C. Rodrigo

An in-depth study of HD 174966 with CoRoT photometry and HARPS spectroscopy - Large separation as a new observable for δ Scuti stars

Aims. The aim of this work was to use a multi-approach technique to derive the most accurate values possible of the physical parameters of the δ Sct star HD 174966, which was observed with the CoRoT satellite. In addition, we searched for a periodic pattern in the frequency spectra with the goal of using it to determine the mean density of the star. Methods. First, we extracted the frequency content from the CoRoT light curve. Then, we derived the physical parameters of HD 174966 and carried a mode identification out from the spectroscopic and photometric observations. We used this information to look for the models fulfilling all the conditions and discussed the inaccuracies of the method because of the rotation effects. In a final step, we searched for patterns in the frequency set using a Fourier transform, discussed its origin, and studied the possibility of using the periodicity to obtain information about the physical parameters of the star. Results. A total of 185 peaks were obtained from the Fourier analysis of the CoRoT light curve, all of which were reliable pulsating frequencies. From the spectroscopic observations, 18 oscillation modes were detected and identified, and the inclination angle (62.5 ◦+7.5 −17.5 ) and the rotational velocity of the star (142 km s −1 ) were estimated. From the multi-colour photometric observations, only three frequencies were detected that correspond to the main ones in the CoRoT light curve. We looked for periodicities within the 185 frequencies and found a quasiperiodic pattern Δν ∼ 64 μHz. Using the inclination angle, the rotational velocity, and an Echelle diagram (showing a double comb outside the asymptotic regime), we concluded that the periodicity corresponds to a large separation structure. The quasiperiodic pattern allowed us to discriminate models from a grid. As a result, the value of the mean density is achieved with a 6% uncertainty. So, the Δν pattern could be used as a new observable for A-F type stars.

Proper motions of young stars in Chamaeleon - I. A Virtual Observatory study of spectroscopically confirmed members

Context. The study of the motion of the members of a given open cluster or stellar association provides key information about their formation and early evolution. The Chamaeleon cloud complex constitutes one of the closest and best studied low-mass star-forming regions in the Galaxy. Aims. We want to provide further evidence of the origin of the proposed stellar members of Chamaeleon and to identify interlopers from the foreground Cha and Cha associations. Methods. We compile lists of spectroscopically confirmed members of Chamaeleon I and II, Cha and Cha, and of background objects in the same line of sight. Using Virtual Observatory tools, we cross-match these lists with the UCAC3 catalogue to get the proper motions of the objects. In the vector point diagram, we identify the di erent moving groups, and use this information to study the membership of proposed candidate members of the associations from the literature. For those objects with available radial velocities, we compute their Galactic space velocities. We look for correlations between the known properties of the objects and their proper motions. Results. The members of the dark clouds exhibit clearly di erent proper motions from those of the foreground associations and of the background stars. The data suggest that Chamaeleon II could have di erent dynamical properties from Chamaeleon I. Although the two foreground clusters and Chamaeleontis constitute two di erent proper motion groups, they have similar spatial motions, which are di erent from the spatial motion of Chamaeleon I. On the other hand, the space motions of the Chamaeleon II stars look more similar to those of the foreground clusters than to the Chamaeleon I stars, but the numbers are low. We find no correlations between the proper motions and the properties of the objects in either of the clouds. Conclusions. On the basis of proper motion, Chamaeleon I and II constitute two physical entities unrelated to the foreground and Chamaeleontis clusters, but with the available data it is unclear to what extent the stellar populations in both clouds are physically connected to each other.

Measuring mean densities of δ Scuti stars with asteroseismology - Theoretical properties of large separations using TOUCAN

Aims. We study the theoretical properties of the regular spacings found in the oscillation spectra of δ Scuti stars. Methods. We performed a multivariable analysis that covered a wide range of stellar structure, seismic properties and model parameters that are representative of intermediate-mass, main-sequence stars. The workflow was entirely performed using a new Virtual Observatory tool: TOUCAN (the VO gateway for asteroseismic models), which is presented in this paper. Results. A linear relation between the large separation and the mean density is predicted to be found in the low-frequency domain (i.e. radial orders spanning from 1 to 8, approximately) of the main-sequence, δ Scuti stars’ oscillation spectrum. We found that this linear behavior remains the same whatever the mass, metallicity, mixing length, and overshooting parameters considered. The intrinsic error of the method is discussed. This includes the uncertainty in the large separation determination and the role of rotation. The validity of the relation found is only guaranteed for stars rotating up to 40% of their break-up velocity. Finally, we applied the diagnostic method presented in this work to five stars for which regular patterns have been found. Our estimates for the mean density and the frequency of the fundamental radial mode match with those given in the literature within a 20% of deviation. Conclusions. Asteroseismology has thus revealed an independent direct measure of the average density of δ Scuti stars, which is analogous to that of the Sun. This places tight constraints on the mode identification and hence on the stellar internal structure and dynamics, and allows determining the radius of planets orbiting δ Scuti stars with unprecedented precision. This opens the way for studying the evolution of regular patterns in pulsating stars, and its relation with stellar structure and evolution.

