55 research outputs found
Tachoastrometry: astrometry with radial velocities
Spectra of composite systems (e.g., spectroscopic binaries) contain spatial
information that can be retrieved by measuring the radial velocities (i.e.,
Doppler shifts) of the components in four observations with the slit rotated by
90 degrees in the sky. By using basic concepts of slit spectroscopy we show
that the geometry of composite systems can be reliably retrieved by measuring
only radial velocity differences taken with different slit angles. The spatial
resolution is determined by the precision with which differential radial
velocities can be measured. We use the UVES spectrograph at the VLT to observe
the known spectroscopic binary star HD 188088 (HIP 97944), which has a maximum
expected separation of 23 milli-arcseconds. We measure an astrometric signal in
radial velocity of 276 \ms, which corresponds to a separation between the two
components at the time of the observations of 18 milli-arcseconds. The
stars were aligned east-west. We describe a simple optical device to
simultaneously record pairs of spectra rotated by 180 degrees, thus reducing
systematic effects. We compute and provide the function expressing the shift of
the centroid of a seeing-limited image in the presence of a narrow slit.The
proposed technique is simple to use and our test shows that it is amenable for
deriving astrometry with milli-arcsecond accuracy or better, beyond the
diffraction limit of the telescope. The technique can be further improved by
using simple devices to simultaneously record the spectra with 180 degrees
angles.With tachoastrometry, radial velocities and astrometric positions can be
measured simultaneously for many double line system binaries in an easy way.
The method is not limited to binary stars, but can be applied to any
astrophysical configuration in which spectral lines are generated by separate
(non-rotational symmetric) regions.Comment: Accepted for publication in A&
Instability patterns in ultrathin nematic films: comparison between theory and experiment
Motivated by recent experimental observations [U. Delabre et al, Langmuir 24,
3998, 2008] we reconsider an instability of ultrathin nematic films, spread on
liquid substrates. Within a continuum elastic theory of liquid crystals, in the
harmonic approximation, we find an analytical expressions for the critical
thickness as well as for the critical wavenumber, characterizing the onset of
instability towards the stripe phase. Comparing theoretical predictions with
experimental observations, we establish the utility of surface-like term such
as an azimuthal anchoring.Comment: 6 pages, 3 figures, LaTeX macros EPL draft, accepted for publication
in EP
Transformation archetypes in global food systems
Food systems are primary drivers of human and environmental health, but the understanding of their diverse and dynamic co-transformation remains limited. We use a data-driven approach to disentangle different development pathways of national food systems (i.e. ‘transformation archetypes’) based on historical, intertwined trends of food system structure (agricultural inputs and outputs and food trade), and social and environmental outcomes (malnutrition, biosphere integrity, and greenhouse gases emissions) for 161 countries, from 1995 to 2015. We found that whilst agricultural total factor productivity has consistently increased globally, a closer analysis suggests a typology of three transformation archetypes across countries: rapidly expansionist, expansionist, and consolidative. Expansionist and rapidly expansionist archetypes increased in agricultural area, synthetic fertilizer use, and gross agricultural output, which was accompanied by malnutrition, environmental pressures, and lasting socioeconomic disadvantages. The lowest rates of change in key structure metrics were found in the consolidative archetype. Across all transformation archetypes, agricultural greenhouse gases emissions, synthetic fertilizer use, and ecological footprint of consumption increased faster than the expansion of agricultural area, and obesity levels increased more rapidly than undernourishment decreased. The persistence of these unsustainable trajectories occurred independently of improvements in productivity. Our results underscore the importance of quantifying the multiple human and environmental dimensions of food systems transformations and can serve as a starting point to identify potential leverage points for sustainability transformations. More attention is thus warranted to alternative development pathways able of delivering equitable benefits to both productivity and to human and environmental health
Toward the final optical design MOONS, the Multi-Object Optical and Near infrared Spectrometer for the VLT
MOONS (Multi-Object Optical and Near-infrared Spectrograph for the VLT) is entering into the final design phase. This paper presents and discusses the latest proposed version of the optical design of the cryogenic spectrograph. The main developments and modifications were aimed at minimizing the overall size and mass of the cryogenic spectrograph. The most remarkable new feature is the design of an extremely fast (F/0.95), light and compact (40 kg in less than 80 dm3) camera with superb image quality over a very large field of view (9 degrees on a collimated beam of 265 mm). The camera consists of only three optical elements: two lenses and one mirror. All elements are made of fused-silica. The optical performances are independent on the temperature, i.e. the camera can be fully characterized at room temperatures
ESPRESSO: The next European exoplanet hunter
The acronym ESPRESSO stems for Echelle SPectrograph for Rocky Exoplanets and
Stable Spectroscopic Observations; this instrument will be the next VLT high
resolution spectrograph. The spectrograph will be installed at the
Combined-Coud\'e Laboratory of the VLT and linked to the four 8.2 m Unit
Telescopes (UT) through four optical Coud\'e trains. ESPRESSO will combine
efficiency and extreme spectroscopic precision. ESPRESSO is foreseen to achieve
a gain of two magnitudes with respect to its predecessor HARPS, and to improve
the instrumental radial-velocity precision to reach the 10 cm/s level. It can
be operated either with a single UT or with up to four UTs, enabling an
additional gain in the latter mode. The incoherent combination of four
telescopes and the extreme precision requirements called for many innovative
design solutions while ensuring the technical heritage of the successful HARPS
experience. ESPRESSO will allow to explore new frontiers in most domains of
