570 research outputs found
Mid-infrared laser light nulling experiment using single-mode conductive waveguides
Aims: In the context of space interferometry missions devoted to the search
of exo-Earths, this paper investigates the capabilities of new single mode
conductive waveguides at providing modal filtering in an infrared and
monochromatic nulling experiment; Methods: A Michelson laser interferometer
with a co-axial beam combination scheme at 10.6 microns is used. After
introducing a Pi phase shift using a translating mirror, dynamic and static
measurements of the nulling ratio are performed in the two cases where modal
filtering is implemented and suppressed. No additional active control of the
wavefront errors is involved. Results: We achieve on average a statistical
nulling ratio of 2.5e-4 with a 1-sigma upper limit of 6e-4, while a best null
of 5.6e-5 is obtained in static mode. At the moment, the impact of external
vibrations limits our ability to maintain the null to 10 to 20 seconds.;
Conclusions: A positive effect of SM conductive waveguide on modal filtering
has been observed in this study. Further improvement of the null should be
possible with proper mechanical isolation of the setup.Comment: Accepted in A&A, 7 pages, 5 figure
Design of Efficient Water Pricing Policies Integrating Basinwide Resource Opportunity Costs
By ignoring the opportunity cost of water use, water is undervalued, which can lead to significant errors in investments and water
allocation decisions. The marginal resource opportunity cost (MROC) varies in time and space, as resource availability, demands, and users’
WTP vary. This spatial and temporal variability can only be captured by basinwide hydro-economic models integrating water demands and
environmental requirements, resources, infrastructure, and operational and institutional restrictions. This paper presents a method for the
simulation of water pricing policies linked to water availability, and the design of efficient pricing policies that incorporate the basinwide
marginal value of water. Two approaches were applied: priority-based simulation and economic optimization. The improvement in economic
efficiency was assessed by comparing the results from simulation of the current system operation and the pricing schedule. The difference
between the benefits for the simulated current management and the upper bound benefits from optimization indicates the maximum gap that
could be bridged with pricing. In the application to a synthetic case, a storage-dependent step pricing schedule derived from average MROC
values led to benefits that capture 80% of the gap of net benefits between management without pricing and the economically optimal management.
Different pricing policies were tested, depending not only on reservoir storage but also on previous inflows. The results show that
the method is useful for designing pricing policies that enhance the economic benefits, leading to more efficient resource allocations over time
and across the competing uses.This study has been partially funded by the EU 6th FP project AQUAMONEY (SSPI-022723), the 7th FP GENESIS project (226536), and SAWARES (Plan Nacional I+D+i 2008-2011, CGL2009-13238-C02-01 and C02-02) and SCARCE (Consolider-Ingenio 2010 CSD2009-00065) of the Spanish Ministry of Economy and Competitiveness.Pulido-Velazquez, M.; Álvarez Mendiola, E.; Andreu Álvarez, J. (2013). Design of Efficient Water Pricing Policies Integrating Basinwide Resource Opportunity Costs. Journal of Water Resources Planning and Management. 139(5):583-592. https://doi.org/10.1061/(ASCE)WR.1943-5452.0000262S583592139
Planet Formation Imager (PFI): Introduction and Technical Considerations
Complex non-linear and dynamic processes lie at the heart of the planet
formation process. Through numerical simulation and basic observational
constraints, the basics of planet formation are now coming into focus. High
resolution imaging at a range of wavelengths will give us a glimpse into the
past of our own solar system and enable a robust theoretical framework for
predicting planetary system architectures around a range of stars surrounded by
disks with a diversity of initial conditions. Only long-baseline interferometry
can provide the needed angular resolution and wavelength coverage to reach
these goals and from here we launch our planning efforts. The aim of the
"Planet Formation Imager" (PFI) project is to develop the roadmap for the
construction of a new near-/mid-infrared interferometric facility that will be
optimized to unmask all the major stages of planet formation, from initial dust
coagulation, gap formation, evolution of transition disks, mass accretion onto
planetary embryos, and eventual disk dispersal. PFI will be able to detect the
emission of the cooling, newly-formed planets themselves over the first 100
Myrs, opening up both spectral investigations and also providing a vibrant look
into the early dynamical histories of planetary architectures. Here we
introduce the Planet Formation Imager (PFI) Project
(www.planetformationimager.org) and give initial thoughts on possible facility
architectures and technical advances that will be needed to meet the
challenging top-level science requirements.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2014, Paper ID 9146-35, 10 pages, 2 Figure
FU Orionis disk outburst: evidence for a gravitational instability scenario triggered in a magnetically dead zone
Context: FUors outbursts are a crucial stage of accretion in young stars.
