704 research outputs found
Detection of magnetic moment in thin films with a home-made vibrating sample magnetometer
This paper explores the optimization of an array of pick-up coils in a home-made vibrating sample magnetometer for the detection of magnetic moment in thin films. Sensitivity function of a 4-coils Mallinson configuration was numerically studied for the determination of the physical dimensions that enhance the sensitivity of the magnetometer. By performing numerical simulations using the Biot-Savart law combined with the principle of reciprocity we were able to determine the maximum values of sensitivity and the influence of the separation of the coils on the sensitivity function. After the optimization of the pick-up coils, the vibrating sample magnetometer was able to detect the magnetic moment of a 100 nm-thickness Fe19Ni81 magnetic thin film along and perpendicular to the in-plane anisotropy easy axis. The implemented vibrating sample magnetometer is able to detect changes in the magnetic moment of ∼2 × 10-4 emu.Fil: Jordán, D.. Universidad Nacional de Ingeniería. Facultad de Ciencias; PerúFil: González Chávez, D.. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Laura, D.. Universidad Nacional de Ingeniería. Facultad de Ciencias; PerúFil: Leon Hilario, Ludwin Misael. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Ingeniería. Facultad de Ciencias; PerúFil: Monteblanco, E.. Universite de Lorraine; FranciaFil: Gutarra Espinoza, Abel. Universidad Nacional de Ingeniería. Facultad de Ciencias; PerúFil: Aviles Felix, Luis Steven. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
K2-113b: A dense hot-Jupiter transiting a solar analogue
We present the discovery of K2-113b, a dense hot-Jupiter discovered using
photometry from Campaign 8 of the Kepler-2 (K2) mission and high-resolution
spectroscopic follow up obtained with the FEROS spectrograph. The planet orbits
a solar analogue in a day orbit,
has a radius of and a mass of
. With a density of gr/cm,
the planet is among the densest systems known having masses below 2 and
, and is just above the temperature limit at which inflation
mechanisms are believed to start being important. Based on its mass and radius,
we estimate that K2-113b should have a heavy element content on the order of
110 or greater.Comment: 8 pages, 7 figures. Accepted to MNRAS; added new photometry from
newest version of EVEREST, which allows for a constrain on the secondary
eclipse dept
Simulating Food Web Dynamics along a Gradient: Quantifying Human Influence
Realistically parameterized and dynamically simulated food-webs are useful tool to explore the importance of the functional diversity of ecosystems, and in particular relations between the dynamics of species and the whole community. We present a stochastic dynamical food web simulation for the Kelian River (Borneo). The food web was constructed for six different locations, arrayed along a gradient of increasing human perturbation (mostly resulting from gold mining activities) along the river. Along the river, the relative importance of grazers, filterers and shredders decreases with increasing disturbance downstream, while predators become more dominant in governing eco-dynamics. Human activity led to increased turbidity and sedimentation which adversely impacts primary productivity. Since the main difference between the study sites was not the composition of the food webs (structure is quite similar) but the strengths of interactions and the abundance of the trophic groups, a dynamical simulation approach seemed to be useful to better explain human influence. In the pristine river (study site 1), when comparing a structural version of our model with the dynamical model we found that structurally central groups such as omnivores and carnivores were not the most important ones dynamically. Instead, primary consumers such as invertebrate grazers and shredders generated a greater dynamical response. Based on the dynamically most important groups, bottom-up control is replaced by the predominant top-down control regime as distance downstream and human disturbance increased. An important finding, potentially explaining the poor structure to dynamics relationship, is that indirect effects are at least as important as direct ones during the simulations. We suggest that our approach and this simulation framework could serve systems-based conservation efforts. Quantitative indicators on the relative importance of trophic groups and the mechanistic modeling of eco-dynamics could greatly contribute to understanding various aspects of functional diversity
The Mass-Radius Relationship for Very Low Mass Stars: Four New Discoveries from the HATSouth Survey
We report the discovery of four transiting F-M binary systems with companions
between 0.1-0.2 Msun in mass by the HATSouth survey. These systems have been
characterised via a global analysis of the HATSouth discovery data, combined
with high-resolution radial velocities and accurate transit photometry
observations. We determined the masses and radii of the component stars using a
combination of two methods: isochrone fitting of spectroscopic primary star
parameters, and equating spectroscopic primary star rotation velocity with
spin-orbit synchronisation. These new very low mass companions are HATS550-016B
(0.110 -0.006/+0.005 Msun, 0.147 -0.004/+0.003 Rsun), HATS551-019B (0.17
-0.01/+0.01 Msun, 0.18 -0.01/+0.01 Rsun), HATS551-021B (0.132 -0.005/+0.014
Msun, 0.154 -0.008/+0.006 Rsun), HATS553-001B (0.20 -0.02/+0.01 Msun, 0.22
-0.01/+0.01 Rsun). We examine our sample in the context of the radius anomaly
for fully-convective low mass stars. Combining our sample with the 13 other
well-studied very low mass stars, we find a tentative 5% systematic deviation
between the measured radii and theoretical isochrone models.Comment: 17 pages, 8 figures, accepted for publication in MNRA
Observability of the General Relativistic Precession of Periastra in Exoplanets
The general relativistic precession rate of periastra in close-in exoplanets
can be orders of magnitude larger than the magnitude of the same effect for
Mercury. The realization that some of the close-in exoplanets have significant
eccentricities raises the possibility that this precession might be detectable.
