arXiv subjects

N. Huélamo

Publications and source records attributed to N. Huélamo.

At least 19 recordsLinked to original sources

arXiv2026

Complex morphology and kinematics at the heart of the very low luminosity object IRAM 04191+1522

The formation of the majority of brown dwarfs (BDs) remains uncertain. They may form in molecular cloud cores in a process akin to low mass star formation, or via fragmentation in circumstellar discs. Studying the youngest, most embedded sources is crucial for distinguishing these scenarios. We investigate molecular gas morphology and kinematics around one young & embedded very low luminosity object (VeLLO), IRAM 04191+1522, utilising archival ALMA observations of 13CO, C18O, and SO. We trace gas on scales of a few 10s to 100s of au around the source to search for outflowing and/or infalling structures. The red and blueshifted 13CO (3-2) emission show distinct morphologies and kinematics. The blueshifted emission to the north-west may trace shocked material oriented differently from the previously reported approx. 0.1 pc CO outflow. Redshifted emission mainly to the south-east and south-west may trace the base of an outflow cavity. The position angle of this cavity suggests the presence of a second outflow, which supports the possible binary nature of this VeLLO. The C18O (2-1) emission is highly complex, comprising structures at different spatial scales and distances from the source. These may trace a mix of molecular outflow, outflow cavity, and disc emission. SO 65-54 reveals evidence for anticlockwise rotation around the central source, together with a northern structure of uncertain origin. We have identified a complex set of 13CO (3-2) and C18O (2-1) structures alongside evidence of a new outflow cavity at a distinct position angle from previously detected outflows. This supports the scenario that IRAM 04191+1522 is a binary system. The northern SO gas structure remains unexplained. Higher spectral resolution observations at intermediate scales are needed to characterise these substructures, their connection to larger scale structures, and to determine this system's final fate.

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arXiv2026

Euclid Early Release Observations of the Barnard 30 dark cloud I. Brown dwarfs and planetary mass candidate members at the core of the association

This study aims to identify very low-mass members within the Barnard 30 dark cloud, with a particular focus on detecting objects in the substellar domain, including those within the planetary-mass regime. We employed deep photometric observations using data from the Euclid mission, incorporating advanced data processing techniques, in particular the DeNeb tool for optimized source detection. We also analyze multi-wavelength ancillary observations and perform a Spectral Energy Distribution analysis for each candidate member. In addition, low-resolution near-infrared spectroscopy was obtained for one candidate to further assess its nature and properties. Our initial photometric analysis yielded a initial sample of nearly one hundred candidate members in the substellar mass range. A subsample of 23 probable members, located close to the 3 Myr isochrone, has been identified. Thus, we have substantially expanded the known population of faint, cool sources associated with the region. Low resolution near-IR spectroscopic analysis of one candidate reveals an L2 spectral type with low gravity, consistent with a young ultra-cool dwarf. If its membership is confirmed, its estimated mass lies in the range 15-20 Mjup. These findings validate the reliability of our multi-wavelength photometric selection methodology. These results offer valuable insights into the low-mass end of the initial mass function (IMF) and demonstrate the effectiveness of Euclid in identifying brown dwarf and planetary-mass candidates in nearby, densely packed star-forming regions.

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arXiv2026

Two inner dust clumps in PDS 70. A third protoplanet traced by trojan material or a substructured inner disk?

The PDS 70 cavity hosts two confirmed directly imaged protoplanets and a third inner planet candidate at 13au, labeled PDS 70 d. Despite its Keplerian motion, its unusually blue spectrum challenges a planetary interpretation. We further investigate the presence and nature of a third inner planet using new SPHERE and GRAVITY+ observations. Using the star-hopping strategy, we obtained coronagraphic IRDIS polarimetric observations in the H-band, and non-coronagraphic observations with IRDIFS in the YJHK-bands. We also searched for a planetary signal with GRAVITY in the 4UT configuration. We consistently detect two elongated inner emissions with SPHERE: the previously proposed planet candidate and another feature that appears to share the same orbit while leading it by ~120$^\circ$. Both features show dust-scattered-light spectra but different colors, possibly indicating different grain sizes. Such configuration is consistent with co-orbital dust accumulated at the stable Lagrangian regions of a distinct and yet undetected planet. GRAVITY yields a marginal (3$σ$) detection at the predicted location along the same orbit ($ρ=76.2\pm0.29$mas, PA=$226.50\pm0.21^\circ$), and consistent with a ~3$M_{\rm Jup}$ planet. This planet-like signal is aligned with a narrow shadow that we detect in the outer disk. We also detect polarized emission very close to the star likely arising from the inner disk. The apparent embedding of the two dust clumps within it motivates an inner-disk origin as an alternative scenario. We conclude that the previously reported third planet candidate traces a dust clump either trailing an unseen planet on the same orbit or a rotating substructure within the inner disk. Further observations are needed to test these scenarios. Confirming the new GRAVITY planet-like signal would support co-orbital substructures as indirect tracers of protoplanets.

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arXiv2026

IRAM 04191+1522: a compact proto-brown dwarf binary candidate

Very low-luminosity objects in nearby star-forming regions have been identified as promising proto-brown dwarf candidates. The study of their multiplicity can shed light on the dominant formation mechanism of these substellar objects. We aim at studying the multiplicity of the very low luminosity object IRAM 04191+1522. To do so, we have obtained 0.89mm ALMA observations with a very extended configuration, achieving an angular resolution of ~0.04 arcsec (6 au at 140 pc). We have complemented our data with new VLA observations, and ALMA archival data at 1.3mm. As a result, we resolve IRAM04191+1522 into a close binary candidate for the first time. The binary is detected in the ALMA continuum data with a projected separation of ~80 mas, or 11 au at a distance of 140 pc. The two sources are oriented in the East-West direction, with the eastern component being brighter and more extended than the western one, which is marginally resolved. The analysis of C18O(2-1) archival data reveals gaseous material in rotation around the binary, presumably from a circumbinary disk with ~27 au of radius centered on the faintest ALMA component. A fit of the position-velocity diagram allows us to estimate a total dynamical mass for the system of 50+-40 MJup. Therefore, we classify IRAM04191 as a tight proto-brown dwarf binary candidate. The VLA data reveals the detection of a single object closer to the western ALMA source, and with a spectral index consistent with a radio jet.

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arXiv2026

Multiplicity of young isolated planetary mass objects in Taurus and Upper Scorpius

Free-floating planetary mass objects--worlds that roam interstellar space untethered to a parent star--challenge conventional notions of planetary formation and migration, but also of star and brown dwarf formation. We focus on the multiplicity among free-floating planets. By virtue of their low binding energy (compared to other objects formed in these environments), these low-mass substellar binaries represent a most sensitive probe of the mechanisms at play during the star formation process. We use the HST and its WFC3 and the VLT and its ERIS AO facility to search for visual companions among a sample of 77 objects members of the USco and Taurus young nearby associations with estimated masses in the range between approximately 6-66 M$_{\rm Jup}$. We report the discovery of one companion candidate around a Taurus member with a separation of 111.9$\pm$0.4~mas, or $\sim$18~au assuming a distance of 160~pc, with an estimated primary mass in the range between 3--6~M$_{\rm Jup}$and a secondary mass between 2.6--5.2~M$_{\rm Jup}$ depending on the assumed age. This corresponds to an overall binary fraction of 1.8$^{+2.6}_{-1.3}$\% among low-mass brown dwarfs and free-floating planetary mass objects over the separation range $\ge$7~au. Despite the limitations of small-number statistics and variations in spatial resolution and sensitivity, our results, combined with previous high-spatial-resolution surveys, suggest a notable difference in the multiplicity properties of objects below $\sim$30--50~M$_{\rm Jup}$ between USco and Taurus. In Taurus, a binary fraction of $5.6^{+3.2}_{-2.3}$\% is found for objects with masses below 30M$_{\rm Jup}$, and of $7.8^{+3.0}_{-2.4}$\% for objects with masses below 50M$_{\rm Jup}$, whereas no binary were found among 80 objects over the matching luminosity range in USco, corresponding to an upper limit of $\le$1.2\%.

