arXiv subjects

E. Corsaro

Publications and source records attributed to E. Corsaro.

At least 19 recordsLinked to original sources

arXiv2026

The Stellar Observations Network Group (SONG) -- A Legacy Archive of Stellar Time-Domain Spectroscopy

The Stellar Observations Network Group (SONG) network has operated for more than a decade, providing long-baseline, high-cadence spectroscopic observations of bright stars and the Sun. The observations, from 2014 through 2025, constitute a substantial archive of high-resolution spectra and precise radial velocities for a broad range of time-domain stellar astrophysics. We present an overview of the status, instrumentation, and scientific capabilities of the SONG network, and describe the scope and accessibility of the SONG Data Archive (SODA). We further illustrate the breadth of science enabled by SONG observations, including asteroseismology, stellar variability studies, binary-star characterisation, and exoplanet research. We summarise the operational status and observing strategies of the SONG facilities, describe the available data products and archive infrastructure, and outline procedures for accessing archival observations and proposing new observations within the SONG community framework. The SODA archive currently contains more than 580,000 spectra of 3091 stars obtained with SONG using either iodine-cell or Thorium-Argon wavelength calibration. The archive spans over a decade and includes extensive time-series data for bright targets across a wide range of stellar types and variability classes. Access to the archive is available to members of the SONG community, which remains open to new participants who agree to follow the community policies. The SONG archive has developed into a major long-baseline resource for stellar spectroscopy and radial-velocity time-series analysis. Continued expansion of the archive, together with coordinated observations obtained contemporaneously with TESS and future PLATO observations, is expected to enable new studies of stellar oscillations, variability, and exoplanet host stars through combined radial-velocity and photometric analyses.

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arXiv2026

Luminaries in the Sky: The TESS LEGACY sample of bright stars. II. In-depth seismic characterisation of 32 naked-eye stars in the PLATO LOP fields

The NASA TESS mission is conducting a nearly full-sky survey, enabling the photometric characterisation of millions of stars. The forthcoming ESA PLATO mission will provide long-duration, high-precision photometry of tens of thousands of bright stars to be characterised through asteroseismology. The TESS Luminaries sample is a catalogue of 196 bright naked-eye (V < 6) main-sequence (MS) and sub-giant (SG) stars exhibiting solar-like oscillations. Among them, the subset located within the PLATO long-duration observation phase (LOP) fields constitutes an exceptional set of targets that will be observable by PLATO from the earliest phases of the mission, making them ideal calibrators during commissioning and the first months of science operations. This paper aims to provide an in-depth asteroseismic characterisation of 32 Luminaries stars that fall within the PLATO LOP fields of view. Individual mode parameters were extracted for the first time for 26 of them. We used three independent seismic pipelines, one of which is similar to the algorithms used in the official PLATO pipeline. Statistical criterion were applied to identify the optimal combination of data calibration, observing cadence, and fitting pipeline for each star. For all stars, we derived large and small separations, the asymptotic phase term, radial mode amplitudes, and mean linewidths per order. Comparisons reveal consistent trends in the seismic parameters, confirming the robustness of our analysis. In SGs, mixed-mode identification differs in the three pipelines, revealing extraction inconsistencies requiring longer datasets to improve our mode identifications. The Luminaries stars located in the PLATO LOP fields constitute a unique sample that will play a crucial role in validating, calibrating, and optimising PLATO's seismic performance.

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arXiv2024

Measuring stellar surface rotation and activity with the PLATO mission -- I. Strategy and application to simulated light curves

The Planetary Transits and Oscillations of stars mission (PLATO) will allow us to measure surface rotation and monitor photometric activity of tens of thousands of main sequence solar-type and subgiant stars. This paper is the first of a series dedicated to the preparation of the analysis of stellar surface rotation and photospheric activity with the near-future PLATO data. We describe in this work the strategy that will be implemented in the PLATO pipeline to measure stellar surface rotation, photometric activity, and long-term modulations. The algorithms are applied on both noise-free and noisy simulations of solar-type stars, which include activity cycles, latitudinal differential rotation, and spot evolution. PLATO simulated systematics are included in the noisy light curves. We show that surface rotation periods can be recovered with confidence for most of the stars with only six months of observations and that the {recovery rate} of the analysis significantly improves as additional observations are collected. This means that the first PLATO data release will already provide a substantial set of measurements for this quantity, with a significant refinement on their quality as the instrument obtains longer light curves. Measuring the Schwabe-like magnetic activity cycle during the mission will require that the same field be observed over a significant timescale (more than four years). Nevertheless, PLATO will provide a vast and robust sample of solar-type stars with constraints on the activity-cycle length. Such a sample is lacking from previous missions dedicated to space photometry.

