1,720,961 research outputs found
Mid-Infrared Photometry of Mass-losing Asymptotic Giant Branch Stars
No full textWe present ground-based mid-infrared imaging for 27 M-, S- and C-type Asymptotic Giant Branch (AGB) stars. The data are compared with those of the database available thanks to the IRAS, ISO, MSX and 2MASS catalogues. Our goal is to establish relations between the IR colors, the effective temperature , the luminosity and the mass loss rate , for improving the effectiveness of AGB modelling. Bolometric (absolute) magnitudes are obtained through distance compilations, and by applying previously-derived bolometric corrections; the variability is also studied, using data accumulated since the IRAS epoch. The main results are: i) Values of and for C stars fit relations previously established by us, with Miras being on average more evolved and mass losing than Semiregulars. ii) Moderate IR excesses (as compared to evolutionary tracks) are found for S and M stars in our sample: they are confirmed to originate from the dusty circumstellar environment. iii) A larger reddening characterizes C-rich Miras and post-AGBs. In this case, part of the excess is due to AGB models overestimating for C-stars, as a consequence of the lack of suitable molecular opacities. This has a large effect on the colors of C-rich sources and sometimes disentangling the photospheric and circumstellar contributions is difficult; better model atmospheres should be used in stellar evolutionary codes for C stars. iv) The presence of a long-term variability at mid-IR wavelengths seems to be limited to sources with maximum emission in the 8 -- 20 m region, usually Mira variables (1/3 of our sample). Most Semiregular and post-AGB stars studied here remained remarkably constant in mid-IR over the last twenty years
The symbiotic star BX Monocerotis
No full textThe nature of BX Mon, a peculiar star characterized by a composite spectrum and very long period photometric variability, has been investigated. The star has been included in an extensive program of ESO observations of emission line stars. New results are discussed based on coordinated optical (IDS) and infrared observations made in February 1983, on high resolution H alpha spectrophotometry made with CAT-CES in February 1984, and on infrared photometry of March 1985. The 1983 spectrum is composite with prominent hydrogen and weak He I emission lines, and a cool continuum with strong TiO absorptions. The red-infrared energy distribution, corrected for an interstellar extinction of (B-V) = 0.2, suggests for the cool component an M5 III spectral type in agreement with the strength of the TiO red bands. A distance of 2800 pc is estimated for the system. An excess with respect to the M continuum is present shortward of 600 nm and is attributed to a hotter component and to nebular emission. The 1984 H alpha profile is complex, with two-component emission, and a broad red red-shifted shell absorption probably produced in a wind from the cool giant with a velocity of 59 km/s. The observations indicate that presently the cool M-type component of BX Mon is rather stable - certainly not a Mira variable in agreement with its being an S-type symbiotic. The reported photometric variability could be attributed to the hot component
Shocked molecular hydrogen emission in the bipolar outflow NGC 6334 I
No full textSub-arcsec images in the J,H,K and H_2_ and nearby continuum of the bipolar outflow NGC 6334 I are presented. Three knots of H_2_ emission are found which coincide with recently discovered NH_3_(3,3) masers. Two of these are aligned along the CO bipolar outflow, indicating that the hydrogen molecular emission is shock excited. We have also detected a loop-shaped infrared nebula extending to the east of the massive mid-infrared source IRS1 which illuminates the reflection nebula. IRS1 consists of at least four components in the near-infrared. The interaction of the stellar wind from these young stellar objects with the surrounding medium could excite the third H_2_ emission knot and associated ammonia maser
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
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