1,019 research outputs found
A spectroscopic look at the gravitationally lensed type Ia SN 2016geu at z=0.409
The spectacular success of type Ia supernovae (SNe Ia) in SN-cosmology is
based on the assumption that their photometric and spectroscopic properties are
invariant with redshift. However, this fundamental assumption needs to be
tested with observations of high-z SNe Ia. To date, the majority of SNe Ia
observed at moderate to large redshifts (0.4 < z < 1.0) are faint, and the
resultant analyses are based on observations with modest signal-to-noise ratios
that impart a degree of ambiguity in their determined properties. In rare cases
however, the Universe offers a helping hand: to date a few SNe Ia have been
observed that have had their luminosities magnified by intervening galaxies and
galaxy clusters acting as gravitational lenses. In this paper we present
long-slit spectroscopy of the lensed SNe Ia 2016geu, which occurred at a
redshift of z=0.409, and was magnified by a factor of ~55 by a galaxy located
at z=0.216. We compared our spectra, which were obtained a couple weeks to a
couple months past peak light, with the spectroscopic properties of
well-observed, nearby SNe Ia, finding that SN 2016geu's properties are
commensurate with those of SNe Ia in the local universe. Based primarily on the
velocity and strength of the Si II 6355 absorption feature, we find that SN
2016geu can be classified as a high-velocity, high-velocity gradient and
"core-normal" SN Ia. The strength of various features (measured though their
pseudo-equivalent widths) argue against SN 2016geu being a faint, broad-lined,
cool or shallow-silicon SN Ia. We conclude that the spectroscopic properties of
SN 2016geu imply that it is a normal SN Ia, and when taking previous results by
other authors into consideration, there is very little, if any, evolution in
the observational properties of SNe Ia up to z~0.4. [Abridged]Comment: 12 pages, 5 figures, 4 tables. Submitted to MNRAS. Comments welcome
The Classification of Highly Supersymmetric Supergravity Solutions
The spinorial geometry method is an effective method for constructing
systematic classifications of supersymmetric supergravity solutions. Recent
work on analysing highly supersymmetric solutions in type IIB supergravity
using this method is reviewed [arXiv:hep-th/0606049, arXiv:0710.1829]. It is
shown that all supersymmetric solutions of IIB supergravity with more than 28
Killing spinors are locally maximally supersymmetric.Comment: 23 pages, latex. To appear in the proceedings of the Special Metrics
and Supersymmetry conference at Universidad del Pais Vasco, May 2008.
References correcte
Network oscillations at the boundary of an equatorial coronal hole
We investigate intensity oscillations observed simultaneously in the quiet
chromosphere and in the corona, above an enhanced network area at the boundary
of an equatorial coronal hole. A Fourier analysis is applied to a sequence of
images observed in the 171 A and 1600 A passbands of TRACE. Four interesting
features above the magnetic network are further investigated by using a wavelet
analysis. Our results reveal that, in both the 171 A and 1600 A passbands,
oscillations above the magnetic network show a lack of power at high
frequencies (5.0-8.3 mHz), and a significant power at low (1.3-2.0 mHz) and
intermediate frequencies (2.6-4.0 mHz). The global 5-min oscillation is clearly
present in the 4 analyzed features when seen in the 1600 A passband, and is
also found with enhanced power in feature 1 (leg of a large coronal loop) and
feature 2 (legs of a coronal bright point loop) when seen in the 171 A
passband. Two features above an enhanced network element (feature 3 and feature
4) show repeated propagating behaviors with a dominant period of 10 min and 5
min, respectively. We suggest these oscillations are likely to be slow
magneto-acoustic waves propagating along inclined magnetic field lines, from
the lower solar atmosphere into the corona. The energy flux carried by these
waves is estimated of the order of 40 erg cm\^{-2} s\^{-1} for the 171 A
passband and is far lower than the energy required to heat the quiet corona.