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arXiv2024

Expanding the frontiers of cool-dwarf asteroseismology with ESPRESSO. Detection of solar-like oscillations in the K5 dwarf $ε$ Indi

Fuelled by space photometry, asteroseismology is vastly benefitting the study of cool main-sequence stars, which exhibit convection-driven solar-like oscillations. Even so, the tiny oscillation amplitudes in K dwarfs continue to pose a challenge to space-based asteroseismology. A viable alternative is offered by the lower stellar noise over the oscillation timescales in Doppler observations. In this letter we present the definite detection of solar-like oscillations in the bright K5 dwarf $ε$ Indi based on time-intensive observations collected with the ESPRESSO spectrograph at the VLT, thus making it the coolest seismic dwarf ever observed. We measured the frequencies of a total of 19 modes of degree $\ell=0$--2 along with $ν_{\rm max}=5305\pm176\:{\rm μHz}$ and $Δν=201.25\pm0.16\:{\rm μHz}$. The peak amplitude of radial modes is $2.6\pm0.5\:{\rm cm\,s^{-1}}$, or a mere ${\sim} 14\%$ of the solar value. Measured mode amplitudes are ${\sim} 2$ times lower than predicted from a nominal $L/M$ scaling relation and favour a scaling closer to $(L/M)^{1.5}$ below ${\sim} 5500\:{\rm K}$, carrying important implications for our understanding of the coupling efficiency between pulsations and near-surface convection in K dwarfs. This detection conclusively shows that precise asteroseismology of cool dwarfs is possible down to at least the mid-K regime using next-generation spectrographs on large-aperture telescopes, effectively opening up a new domain in observational asteroseismology.

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arXiv2024

A new catalog of magnetically active solar-like oscillators

We present a new catalog of stars for which detected solar-like oscillations and magnetic activity measurements are both available from chromospheric spectroscopic observations. Our results were obtained by exploiting NASA TESS mission light curves for active stars observed within the Mount Wilson Observatory HK project and the HK survey of the Hamburg Robotic Telescope TIGRE. We analyzed the light curves for a total of 191 stars by adopting recent techniques based on Bayesian analysis and model comparison to assess the detection of a power excess originating from solar-like oscillations. We characterized the oscillations in a total of 34 targets, for which we provide estimates for the global asteroseismic parameters of $ν_\mathrm{max}$ (the frequency of maximum oscillation power), $Δν$ (the large frequency separation), and for the amplitude of the solar-like oscillation envelope $A_\mathrm{max}$. We provide strong statistical evidence for the detection of solar-like oscillations in 15 stars of our sample, identify six further stars where a detection is likely, and 13 stars for which oscillations cannot be ruled out. The key parameters extracted in this work will be exploited for a detailed stellar modeling of the targets and to calibrate relations that connect the level of the measured magnetic activity to the suppression induced on the global oscillation amplitudes. This opens the possibility of shedding light on the interplay between magnetic fields and oscillations. Because of their relatively high brightness, the targets may also be of interest for future dedicated follow-up observations using both photometry and spectropolarimetry.

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arXiv2023

Constraining stellar and orbital co-evolution through ensemble seismology of solar-like oscillators in binary systems -- A census of oscillating red-giants and main-sequence stars in Gaia DR3 binaries

