Search for associations containing young stars (SACY). V. Is multiplicity universal? Tight multiple systems

Context: Dynamically undisrupted, young populations of stars are crucial to study the role of multiplicity in relation to star formation. Loose nearby associations provide us with a great sample of close ($<$150 pc) Pre-Main Sequence (PMS) stars across the very important age range ($\approx$5-70 Myr) to conduct such research. Aims: We characterize the short period multiplicity fraction of the SACY (Search for Associations Containing Young stars) accounting for any identifiable bias in our techniques and present the role of multiplicity fractions of the SACY sample in the context of star formation. Methods: Using the cross-correlation technique we identified double-lined spectroscopic systems (SB2), in addition to this we computed Radial Velocity (RV) values for our subsample of SACY targets using several epochs of FEROS and UVES data. These values were used to revise the membership of each association then combined with archival data to determine significant RV variations across different data epochs characteristic of multiplicity; single-lined multiple systems (SB1). Results: We identified 7 new multiple systems (SB1s: 5, SB2s: 2). We find no significant difference between the short period multiplicity fraction ($F_\mathrm{m}$) of the SACY sample and that of nearby star forming regions ($\approx$1-2 Myr) and the field ($F_\mathrm{m}\leq$10%) both as a function of age and as a function of primary mass, $M_1$, in the ranges $P$ [1:200 day] and $M_2$ [0.08 $M_{\odot}$-$M_1$]. Conclusions: Our results are consistent with the picture of universal star formation, when compared to the field and nearby star forming regions (SFRs). We comment on the implications of the relationship between increasing multiplicity fraction with primary mass, within the close companion range, in relation to star formation.Comment: 14 pages, 18 figures, published, A&A http://dx.doi.org/10.1051/0004-6361/20142385

Dynamical Analysis of Nearby ClustErs. Automated astrometry from the ground: precision proper motions over wide field

The kinematic properties of the different classes of objects in a given association hold important clues about its member's history, and offer a unique opportunity to test the predictions of the various models of stellar formation and evolution. DANCe (standing for Dynamical Analysis of Nearby ClustErs) is a survey program aimed at deriving a comprehensive and homogeneous census of the stellar and substellar content of a number of nearby (<1kpc) young (<500Myr) associations. Whenever possible, members will be identified based on their kinematics properties, ensuring little contamination from background and foreground sources. Otherwise, the dynamics of previously confirmed members will be studied using the proper motion measurements. We present here the method used to derive precise proper motion measurements, using the Pleiades cluster as a test bench. Combining deep wide field multi-epoch panchromatic images obtained at various obervatories over up to 14 years, we derive accurate proper motions for the sources present in the field of the survey. The datasets cover ~80 square degrees, centered around the Seven Sisters. Using new tools, we have computed a catalog of 6116907 unique sources, including proper motion measurements for 3577478 of them. The catalogue covers the magnitude range between i=12~24mag, achieving a proper motion accuracy <1mas/yr for sources as faint as i=22.5mag. We estimate that our final accuracy reaches 0.3mas/yr in the best cases, depending on magnitude, observing history, and the presence of reference extragalactic sources for the anchoring onto the ICRS.Comment: Accepted for publication in A&

Search for associations containing young stars (SACY) VII. New stellar and substellar candidate members in the young associations

The young associations offer us one of the best opportunities to study the properties of young stellar and substellar objects and to directly image planets thanks to their proximity ($<$200 pc) and age ($\approx$5-150 Myr). However, many previous works have been limited to identifying the brighter, more active members ($\approx$1 M$_\odot$) owing to photometric survey sensitivities limiting the detections of lower mass objects. We search the field of view of 542 previously identified members of the young associations to identify wide or extremely wide (1000-100,000 au in physical separation) companions. We combined 2MASS near-infrared photometry ($J$, $H$, $K$) with proper motion values (from UCAC4, PPMXL, NOMAD) to identify companions in the field of view of known members. We collated further photometry and spectroscopy from the literature and conducted our own high-resolution spectroscopic observations for a subsample of candidate members. This complementary information allowed us to assess the efficiency of our method. We identified 84 targets (45: 0.2-1.3 M$_\odot$, 17: 0.08-0.2 M$_\odot$, 22: $<$0.08 M$_\odot$) in our analysis, ten of which have been identified from spectroscopic analysis in previous young association works. For 33 of these 84, we were able to further assess their membership using a variety of properties (X-ray emission, UV excess, H$_\alpha$, lithium and K I equivalent widths, radial velocities, and CaH indices). We derive a success rate of 76-88% for this technique based on the consistency of these properties. Once confirmed, the targets identified in this work would significantly improve our knowledge of the lower mass end of the young associations. Additionally, these targets would make an ideal new sample for the identification and study of planets around nearby young stars.Comment: 28 pages, 24 figures, accepted in A&

