498 research outputs found
HD 80606: Searching the chemical signature of planet formation
(Abridged) Binary systems with similar components are ideal laboratories
which allow several physical processes to be tested, such as the possible
chemical pattern imprinted by the planet formation process. Aims. We explore
the probable chemical signature of planet formation in the remarkable binary
system HD 80606 - HD 80607. The star HD 80606 hosts a giant planet with 4 MJup
detected by both transit and radial velocity techniques, being one of the most
eccentric planets detected to date. We study condensation temperature Tc trends
of volatile and refractory element abundances to determine whether there is a
depletion of refractories that could be related to the terrestrial planet
formation. Methods. We carried out a high-precision abundance determination in
both components of the binary system, using a line-by-line strictly
differential approach, using the Sun as a reference and then using HD 80606 as
reference. We used an updated version of the program FUNDPAR, together with
ATLAS9 model atmospheres and the MOOG code. Conclusions. From the study of Tc
trends, we concluded that the stars HD 80606 and HD 80607 do not seem to be
depleted in refractory elements, which is different for the case of the Sun.
Then, the terrestrial planet formation would have been less efficient in the
components of this binary system than in the Sun. The lack of a trend for
refractory elements with Tc between both stars implies that the presence of a
giant planet do not neccesarily imprint a chemical signature in their host
stars, similar to the recent result of Liu et al. (2014). This is also in
agreement with Melendez et al. (2009), who suggest that the presence of
close-in giant planets might prevent the formation of terrestrial planets.
Finally, we speculate about a possible planet around the star HD 80607.Comment: 19 pages, 9 figures, A&A accepte
Brain regions concerned with perceptual skills in tennis: An fMRI study
Sporting performance makes special demands on perceptual skills, but the neural mechanisms underlying such performance are little understood. We address this issue, making use of fMRI to identify the brain areas activated in viewing and responding to video sequences of tennis players, filmed from the opponent’s perspective. In a block-design, fMRI study, 9 novice tennis players watched video clips of tennis play. The main stimulus conditions were (1) serve sequences, (2) non-serve behaviour (ball bouncing) and (3) static control sequences. A button response was required indicating the direction of serve (left or right for serve sequences, middle button for non-serve and static sequences). By comparing responses to the three stimulus conditions, it was possible to identify two groups of brain regions responsive to different components of the task. Areas MT/MST and STS in the posterior part of the temporal lobe responded either to serve and to non-serve stimuli, relative to static controls. Serve sequences produced additional regions of activation in parietal lobe (bilateral IPL, right SPL) and in right frontal cortex (IFGd, IFGv), and these areas were not activated by non-serve sequences. These regions of parietal and frontal cortex have been implicated in a “mirror neuron” network in the human brain. It is concluded that the task of judgement of serve direction produces two different patterns of response: activations in MT/MST and STS concerned with primarily with the analysis of motion and body actions, and activations in parietal and frontal cortex associated specifically with the task of identification of direction of serve
Long-term chromospheric activity in southern M dwarfs: Gl 229 A and Gl 752 A
Several late-type stars present activity cycles similar to that of the Sun.
However, these cycles have been mostly studied in F to K stars. Due to their
small intrinsic brightness, M dwarfs are not usually the targets of long-term
observational studies of stellar activity, and their long-term variability is
generally not known. In this work, we study the long-term activity of two M
dwarf stars: Gl 229 A (M1/2) and Gl 752 A (M2.5). We employ medium resolution
echelle spectra obtained at the 2.15 m telescope at the Argentinian observatory
CASLEO between the years 2000 and 2010 and photometric observations obtained
from the ASAS database. We analyzed Ca \II K line-core fluxes and the mean V
magnitude with the Lomb-Scargle periodogram, and we obtain possible activity
cycles of 4 yr and 7 yr for Gl 229 A and Gl 752 A respectively.Comment: Accepted for publication by Astronomical Journal (AJ
The spectroscopic binary system Gl 375. I. Orbital parameters and chromospheric activity
We study the spectroscopic binary system Gl 375. We employ medium resolution
echelle spectra obtained at the 2.15 m telescope at the Argentinian observatory
CASLEO and photometric observations obtained from the ASAS database. We
separate the composite spectra into those corresponding to both components. The
separated spectra allow us to confirm that the spectral types of both
components are similar (dMe3.5) and to obtain precise measurements of the
orbital period (P = 1.87844 days), minimum masses (M_1 sin^3 i = 0.35 M_sun and
M_2 sin^3 i =0.33 M_sun) and other orbital parameters. The photometric
observations exhibit a sinusoidal variation with the same period as the orbital
period. We interpret this as signs of active regions carried along with
rotation in a tidally synchronized system, and study the evolution of the
amplitude of the modulation in longer timescales. Together with the mean
magnitude, the modulation exhibits a roughly cyclic variation with a period of
around 800 days. This periodicity is also found in the flux of the Ca II K
lines of both components, which seem to be in phase. The periodic changes in
the three observables are interpreted as a sign of a stellar activity cycle.