Binary systems constitute a valuable astrophysics tool for testing our understanding of stellar structure and evolution. Systems containing a oscillating component are interesting as asteroseismology offers independent parameters for the oscillating component that aid the analysis. About 150 of such systems are known in the literature. To enlarge the sample of these benchmark objects, we crossmatch the Two-Body-Orbit Catalogue (TBO) of Gaia DR3, with catalogs of confirmed solar-like oscillators on the main-sequence and red-giant phase from NASA Kepler and TESS. We obtain 954 new binary system candidates hosting solar-like oscillators, of which 45 and 909 stars are on the main sequence and red-giant, resp., including 2 new red giants in eclipsing systems. 918 oscillators in potentially long-periodic systems are reported. We increase the sample size of known solar-like oscillators in binary systems by an order of magnitude. We present the seismic properties of the full sample and conclude that the grand majority of the orbital elements in the TBO is physically reasonable. 82% of all TBO binary candidates with multiple times with APOGEE are confirmed from radial-velocity measurement. However, we suggest that due to instrumental noise of the TESS satellite the seismically inferred masses and radii of stars with $ν_\textrm{max}$$\lesssim$30$μ$Hz could be significantly overestimated. For 146 giants the seismically inferred evolutionary state has been determined and shows clear differences in their distribution in the orbital parameters, which are accounted the accumulative effect of the equilibrium tide acting in these evolved binary systems. For other 146 systems hosting oscillating stars values for the orbital inclination were found in the TBO. From testing the TBO on the SB9 catalogue, we obtain a completeness factor of 1/3.

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arXiv2022

Asteroseismology of the multiple stellar populations in the Globular Cluster M4

We present a new asteroseismic analysis of the stars in the Globular Cluster (GC) M4 based on the data collected by the K2 mission. We report the detection of solar-like oscillation in 37 stars, 32 red giant branch (RGB) and 6 red horizontal branch (rHB) stars, the largest sample for this kind of study in GC up to date. Combining information from asteroseismology and multi-band photometry we estimate both the masses and the radii of our targets. Our estimates are in agreement with independent sources, serving as a crucial verification of asteroseismology in the low metallicity regime. As M4 is an old GC, it hosts multiple stellar populations differing in light-element abundances and in helium mass fraction. This generates a mass difference between the populations along the RGB, which in the case of M4 is estimated to be $0.017 M_\odot$. With this wealth of information we can assign population membership and estimate the average mass of the stellar populations, but the current uncertainties do not allow us to resolve this mass difference. The population membership and the seismic data of RGB and HB stars, allow us, however, to assess the integrated mass loss along the RGB of the first generation stars in the cluster. We obtain $\rm ΔM=0.227 \pm0.028 M_\odot$, in good agreement with independent estimates. Finally, we observe the presence of a statistically significant mass-temperature gradient in the rHB stars. This represents the first direct, model-independent observation of the colour-temperature-mass correlation predicted by the theory.

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arXiv2021

A calibration of the Rossby number from asteroseismology

Stellar activity and rotation are tightly related in a dynamo process. Our understanding of this mechanism is mainly limited by our capability of inferring the properties of stellar turbulent convection. In particular, the convective turnover time is a key ingredient through the estimation of the stellar Rossby number, which is the ratio of the rotation period and the convective turnover time. In this work we propose a new calibration of the $(B-V)$ color index dependence of the convective turnover time, hence of the stellar Rossby number. Our new calibration is based on the stellar structure properties inferred through the detailed modeling of solar-like pulsators using asteroseismic observables. We show the impact of this calibration in a stellar activity -- Rossby number diagram by applying it to a sample of about 40,000 stars observed with Kepler and for which photometric activity proxy $S_\mathrm{\!ph}$ and surface rotation periods are available. Additionally, we provide a new calibration of the convective turnover time as function of the $(G_\mathrm{BP}-G_\mathrm{RP})$ color index for allowing applicability in the ESA Gaia photometric passbands.

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arXiv2021

Uncovering the ultimate planet impostor. An eclipsing brown dwarf in a hierarchical triple with two evolved stars

