106 research outputs found
Unveiling the optical properties of a metamaterial synthesized by electron-beam-induced deposition
The direct writing using a focused electron beam allows for fabricating truly
three-dimensional structures of sub-wavelength dimensions in the visible
spectral regime. The resulting sophisticated geometries are perfectly suited
for studying light-matter interaction at the nanoscale. Their overall optical
response will strongly depend not only on geometry but also on the optical
properties of the deposited material. In case of the typically used
metal-organic precursors, the deposits show a substructure of metallic
nanocrystals embedded in a carbonaceous matrix. Since gold-containing precursor
media are especially interesting for optical applications, we experimentally
determine the effective permittivity of such an effective material. Our
experiment is based on spectroscopic measurements of planar deposits. The
retrieved permittivity shows a systematic dependence on the gold particle
density and cannot be sufficiently described using the common Maxwell-Garnett
approach for effective medium.Comment: 7 pages, 4 figure
The Early Asymmetries of Supernova 2008D / XRF 080109
Spectropolarimetry of the Type Ib SN 2008D, associated with the XRF 080109,
at two separate epochs, are presented. The epochs of these observations
correspond to V-band light curve maximum and 15 days after light curve maximum
(or 21 and 36 days after the XRF). We find SN 2008D to be significantly
polarized, although the largest contribution is due to the interstellar
polarization component of Q_ISP=0+/-0.1% and U_ISP=-1.2+/-0.1%. At the two
epochs, the spectropolarimetry of SN 2008D is classified as being
D1+L(HeI)+L(Ca II). The intrinsic polarization of continuum wavelength regions
is <0.4%, at both epochs, implying an asymmetry of the photosphere of <10%.
Similar to other Type Ibc SNe, such as 2005bf, 2006aj and 2007gr, we observed
significant polarization corresponding to the spectral features of Ca II, He I,
Mg I, Fe II and, possibly, O I 7774, about a close-to-spherically-symmetric
photosphere. We introduce a new plot showing the chemically distinct line
forming regions in the ejecta and comment on the apparent ubiquity of highly
polarized high-velocity Ca II features in Type Ibc SNe. The polarization angle
of Ca II IR triplet was significantly different, at both epochs, to those of
the other species, suggesting high-velocity Ca II forms in a separate part of
the ejecta. The apparent structure in the outer layers of SN 2008D has
implications for the interpretation of the early-time X-ray emission associated
with shock break-out. (abridged)Comment: ApJ Subm., 45 pages, 13 figure
Early-time Spitzer observations of the type II-Plateau supernova, 2004dj
We present mid-infrared observations with the Spitzer Space Telescope of the
nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have
obtained the first mid-IR spectra of any supernova apart from SN 1987A. A
prominent [NiII] 6.64 micron line is observed, from which we deduce that the
mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red
wing of the CO-fundamental band. We relate our findings to possible progenitors
and favour an evolved star, most likely a red supergiant, with a probable
initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted
Spectropolarimetry of the Type Ib/c SN 2005bf
We present spectropolarimetric observations of the peculiar Type Ib/c SN
2005bf, in MCG+00-27-005, from 3600-8550\AA. The SN was observed on 2005 April
30.9, 18 days after the first B-band light-curve maximum and 6 days before the
second B-band light-curve maximum. The degree of the Interstellar Polarization,
determined from depolarized emission lines in the spectrum, is found to be
large with and \fdg, but this may
be an upper limit on the real value of the ISP. After ISP subtraction,
significant polarization is observed over large wavelength regions, indicating
a significant degree of global asymmetry, . Polarizations of 3.5%
and 4% are observed for absorption components of Ca II H&K and IR triplet, and
1.3% for He I 5876\AA and Fe II. On the plane clear velocity-dependent
loop structure is observed for the He I 5876\AA line, suggestive of departures
from an axial symmetry and possible clumping of the SN ejecta. Weak High
Velocity components of , and
are observed, with velocities of -15 000\kms. The low degree
of polarization observed at H suggests that the polarization observed
for the other Balmer lines ( above the background polarization) may
rather be due to blending of and with
polarized Si II and Fe II lines, respectively. We suggest a model in which a
jet of material, that is rich in , has penetrated the C-O
core, but not the He mantle. The jet axis is tilted with respect to the axis of
the photosphere. This accounts for the lack of significant polarization of O I
7774\AA, the delayed excitation and, hence, observability of He I and,
potentially, the varied geometries of He and Ca.Comment: 12 pages, 7 figures (3 colour), MNRAS accepte
Polarimetry of the Type Ia Supernova SN 1996X
We present broad-band and spectropolarimetry of the Type Ia SN 1996X obtained
on April 14, 1996 (UT), and broad-band polarimetry of SN 1996X on May 22,1996,
when the supernova was about a week before and 4 weeks after optical maximum,
respectively. The Stokes parameters derived from the broad-band polarimetry are
consistent with zero polarization. The spectropolarimetry, however, shows broad
spectral features which are due intrinsically to an asymmetric SN atmosphere.
