1,721,374 research outputs found
Fragmentation in the massive star-forming region IRAS 19410+2336
No full textContext. The core mass functions (CMFs) of low-mass star-forming regions
are found to resemble the shape of the initial mass function (IMF). A similar result is
observed for the dust clumps in high-mass star-forming regions, although on spatial scales
of clusters that do not resolve the substructure that is found in these massive clumps.
The region IRAS 19410+2336 is one exception, having been observed on spatial scales on the
order of ~2500 AU, which are sufficient to resolve the clump substructure into
individual cores.
Aims. We investigate the protostellar content of IRAS 19410+2336 at high
spatial resolution at 1.4 mm, determining the temperature structure of the region and
deriving its CMF.
Methods. The massive star-forming region IRAS 19410+2336 was mapped with
the PdBI (BCD configurations) at 1.4 mm and 3 mm in the continuum and several transitions
of formaldehyde (H2CO) and methyl cyanide (CH3CN). The
H2CO transitions were also observed with the IRAM 30 m Telescope.
Results. We detect 26 continuum sources at 1.4 mm with a spatial
resolution as low as ~2200 AU, several of them with counterparts at near- and
mid-infrared wavelengths, distributed in two (proto)clusters. With the PdBI
CH3CN and PdBI/IRAM 30 m H2CO emission, we derive the temperature
structure of the region, ranging from 35 K to 90 K. Using these temperatures, we
calculate the core masses of the detected sources, ranging from
~0.7 M⊙ to ~8 M⊙. These masses are strongly affected by the
spatial filtering of the interferometer, which removes a common envelope with ~90%
of the single-dish flux. Considering only the detected dense cores and accounting for
binning effects as well as cumulative distributions, we derive a CMF, with a power-law
index β = −2.3 ± 0.2. We resolve the Jeans length of the (proto)clusters
by one order of magnitude, and only find a small velocity dispersion between the different
subsources.
Conclusions. Since we cannot unambiguously differentiate between
protostellar and prestellar cores, the derived CMF is not prestellar. Furthermore, because
of the large fraction of missing flux, we cannot establish a firm link between the CMF and
the IMF. This implies that future high-mass CMF studies will need to complement the
interferometer continuum data with the short spacing information, a task suitable for
ALMA. We note that the method of extracting temperatures using H2CO lines
becomes less applicable when reaching the dense core scales of the interferometric
observations because most of the H2CO appears to originate in the envelope
structure
Spatially resolved near-infrared spectroscopy of the massive star-forming region IRAS 19410+2336
No full text16 pages, 9 figures, 3 tables.-- Pre-print archive.Aims: IRAS 19410+2336 is a young massive star forming region with an intense outflow activity. Outflows are frequently studied in the near-infrared (NIR) since the H2 emission in this wavelength range often traces the shocked molecular gas. However, the mechanisms behind the H2 emission detected in IRAS 19410+2336 have not been clarified yet. We present here spatially resolved NIR spectroscopy which allows us to verify whether the H2 emission originates from thermal emission in shock fronts or from fluorescence excitation by non-ionizing UV photons. Moreover, NIR spectroscopy also offers the possibility of studying the characteristics of the putative driving source(s) of the H2 emission by the detection of photospheric and circumstellar spectral features, and of the environmental conditions (e.g. extinction).Methods: We obtained long-slit, intermediate-resolution, NIR spectra of IRAS 19410+2336 using LIRIS, the NIR imager/
spectrographer mounted on the 4.2m William Herschel Telescope. As a complement, we also obtained J, H and Ks images
with the Las Campanas 2.5m Du Pont Telescope, and archival mid-infrared (MIR) Spitzer images at 3.6, 4.5, 5.8 and 8.0 μm.Results: We confirm the shocked nature of the H2 emission, with an excitation temperature of about 2000 K, based on the analysis
of relevant H2 line ratios, ortho-to-para ratios and excitation diagrams. We have also identified objects with very different properties
and evolutionary stages in IRAS 19410+2336. The most massive source at millimeter wavelengths, mm1, with a mass of a few tens
of solar masses, has a bright NIR (and MIR) counterpart. This suggests that emission –probably coming through a cavity created by