For the 1600 A passband, the energy flux is about 1.4*10^6 erg cm\^{-2}
s\^{-1}, which is about one third of the required energy budget for the
chromosphere.Comment: 7 pages, 8 figure
The host of the Type I SLSN 2017egm: A young, sub-solar metallicity environment in a massive spiral galaxy
Here we present an integral-field study of the massive, high-metallicity
spiral NGC 3191, the host of SN 2017egm, the closest SLSN Type I to date. We
use data from PMAS/CAHA and the public MaNGA survey to shed light on the
properties of the SLSN site and the origin of star-formation in this
non-starburst spiral galaxy. We map the physical properties different
\ion{H}{II} regions throughout the galaxy and characterize their stellar
populations using the STARLIGHT fitting code. Kinematical information allows to
study a possible interaction with its neighbouring galaxy as the origin of
recent star formation activity which could have caused the SLSN. NGC 3191 shows
intense star-formation in the western part with three large SF regions of low
metallicity. The central regions of the host have a higher metallicity, lower
specific star-formation rate and lower ionization. Modeling the stellar
populations gives a different picture: The SLSN region has two dominant stellar
populations with different ages, the youngest one with an age of 2-10 Myr and
lower metallicity, likely the population from which the SN progenitor
originated. Emission line kinematics of NGC 3191 show indications of
interaction with its neighbour MCG+08-19-017 at 45 kpc, which might be
responsible for the recent starburst. In fact, this galaxy pair has in total
hosted 4 SNe, 1988B (Type Ia), SN 2003ds (Type Ic in MCG+08-19-017), PTF10bgl
(SLSN-Type II) and 2017egm, underlying the enhanced SF in both galaxies due to
interaction. Our study shows that one has to be careful interpreting global
host and even gas properties without looking at the stellar population history
of the region. SLSNe seem to still be consistent with massive stars ( 20
M) requiring low () metallicity and those environments
can also occur in massive, late-type galaxies but not necessarily starbursts.Comment: Accepted for publication in A&A, 13 pages, 11 figures, 7 tables.
Abstract has been reduced to match arXiv form requirement
Remote Sensing Of Rice-Based Irrigated Agriculture: A Review
The âGreen Revolutionâ in rice farming of the late 1960âs denotes the beginning of the extensive breeding programs that have led to the many improved rice varieties that are now planted on more than 60% of the worldâs riceland (Khush, 1987). This revolution led to increases in yield potential of 2 to 3 times that of traditional varieties (Khush, 1987). Similar trends have also been seen in the Irrigation Areas and Districts of southern New South Wales (NSW) as the local breeding program has produced many improved varieties of rice adapted to local growing conditions since the 1960âs (Brennan et al., 1994). Increases in area of rice planted, rice quality, and paddy yield resulted (Brennan et al., 1994). Increased rice area, however, has led to the development of high water tables and risk of large tracts of land becoming salt-affected in southern NSW (Humphreys et al., 1994b). These concerns have led to various environmental regulations on rice in the region, culminating in 1994 when restrictions on rice area, soil suitability, and water consumption were fully enacted (Humphreys et al., 1994b). Strict environmental restrictions in combination with large areas of land make the management of this region a difficult task. Land managers require, among other things, a way of regulating water use, assessing or predicting crop area and productivity, and making management decisions in support of environmentally and economically sustainable agriculture. In the search for more time and cost effective methods for attaining these goals, while monitoring complex management situations, many have turned to remote sensing and Geographic Information System (GIS) technologies for assistance. The spectral information and spatial density of remote sensing data lends itself well to the measurement of large areas. Since the launch of LANDSAT-1 in 1972, this technology has been used extensively in agricultural systems for crop identification and area estimation, crop yield estimation and prediction, and crop damage assessment. The incorporation of remote sensing and GIS can also help integrate management practices and develop effective management plans. However, in order to take advantage of these tools, users must have an understanding of both what remote sensing is and what sensors are now available, and how the technology is being used in applied agricultural research. Accordingly, a description of both follows: first a description of the technology, and then how it is currently being applied. The applications of remote sensing relevant to this discussion can be separated into crop type identification; crop area measurement; crop yield; crop damage; water use/ moisture availability (ma) mapping; and water use efficiency monitoring/mapping. This report focuses on satellite remote sensing for broad-scale rice-based irrigation agricultural applications. It also discusses related regional GIS analyses that may or may not include remote sensing data, and briefly addresses other sources of finer-scale remote sensing and geospatial data as they relate to agriculture. Since a complete review of the remote sensing research was not provided in the rice literature alone, some generic agricultural issues have been learned from applications not specifically dealing with rice. Remote sensing specialists may wish to skip to section 2
Near-infrared follow-up to the May 2008 activation of SGR 1627-41
On 28 May 2008, the Swift satellite detected the first reactivation of SGR
1627-41 since its discovery in 1998.
Following this event we began an observing campaign in near infrared
wavelengths to search for a possible counterpart inside the error circle of
this SGR, which is expected to show flaring activity simultaneous to the high
energy flares or at least some variability as compared to the quiescent state.
For the follow-up we used the 0.6m REM robotic telescope at La Silla
Observatory, which allowed a fast response within 24 hours and, through
director discretionary time, the 8.2m Very Large Telescope at Paranal
Observatory. There, we observed with NACO to produce high angular resolution
imaging with the aid of adaptive optics.
These observations represent the fastest near infrared observations after an
activation of this SGR and the deepest and highest spatial resolution
observations of the Chandra error circle.