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arXiv2025

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake. How do Planetary Systems Form?

The detection and characterization of protoplanets in protoplanetary disks around young stars is emerging as a transformative field that will redefine our understanding of how planetary systems form. While current facilities have revealed the diversity of mature exoplanets and the complex structures of disks, we still lack the crucial observational link between them: a statistically meaningful census of planets caught in the act of formation. This white paper argues that such a breakthrough requires access to the nearest and most informative star-forming regions, roughly half of which are poorly accessible or entirely unreachable from Cerro Armazones. Although the ELT alone will strongly impact our knowledge of planet formation, its location prevents Europe from fully exploiting the necessary parameter space. A 30-40 m telescope in the northern hemisphere is therefore essential for obtaining diffraction-limited imaging of protoplanets and disks across the entire sky, enabling robust demographics, exploiting synergies with ngVLA, Gaia, and other facilities covering the north, and ensuring that Europe remains at the forefront of the planet-formation revolution in the coming decades.

astro-ph.IM↗

arXiv2025

Euclid Quick Data Release (Q1) Ultracool dwarfs in the Euclid Deep Field North

Ultracool dwarfs (UCDs) encompass the lowest mass stars and brown dwarfs, defining the stellar substellar boundary. They have significant potential for advancing the understanding of substellar physics; however, these objects are challenging to detect due to their low luminosity. The wide coverage and deep sensitivity of the Euclid survey will increase the number of confirmed and well characterised UCDs by several orders of magnitude. In this study, we take advantage of the Euclid Quick Data Release (Q1) and in particular we look in detail at the known and new UCDs in the Euclid Deep Field North (22.9 deg2 down to JE = 24.5 mag), to understand the advantages of using the slitless Euclid spectroscopy. We compile a comparison sample of known UCDs and use their spectra to demonstrate the capability of Euclid to derive spectral types using a template matching method. This method is then applied to the spectra of the newly identified candidates. We confirm that 33 of these candidates are new UCDs, with spectral types ranging from M7 to T1 and JE = 17 to 21 mag. We look at their locus in colour colour diagrams and compare them with the expected colours of QSOs. A machine readable catalogue is provided for further study, containing both the comparison sample and the newly identified UCDs, along with their spectral classifications where the Q1 spectra quality allows for confident determination

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arXiv2025

Free-floating planetary mass objects in LDN 1495 from Euclid Early Release Observations

Context. Substellar objects, including brown dwarfs and free-floating planetary-mass objects, are a significant product of star formation. Their sensitivity to initial conditions and early dynamical evolution makes them especially valuable for studying planetary and stellar formation processes. Aims. We search for brown dwarfs and isolated planetary mass objects in a young star-forming region to better constrain their formation mechanisms. Methods. We took advantage of the Euclid unprecedented sensitivity, spatial resolution and wide field of view to search for brown dwarfs and free-floating planetary mass objects in the LDN 1495 region of the Taurus molecular clouds. We combined the recent Euclid Early Release Observations with older very deep ground-based images obtained over more than 20 yr to derive proper motions and multiwavelength photometry and to select members based on their morphology and their position in a proper motion diagram and in nine color-magnitude diagrams. Results. We identified 15 point sources whose proper motions, colors, and luminosity are consistent with being members of LDN 1495. Six of these objects were already known M9-L1 members. The remaining nine are newly identified sources whose spectral types might range from late-M to early-T types, with masses potentially as low as 1~2 MJup based on their luminosity and according to evolutionary models. However, follow-up observations are needed to confirm their nature, spectral type, and membership. When it is extrapolated to the entire Taurus star-forming region, this result suggests the potential presence of several dozen free-floating planetary mass objects.