However a complete mechanism at the origin of the outburst still remains
missing. Aims: We aim at constraining the instability mechanism in FU Orionis
star itself, by directly probing the size and the evolution in time of the
outburst region with near-infrared interferometry, and to confront it to
physical models of this region. Methods: FU Orionis has been a regular target
of near-infrared interferometry. In this paper, we analyze more than 20 years
of interferometric observations to perform a temporal monitoring of the region
of the outburst, and compare it to the spatial structure deduced from 1D MHD
simulations. Results: We measure from the interferometric observations that the
size variation of the outburst region is compatible with a constant or slightly
decreasing size over time in the H and K band. The temporal variation and the
mean sizes are consistently reproduced by our 1D MHD simulations. We find that
the most compatible scenario is a model of an outburst occurring in a
magnetically layered disk, where a Magneto-Rotational Instability (MRI) is
triggered by a Gravitational Instability (GI) at the outer edge of a dead-zone.
The scenario of a pure Thermal Instability (TI) fails to reproduce our
interferometric sizes since it can only be sustained in a very compact zone of
the disk <0.1 AU. The scenario of MRI-GI could be compatible with an external
perturbation enhancing the GI, such as tidal interactions with a stellar
companion, or a planet at the outer edge of the dead-zone. Conclusions: The
layered disk model driven by MRI turbulence is favored to interpret the spatial
structure and temporal evolution of FU Orionis outburst region. Understanding
this phase gives a crucial link between the early phase of disk evolution and
the process of planet formation in the first inner AUs.Comment: Accepted for publication in A&
The science case for the Planet Formation Imager (PFI)
archiveprefix: arXiv primaryclass: astro-ph.IM eid: 914611 adsurl: http://adsabs.harvard.edu/abs/2014SPIE.9146E..11K adsnote: Provided by the SAO/NASA Astrophysics Data SystemAmong the most fascinating and hotly-debated areas in contemporary astrophysics are the means by which planetary systems are assembled from the large rotating disks of gas and dust which attend a stellar birth. Although important work has already been, and is still being done both in theory and observation, a full understanding of the physics of planet formation can only be achieved by opening observational windows able to directly witness the process in action. The key requirement is then to probe planet-forming systems at the natural spatial scales over which material is being assembled. By definition, this is the so-called Hill Sphere which delineates the region of influence of a gravitating body within its surrounding environment. The Planet Formation Imager project (PFI; http://www.planetformationimager.org) has crystallized around this challenging goal: to deliver resolved images of Hill-Sphere-sized structures within candidate planethosting disks in the nearest star-forming regions. In this contribution we outline the primary science case of PFI. For this purpose, we briefly review our knowledge about the planet-formation process and discuss recent observational results that have been obtained on the class of transition disks. Spectro-photometric and multi-wavelength interferometric studies of these systems revealed the presence of extended gaps and complex density inhomogeneities that might be triggered by orbiting planets. We present detailed 3-D radiation-hydrodynamic simulations of disks with single and multiple embedded planets, from which we compute synthetic images at near-infrared, mid-infrared, far-infrared, and sub-millimeter wavelengths, enabling a direct comparison of the signatures that are detectable with PFI and complementary facilities such as ALMA. From these simulations, we derive some preliminary specifications that will guide the array design and technology roadmap of the facility
HD 42477: coupled r modes, g modes and a p mode in an A0Vnne star
Several studies have shown that a number of stars pulsating in p modes lie between the β Cep and δ Sct instability strips in the Hertzsprung-Russell (HR) Diagram. At present, there is no certain understanding of how p~modes can be excited in this Teff range. The goal of this work is to disprove the conjecture that all stars pulsating in p modes and lying in this Teff range are the result of incorrect measurements of Teff, contamination, or the presence of unseen cooler companions lying in the δ Sct instability strip (given the high binary fraction of stars in this region of the HR Diagram). Using TESS data, we show that the A0Vnne star HD 42477 has a single p mode coupled to several r modes and/or g modes. We rule out a contaminating background star with a pixel-by-pixel examination, and we essentially rule out the possibility of a companion δ Sct star in a binary. We model the pulsations in HD 42477 and suggest that the g modes are excited by overstable convective core modes. We also conjecture that the single p mode is driven by coupling with the g modes, or that the oblateness of this rapidly-rotating star permits driving by He II ionization in the equatorial region