A Virtual Observatory Census to Address Dwarfs Origins AVOCADO - I. Science goals, sample selection and analysis tools

Context. In spite of being, by far, the most abundant of all galaxy types, the detailed properties of dwarf galaxies are still poorly characterised ‐ especially due to the observational challenge that their intrinsic faintness and weak clustering properties represent. Aims. AVOCADO aims at establishing firm conclusions on the formation and evolution of dwarf galaxies by constructing and analysing a homogeneous, multiwavelength dataset for a statistically significant sample of approximately 6500 nearby dwarfs (Mi 5 logh100 > 18 mag). The sample is selected to lie within the 20 < D < 60 h 1 100 Mpc volume covered by the SDSS-DR7 footprint, and is thus volume-limited for Mi 5 logh100 < 16 mag dwarfs ‐ but includes 1500 fainter systems. We will investigate the roles of mass and environment in determining the current properties of the di erent dwarf morphological types ‐ including their structure, their star formation activity, their chemical enrichment history and a breakdown of their stellar, dust and gas content. Methods. We present the sample selection criteria and describe the suite of analysis tools, some of them developed in the framework of the Virtual Observatory. We make use of optical spectra and UV-to-NIR imaging of the dwarf sample to derive star formation rates, stellar masses, ages and metallicities ‐ which are further supplemented with structural parameters that are used to classify them morphologically. This unique dataset, coupled with a detailed characterisation of each dwarf’s environment, allows for a fully comprehensive investigation of their origins and to track the (potential) evolutionary paths between the di erent dwarf types. Results. We characterise the local environment of all dwarfs in our sample, paying special attention to trends with current star formation activity. We find that virtually all quiescent dwarfs are located in the vicinity (projected distances . 1:5h 1 100 Mpc) of & L companions, consistent with recent results. While star-forming dwarfs are preferentially found at separations of the order of 1h 1 100 Mpc, there appears to be a tail towards low separations (. 100h 1 100 kpc) in the distribution of projected distances. We speculate that, modulo projection e ects, this probably represents a genuine population of late-type dwarfs caught upon first infall about their host and before environmental quenching has fully operated. In this context, these results suggest that internal mechanisms ‐such as gas exhaustion via star formation or feedback e ects‐ are not su cient to completely cease the star formation activity in dwarf galaxies, and that becoming the satellite of a massive central galaxy appears to be a necessary condition to create a quiescent dwarf.

Proper motions of young stars in Chamaeleon II. New kinematical candidate members of Chamaeleon I and II

Context. The Chamaeleon star-forming region has been extensively studied in the last decades. However, most studies have been confined to the densest parts of the clouds. In a previous paper, we analysed the kinematical properties of the spectroscopically confirmed population of the Chamaeleon I and II clouds. Aims. We want to search for new kinematical candidate members to the Chamaeleon I and II moving groups, extending the studied area beyond the clouds, and to characterize these new populations using available information from public databases and catalogues. We also want to check if the populations of the moving groups are confined to the present dark clouds. Methods. Kinematic candidate members were initially selected on the basis of proper motions and colours using the Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4). The SEDs of the objects were constructed using photometry retrieved from the Virtual Observatory and other resources, and fitted to models of stellar photospheres to derive effective temperatures, gravity values, and luminosities. Masses and ages were estimated by comparison with theoretical evolutionary tracks in a Hertzprung-Russell diagram. Objects with ages 20 Myr were selected as probable members of the moving groups. Results. We have identified 51 and 14 candidate members to the Chamaeleon I and II moving groups, respectively, of which 17 and 1, respectively, are classified as probable young stars according to the SED analysis. Another object in Chamaeleon I located slightly above the 1 Myr isochrone is classified as a possible young star. All these objects are diskless stars with masses in the range 0.3 M/M� 1.4 and ages consistent with those reported for the corresponding confirmed members. They tend to be located at the boundaries of or outside the dark clouds, preferably to the north-east and south-east in the case of Chamaeleon I, and to the north-east in the case of Chamaeleon II. Conclusions. The kinematical population of Chamaeleon I and II could be larger and spread over a larger area of the sky than suggested by previous studies. However, the results of this study should be confirmed with spectroscopic data and more precise kinematic information.

