Context. The solar neighbourhood is populated by nearby (<200 pc), young (<100 Myr) moving groups (NYMGs) of stars, whose origins are still a matter of debate. One plausible explanation is that they are remnants of individual stellar clusters and associations that are currently dispersing throughout the galactic disc. Aims. We aim to derive the initial mass function (IMF) of a large sample of NYMGs. Methods. We developed and applied an algorithm that uses photometric and astrometric data from Gaia DR3 to detect NYMGs as over-densities in a kinematic space, whose members distribute along young isochrones. We inferred individual masses from the photometry of both the detected and the previously known candidates. We estimated the IMFs for 33 groups, 30 of them for the first time, in an average mass range 0.1 < m/M⊙ < 5, with some groups going as low as 0.02 M⊙ and as high as 10 M⊙. We parameterised these IMFs using a log-normal for m < 1 M⊙ and a power-law for m > 1 M⊙. Results. We detected 4166 source candidate members of 44 known groups, including 2545 new candidates. We recovered 44-54% of the literature candidates and estimated a contamination rate from old field stars of 16-24%. The candidates of the detected groups distribute along young isochrones, which suggests that they are potential members of NYMGs. Parameterisations of both the average of the 3 3 IMFs based on our detections (mc = 0.25 ± 0.17 M⊙, σc = 0.45 ± 0.17, and α = −2.26 ± 0.09) and the one based on the known candidates from the literature (mc = 0.22 ± 0.14 M⊙, σc = 0.45 ± 0.17, and α = −2.45 ± 0.06) are in agreement with the IMF parameterisation of the solar neighbourhood and young stellar associations. Conclusions. Our parameterisation of the average IMF, together with the distribution of the detected group members along young isochrones offer strong evidence suggesting that the NYMGs are remnants of individual stellar associations and clusters. We confirm that there are no systematic biases in our detection and in the literature in the range of 0.1 < m/M⊙ < 10.

Context. RR Lyrae stars have long been considered unequivocal tracers of old (>10 Gyr) and metal-poor ([Fe/H] < −0.5) stellar populations. First, because these populations is where they are readily found and because, according to canonical stellar evolution models for isolated stars, these are the only populations where RR Lyrae are expected to exist. However, recent independent results are challenging this view and pointing to the existence of intermediate-age RR Lyrae (i.e. only about 2-5 Gyr old). Aims. Our goal in this work is to provide direct evidence of the existence of intermediate-age RR Lyrae by searching for these stars in Milky Way open clusters, where the age association would be direct and robust. Methods. We searched a catalogue of over 3000 open clusters with published kinematically associated member stars by cross-matching it against a compilation of the largest publicly available RR Lyrae surveys (Gaia, ASAS-SN, Pan-STARRS1, Zwicky Transient Facility, and OGLE-IV). Results. We identified a star as a bona fide RR Lyrae variable and robust member of the 2-4 Gyr old Trumpler 5 cluster, based on its parallax and proper motions and their agreement with confirmed cluster members. We derived an extremely low probability (0.049 ± 0.013%) of the star being a background field RR Lyrae and we provide initial constraints on a possible binary companion based on its position in the colour-absolute-magnitude diagram. Conclusions. As a current source of debate, the Trumpler 5 RR Lyrae star provides the most direct evidence to date of the existence of RR Lyrae stars at much younger ages than traditionally expected, adding to the mounting evidence supporting their existence.

We present a new spectroscopic view of the brown dwarf population in the young star-forming region IC 1396 and investigate the impact of environment on low-mass star formation. We use deep optical photometry from Subaru-HSC to identify the candidate low-mass stars and brown dwarfs in the region. Our follow-up low-resolution spectroscopic survey with GTC-EMIR and IRTF-SpeX has identified 32 new members in the region with spectral types between M3 and M9, among which 25 are brown dwarfs with spectral types M6 or later. We use the BT-Settl atmospheric models to derive the effective temperatures of the members. Using a comprehensive catalogue of known members and candidates, we estimate the star to brown dwarf ratio for IC 1396 to be 5.0±0.4, for a mass range between 1-0.03 M_⊙. This ratio is largely consistent with measurements in other young clusters spanning a range of UV radiation fields and stellar densities, supporting formation scenarios in which the relative abundance of brown dwarfs is not strongly influenced by the local environmental conditions.

