7,050 research outputs found
Kepler-539: a young extrasolar system with two giant planets on wide orbits and in gravitational interaction
We confirm the planetary nature of Kepler-539b (aka Kepler object of interest
K00372.01), a giant transiting exoplanet orbiting a solar-analogue G2 V star.
The mass of Kepler-539b was accurately derived thanks to a series of precise
radial velocity measurements obtained with the CAFE spectrograph mounted on the
CAHA 2.2m telescope. A simultaneous fit of the radial-velocity data and Kepler
photometry revealed that Kepler-539b is a dense Jupiter-like planet with a mass
of Mp = 0.97 Mjup and a radius of Rp = 0.747 Rjup, making a complete circular
revolution around its parent star in 125.6 days. The semi-major axis of the
orbit is roughly 0.5 au, implying that the planet is at roughly 0.45 au from
the habitable zone. By analysing the mid-transit times of the 12 transit events
of Kepler-539b recorded by the Kepler spacecraft, we found a clear modulated
transit time variation (TTV), which is attributable to the presence of a planet
c in a wider orbit. The few timings available do not allow us to precisely
estimate the properties of Kepler-539c and our analysis suggests that it has a
mass between 1.2 and 3.6 Mjup, revolving on a very eccentric orbit (0.4<e<0.6)
with a period larger than 1000 days. The high eccentricity of planet c is the
probable cause of the TTV modulation of planet b. The analysis of the CAFE
spectra revealed a relatively high photospheric lithium content, A(Li)=2.48
dex, which, together with both a gyrochronological and isochronal analysis,
suggests that the parent star is relatively young.Comment: 11 pages, 14 figures, accepted for publication in Astronomy &
Astrophysic
Eclipsing binaries and fast rotators in the Kepler sample. Characterization via radial velocity analysis from Calar Alto
The Kepler mission has provided high-accurate photometric data in a long time
span for more than two hundred thousands stars, looking for planetary transits.
Among the detected candidates, the planetary nature of around 15% has been
established or validated by different techniques. But additional data is needed
to characterize the rest of the candidates and reject other possible
configurations. We started a follow-up program to validate, confirm, and
characterize some of the planet candidates. In this paper we present the radial
velocity analysis (RV) of those presenting large variations, compatible with
being eclipsing binaries. We also study those showing large rotational
velocities, which prevents us from obtaining the necessary precision to detect
planetary-like objects. We present new RV results for 13 Kepler objects of
interest (KOIs) obtained with the CAFE spectrograph at the Calar Alto
Observatory, and analyze their high-spatial resolution images and the Kepler
light curves of some interesting cases. We have found five spectroscopic and
eclipsing binaries. Among them, the case of KOI-3853 is of particular interest.
This system is a new example of the so-called heartbeat stars, showing dynamic
tidal distortions in the Kepler light curve. We have also detected duration and
depth variations of the eclipse. We suggest possible scenarios to explain such
effect, including the presence of a third substellar body possibly detected in
our RV analysis. We also provide upper mass limits to the transiting companions
of other six KOIs with large rotational velocities. This property prevents the
RV method to obtain the necessary precision to detect planetary-like masses.
Finally, we analyze the large RV variations of other two KOIs, incompatible
with the presence of planetary-mass objects. These objects are likely to be
stellar binaries but a longer timespan is still needed.Comment: Accepted for publication in A&A. 18 pages, 9 figures, 17 tables. This
version fixes an error affecting the values of tables A.1-A.13. The text
remains unaltere
Very Low-Mass Objects in the Coronet Cluster: The Realm of the Transition Disks
We present optical and IR spectra of a set of low-mass stars and brown dwarfs
in the Coronet cluster (aged ~1Myr), obtained with the multifiber spectrograph
FLAMES/VLT and IRS/Spitzer. The optical spectra reveal spectral types between
M1 and M7.5, confirm the youth of the objects (via Li 6708 A absorption), and
show the presence of accretion (via Halpha) and shocks (via forbidden line
emission). The IRS spectra, together with IR photometry from the IRAC/MIPS
instruments on Spitzer and 2MASS, confirm the presence of IR excesses
characteristic of disks around ~70% of the objects. Half of the disks do not
exhibit any silicate emission, or present flat features characteristic of large
grains. The rest of the disks show silicate emission typical of amorphous and
crystalline silicate grains a few microns in size. About 50% of the objects
with disks do not show near-IR excess emission, having "transitional" disks,
according to their classical definition. This is a very high fraction for such
a young cluster. The large number of "transitional" disks suggests lifetimes
comparable to the lifetimes of typical optically thick disks. Therefore, these
disks may not be in a short-lived phase, intermediate between Class II and
Class III objects. The median spectral energy distribution of the disks in the
Coronet cluster is also closer to a flat disk than observed for the disks
around solar-type stars in regions with similar age. The differences in the
