37 research outputs found
Lithium abundance evolution in open clusters: Hyades, NGC752, and M67
Mixing mechanisms bring the Li from the base of the convective zone to deeper
and warmer layers where it is destroyed. These mechanisms are investigated by
comparing observations of Li abundances in stellar atmospheres to models of
stellar evolution. Observations in open cluster are especially suitable for
this comparison, since their age and metallicity are homogeneous among their
members and better determined than in field stars. In this work, we compare the
evolution of Li abundances in three different clusters: the Hyades, NGC752, and
M67. Our models are calculated with microscopic diffusion and transport of
chemicals by meridional circulation, and calibrated on the Sun. These
comparisons allow us to follow the evolution of Li abundance as a function of
stellar mass in each cluster and as a function of the age by comparing this
evolution in each cluster. We evaluate the efficiency of the mixing mechanisms
used in the models, and we try to identify the lacking mechanisms to reproduce
the observed evolution of Li abundance.Comment: 6 pages, 4 figures, conference publication of "New advances in
stellar physics: from microscopic to macroscopic processes
Stellar Cycles in Fully Convective Stars and a New Interpretation of Dynamo Evolution
An dynamo, combining shear and cyclonic convection in the
tachocline, is believed to generate the solar cycle. However, this model cannot
explain cycles in fast rotators (with minimal shear) or in fully convective
stars (no tachocline); analysis of such stars could therefore provide key
insights into how these cycles work. We reexamine ASAS data for 15 M dwarfs, 11
of which are presumed fully convective; the addition of newer ASAS-SN data
confirms cycles in roughly a dozen of them, while presenting new or revised
rotation periods for five. The amplitudes and periods of these cycles follow
, with (where Ro is the Rossby number), very
similar to that we
find for 40 previously studied FGK stars, although
and are a factor of 20 smaller in the M stars. The very
different -Ro relationship seen here compared to
previous work suggests that two types of dynamo, with opposite Ro dependences,
operate in cool stars. Initially, a (likely or )
dynamo operates throughout the convective zone in mid-late M and fast rotating
FGK stars, but once magnetic breaking decouples the core and convective
envelope, a tachocline dynamo begins and eventually dominates in
older FGK stars. A change in in the tachocline dynamo generates the
fundamentally different -Ro relationship.Comment: 26 pages, 18 figures, submitted to ApJ. Figure sets will be available
in the final prin
The effects of stellar winds on the magnetospheres and potential habitability of exoplanets
Context: The principle definition of habitability for exoplanets is whether
they can sustain liquid water on their surfaces, i.e. that they orbit within
the habitable zone. However, the planet's magnetosphere should also be
considered, since without it, an exoplanet's atmosphere may be eroded away by
stellar winds. Aims: The aim of this paper is to investigate magnetospheric
protection of a planet from the effects of stellar winds from solar-mass stars.
Methods: We study hypothetical Earth-like exoplanets orbiting in the host
star's habitable zone for a sample of 124 solar-mass stars. These are targets
that have been observed by the Bcool collaboration. Using two wind models, we
calculate the magnetospheric extent of each exoplanet. These wind models are
computationally inexpensive and allow the community to quickly estimate the
magnetospheric size of magnetised Earth-analogues orbiting cool stars. Results:
Most of the simulated planets in our sample can maintain a magnetosphere of ~5
Earth radii or larger. This suggests that magnetised Earth analogues in the
habitable zones of solar analogues are able to protect their atmospheres and is
in contrast to planets around young active M dwarfs. In general, we find that
Earth-analogues around solar-type stars, of age 1.5 Gyr or older, can maintain
at least a Paleoarchean Earth sized magnetosphere. Our results indicate that
planets around 0.6 - 0.8 solar-mass stars on the low activity side of the
Vaughan-Preston gap are the optimum observing targets for habitable Earth
analogues.Comment: 8 pages, 3 figures, accepted to Astronomy and Astrophysic
InformaçÔes dos profissionais de educação fĂsica em programa de exercĂcios fĂsicos para indivĂduos com condromalĂĄcia patelar
The aim of this study was to investigate information from Physical Education professionals about the prescription of physical exercise for patients with patellar chondromalacia. This is a cross-sectional study. The sample consisted of 50 Physical Education professionals, who worked in gym rooms in MaringĂĄ - PR. Data collection was performed through a questionnaire semi-structured by the authors, consisting of questions regarding sociodemographic data, clinical knowledge about patellar chondromalacia and about physical exercises for patients with the disease. The analysis was performed using a descriptive statistics approach. For the presentation of the results, frequency and percentage were used for the categorical variables and, mean and standard deviation for the numerical variables. Of the professionals participating, there was a prevalence of female students (64%) aged 26 to 30 years (46%). Most of the professionals had graduated 5 years (86%), did not attend another undergraduate (86%) or specialization (74%), had some content on patellar chondromalacia during graduation (54%), was knee (82%), the quadriceps femoris muscle being the main muscle involved in the pathology (78%), and 80% of the participants recognized the oblique fibers of the vastus medialis muscle as mediating the patella. Most of the Physical Education professionals who work in the gymnasium rooms of the municipalities of MaringĂĄ, reported having undergraduate information about chondromalacia patelar, have basic knowledge of the pathology and the care it requires
The Solar Twin Planet Search IV. The Sun as a typical rotator and evidence for a new rotational braking law for Sun-like stars
Context. It is still unclear how common the Sun is when compared to other similar stars in regards to some of its physical properties, such as rotation. Considering that gyrochronology relations are widely used today to estimate ages of stars in the main sequence, and that the Sun is used to calibrate it, it is crucial to assess whether these procedures are acceptable.
Aims. We analyze the rotational velocities, limited by the unknown rotation axis inclination angle, of an unprecedented large sample of solar twins to study the rotational evolution of Sun-like stars, and assess whether the Sun is a typical rotator.
Methods. We used high-resolution (R = 115 000) spectra obtained with the HARPS spectrograph and the 3.6 m telescope at La Silla Observatory. The projected rotational velocities for 81 solar twins were estimated by line profile fitting with synthetic spectra. Macroturbulence velocities were inferred from a prescription that accurately reflects their dependence with effective temperature and luminosity of the stars.
Results. Our sample of solar twins include some spectroscopic binaries with enhanced rotational velocities, and we do not find any nonspectroscopic binaries with unusually high rotation velocities. We verified that the Sun does not have a peculiar rotation, but the solar twins exhibit rotational velocities that depart from the Skumanich relation.
Conclusions. The Sun is a regular rotator when compared to solar twins with a similar age. Additionally, we obtain a rotational braking law that better describes the stars in our sample (v â t-0.6) in contrast to previous, often-used scalings
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
Pervasive gaps in Amazonian ecological research
Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4
While the increasing availability of global databases on ecological communities has advanced our knowledge
of biodiversity sensitivity to environmental changes,5â7 vast areas of the tropics remain understudied.8â11 In
the American tropics, Amazonia stands out as the worldâs most diverse rainforest and the primary source of
Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13â15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazonâs biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus
crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced
environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian
Amazonia, while identifying the regionâs vulnerability to environmental change. 15%â18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by
2050. This means that unless we take immediate action, we will not be able to establish their current status,
much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio