Laboratório Nacional de Astrofísica

We report results from a high-resolution optical spectroscopic survey aimed to search for nearby young associations and young stars among optical counterparts of ROSAT All-Sky Survey X-ray sources in the Southern Hemisphere. We selected 1953 late-type (), potentially young, optical counterparts out of a total of 9574 1RXS sources for follow-up observations. At least one high-resolution spectrum was obtained for each of 1511 targets. This paper is the first in a series presenting the results of the SACY survey. Here we describe our sample and our observations. We describe a convergence method in the (UVW) velocity space to find associations. As an example, we discuss the validity of this method in the framework of the β Pic Association.

We discuss a class of phase computer-generated holograms for the encoding of arbitrary scalar complex fields. We describe two holograms of this class that allow high quality reconstruction of the encoded field, even if they are implemented with a low-resolution pixelated phase modulator. In addition, we show that one of these holograms can be appropriately implemented with a phase modulator limited by a reduced phase depth.

Libraries of stellar spectra are fundamental tools for the study of stellar populations, and both empirical and synthetic libraries have been used for this purpose. In this paper, a new library of high resolution synthetic spectra is presented, ranging from the near-ultraviolet (300 nm) to the near-infrared (1.8 m). The library spans all the stellar types that are relevant to the integrated light of old and intermediate-age stellar populations in the involved spectral region (spectral types F through M and all luminosity classes). The grid was computed for metallicities ranging from [Fe/H] = –2.5 to +0.5, including both solar and α-enhanced ([ α/Fe] = 0.4) chemical compositions. The synthetic spectra are a good match to observations of stars throughout the stellar parameter space encompassed by the library and over the whole spectral region covered by the computations.

<i>Context.<i/> The ESO public survey VISTA variables in the Vía Láctea (VVV) started in 2010. VVV targets 562 sq. deg in the Galactic bulge and an adjacent plane region and is expected to run for about five years.<i>Aims.<i/> We describe the progress of the survey observations in the first observing season, the observing strategy, and quality of the data obtained. <i>Methods.<i/> The observations are carried out on the 4-m VISTA telescope in the <i>ZYJH<i/><i>K<i/><sub>s<sub/> filters. In addition to the multi-band imaging the variability monitoring campaign in the <i>K<i/><sub>s<sub/> filter has started. Data reduction is carried out using the pipeline at the Cambridge Astronomical Survey Unit. The photometric and astrometric calibration is performed via the numerous 2MASS sources observed in each pointing.<i>Results.<i/> The first data release contains the aperture photometry and astrometric catalogues for 348 individual pointings in the <i>ZYJH<i/><i>K<i/><sub>s<sub/> filters taken in the 2010 observing season. The typical image quality is ~ . The stringent photometric and image quality requirements of the survey are satisfied in 100% of the <i>JH<i/><i>K<i/><sub>s<sub/> images in the disk area and 90% of the <i>JH<i/><i>K<i/><sub>s<sub/> images in the bulge area. The completeness in the <i>Z<i/> and <i>Y<i/> images is 84% in the disk, and 40% in the bulge. The first season catalogues contain 1.28 × 10<sup>8<sup/> stellar sources in the bulge and 1.68 × 10<sup>8<sup/> in the disk area detected in at least one of the photometric bands. The combined, multi-band catalogues contain more than 1.63 × 10<sup>8<sup/> stellar sources. About 10% of these are double detections because of overlapping adjacent pointings. These overlapping multiple detections are used to characterise the quality of the data. The images in the <i>JH<i/><i>K<i/><sub>s<sub/> bands extend typically ~4 mag deeper than 2MASS. The magnitude limit and photometric quality depend strongly on crowding in the inner Galactic regions. The astrometry for <i>K<i/><sub>s<sub/> = 15−18 mag has rms ~35−175 mas. <i>Conclusions.<i/> The VVV Survey data products offer a unique dataset to map the stellar populations in the Galactic bulge and the adjacent plane and provide an exciting new tool for the study of the structure, content, and star-formation history of our Galaxy, as well as for investigations of the newly discovered star clusters, star-forming regions in the disk, high proper motion stars, asteroids, planetary nebulae, and other interesting objects.

