2,220 research outputs found
PHotometry Assisted Spectral Extraction (PHASE) and identification of SNLS supernovae
Aim: We present new extraction and identification techniques for supernova
(SN) spectra developed within the Supernova Legacy Survey (SNLS) collaboration.
Method: The new spectral extraction method takes full advantage of
photometric information from the Canada-France-Hawai telescope (CFHT) discovery
and reference images by tracing the exact position of the supernova and the
host signals on the spectrogram. When present, the host spatial profile is
measured on deep multi-band reference images and is used to model the host
contribution to the full (supernova + host) signal. The supernova is modelled
as a Gaussian function of width equal to the seeing. A chi-square minimisation
provides the flux of each component in each pixel of the 2D spectrogram. For a
host-supernova separation greater than <~ 1 pixel, the two components are
recovered separately and we do not use a spectral template in contrast to more
standard analyses. This new procedure permits a clean extraction of the
supernova separately from the host in about 70% of the 3rd year ESO/VLT spectra
of the SNLS. A new supernova identification method is also proposed. It uses
the SALT2 spectrophotometric template to combine the photometric and spectral
data. A galaxy template is allowed for spectra for which a separate extraction
of the supernova and the host was not possible.
Result: These new techniques have been tested against more standard
extraction and identification procedures. They permit a secure type and
redshift determination in about 80% of cases. The present paper illustrates
their performances on a few sample spectra.Comment: 27 pages, 18 Figures, 1 Table. Accepted for publication in A&
Characterising native plant resins from Australian Aboriginal artefacts using ATR-FTIR and GC/MS
Resin use by Australian Aborigines has been documented in ethnographic accounts across the continent and is also evident from archaeological and anthropological artefacts. This research assesses the use of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and gas chromatography coupled mass spectrometry (GC/MS) for the identification of native plant resins on museum artefacts. A collection of thirteen museum artefacts were analysed using light microscopy and characterised using both ATR-FTIR and GC/MS. The resins were identified to the plant genus and one to the species level, as spinifex (. Triodia spp. R.Br.), ironwood (. Erythrophleum chlorostachys (F. Muell.) Baill.) and grass tree (. Xanthorrhoea spp. Sm.) by comparison to a reference collection of modern exudates from 34 Australian plant species. The two analytical methods used, produced a significant agreement in results but one has practical advantages. On eight of the artefacts, ATR-FTIR was able to be performed on the residue in situ, without removal, presenting a non-destructive analytical method for the identification of resins which is applicable to rare and delicate artefacts from museum collections. Permission to remove the residue off the artefact is not always granted or feasible, so ATR-FTIR has a significant advantage over GC/MS and other methods which require chemical treatment or even destruction of the archaeological sample. Both of the methods examined are demonstrated to accurately infer the botanical origin of archaeological and anthropological resins, providing insight on the use, preparation and trading of resins, with the consequent contribution to an understanding of the development and use of hafted tools and other aspects of cultural development
Low Carbon Abundance in Type Ia Supernovae
We investigate the quantity and composition of unburned material in the outer
layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr and 20 04bw.
Pristine matter from a white dwarf progenitor is expected to be a mixture of
oxygen and carbon in approximately equal abundance. Using near-infrared (NIR,
0.7-2.5 microns) spectra, we find that oxygen is abundant while carbon is
severely depleted with low upper limits in the outer third of the ejected mass.
Strong features from the OI line at rest wavelength = 0.7773 microns are
observed through a wide range of expansion velocities approx. 9,000 - 18,000
km/s. This large velocity domain corresponds to a physical region of the
supernova with a large radial depth. We show that the ionization of C and O
will be substantially the same in this region. CI lines in the NIR are expected
to be 7-50 times stronger than those from OI but there is only marginal
evidence of CI in the spectra and none of CII. We deduce that for these three
normal SNe Ia, oxygen is more abundant than carbon by factors of 100 - 1,000.