The solar neighbourhood is populated by nearby, young moving groups (NYMGs) of stars that are candidates to be remnants of individual stellar clusters and associations, currently dispersing in the galactic disc. To derive the initial mass function (IMF) of a large sample of NYMGs, we developed and applied an algorithm that uses photometry and astrometry from Gaia DR3 to detect NYMGs in a kinematic space. We inferred individual masses from the photometry of both the detected and the previously known candidates. We estimated the IMFs for 33 groups, 30 of them for the first time, in an average mass range $0.11~M_\odot$. We detected 4166 source candidate members of 44 known groups, including 2545 new candidates. We recovered 44-54\% of the literature candidates and estimated a contamination rate from old field stars of 16-24\%. The candidates of the detected groups distribute along young isochrones, which suggests that they are potential members of NYMGs. Parameterizations of both the average of the 33 IMFs based on our detections ($m_c=0.25\pm0.17~M_{\odot}$, $σ_c=0.45\pm0.17$, and $α=-2.26\pm0.09$) and the one based on the known candidates from the literature ($m_c=0.22\pm0.14~M_{\odot}$, $σ_c=0.45\pm0.17$, and $α=-2.45\pm0.06$) are in agreement with the IMF parameterization of the solar neighbourhood and young stellar associations. Our parameterization of the average IMF together with the distribution of the detected group members along young isochrones provide strong evidence suggesting that the NYMGs are remnants of individual stellar associations and clusters and that there are no systematic biases in our detection and in the literature in the range $0.1

The Sloan Digital Sky Survey IV APOGEE-2 primary science goal was to observe red giant stars throughout the Galaxy to study its dynamics, morphology, and chemical evolution. The APOGEE instrument, a high-resolution 300-fiber H -band (1.55–1.71 μ m) spectrograph, is also ideal to study other stellar populations in the Galaxy, among which are a number of star-forming regions and young open clusters. We present the results of the determination of six stellar properties ( T eff , log g , [Fe/H], L / L ⊙ , M / M ⊙ , and age) for a sample that is composed of 3360 young stars, of subsolar to supersolar types, in 16 Galactic star formation and young open cluster regions. Those sources were selected by using a clustering method that removes most of the field contamination. Samples were also refined by removing targets affected by various systematic effects of the parameter determination. The final samples are presented in a comprehensive catalog that includes all six estimated parameters. This overview study also includes parameter spatial distribution maps for all regions and Hertzsprung–Russell ( log L / L ⊙ vs. T eff ) diagrams. This study serves as a guide for detailed studies on individual regions and paves the way for the future studies on the global properties of stars in the pre-main-sequence phase of stellar evolution using more robust samples.

Context. The confirmed exoplanet population around very low mass stars is increasing considerable through data from the latest space missions and improvements in ground-based observations, particularly with the detection of Earth-like planets in the habitable zones. However, theoretical models need to improve in the study of planet formation and evolution around low-mass hosts. Aims. Our main goal is to study the formation of rocky planets and the first 100 Myr of their dynamical evolution around a star with a mass of 0.08 M ⊙ , which is close to the substellar mass limit. Methods. We developed two sets of N -body simulations assuming an embryo population affected by tidal and general relativistic effects, refined by the inclusion of the spin-up and contraction of the central star. This population is immersed in a gas disk during the first 10 Myr. Each set of simulations incorporated a different prescription from the literature to calculate the interaction between the gas-disk and the embryos: one widely used prescription which is based on results from hydrodynamics simulations, and a recent prescription that is based on the analytic treatment of dynamical friction. Results. We found that in a standard disk model, the dynamical evolution and the final architectures of the resulting rocky planets are strongly related with the prescription used to treat the interaction within the gas and the embryos. Its impact on the resulting close-in planet population and particularly on those planets that are located inside the habitable zone is particularly strong. Conclusions. The distribution of the period ratio of adjacent confirmed exoplanets observed around very low mass stars and brown dwarfs and the exoplanets that we obtained from our simulations agrees well only when the prescription based on dynamical friction for gas-embryo interaction was used. Our results also reproduce a close-in planet population of interest that is located inside the habitable zone. A fraction of these planets will be exposed for a long period of time to the stellar irradiation inside the inner edge of the evolving habitable zone until the zone reaches them.

The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is a dual-hemisphere, near-infrared (NIR), spectroscopic survey with the goal of producing a chemodynamical mapping of the Milky Way. The targeting for APOGEE-2 is complex and has evolved with time. In this paper, we present the updates and additions to the initial targeting strategy for APOGEE-2N presented in Zasowski et al. (2017). These modifications come in two implementation modes: (i) “Ancillary Science Programs” competitively awarded to Sloan Digital Sky Survey IV PIs through proposal calls in 2015 and 2017 for the pursuit of new scientific avenues outside the main survey, and (ii) an effective 1.5 yr expansion of the survey, known as the Bright Time Extension (BTX), made possible through accrued efficiency gains over the first years of the APOGEE-2N project. For the 23 distinct ancillary programs, we provide descriptions of the scientific aims, target selection, and how to identify these targets within the APOGEE-2 sample. The BTX permitted changes to the main survey strategy, the inclusion of new programs in response to scientific discoveries or to exploit major new data sets not available at the outset of the survey design, and expansions of existing programs to enhance their scientific success and reach. After describing the motivations, implementation, and assessment of these programs, we also leave a summary of lessons learned from nearly a decade of APOGEE-1 and APOGEE-2 survey operations. A companion paper, F. Santana et al. (submitted; AAS29036), provides a complementary presentation of targeting modifications relevant to APOGEE-2 operations in the Southern Hemisphere.

