MADYS: the Manifold Age Determination for Young Stars

The unrivalled astrometric and photometric capabilities of the Gaia mission have given new impetus to the study of young stars: both from an environmental perspective, as members of comoving star-forming regions, and from an individual perspective, as targets amenable to planet-hunting direct-imaging observations. In view of the large availability of theoretical evolutionary models, both fields would benefit from a unified framework that allows a straightforward comparison of physical parameters obtained by different stellar and substellar models. To this aim, we developed the Manifold Age Determination for Young Stars (MADYS), a flexible Python tool for the age and mass determination of young stellar and substellar objects. In this first release, MADYS automatically retrieves and crossmatches photometry from several catalogs, estimates interstellar extinction, and derives age and mass estimates for individual objects through isochronal fitting. Harmonizing the heterogeneity of publicly available isochrone grids, the tool allows one to choose amongst 17 models, many of which with customizable astrophysical parameters, for a total of $\sim 110$ isochrone grids. Several dedicated plotting functions are provided to allow for an intuitive visual perception of the numerical output. After extensive testing, we have made the tool publicly available. Here, we demonstrate the capabilities of MADYS, summarizing previously published results as well providing several new examples.Comment: 11 pages, 5 figures, 4 tables. Accepted for publication in A&

Detecting planetary mass companions near the water frost-line using <i>JWST</i> interferometry

JWST promises to be the most versatile infrared observatory for the next two decades. The Near Infrared and Slitless Spectrograph (NIRISS) instrument, when used in the Aperture Masking Interferometry (AMI) mode, will provide an unparalleled combination of angular resolution and sensitivity compared to any existing observatory at mid-infrared wavelengths. Using simulated observations in conjunction with evolutionary models, we present the capability of this mode to image planetary mass companions around nearby stars at small orbital separations near the circumstellar water frost-line for members of the young, kinematic moving groups β Pictoris, TW Hydrae, as well as the Taurus-Auriga association. We show that for appropriately chosen stars, JWST /NIRISS operating in the AMI mode can image sub-Jupiter companions near the water frost-lines with ∼68% confidence. Among these, M-type stars are the most promising. We also show that this JWST mode will improve the minimum inner working angle by as much as ∼50% in most cases when compared to the survey results from the best ground-based exoplanet direct imaging facilities (e.g. VLT/SPHERE). We also discuss how the NIRISS/AMI mode will be especially powerful for the mid-infrared characterization of the numerous exoplanets expected to be revealed by Gaia. When combined with dynamical masses from Gaia, such measurements will provide a much more robust characterization of the initial entropies of these young planets, thereby placing powerful constraints on their early thermal histories

BEAST detection of a brown dwarf and a low-mass stellar companion around the young bright B star HIP 81208

Recent observations from B-star Exoplanet Abundance Study (BEAST) have illustrated the existence of sub-stellar companions around very massive stars. In this paper, we present the detection of two lower mass companions to a relatively nearby ($148.7^{+1.5}_{-1.3}$ pc), young ($17^{+3}_{-4}$ Myr), bright (V=$6.632\pm0.006$ mag), $2.58\pm0.06~ M_{\odot}$ B9V star HIP 81208 residing in the Sco-Cen association, using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large Telescope (VLT) in Chile. Analysis of the photometry obtained gives mass estimates of $67^{+6}_{-7}~M_J$ for the inner companion and $0.135^{+0.010}_{-0.013}~M_{\odot}$ for the outer companion, indicating the former to be most likely a brown dwarf and the latter to be a low-mass star. The system is compact but unusual, as the orbital planes of the two companions are likely close to orthogonal. The preliminary orbital solutions we derived for the system indicate that the star and the two companions are likely in a Kozai resonance, rendering the system dynamically very interesting for future studies.Comment: 18 pages, 14 figures, 5 tables Accepted for publication in the 10. Planets and planetary systems section of A&