We report results from a high-resolution optical spectroscopic survey aimed to search for nearby young associations and young stars among optical counterparts of ROSAT All-Sky Survey X-ray sources in the Southern Hemisphere. We selected 1953 late-type (B-V &gt;= 0.6), potentially young, optical counterparts out of a total of 9574 1RXS sources for follow-up observations. At least one high-resolution spectrum was obtained for each of 1511 targets. This paper is the first in a series presenting the results of the SACY survey. Here we describe our sample and our observations. We describe a convergence method in the (UVW) velocity space to find associations. As an example, we discuss the validity of this method in the framework of the beta Pic Association.

We present a new catalog of 108 Herbig Ae/Be candidate stars identified in the Pico dos Dias Survey, together with 19 previously known candidates and four objects selected from the IRAS Faint Source Catalog. These 131 stars were observed with low- and/or medium-resolution spectroscopy, and we complement these data with high-resolution spectra of 39 stars. The objects present a great variety of Hα line profiles and were separated according to them. Our study suggests that most of the time a Herbig Ae/Be star will present a double peak Hα line profile. Correlations among different physical parameters, such as spectral type and v sin i with Hα line profiles were searched. We found no correlation among Hα line profiles and spectral type or v sin i except for stars with P Cygni profiles, where there is a correlation with v sin i . We also use preliminary spectral energy distributions to seek for any influence of the circumstellar medium in the Hα line profiles. The presence of [O I] and [S II] forbidden lines is used together with the Hα line profiles and these preliminary spectral energy distributions to discuss the circumstellar environment of the Herbig Ae/Be candidates. The distribution of the detected [O I] and [S II] forbidden lines among different spectral types points to a significantly higher occurrence of these lines among B stars, whereas the distribution among different Hα profile types indicates that forbidden lines are evenly distributed among each Hα line-profile type. Combining the distance estimates of the Herbig candidates with the knowledge of the interstellar medium distribution, we have found that 84 candidates can be associated with some of the more conspicuous SFRs, being in the right direction and at a compatible distance. As a further means of checking the properties of the HAeBe candidates, as well as their present evolutionary status, the derived luminosities and effective temperatures of the stars with possible association to the star-forming regions and/or Hipparcos distances were plotted together with a set of pre–main-sequence evolutionary tracks on an HR diagram. A set of 14 stars were found out of their expected positions in the HR diagram.

Evidence of relative sea-level fluctuations during the Upper Quaternary are represented by numerous geological, biological, and pre-historical (shell-middens) records found along the Brazilian coast line. About 700 of these records, dated mostly by the radiocarbon method, are distributed through the States of Alagoas, Sergipe, Bahia, Espírito Santo, Rio de Janeiro, São Paulo, Paraná, and Santa Catarina. The coastal plains of these states, representing about 50% of the Brazilian coast, have been geologically mapped, in part or entirely during the last 10 years. The geological maps are accompanied by sea level fluctuation curves for the past 7,000 years for the States of Bahia (Salvador, Ilhéus, and Caravelas sectors), Rio de Janeiro (Angra dos Reis sector), São Paulo (Santos and Cananéia-Iguape sectors), Paraná (Paranaguá sector) and Santa Catarina (Itajaí-Laguna sector). These informations allowed us to know that the relative sea level fluctuations during the last thousand years played a very important role in the construction of the Brazilian Coastal plains. It was also demonstrated that the relative sea level fluctuations during the Upper Quaternary have been important for the construction of the river mouth coastal plains of São Francisco (SE/AL), Jequitinhonha (BA), Doce (ES) and Paraíba do Sul (RJ) rivers, whose evolutionary histories were quite different in relation to the classical delta plains presented in the geological literature.