disk morphology and evolution in the Coronet cluster could be related to fact
that these objects have very late spectral types compared to the solar-type
stars in other cluster studies. Finally, the optical spectroscopy reveals that
one of the X-ray sources is produced by a Herbig Haro object in the cloud.Comment: 51 pages, 13 figures, 10 table
Kepler-447b: a hot-Jupiter with an extremely grazing transit
We present the radial velocity confirmation of the extrasolar planet
Kepler-447b, initially detected as a candidate by the Kepler mission. In this
work, we analyze its transit signal and the radial velocity data obtained with
the Calar Alto Fiber-fed Echelle spectrograph (CAFE). By simultaneously
modeling both datasets, we obtain the orbital and physical properties of the
system. According to our results, Kepler-447b is a Jupiter-mass planet
(), with an estimated radius of
(uncertainties provided in this work are
unless specified). This translates into a sub-Jupiter density. The
planet revolves every days in a slightly eccentric orbit
() around a G8V star with detected activity in the
Kepler light curve. Kepler-447b transits its host with a large impact parameter
(), being one of the few planetary grazing transits
confirmed so far and the first in the Kepler large crop of exoplanets. We
estimate that only around 20% of the projected planet disk occults the stellar
disk. The relatively large uncertainties in the planet radius are due to the
large impact parameter and short duration of the transit. Planets with such an
extremely large impact parameter can be used to detect and analyze interesting
configurations such as additional perturbing bodies, stellar pulsations,
rotation of a non-spherical planet, or polar spot-crossing events. All these
scenarios would periodically modify the transit properties (depth, duration,
and time of mid-transit), what could be detectable with sufficient accurate
photometry. Short-cadence photometric data (at the 1 minute level) would help
in the search for these exotic configurations in grazing planetary transits
like that of Kepler-447b.Comment: Accepted for publication in A&A. 13 pages, 8 figures, 4 tables. This
version replaces an earlier version of the pape
Simultaneous follow-up of planetary transits: revised physical properties for the planetary systems HAT-P-16 and WASP-21
Context. By now more than 300 planets transiting their host star have been
found, and much effort is being put into measuring the properties of each
system. Light curves of planetary transits often contain deviations from a
simple transit shape, and it is generally difficult to differentiate between
anomalies of astrophysical nature (e.g. starspots) and correlated noise due to
instrumental or atmospheric effects. Our solution is to observe transit events
simultaneously with two telescopes located at different observatories. Aims.
Using this observational strategy, we look for anomalies in the light curves of
two transiting planetary systems and accurately estimate their physical
parameters. Methods. We present the first photometric follow-up of the
transiting planet HAT-P-16 b, and new photometric observations of WASP-21 b,
obtained simultaneously with two medium-class telescopes located in different
countries, using the telescope defocussing technique. We modeled these and
other published data in order to estimate the physical parameters of the two
planetary systems. Results. The simultaneous observations did not highlight
particular features in the light curves, which is consistent with the low
activity levels of the two stars. For HAT-P-16, we calculated a new ephemeris
and found that the planet is 1.3 \sigma colder and smaller (Rb = 1.190 \pm
0.037 RJup) than the initial estimates, suggesting the presence of a massive
core. Our physical parameters for this system point towards a younger age than
previously thought. The results obtained for WASP-21 reveal lower values for
the mass and the density of the planet (by 1.0 \sigma and 1.4 \sigma
respectively) with respect to those found in the discovery paper, in agreement
with a subsequent study. We found no evidence of any transit timing variations
in either system.Comment: 8 pages, 6 figures, accepted for publication in A&
Dust sedimentation and self-sustained Kelvin-Helmholtz turbulence in protoplanetary disk mid-planes. I. Radially symmetric simulations
We perform numerical simulations of the Kelvin-Helmholtz instability in the
mid-plane of a protoplanetary disk. A two-dimensional corotating slice in the
azimuthal--vertical plane of the disk is considered where we include the
Coriolis force and the radial advection of the Keplerian rotation flow. Dust
grains, treated as individual particles, move under the influence of friction
with the gas, while the gas is treated as a compressible fluid. The friction
force from the dust grains on the gas leads to a vertical shear in the gas
rotation velocity. As the particles settle around the mid-plane due to gravity,
the shear increases, and eventually the flow becomes unstable to the
Kelvin-Helmholtz instability. The Kelvin-Helmholtz turbulence saturates when
the vertical settling of the dust is balanced by the turbulent diffusion away
from the mid-plane. The azimuthally averaged state of the self-sustained
Kelvin-Helmholtz turbulence is found to have a constant Richardson number in
the region around the mid-plane where the dust-to-gas ratio is significant.