L'impatto della massa stellare sulla formazione dei pianeti

Superato di recente il considerevole traguardo del 5000° pianeta extrasolare confermato, la semplice rivelazione sta cedendo il passo a una fase di più intensa e minuziosa caratterizzazione e di ricerca di relazioni statistiche in grado di connettere le proprietà osservate della popolazione di esopianeti. Portare alla luce i processi fisici nascosti dietro la multiforme varietà delle architetture planetarie – e i limiti al di fuori dei quali tali processi smettono di operare – è, difatti, il fine ultimo della demografia esoplanetaria. Eppure, il ruolo della stella centrale nel plasmare questi processi non è ancora completamente compreso. Questa tesi è incentrata sullo studio dell’abbondanza di pianeti attorno a stelle B (BEAST): basato sulla tecnica del direct imaging, esso sta cercando le prime prove dell’esistenza di una popolazione di pianeti giganti nelle regioni esterne attorno a stelle B (2.4 M⊙ ≲ M ≲ 16 M⊙) appartenenti alla giovane (5 – 30 milioni di anni) associazione Scorpius-Centaurus. Passaggio necessario per la caratterizzazione delle potenziali scoperte, ci siamo concentrati anzitutto sulla determinazione delle età stellari. Onde evitare di incorrere nei noti problemi delle stime dirette di età per le stelle B, abbiamo sviluppato una tecnica indiretta, basata sull’appartenenza delle stelle di BEAST a piccoli gruppi di stelle all’interno dell’associazione. Tale analisi cinematica, resa possibile dalla grande precisione dei dati forniti dal satellite Gaia, è stata in seguito estesa all’intero Scorpione Superiore (US), una delle tre sottoregioni di Scorpius-Centaurus. Spinti dalla necessità di determinare le età stellari per un gran numero di stelle, abbiamo poi iniziato a sviluppare un programma, MADYS, capace di automatizzare l’intero processo. Il programma mette insieme una larga collezione di modelli di letteratura in una cornice omogenea, e ciò lo rende particolarmente adatto a determinare i parametri fisici dei compagni substellari scoperti tramite imaging. I risultati preliminari di BEAST, attualmente in corso, sono già estremamente interessanti. Un oggetto di 10.9 ± 1.6 MJ è stato scoperto nel sistema binario (M = 6 - 10M⊙) b Centauri, stabilendo il record del sistema planetario più massiccio noto ad oggi. Poco dopo, abbiamo trovato evidenze dell’esistenza di un compagno stellare comovente con µ2 Scorpii a una separazione proiettata di 290 ± 10 au. Dopo aver ricalcolato le proprietà della stella, abbiamo determinato la massa del compagno: M = 14.4±0.8 MJ, poco sopra il limite di bruciamento del deuterio usato per distinguere tra pianeti e nane brune. Nascosto dall’intensa luce stellare, abbiamo probabilmente osservato un secondo candidato compagno a una separazione molto ridotta (0.12′′ ≈ 20 au). La natura di questi oggetti è incerta e mette parzialmente in discussione l’attuale concezione della formazione planetaria. Se da una parte questi oggetti sono vicini al limite di bruciamento del deuterio, dall’altra le loro proprietà ricordano quelle dei pianeti giganti attorno a stelle meno massicce e sono riprodotte più facilmente assumendo che si siano formati in uno scenario simil-planetario piuttosto che in uno scenario simil-stellare. Mettendo queste considerazioni nel contesto dei modelli di formazione di core accretion e gravitational instability, concludiamo che l’attuale modellizzazione di entrambi i meccanismi non è ancora in grado di produrre questo tipo di compagni e necessita pertanto di un’estensione a masse stellari maggiori. La survey BEAST ha già dimostrato che le stelle B possono possedere sistemi planetari — o almeno simil-planetari –, mettendo in discussione molte delle nostre aspettative iniziali. Nei prossimi anni sapremo quanto sono frequenti questi sistemi, e la combinazione di minuziosi studi di follow-up e di nuovi modelli potrà fare chiarezza sulla loro sfuggevole origine.Having recently reached the impressive milestone of 5000 confirmed extrasolar planets, the exoplanetary field has attained in less than 30 years a remarkable degree of maturity. While a purely detection-oriented phase is giving way to a subtler and more intense characterization phase, the quest for statistical trends connecting the observed properties of the exoplanet population is rapidly emerging as the next big step forward for the field. Unveiling the physical processes lurking behind the multifaceted hues of observed planetary architectures – and the limits outside which these processes no longer work – is indeed the ultimate purpose of exoplanet demographics. Still, the role played by the central star in carving these processes, and hence in shaping its own planetary system, is not completely understood. This thesis revolves around the B-Star Exoplanet Abundance Study (BEAST), an ongoing direct-imaging survey that is searching for the first time for a wide-orbit giant planet population around young B-type (2.4 M⊙ ≲ M ≲ 16 M⊙) stars, belonging to the Scorpius-Centaurus association. As a first step in preparation for forthcoming detections, we focused our efforts in constraining stellar ages, a crucial parameter for companion characterization. In order to circumvent the well-known issues of direct age determination for B stars, we devised an indirect technique which hinges upon the membership of BEAST targets to small groups of stars within the association. This kinematic analysis, enabled by the extreme precision of data delivered by the Gaia satellite, was later extended to encompass the whole Upper Scorpius (US), one of the three subregions in which Scorpius-Centaurus is classically divided. Prompted by the necessity to evaluate isochronal ages for large lists of stars in a fast and robust way, we began developing a tool, MADYS, to automatize the entire process. The tool gathers from the literature a large set of stellar evolutionary models and puts them in a unified framework, allowing extensive customization of input parameters. The versatility of MADYS turned it into the ideal tool to determine the physical parameters of direct-imaged substellar companions. While BEAST is still in progress, its provisional results are already intriguing. A 10.9 ± 1.6 MJ object was found around the 6 - 10M⊙ binary b Centauri, setting the record for the most massive planet-bearing system to date. Shortly thereafter, we found evidence of a comoving substellar companion to µ2 Scorpii at a projected separation of 290 ± 10 au. After undertaking a complete reassessment of the properties of the star, we determined the mass of the companion to be 14.4 ± 0.8 MJ, slightly above the deuterium-burning limit that classically marks the transition between planets and brown dwarfs. Lurking beneath the glaring light of the star, a second companion candidate was tentatively spotted at an extremely small separation (0.12′′ ≈ 20 au). The nature of these objects is uncertain, and challenges our current view of planet formation. While their masses are near the deuterium burning limit, their properties better resemble those of giant planets around less massive stars and are better reproduced by assuming that they formed under a planet-like, rather than a star-like scenario. When putting this finding in the context of core accretion and gravitational instability formation scenarios, we conclude that the current modeling of both mechanisms is not able to produce this kind of companion and needs being extended to higher stellar masses. The BEAST survey has already shown that B stars can possess planetary – or at least planet-like – systems, challenging many of our prior expectations. In the next few years, we will know how frequent these systems are, and the combination of thorough follow-up efforts and dedicated models will hopefully shed light on their elusive origin

