/H], [Mg/H], and age all suggest that C is primarily produced in massive stars like Mg. The increase of [C/Mg] for young thin disk stars indicates a contribution from low-mass stars or the increased C production from massive stars at high metallicities due to the enhanced mass loss. The analysis of the orbital parameters Rmed and |Zmax| support an "inside-out" and "upside-down" formation scenario for the disks of Milky Way.

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arXiv2019

TESS Asteroseismology of the known red-giant host stars HD 212771 and HD 203949

The Transiting Exoplanet Survey Satellite (TESS) is performing a near all-sky survey for planets that transit bright stars. In addition, its excellent photometric precision enables asteroseismology of solar-type and red-giant stars, which exhibit convection-driven, solar-like oscillations. Simulations predict that TESS will detect solar-like oscillations in nearly 100 stars already known to host planets. In this paper, we present an asteroseismic analysis of the known red-giant host stars HD 212771 and HD 203949, both systems having a long-period planet detected through radial velocities. These are the first detections of oscillations in previously known exoplanet-host stars by TESS, further showcasing the mission's potential to conduct asteroseismology of red-giant stars. We estimate the fundamental properties of both stars through a grid-based modeling approach that uses global asteroseismic parameters as input. We discuss the evolutionary state of HD 203949 in depth and note the large discrepancy between its asteroseismic mass ($M_\ast = 1.23 \pm 0.15\,{\rm M}_\odot$ if on the red-giant branch or $M_\ast = 1.00 \pm 0.16\,{\rm M}_\odot$ if in the clump) and the mass quoted in the discovery paper ($M_\ast = 2.1 \pm 0.1\,{\rm M}_\odot$), implying a change $>30\,\%$ in the planet's mass. Assuming HD 203949 to be in the clump, we investigate the planet's past orbital evolution and discuss how it could have avoided engulfment at the tip of the red-giant branch. Finally, HD 212771 was observed by K2 during its Campaign 3, thus allowing for a preliminary comparison of the asteroseismic performances of TESS and K2. We estimate the ratio of the observed oscillation amplitudes for this star to be $A_{\rm max}^{\rm TESS}/A_{\rm max}^{\rm K2} = 0.75 \pm 0.14$, consistent with the expected ratio of $\sim0.85$ due to the redder bandpass of TESS.

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arXiv2016

A Comparison of Stellar Elemental Abundance Techniques and Measurements

Stellar elemental abundances are important for understanding the fundamental properties of a star or stellar group, such as age and evolutionary history, as well as the composition of an orbiting planet. However, as abundance measurement techniques have progressed, there has been little standardization between individual methods and their comparisons. As a result, different stellar abundance procedures determine measurements that vary beyond quoted error for the same elements within the same stars (Hinkel et al. 2014). The purpose of this paper is to better understand the systematic variations between methods and offer recommendations for producing more accurate results in the future. We have invited a number of participants from around the world (Australia, Portugal, Sweden, Switzerland, and USA) to calculate ten element abundances (C, O, Na, Mg, Al, Si, Fe, Ni, Ba, and Eu) using the same stellar spectra for four stars (HD361, HD10700, HD121504, HD202206). Each group produced measurements for each of the stars using: 1) their own autonomous techniques, 2) standardized stellar parameters, 3) standardized line list, and 4) both standardized parameters and line list. We present the resulting stellar parameters, absolute abundances, and a metric of data similarity that quantifies homogeneity of the data. We conclude that standardization of some kind, particularly stellar parameters, improves the consistency between methods. However, because results did not converge as more free parameters were standardized, it is clear there are inherent issues within the techniques that need to be reconciled. Therefore, we encourage more conversation and transparency within the community such that stellar abundance determinations can be reproducible as well as accurate and precise.

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arXiv2012

Low Mg/Si planetary host stars and their Mg-depleted terrestrial planets

Simulations have shown that a diverse range of extrasolar terrestrial planet bulk compositions are likely to exist, based on the observed variations in host star elemental abundances. Based on recent studies, it is expected that a significant proportion of host stars may have Mg/Si ratios below 1. Here we examine this previously neglected group of systems. Planets simulated as forming within these systems are found to be Mg-depleted (compared to the Earth), consisting of silicate species such as pyroxene and various feldspars. Planetary carbon abundances also vary in accordance with the host stars C/O ratio. The predicted abundances are in keeping with observations of polluted white dwarfs, lending validity to this approach. Further studies are required to determine the full planetary impacts of the bulk compositions predicted here.

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arXiv2010

Measuring Be depletion in cool stars with exoplanets

We present new UVES spectra of a sample of 14 mostly cool unevolved stars with planetary companions with the aim of studying possible differences in Be abundance with respect to stars without detected planets. We determine Be abundances for these stars that show an increase in Be depletion as we move to lower temperatures. We carry out a differential analysis of spectra of analog stars with and without planets to establish a possible difference in Be content. While for hot stars no measurable difference is found in Be, for the only cool (Teff ~ 5000 K) planet host star with several analogs in the sample we find enhanced Be depletion by 0.25 dex. This is a first indication that the extra-depletion of Li in solar-type stars with planets may also happen for Be, but shifted towards lower temperatures (Teff < 5500 K) due to the depth of the convective envelopes. The processes that take place in the formation of planetary systems may affect the mixing of material inside their host stars and hence the abundances of light elements.

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arXiv2010

Chemical Clues on the Formation of Planetary Systems: C/O vs Mg/Si for HARPS GTO Sample

Theoretical studies suggest that C/O and Mg/Si are the most important elemental ratios in determining the mineralogy of terrestrial planets. The C/O ratio controls the distribution of Si among carbide and oxide species, while Mg/Si gives information about the silicate mineralogy. We present a detailed and uniform study of C, O, Mg and Si abundances for 61 stars with detected planets and 270 stars without detected planets from the homogeneous high-quality unbiased HARPS GTO sample, together with 39 more planet-host stars from other surveys. We determine these important mineralogical ratios and investigate the nature of the possible terrestrial planets that could have formed in those planetary systems. We find mineralogical ratios quite different from those of the Sun, showing that there is a wide variety of planetary systems which are not similar to Solar System. Many of planetary host stars present a Mg/Si value lower than 1, so their planets will have a high Si content to form species such as MgSiO$_{3}$. This type of composition can have important implications for planetary processes like plate tectonics, atmospheric composition or volcanism.

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