Exoplanet searches through space-based photometric time series have shown to be very efficient in recent years. However, follow-up efforts on the detected planet candidates have been demonstrated to be critical to uncover the true nature of the transiting objects. In this paper we show a detailed analysis of one of those false positives hidden as planetary signals. In this case, the candidate KOI-3886.01 showed clear evidence of a planetary nature from various techniques. Indeed, the properties of the fake planet set it among the most interesting and promising for the study of planetary evolution as the star leaves the main sequence. To unveil the true nature of this system, we present a complete set of observational techniques including high-spatial resolution imaging, high-precision photometric time series (showing eclipses, phase curve variations and asteroseismology signals), high-resolution spectroscopy and derived radial velocities, to unveil the true nature of this planet candidate. We find that KOI-3886.01 is an interesting false positive case: a hierarchical triple system composed by a $\sim$K2III giant star (KOI-3886A) accompanied by a close-in eclipsing binary formed by a subgiant $\sim$G4IV star (KOI-3886B) and a brown dwarf (KOI-3886C). In particular, KOI-3886C is one of the most irradiated brown dwarfs known to date, showing the largest radius in this substellar regime. It is also the first eclipsing brown dwarf known around an evolved star. In this paper we highlight the relevance of complete sets of follow-up observations to extrasolar planets detected by the transit technique using large-pixel photometers such as Kepler and TESS, and in the future, PLATO. In particular, multi-color high-spatial resolution imaging was the first hint toward ruling out the planet scenario in this system.

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arXiv2020

Searching for solar-like oscillations in pre-main sequence stars using APOLLO

In recent years, our understanding of solar-like oscillations from main sequence to red giant stars has improved dramatically thanks to pristine data collected from space telescopes. One of the remaining open questions focuses around the observational identification of solar-like oscillations in pre-main sequence stars. We aim to develop an improved method to search for solar-like oscillations in pre-main sequence stars and apply it to data collected by the Kepler K2 mission. Our software APOLLO includes a novel way to detect low signal-to-noise ratio solar like oscillations in the presence of a high background level. By calibrating our method using known solar-like oscillators from the main Kepler mission, we apply it to T Tauri stars observed by Kepler K2 and identify several candidate pre-main sequence solar-like oscillators. We find that our method is robust even when applied to time-series of observational lengths as short as those obtained with the TESS satellite in one sector. We identify EPIC 205375290 as a possible candidate for solar-like oscillations in a pre-main sequence star with $ν_\mathrm{max} \simeq 242\,μ$Hz. We also derive EPIC 205375290's fundamental parameters to be $T_\mathrm{eff}$ = 3670$\pm$180 K, log $g$ = 3.85$\pm$0.3, $v$sin$i$ = 8 $\pm$ 1 km s$^{-1}$, and about solar metallicity from a high-resolution spectrum obtained from the Keck archive.

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arXiv2020

PBjam: A Python package for automating asteroseismology of solar-like oscillators

Asteroseismology is an exceptional tool for studying stars by using the properties of observed modes of oscillation. So far the process of performing an asteroseismic analysis of a star has remained somewhat esoteric and inaccessible to non-experts. In this software paper we describe PBjam, an open-source Python package for analyzing the frequency spectra of solar-like oscillators in a simple but principled and automated way. The aim of PBjam is to provide a set of easy-to-use tools to extract information about the radial and quadrupole oscillations in stars that oscillate like the Sun, which may then be used to infer bulk properties such as stellar mass, radius and age or even structure. Asteroseismology and its data analysis methods are becoming increasingly important as space-based photometric observatories are producing a wealth of new data, allowing asteroseismology to be applied in a wide range of contexts such as exoplanet, stellar structure and evolution, and Galactic population studies.

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arXiv2020

Fast and Automated Peak Bagging with DIAMONDS (FAMED)

Stars of low and intermediate mass that exhibit oscillations may show tens of detectable oscillation modes each. Oscillation modes are a powerful to constrain the internal structure and rotational dynamics of the star, hence tool allowing one to obtain an accurate stellar age. The tens of thousands of solar-like oscillators that have been discovered thus far are representative of the large diversity of fundamental stellar properties and evolutionary stages available. Because of the wide range of oscillation features that can be recognized in such stars, it is particularly challenging to properly characterize the oscillation modes in detail, especially in light of large stellar samples. Overcoming this issue requires an automated approach, which has to be fast, reliable, and flexible at the same time. In addition, this approach should not only be capable of extracting the oscillation mode properties of frequency, linewidth, and amplitude from stars in different evolutionary stages, but also able to assign a correct mode identification for each of the modes extracted. Here we present the new freely available pipeline FAMED (Fast and AutoMated pEak bagging with DIAMONDS), which is capable of performing an automated and detailed asteroseismic analysis in stars ranging from the main sequence up to the core-Helium-burning phase of stellar evolution. This, therefore, includes subgiant stars, stars evolving along the red giant branch (RGB), and stars likely evolving toward the early asymptotic giant branch. In this paper, we additionally show how FAMED can detect rotation from dipolar oscillation modes in main sequence, subgiant, low-luminosity RGB, and core-Helium-burning stars. FAMED can be downloaded from its public GitHub repository (https://github.com/EnricoCorsaro/FAMED).

