309 research outputs found
Estimating Quasi-long-range Order via Renyi Entropies
We show how entanglement entropies allow for the estimation of
quasi-long-range order in one dimensional systems whose low-energy physics is
well captured by the Tomonaga-Luttinger liquid universality class. First, we
check our procedure in the exactly solvable XXZ spin-1/2 chain in its entire
critical region, finding very good agreement with Bethe ansatz results. Then,
we show how phase transitions between different dominant orders may be
efficiently estimated by considering the superfluid-charge density wave
transition in a system of dipolar bosons. Finally, we discuss the application
of this method to multispecies systems such as the one dimensional Hubbard
model. Our work represent the first proof of a direct relationship between the
Luttinger parameter and R\'enyi entropies in both bosonics and fermionic
lattice models.Comment: v2: minimal changes, 6 pages, 7 figures, accepted for publication in
Phys. Rev.
No trace of a single-degenerate companion in late spectra of SNe 2011fe and 2014J
Left-over, ablated material from a possible non-degenerate companion can
reveal itself after about one year in spectra of Type Ia SNe (SNe Ia). We have
searched for such material in spectra of SN 2011fe (at 294 days after the
explosion) and for SN 2014J (315 days past explosion). The observations are
compared with numerical models simulating the expected line emission. The
spectral lines sought for are H-alpha, [O I] 6300 and [Ca II] 7291,7324, and
the expected width of these lines is about 1000 km/s. No signs of these lines
can be traced in any of the two supernovae. When systematic uncertainties are
included, the limits on hydrogen-rich ablated gas in SNe 2011fe and 2014J are
0.003 M_sun and 0.0085 M_sun, respectively, where the limit for SN 2014J is the
second lowest ever, and the limit for SN 2011fe is a revision of a previous
limit. Limits are also put on helium-rich ablated gas. These limits are used,
in conjunction with other data, to argue that these supernovae can stem from
double-degenerate systems, or from single-degenerate systems with a spun
up/spun down super-Chandrasekhar white dwarf. For SN 2011fe, other types of
hydrogen-rich donors can likely be ruled out, whereas for SN 2014J a
main-sequence donor system with large intrinsic separation is still possible.
Helium-rich donor systems cannot be ruled out for any of the two supernovae,
but the expected short delay time for such progenitors makes this possibility
less likely, especially for SN 2011fe. The broad [Ni II] 7378 emission in SN
2014J is redshifted by about +1300 km/s, as opposed to the known blueshift of
roughly -1100 km/s for SN 2011fe. [Fe II] 7155 is also redshifted in SN 2014J.
SN 2014J belongs to a minority of SNe Ia that both have a nebular redshift of
[Fe II] 7155 and [Ni II] 7378, and a slow decline of the Si II 6355 absorption
trough just after B-band maximum.Comment: 13 pages, submitted to A&
Critical properties and R\'enyi entropies of the spin-3/2 XXZ chain
We discuss entanglement and critical properties of the spin-3/2 XXZ chain in
its entire gapless region. Employing density-matrix renormalization group
calculations combined with different methods based on level spectroscopy,
correlation functions and entanglement entropies, we determine the sound
velocity and the Luttinger parameter of the model as a function of the
anisotropy parameter. Then, we focus on entanglement properties by
systematically studying the behavior of R\'enyi entropies under both open and
periodic boundary conditions, providing further evidence of recent findings
about entanglement entropies of excited states in conformal field theory.Comment: 8 pages, 10 figures; small text revisions and a new figure. Accepted
for publication in Phys. Rev.
UAVS TO ASSESS THE EVOLUTION OF EMBRYO DUNES
The balance of a coastal environment is particularly complex: the continuous formation of dunes, their destruction as a result of violent storms, the growth of vegetation and the consequent growth of the dunes themselves are phenomena that significantly affect this balance. This work presents an approach to the long-term monitoring of a complex dune system by means of Unmanned Aerial Vehicles (UAVs). Four different surveys were carried out between November 2015 and November 2016. Aerial photogrammetric data were acquired during flights by a DJI Phantom 2 and a DJI Phantom 3 with cameras in a nadiral arrangement. GNSS receivers in Network Real Time Kinematic (NRTK) mode were used to frame models in the European Terrestrial Reference System. Processing of the captured images consisted in reconstruction of a three-dimensional model using the principles of Structure from Motion (SfM). Particular care was necessary due to the vegetation: filtering of the dense cloud, mainly based on slope detection, was performed to minimize this issue. Final products of the SfM approach were represented by Digital Elevation Models (DEMs) of the sandy coastal environment. Each model was validated by comparison through specially surveyed points. Other analyses were also performed, such as cross sections and computing elevation variations over time. The use of digital photogrammetry by UAVs is particularly reliable: fast acquisition of the images, reconstruction of high-density point clouds, high resolution of final elevation models, as well as flexibility, low cost and accuracy comparable with other available techniques
The Carnegie Supernova Project I: methods to estimate host-galaxy reddening of stripped-envelope supernovae
We aim to improve upon contemporary methods to estimate host-galaxy reddening
of stripped-envelope (SE) supernovae (SNe). To this end the Carnegie Supernova
Project (CSP-I) SE SNe photometry data release, consisting of nearly three
dozen objects, is used to identify a minimally reddened sub-sample for each
traditionally defined spectroscopic sub-types (i.e, SNe~IIb, SNe~Ib, SNe~Ic).
