975 research outputs found
Discovery of Raman-scattered lines in the massive luminous emission-line star LHA 115-S 18
LHA 115-S 18 is a very peculiar emission-line star exhibiting the B[e]
phenomenon. Located in the Small Magellanic Cloud, its spectrum shows features
of an extremely wide range of excitation and ionization stages, extending from
highly ionized atomic lines (Si IV, C IV, He II) in the UV and optical regions
to molecular emission bands of CO and TiO in the optical and IR regions. The
most distinguishing spectral characteristic of LHA 115-S 18 is the high
variability detected in the He II {\lambda}4686 emission line, which can be a
very conspicuous or completely invisible feature.
In this work, we report on another peculiarity of LHA 115-S 18. From
high-resolution optical spectra taken between 2000 and 2008, we discovered the
appearance and strengthening of two emission features at {\lambda}6825 \AA, and
{\lambda}7082 \AA,, which we identified as Raman-scattered lines. This is the
first time these lines have been detected in the spectrum of a massive luminous
B[e] star. As the classification of LHA 115-S 18 is highly controversial, we
discuss how the discovery of the appearance of Raman-scattered lines in this
peculiar star might help us to solve this puzzle.Comment: Letter accepted for publication in MNRAS. 5 pages, 3 figure
Detection of curved lines with B-COSFIRE filters: A case study on crack delineation
The detection of curvilinear structures is an important step for various
computer vision applications, ranging from medical image analysis for
segmentation of blood vessels, to remote sensing for the identification of
roads and rivers, and to biometrics and robotics, among others. %The visual
system of the brain has remarkable abilities to detect curvilinear structures
in noisy images. This is a nontrivial task especially for the detection of thin
or incomplete curvilinear structures surrounded with noise. We propose a
general purpose curvilinear structure detector that uses the brain-inspired
trainable B-COSFIRE filters. It consists of four main steps, namely nonlinear
filtering with B-COSFIRE, thinning with non-maximum suppression, hysteresis
thresholding and morphological closing. We demonstrate its effectiveness on a
data set of noisy images with cracked pavements, where we achieve
state-of-the-art results (F-measure=0.865). The proposed method can be employed
in any computer vision methodology that requires the delineation of curvilinear
and elongated structures.Comment: Accepted at Computer Analysis of Images and Patterns (CAIP) 201
A Search for Wolf-Rayet Stars in the Small Magellanic Cloud
We conducted an extensive search for Wolf-Rayet stars (W-Rs) in the SMC,
using the same interference filter imaging techniques that have proved
successful in finding W-Rs in more distant members of the Local Group.
Photometry of some 1.6 million stellar images resulted in some 20 good
candidates, which we then examined spectroscopically. Two of these indeed
proved to be newly found W-Rs, bringing the total known in the SMC from 9 to
11. Other finds included previously unknown Of-type stars (one as early as
O5f?p)),the recovery of the Luminous Blue Variable S18, and the discovery of a
previously unknown SMC symbiotic star. More important, however, is the fact
that there does not exist a significant number of W-Rs waiting to be discovered
in the SMC. The number of W-Rs in the SMC is a factor of 3 lower than in the
LMC (per unit luminosity), and we argue this is the result of the SMC's low
metallicity on the evolution of the most massive stars.Comment: Accepted by Astrophysical Journal. Postscript version available via
ftp.lowell.edu/pub/massey/smcwr.ps.gz Revised version contains slightly
revised spectral types for the Of stars but is otherwise unchange
VLT spectroscopy of blue supergiants in IC 1613
We present multi-object spectroscopy of young, massive stars in the Local
Group galaxy IC 1613. We provide the spectral classification and a detailed
spectral catalog for 54 OBA stars in this galaxy. The majority of the
photometrically selected sample is composed of B- and A-type supergiants. The
remaining stars include early O-type dwarfs and the only Wolf-Rayet star known
in this galaxy. Among the early B stars we have serendipitously uncovered 6 Be
stars, the largest spectroscopically confirmed sample of this class of objects
beyond the Magellanic Clouds. We measure chemical abundances for 9 early-B
supergiants, and find a mean oxygen abundance of 12+log(O/H)=7.90 +/- 0.08.
