2,722 research outputs found
Star clusters and the structure of the ISM. Tunnels and wakes in giant extragalactic HII regions
Several structures have been discovered embedded in regions of recent or
ongoing star formation, which point to the importance of the interaction
between fast moving wind-blowing stars and their environment. Using
hydrodynamic simulations, we investigate the passage through the interstellar
medium of a supersonic stellar wind source, and show how it can naturally lead
to the formation of tubes, channels and swamps of globules as interfaces are
crossed. The results are in excellent agreement with observation of 30 Doradus.Comment: 12 pages + 5 figures (GIF format) - Accepted for pub. in Astrophys.
J. Letter
Star formation in the large Magellanic cloud
What role the Large Magellanic Cloud (LMC), a dwarf irregular galaxy, plays in understanding infrared luminous galaxies is discussed. There are two main reasons the LMC may prove helpful. One, the LMC is only 55 kpc away, very nearby compared to much rarer high luminosity systems. Second, the environment in the LMC is distinctly different than in the Milky Way, at least those parts of the Milky Way interior to the sun, where most of the studies of massive star formation were concentrated. The LMC is an interacting system with a large amount of neutral hydrogen that is pushed around by the galaxy's encounter with the Milky Way. Perhaps a good understanding of star formation process in the LMC will provide guidance in the study of the infrared luminous galaxies. Two questions which will be addressed are: how is star formation in the LMC similar to the Milky Way Galaxy, and how is it different
Far-infrared observations of young clusters embedded in the R Coronae Austrinae and RHO Ophiuchi dark clouds
Multicolor far infrared maps in two nearby dark clouds, R Coronae Austrinae and rho Ophiuchi, were made in order to investigate the individual contribution of low mass stars to the energetics and dynamics of the surrounding gas and dust. Emission from cool dust associated with five low mass stars in Cr A and four in rho Oph was detected; their far infrared luminosities range from 2 far infrared luminosities L. up to 40 far infrared luminosities. When an estimate of the bolometric luminosity was possible, it was found that typically more than 50% of the star's energy was radiated longward of 20 micrometers. meaningful limits to the far infrared luminosities of an additional eleven association members in Cr A and two in rho Oph were also obtained. The dust optical depth surrounding the star R Cr A appears to be asymmetric and may control the dynamics of the surrounding molecular gas. The implications of the results for the cloud energetics and star formation efficiency in these two clouds are discussed
Paradigms lost and gained: stakeholder experiences of crisis distance learning during the Covid-19 pandemic
The physical distancing requirements designed to slow the contagion of COVID-19 instigated sweeping changes to the education sector. School closures in 193 countries brought significant disruption to education and to the lives of children, parents, and teachers. This study explored the experiences of school stakeholders during this period of crisis distance learning (DL). The perspectives of participants in six discrete focus groups of pupils, parents, and teachers at a private school in Dubai, United Arab Emirates, were subject to thematic analysis. Researchers identified three key themes, including āa need for stakeholder supportā, ācurriculum delivery implicationsā, and āeducational outcomes of crisis distance learningā. Conclusions and recommendations will be of interest to researchers, teachers, school leaders, and teacher education providers
Near-UV and optical spectroscopy of comets using the ISIS spectrograph on the <i>WHT</i>
We present an analysis of long-slit cometary spectroscopy using the dual-arm ISIS spectrograph on the 4.2 m WHT. Eleven comets were observed over two nights in 2016 March and we detected the OH (0-0) emission band at 3085 Ć
in the spectra of five of these comets. Emission bands of the species NH, CN, C3, C2, NH2 and [OI] were also detected. We used Haser modelling to determine molecular production rates and abundance ratios for the observed species. We found that our average abundances relative to OH and CN were generally consistent with those measured in previous studies
Layer by layer - Combining Monads
We develop a method to incrementally construct programming languages. Our
approach is categorical: each layer of the language is described as a monad.