Precovery of near-Earth asteroids by a citizen-science project of the Spanish Virtual Observatory

This article describes a citizen-science project conducted by the Spanish Virtual Observatory (SVO) to improve the orbits of near-Earth asteroids (NEAs) using data from astronomical archives. The list of NEAs maintained at the Minor Planet Center (MPC) is checked daily to identify new objects or changes in the orbital parameters of already catalogued objects. Using NEODyS we compute the position and magnitude of these objects at the observing epochs of the 938 046 images comprising the Eigth Data Release of the Sloan Digitised Sky Survey (SDSS). If the object lies within the image boundaries and the magnitude is brighter than the limiting magnitude, then the associated image is visually inspected by the projects collaborators (the citizens) to confirm or discard the presence of the NEA. If confirmed, accurate coordinates and, sometimes, magnitudes are submitted to the MPC. Using this methodology, 3,226 registered users have made during the first fifteen months of the project more than 167,000 measurements which have improved the orbital elements of 551 NEAs (6% of the total number of this type of asteroids). Even more remarkable is the fact that these results have been obtained at zero cost to telescope time as NEAs were serendipitously observed while the survey was being carried out. This demonstrates the enormous scientific potential hidden in astronomical archives. The great reception of the project as well as the results obtained makes it a valuable and reliable tool for improving the orbital parameters of near-Earth asteroids.

New ultracool subdwarfs identified in large-scale surveys using Virtual Observatory tools - II. SDSS DR7 vs. UKIDSS LAS DR6, SDSS DR7 vs. UKIDSS LAS DR8, SDSS DR9 vs. UKIDSS LAS DR10, and SDSS DR7 vs. 2MASS

Aims. We aim to develop an efficient method to search for late-type subdwarfs (metal-depleted dwarfs with spectral types ≥M5) to improve the current statistics. Our objectives are to improve our knowledge of metal-poor low-mass dwarfs, bridge the gap between the late-M and L types, determine their surface density, and understand the impact of metallicity on the stellar and substellar mass function. Methods. We carried out a search cross-matching the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) and the Two Micron All Sky Survey (2MASS), and different releases of SDSS and the United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) using STILTS, Aladin, and Topcat developed as part of the Virtual Observatory tools. We considered different photometric and proper motion criteria for our selection. We identified 29 and 71 late-type subdwarf candidates in each cross-correlation over 8826 and 3679 sq. deg, respectively (2312 sq. deg overlap). We obtained our own low-resolution optical spectra for 71 of our candidates: 26 were observed with the Gran Telescopio de Canarias (GTC; R  ~ 350, λλ 5000–10 000  A), six with the Nordic Optical Telescope (NOT; R  ~ 450, λλ 5000–10 700  A), and 39 with the Very Large Telescope (VLT; R  ~ 350, λλ 6000–11 000  A). We also retrieved spectra for 30 of our candidates from the SDSS spectroscopic database ( R  ~ 2000 and λλ  3800–9400  A), nine of these 30 candidates with an independent spectrum in our follow-up. We classified 92 candidates based on 101 optical spectra using two methods: spectral indices and comparison with templates of known subdwarfs. Results. We developed an efficient photometric and proper motion search methodology to identify metal-poor M dwarfs. We confirmed 86% and 94% of the candidates as late-type subdwarfs from the SDSS vs. 2MASS and SDSS vs. UKIDSS cross-matches, respectively. These subdwarfs have spectral types ranging between M5 and L0.5 and SDSS magnitudes in the r  = 19.4–23.3 mag range. Our new late-type M discoveries include 49 subdwarfs, 25 extreme subdwarfs, six ultrasubdwarfs, one subdwarf/extreme subdwarf, and two dwarfs/subdwarfs. In addition, we discovered three early-L subdwarfs to add to the current compendium of L-type subdwarfs known to date. We doubled the numbers of cool subdwarfs (11 new from SDSS vs. 2MASS and 50 new from SDSS vs. UKIDSS). We derived a surface density of late-type subdwarfs of 0.040 +0.012 -0.007 per square degree in the SDSS DR7 vs. UKIDSS LAS DR10 cross-match ( J  = 15.9–18.8 mag) after correcting for incompleteness. The density of M dwarfs decreases with decreasing metallicity. We also checked the Wide Field Survey Explorer (AllWISE) photometry of known and new subdwarfs and found that mid-infrared colours of M subdwarfs do not appear to differ from their solar-metallicity counterparts of similar spectral types. However, the near-to-mid-infrared colours J − W 2 and J − W 1 are bluer for lower metallicity dwarfs, results that may be used as a criterion to look for late-type subdwarfs in future searches.

A white dwarf catalogue from Gaia-DR2 and the Virtual Observatory

We present a catalogue of 73,221 white dwarf candidates extracted from the astrometric and photometric data of the recently published Gaia DR2 catalogue. White dwarfs were selected from the Gaia Hertzsprung-Russell diagram with the aid of the most updated population synthesis simulator. Our analysis shows that Gaia has virtually identified all white dwarfs within 100 pc from the Sun. Hence, our sub-population of 8,555 white dwarfs within this distance limit and the colour range considered,

A search for new hot subdwarf stars by means of virtual observatory tools II

-\,0.52<(G_{\rm BP}-G_{\rm RP})<0.80

VOSA: virtual observatory SED analyzer - An application to the Collinder 69 open cluster

, is the largest and most complete volume-limited sample of such objects to date. From this sub-sample we identified 8,343 CO-core and 212 ONe-core white dwarf candidates and derived a white dwarf space density of