1,260 research outputs found
Stellar 3-D kinematics in the Draco dwarf spheroidal galaxy
Aims. We present the first three-dimensional internal motions for individual
stars in the Draco dwarf spheroidal galaxy. Methods. By combining first-epoch
observations and second-epoch Data Release
2 positions, we measured the proper motions of sources in the direction
of Draco. We determined the line-of-sight velocities for a sub-sample of
red giant branch stars using medium resolution spectra acquired with the DEIMOS
spectrograph at the Keck II telescope. Altogether, this resulted in a final
sample of Draco members with high-precision and accurate 3D motions, which
we present as a table in this paper. Results. Based on this high-quality
dataset, we determined the velocity dispersions at a projected distance of
pc from the centre of Draco to be
km/s, km/s and
km/s in the projected radial, tangential, and line-of-sight directions. This
results in a velocity anisotropy at
pc. Tighter constraints may be obtained using the spherical Jeans equations and
assuming constant anisotropy and Navarro-Frenk-White (NFW) mass profiles, also
based on the assumption that the 3D velocity dispersion should be lower than
of the escape velocity of the system. In this case, we constrain
the maximum circular velocity of Draco to be in the range of
km/s. The corresponding mass range is in good agreement with
previous estimates based on line-of-sight velocities only. Conclusions. Our
Jeans modelling supports the case for a cuspy dark matter profile in this
galaxy. Firmer conclusions may be drawn by applying more sophisticated models
to this dataset and with new datasets from upcoming releases.Comment: 12 pages, 15 figures, 3 tables. Accepted for publication by A&
Constraining the evolution of stellar rotation using solar twins
The stellar Rotation Age relation is commonly considered as a useful
tool to derive reliable ages for Sun-like stars. However, in the light of
\kepler\ data, the presence of apparently old and fast rotators that do not
obey the usual gyrochronology relations led to the hypothesis of weakened
magnetic breaking in some stars. In this letter, we constrain the solar
rotation evolutionary track using solar twins. Predicted rotational periods as
a function of mass, age, [Fe/H] and given critical Rossby number () were estimated for the entire rotational sample. Our analysis favors
the smooth rotational evolution scenario and suggests that, if the magnetic
weakened breaking scenario takes place at all, it should arise after or ages 5.3 Gyr (at 95 confidence level).Comment: 5 pages, 3 figures, accepted for publication in MNRA
New cue-conflict experiments suggest a leading role of visual cues in the migratory orientation of Pied Flycatchers Ficedula hypoleuca
Migratory birds use both geomagnetic and celestial cues to select and maintain their seasonally appropriate migratory direction. The integration of the different compass cues is still poorly understood. Previous cue-conflict experiments suggested that Pied Flycatchers Ficedula hypoleuca did not recalibrate their magnetic compass against the polarization pattern at twilight, but the available evidence is problematic given the high variability of birdsâ directional preferences. We performed a new set of cue-conflict experiments where (1) we modified the protocol in order to try to reduce scatter of data and (2) we integrated the results of two experimental approaches, i.e. orientation cages and releases of radio-tagged birds. Pied Flycatchers were tested in Emlen funnels without access to celestial cues before and after being exposed to conflicting visual and geomagnetic information. After the second test, birds were equipped with radio-transmitters and followed until the vanishing of the radio signal. Contrary to previous experiments, our data showed a general dominance of celestial cues: polarized light sun-related pattern in captive birds tested without access to stars and stellar
dominance in free-flying birds released under a starry sky at night-time. These results underline the importance of experimental protocols when testing ways in which birds integrate their compass systems
Spectroscopic binaries in the Solar Twin Planet Search program: from substellar-mass to M dwarf companions
Previous studies on the rotation of Sun-like stars revealed that the
rotational rates of young stars converge towards a well-defined evolution that
follows a power-law decay. It seems, however, that some binary stars do not
obey this relation, often by displaying enhanced rotational rates and activity.
In the Solar Twin Planet Search program we observed several solar twin
binaries, and found a multiplicity fraction of in the whole
sample; moreover, at least three of these binaries (HIP 19911, HIP 67620 and
HIP 103983) clearly exhibit the aforementioned anomalies. We investigated the
configuration of the binaries in the program, and discovered new companions for
HIP 6407, HIP 54582, HIP 62039 and HIP 30037, of which the latter is orbited by
a M brown dwarf in a 1-month long orbit. We report the orbital
parameters of the systems with well-sampled orbits and, in addition, the lower
limits of parameters for the companions that only display a curvature in their
radial velocities. For the linear trend binaries, we report an estimate of the
masses of their companions when their observed separation is available, and a
minimum mass otherwise. We conclude that solar twin binaries with low-mass
stellar companions at moderate orbital periods do not display signs of a
distinct rotational evolution when compared to single stars. We confirm that
the three peculiar stars are double-lined binaries, and that their companions
are polluting their spectra, which explains the observed anomalies.Comment: 13 pages, 7 figures, accepted for publication in MNRA
Revisiting the 16 Cygni planet host at unprecedented precision and exploring automated tools for precise abundances
The binary system 16 Cygni is key in studies of the planet-star chemical
composition connection, as only one of the stars is known to host a planet.