Our method either (i) concretely builds a distributive law between two monads,
i.e. layers of the language, which then provides a monad structure to the
composition of layers, or (ii) identifies precisely the algebraic obstacles to
the existence of a distributive law and gives a best approximant language. The
running example will involve three layers: a basic imperative language enriched
first by adding non-determinism and then probabilistic choice. The first
extension works seamlessly, but the second encounters an obstacle, which
results in a best approximant language structurally very similar to the
probabilistic network specification language ProbNetKAT
Reworking research: interactions in academic articles and blogs
The blog is an increasingly familiar newcomer to the panoply of academic genres, offering researchers the opportunity to disseminate their work to new and wider audiences of experts and interested lay people. This digital medium, however, also brings challenges to writers in the form of a relatively unpredictable readership and the potential for immediate, public and potentially hostile criticism. To understand how academics in the social sciences respond to this novel rhetorical situation, we explore how they discoursally recontextualise in blogs the scientific information they have recently published in journal articles. Based on two corpora of 30 blog posts and 30 journal articles with the same authors and topics, we examine the ways researchers carefully reconstruct a different writer persona and relationship with their readers using stance and engagement (Hyland, 2005). In addition to supporting the view that the academic blog is a hybrid genre situated between academic and journalistic writing, we show how writersā rhetorical choices help define different rhetorical contexts
The Optical/Near-IR Colors of Broad Absorption Line Quasars, Including the Candidate Radio-Loud BAL Quasar 1556+3517
A candidate radio-loud broad absorption line quasar (RLBAL) has been reported
by Becker et al. (1997). We present JHK observations of this object and three
other radio-detected BALs taken with the new Michigan-Dartmouth-MIT/Ohio
State/Aladdin IR Camera (MOSAIC) on the KPNO 4-meter. The candidate RLBAL
1556+3517 has B-K=6.63, redder than all but one or two known z>1 quasars. This
strongly suggests the observed continuum of this quasar is reddened by dust.
Even when this extreme reddening is taken into account 1556+3517 is still
probably radio-loud, although near-IR spectroscopy to measure its Balmer
decrement will be needed to verify this. In addition, since it is a
flat-spectrum object, VLBI observations to determine the extent (if any) to
which beaming affects our estimate of its radio luminosity will be needed
before 1556+3517 can be unequivocally declared a radio-loud BAL. We also use
our data and data from the literature to show that optically selected BALs as a
class have B-K colors consistent with the observed distribution for optically
selected quasars as a whole. Thus there is currently no evidence that the
tendency of optically selected BALs to be preferentially radio-intermediate
(Hooper, Francis, & Impey 1993) is due to extinction artificially lowering
estimated BAL optical luminosities. However, as most quasar surveys, both radio
and optical, would be insensitive to a population of reddened radio-quiet BALs,
the existence of a large population of reddened BALs similar to 1556+3517
cannot yet be ruled out.Comment: Accepted to ApJ Letters; 10 pages including 1 figure and 2 tables.
This version somewhat revised from initial submission, with a better figur
Axial Symmetry and Rotation in the SiO Maser Shell of IK Tauri
We observed v=1, J=1-0 43-GHz SiO maser emission toward the Mira variable IK
Tauri (IK Tau) using the Very Long Baseline Array (VLBA). The images resulting
from these observations show that SiO masers form a highly elliptical ring of
emission approximately 58 x 32 mas with an axial ratio of 1.8:1. The major axis
of this elliptical distribution is oriented at position angle of ~59 deg. The
line-of-sight velocity structure of the SiO masers has an apparent axis of
symmetry consistent with the elongation axis of the maser distribution.
Relative to the assumed stellar velocity of 35 km/s, the blue- and red-shifted
masers were found to lie to the northwest and southeast of this symmetry axis
respectively. This velocity structure suggests a NW-SE rotation of the SiO
maser shell with an equatorial velocity, which we determine to be ~3.6 km/s.
Such a NW-SE rotation is in agreement with a circumstellar envelope geometry
invoked to explain previous water and OH maser observations. In this geometry,
water and OH masers are preferentially created in a region of enhanced density
along the NE-SW equator orthogonal to the rotation/polar axis suggested by the
SiO maser velocities.Comment: 17 Pages, 4 figures (2 color); accepted for publication in Ap
The late infrared development of Nova Serpentis 1970
Broad-band infrared observations of FH Ser (Nova Ser 1970) covering the period 40 to 529 days after discovery are presented. Strong quantitative evidence for grain growth in the period 60ā111 days is derived from the agreement between predictions of dust shell models and the observations. Between days 111 and 129 the grains undergo a significant reduction in size. The infrared luminosity is found to fall as tā»Ā³ for t ā³ 100. However, up until day 200 this is due to a continuing grain size reduction, while the bolometric luminosity remains approximately constant. After day 200 the bolometric luminosity falls off as ā¼tā»Ā¹. At late times, an excess flux in the 1-3 Āµm region appears above the dominant cool dust emission component. This excess flux is probably due to increasing line emission in the J, H and K bandpasses as the ejected shell expands
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