Inspection of the optical and near-infrared (NIR) colors and color evolution of
the minimally reddened sub-samples reveals a high degree of homogeneity,
particularly between 0d to +20d relative to B-band maximum. This motivated the
construction of intrinsic color-curve templates, which when compared to the
colors of reddened SE SNe, yields an entire suite of optical and NIR color
excess measurements. Comparison of optical/optical vs. optical/NIR color excess
measurements indicates the majority of the CSP-I SE SNe suffer relatively low
amounts of reddening and we find evidence for different R_(V)^(host) values
among different SE SN. Fitting the color excess measurements of the seven most
reddened objects with the Fitzpatrick (1999) reddening law model provides
robust estimates of the host visual-extinction A_(V)^(host) and R_(V)^(host).
In the case of the SE SNe with relatively low amounts of reddening, a preferred
value of R_(V)^(host) is adopted for each sub-type, resulting in estimates of
A_(V)^(host) through Fitzpatrick (1999) reddening law model fits to the
observed color excess measurements. Our analysis suggests SE SNe reside in
galaxies characterized by a range of dust properties. We also find evidence SNe
Ic are more likely to occur in regions characterized by larger R_(V)^(host)
values compared to SNe IIb/Ib and they also tend to suffer more extinction.
These findings are consistent with work in the literature suggesting SNe Ic
tend to occur in regions of on-going star formation.Comment: Abstract abridged to fit allowed limit. Resubmitted to A&A, 34 pages,
19 figures, 6 tables. Constructive comments welcome
Three-dimensional distribution of ejecta in Supernova 1987A at 10 000 days
Due to its proximity, SN 1987A offers a unique opportunity to directly
observe the geometry of a stellar explosion as it unfolds. Here we present
spectral and imaging observations of SN 1987A obtained ~10,000 days after the
explosion with HST/STIS and VLT/SINFONI at optical and near-infrared
wavelengths. These observations allow us to produce the most detailed 3D map of
H-alpha to date, the first 3D maps for [Ca II] \lambda \lambda 7292, 7324, [O
I] \lambda \lambda 6300, 6364 and Mg II \lambda \lambda 9218, 9244, as well as
new maps for [Si I]+[Fe II] 1.644 \mu m and He I 2.058 \mu m. A comparison with
previous observations shows that the [Si I]+[Fe II] flux and morphology have
not changed significantly during the past ten years, providing evidence that it
is powered by 44Ti. The time-evolution of H-alpha shows that it is
predominantly powered by X-rays from the ring, in agreement with previous
findings. All lines that have sufficient signal show a similar large-scale 3D
structure, with a north-south asymmetry that resembles a broken dipole. This
structure correlates with early observations of asymmetries, showing that there
is a global asymmetry that extends from the inner core to the outer envelope.
On smaller scales, the two brightest lines, H-alpha and [Si I]+[Fe II] 1.644
\mu m, show substructures at the level of ~ 200 - 1000 km/s and clear
differences in their 3D geometries. We discuss these results in the context of
explosion models and the properties of dust in the ejecta.Comment: Accepted for publication in Ap
The bumpy light curve of supernova iPTF13z
A Type IIn supernova (SN) is dominated by the interaction of SN ejecta with
the circumstellar medium (CSM). Some SNe IIn (e.g., SN 2006jd) have episodes of
re-brightening ("bumps") in their light curves. We present iPTF13z, a SN IIn
discovered by the intermediate Palomar Transient Factory (iPTF) and
characterised by several bumps in its light curve. We analyse this peculiar
behaviour trying to infer the properties of the CSM and of the SN explosion, as
well as the nature of its progenitor star. We obtained multi-band optical
photometry for over 1000 days after discovery with the P48 and P60 telescopes
at Palomar Observatory. We obtained low-resolution optical spectra in the same
period. We did an archival search for progenitor outbursts. We analyse our
photometry and spectra, and compare iPTF13z to other SNe IIn. A simple
analytical model is used to estimate properties of the CSM. iPTF13z was a SN
IIn showing a light curve with five bumps during its decline phase. The bumps
had amplitudes between 0.4 and 0.9 mag and durations between 20 and 120 days.