This allows us to better assess the possible influence of planet interactions
on the chemical composition of stars that are born from the same cloud and
thus, should have a similar abundance pattern. In our previous work, we found
clear abundance differences for elements with Z between both components
of this system, and a trend of these abundances as a function of the
condensation temperature (T), which suggests a spectral chemical
signature related to planet formation. In this work we show that our previous
findings are still consistent even if we include more species, like the
volatile N and neutron capture elements (Z 30). We report a slope with
T of dex K, that is good agreement
with both our previous work and recent results by Nissen and collaborators. We
also performed some tests using ARES and iSpec to automatic measure the
equivalent width and found T slopes in reasonable agreement with our
results as well. In addition, we determine abundances for Li and Be by spectral
synthesis, finding that 16 Cyg A is richer not only in Li but also in Be, when
compared to its companion. This may be evidence of planet engulfment,
indicating that the T trend found in this binary system may be a chemical
signature of planet accretion in the A component, rather than a imprint of the
giant planet rocky core formation on 16 Cyg B.Comment: 11 pages, 5 figures, accepted for publication in A&
The temporal evolution of neutron-capture elements in the Galactic discs
Important insights into the formation and evolution of the Galactic disc(s)
are contained in the chemical compositions of stars. We analysed
high-resolution and high signal to noise HARPS spectra of 79 solar twin stars
in order to obtain precise determinations of their atmospheric parameters, ages
(0.4 Gyr) and chemical abundances (0.01~dex) of 12
neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy).
This valuable dataset allows us to study the [X/Fe]-age relations over a time
interval of 10 Gyr and among stars belonging to the thin and thick discs.
These relations show that i) the -process has been the main channel of
nucleosynthesis of -capture elements during the evolution of the thin disc;
ii) the thick disc is rich in -process elements which suggests that its
formation has been rapid and intensive. %; iii) a chemical continuity between
the thin and thick discs is evident in the abundances of Ba. In addition, the
heavy (Ba, La, Ce) and light (Sr, Y, Zr) -process elements revealed details
on the dependence between the yields of AGB stars and the stellar mass or
metallicity. Finally, we confirmed that both [Y/Mg] and [Y/Al] ratios can be
employed as stellar clocks, allowing ages of solar twin stars to be estimated
with an average precision of 0.5~Gyr
Chemical inhomogeneities in the Pleiades: signatures of rocky-forming material in stellar atmospheres
The aim of Galactic archaeology is to recover the history of our Galaxy
through the information encoded in stars. An unprobed assumption of this field
is that the chemical composition of a star is an immutable marker of the gas
from which it formed. It is vital to test this assumption on open clusters,
group of stars formed from the same gas. Previous investigations have shown
that unevolved stars in clusters are chemically homogeneous within the typical
uncertainties of these analysis, i.e. 15 of the elemental abundances. Our
strictly differential analysis on five members of the Pleiades allows us to
reach precisions of 5 for most elements and to unveil chemical anomalies
within the cluster that could be explained by planet engulfment events. These
results reveal that the evolution of planetary systems may alter the chemical
composition of stars, challenging our capability of tagging them to their
native environments, and also paving the way for the study of planetary
architectures and their evolution, through the chemical pattern of their host
stars.Comment: 10 pages, 2 figures. Accepted for publication in Ap
FAMA: An automatic code for stellar parameter and abundance determination
The large amount of spectra obtained during the epoch of extensive
spectroscopic surveys of Galactic stars needs the development of automatic
procedures to derive their atmospheric parameters and individual element
abundances. Starting from the widely-used code MOOG by C. Sneden, we have
developed a new procedure to determine atmospheric parameters and abundances in
a fully automatic way. The code FAMA (Fast Automatic MOOG Analysis) is
presented describing its approach to derive atmospheric stellar parameters and
element abundances. The code, freely distributed, is written in Perl and can be
used on different platforms. The aim of FAMA is to render the computation of
the atmospheric parameters and abundances of a large number of stars using
measurements of equivalent widths as automatic and as independent of any
subjective approach as possible. It is based on the simultaneous search for
three equilibria: excitation equilibrium, ionization balance, and the
relationship between \fei\ and the reduced equivalent widths. FAMA also
evaluates the statistical errors on individual element abundances and errors
due to the uncertainties in the stellar parameters. The convergence criteria
are not fixed 'a priori' but are based on the quality of the spectra. In this
paper we present tests performed on the Solar spectrum EWs which tests the
dependency on the initial parameters, and the analysis of a sample of stars
observed in Galactic open and globular clusters.Comment: A&A accepted, 12 pages, 6 figures, 3 table
Aluminum nitride for heatspreading in RF IC’s
To reduce the electrothermal instabilities in silicon-on-glass high-frequency bipolar devices, the integration of thin-film aluminum nitride as a heatspreader is studied. The AlN is deposited by reactive sputtering and this material is shown to fulfill all the requirements for actively draining heat from RF ICâs, i.e., it has good process compatibility, sufficiently high thermal conductivity and good electrical isolation also at high frequencies. The residual stress and the piezoelectric character of the material, both of which can be detrimental for the present application, are minimized by a suitable choice of deposition conditions including variable biasing of the substrate in a multistep deposition cycle. Films of AlN as thick as 4 lm are successfully integrated in RF silicon-on-glass bipolar junction transistors that display a reduction of more than 70% in the value of the thermal resistance
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