2,239 research outputs found
Impact of Si nanocrystals in a-SiOx<Er> in C-Band emission for applications in resonators structures
Si nanocrystals (Si-NC) in a-SiOx were created by high temperature
annealing. Si-NC samples have large emission in a broadband region, 700nm to
1000nm. Annealing temperature, annealing time, substrate type, and erbium
concentration is studied to allow emission at 1550 nm forsamples with erbium.
Emission in the C-Band region is largely reduced by the presence of Si-NC. This
reduction may be due to less efficient energy transfer processes from the
nanocrystals than from the amorphous matrix to the Er3+ ions, perhaps due to
the formation of more centro-symmetric Er3+ sites at the nanocrystal surfaces
or to very different optimal erbium concentrations between amorphous and
crystallized samples.Comment: 3 pages, 4 figure
Impact of stellar companions on precise radial velocities
Context: With the announced arrival of instruments such as ESPRESSO one can
expect that several systematic noise sources on the measurement of precise
radial velocity will become the limiting factor instead of photon noise. A
stellar companion within the fiber is such a possible noise source. Aims: With
this work we aim at characterizing the impact of a stellar companion within the
fiber to radial velocity measurements made by fiber-fed spectrographs. We
consider the contaminant star either to be part of a binary system whose
primary star is the target star, or as a background/foreground star. Methods:
To carry out our study, we used HARPS spectra, co-added the target with
contaminant spectra, and then compared the resulting radial velocity with that
obtained from the original target spectrum. We repeated this procedure and used
different tunable knobs to reproduce the previously mentioned scenarios.
Results: We find that the impact on the radial velocity calculation is a
function of the difference between individual radial velocities, of the
difference between target and contaminant magnitude, and also of their spectral
types. For the worst-case scenario in which both target and contaminant star
are well centered on the fiber, the maximum contamination for a G or K star may
be higher than 10 cm/s, on average, if the difference between target and
contaminant magnitude is < 10, and higher than 1 m/s if <
8. If the target star is of spectral type M, < 8 produces the same
contamination of 10 cm/s, and a contamination may be higher than 1 m/sComment: Accepted for publication in A&A on 29/12/2019 - 14 page
The quantum brachistochrone problem for non-Hermitian Hamiltonians
Recently Bender, Brody, Jones and Meister found that in the quantum brachistochrone problem the passage time needed for the evolution of certain initial states into specified final states can be made arbitrarily small, when the time-evolution operator is taken to be non-Hermitian but PT-symmetric. Here we demonstrate that such phenomena can also be obtained for non-Hermitian Hamiltonians for which PT-symmetry is completely broken, i.e. dissipative systems. We observe that the effect of a tunable passage time can be achieved by projecting between orthogonal eigenstates by means of a time-evolution operator associated with a non-Hermitian Hamiltonian. It is not essential that this Hamiltonian is PT-symmetric
Impact of micro-telluric lines on precise radial velocities and its correction
Context: In the near future, new instruments such as ESPRESSO will arrive,
allowing us to reach a precision in radial-velocity measurements on the order
of 10 cm/s. At this level of precision, several noise sources that until now
have been outweighed by photon noise will start to contribute significantly to
the error budget. The telluric lines that are not neglected by the masks for
the radial velocity computation, here called micro-telluric lines, are one such
noise source. Aims: In this work we investigate the impact of micro-telluric
lines in the radial velocities calculations. We also investigate how to correct
the effect of these atmospheric lines on radial velocities. Methods: The work
presented here follows two parallel lines. First, we calculated the impact of
the micro-telluric lines by multiplying a synthetic solar-like stellar spectrum
by synthetic atmospheric spectra and evaluated the effect created by the
presence of the telluric lines. Then, we divided HARPS spectra by synthetic
atmospheric spectra to correct for its presence on real data and calculated the
radial velocity on the corrected spectra. When doing so, one considers two
atmospheric models for the synthetic atmospheric spectra: the LBLRTM and TAPAS.
Results: We find that the micro-telluric lines can induce an impact on the
radial velocities calculation that can already be close to the current
precision achieved with HARPS, and so its effect should not be neglected,
especially for future instruments such as ESPRESSO. Moreover, we find that the
micro-telluric lines' impact depends on factors, such as the radial velocity of
the star, airmass, relative humidity, and the barycentric Earth radial velocity
projected along the line of sight at the time of the observation.Comment: Accepted in A&
Eclipsing binaries and fast rotators in the Kepler sample. Characterization via radial velocity analysis from Calar Alto
The Kepler mission has provided high-accurate photometric data in a long time
span for more than two hundred thousands stars, looking for planetary transits.
