76 research outputs found
Unsigned magnetic flux as a proxy for radial-velocity variations in Sun-like stars
We estimate disc-averaged RV variations of the Sun over the last magnetic
cycle, from the single Fe I line observed by SDO/HMI, using a physical model
for rotationally modulated magnetic activity that was previously validated
against HARPS-N solar observations. We estimate the disc-averaged, unsigned
magnetic flux and show that a simple linear fit to it reduces the RMS of RV
variations by 62%, i.e. a factor of 2.6. We additionally apply the FF' method,
which predicts RV variations based on a star's photometric variations. At cycle
maximum, we find that additional physical processes must be at play beyond
suppression of convective blueshift and velocity imablances resulting from
brightness inhomogeneities, in agreement with recent studies of solar RV
variations. By modelling RV variations over the magnetic cycle using a linear
fit to the unsigned magnetic flux, we recover injected planets at an orbital
period of about 300 days with RV semi-amplitudes down to 0.3 m/s. To reach
semi-amplitudes of 0.1 m/s, we will need to identify and model additional
physical phenomena that are not well traced by the unsigned magnetic flux or
FF'. The unsigned magnetic flux is an excellent proxy for rotationally
modulated, activity-induced RV variations, and could become a key tool in
confirming and characterising Earth analogs orbiting Sun-like stars. The
present study motivates ongoing and future efforts to develop observation and
analysis techniques to measure the unsigned magnetic flux at high precision in
slowly rotating, relatively inactive stars like the Sun.Comment: 25 pages, 11 figures, 3 tables, submitted to Ap
Alternative optical concept for electron cyclotron emission imaging
The implementation of advanced electron cyclotron emission imaging (ECEI) systems on tokamak experiments has revolutionized the diagnosis of magnetohydrodynamic (MHD) activities and improved our understanding of instabilities, which lead to disruptions. It is therefore desirable to have an ECEI system on the ITER tokamak. However, the large size of optical components in presently used ECEI systems have, up to now, precluded the implementation of an ECEI system on ITER. This paper describes a new optical ECEI concept that employs a single spherical mirror as the only optical component and exploits the astigmatism of such a mirror to produce an image with one-dimensional spatial resolution on the detector. Since this alternative approach would only require a thin slit as the viewing port to the plasma, it would make the implementation of an ECEI system on ITER feasible. The results obtained from proof-of-principle experiments with a 125 GHz microwave system are presented.open0
Social marketing applied to HIV/AIDS prevention: the case of a five-year governmental response in Portugal
HIV infection has been a concerning health issue prioritised by health governmental institutions that has required the development of public health policies with an integrated social marketing intervention in an upstream dimension. A behaviour change strategy should invest in segmented communication for priority targets, in partnership with multiple stakeholders. This case explores and discusses the integrated social marketing programme developed by the Portuguese Ministry of Health to prevent HIV/AIDS in the period 2006â2011 and its long-term evaluation in behaviour change, comparing data from 2005 and 2017. This case shows the initial diagnosis; the social marketing strategy developed for different targets in partnership with civil society organisations, following a variety of theoretical frameworks; and effectiveness evaluation in epidemic outcomes. A guide is provided with questions for discussion.FCT - Fundação para a CiĂȘncia e a Tecnologia(UID/SOC/04521/2013
Beyond Legalism in Turbulent Times: Re-grounding UK Social Work in a Richer International Human Rights Perspective
Human rights have always been intrinsically woven into social work, but in the UK, often in a way that is either vague or wholly legalistic. In this article, we make a case for embedding a broader and richer concept of human rights in UK social work practice and education. We contrast the international social work perspective on human rights with that of UK professional codes and suggest that the narrow and uninterrogated conceptualisation of human rights in the UK may be acting as a barrier to UK social workers fully understanding and engaging with broader human rights agendas of the sort found in international practice. We argue for the merits of regrounding UK social work in this broader human rights concept, in which radical and emancipatory approaches can be underpinned by a common and unifying rights-orientated perspective. We make this argument, initially, in the context of the Human Rights Act 1998 remaining in UK law, which we see as entirely necessary for the protection of human rights in social work in the country, but insufficient for a broader, richer concept. We also, however, consider a scenario in which the Act is replaced by a British Bill of Rights and argue that such a development would present a further urgent need for embedding a broader human rights concept in UK social work. We close by setting out some of what such a concept might involve
HARPS-N Solar Radial-Velocity Variations Are Dominated By Large, Bright Magnetic Regions
State of the art radial-velocity (RV) exoplanet searches are currently
limited by RV signals arising from stellar magnetic activity. We analyze solar
observations acquired over a 3-year period during the decline of Carrington
Cycle 24 to test models of RV variation of Sun-like stars. A purpose-built
solar telescope at the High Accuracy Radial velocity Planet Searcher for the
Northern hemisphere (HARPS-N) provides disk-integrated solar spectra, from
which we extract RVs and . The Solar Dynamics Observatory
(SDO) provides disk-resolved images of magnetic activity. The Solar Radiation
and Climate Experiment (SORCE) provides near-continuous solar photometry,
analogous to a Kepler light curve. We verify that the SORCE photometry and
HARPS-N correlate strongly with the SDO-derived magnetic
filling factor, while the HARPS-N RV variations do not. To explain this
discrepancy, we test existing models of RV variations. We estimate the
contributions of the suppression of convective blueshift and the rotational
imbalance due to brightness inhomogeneities to the observed HARPS-N RVs. We
investigate the time variation of these contributions over several rotation
periods, and how these contributions depend on the area of active regions. We
find that magnetic active regions smaller than do not
significantly suppress convective blueshift. Our area-dependent model reduces
the amplitude of activity-induced RV variations by a factor of two. The present
study highlights the need to identify a proxy that correlates specifically with
large, bright magnetic regions on the surfaces of exoplanet-hosting stars.Comment: 16 pages, 7 figures, accepted by Ap
Molecular characterization and genetic diversity of potato cultivars using SSR and RAPD markers
Three years of Sun-as-a-star radial-velocity observations on the approach to solar minimum
The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planetsâ masses, obstructing detection of Earth twins. Since 2015 July, we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 yr of observation, interpreting them in the context of spatially resolved solar observations. We describe a Bayesian mixture-model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise-limited radial-velocity precision better than 0.43 m sâ1 per 5-min observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m sâ1. We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m sâ1 and an autocorrelation half-life of 15 min. On longer time-scales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m sâ1 and is correlated with the line asymmetry, but leads it by 3 d. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity.Publisher PDFPeer reviewe
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