MADYS

The Manifold Age Determination for Young Stars (MADYS) is a flexible Python tool for age and mass determination of young stellar and substellar objects. In this first full release, MADYS automatically retrieves and cross-matches photometry from several catalogs, estimates interstellar extinction, and derives age and mass estimates for individual objects through isochronal fitting. Harmonising the heterogeneity of publicly-available isochrone grids, the tool allows to choose amongst 17 models, many of which with customisable astrophysical parameters (for a total of about 120 grids). Note that the grids are not downloaded when installing MADYS. Instructions on how to download them are provided in the .ipynb notebook in GitHub's /example directory. Several dedicated plotting function are provided to allow a visual perception of the numerical output.Please cite this software using the metadata from 'preferred-citation'

Super-Earths, M Dwarfs, and Photosynthetic Organisms: Habitability in the Lab

In a few years, space telescopes will investigate our Galaxy to detect evidence of life, mainly by observing rocky planets. In the last decade, the observation of exoplanet atmospheres and the theoretical works on biosignature gasses have experienced a considerable acceleration. The most attractive feature of the realm of exoplanets is that 40% of M dwarfs host super-Earths with a minimum mass between 1 and 30 Earth masses, orbital periods shorter than 50 days, and radii between those of the Earth and Neptune (1–3.8 R⊕). Moreover, the recent finding of cyanobacteria able to use far-red (FR) light for oxygenic photosynthesis due to the synthesis of chlorophylls d and f, extending in vivo light absorption up to 750 nm, suggests the possibility of exotic photosynthesis in planets around M dwarfs. Using innovative laboratory instrumentation, we exposed different cyanobacteria to an M dwarf star simulated irradiation, comparing their responses to those under solar and FR simulated lights. As expected, in FR light, only the cyanobacteria able to synthesize chlorophyll d and f could grow. Surprisingly, all strains, both able or unable to use FR light, grew and photosynthesized under the M dwarf generated spectrum in a similar way to the solar light and much more efficiently than under the FR one. Our findings highlight the importance of simulating both the visible and FR light components of an M dwarf spectrum to correctly evaluate the photosynthetic performances of oxygenic organisms exposed under such an exotic light condition.ISSN:2075-172