Context. The ESO public survey VISTA variables in the Vía Láctea (VVV) started in 2010. VVV targets 562 sq. deg in the Galactic bulge and an adjacent plane region and is expected to run for about five years. &#13;\nAims. We describe the progress of the survey observations in the first observing season, the observing strategy, and quality of the data obtained. &#13;\nMethods. The observations are carried out on the 4-m VISTA telescope in the ZYJHK&lt;SUB&gt;s&lt;/SUB&gt; filters. In addition to the multi-band imaging the variability monitoring campaign in the K&lt;SUB&gt;s&lt;/SUB&gt; filter has started. Data reduction is carried out using the pipeline at the Cambridge Astronomical Survey Unit. The photometric and astrometric calibration is performed via the numerous 2MASS sources observed in each pointing. &#13;\nResults. The first data release contains the aperture photometry and astrometric catalogues for 348 individual pointings in the ZYJHK&lt;SUB&gt;s&lt;/SUB&gt; filters taken in the 2010 observing season. The typical image quality is ∼0′′.9-1′′.0. The stringent photometric and image quality requirements of the survey are satisfied in 100% of the JHK&lt;SUB&gt;s&lt;/SUB&gt; images in the disk area and 90% of the JHK&lt;SUB&gt;s&lt;/SUB&gt; images in the bulge area. The completeness in the Z and Y images is 84% in the disk, and 40% in the bulge. The first season catalogues contain 1.28 × 10&lt;SUP&gt;8&lt;/SUP&gt; stellar sources in the bulge and 1.68 × 10&lt;SUP&gt;8&lt;/SUP&gt; in the disk area detected in at least one of the photometric bands. The combined, multi-band catalogues contain more than 1.63 × 10&lt;SUP&gt;8&lt;/SUP&gt; stellar sources. About 10% of these are double detections because of overlapping adjacent pointings. These overlapping multiple detections are used to characterise the quality of the data. The images in the JHK&lt;SUB&gt;s&lt;/SUB&gt; bands extend typically ∼4 mag deeper than 2MASS. The magnitude limit and photometric quality depend strongly on crowding in the inner Galactic regions. The astrometry for K&lt;SUB&gt;s&lt;/SUB&gt; = 15-18 mag has rms ∼35-175 mas. &#13;\nConclusions. The VVV Survey data products offer a unique dataset to map the stellar populations in the Galactic bulge and the adjacent plane and provide an exciting new tool for the study of the structure, content, and star-formation history of our Galaxy, as well as for investigations of the newly discovered star clusters, star-forming regions in the disk, high proper motion stars, asteroids, planetary nebulae, and other interesting objects.

Aims.We present a near-infrared spectral atlas of 47 active galactic nuclei (AGN) of all degrees of activity in the wavelength interval of 0.8–2.4 μm, including the fluxes of the observed emission lines. We analyze the spectroscopic properties of the continuum and emission line spectra of the sources.

The results of the first part of a survey for new T Tauri stars, with spectroscopic and photometric observations of about 100 stars, are presented. A list of candidates has been selected by means of the IRAS Point Source Catalog, based on appropriate far-infrared colors. Coude spectra of the selected objects in the 655-673 nm wavelength range, which includes H-alpha and the resonance Li I line, have been obtained. Thirty-three new T Tauri stars, and a number of other interesting objects, like early type premain-sequence stars and Li-rich K giants, have been detected. Several new isolated T Tauri were found, including Hen 1, which may be the T Tauri star with the highest galactic latitude known, if its nature is confirmed.

ABSTRACT This paper presents an overview of SPIRou, the new-generation near-infrared spectropolarimeter/precision velocimeter recently installed on the 3.6-m Canada–France–Hawaii Telescope (CFHT). Starting from the two main science goals, i.e., the quest for planetary systems around nearby M dwarfs and the study of magnetized star/planet formation, we outline the instrument concept that was designed to efficiently address these forefront topics, and detail the in-lab and on-sky instrument performances measured throughout the intensive testing phase that SPIRou was submitted to before passing the final acceptance review in early 2019 and initiating science observations. With a central position among the newly started programmes, the SPIRou Legacy Survey (SLS) Large Programme was allocated 300 CFHT nights until at least mid 2022. We also briefly describe a few of the first results obtained in the various science topics that SPIRou started investigating, focusing in particular on planetary systems of nearby M dwarfs, transiting exoplanets and their atmospheres, magnetic fields of young stars, but also on alternate science goals like the atmospheres of M dwarfs and the Earth’s atmosphere. We finally conclude on the key role that SPIRou and the CFHT can play in coordination with forthcoming major facilities like the JWST, the ELTs, PLATO, and ARIEL over the decade.