Context. Recent observational results show that very low mass stars and brown dwarfs are able to host close-in rocky planets. Low-mass stars are the most abundant stars in the Galaxy, and the formation efficiency of their planetary systems is relevant in the computation of a global probability of finding Earth-like planets inside habitable zones. Tidal forces and relativistic effects are relevant in the latest dynamical evolution of planets around low-mass stars, and their effect on the planetary formation efficiency still needs to be addressed.Aims. Our goal is to evaluate the impact of tidal forces and relativistic effects on the formation of rocky planets around a star close to the substellar mass limit in terms of the resulting planetary architectures and its distribution according to the corresponding evolving habitable zone.Methods. We performed a set of N-body simulations spanning the first 100 Myr of the evolution of two systems composed of 224 embryos with a total mass 0.25 M-circle plus and 74 embryos with a total mass 3 M-circle plus around a central object of 0.08 M-circle dot. For these two scenarios we compared the planetary architectures that result from simulations that are purely gravitational with those from simulations that include the early contraction and spin-up of the central object, the distortions and dissipation tidal terms, and general relativistic effects.Results. We found that including these effects allows the formation and survival of a close-in (r < 0.07 au) population of rocky planets with masses in the range 0.001 < m/M-circle plus < 0.02 in all the simulations of the less massive scenario, and a close-in population with masses m 0.35 M-circle plus in just a few of the simulations of the more massive scenario. The surviving close-in bodies suffered more collisions during the integration time of the simulations. These collisions play an important role in their final masses. However, all of these bodies conserved their initial amount of water in mass throughout the integration time.Conclusions. The incorporation of tidal and general relativistic effects allows the formation of an in situ close-in population located in the habitable zone of the system. This means that both effects are relevant during the formation of rocky planets and their early evolution around stars close to the substellar mass limit, in particular when low-mass planetary embryos are involved.

The realistic simulation of variable star populations is fundamental to determine the selection function and contamination in existing and upcoming multi-epoch surveys. We present ELLISA, a simulator that produces an ensemble of mock light curves for a population of eclipsing binaries obtained from physical and orbital parameters consistent with different Galactic populations, and which considers user-supplied time sampling and photometric errors to represent any given survey. We carried out a search for eclipsing binaries in the QUEST low Galactic latitude catalogue of variable stars, spanning an area of 476 deg(2) at -25 degrees less than or similar to b less than or similar to 30 degrees and 190 degrees <= l <= 230 degrees towards the Galactic anticentre, and use ELLISA to characterize the completeness of the resulting catalogue in terms of amplitudes and periods of variation as well as eclipsing binary type. The resulting catalogue consists of 1125 eclipsing binaries, out of which 179, 60, and 886 are EA, EB, and EW types, respectively. We estimate, on average, 30 per cent completeness in the period range 0.25 less than or similar to P/d less than or similar to 1 for EB-FEW binaries and 15 per cent completeness for EA binaries with periods 2 less than or similar to P/d less than or similar to 10, being the time sampling the primary factor determining the completeness of each type of eclipsing binary. This is one of few eclipsing binary catalogues reported with an estimate of the selection function. Mock eclipsing binary light-curve libraries produced with ELLISA can be used to estimate the selection function and optimize eclipsing binary searches in upcoming multi-epoch surveys such as Gaia, the Panoramic Survey Telescope and Rapid Response System, the Zwicky Transient Factory, or the Large Synoptic Survey Telescope.

The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases has it been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory for investigating the IMF across the entire mass range of the population, from planetarymass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1 degrees radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1 M-circle dot. This system IMF is well described by a two-segment power law with Gamma = -0.74 +/- 0.04 for m < 0.4M(circle dot) and Gamma = 1.50 +/- 0.11 for m >= 0.4 M-circle dot. It is also well described over the whole mass range by a tapered power-law function with Gamma = 1.10 +/- 0.09, m(p) = 0.31 +/- 0.03 and beta = 2.11 +/- 0.09. The best lognormal representation of the system IMF has m(c) = 0.31 +/- 0.04 and sigma = 0.46 +/- 0.05 for m < 1 M-circle dot. This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the brown dwarf/star ratio of 0.16 +/- 0.03 that we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star-formation mechanisms are probably not strongly dependent on environmental conditions. We found that the substellar and stellar objects in 25 Ori do not have any preferential spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.