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arXiv2025

KOBE-1: The first planetary system from the KOBE survey. Two planets likely residing in the sub-Neptune mass regime around a late K-dwarf

K-dwarf stars are promising targets in the exploration of potentially habitable planets. Their properties, falling between G and M dwarfs, provide an optimal trade-off between the prospect of habitability and ease of detection. The KOBE experiment is a blind-search survey exploiting this niche, monitoring the radial velocity of 50 late-type K-dwarf stars. It employs the CARMENES spectrograph, with an observational strategy designed to detect planets in the habitable zone of their system. In this work, we exploit the KOBE data set to characterize planetary signals in the K7V star HIP 5957 (KOBE-1) and to constrain the planetary population within its habitable zone. We used 82 CARMENES spectra over a time span of three years. We employed a GLS periodogram to search for significant periodic signals that would be compatible with Keplerian motion on KOBE-1. We carried out a model comparison within a Bayesian framework to ensure the significance of the planetary model over alternative configurations of lower complexity. We also inspected two available TESS sectors in search of planetary signals. We identified two signals: at 8.5d and 29.7d. We confirmed their planetary nature through ruling out other non-planetary configurations. Their minimum masses are 8.80+/-0.76ME and 12.4+/-1.1ME, corresponding to absolute masses within the planetary regime at a high certainty (>99.7%). By analyzing the sensitivity of the CARMENES time series to additional signals, we discarded planets above 8.5ME within the habitable zone. We identified a single transit-like feature in TESS, whose origin is still uncertain, but still compatible within 1sigma with a transit from planet c. We have explored future prospects for characterizing this system, concluding that nulling interferometry with the LIFE mission could be capable of directly imaging both planets and characterizing their atmospheres in future studies.

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arXiv2024

Substellar candidates at the earliest stages: the SUCANES database

Brown dwarfs are the bridge between low-mass stars and giant planets. One way of shedding light on their dominant formation mechanism is to study them at the earliest stages of their evolution, when they are deeply embedded in their parental clouds. Several works have identified pre- and proto-brown dwarfs candidates using different observational approaches. The aim of this work is to create a database with all the objects classified as very young substellar candidates in the litearature in order to study them in an homogeneous way. We have gathered all the information about very young substellar candidates available in the literature until 2020. We have retrieved their published photometry from the optical to the centimeter regime, and we have written our own codes to derive their bolometric temperatures and luminosities, and their internal luminosities. We have also populated the database with other parameters extracted from the literature, like e.g. the envelope masses, their detection in some molecular species, and presence of outflows. The result of our search is the SUCANES database, containing 174 objects classified as potential very young substellar candidates in the literature. We present an analysis of the main properties of the retrieved objects. Since we have updated the distances to several star forming regions, this has allowed us to reject some candidates based on their internal luminosities. We have also discussed the derived physical parameters and envelope masses for the best substellar candidates isolated in SUCANES. As an example of a scientific exploitation of this database, we present a feasibility study for the detection of radiojets with upcoming facilities: the ngVLA and the SKA interferometers. The SUCANES database is accessible through a Graphical User Interface and it is open to any potential user.

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arXiv2024

Euclid: Early Release Observations -- A glance at free-floating new-born planets in the sigma Orionis cluster

We provide an early assessment of the imaging capabilities of the Euclid space mission to probe deeply into nearby star-forming regions and associated very young open clusters, and in particular to check to what extent it can shed light on the new-born free-floating planet population. This paper focuses on a low-reddening region observed in just one Euclid pointing where the dust and gas has been cleared out by the hot sigma Orionis star. One late-M and six known spectroscopically confirmed L-type substellar members in the sigma Orionis cluster are used as benchmarks to provide a high-purity procedure to select new candidate members with Euclid. The exquisite angular resolution and depth delivered by the Euclid instruments allow us to focus on bona-fide point sources. A cleaned sample of sigma Orionis cluster substellar members has been produced and the initial mass function (IMF) has been estimated by combining Euclid and Gaia data. Our sigma Orionis substellar IMF is consistent with a power-law distribution with no significant steepening at the planetary-mass end. No evidence of a low-mass cutoff is found down to about 4 Jupiter masses at the young age (3 Myr) of the sigma Orionis open cluster.