5 sources are detected in the immediate vicinity of the most precise X-ray
localisation of this source. For 4 of them we do not detect variability,
although the X-ray counterpart experimented a significant decay during our
observation period. The 5th source is only detected in one epoch, where we have
the best image quality, so no variability constrains can be imposed and remains
as the only plausible counterpart. We can impose a limit of Ks > 21.6
magnitudes to any other counterpart candidate one week after the onset of the
activity. Our adaptive optics imaging, with a resolution of 0.2" provides a
reference frame for subsequent studies of future periods of activity.Comment: Accepted for publication in A&
Polarimetry of the superluminous supernova LSQ14mo: no evidence for significant deviations from spherical symmetry
We present the first polarimetric observations of a Type I superluminous
supernova (SLSN). LSQ14mo was observed with VLT/FORS2 at five different epochs
in the V band, with the observations starting before maximum light and spanning
26 days in the rest frame (z=0.256). During this period, we do not detect any
statistically significant evolution (< 2) in the Stokes parameters. The
average values we obtain, corrected for interstellar polarisation in the
Galaxy, are Q = -0.01% ( 0.15%) and U = - 0.50% ( 0.14%). This low
polarisation can be entirely due to interstellar polarisation in the SN host
galaxy. We conclude that, at least during the period of observations and at the
optical depths probed, the photosphere of LSQ14mo does not present significant
asymmetries, unlike most lower-luminosity hydrogen-poor SNe Ib/c.
Alternatively, it is possible that we may have observed LSQ14mo from a special
viewing angle. Supporting spectroscopy and photometry confirm that LSQ14mo is a
typical SLSN I. Further studies of the polarisation of Type I SLSNe are
required to determine whether the low levels of polarisation are a
characteristic of the entire class and to also study the implications for the
proposed explosion models.Comment: ApJ Letters, 4 Figures, 3 Tables. The previous version was accepted.
This version contains minor modifications to match proofs (as much as
possible
Variable Ly alpha sheds light on the environment surrounding GRB 090426
Long duration gamma-ray bursts are commonly associated with the deaths of
massive stars. Spectroscopic studies using the afterglow as a light source
provide a unique opportunity to unveil the medium surrounding it, probing the
densest region of their galaxies. This material is usually in a low ionisation
state and at large distances from the burst site, hence representing the normal
interstellar medium in the galaxy. Here we present the case of GRB 090426 at
z=2.609, whose optical spectrum indicates an almost fully ionised medium
together with a low column density of neutral hydrogen. For the first time, we
also observe variations in the Ly alpha absorption line. Photoionisation
modeling shows that we are probing material from the vicinity of the burst (~80
pc). The host galaxy is a complex of two luminous interacting galaxies, which
might suggest that this burst could have occurred in an isolated star-forming
region outside its host galaxy created in the interaction of the two galaxies.Comment: 11 pages, 9 figures, submitted to MNRA
The structure and dynamics of a bright point as seen with Hinode, SoHO and TRACE
Our aim is to determine the plasma properties of a coronal bright point and
compare its magnetic topology extrapolated from magnetogram data with its
appearance in X-ray images. We analyse spectroscopic data obtained with
EIS/Hinode, Ca II H and G-band images from SOT/Hinode, UV images from TRACE,
X-ray images from XRT/Hinode and high-resolution/high-cadence magnetogram data
from MDI/SoHO. The BP comprises several coronal loops as seen in the X-ray
images, while the chromospheric structure consists of tens of small bright
points as seen in Ca II H. An excellent correlation exists between the Ca II
BPs and increases in the magnetic field, implying that the Ca II H passband is
a good indicator for the concentration of magnetic flux. Doppler velocities
between 6 and 15 km/s are derived from the Fe XII and Fe XIII lines for the BP
region, while for Fe XIV and Si VII they are in the range from -15 to +15 km/s.
The coronal electron density is 3.7x10^9 cm^-3. An excellent correlation is
found between the positive magnetic flux and the X-ray light-curves. The
remarkable agreement between the extrapolated magnetic field configuration and
some of the loops composing the BP as seen in the X-ray images suggests that a
large fraction of the magnetic field in the bright point is close to potential.
The close correlation between the positive magnetic flux and the X-ray emission
suggests that energy released by magnetic reconnection is stimulated by flux
emergence or cancellation.Comment: 10 pages with 11 figures. Accepted in Astronomy and Astrophysic
Stability of gold nanowires at large Au-Au separations
The unusual structural stability of gold nanowires at large separations of
gold atoms is explained from first-principles quantum mechanical calculations.
We show that undetected light atoms, in particular hydrogen, stabilize the
experimentally observed structures, which would be unstable in pure gold wires.
The enhanced cohesion is due to the partial charge transfer from gold to the
light atoms. This finding should resolve a long-standing controversy between
theoretical predictions and experimental observations.Comment: 7 pages, 3 figure
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