<i>Context. <i/>Our study is a follow-up of the SACY project, an extended high spectral resolution survey of more than two thousand optical counterparts to X-ray sources in the southern hemisphere targeted to search for young nearby association. Nine associations have either been newly identified, or have had their member list revised. Groups belonging to the Sco-Cen-Oph complex are not considered in the present study.<i>Aims. <i/>These nine associations, with ages of between about 6 Myr and 70 Myr, form an excellent sample to study the Li depletion in the pre-main sequence (PMS) evolution. In the present paper, we investigate the use of Li abundances as an independent clock to constrain the PMS evolution.<i>Methods. <i/>Using our measurements of the equivalent widths of the Li resonance line and assuming fixed metallicities and microturbulence, we calculated the LTE Li abundances for 376 members of various young associations. In addition, we considered the effects of their projected stellar rotation.<i>Results. <i/>We present the Li depletion as a function of age in the first hundred million years for the first time for the most extended sample of Li abundances in young stellar associations.<i>Conclusions. <i/>A clear Li depletion can be measured in the temperature range from 5000 K to 3500 K for the age span covered by the nine associations studied in this paper. The age sequence based on the Li-clock agrees well with the isochronal ages, the <i>ϵ<i/>Cha association being the only possible exception. The lithium depletion patterns for the associations presented here resemble those of the young open clusters with similar ages, strengthening the notion that the members proposed for these loose young associations have indeed a common physical origin. The observed scatter in the Li abundances hampers the use of Li in determining reliable ages for individual stars. For velocities above 20 km s<sup>-1<sup/>, rotation seems to play an important role in inhibiting the Li depletion.

Observing ROSAT sources in 20 x 25 deg centered at the high latitude active star ER Eri, we found evidences for a new young nearby association (~30Myr at~60pc), the Horologium Association (HorA), formed by at least 10 probable and 6 possible members, some being Post-T Tauri stars. We examine several requirements that characterize a young association and they, together, create a strong evidence for the reality of the HorA. In fact, the Li line intensities are between those of the oldest classical T Tauri stars and the ones of the Local Association stars. The space velocities of the HorA relative to the Sun, U= -9.5+/-1.0, V = -20.9 +/- 1.1, W = -2.1 +/- 1.9, are not far from those of the Local Association. We suggest that some hotter and non-X-ray active stars, with similar space velocities, could be massive members of the HorA, among them, the nearby Be star Achernar. The maximum of the mass distribution function of the HorA is around 0.8 solar masses. At its distance, the projected size of the HorA, ~50 pc, would be larger than our surveyed area and many other members could have been missed. We also observed 3 control regions, two at northern and southern galactic latitudes and a third one in the known TW Hya Association (TWA), and the properties and distribution of their young stars strengthen the reality of the HorA. Contrary to the TWA, the only known binaries in the HorA are 2 very wide systems. The HorA is much more isolated from clouds and older than the TWA and could give some clues about the lifetime of the disks around T Tauri stars. Actually, none of the proposed members is an IRAS source indicating an advanced stage of the evolution of their accreting disks. ER Eri itself was found to be a RS CVn-like system.

We study the role played by the shear and shearing viscosity in the onset of dynamical instabilities. For both the Newtonian and the relativistic regimes, the shearing viscosity decreases the instability of the fluid. The corrections due to the shear, which appear only in the post-Newtonian approximation, decrease the range of values of the ‘ratio of specific heats’ for which the system is unstable. This result is the consequence of the fact that the collapse with shear proceeds faster than the corresponding shear-free collapse. Under otherwise identical conditions, therefore, the material of the collapsing sphere with shear should be softer than the material of the shear-free collapsing sphere.

PFS (Prime Focus Spectrograph), a next generation facility instrument on the 8.2-meter Subaru Telescope, is a very wide-field, massively multiplexed, optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394 reconfigurable fibers will be distributed over the 1.3 deg field of view. The spectrograph has been designed with 3 arms of blue, red, and near-infrared cameras to simultaneously observe spectra from 380nm to 1260nm in one exposure at a resolution of ~1.6 - 2.7&Aring;. An international collaboration is developing this instrument under the initiative of Kavli IPMU. The project is now going into the construction phase aiming at undertaking system integration in 2017-2018 and subsequently carrying out engineering operations in 2018-2019. This article gives an overview of the instrument, current project status and future paths forward.

We present a digital signal processing technique that reduces the speckle content in reconstructed digital holograms. The method is based on sequential sampling of the discrete Fourier transform of the reconstructed image field. Speckle reduction is achieved at the expense of a reduced intensity and resolution, but this trade-off is shown to be greatly superior to that imposed by the traditional mean and median filtering techniques. In particular, we show that the speckle can be reduced by half with no loss of resolution (according to standard definitions of both metrics).