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arXiv2019

Acoustic oscillations and dynamo action in the G8 sub-giant EK Eri

We present further evidence of the presence of acoustic oscillations on the slowly-rotating, over-active G8 sub-giant EK Eri. This star was observed with the 1-m Hertzsprung SONG telescope, at the Observatorio del Teide for two different runs of 8 and 13 nights, respectively, and separated by about a year. We determined a significant excess of power around $ν_\mathrm{max} = 253 \pm 3\,μ$Hz in the first observing run and we were able to determine the large separation $Δν= 16.43 \pm 0.22\,μ$Hz. No significant excess of power was instead detected in a subsequent SONG observing season, as also supported by our analysis of the simultaneous TESS photometric observations. We propose a new amplitude-luminosity relation in order to account for the missing power in the power spectrum. Based on the evolutionary stage of this object we argue that standard $α^2Ω$ dynamo cannot be excluded as a possible origin for the observed magnetic field.

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arXiv2018

FliPer: A global measure of power density to estimate surface gravities of main-sequence Solar-like stars and red giants

Asteroseismology provides global stellar parameters such as masses, radii or surface gravities using the mean global seismic parameters as well as the effective temperature for thousands of low-mass stars $(0.8 M_\odot <M<3 M_\odot)$. This methodology has been successfully applied to stars in which acoustic modes excited by turbulent convection are measured. Other techniques such as the Flicker can also be used to determine stellar surface gravities, but only works for $\log{g}$ above $2.5$ dex. In this work, we present a new metric called FliPer (the acronym stands for Flicker in spectral power density, in opposition to the standard Flicker measurement which is computed in the time domain that is able to extend the range for which reliable surface gravities can be obtained ($0.1<\log{g}<4.6$ dex) without performing any seismic analysis for stars brighter than $\textit{Kp}$ $<$ 14. FliPer takes into account the average variability of a star measured in the power density spectrum in a given range of frequencies. However, FliPer values calculated on several ranges of frequency are required to better characterize a star. Using a large set of asteroseismic targets it is possible to calibrate the behavior of surface gravity with FliPer through machine learning. This calibration made with a random forest regressor covers a wide range of surface gravities from main-sequence stars to subgiants and red giants, with very small uncertainties from $0.04$ to $0.1$ dex. FliPer values can be inserted in automatic global seismic pipelines to either give an estimation of the stellar surface gravity or to assess the quality of the seismic results by detecting any outliers in the obtained $ν_{max}$ values. FliPer also constrain the surface gravities of main-sequence dwarfs using only long cadence data for which the Nyquist frequency is too low to measure the acoustic-mode properties.

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arXiv2018

The rotational shear layer inside the early red-giant star KIC 4448777

We present the asteroseismic study of the early red-giant star KIC 4448777, complementing and integrating a previous work (Di Mauro et al. 2016), aimed at characterizing the dynamics of its interior by analyzing the overall set of data collected by the {\it Kepler} satellite during the four years of its first nominal mission. We adopted the Bayesian inference code DIAMOND (Corsaro \& De Ridder 2014) for the peak bagging analysis and asteroseismic splitting inversion methods to derive the internal rotational profile of the star. The detection of new splittings of mixed modes, more concentrated in the very inner part of the helium core, allowed us to reconstruct the angular velocity profile deeper into the interior of the star and to disentangle the details better than in Paper I: the helium core rotates almost rigidly about 6 times faster than the convective envelope, while part of the hydrogen shell seems to rotate at a constant velocity about 1.15 times lower than the He core. In particular, we studied the internal shear layer between the fast-rotating radiative interior and the slow convective zone and we found that it lies partially inside the hydrogen shell above $r \simeq 0.05R$ and extends across the core-envelope boundary. Finally, we theoretically explored the possibility for the future to sound the convective envelope in the red-giant stars and we concluded that the inversion of a set of splittings with only low-harmonic degree $l\leq 3$, even supposing a very large number of modes, will not allow to resolve the rotational profile of this region in detail.