Both components appear to be in phase, which implies that they are magnetically
connected. The measured cycle of approximately 2.2 years (800 days) is
consistent with previous determinations of activity cycles in similar stars.Comment: 10 pages, including 11 figures and 3 tables. Accepted for publication
in Astronomy & Astrophysic
Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program II. Activity and radial velocity
Due to their low mass and luminosity, M dwarfs are ideal targets if one hopes
to find low-mass planets similar to Earth by using the radial velocity (RV)
method. However, stellar magnetic cycles could add noise or even mimic the RV
signal of a long-period companion. Following our previous work that studied the
correlation between activity cycles and long-term RV variations for K dwarfs we
now expand that research to the lower-end of the main sequence. Our objective
is to detect any correlations between long-term activity variations and the
observed RV of a sample of M dwarfs. We used a sample of 27 M-dwarfs with a
median observational timespan of 5.9 years. The cross-correlation function
(CCF) with its parameters RV, bisector inverse slope (BIS), full-width-at-half-
maximum (FWHM) and contrast have been computed from the HARPS spectrum. The
activity index have been derived using the Na I D doublet. These parameters
were compared with the activity level of the stars to search for correlations.
We detected RV variations up to ~5 m/s that we can attribute to activity cycle
effects. However, only 36% of the stars with long-term activity variability
appear to have their RV affected by magnetic cycles, on the typical timescale
of ~6 years. Therefore, we suggest a careful analysis of activity data when
searching for extrasolar planets using long-timespan RV data.Comment: 20 pages, 12 figures, 3 tables, accepted for publication in Astronomy
and Astophysic
The beta Pictoris association: Catalog of photometric rotational periods of low-mass members and candidate members
We intended to compile the most complete catalog of bona fide members and
candidate members of the beta Pictoris association, and to measure their
rotation periods and basic properties from our own observations, public
archives, and exploring the literature. We carried out a multi-observatories
campaign to get our own photometric time series and collected all archived
public photometric data time series for the stars in our catalog. Each time
series was analyzed with the Lomb-Scargle and CLEAN periodograms to search for
the stellar rotation periods. We complemented the measured rotational
properties with detailed information on multiplicity, membership, and projected
rotational velocity available in the literature and discussed star by star. We
measured the rotation periods of 112 out of 117 among bona fide members and
candidate members of the beta Pictoris association and, whenever possible, we
also measured the luminosity, radius, and inclination of the stellar rotation
axis. This represents to date the largest catalog of rotation periods of any
young loose stellar association. We provided an extensive catalog of rotation
periods together with other relevant basic properties useful to explore a
number of open issues, such as the causes of spread of rotation periods among
coeval stars, evolution of angular momentum, and lithium-rotation connection.Comment: Forthcoming article, Received: 20 June 2016 / Accepted: 09 September
2016; 40 pages, 2 figures. The online figures A1-A73 are available at CD
Habitable Zones and UV Habitable Zones around Host Stars
Ultraviolet radiation is a double-edged sword to life. If it is too strong,
the terrestrial biological systems will be damaged. And if it is too weak, the
synthesis of many biochemical compounds can not go along. We try to obtain the
continuous ultraviolet habitable zones, and compare the ultraviolet habitable
zones with the habitable zones of host stars. Using the boundary ultraviolet
radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable
zones of host stars with masses from 0.08 to 4.00 \mo. For the host stars with
effective temperatures lower than 4,600 K, the ultraviolet habitable zones are
closer than the habitable zones. For the host stars with effective temperatures
higher than 7,137 K, the ultraviolet habitable zones are farther than the
habitable zones. For hot subdwarf as a host star, the distance of the
ultraviolet habitable zone is about ten times more than that of the habitable
zone, which is not suitable for life existence.Comment: 5 pages, 3 figure
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