The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases it has been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory to investigate the IMF across the entire mass range of the population, from planetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1^∘ radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1 M_⊙. This system IMF is well described by a two-segment power-law with Γ=-0.74±0.04 for m<0.4 M_⊙ and Γ=1.50±0.11 for m≥0.4 M_⊙. It is also well described over the whole mass range by a tapered power-law function with Γ=1.10±0.09, m_p=0.31±0.03 and β=2.11±0.09. The best lognormal representation of the system IMF has m_c=0.31±0.04 and σ=0.46±0.05 for m<1 M_⊙. This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the BD/star ratio of 0.16±0.03 we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star formation mechanisms are probably not strongly dependent to environmental conditions. We found that the substellar and stellar objects in 25 Ori have similar spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.

We present results of our large-scale, optical, multi-epoch photometric survey across ∼180 square degrees in the Orion OB1 association, complemented with extensive follow-up spectroscopy. Our focus is mapping and characterizing the off-cloud, low-mass, pre-main-sequence (PMS) populations. We report 2062 K- and M-type confirmed T Tauri members; 59% are located in the OB1a subassociation, 27% in the OB1b subassociation, and the remaining 14% in the A and B molecular clouds. We characterize two new clusterings of T Tauri stars, the HD 35762 and HR 1833 groups, both located in OB1a not far from the 25 Ori cluster. We also identify two stellar overdensities in OB1b, containing 231 PMS stars, and find that the OB1b region is composed of two populations at different distances, possibly due to the OB1a subassociation overlapping with the front of OB1b. A ∼2 deg wide halo of young stars surrounds the Orion Nebula Cluster, corresponding in part to the low-mass populations of NGC 1977 and NGC 1980. We use the strength of H α in emission, combined with the IR excess and optical variability, to define a new type of T Tauri star, the C/W class, stars we propose may be nearing the end of their accretion phase, in an evolutionary state between classical and weak-lined T Tauri stars. The evolution of the ensemble-wide equivalent width of Li i λ 6707 indicates a Li depletion timescale of ∼8.5 Myr. Disk accretion declines with an e-folding timescale of ∼2 Myr, consistent with previous studies.

We present Herschel PACS observations of eight classical T Tauri Stars in the ∼7–10 Myr old OB1a and the ∼4–5 Myr old OB1b Orion subassociations. Detailed modeling of the broadband spectral energy distributions, particularly the strong silicate emission at 10 μm, shows that these objects are (pre-)transitional disks with some amount of small optically thin dust inside their cavities, ranging from ∼4 to ∼90 au in size. We analyzed Spitzer IRS spectra for two objects in the sample: CVSO-107 and CVSO-109. The IRS spectrum of CVSO-107 indicates the presence of crystalline material inside its gap, while the silicate feature of CVSO-109 is characterized by a pristine profile produced by amorphous silicates; the mechanisms creating the optically thin dust seem to depend on disk local conditions. Using millimeter photometry, we estimated dust disk masses for CVSO-107 and CVSO-109 lower than the minimum mass of solids needed to form the planets in our solar system, which suggests that giant planet formation should be over in these disks. We speculate that the presence and maintenance of optically thick material in the inner regions of these pre-transitional disks might point to low-mass planet formation.

We present preliminary results to demonstrate that our method for detection and location of Space Debris (SD) in the geostationary Earth orbit (GEO) ring, based on observations at the OAN of Venezuela is of high astrometric precision. A detailed explanation of the method, its validation and first results is available in (Lacruz et al. 2017).

There are different populations of space debris (SD) in the geostationary (GEO) region. It is of great interest to know their dynamics, in order to contribute to aspects such as alerts against possible collisions, repositioning of GEO satellites or placing those satellites that come into service. In this contribution we present a study about the detection and dynamic analysis of SD located in the GEO ring. Using the telescopes of the Venezuelan Obseratory National (VON), a large amount of astrometric observations have been acquired. A preliminary dynamic analysis of them has been carried out, which evidences the average relative motion of these orbiters with a mean absolute error for coordinates of approximate to 0.09 pix.

We present an astrometric method for the calculation of the positions of orbiters in the GEO ring with a high precision, through a rigorous astrometric treatment of observations with a 1-m class telescope, which are part of the CIDA. survey of the GEO ring. We compute the distortion pattern to correct for the systematic errors introduced by the optics and electronies of the telescope, resulting in absolute mean errors of 0.16 '' and 0.12 '' in right ascension and declination, respectively. These correspond to approximate to 25 in at the mean distance of the GEO ring, and are thus good quality results.