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arXiv2024

ExoplANETS-A: A VO database for host stars and planetary systems: The effect of XUV on planet atmospheres

ExoplANETS-A is an EU Horizon-2020 project with the primary objective of establishing new knowledge on exoplanet atmospheres. Intimately related to this topic is the study of the host-stars radiative properties in order to understand the environment in which exoplanets lie. The aim of this work is to exploit archived data from space-based observatories and other public sources to produce uniform sets of stellar data that can establish new insight on the influence of the host star on the planetary atmosphere. We have compiled X-ray and UV luminosities, which affect the formation and the atmospheric properties of the planets, and stellar parameters, which impact the retrieval process of the planetary-atmosphere's properties and its errors. Our sample is formed of all transiting-exoplanet systems observed by HST or Spitzer. It includes 205 exoplanets and their 114 host-stars. We have built a catalogue with information extracted from public, online archives augmented by quantities derived by the Exoplanets-A work. With this catalogue we have implemented an online database which also includes X-ray and OHP spectra and TESS light curves. In addition, we have developed a tool, exoVOSA, which is able to fit the spectral energy distribution of exoplanets. We give an example of using the database to study the effects of the host-star high-energy emission on the exoplanet atmosphere. The sample has a planet radius valley which is located at 1.8 Earth radii, in agreement with previous studies. Multiplanet systems in our sample were used to test the photoevaporation model and we find that out of 14 systems, only one significant case poses a contradiction to it (K2-3). In summary, the exoplanet and stellar resources compiled and generated by ExoplANETS-A form a sound basis for current JWST observations and for future work in the era of Ariel.

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arXiv2024

Gas, not dust: Migration of TESS/Gaia hot Jupiters possibly halted by the magnetospheres of protoplanetary disks

(Abridged) The presence of short-period (< 10 days) planets around main sequence (MS) stars has been associated either with the dust-destruction region or with the magnetospheric gas-truncation radius in the protoplanetary disks that surround them during the pre-MS phase. However, previous analyses have only considered low-mass FGK stars, making it difficult to disentangle the two scenarios. This exploratory study is aimed at testing whether it is the inner dust or gas disk driving the location of short-period, giant planets. By combining TESS and Gaia DR3 data, we identified a sample of 47 intermediate-mass (1.5-3 M$_{\odot}$) MS stars hosting confirmed and firm candidate hot Jupiters. We compared their orbits with the rough position of the inner dust and gas disks, which are well separated around their Herbig stars precursors. We also made a comparison with the orbits of confirmed hot Jupiters around a similarly extracted TESS/Gaia sample of low-mass sources (0.5-1.5 M$_{\odot}$). Our results suggest that the inner gas (and not the dust) disk limits the innermost orbits of hot Jupiters around intermediate-mass stars. These findings also provide tentative support to previous works that have claimed this is indeed the case for low-mass sources. We propose that hot Jupiters could be explained via a combination of the core-accretion paradigm and migration up to the gas-truncation radius, which may be responsible for halting inward migration regardless of the stellar mass regime. Larger samples of intermediate-mass stars with hot Jupiters are necessary to confirm our hypothesis, which implies that massive Herbig stars without magnetospheres (> 3-4 M$_{\odot}$) may be the most efficient in swallowing their newborn planets.

