52 research outputs found
Observations of snowpack properties to evaluate ground-based microwave remote sensing
Active microwave radar has been shown to have great potential for estimating snow water equivalent (SWE) globally from space. To help evaluate optimal active microwave sensor configurations to observe SWE, we evaluated ground-based Frequency Modulated Continuous Wave (FMCW) radar (12ā18 GHz, cross-polarisation) using very high resolution in-situ observations of snowpack layering, dielectric permittivity and density over a 10 m snow trench on Toolik Lake, Alaska.
Results showed that the thicknesses of layers within the 10 m trench were highly variable over short distances (< 1 m), even where total snow depth changed very little. Layer boundaries observed using NIR photography identified all bands of high radar backscatter. Although additional observations of density and dielectric permittivity helped to explain the causes of backscatter, not all snowpack properties which cause backscatter were coincident with strong vertical changes in density or permittivity. Further observations of high surface roughness in layer boundaries explained some areas of weak backscatter, nonetheless it was shown that a suite of coincident observations, rather than a single technique in isolation, were required to adequately explain the variability of backscatter and the influence of snowpack properties upon it
Substellar companions and the formation of hot subdwarf stars
"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics."We give a brief review over the observational evidence for close substellar companions to hot subdwarf stars. The formation of these core helium-burning objects requires huge mass loss of their red giant progenitors. It has been suggested that besides stellar companions substellar objects in close orbits may be able to trigger this mass loss. Such objects can be easily detected around hot subdwarf stars by medium or high resolution spectroscopy with an RV accuracy at the km s(-1)-level. Eclipsing systems of Vir type stick out of transit surveys because of their characteristic light curves. The best evidence that substellar objects in close orbits around sdBs exist and that they are able to trigger the required mass loss is provided by the eclipsing system SDSS J0820+0008, which was found in the course of the MUCHFUSS project. Furthermore, several candidate systems have been discovered.Final Accepted Versio
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Rand- und Kƶrperfragment einer Tasse. Konkaves Oberteilprofil, scharfe Knickwand und niedriger Unterteil. Schwarze Farbe. AuĆen: An Schulter umlaufenden Rillen. Am Kƶrper bis zum Knick Stempeldekor mit senkrechten Winkeln und einem Punkt innen
Two temperate super-Earths transiting a nearby late-type M dwarf
peer reviewedIn the age of JWST, temperate terrestrial exoplanets transiting nearby late-type M dwarfs provide unique opportunities for characterising their atmospheres, as well as searching for biosignature gases. We report here the discovery and validation of two temperate super-Earths transiting LP 890-9 (TOI-4306, SPECULOOS-2), a relatively low-activity nearby (32 pc) M6V star. The inner planet, LP 890-9b, was first detected by TESS (and identified as TOI-4306.01) based on four sectors of data. Intensive photometric monitoring of the system with the SPECULOOS Southern Observatory then led to the discovery of a second outer transiting planet, LP 890-9c (also identified as SPECULOOS-2c), previously undetected by TESS. The orbital period of this second planet was later confirmed by MuSCAT3 follow-up observations. With a mass of 0.118Ā±0.002 Mā, a radius of 0.1556Ā±0.0086 Rā, and an effective temperature of 2850Ā±75 K, LP 890-9 is the second-coolest star found to host planets, after TRAPPIST-1. The inner planet has an orbital period of 2.73 d, a radius of 1.320+0.053ā0.027 Rā, and receives an incident stellar flux of 4.09Ā±0.12 Sā. The outer planet has a similar size of 1.367+0.055ā0.039 Rā and an orbital period of 8.46 d. With an incident stellar flux of 0.906 Ā± 0.026 Sā, it is located within the conservative habitable zone, very close to its inner limit. Although the masses of the two planets remain to be measured, we estimated their potential for atmospheric characterisation via transmission spectroscopy using a mass-radius relationship and found that, after the TRAPPIST-1 planets, LP 890-9c is the second-most favourable habitable-zone terrestrial planet known so far. The discovery of this remarkable system offers another rare opportunity to study temperate terrestrial planets around our smallest and coolest neighbours
Prompt and nonprompt Ļ (2S) production in pPb collisions at āsNN = 8. 16 TeV
The production of Ļ(2S) mesons in proton-lead collisions at a centre-of-mass energy per nucleon pair of āsNN = 8.16 TeV is studied with the LHCb detector using data corresponding to an integrated luminosity of 34 nbā1. The prompt and nonprompt Ļ(2S) production cross-sections and the ratio of the Ļ(2S) to J/Ļ cross-section are measured as a function of the meson transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame, together with forward-to-backward ratios and nuclear modification factors. The production of prompt Ļ(2S) is observed to be more suppressed compared to pp collisions than the prompt J/Ļ production, while the nonprompt productions have similar suppression factors
Search for CP violation in the phase space of D0 ā KS0KĀ±Ļā decays with the energy test
A search for CP violation in D0 ā KS0K+Ļā and D0 ā KS0KāĻ+ decays is reported. The search is performed using an unbinned model-independent method known as the energy test that probes local CP violation in the phase space of the decays. The data analysed correspond to an integrated luminosity of 5.4 fbā1 collected in proton-proton collisions by the LHCb experiment at a centre-of-mass energy of ās = 13 TeV, amounting to approximately 950 thousand and 620 thousand signal candidates for the D0 ā KS0KāĻ+ and D0 ā KS0K+Ļā modes, respectively. The method is validated using D0 ā KāĻ+ĻāĻ+ and D0 ā KS0Ļ+Ļā decays, where CP-violating effects are expected to be negligible, and using background-enhanced regions of the signal decays. The results are consistent with CP symmetry in both the D0 ā KS0KāĻ+ and the D0 ā KS0K+Ļā decays, with p-values for the hypothesis of no CP violation of 70% and 66%, respectively
Measurement of the CKM angle Ī³ using the BĀ± ā D*hĀ± channels
A measurement of the CP-violating observables from BĀ± ā D*KĀ± and BĀ± ā D*ĻĀ± decays is presented, where D*(D) is an admixture of D*0 and DĀÆā0 (D0 and DĀÆ0) states and is reconstructed through the decay chains D*ā DĻ0/Ī³ and DāKS0Ļ+Ļā/KS0K+Kā. The measurement is performed by analysing the signal yield variation across the D decay phase space and is independent of any amplitude model. The data sample used was collected by the LHCb experiment in proton-proton collisions and corresponds to a total integrated luminosity of 9 fbā1 at centre-of-mass energies of 7, 8 and 13 TeV. The CKM angle Ī³ is determined to be 69ā14+13ā using the measured CP-violating observables. The hadronic parameters rBDāKĀ±, rBDāĻĀ±, Ī“BDāKĀ±, Ī“BDāĻĀ±, which are the ratios and strong phase differences between favoured and suppressed BĀ± decays, are also reported
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