one of the outflows present in the region, or from the outflow cavity itself– is leaking at these wavelengths. The second most massive
millimeter source, mm2, is only detected at & 6 μm, suggesting that it could be a high-mass protostar still in its main accretion
phase. The NIR spectra of some neighboring sources show CO first-overtone bandhead emission which is associated with neutral
material located in the inner regions of the circumstellar environment of YSOs.During this work, NLMH has
been supported by a Juan de la Cierva fellowship from the Spanish Ministerio
de Ciencia y Tecnología (MCyT). This work has also been partially funded by
the Spanish MCyT under project AYA2004-07466. LB acknowledges support by
Chilean FONDAP Center of Astrophysics 15010003Peer reviewe
Spatially resolved near-infrared spectroscopy of the massive star-forming region IRAS 19410+2336
Get PDFAims. IRAS 19410+2336 is a young massive star forming region with an intense outflow activity. Outflows are frequently studied in
the near-infrared (NIR) since the H2 emission in this wavelength range often traces the shocked molecular gas. However, the mechanisms
behind the H2 emission detected in IRAS 19410+2336 have not been clarified yet. We present here spatially resolved NIR
spectroscopy which allows us to verify whether the H2 emission originates from thermal emission in shock fronts or from fluorescence
excitation by non-ionizing UV photons. Moreover, NIR spectroscopy also offers the possibility of studying the characteristics
of the putative driving source(s) of the H2 emission by the detection of photospheric and circumstellar spectral features, and of the
environmental conditions (e.g. extinction).
Methods. We obtained long-slit, intermediate-resolution, NIR spectra of IRAS 19410+2336 using LIRIS, the NIR imager/
spectrographer mounted on the 4.2m William Herschel Telescope. As a complement, we also obtained J, H and Ks images
with the Las Campanas 2.5m Du Pont Telescope, and archival mid-infrared (MIR) Spitzer images at 3.6, 4.5, 5.8 and 8.0 μm.
Results. We confirm the shocked nature of the H2 emission, with an excitation temperature of about 2000 K, based on the analysis
of relevant H2 line ratios, ortho-to-para ratios and excitation diagrams. We have also identified objects with very different properties
and evolutionary stages in IRAS 19410+2336. The most massive source at millimeter wavelengths, mm1, with a mass of a few tens
of solar masses, has a bright NIR (and MIR) counterpart. This suggests that emission – probably coming through a cavity created by
one of the outflows present in the region, or from the outflow cavity itself – is leaking at these wavelengths. The second most massive
millimeter source, mm2, is only detected at λ >∼ 6 μm, suggesting that it could be a high-mass protostar still in its main accretion
phase. The NIR spectra of some neighboring sources show CO first-overtone bandhead emission which is associated with neutral
material located in the inner regions of the circumstellar environment of YSOs.This work has also been partially funded by
the Spanish MCyT under project AYA2004-07466. LB acknowledges support by
Chilean FONDAP Center of Astrophysics 1501000
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Multiple outflows in IRAS 19410+2336
No full textPlateau de Bure Interferometer high-spatial resolution CO observations combined with near-infrared H2 data disentangle at
least seven (possibly even nine) molecular outflows in the massive
star-forming region IRAS 19410+2336. Position–velocity diagrams of
the outflows reveal Hubble-like relationships similar to outflows
driven by low-mass objects. Estimated accretion rates are of
the order of yr-1, sufficiently high to
overcome the radiation pressure and form massive stars via
disk-mediated accretion processes. The single-dish large-scale mm
continuum cores fragment into several compact condensations at the
higher spatial resolution of the PdBI which is expected due to the
clustering in massive star formation. While single-dish data give a
simplified picture of the source, sufficiently high spatial
resolution resolves the structures into outflows resembling those
of low-mass star-forming cores. We interpret this as further
support for the hypothesis that massive stars do form via
disk-accretion processes similar to low-mass stars
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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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