We report the recovery of a spectroscopic event in eta Carinae in 1997/1998 after a prediction by Damineli in 1996. A true periodicity with P=2020+/-5 days (0.2% uncertainty) is obtained. The line intensities and the radial velocity curve display a phase-locked behavior, implying that the energy and dynamics of the event repeat from cycle to cycle. This rules out S Doradus oscillation or multiple shell ejection by an unstable star as the explanation of the spectroscopic events. A colliding-wind binary scenario is supported by our spectroscopic data and by X-ray observations. Although deviations from a simple case exist around periastron, intensive monitoring during the next event (mid-2003) will be crucial to our understanding of the system.

Near-infrared spectroscopy is used to study the kinematics and excitation mechanisms of H2 and [Fe ii] lines in a sample of mostly Seyfert 1 galaxies. The spectral coverage allows simultaneous observation of the JHK bands, thus eliminating the aperture and seeing effects that have usually plagued previous works. The H2 lines are unresolved in all objects in which they were detected while the [Fe ii] lines have widths implying gas velocities of up to 650 km s-1. This suggests that, very likely, the H2 and [Fe ii] emission does not originate from the same parcel of gas. Molecular H2 lines were detected in 90% of the sample, including PG objects, indicating detectable amounts of molecular material even in objects with low levels of circumnuclear starburst activity. Analysis of the observations favors thermal excitation mechanisms for the H2 lines. Indeed, in NGC 3227, Mrk 766, NGC 4051 and NGC 4151, the molecular emission is found to be purely thermal but with heating processes that vary between the objects. Thermal excitation is also confirmed by the rather similar vibrational and rotational temperatures in the objects for which data were available. [Fe ii] lines are detected in all of the sample AGN. The [Fe ii] 1.254 μm/Paβ ratio is compatible with excitation of the [Fe ii] lines by the active nucleus in most Seyfert 1 galaxies, but in Mrk 766 the ratio implies a stellar origin. A correlation between H2/Brγ and [Fe ii]/Paβ is found for our sample objects supplemented by data from the literature. The correlation of these line ratios is a useful diagnostic tool in the NIR to separate emitting line objects by their level of nuclear activity. X-ray excitation models are able to explain the observed H2 and part of the [Fe ii] emission but fail to explain the observations in Seyfert 2 galaxies. Most likely, a combination of X-ray heating, shocks driven by the radio jet and circumnuclear star formation contributes, in different proportions, to the H2 and [Fe ii] lines observed. In most of our sample objects, the [Fe ii] 1.257 μm/1.644 μm ratio is found to be 30% lower than the intrinsic value based on current atomic data. This implies either that the extinction towards the [Fe ii]-emitting clouds is very similar in most objects or there are possible inaccuracies in the A-values in the transitions.

We investigate the spatial distribution, the space velocities and age distribution of the pre-main sequence (PMS) stars belonging to Ophiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of the young early-type star members of the Scorpius-Centaurus OB association. These young stellar associations extend over the galactic longitude range from to , and are at a distance interval of around 100 and 200 pc. This study is based on a compilation of distances, proper motions and radial velocities from the literature for the kinematic properties, and of basic stellar data for the construction of Hertzsprung-Russel diagrams. Although there was no well-known OB association in Chamaeleon, the distances and the proper motions of a group of 21 B- and A-type stars, taken from the Hipparcos Catalogue, lead us to propose that they form a young association. We show that the young early-type stars of the OB associations and the PMS stars of the SFRs follow a similar spatial distribution, i.e., there is no separation between the low and the high-mass young stars. We find no difference in the kinematics nor in the ages of these two populations studied. Considering not only the stars selected by kinematic criteria but the whole sample of young early-type stars, the scattering of their proper motions is similar to that of the PMS stars and all the young stars exhibit a common direction of motion. The space velocities of the Hipparcos PMS stars of each SFR are compatible with the mean values of the OB associations. The PMS stars in each SFR span a wide range of ages (from 1 to 20 Myr). The ages of the OB subgroups are 8–10 Myr for Upper Scorpius (US), and 16–20 Myr for Upper Centaurus Lupus (UCL) and for Lower Centaurus Crux (LCC). Thus, our results do not confirm that UCL is older than the LCC association. Based on these results and the uncertainties associated with the age determination, we cannot say that there is indeed a difference in the age of the two populations. We analyze the different scenarios for the triggering of large-scale star-formation that have been proposed up to now, and argue that most probably we are observing a spiral arm that passes close to the Sun. The alignment of young stars and molecular clouds and the average velocity of the stars in the opposite direction to the Galactic rotation agree with the expected behavior of star formation in nearby spiral arms.

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