395 research outputs found
Primeval very low-mass stars and brown dwarfs - IV. New L subdwarfs, Gaia astrometry, population properties, and a blue brown dwarf binary
30 pages, 23 figuresWe present 27 new L subdwarfs and classify five of them as esdL and 22 as sdL. Our L subdwarf candidates were selected with the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Spectroscopic follow-up was carried out primarily with the OSIRIS spectrograph on the Gran Telescopio Canarias. Some of these new objects were followed up with the X-shooter instrument on the Very Large Telescope. We studied the photometric properties of the population of known L subdwarfs using colour-spectral type diagrams and colour-colour diagrams, by comparison with L dwarfs and main-sequence stars, and identified new colour spaces for L subdwarf selection/study in current and future surveys. We further discussed the brown dwarf transition-zone and the observational stellar/substellar boundary. We found that about one-third of 66 known L subdwarfs are substellar objects, with two-thirds being very low-mass stars. We also present the Hertzsprung-Russell diagrams, spectral type-absolute magnitude corrections, and tangential velocities of 20 known L subdwarfs observed by the Gaia astrometry satellite. One of our L subdwarf candidates, ULAS J233227.03+123452.0, is a mildly metal-poor spectroscopic binary brown dwarf: a ~L6p dwarf and a ~T4p dwarf. This binary is likely a thick disc member according to its kinematics.Peer reviewedFinal Accepted Versio
Mesoscale eddy variability in the Caribbean Sea
The spatial distribution, and the monthly and seasonal variability of mesoscale eddy observations derived from the AVISO eddy atlas are assessed in the Caribbean Sea during 1993–2019. The average lifetime for the whole set of eddies is 62 ± 37 days, mean amplitude of 7 ± 4 cm for cyclonic and 7 ± 4 cm for anticyclonic and mean radius of 100 ± 31 km for cyclonic and 108 ± 32 km for anticyclonic. Cyclonic eddies are on average more nonlinear than anticyclonic ones. The spatio-temporal variability in the number of eddy observations is evaluated against the Mean Eddy Kinetic Energy (MEKE) derived from geostrophic currents as well as from seasonal winds. Spatial distribution of eddy observations is correlated with MEKE while the migration of the intertropical convergence zone explains the advection of eddies towards the southern part of the basin.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. JMS received the joint funding from the Generalitat Valenciana and the European Social Fund under Grant APOSTD/2020/254. AO received financial support from projects Mocca and Lamarca (grants # RTI2018-093941-B-C31 and PID2021-123352OB-C31) funded by MCIN/AEI/ and by “ERDF A way of making Europe”, and from Fundación Iberostar and Université de Toulon-VAR. MELA is funded by Corporación CE-Marin through Convocatoria 14, 2018 supporting PhD candidates
Using the second-order information for reconfigurability analysis and design in the fault tolerant framework
The control reconfigurability measure defines the capability of a control system to allow recovery of performance when faults occur; therefore, it has been intended to be a tool for designing and synthesizing approaches in the fault tolerant control context. Reconfigurability depends on the controllability gramian, also known as the second-order information (SOI) in a broad sense. This paper proposes the assignation, by feedback, of the deterministic SOI in order to set the control reconfigurability of a given linear system. The theory concerned with this assignation is reviewed, then constructive theorems are given for finding constant feedback gains that approximate a required control reconfigurability for ease implementation. Also an unification of the reconfigurability measures proposed in the fault tolerance literature is given. Once the SOI is assigned by feedback, it can be computed online by using an identification method, which uses process input/output data. Results from simulation of the three tanks hydraulic benchmark, show that this approach can provide information about the system performance for fault tolerant purposes, thus online control reconfigurability computation and fault accommodation are considered. The approach presented in the paper gives an alternative for supervision taking into account the reconfigurability assigned by design
High contrast optical imaging of companions: the case of the brown dwarf binary HD-130948BC
High contrast imaging at optical wavelengths is limited by the modest
correction of conventional near-IR optimized AO systems.We take advantage of
new fast and low-readout-noise detectors to explore the potential of fast
imaging coupled to post-processing techniques to detect faint companions to
stars at small separations. We have focused on I-band direct imaging of the
previously detected brown dwarf binary HD130948BC,attempting to spatially
resolve the L2+L2 benchmark system. We used the Lucky-Imaging instrument
FastCam at the 2.5-m Nordic Telescope to obtain quasi diffraction-limited
images of HD130948 with ~0.1" resolution.In order to improve the detectability
of the faint binary in the vicinity of a bright (I=5.19 \pm 0.03) solar-type
star,we implemented a post-processing technique based on wavelet transform
filtering of the image which allows us to strongly enhance the presence of
point-like sources in regions where the primary halo dominates. We detect for
the first time the BD binary HD130948BC in the optical band I with a SNR~9 at
2.561"\pm 0.007" (46.5 AU) from HD130948A and confirm in two independent
dataset that the object is real,as opposed to time-varying residual speckles.We
do not resolve the binary, which can be explained by astrometric results
posterior to our observations that predict a separation below the NOT
resolution.We reach at this distance a contrast of dI = 11.30 \pm 0.11, and
estimate a combined magnitude for this binary to I = 16.49 \pm 0.11 and a I-J
colour 3.29 \pm 0.13. At 1", we reach a detectability 10.5 mag fainter than the
primary after image post-processing. We obtain on-sky validation of a technique
based on speckle imaging and wavelet-transform processing,which improves the
high contrast capabilities of speckle imaging.The I-J colour measured for the
BD companion is slightly bluer, but still consistent with what typically found
for L2 dwarfs(~3.4-3.6).Comment: accepted in A\&
Ground-based detection of an extended helium atmosphere in the Saturn-mass exoplanet WASP-69b
Hot gas giant exoplanets can lose part of their atmosphere due to strong
stellar irradiation, affecting their physical and chemical evolution. Studies
of atmospheric escape from exoplanets have mostly relied on space-based
observations of the hydrogen Lyman-{\alpha} line in the far ultraviolet which
is strongly affected by interstellar absorption. Using ground-based
high-resolution spectroscopy we detect excess absorption in the helium triplet
at 1083 nm during the transit of the Saturn-mass exoplanet WASP-69b, at a
signal-to-noise ratio of 18. We measure line blue shifts of several km/s and
post transit absorption, which we interpret as the escape of part of the
atmosphere trailing behind the planet in comet-like form.
