1,088 research outputs found
Micron-sized forsterite grains in the pre-planetary nebula of IRAS 17150-3224 - Searching for clues on the mysterious evolution of massive AGB stars
We study the grain properties and location of the forsterite crystals in the
circumstellar environment of the pre-planetary nebula (PPN) IRAS 17150-3224 in
order to learn more about the as yet poorly understood evolutionary phase prior
to the PPN. We use the best-fit model for IRAS 17150-3224 of Meixner et al.
(2002) and add forsterite to this model. We investigate different spatial
distributions and grain sizes of the forsterite crystals in the circumstellar
environment. We compare the spectral bands of forsterite in the mid-infrared
and at 69 micrometre in radiative transport models to those in ISO-SWS and
Herschel/PACS observations. We can reproduce the non-detection of the
mid-infrared bands and the detection of the 69 micrometre feature with models
where the forsterite is distributed in the whole outflow, in the superwind
region, or in the AGB-wind region emitted previous to the superwind, but we
cannot discriminate between these three models. To reproduce the observed
spectral bands with these three models, the forsterite crystals need to be
dominated by a grain size population of 2 micrometre up to 6 micrometre. We
hypothesise that the large forsterite crystals were formed after the superwind
phase of IRAS 17150-3224, where the star developed an as yet unknown hyperwind
with an extremely high mass-loss rate (10^-3 Msol/yr). The high densities of
such a hyperwind could be responsible for the efficient grain growth of both
amorphous and crystalline dust in the outflow. Several mechanisms are discussed
that might explain the lower-limit of 2 micrometre found for the forsterite
grains, but none are satisfactory. Among the mechanisms explored is a possible
selection effect due to radiation pressure based on photon scattering on
micron-sized grains.Comment: Accepted by A&
Superdiversity in Music Education
Globalization has changed the social, cultural, and linguistic diversity in societies all over the world (Blommaert, J & Rampton, B. Diversities, 13(2), 1–22 (2011)). As new technologies have rapidly developed alongside increased forms of transnational flow, so have new forms of language, art, music, communication, and expression. This rapid and varied blending of cultures, ideas, and modes of communication is what Vertovec (2007) describes as super-diversity—diversity within diversity. In this narrative, I explore the theoretical and methodological pluralism that has aided my research in diverse settings, drawing from post-structuralism, critical theory, sociolinguistics, complexity theory, and discourse analysis—specifically Scollon and Scollon’s (Scollon, R & Scollon, W S. Discourses in place: Language in the material world. London: Routledge (2003), 10.4324/9780203422724; Scollon, R & Scollon, W S. Nexus analysis: Discourse and the emerging internet. New York: Routledge (2004)) recommendations for nexus analysis and Blommaert’s theoretical principles and concepts of ethnography, globalization, and superdiversity (Blommaert, J. Discourse. Cambridge, UK: Cambridge University Press (2005), 10.1017/CBo9780511610295; Blommaert, J. The sociolinguistics of globalization. Cambridge, UK: Cambridge University Press (2010), 10.1017/CBO9780511845307; Blommaert, J. Ethnography, superdiversity and linguistic landscapes: Chronicles of complexity. Bristol, UK: Multilingual Matters (2013)). I promote a need to develop a robust toolkit for music education that (1) better analyzes how we position and are positioned as part of larger groups and practices operating within multiple layers of social, cultural, and historical context, and (2) better advocates for equitable practices and inclusive spaces in our field
Understanding AGB evolution in Galactic bulge stars from high-resolution infrared spectroscopy
An analysis of high-resolution near-infrared spectra of a sample of 45
asymptotic giant branch (AGB) stars towards the Galactic bulge is presented.