Epifisiolisis de la extremidad interna de la clavícula: Revisión de la literatura a propósito de un caso

La fractura de la parte interna de la clavícula con desplazamiento anterosuperior del fragmento externo clavicular, es una lesión relativamente inusual en todos los grupos de edad. Presentamos el caso de un paciente de 11 años de edad que sufrió una epifisiolisis tipo II de Salter y Harris de la extremidad interna de la clavícula con desplazamiento anterior, con un tiempo de seguimiento de 9 meses. El diagnóstico se basa en la sospecha clínica y en las pruebas de imagen, siendo la TAC de particular utilidad. Se compara el tratamiento realizado con otros publicados, y se constata que la terapéutica conservadora con un vendaje de Velpeau dio excelentes resultados. Se discute el diagnóstico diferencia con otras lesiones en esta localización, especialmente con la luxación esternoclavicular pura, realizando una revisión de la literatura al respecto.Anterior displacement of the fractured lateral end of the clavicle is an unusual lesion regardless of the age group. We are reporting a case of an eleven-year-old patient who presented a Salter and Harris type II epiphyseal fracture of the internal end of the clavicle with anterior displacement. The follow-up period was 9 months. Diagnosis is based on clinical suspicion and imaging tests, being CT scan particularly useful. Performed treatment is compared with other ones published. Conservative treatment with a Velpeau bandage gave excellent results. Differential diagnosis with other injuries at this location is presented, especially with pure sternoclavicular dislocation. A review of the literature is made

The extended HeII4686-emitting region in IZw18 unveiled: clues for peculiar ionizing sources

New integral field spectroscopy has been obtained for IZw18, the nearby lowest-metallicity galaxy considered our best local analog of systems forming at high-z. Here we report the spatially resolved spectral map of the nebular HeII4686 emission in IZw18, from which we derived for the first time its total HeII-ionizing flux. Nebular HeII emission implies the existence of a hard radiation field. HeII-emitters are observed to be more frequent among high-z galaxies than for local objects. So investigating the HeII-ionizing source(s) in IZw18 may reveal the ionization processes at high-z. HeII emission in star-forming galaxies, has been suggested to be mainly associated with Wolf-Rayet stars (WRs), but WRs cannot satisfactorily explain the HeII-ionization at all times, in particular at lowest metallicities. Shocks from supernova remnants, or X-ray binaries, have been proposed as additional potential sources of HeII-ionizing photons. Our data indicate that conventional HeII-ionizing sources (WRs, shocks, X-ray binaries) are not sufficient to explain the observed nebular HeII4686 emission in IZw18. We find that the HeII-ionizing radiation expected from models for either low-metallicity super-massive O stars or rotating metal-free stars could account for the HeII-ionization budget measured, while only the latter models could explain the highest values of HeII4686/Hbeta observed. The presence of such peculiar stars in IZw18 is suggestive and further investigation in this regard is needed. This letter highlights that some of the clues of the early Universe can be found here in our cosmic backyard.Comment: 6 pages, 3 figures. Accepted for publication in ApJ Letter

Search for associations containing young stars (SACY). VI. Is multiplicity universal? Stellar multiplicity in the range 3-1000 au from adaptive-optics observations

Context. Young loose nearby associations are unique samples of close (<150 pc), young (approx 5-100 Myr) pre-main sequence (PMS) stars. A significant number of members of these associations have been identified in the SACY collaboration. We can use the proximity and youth of these members to investigate key ingredients in star formation processes, such as multiplicity. Aims. We present the statistics of identified multiple systems from 113 confirmed SACY members. We derive multiplicity frequencies, mass-ratio, and physical separation distributions in a consistent parameter space, and compare our results to other PMS populations and the field. Methods. We have obtained adaptive-optics assisted near-infrared observations with NACO (ESO/VLT) and IRCAL (Lick Observatory) for at least one epoch of all 113 SACY members. We have identified multiple systems using co-moving proper-motion analysis and using contamination estimates. We have explored ranges in projected separation and mass-ratio of a [3-1000 au], and q [0.1-1], respectively. Results. We have identified 31 multiple systems (28 binaries and 3 triples). We derive a multiplicity frequency (MF) of MF_(3-1000au)=28.4 +4.7, -3.9% and a triple frequency (TF) of TF_(3-1000au)=2.8 +2.5, -0.8% in the separation range of 3-1000 au. We do not find any evidence for an increase in the MF with primary mass. The estimated mass-ratio of our statistical sample (with power-law index gamma=-0.04 +/- 0.14) is consistent with a flat distribution (gamma = 0). Conclusions. We show further similarities (but also hints of discrepancies) between SACY and the Taurus region: flat mass-ratio distributions and statistically similar MF and TF values. We also compared the SACY sample to the field (in the separation range of 19-100 au), finding that the two distributions are indistinguishable, suggesting a similar formation mechanism.Comment: 16 Pages, accepted in A&A 28 May 201