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arXiv2018

Oscillating red giants in eclipsing binary systems: empirical reference value for asteroseismic scaling relation

The internal structures and properties of oscillating red-giant stars can be accurately inferred through their global oscillation modes (asteroseismology). Based on 1460 days of Kepler observations we perform a thorough asteroseismic study to probe the stellar parameters and evolutionary stages of three red giants in eclipsing binary systems. We present the first detailed analysis of individual oscillation modes of the red-giant components of KIC 8410637, KIC5640750 and KIC9540226. We obtain estimates of their asteroseismic masses, radii, mean densities and logarithmic surface gravities by using the asteroseismic scaling relations as well as grid-based modelling. As these red giants are in double-lined eclipsing binaries, it is possible to derive their independent dynamical masses and radii from the orbital solution and compare it with the seismically inferred values. For KIC 5640750 we compute the first spectroscopic orbit based on both components of this system. We use high-resolution spectroscopic data and light curves of the three systems to determine up-to-date values of the dynamical stellar parameters. With our comprehensive set of stellar parameters we explore consistencies between binary analysis and asteroseismic methods, and test the reliability of the well-known scaling relations. For the three red giants under study, we find agreement between dynamical and asteroseismic stellar parameters in cases where the asteroseismic methods account for metallicity, temperature and mass dependence as well as surface effects. We are able to attain agreement from the scaling laws in all three systems if we use $Δν_{\rm ref,emp} = 130.8 \pm 0.9\,μ$Hz instead of the usual solar reference value.

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arXiv2018

Seismic probing of the first dredge-up event through the eccentric red-giant & red-giant spectroscopic binary KIC9163796

Binaries in double-lined spectroscopic systems provide a homogeneous set of stars. Differences of parameters, such as age or initial conditions, which otherwise would have strong impact on the stellar evolution, can be neglected. The observed differences are determined by the difference in stellar mass between the two components. The mass ratio can be determined with much higher accuracy than the actual stellar mass. In this work, we aim to study the eccentric binary system KIC9163796, whose two components are very close in mass and both are low-luminosity red-giant stars from four years of Kepler space photometry and high-resolution spectroscopy with Hermes. Mass and radius of the primary were determined through asteroseismology to be 1.39+/-0.06 Mo and 5.35+/-0.09 Ro, resp. From spectral disentangling the mass ratio was found to be 1.015+/-0.005 and that the secondary is ~600K hotter than the primary. Evolutionary models place both components, in the early and advanced stage of the first dredge-up event on the red-giant branch. From theoretical models of the primary, we derived the internal rotational gradient. From a grid of models, the measured difference in lithium abundance is compared with theoretical predictions. The surface rotation of the primary is determined from the Kepler light curve and resembles the orbital period within 10 days. The radial rotational gradient between the surface and core is found to be 6.9+2.0/-1.0. The agreement between the surface rotation with the seismic result indicates that the full convective envelope is rotating quasi-rigidly. The models of the lithium abundance are compatible with a rigid rotation in the radiative zone during the main sequence. Because of the many constraints offered by oscillating stars in binary systems, such objects are important test beds of stellar evolution.

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arXiv2017

FliPer: Checking the reliability of global seismic parameters from automatic pipelines

Our understanding of stars through asteroseismic data analysis is limited by our ability to take advantage of the huge amount of observed stars provided by space missions such as CoRoT, Kepler, K2, and soon TESS and PLATO. Global seismic pipelines provide global stellar parameters such as mass and radius using the mean seismic parameters, as well as the effective temperature. These pipelines are commonly used automatically on thousands of stars observed by K2 for 3 months (and soon TESS for at least around 1 month). However, pipelines are not immune from misidentifying noise peaks and stellar oscillations. Therefore, new validation techniques are required to assess the quality of these results. We present a new metric called FliPer (Flicker in Power), which takes into account the average variability at all measured time scales. The proper calibration of FliPer enables us to obtain good estimations of global stellar parameters such as surface gravity that are robust against the influence of noise peaks and hence are an excellent way to find faults in asteroseismic pipelines.

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