The sample consists of two subsamples, a larger one in the inner and
intermediate bulge, and a smaller one in the outer bulge. The data are analysed
with the help of hydrostatic model atmospheres and spectral synthesis. We
derive the radial velocity of all stars, and the atmospheric chemical mix
([Fe/H], C/O, C/C, Al, Si, Ti, and Y) where possible. Our ability
to model the spectra is mainly limited by the (in)completeness of atomic and
molecular line lists, at least for temperatures down to K. We find that the subsample in the inner and intermediate
bulge is quite homogeneous, with a slightly sub-solar mean metallicity and only
few stars with super-solar metallicity, in agreement with previous studies of
non-variable M-type giants in the bulge. All sample stars are oxygen-rich,
C/O1.0. The C/O and carbon isotopic ratios suggest that third dredge-up
(3DUP) is absent among the sample stars, except for two stars in the outer
bulge that are known to contain technetium. These stars are also more
metal-poor than the stars in the intermediate or inner bulge. Current stellar
masses are determined from linear pulsation models. The masses, metallicities
and 3DUP behaviour are compared to AGB evolutionary models. We conclude that
these models are partly in conflict with our observations. Furthermore, we
conclude that the stars in the inner and intermediate bulge belong to a more
metal-rich population that follows bar-like kinematics, whereas the stars in
the outer bulge belong to the metal-poor, spheroidal bulge population.Comment: 21 pages, 13 figures, 6 tables (incl. appendix), years of work,
published in MNRA
The problematically short superwind of OH/IR stars - Probing the outflow with the 69 {\mu}m spectral band of forsterite
Spectra of OH/IR stars show prominent spectral bands of crystalline olivine
(MgFeSiO). To learn more about the timescale of the
outflows of OH/IR stars, we study the spectral band of crystalline olivine at
69 {\mu}m. The 69 {\mu}m band is of interest because its width and peak
wavelength position are sensitive to the grain temperature and to the exact
composition of the crystalline olivine. With Herschel/PACS, we observed the 69
{\mu}m band in the outflow of 14 OH/IR stars. By comparing the crystalline
olivine features of our sample with those of model spectra, we determined the
size of the outflow and its crystalline olivine abundance.
The temperature indicated by the observed 69 {\mu}m bands can only be
reproduced by models with a geometrically compact superwind
( 2500 AU = 1400 R).This means that the superwind
started less than 1200 years ago (assuming an outflow velocity of 10 km/s). The
small amount of mass lost in one superwind and the high progenitor mass of the
OH/IR stars introduce a mass loss and thus evolutionary problem for these
objects, which has not yet been understood.Comment: Accepted by A&
Dusty shells surrounding the carbon variables S Scuti and RT Capricorni
For the Mass-loss of Evolved StarS (MESS) programme, the unprecedented
spatial resolution of the PACS photometer on board the Herschel space
observatory was employed to map the dusty environments of asymptotic giant
branch (AGB) and red supergiant (RSG) stars. Among the morphologically
heterogeneous sample, a small fraction of targets is enclosed by spherically
symmetric detached envelopes. Based on observations in the 70 {\mu}m and 160
{\mu}m wavelength bands, we investigated the surroundings of the two carbon
semiregular variables S Sct and RT Cap, which both show evidence for a history
of highly variable mass-loss. S Sct exhibits a bright, spherically symmetric
detached shell, 138" in diameter and co-spatial with an already known CO
structure. Moreover, weak emission is detected at the outskirts, where the
morphology seems indicative of a mild shaping by interaction of the wind with
the interstellar medium, which is also supported by the stellar space motion.
Two shells are found around RT Cap that were not known so far in either dust
emission or from molecular line observations. The inner shell with a diameter
of 188" shows an almost immaculate spherical symmetry, while the outer ~5'
structure is more irregularly shaped. MoD, a modification of the DUSTY
radiative transfer code, was used to model the detached shells. Dust
temperatures, shell dust masses, and mass-loss rates are derived for both
targets
Explanatory Supplement of the ISOGAL-DENIS Point Source Catalogue
We present version 1.0 of the ISOGAL-DENIS Point Source Catalogue (PSC),
containing more than 100,000 point sources detected at 7 and/or 15 micron in
the ISOGAL survey of the inner Galaxy with the ISOCAM instrument on board the
Infrared Space Observatory (ISO). These sources are cross-identified, wherever
possible, with near-infrared (0.8-2.2 micron) data from the DENIS survey. The
overall surface covered by the ISOGAL survey is about 16 square degrees, mostly
(95%) distributed near the Galactic plane (|b| < 1 deg), where the source
extraction can become confusion limited and perturbed by the high background
emission. Therefore, special care has been taken aimed at limiting the
photometric error to ~0.2 magnitude down to a sensitivity limit of typically 10
mJy. The present paper gives a complete description of the entries and the
information which can be found in this catalogue, as well as a detailed
discussion of the data processing and the quality checks which have been
completed. The catalogue is available via the VizieR Service at the Centre de
Donn\'ees Astronomiques de Strasbourg (CDS,
http://vizier.u-strasbg.fr/viz-bin/VizieR/) and also via the server at the
Institut d'Astrophysique de Paris (http://www-isogal.iap.fr/). A more complete
version of this paper, including a detailed description of the data processing,
is available in electronic form through the ADS service.Comment: 21 pages, 7 figures. A&A in press. Full length version with 32
figures and detailed description of the data processing is available here:
http://www-isogal.iap.fr/Publications/ExplSupplFull.ps.g
- …