KELT-18b: Puffy Planet, Hot Host, Probably Perturbed
We report the discovery of KELT-18b, a transiting hot Jupiter in a 2.87-day orbit around the bright ( V = 10.1), hot, F4V star BD+60 1538 (TYC 3865-1173-1). We present follow-up photometry, spectroscopy, and adaptive optics imaging that allow a detailed characterization of the system. Our preferred model fits yield a host stellar temperature of K and a mass of , situating it as one of only a handful of known transiting planets with hosts that are as hot, massive, and bright. The planet has a mass of , a radius of , and a density of , making it one of the most inflated planets known around a hot star. We argue that KELT-18b’s high temperature and low surface gravity, which yield an estimated ∼600 km atmospheric scale height, combined with its hot, bright host, make it an excellent candidate for observations aimed at atmospheric characterization. We also present evidence for a bound stellar companion at a projected separation of ∼1100 au, and speculate that it may have contributed to the strong misalignment we suspect between KELT-18\u27s spin axis and its planet’s orbital axis. The inferior conjunction time is 2457542.524998 ± 0.000416 (BJD TDB ) and the orbital period is 2.8717510 ± 0.0000029 days. We encourage Rossiter–McLaughlin measurements in the near future to confirm the suspected spin–orbit misalignment of this system
KELT-20b: A Giant Planet With A Period Of P ~ 3.5 Days Transiting The V ~ 7.6 Early A Star HD 185603
We report the discovery of KELT-20b, a hot Jupiter transiting a early A star, HD 185603, with an orbital period of days. Archival and follow-up photometry, Gaia parallax, radial velocities, Doppler tomography, and AO imaging were used to confirm the planetary nature of KELT-20b and characterize the system. From global modeling we infer that KELT-20 is a rapidly rotating ( ) A2V star with an effective temperature of K, mass of , radius of , surface gravity of , and age of . The planetary companion has a radius of , a semimajor axis of au, and a linear ephemeris of . We place a upper limit of on the mass of the planet. Doppler tomographic measurements indicate that the planetary orbit normal is well aligned with the projected spin axis of the star ( ). The inclination of the star is constrained to , implying a three-dimensional spin–orbit alignment of . KELT-20b receives an insolation flux of , implying an equilibrium temperature of of ∼2250 K, assuming zero albedo and complete heat redistribution. Due to the high stellar , KELT-20b also receives an ultraviolet (wavelength nm) insolation flux of , possibly indicating significant atmospheric ablation. Together with WASP-33, Kepler-13 A, HAT-P-57, KELT-17, and KELT-9, KELT-20 is the sixth A star host of a transiting giant planet, and the third-brightest host (in V ) of a transiting planet
An overview of the mid-infrared spectro-interferometer MATISSE: science, concept, and current status
MATISSE is the second-generation mid-infrared spectrograph and imager for the
Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric
instrument will allow significant advances by opening new avenues in various
fundamental research fields: studying the planet-forming region of disks around
young stellar objects, understanding the surface structures and mass loss
phenomena affecting evolved stars, and probing the environments of black holes
in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the
spectral domain of current optical interferometers by offering the L and M
bands in addition to the N band. This will open a wide wavelength domain,
ranging from 2.8 to 13 um, exploring angular scales as small as 3 mas (L band)
/ 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared
imaging - closure-phase aperture-synthesis imaging - with up to four Unit
Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE
will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we
present one of the main science objectives, the study of protoplanetary disks,
that has driven the instrument design and motivated several VLTI upgrades
(GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a
description of the signal on the detectors and an evaluation of the expected
performances. We also discuss the current status of the MATISSE instrument,
which is entering its testing phase, and the foreseen schedule for the next two
years that will lead to the first light at Paranal.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2016, 11 pages, 6 Figure
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