BEAST detection of a brown dwarf and a low-mass stellar companion around the young bright B star HIP 81208

Recent observations by the B-star Exoplanet Abundance Study (BEAST) illustrate the existence of substellar companions around very massive stars. Here, we present the detection of two lower mass companions to a relatively nearby (148.7₋₁.₃⁺¹.⁵ pc), young (17₋₄⁺³ Myr), bright (V = 6.632 ± 0.006 mag), 2.58 ± 0.06 MʘB9V star HIP 81208 residing in the Sco-Cen association using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large Telescope (VLT) in Chile. Our analysis of the photometry obtained gives mass estimates of 67₋₇⁺⁶ MJ for the inner companion and 0.135₋₀.₀₁₃⁺⁰.⁰¹⁰ Mʘ for the outer companion, indicating that the former is most likely a brown dwarf and the latter a low-mass star. The system is compact but unusual, as the orbital planes of the two companions are likely close to orthogonal. The preliminary orbital solutions we derive for the system indicate that the star and the two companions are likely in a Kozai resonance, rendering the system dynamically very interesting for future studies.ISSN:0004-6361ISSN:1432-074

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): HD 34700 A unveils an inner ring

Context. The study of protoplanetary disks is fundamental to understand their evolution and interaction with the surrounding environment, and to constrain planet formation mechanisms. Aims. We aim to characterise the young binary system HD34700A, which shows a wealth of structures. Methods. Taking advantage of the high-contrast imaging instruments SPHERE at the VLT, LMIRCam at the LBT, and of ALMA observations, we analyse this system at multiple wavelengths. We study the morphology of the rings and spiral arms and the scattering properties of the dust. We discuss the possible causes of all the observed features. Results. We detect for the first time, in the Hα band, a ring extending from ∼65 au to ∼120 au, inside the ring which is already known from recent studies. These two have different physical and geometrical properties. Based on the scattering properties, the outer ring may consist of grains with a typical size of aout ≥ 4 μm, while the inner ring has a smaller typical size of ain ≤ 0.4 μm. Two extended logarithmic spiral arms stem from opposite sides of the disk. The outer ring appears as a spiral arm itself, with a variable radial distance from the centre and extended substructures. ALMA data confirm the presence of a millimetric dust substructure centred just outside the outer ring, and detect misaligned gas rotation patterns for HD34700 A and B. Conclusions. The complexity of HD34700A, revealed by the variety of observed features, suggests the existence of one or more diskshaping physical mechanisms. Our findings are compatible with the presence inside the disk of an as of yet undetected planet of several Jupiter masses and the system interaction with the surroundings, by means of gas cloudlet capture or flybys. Further observations with JWST/MIRI or ALMA (gas kinematics) could shed more light on them.ISSN:0004-6361ISSN:1432-074

BEAST begins: sample characteristics and survey performance of the B-star Exoplanet Abundance Study

While the occurrence rate of wide giant planets appears to increase with stellar mass at least up through the A-type regime, B-type stars have not been systematically studied in large-scale surveys so far. It therefore remains unclear up to what stellar mass this occurrence trend continues. The B-star Exoplanet Abundance Study (BEAST) is a direct imaging survey with the extreme adaptive optics instrument SPHERE, targeting 85 B-type stars in the young Scorpius-Centaurus (Sco-Cen) region with the aim to detect giant planets at wide separations and constrain their occurrence rate and physical properties. The statistical outcome of the survey will help determine if and where an upper stellar mass limit for planet formation occurs. In this work, we describe the selection and characterization of the BEAST target sample. Particular emphasis is placed on the age of each system, which is a central parameter in interpreting direct imaging observations. We implement a novel scheme for age dating based on kinematic sub-structures within Sco-Cen, which complements and expands upon previous age determinations in the literature. We also present initial results from the first epoch observations, including the detections of ten stellar companions, of which six were previously unknown. All planetary candidates in the survey will need follow up in second epoch observations, which are part of the allocated observational programme and will be executed in the near future