[Additional notes by authors: Furthermore, we provide upper limits for helium
signals in the atmospheres of the exoplanets HD 209458b, KELT-9b, and GJ 436b.
We investigate the host stars of all planets with detected helium signals and
those of the three planets we derive upper limits for. In each case we
calculate the X-ray and extreme ultraviolet flux received by these planets. We
find that helium is detected in the atmospheres of planets (orbiting the more
active stars and) receiving the larger amount of irradiation from their host
stars.]Comment: Submitted to Science on 14 March 2018; Accepted by Science on 16
November 2018; Published by Science on 6 December 2018. This is the author's
version of the work. It is posted here by permission of the AAAS for personal
use. The definitive version was published in Science, on 6 December 2018 -
Report: pages 21 (preprint), 4 figures - Supplementary materials: 22 pages,
10 figures, 3 table
HRC-I/Chandra X-ray observations towards sigma Orionis
Aims: We investigated the X-ray emission from young stars and brown dwarfs in
the sigma Orionis cluster (tau~3 Ma, d~385 pc) and its relation to mass,
presence of circumstellar discs, and separation to the cluster centre by taking
advantage of the superb spatial resolution of the Chandra X-ray Observatory.
Methods: We used public HRC-I/Chandra data from a 97.6 ks pointing towards the
cluster centre and complemented them with X-ray data from IPC/Einstein,
HRI/ROSAT, EPIC/XMM-Newton, and ACIS-S/Chandra together with optical and
infrared photometry and spectroscopy from the literature and public catalogues.
On our HRC-I/Chandra data, we measured count rates, estimated X-ray fluxes, and
searched for short-term variability. We also looked for long-term variability
by comparing with previous X-ray observations. Results: Among the 107 detected
X-ray sources, there were 70 cluster stars with known signposts of youth, two
young brown dwarfs, 12 cluster member candidates, four field dwarfs, and two
galaxies with optical-infrared counterpart. The remaining sources had
extragalactic nature. Based on a robust Poisson-chi^2 analysis, nine cluster
stars displayed flares or rotational modulation during the HRC-I observations,
while other eight stars and one brown dwarf showed long-term X-ray flux
variations. We constructed a cluster X-ray luminosity function from O9.5 (~18
Msol) to M6.5 (~0.06 Msol). We found: a tendency of early-type stars in
multiple systems or with spectroscopic peculiarities to display X-ray emission,
that the two detected brown dwarfs and the least-massive star are among the
sigma Orionis objects with the highest L_X/L_J ratios, and that a large
fraction of known classical T Tauri stars in the cluster are absent in this and
other X-ray surveys. We concluded that dozens X-ray sigma Orionis stars and
brown dwarfs are still to be detected [abridged].Comment: A&A, in pres
Diseño y construcción de un fonocardiógrafo digital con visualización en LabVIEW
Un buen diagnóstico de enfermedades relacionadas con válvulas cardiacas se debería dar a partir de un
fonocardiograma capaz de suministrarle al médico una información confiable de la situación del paciente. Se presenta el diseño de
un fonocardiógrafo con la capacidad de amplificar y filtrar las señales acústicas derivadas del corazón. Posteriormente se realiza
una conversión análogo-digital de las señales para ser enviadas por puerto serial a un entorno gráfico en LabVIEW para su registro
y análisis en tiempo real.The auscultation of the heart noises has always been an important tool in medicine, a good diagnosis of illnesses
related to the heart valves should be given from a phonocardiogram able to give the doctor a reliable information of the patients
situation. The design presented is a phonocardiograph capable of amplifying and filtering the acoustic signs derived from the heart.
After an analog to digital conversion of those signs the information is sent by serial port to a graphic environment in LabVIEW for
its registration and analysis in real tim
Lucky Imaging Adaptive Optics of the brown dwarf binary GJ569Bab
The potential of combining Adaptive Optics (AO) and Lucky Imaging (LI) to
achieve high precision astrometry and differential photometry in the optical is
investigated by conducting observations of the close 0\farcs1 brown dwarf
binary GJ569Bab. We took 50000 -band images with our LI instrument FastCam
attached to NAOMI, the 4.2-m William Herschel Telescope (WHT) AO facility. In
order to extract the most of the astrometry and photometry of the GJ569Bab
system we have resorted to a PSF fitting technique using the primary star
GJ569A as a suitable PSF reference which exhibits an -band magnitude of
. The AO+LI observations at WHT were able to resolve the binary
system GJ569Bab located at 4\farcs 92 \pm 0\farcs05 from GJ569A. We measure a
separation of mas and -band magnitudes of
and and colors of 2.720.08 and 2.830.08 for
the Ba and Bb components, respectively. Our study rules out the presence of any
other companion to GJ569A down to magnitude I 17 at distances larger than
1\arcsec. The colors measured are consistent with M8.5-M9 spectral types
for the Ba and Bb components. The available dynamical, photometric and
spectroscopic data are consistent with a binary system with Ba being slightly
(10-20%) more massive than Bb. We obtain new orbital parameters which are in
good agreement with those in the literature.Comment: 13 pages, 9 figures, 7 tables, in press in MNRA
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