The spectral features in the flux spectrum and the polarization spectrum show
correlations in the wavelength range from 4900 AA up to 5500 AA. The degree of
this intrinsic component is low (<0.3 %). Theoretical polarization spectra have
been calculated. It is shown that the polarization spectra are governed by line
blending. Consequently, for similar geometrical distortions, the residual
polarization is smaller by about a factor of 2 to 3 compared to the less
blended Type II atmosphere, making it intrinsically harder to detect
asphericities in SNIa. Comparison with theoretical model polarization spectra
shows a resemblance to the observations. Taken literally, this implies an
asphericity of about 11 % in the chemical distribution in the region of partial
burning. This may not imperil the use of Type Ia supernovae as standard candles
for distance determination, but nontheless poses a source of uncertainty. SN
1996X is the first Type Ia supernova for which spectropolarimetry revealed a
polarized component intrinsic to the supernova and the first Type Ia with
spectropolarimetry well prior to optical maximum.Comment: 7 pages, 5 figures, macros 'aas2pp4.sty,psfig.tex'. LaTeX Style.
Astrophysical Journal Letters, submitted September 199
A Study of Carbon Features in Type Ia Supernova Spectra
One of the major differences between various explosion scenarios of Type Ia
supernovae (SNe Ia) is the remaining amount of unburned (C+O) material and its
velocity distribution within the expanding ejecta. While oxygen absorption
features are not uncommon in the spectra of SNe Ia before maximum light, the
presence of strong carbon absorption has been reported only in a minority of
objects, typically during the pre-maximum phase. The reported low frequency of
carbon detections may be due to low signal-to-noise data, low abundance of
unburned material, line blending between C II 6580 and Si II 6355, ejecta
temperature differences, asymmetrical distribution effects, or a combination of
these. However, a survey of published pre-maximum spectra reveals that more SNe
Ia than previously thought may exhibit C II 6580 absorption features and relics
of line blending near 6300 Angstroms. Here we present new SN Ia observations
where spectroscopic signatures of C II 6580 are detected, and investigate the
presence of C II 6580 in the optical spectra of 19 SNe Ia using the
parameterized spectrum synthesis code, SYNOW. Most of the objects in our sample
that exhibit C II 6580 absorption features are of the low-velocity gradient
subtype. Our study indicates that the morphology of carbon-rich regions is
consistent with either a spherical distribution or a hemispheric asymmetry,
supporting the recent idea that SN Ia diversity may be a result of off-center
ignition coupled with observer line-of-sight effects.Comment: 10 papges, 9 figures, 3 table
An independent determination of the distance to supernova SN 1987A by means of the light echo AT 2019xis
Accurate distance determination to astrophysical objects is essential for the
understanding of their intrinsic brightness and size. The distance to SN 1987A
has been previously measured by the expanding photosphere method, and by using
the angular size of the circumstellar rings with absolute sizes derived from
light curves of narrow UV emission lines, with reported distances ranging from
46.77 kpc to 55 kpc. In this study, we independently determined the distance to
SN 1987A using photometry and imaging polarimetry observations of AT 2019xis, a
light echo of SN 1987A, by adopting a radiative transfer model of the light
echo developed in Ding et al. (2021). We obtained distances to SN 1987A in the
range from 49.09 2.16 kpc to 59.39 3.27 kpc, depending on the
interstellar polarization and extinction corrections, which are consistent with
the literature values. This study demonstrates the potential of using light
echoes as a tool for distance determination to astrophysical objects in the
Milky Way, up to kiloparsec level scales.Comment: Accepted for publication in ApJ
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