astrophysics that require precision and sensitivity. The main scientific
drivers are the search and characterization of rocky exoplanets in the
habitable zone of quiet, nearby G to M-dwarfs and the analysis of the
variability of fundamental physical constants. The project passed the final
design review in May 2013 and entered the manufacturing phase. ESPRESSO will be
installed at the Paranal Observatory in 2016 and its operation is planned to
start by the end of the same year.Comment: 12 pages, figures included, accepted for publication in Astron. Nach
The SPOTT Index: a proof-of-concept measure for tracking public disclosure in the Palm Oil industry
The production of palm oil has considerable implications for tropical biodiversity. Increasing the environmental, social and governance (ESG) transparency and disclosure of the industry will contribute towards sustainable consumption and production practices. Here, we present a method for producing an index to measure changes in ESG disclosure in the palm oil sector over time based on data collected on SPOTT (Sustainability Policy Transparency Toolkit). The SPOTT Index is based on the number of points scored by a company during an annual assessment, and the number of companies that were included in that assessment time period. The SPOTT Index shows that ESG disclosure of palm oil companies measured improved between 2014 and 2018. Although we demonstrate proof of concept based on a limited number of companies, continued growth of SPOTT will enable the production of a powerful metric in ESG disclosure beyond palm oil and also serve to incentivise sustainable production and consumption in the sector
X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope
X-shooter is the first 2nd generation instrument of the ESO Very Large
Telescope(VLT). It is a very efficient, single-target, intermediate-resolution
spectrograph that was installed at the Cassegrain focus of UT2 in 2009. The
instrument covers, in a single exposure, the spectral range from 300 to 2500
nm. It is designed to maximize the sensitivity in this spectral range through
dichroic splitting in three arms with optimized optics, coatings, dispersive
elements and detectors. It operates at intermediate spectral resolution
(R~4,000 - 17,000, depending on wavelength and slit width) with fixed echelle
spectral format (prism cross-dispersers) in the three arms. It includes a
1.8"x4" Integral Field Unit as an alternative to the 11" long slits. A
dedicated data reduction package delivers fully calibrated two-dimensional and
extracted spectra over the full wavelength range. We describe the main
characteristics of the instrument and present its performance as measured
during commissioning, science verification and the first months of science
operations.Comment: accepted for publication in A&
Revisiting Proxima with ESPRESSO
We aim to confirm the presence of Proxima b using independent measurements
obtained with the new ESPRESSO spectrograph, and refine the planetary
parameters taking advantage of its improved precision. We analysed 63
spectroscopic ESPRESSO observations of Proxima taken during 2019. We obtained
radial velocity measurements with a typical radial velocity photon noise of 26
cm/s. We ran a joint MCMC analysis on the time series of the radial velocity
and full-width half maximum of the cross-correlation function to model the
planetary and stellar signals present in the data, applying Gaussian process
regression to deal with stellar activity. We confirm the presence of Proxima b
independently in the ESPRESSO data. The ESPRESSO data on its own shows Proxima
b at a period of 11.218 0.029 days, with a minimum mass of 1.29
0.13 Me. In the combined dataset we measure a period of 11.18427 0.00070
days with a minimum mass of 1.173 0.086 Me. We find no evidence of
stellar activity as a potential cause for the 11.2 days signal. We find some
evidence for the presence of a second short-period signal, at 5.15 days with a
semi-amplitude of merely 40 cm/s. If caused by a planetary companion, it would
correspond to a minimum mass of 0.29 0.08 Me. We find that the FWHM of
the CCF can be used as a proxy for the brightness changes and that its gradient
with time can be used to successfully detrend the radial velocity data from
part of the influence of stellar activity. The activity-induced radial velocity
signal in the ESPRESSO data shows a trend in amplitude towards redder
wavelengths. Velocities measured using the red end of the spectrograph are less
affected by activity, suggesting that the stellar activity is spot-dominated.
The data collected excludes the presence of extra companions with masses above
0.6 Me at periods shorter than 50 days.Comment: 25 pages, 26 figure
A precise architecture characterization of the Men planetary system
The bright star Men was chosen as the first target for a radial
velocity follow-up to test the performance of ESPRESSO, the new high-resolution
spectrograph at the ESO's Very-Large Telescope (VLT). The star hosts a
multi-planet system (a transiting 4 M planet at 0.07 au, and a
sub-stellar companion on a 2100-day eccentric orbit) which is
particularly appealing for a precise multi-technique characterization. With the
new ESPRESSO observations, that cover a time span of 200 days, we aim to
improve the precision and accuracy of the planet parameters and search for
additional low-mass companions. We also take advantage of new photometric
transits of Men c observed by TESS over a time span that overlaps with
that of the ESPRESSO follow-up campaign. We analyse the enlarged spectroscopic
and photometric datasets and compare the results to those in the literature. We
further characterize the system by means of absolute astrometry with Hipparcos
and Gaia. We used the spectra of ESPRESSO for an independent determination of
the stellar fundamental parameters. We present a precise characterization of
the planetary system around Men. The ESPRESSO radial velocities alone
(with typical uncertainty of 10 cm/s) allow for a precise retrieval of the
Doppler signal induced by Men c. The residuals show an RMS of 1.2 m/s,
and we can exclude companions with a minimum mass less than 2 M
within the orbit of Men c). We improve the ephemeris of Men c using
18 additional TESS transits, and in combination with the astrometric
measurements, we determine the inclination of the orbital plane of Men b
with high precision ( deg). This leads to the precise
measurement of its absolute mass M, and
shows that the planetary orbital planes are highly misaligned.Comment: Accepted for publication on A&
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