MgII is also detected in a velocity range similar to that of OI. The presence
of O and Mg combined with the absence of C indicates that for these SNe Ia,
nuclear burning has reached all but the extreme outer layers; any unburned
material must have expansion velocities greater than 18,000 km/s. This result
favors deflagration to detonation transition (DD) models over pure deflagration
models for SNe Ia.Comment: accepted for publication in Ap
Visual pursuit behavior in mice maintains the pursued prey on the retinal region with least optic flow
Mice have a large visual field that is constantly stabilized by vestibular ocular reflex (VOR) driven eye rotations that counter head-rotations. While maintaining their extensive visual coverage is advantageous for predator detection, mice also track and capture prey using vision. However, in the freely moving animal quantifying object location in the field of view is challenging. Here, we developed a method to digitally reconstruct and quantify the visual scene of freely moving mice performing a visually based prey capture task. By isolating the visual sense and combining a mouse eye optic model with the head and eye rotations, the detailed reconstruction of the digital environment and retinal features were projected onto the corneal surface for comparison, and updated throughout the behavior. By quantifying the spatial location of objects in the visual scene and their motion throughout the behavior, we show that the prey image consistently falls within a small area of the VOR-stabilized visual field. This functional focus coincides with the region of minimal optic flow within the visual field and consequently area of minimal motion-induced image-blur, as during pursuit mice ran directly toward the prey. The functional focus lies in the upper-temporal part of the retina and coincides with the reported high density-region of Alpha-ON sustained retinal ganglion cells.Mice have a lot to keep an eye on. To survive, they need to dodge predators looming on land and from the skies, while also hunting down the small insects that are part of their diet. To do this, they are helped by their large panoramic field of vision, which stretches from behind and over their heads to below their snouts. To stabilize their gaze when they are on the prowl, mice reflexively move their eyes to counter the movement of their head: in fact, they are unable to move their eyes independently. This raises the question: what part of their large visual field of view do these rodents use when tracking a prey, and to what advantage? This is difficult to investigate, since it requires simultaneously measuring the eye and head movements of mice as they chase and capture insects. In response, Holmgren, Stahr et al. developed a new technique to record the precise eye positions, head rotations and prey location of mice hunting crickets in surroundings that were fully digitized at high resolution. Combining this information allowed the team to mathematically recreate what mice would see as they chased the insects, and to assess what part of their large visual field they were using. This revealed that, once a cricket had entered any part of the mices large field of view, the rodents shifted their head - but not their eyes - to bring the prey into both eye views, and then ran directly at it. If the insect escaped, the mice repeated that behavior. During the pursuit, the crickets position was mainly held in a small area of the mouses view that corresponds to a specialized region in the eye which is thought to help track objects. This region also allowed the least motion-induced image blur when the animals were running forward. The approach developed by Holmgren, Stahr et al. gives a direct insight into what animals see when they hunt, and how this constantly changing view ties to what happens in the eyes. This method could be applied to other species, ushering in a new wave of tools to explore what freely moving animals see, and the relationship between behaviour and neural circuitry
Freely-moving mice visually pursue prey using a retinal area with least optic flow
Mice have a large visual field that is constantly stabilized by vestibular ocular reflex driven eye rotations that counter head-rotations. While maintaining their extensive visual coverage is advantageous for predator detection, mice also track and capture prey using vision. However, in the freely moving animal quantifying object location in the field of view is challenging. Here, we developed a method to digitally reconstruct and quantify the visual scene of freely moving mice performing a visually based prey capture task. By isolating the visual sense and combining amouse eye optic model with the head and eye rotations, the detailed reconstruction of the digital environment and retinal features were projected onto the corneal surface for comparison, and updated throughout the behavior. By quantifying the spatial location of objects in the visual scene and their motion throughout the behavior, we show that the image of the prey is maintained within a small area, the functional focus, in the upper-temporal part of the retina. This functional focus coincides with a region of minimal optic flow in the visual field and consequently minimal motion-induced image blur during pursuit, as well as the reported high density-region of Alpha-ON sustained retinal ganglion cells
Direct Confirmation of the Asymmetry of the Cas A Supernova with Light Echoes
We report the first detection of asymmetry in a supernova (SN) photosphere
based on SN light echo (LE) spectra of Cas A from the different perspectives of
dust concentrations on its LE ellipsoid. New LEs are reported based on
difference images, and optical spectra of these LEs are analyzed and compared.
After properly accounting for the effects of finite dust-filament extent and
inclination, we find one field where the He I and H alpha features are
blueshifted by an additional ~4000 km/s relative to other spectra and to the
spectra of the Type IIb SN 1993J. That same direction does not show any shift
relative to other Cas A LE spectra in the Ca II near-infrared triplet feature.
We compare the perspectives of the Cas A LE dust concentrations with recent
three-dimensional modeling of the SN remnant (SNR) and note that the location
having the blueshifted He I and H alpha features is roughly in the direction of
an Fe-rich outflow and in the opposite direction of the motion of the compact
object at the center of the SNR. We conclude that Cas A was an intrinsically
asymmetric SN. Future LE spectroscopy of this object, and of other historical
SNe, will provide additional insight into the connection of explosion mechanism
to SN to SNR, as well as give crucial observational evidence regarding how
stars explode.Comment: 13 pages, 7 figures, accepted for publication in Ap
The Supernova Gamma-Ray Burst Connection
The chief distinction between ordinary supernovae and long-soft gamma-ray
bursts (GRBs) is the degree of differential rotation in the inner several solar
masses when a massive star dies, and GRBs are rare mainly because of the
difficulty achieving the necessary high rotation rate. Models that do provide
the necessary angular momentum are discussed, with emphasis on a new single
star model whose rapid rotation leads to complete mixing on the main sequence
and avoids red giant formation. This channel of progenitor evolution also gives
a broader range of masses than previous models, and allows the copious
production of bursts outside of binaries and at high redshifts. However, even
the production of a bare helium core rotating nearly at break up is not, by
itself, a sufficient condition to make a gamma-ray burst. Wolf-Rayet mass loss
must be low, and will be low in regions of low metallicity. This suggests that
bursts at high redshift (low metallicity) will, on the average, be more
energetic, have more time structure, and last longer than bursts nearby. Every
burst consists of three components: a polar jet (~0.1 radian), high energy,
subrelativistic mass ejection (~1 radian), and low velocity equatorial mass
that can fall back after the initial explosion. The relative proportions of
these three components can give a diverse assortment of supernovae and high
energy transients whose properties may vary with redshift.Comment: 10 pages, to appear in AIP Conf. Proc. "Gamma Ray Bursts in the Swift
Era", Eds. S. S. Holt, N. Gehrels, J. Nouse
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