120 research outputs found
LACO-Wiki: A New Online Land Cover Validation Tool Demonstrated Using GlobeLand30 for Kenya
Accuracy assessment, also referred to as validation, is a key process in the workflow of developing a land cover map. To make this process open and transparent, we have developed a new online tool called LACO-Wiki, which encapsulates this process into a set of four simple steps including uploading a land cover map, creating a sample from the map, interpreting the sample with very high resolution satellite imagery and generating a report with accuracy measures. The aim of this paper is to present the main features of this new tool followed by an example of how it can be used for accuracy assessment of a land cover map. For the purpose of illustration, we have chosen GlobeLand30 for Kenya. Two different samples were interpreted by three individuals: one sample was provided by the GlobeLand30 team as part of their international efforts in validating GlobeLand30 with GEO (Group on Earth Observation) member states while a second sample was generated using LACO-Wiki. Using satellite imagery from Google Maps, Bing and Google Earth, the results show overall accuracies between 53% to 61%, which is lower than the global accuracy assessment of GlobeLand30 but may be reasonable given the complex landscapes found in Kenya. Statistical models were then fit to the data to determine what factors affect the agreement between the three interpreters such as the land cover class, the presence of very high resolution satellite imagery and the age of the image in relation to the baseline year for GlobeLand30 (2010). The results showed that all factors had a significant effect on the agreement
The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary stars
Context. The CARMENES spectrograph is surveying ~300 M dwarf stars in search
for exoplanets. Among the target stars, spectroscopic binary systems have been
discovered, which can be used to measure fundamental properties of stars. Aims.
Using spectroscopic observations, we determine the orbital and physical
properties of nine new double-line spectroscopic binary systems by analysing
their radial velocity curves. Methods. We use two-dimensional cross-correlation
techniques to derive the radial velocities of the targets, which are then
employed to determine the orbital properties. Photometric data from the
literature are also analysed to search for possible eclipses and to measure
stellar variability, which can yield rotation periods. Results. Out of the 342
stars selected for the CARMENES survey, 9 have been found to be double-line
spectroscopic binaries, with periods ranging from 1.13 to ~8000 days and orbits
with eccentricities up to 0.54. We provide empirical orbital properties and
minimum masses for the sample of spectroscopic binaries. Absolute masses are
also estimated from mass-luminosity calibrations, ranging between ~0.1 and ~0.6
Msol . Conclusions. These new binary systems increase the number of double-line
M dwarf binary systems with known orbital parameters by 15%, and they have
lower mass ratios on average.Comment: Accepted for publication in A&A. 17 pages, 4 figure
Generating WUDAPT’s Specific Scale - dependent Urban Modeling and Activity Parameters: Collection of Level 1 and Level 2 Data
HADES RV Programme with HARPS-N at TNG VI. GJ 3942 b behind dominant activity signals
Short- to mid-term magnetic phenomena on the stellar surface of M-type stars
cannot only resemble the effects of planets in radial velocity data, but also
may hide them. We analyze 145 spectroscopic HARPS-N observations of GJ 3942
taken over the past five years and additional photometry to disentangle stellar
activity effects from genuine Doppler signals as a result of the orbital motion
of the star around the common barycenter with its planet. To achieve this, we
use the common methods of pre-whitening, and treat the correlated red noise by
a first-order moving average term and by Gaussian-process regression following
an MCMC analysis. We identify the rotational period of the star at 16.3 days
and discover a new super-Earth, GJ 3942 b, with an orbital period of 6.9 days
and a minimum mass of 7.1 Me. An additional signal in the periodogram of the
residuals is present but we cannot claim it to be related to a second planet
with sufficient significance at this point. If confirmed, such planet candidate
would have a minimum mass of 6.3 Me and a period of 10.4 days, which might
indicate a 3:2 mean-motion resonance with the inner planet
The HADES RV Programme with HARPS-N@TNG II. Data treatment and simulations
The distribution of exoplanets around low-mass stars is still not well
understood. Such stars, however, present an excellent opportunity of reaching
down to the rocky and habitable planet domains. The number of current
detections used for statistical purposes is still quite modest and different
surveys, using both photometry and precise radial velocities, are searching for
planets around M dwarfs. Our HARPS-N red dwarf exoplanet survey is aimed at the
detection of new planets around a sample of 78 selected stars, together with
the subsequent characterization of their activity properties. Here we
investigate the survey performance and strategy. From 2700 observed spectra, we
compare the radial velocity determinations of the HARPS-N DRS pipeline and the
HARPS-TERRA code, we calculate the mean activity jitter level, we evaluate the
planet detection expectations, and we address the general question of how to
define the strategy of spectroscopic surveys in order to be most efficient in
the detection of planets. We find that the HARPS-TERRA radial velocities show
less scatter and we calculate a mean activity jitter of 2.3 m/s for our sample.