The most prominent bumps appeared in all our different optical bands. The
spectra showed typical SN IIn characteristics, with emission lines of H
(with broad component FWHM ~ and narrow
component FWHM ~) and He I, but also with Fe II, Ca II,
Na I D and H P-Cygni profiles (with velocities of ~ ). A pre-explosion outburst was identified lasting days,
with mag around 210 days before discovery. Large, variable
progenitor mass-loss rates (~> 0.01 ) and CSM densities
(~> 10 g cm) are derived. We suggest that the light curve bumps
of iPTF13z arose from SN ejecta interacting with denser regions in the CSM,
possibly produced by the eruptions of a luminous blue variable star.Comment: Version 2: Update to match published paper. 21 pages, 14 figures,
abstract abridged to comply with arXiv length limit. In version 1 of the
paper on arXiv, Table 3 had some erroneous entries. Table 3 is now corrected
and available via VizieR. Version 1 comment: Accepted for publication in
Astronomy & Astrophysics (24 pages, 14 figures, abstract abridged by 20 % not
to exceed the arXiv length limit
Metallicity from Type II supernovae from the (i)PTF
Type IIP supernovae (SNe IIP) have recently been proposed as metallicity (Z) probes. The spectral models of Dessart et al. (2014, MNRAS, 440, 1856) showed that the pseudo-equivalent width of Fe ii λ5018 (pEW 5018 ) during the plateau phase depends on the primordial Z, but there was a paucity of SNe IIP exhibiting pEW 5018 that were compatible with Z < 0.4 Z ⊙ . This lack might be due to some physical property of the SN II population or to the fact that those SNe have been discovered in luminous, metal-rich targeted galaxies. Here we use SN II observations from the untargeted (intermediate) Palomar Transient Factory [(i)PTF] survey, aiming to investigate the pEW 5018 distribution of this SN population and, in particular, to look for the presence of SNe II at lower Z. We perform pEW 5018 measurements on the spectra of a sample of 39 (i)PTF SNe II, selected to have well-constrained explosion epochs and light-curve properties. Based on the comparison with the pEW 5018 spectral models, we subgrouped our SNe into four Z bins from Z ≈ 0.1 Z ⊙ up to Z ≈ 2 Z ⊙ . We also independently investigated the Z of the hosts by using their absolute magnitudes and colors and, in a few cases, using strong-line diagnostics from spectra. We searched for possible correlations between SN observables, such as their peak magnitudes and the Z inferred from pEW 5018 . We found 11 events with pEW 5018 that were small enough to indicate Z ≈ 0.1 Z ⊙ . The trend of pEW 5018 with Z matches the Z estimates obtained from the host-galaxy photometry, although the significance of the correlation is weak. We also found that SNe with brighter peak magnitudes have smaller pEW 5018 and occur at lower Z. © ESO, 2016
Interacting supernovae and supernova impostors. SN 2007sv: the major eruption of a massive star in UGC 5979
We report the results of the photometric and spectroscopic monitoring
campaign of the transient SN 2007sv. The observables are similar to those of
type IIn supernovae, a well-known class of objects whose ejecta interact with
pre-existing circum-stellar material. The spectra show a blue continuum at
early phases and prominent Balmer lines in emission, however, the absolute
magnitude at the discovery of SN 2007sv (M_R = - 14.25 +/- 0.38) indicate it to
be most likely a supernova impostor. This classification is also supported by
the lack of evidence in the spectra of very high velocity material as expected
in supernova ejecta. In addition we find no unequivocal evidence of broad lines
of alpha - and/or Fe-peak elements. The comparison with the absolute light
curves of other interacting objects (including type IIn supernovae) highlights
the overall similarity with the prototypical impostor SN 1997bs. This supports
our claim that SN 2007sv was not a genuine supernova, and was instead a
supernova impostor, most likely similar to the major eruption of a luminous
blue variable.Comment: Accepted for publication in MNRAS. 15 pages, 11 figures, 5 table
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