1,721,287 research outputs found
The LAOG-Planet Imaging Surveys
Full text linkWith the development of high‐contrast imaging techniques and infrared detectors, vast efforts have been devoted during the past decade to detect and characterize lighter, cooler and closer companions to nearby stars, and ultimately image new planetary systems. Complementary to other observing techniques (radial velocity (RV), transit, micro‐lensing, pulsar‐timing), this approach has opened a new astrophysical window to study the physical properties and the formation mechanisms of brown dwarfs and planets. Here, I will briefly present the observing challenges, the different observing techniques, strategies and samples of current exoplanet imaging searches that have been selected in the context of the LAOG‐Planet Imaging Surveys. Finally, I will describe the most recent results that led to the discovery of giant planets that probably formed like those in our solar system, offering exciting and attractive perspectives for the future generation of deep imaging instruments
Collaboration and Competition in Exoplanet Research
Full text linkCollaboration and competition are strong driving forces in the modern search for exoplanets, appears between individuals, agencies and nations as well as between observing techniques and theoretical interpretation. I will argue that these forces, taken in balance, are beneficial to the field and are partly responsible for the rapid progress in the search for planets and ultimately the search for life beyond the solar system. Specific examples will include indirect detection of Earth analogs from ground and space and the direct detection of gas giant and terrestrial planets
Grain Growth and Global Structure of the Protoplanetary Disk Associated with the Mature Classical T Tauri Star, PDS 66
Full text linkWe present ATCA interferometric observations of the old (13 Myr), nearby (86 pc) classical T Tauri star (CTTs), PDS 66. Unresolved 3 and 12 mm continuum emission is detected towards PDS 66, and upper limits are derived for the 3 and 6 cm flux densities. The mm data show a spectral slope flatter than that expected for ISM‐sized dust particles, which is most likely a result of grain growth. We also present HST/NICMOS 1.1 μm PSF‐subtracted coronagraphic imaging observations of PDS 66. The HST observations reveal a circumstellar region of dust scattering ∼0.32% of the central starlight, declining in surface brightness as r^(−4.53). The disk is inclined 32±5° from face‐on, and extends to a radius of 170 AU. These data are combined with published optical and longer‐λ observations to make qualitative comparisons between the median Taurus and PDS 66 spectral energy distributions (SEDs). By comparing the near‐infrared emission to a simple model, we det ermine that the location of the inner disk radius is consistent with being at dust sublimation (∼1400 K at 0.1 AU). We place constraints on the mass surface density of the disk at 5 AU assuming a flat‐disk model and find that it is probably too low to form gas giant planets according to current models. Despite the fact that PDS 66 is much older than a typical classical T Tauri star (⩽5 Myr), its physical properties are not much different
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
IDENTIFYING THE YOUNG LOW-MASS STARS WITHIN 25 pc. II. DISTANCES, KINEMATICS, AND GROUP MEMBERSHIP
No full textWe have conducted a kinematic study of 165 young M dwarfs with ages of less than or similar to 300 Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of less than or similar to 25 pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5 m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (less than or similar to 3 Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and beta Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages less than or similar to 150 Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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