For a general radial velocity survey with limited observing time, the number of
observations per star is key for the detection efficiency. In the case of an
early M-type target sample, we conclude that approximately 50 observations per
star with exposure times of 900 s and precisions of about 1 m/s maximizes the
number of planet detections
A Machine Learning approach for correcting radial velocities using physical observables
Precision radial velocity (RV) measurements continue to be a key tool to
detect and characterise extrasolar planets. While instrumental precision keeps
improving, stellar activity remains a barrier to obtain reliable measurements
below 1-2 m/s accuracy. Using simulations and real data, we investigate the
capabilities of a Deep Neural Network approach to produce activity free Doppler
measurements of stars. As case studies we use observations of two known stars
(Eps Eridani and AUMicroscopii), both with clear signals of activity induced RV
variability. Synthetic data using the starsim code are generated for the
observables (inputs) and the resulting RV signal (labels), and used to train a
Deep Neural Network algorithm. We identify an architecture consisting of
convolutional and fully connected layers that is adequate to the task. The
indices investigated are mean line-profile parameters (width, bisector,
contrast) and multi-band photometry. We demonstrate that the RV-independent
approach can drastically reduce spurious Doppler variability from known
physical effects such as spots, rotation and convective blueshift. We identify
the combinations of activity indices with most predictive power. When applied
to real observations, we observe a good match of the correction with the
observed variability, but we also find that the noise reduction is not as good
as in the simulations, probably due to the lack of detail in the simulated
physics. We demonstrate that a model-driven machine learning approach is
sufficient to clean Doppler signals from activity induced variability for well
known physical effects. There are dozens of known activity related observables
whose inversion power remains unexplored indicating that the use of additional
indicators, more complete models, and more observations with optimised sampling
strategies can lead to significant improvements in our detrending capabilities
Usability of VGI for validation of land cover maps
Volunteered Geographic Information (VGI) represents a growing source of potentially valuable data for many applications, including land cover map validation. It is still an emerging field and many different approaches can be used to take value from VGI, but also many pros and cons are related to its use. Therefore, since it is timely to get an overview of the subject, the aim of this article is to review the use of VGI as reference data for land cover map validation. The main platforms and types of VGI that are used and that are potentially useful are analysed. Since quality is a fundamental issue in map validation, the quality procedures used by the platforms that collect VGI to increase and control data quality are reviewed and a framework for addressing VGI quality assessment is proposed. A review of cases where VGI was used as an additional data source to assist in map validation is made, as well as cases where only VGI was used, indicating the procedures used to assess VGI quality and fitness for use. A discussion and some conclusions are drawn on best practices, future potential and the challenges of the use of VGI for land cover map validation
The CARMENES search for exoplanets around M dwarfs: Convective shift and starspot constraints from chromatic radial velocities
Context. Variability caused by stellar activity represents a challenge to the
discovery and characterization of terrestrial exoplanets and complicates the
interpretation of atmospheric planetary signals.
Aims. We aim to use a detailed modeling tool to reproduce the effect of
active regions on radial velocity measurements, which aids the identification
of the key parameters that have an impact on the induced variability.
Methods. We analyzed the effect of stellar activity on radial velocities as a
function of wavelength by simulating the impact of the properties of spots,
shifts induced by convective motions, and rotation. We focused our modeling
effort on the active star YZ CMi (GJ 285), which was photometrically and
spectroscopically monitored with CARMENES and the Telescopi Joan Or\'o.
Results. We demonstrate that radial velocity curves at different wavelengths
yield determinations of key properties of active regions, including spot
filling factor, temperature contrast, and location, thus solving the degeneracy
between them. Most notably, our model is also sensitive to convective motions.
Results indicate a reduced convective shift for M dwarfs when compared to
solar-type stars (in agreement with theoretical extrapolations) and points to a
small global convective redshift instead of blueshift.
Conclusions. Using a novel approach based on simultaneous chromatic radial
velocities and light curves, we can set strong constraints on stellar activity,
including an elusive parameter such as the net convective motion effect.Comment: A&A, in pres
The CARMENES search for exoplanets around M dwarfs -- Planet occurrence rates from a subsample of 71 stars
The CARMENES exoplanet survey of M dwarfs has obtained more than 18 000
spectra of 329 nearby M dwarfs over the past five years as part of its
guaranteed time observations (GTO) program. We determine planet occurrence
rates with the 71 stars from the GTO program for which we have more than 50
observations. We use injection-and-retrieval experiments on the radial-velocity
(RV) time series to measure detection probabilities. We include 27 planets in
21 planetary systems in our analysis. We find 0.06+0.04-0.03 giant planets (100
M_Earth < M_pl sin i < 1000 M_Earth) per star in periods of up to 1000 d, but
due to a selection bias this number could be up to a factor of five lower in
the whole 329-star sample. The upper limit for hot Jupiters (orbital period of
less than 10 d) is 0.03 planets per star, while the occurrence rate of planets
with intermediate masses (10 M_Earth < M_pl sin i < 100 M_Earth) is
0.18+0.07-0.05 planets per star. Less massive planets with 1 M_Earth < M_pl sin
i < 10 M_Earth are very abundant, with an estimated rate of 1.32+0.33-0.31
planets per star for periods of up to 100 d. When considering only late M
dwarfs with masses M_star < 0.34 M_sol, planets more massive than 10 M_Earth
become rare. Instead, low-mass planets with periods shorter than 10 d are
significantly overabundant. For orbital periods shorter than 100 d, our results
confirm the known stellar mass dependences from the Kepler survey: M dwarfs
host fewer giant planets and at least two times more planets with M_pl sin i <
10 M_Earth than G-type stars. In contrast to previous results, planets around
our sample of very low-mass stars have a higher occurrence rate in short-period
orbits of less than 10 d. Our results demonstrate the need to take into account
host star masses in planet formation models.Comment: 15 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
Спостереження як метод державного фінансового контролю за сплатою податків суб'єктами малого підприємництва
У статті проаналізовано особливості державного контролю за діяльністю суб’єктів малого підприємництва. Наведено авторське визначення методу спостереження в державному фінансовому контролі за сплатою податків та обґрунтовано доцільність його застосування в перспективі.
(The features of state control over the activities of small businesses are analyzed. The author’s definition of the method of monitoring in the state financial control over tax payments is given, and the expedience for its use in the prospects is grounded.
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