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arXiv2024

The AstraLux-TESS high-spatial resolution imaging survey. Search for stellar companions of 215 planet candidates from TESS

Chance-aligned sources or blended companions can cause false positives in planetary transit detections or simply bias the determination of the candidate properties. In the era of high-precision space-based photometers, the need for high-spatial resolution images has demonstrated to be critical for validating and confirming transit signals. This already applied to the Kepler mission, it is now applicable to the TESS survey and will be critical for PLATO. We present the results of the AstraLux-TESS survey, a catalog of high-spatial resolution images obtained with the AstraLux instrument (Calar Alto) in the context of the TESS Follow-up Observing Program. We use the lucky-imaging technique to obtain high-spatial resolution images from planet candidate hosts included mostly in two relevant regimes: exoplanet candidates belonging to the level-one requirement of the TESS mission (planets with radii $R<4~R_{\oplus}$), and candidates around intermediate-mass stars. Among the 185 planet host candidate stars observed, we found 13 (7%) to be accompanied by additional sources within 2.2 arcsec separation. Among them, six are not associated to sources in the Gaia DR3 catalog, thus contaminating the TESS light curve. We provide upper limits and probabilities to the possible existence of field contaminants through the sensitivity limits of our images. Among the isolated hosts, we can discard hazardous companions (bright enough to mimic a planetary transit signals) for all their planets. The results from this catalog are key for the statistical validation of small planets (prime targets of the TESS mission) and planets around intermediate-mass stars in the main-sequence. These two populations of planets are hard to confirm with the radial velocity technique. Our results also demonstrate the importance of this type of follow-up observations for future transit missions like PLATO, even in the Gaia era.

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arXiv2022

$\tt{KOBEsim}$: a Bayesian observing strategy algorithm for planet detection in radial velocity blind-search surveys

Ground-based observing time is precious in the era of exoplanet follow-up and characterization, especially in high-precision radial velocity instruments. Blind-search radial velocity surveys thus require a dedicated observational strategy in order to optimize the observing time, which is particularly crucial for the detection of small rocky worlds at large orbital periods. We develop an algorithm with the purpose of improving the efficiency of radial velocity observations in the context of exoplanet searches, and we apply it to the K-dwarfs Orbited By habitable Exoplanets (KOBE) experiment. We aim at accelerating exoplanet confirmations or, alternatively, rejecting false signals as early as possible in order to save telescope time and increase the efficiency of both blind-search surveys and follow-up of transiting candidates. Once a minimum initial number of radial velocity datapoints is reached in such a way that a periodicity starts to emerge according to generalized Lomb-Scargle (GLS) periodograms, that period is targeted with the proposed algorithm, named $\texttt{KOBEsim}$. The algorithm selects the next observing date that maximizes the Bayesian evidence for such periodicity in comparison with a model with no Keplerian orbits. By means of simulated data, we prove that the algorithm accelerates the exoplanet detection, needing $29 - 33\,\%$ less observations and $41 - 47\,\%$ less timespan of the full dataset for low-mass planets ($m_{\rm p}\,<\,10\,M_{\oplus}$) in comparison with a conventional monotonic cadence strategy. The enhancement in the number of datapoints for $20\,M_{\oplus}$ planets is also appreciable, $16\,\%$. We also test $\texttt{KOBEsim}$ with real data for a particular KOBE target, and for the confirmed planet $HD~102365\,b$. Both of them demonstrate that the strategy is capable of speeding up the detection up to a factor of $2$.

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arXiv2022

Searching for H$_α$-emitting sources in the gaps of five transitional disks. SPHERE/ZIMPOL high-contrast imaging

(Pre-)transitional disks show gaps and cavities that can be related with on-going planet formation. According to theory, young embedded planets can accrete material from the circumplanetary and circumstellar disks, so that they could be detected in accretion tracers, like the H$_α$ emission line. In this work, we present spectral angular differential imaging AO-assisted observations of five (pre-)transitional disks obtained with SPHERE/ZIMPOL at the Very Large Telescope (VLT). They were obtained in the H$_α$ line and the adjacent continuum. We have combined spectral and angular differential imaging techniques to increase the contrast in the innermost regions close to the star, and search for the signature of young accreting protoplanets. As a result, the reduced images do not show any clear H$_α$ point source around any of the targets. We report faint H$_α$ emissions around TW Hya and HD163296: while the former is most probably an artifact related with a spike, the nature of the latter remains unclear. The spectral and angular differential images yield contrasts of 6--8 magnitudes at separations of $\sim$ 100 mas from the central stars, except in the case of LkCa15, with values of $\sim$3 mag. We have estimated upper limits to the accretion luminosity of potential protoplanets, obtaining that planetary models provide an average value of $L_{\rm acc} \sim 10^{-4}$ $L_{\odot}$ at 200 mas, which is $\sim$2 orders of magnitude higher than the $L_{\rm acc}$ estimated from the extrapolation of the $L_{H_α}$ - $L_{acc}$ stellar relationship. We explain the lack of protoplanet detections as a combination of different factors, like e.g. episodic accretion, extinction from the circumstellar and circumplanetray disks, and/or a majority of low-mass, low-accreting planets.

