Search results for "Planetary Science"
showing 10 items of 4367 documents
Carbon Monoxide in the Cold Debris of Supernova 1987A
2013
We report spectroscopic and imaging observations of rotational transitions of cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a supernova remnant. In addition to line luminosities for the CO J=1-0, 2-1, 6-5, and 7-6 transitions, we present upper limits for all other transitions up to J=13-12, collectively measured from the Atacama Large Millimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), and the Herschel Spectral and Photometric Imaging REceiver (SPIRE). Simple models show the lines are emitted from at least 0.01 solar masses of CO at a temperature > 14 K, confined within at most 35% of a spherical volume expanding at ~ 2000 km/s. Moreover, we…
Correcting the effect of stellar spots on ARIEL transmission spectra
2020
The goal of this study is to assess the impact of the stellar spots on the extraction of the planetary transmission spectra observed by ARIEL. We develop a method to model the stellar spectrum of a star in the presence of spots by using the out-of-transit observations. It is based on a chi squared minimization procedure of the out-of-transit spectrum on a grid of stellar spectra with different sizes and temperatures of the spots. The approach allows us also to study the temporal evolution of the spots when comparing stellar spectra observed at different epochs. We also present a method to correct the transit depth variations due to non-occulted stellar spots and estimate the error we introd…
Assessment of a high-resolution central scheme for the solution of the relativistic hydrodynamics equations
2004
We assess the suitability of a recent high-resolution central scheme developed by Kurganov & Tadmor (2000) for the solution of the relativistic hydrodynamics equations. The novelty of this approach relies on the absence of Riemann solvers in the solution procedure. The computations we present are performed in one and two spatial dimensions in Minkowski spacetime. Standard numerical experiments such as shock tubes and the relativistic flat-faced step test are performed. As an astrophysical application the article includes two-dimensional simulations of the propagation of relativistic jets using both Cartesian and cylindrical coordinates. The simulations reported clearly show the capabili…
Variable X-ray emission from the accretion shock in the classical T Tauri star V2129 Ophiuchi
2011
The soft X-ray emission from high density plasma in CTTS is associated with the accretion process. It is still unclear whether this high density cool plasma is heated in the accretion shock, or if it is coronal plasma fed/modified by the accretion process. We conducted a coordinated quasi-simultaneous optical and X-ray observing campaign of the CTTS V2129 Oph (Chandra/HETGS data to constrain the X-ray emitting plasma components, and optical observations to constrain the characteristics of accretion and magnetic field). We analyze a 200 ks Chandra/HETGS observation of V2129 Oph, subdivided into two 100 ks segments, corresponding to two different phases within one stellar rotation. The X-ray …
Warren Buffett versus Zvi Bodie: Should You Buy Or Sell Put Options?
2021
Academics and investment professionals often disagree when it comes to investment advice. Legendary investor Warren Buffett is a proponent of time diversification and firmly believes that stocks are less risky in the long run. Therefore, he often sells long-term put options instead of buying them for portfolio protection. By contrast, the famous finance professor Zvi Bodie argues that time diversification is a fallacy and, therefore, his advice to fund managers is to buy long-term portfolio insurance. In this article, we consider the optimal portfolio choice problem for a loss-averse investor. First, we demonstrate that our loss-averse investor subscribes to the principle of time diversific…
El hombre unidimensional fragmentado
2013
Parafraseamos el título del conocido ensayo de Herbert Marcuse, puesto que la imagen que tradicionalmente se ha generado del hombre, de la masculinidad, ha sido unidimensional. Es decir, el hombre se caracterizaba por unos rasgos y conductas establecidos y afianzados desde tiempos remotos, considerándose todas las demás señas diferenciadoras como meras desviaciones impropias de lo normativo. Pero observaremos que esta realidad incuestionable, tal y como han analizado diversos investigadores a través de lo que se ha venido en denominar Men’s studies, ha demostrado ser una falacia difícil de mantener a lo largo de la historia y que en la actualidad deviene en falaz e inoperante frente a los c…
Geochemical characteristics of Archaean and Late Proterozoic to Palaeozoic fine-grained sediments from Southern Africa and significance for the evolu…
1985
Chemical data for pelitic rocks (shallow-marine platform sediments) of the ∼ 2.9 Ga old Pongola Supergroup, South Africa, and the 550–700 Ma old Nama Group, Namibia, revealed clearly different compositions in both groups. A comparison of the Pongola and Nama data with literature values for sedimentary rocks shows a trend for Cr/TiO2 and Cr/Zn ratios as well as the absolute Cr and Ni concentrations to lower values with decreasing age, whereas the Cr/Ni ratios seem to remain broadly constant through time. REE patterns of Pongola and Nama sediments show no significant difference, thus giving the impression of a post-Archaean origin for the demonstrably Archaean Pongola sediments. However, a pl…
Multiple zircon growth within early Archaean tonalitic gneiss from the Ancient Gneiss Complex, Swaziland
1988
Abstract U Pb age determinations by ion microprobe reveal multiple episodes of zircon growth and recrystallization within a single sample of tonalitic gneiss from the Ancient Gneiss Complex. The oldest episode at3644 ± 4Ma(2σ) produced the dominant type of zircon, characteristically purplish-brown and massive in texture; this probably constitutes unaltered zircon precipitated from the original magma. Recrystallization accompanied (and obscured) by early Pb loss took place within the oldest grains at3504 ± 6Ma and3433 ± 8Ma. Whole new grains grew at these times also. We interpret the post-3644 Ma growth as due to episodic deformational and metamorphic events that transformed the tonalite plu…
Soil Moisture Effect on Thermal Infrared (8–13-μm) Emissivity
2010
Thermal infrared (TIR) emissivities of soils with different textures were measured for several soil moisture (SM) contents under controlled conditions using the Box method and a high-precision multichannel TIR radiometer. The results showed a common increase of emissivity with SM at water contents lower than the field capacity. However, this dependence is negligible for higher water contents. The highest emissivity variations were observed in sandy soils, particularly in the 8-9-μm range due to water adhering to soil grains and decreasing the reflectance in the 8-9-μm quartz doublet region. Thus, in order to model the emissivity dependence on soil water content, different approaches were st…
A mathematical study on effective wavenumber, an operative computation procedure, and its use with radiance-temperature relationships
2003
In this paper we study the existence of effective wavenumber for any sensor by means of simple mathematics. We implement a numeric algorithm, based on the developed mathematical background, into a computer program named 'srf2radi', which is freely available via anonymous File Transfer Protocol (FTP) at ftp://ftp.uv.es/pub/src/. The number of effective wavenumbers for each temperature and their accuracy are also computed and studied for NOAA-16 Advanced Very High Resolution Radiometer Version 3 (AVHRR/3) channel 4. These effective wavenumbers can be used to obtain radiance-temperature relationships with physical meaning for any sensor in user-defined temperature intervals.