This value is consistent with the result we obtain for two HII regions in which
we detect the temperature-sensitive [OIII]4363 auroral line.Comment: 17 pages, accepted for publication in the Astrophysical Journa
Terminal velocities of luminous, early-type SMC stars
Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are
used to determine terminal velocities for 11 O and B-type giants and
supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV
resonance lines. Using archival data from observations with the Goddard
High-Resolution Spectrograph and the International Ultraviolet Explorer
telescope, terminal velocities are obtained for a further five B-type
supergiants. We discuss the metallicity dependence of stellar terminal
velocities, finding no evidence for a significant scaling between Galactic and
SMC metallicities for Teff < 30,000 K, consistent with the predictions of
radiation driven wind theory for supergiant stars. A comparison of the
ratio between the SMC and Galactic samples, while
consistent with the above statement, emphasizes that the uncertainties in the
distances to galactic O-stars are a serious obstacle to a detailed comparison
with theory. For the SMC sample there is considerable scatter in this ratio at
a given effective temperature, perhaps indicative of uncertainties in stellar
masses.Comment: 28 pages, 8 figures, accepted by ApJ; minor revisions prior to
acceptanc
Moderate hypothermia within 6 h of birth plus inhaled xenon versus moderate hypothermia alone after birth asphyxia (TOBY-Xe): a proof-of-concept, open-label, randomised controlled trial
Background Moderate cooling after birth asphyxia is associated with substantial reductions in death and disability, but additional therapies might provide further benefit. We assessed whether the addition of xenon gas, a promising novel therapy, after the initiation of hypothermia for birth asphyxia would result in further improvement. Methods Total Body hypothermia plus Xenon (TOBY-Xe) was a proof-of-concept, randomised, open-label, parallel-group trial done at four intensive-care neonatal units in the UK. Eligible infants were 36–43 weeks of gestational age, had signs of moderate to severe encephalopathy and moderately or severely abnormal background activity for at least 30 min or seizures as shown by amplitude-integrated EEG (aEEG), and had one of the following: Apgar score of 5 or less 10 min after birth, continued need for resuscitation 10 min after birth, or acidosis within 1 h of birth. Participants were allocated in a 1:1 ratio by use of a secure web-based computer-generated randomisation sequence within 12 h of birth to cooling to a rectal temperature of 33·5°C for 72 h (standard treatment) or to cooling in combination with 30% inhaled xenon for 24 h started immediately after randomisation. The primary outcomes were reduction in lactate to N-acetyl aspartate ratio in the thalamus and in preserved fractional anisotropy in the posterior limb of the internal capsule, measured with magnetic resonance spectroscopy and MRI, respectively, within 15 days of birth. The investigator assessing these outcomes was masked to allocation. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00934700, and with ISRCTN, as ISRCTN08886155. Findings The study was done from Jan 31, 2012, to Sept 30, 2014. We enrolled 92 infants, 46 of whom were randomly assigned to cooling only and 46 to xenon plus cooling. 37 infants in the cooling only group and 41 in the cooling plus xenon group underwent magnetic resonance assessments and were included in the analysis of the primary outcomes. We noted no significant differences in lactate to N-acetyl aspartate ratio in the thalamus (geometric mean ratio 1·09, 95% CI 0·90 to 1·32) or fractional anisotropy (mean difference −0·01, 95% CI −0·03 to 0·02) in the posterior limb of the internal capsule between the two groups. Nine infants died in the cooling group and 11 in the xenon group. Two adverse events were reported in the xenon group: subcutaneous fat necrosis and transient desaturation during the MRI. No serious adverse events were recorded. Interpretation Administration of xenon within the delayed timeframe used in this trial is feasible and apparently safe, but is unlikely to enhance the neuroprotective effect of cooling after birth asphyxia
What makes re-finding information difficult? A study of email re-finding
Re-nding information that has been seen or accessed before is a task which can be relatively straight-forward, but often it can be extremely challenging, time-consuming and frustrating. Little is known, however, about what makes one re-finding task harder or easier than another. We performed a user study to learn about the contextual factors that influence users' perception of task diculty in the context of re-finding email messages. 21 participants were issued re-nding tasks to perform on their own personal collections. The participants' responses to questions about the tasks combined with demographic data and collection statistics for the experimental population provide a rich basis to investigate the variables that can influence the perception of diculty. A logistic regression model was developed to examine the relationships be- tween variables and determine whether any factors were associated with perceived task diculty. The model reveals strong relationships between diculty and the time lapsed since a message was read, remembering when the sought-after email was sent, remembering other recipients of the email, the experience of the user and the user's ling strategy. We discuss what these findings mean for the design of re-nding interfaces and future re-finding research
Filter-Based Approach for Ornamentation Detection and Recognition in Singing Folk Music
A UBVR CCD Survey of the Magellanic Clouds
We present photometry and a preliminary interpretation of a UBVR survey of
the Large and Small Magellanic Clouds. We determine improved values for the
relative number of blue and red supergiants. We also compare the relative
number of Red Supergiants (RSGs) and Wolf-Rayet stars, demonstrating a strong,
tight correlation with metallicity, and reinvestigate the initial mass function
slope of massive stars found in the field.Comment: complete postscript (including embedded figures) can be found at:
ftp://ftp.lowell.edu/pub/massey/mcatlas.ps.gz Accepted for publication in the
ApJ
Deep ALTAIR + NIRI Imaging of the Disk and Bulge of M31
Deep J, H, and K' images, recorded with the ALTAIR adaptive optics system and
NIRI imager on Gemini North, are used to probe the stellar content of the disk
and bulge of the Local Group galaxy M31. With FWHM near 0.08 arcsec in K, these
are the highest angular resolution near-infrared images yet obtained of this
galaxy. Four fields that sample M31 at galactocentric radii of 62, 9, 4, and 2
arcmin were observed. The RGB-tip occurs between K = 17.0 and 17.2, and the
color of the RGB in the field closest to the center of M31 is consistent with
that of NGC 6528. After accounting for random photometric errors, the upper RGB
in each field has a width on the (K, J-K) CMD that is consistent with a +/- 0.5
dex dispersion in [Fe/H], in rough agreement with what is seen in other disk
and spheroid fields in M31. A population of very bright red stars, which we
identify as C stars, are seen in the three fields that are closest to the
center of M31. The spatial distribution of these objects suggests that they are
well mixed throughout this part of M31, and so likely did not form in a compact
region near the galactic nucleus, but more probably formed in the inner disk.
We speculate that these C stars may be the most luminous members of the
intermediate age population that has been detected previously in studies of the
integrated spectrum of the central regions of M31.Comment: 36 pages of text + 16 eps figures; Astronomical Journal in pres
- …