Among the detected candidates, the planetary nature of around 15% has been
established or validated by different techniques. But additional data is needed
to characterize the rest of the candidates and reject other possible
configurations. We started a follow-up program to validate, confirm, and
characterize some of the planet candidates. In this paper we present the radial
velocity analysis (RV) of those presenting large variations, compatible with
being eclipsing binaries. We also study those showing large rotational
velocities, which prevents us from obtaining the necessary precision to detect
planetary-like objects. We present new RV results for 13 Kepler objects of
interest (KOIs) obtained with the CAFE spectrograph at the Calar Alto
Observatory, and analyze their high-spatial resolution images and the Kepler
light curves of some interesting cases. We have found five spectroscopic and
eclipsing binaries. Among them, the case of KOI-3853 is of particular interest.
This system is a new example of the so-called heartbeat stars, showing dynamic
tidal distortions in the Kepler light curve. We have also detected duration and
depth variations of the eclipse. We suggest possible scenarios to explain such
effect, including the presence of a third substellar body possibly detected in
our RV analysis. We also provide upper mass limits to the transiting companions
of other six KOIs with large rotational velocities. This property prevents the
RV method to obtain the necessary precision to detect planetary-like masses.
Finally, we analyze the large RV variations of other two KOIs, incompatible
with the presence of planetary-mass objects. These objects are likely to be
stellar binaries but a longer timespan is still needed.Comment: Accepted for publication in A&A. 18 pages, 9 figures, 17 tables. This
version fixes an error affecting the values of tables A.1-A.13. The text
remains unaltere
Kepler-447b: a hot-Jupiter with an extremely grazing transit
We present the radial velocity confirmation of the extrasolar planet
Kepler-447b, initially detected as a candidate by the Kepler mission. In this
work, we analyze its transit signal and the radial velocity data obtained with
the Calar Alto Fiber-fed Echelle spectrograph (CAFE). By simultaneously
modeling both datasets, we obtain the orbital and physical properties of the
system. According to our results, Kepler-447b is a Jupiter-mass planet
(), with an estimated radius of
(uncertainties provided in this work are
unless specified). This translates into a sub-Jupiter density. The
planet revolves every days in a slightly eccentric orbit
() around a G8V star with detected activity in the
Kepler light curve. Kepler-447b transits its host with a large impact parameter
(), being one of the few planetary grazing transits
confirmed so far and the first in the Kepler large crop of exoplanets. We
estimate that only around 20% of the projected planet disk occults the stellar
disk. The relatively large uncertainties in the planet radius are due to the
large impact parameter and short duration of the transit. Planets with such an
extremely large impact parameter can be used to detect and analyze interesting
configurations such as additional perturbing bodies, stellar pulsations,
rotation of a non-spherical planet, or polar spot-crossing events. All these
scenarios would periodically modify the transit properties (depth, duration,
and time of mid-transit), what could be detectable with sufficient accurate
photometry. Short-cadence photometric data (at the 1 minute level) would help
in the search for these exotic configurations in grazing planetary transits
like that of Kepler-447b.Comment: Accepted for publication in A&A. 13 pages, 8 figures, 4 tables. This
version replaces an earlier version of the pape
Resynchronizing classes of word relations
A natural approach to defining binary word relations over a finite alphabet A is through two-tape finite state automata, which can be seen as regular language L over {1,2} x A, where (i,a) is interpreted as reading letter a from tape i. Thus, a word w of the language L denotes the pair (u_1,u_2) in A* x A* in which u_i is the projection of w onto i-labelled letters. While this formalism defines the well-studied class of Rational relations (a.k.a. non-deterministic finite state transducers), enforcing restrictions on the reading regime from the tapes, that we call synchronization, yields various sub-classes of relations. Such synchronization restrictions are imposed through regular properties on the projection of the language onto {1,2}. In this way, for each regular language C contained in {1,2}*, one obtains a class Rel(C) of relations, such as the classes of Regular, Recognizable, or length-preserving relations, as well as (infinitely) many other classes. We study the problem of containment for synchronized classes of relations: given C,D subsets of {1,2}*, is Rel(C) contained in Rel(D)? We show a characterization in terms of C and D which gives a decidability procedure to test for class inclusion. This also yields a procedure to re-synchronize languages from {1,2} x A preserving the denoted relation whenever the inclusion holds
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