We explore in this work the observability of the periastra precession using
radial velocity and transit light curve observations. Our analysis is
independent of the source of precession, which can also have significant
contributions due to additional planets and tidal deformations. We find that
precession of the periastra of the magnitude expected from general relativity
can be detectable in timescales of <~ 10 years with current observational
capabilities by measuring the change in the primary transit duration or in the
time difference between primary and secondary transits. Radial velocity curves
alone would be able to detect this precession for super-massive, close-in
exoplanets orbiting inactive stars if they have ~100 datapoints at each of two
epochs separated by ~20 years. We show that the contribution to the precession
by tidal deformations may dominate the total precession in cases where the
relativistic precession is detectable. Studies of transit durations with Kepler
might need to take into account effects arising from the general relativistic
and tidal induced precession of periastra for systems containing close-in,
eccentric exoplanets. Such studies may be able to detect additional planets
with masses comparable to that of Earth by detecting secular variations in the
transit duration induced by the changing longitude of periastron.Comment: 13 pages, 5 figures. Accepted for publication in Ap
The Globular Cluster System of NGC 5846 Revisited: Colours, Sizes and X-Ray Counterparts
NGC 5846 is a giant elliptical galaxy with a previously well studied globular
cluster system (GCS), known to have a bimodal colour distribution with a
remarkably high red fraction. Here we revisit the central galaxy regions
searching for new globular cluster (GC) candidates, and measuring, magnitudes,
colours and sizes for them. We also search for their X-ray counterparts. We use
archival Hubble Space Telescope WFPC2 images, from which we modelled and
subtracted the host light distribution and increased the available sample of
GCs. We performed photometry on the central objects, and measured sizes and
equatorial coordinates for the entire system known in this galaxy. We detect
two dozen previously unknown GC candidates in the central regions. Reliable
sizes are obtained for about 60 GCs; their typical effective radii are in the
range 3-5 pc. The largest clusters are located in the central regions. We find
7 X-ray counterparts to globular clusters, most of them in the central region.
They are among the most luminous X-ray sources in NGC 5846. They are also
optically luminous, compact and belong to the red subpopulation.Comment: 8 pages, 9 figures, A&A accepte
HATS-3b: An inflated hot Jupiter transiting an F-type star
We report the discovery by the HATSouth survey of HATS-3b, a transiting
extrasolar planet orbiting a V=12.4 F-dwarf star. HATS-3b has a period of P =
3.5479d, mass of Mp = 1.07MJ, and radius of Rp = 1.38RJ. Given the radius of
the planet, the brightness of the host star, and the stellar rotational
velocity (vsini = 9.0km/s), this system will make an interesting target for
future observations to measure the Rossiter-McLaughlin effect and determine its
spin-orbit alignment. We detail the low/medium-resolution reconnaissance
spectroscopy that we are now using to deal with large numbers of transiting
planet candidates produced by the HATSouth survey. We show that this important
step in discovering planets produces logg and Teff parameters at a precision
suitable for efficient candidate vetting, as well as efficiently identifying
stellar mass eclipsing binaries with radial velocity semi-amplitudes as low as
1 km/s.Comment: 11 pages, 10 figures, submitted to A
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