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arXiv2022

The KOBE experiment: K-dwarfs Orbited By habitable Exoplanets. Project goals, target selection and stellar characterization

The detection of habitable worlds is one of humanity's greatest endeavors. So far, astrobiological studies show that one of the most critical components for life development is liquid water. Its chemical properties and its capacity to dissolve and hence transport other substances makes this constituent a key piece in the development of life. As a consequence, looking for life as we know it is directly related to the search for liquid water. For a remote detection of life in distant planetary systems, this means looking for planets in the so-called habitable zone. In this sense, K-dwarf stars are the perfect hosts. Contrary to G-dwarfs, the habitable zone is closer, thus making planet detection easier using transit or radial velocity techniques. Contrary to M-dwarfs, the stellar activity is much smaller, hence having a smaller impact in both the detectability and in the true habitability of the planet. Also, K-dwarfs are the quietest in terms of oscillations, and granulation noise. Despite this, there is a dearth of planets in the habitable zone of K-dwarfs due to a lack of observing programs devoted to this parameter space. In response to a call for Legacy Programs of the Calar Alto observatory, we have started the first dedicated and systematic search for habitable planets around K-dwarfs, the K-dwarfs Orbited By habitable Exoplanets (KOBE). This survey is monitoring the radial velocity of 50 carefully pre-selected K-dwarfs with the CARMENES instrument along 5 semesters with an average of 90 data points per target. Based on planet occurrence rates convolved with our detectability limits, we expect to find $1.68\pm 0.25$ planets per star in the KOBE sample and in half of the sample we expect to find one of those planets within the habitable zone. In this paper, we describe the project motivation, goals and target selection and preliminary stellar characterization.

astro-ph.EP↗

arXiv2022

Gaia EDR3 comparative study of protoplanetary disk fractions in young stellar clusters

(Abridged) The lifetime of protoplanetary disks around young stars limits the timescale when planets form. A disk dissipation timescale < 10 Myr was inferred from surveys providing the fraction of stars with disks in young stellar clusters with different ages. However, most previous surveys focused on the compact region within ~ 2 pc from the clusters' centers, for which the disk fraction information considering the outer part is practically absent. We aim to test if disk fraction estimates change when inferred from an extended region around the clusters' centers. Gaia EDR3 data and a best-suited, Virtual Observatory (VO)-based tool -Clusterix-, are used to identify member stars for a representative sample of 19 young clusters considering two concentric fields of view (FOV) with radii ~ 20 pc and ~ 2 pc. Our analysis reveals that the inner disk fractions inferred from the compact and the extended regions are equal within ~ 10%, which does not support a previous hypothesis proposing that disk fractions should be significantly larger considering extended regions. A list of member and disk stars in each cluster is provided and stored in a VO-compliant archive. Averaged values and plots characterizing the whole clusters are also provided, including HR diagrams based on Gaia colors and absolute magnitudes. Our results cover the largest fields ever probed when dealing with disk fractions for all clusters analysed, and imply that their complete characterization requires the use of wide FOVs. The resulting database is a benchmark for future detailed studies of young clusters, whose disk fractions must be accurately determined by using multi-wavelength analysis potentially combined with data from coming Gaia releases.

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