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DISTANCE AND KINEMATICS OF THE TW HYDRAE ASSOCIATION FROM PARALLAXES (vol 762, pg 118, 2013)
No full textDISTANCE AND KINEMATICS OF THE TW HYDRAE ASSOCIATION FROM PARALLAXES
No full textFrom common proper motion and signatures of youth, researchers have identified about 30 members of a putative TW Hydrae Association. Only four of these had parallactic distances from Hipparcos. We have measured parallaxes and proper motions for 14 primary members. We combine these with literature values of radial velocities to show that the Galactic space motions of the stars, with the exception of TWA 9 and 22, are parallel and do not indicate convergence at a common formation point sometime in the last few million years. The space motions of TWA 9 and 22 do not agree with the others and indicate that they are not TWA members. The median parallax is 18 mas or 56 pc. We further analyze the stars' absolute magnitudes on pre-main-sequence evolutionary tracks and find a range of ages with a median of 10.1 Myr and no correlation between age and Galactic location. The TWA stars may have formed from an extended and filamentary molecular cloud but are not necessarily precisely coeval
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An M Sin I=24 M-Circle Plus Planetary Companion To The Nearby M Dwarf Gj 176
No full textWe report the detection of a planetary companion with a minimum mass of m sin i 0.0771 M-Jup 24.5 M-circle plus to the nearby (d 9.4 pc) M2.5 V star GJ 176. The star was observed as part of our M dwarf planet search at the Hobby-Eberly Telescope (HET). The detection is based on 5 years of high-precision differential radial velocity (RV) measurements using the High-Resolution Spectrograph (HRS). The orbital period of the planet is 10.24 days. GJ 176 thus joins the small (but increasing) sample of M dwarfs hosting short-period planets with minimum masses in the Neptune-mass range. Low-mass planets could be relatively common around M dwarfs, and the current detections might represent the tip of a rocky planet population.NASA NNG04G141G NNG05G107GTerrestrial Planet Finderr Foundation Science Program NNX07AL70GMcDonald Observator
GJ 1214 reviewed
No full textContext. GJ 1214 is orbited by a transiting super-Earth-mass planet. It is a primary target for ongoing efforts to understand the emerging population of super-Earth-mass planets around M dwarfs, some of which are detected within the liquid water (habitable) zone of their host stars.
Aims. We present new precision astrometric measurements, a re-analysis of HARPS radial velocity measurements, and new medium-resolution infrared spectroscopy of GJ 1214. We combine these measurements with recent transit follow-up observations and new catalog photometry to provide a comprehensive update of the star-planet properties.
Methods. The distance is obtained with 0.6% relative uncertainty using CAPScam astrometry. The new value increases the nominal distance to the star by ~10% and is significantly more precise than previous measurements. Improved radial velocity measurements have been obtained analyzing public HARPS spectra of GJ 1214 using the HARPS-TERRA software and are 25% more precise than the original ones. The Doppler measurements combined with recently published transit observations significantly refine the constraints on the orbital solution, especially on the planet’s eccentricity. The analysis of the infrared spectrum and photometry confirm that the star is enriched in metals compared to the Sun.
Results. Using all this new fundamental information, combined with empirical mass–luminosity relations for low mass stars, we derive updated values for the bulk properties of the star-planet system. We also use infrared absolute fluxes to estimate the stellar radius and to re-derive the star-planet properties. Both approaches provide very consistent values for the system. Our analysis shows that the updated expected value for the planet mean density is 1.6 ± 0.6 g cm-3, and that a density comparable to the Earth (~5.5 g cm-3) is now ruled out with very high confidence.
Conclusions. This study illustrates how the fundamental properties of M dwarfs are of paramount importance in the proper characterization of the low mass planetary candidates orbiting them. Given that the distance is now known to better than 1%, interferometric measurements of the stellar radius, additional high precision Doppler observations, and/or or detection of the secondary transit (occultation), are necessary to further improve the constraints on the GJ 1214 star-planet properties
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
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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