Nevertheless the dust density has a strong non-axisymmetric component. We
identify a powerful clumping mechanism, caused by the dependence of the
rotation velocity of the dust grains on the dust-to-gas ratio, as the source of
the non-axisymmetry. Our simulations confirm recent findings that the critical
Richardson number for Kelvin-Helmholtz instability is around unity or larger,
rather than the classical value of 1/4Comment: Accepted for publication in ApJ. Some minor changes due to referee
report, most notably that the clumping mechanism has been identified as the
streaming instability of Youdin & Goodman (2005). Movies of the simulations
are still available at http://www.mpia.de/homes/johansen/research_en.ph
Chemical evolution in the early phases of massive star formation. I
Understanding the chemical evolution of young (high-mass) star-forming
regions is a central topic in star formation research. Chemistry is employed as
a unique tool 1) to investigate the underlying physical processes and 2) to
characterize the evolution of the chemical composition. We observed a sample of
59 high-mass star-forming regions at different evolutionary stages varying from
the early starless phase of infrared dark clouds to high-mass protostellar
objects to hot molecular cores and, finally, ultra-compact HII regions at 1mm
and 3mm with the IRAM 30m telescope. We determined their large-scale chemical
abundances and found that the chemical composition evolves along with the
evolutionary stages. On average, the molecular abundances increase with time.
We modeled the chemical evolution, using a 1D physical model where density and
temperature vary from stage to stage coupled with an advanced gas-grain
chemical model and derived the best-fit chi^2 values of all relevant
parameters. A satisfying overall agreement between observed and modeled column
densities for most of the molecules was obtained. With the best-fit model we
also derived a chemical age for each stage, which gives the timescales for the
transformation between two consecutive stages. The best-fit chemical ages are
~10,000 years for the IRDC stage, ~60,000 years for the HMPO stage, ~40,000
years for the HMC stage, and ~10,000 years for the UCHII stage. The total
chemical timescale for the entire evolutionary sequence of the high-mass star
formation process is on the order of 10^5 years, which is consistent with
theoretical estimates. Furthermore, based on the approach of a multiple-line
survey of unresolved data, we were able to constrain an intuitive and
reasonable physical and chemical model. The results of this study can be used
as chemical templates for the different evolutionary stages in high-mass star
formation.Comment: 31 pages, 11 figures, 21 tables, accepted by A&A; typos adde
The Quantum Hall Effect and Inter-edge State Tunneling Within a Barrier
We have introduced a controllable nano-scale incursion into a potential
barrier imposed across a two-dimensional electron gas, and report on the
phenomena that we observe as the incursion develops. In the quantum Hall
regime, the conductance of this system displays quantized plateaus, broad
minima and oscillations. We explain these features and their evolution with
electrostatic potential geometry and magnetic field as a progression of current
patterns formed by tunneling between edge and localized states within the
barrier.Comment: RevTeX + 4 postscript figures. Self-unpacking uuencoded files.
Unpacking instructions are at the beginning of the files. To appear in
Physical Review
Physical properties, starspot activity, orbital obliquity, and transmission spectrum of the Qatar-2 planetary system from multi-colour photometry
We present seventeen high-precision light curves of five transits of the
planet Qatar-2b, obtained from four defocussed 2m-class telescopes. Three of
the transits were observed simultaneously in the SDSS griz passbands using the
seven-beam GROND imager on the MPG/ESO 2.2-m telescope. A fourth was observed
simultaneously in Gunn grz using the CAHA 2.2-m telescope with BUSCA, and in r
using the Cassini 1.52-m telescope. Every light curve shows small anomalies due
to the passage of the planetary shadow over a cool spot on the surface of the
host star. We fit the light curves with the prism+gemc model to obtain the
photometric parameters of the system and the position, size and contrast of
each spot. We use these photometric parameters and published spectroscopic
measurements to obtain the physical properties of the system to high precision,
finding a larger radius and lower density for both star and planet than
previously thought. By tracking the change in position of one starspot between
two transit observations we measure the orbital obliquity of Qatar-2 b to be
4.3 \pm 4.5 degree, strongly indicating an alignment of the stellar spin with
the orbit of the planet. We calculate the rotation period and velocity of the
cool host star to be 11.4 \pm 0.5 d and 3.28 \pm 0.13 km/s at a colatitude of
74 degree. We assemble the planet's transmission spectrum over the 386-976 nm
wavelength range and search for variations of the measured radius of Qatar-2 b
as a function of wavelength. Our analysis highlights a possible H2/He Rayleigh
scattering in the blue.Comment: 20 pages, 14 figures, to appear in Monthly Notices of the Royal
Astronomical Societ
Susceptibility to weathering damage and oxidative stress on soybean seeds with different lignin contents in the seed coat.
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