We present an analytic model for the interaction between planetary atmospheres and stellar winds from main sequence M stars, with the purpose of obtaining a quick test-model that estimates the ...timescale for total atmospheric mass loss due to this interaction. Planets in the habitable zone of M dwarfs may be tidally locked and may have weak magnetic fields, because of this we consider the extreme case of planets with no magnetic field. The model gives the planetary atmosphere mass loss rate as a function of the stellar wind and planetary properties (mass, atmospheric pressure and orbital distance) and an entrainment efficiency coefficient
α. We use a mixing layer model to explore two different cases: a time-independent stellar mass loss and a stellar mass loss rate that decreases with time. For both cases we consider planetary masses within the range of 1
→
10
M
⊕ and atmospheric pressures with values of 1, 5 and 10
atm. We apply our model to Venus by estimating its atmospheric mass loss rate by the interaction with the solar wind and compare our model with more detailed simulations. We find a good agreement between our results and the atmospheric mass loss obtained by more detailed models, and it is therefore appropriate for carrying out an exploration of the broad parameter space of exoplanetary systems. For the time-dependent case, planets without magnetic field in the habitable zone of M dwarfs with initial stellar mass losses of
M
˙
w
<
10
-
11
M
⊙
year
−1, may retain their atmospheres for at least 1
Gyr. This case may be applied to early spectral type M dwarfs (earlier than M5). Studies have shown that late type M dwarfs (later than M5) may be active for long periods of time (⩾4
Gyr), and because of that our model with constant stellar mass loss rate may be more accurate. For these stars most planets may have lost their atmospheres in 1
Gyr or less because most of the late type M dwarfs are expected to be active. We emphasize that our model only considers planets without magnetic fields. Clearly we must expect a higher resistance to atmospheric erosion if we include the presence of a magnetic field. Nevertheless, as a first approximation our model is able to give a reliable timescale, as evidence by comparing our results with more detailed models.
Although substantial economic barriers exist, marine diatoms such as Thalassiosira pseudonana and Phaeodactylum tricornutum hold promise as feedstock for biodiesel because of their ability to ...manufacture and store triacylglycerols (TAGs). The recent sequencing of these two marine diatom genomes by the United States Department of Energy Joint Genome Institute and the development of improved systems for genetic manipulation should allow a more systematic approach to understanding and maximizing TAG production. However, in order to best utilize these genomes and genetic tools, we must first gain a deeper understanding of the nutrient-mediated regulation of TAG anabolism. By determining both the yield and molecular species distribution of TAGs we will, in the future, be able to fully characterize the effects of genetic manipulation. Here, we lay the groundwork for understanding TAG production in T. pseudonana and P. tricornutum, as a function of nitrate and silicate depletion. Diatoms were starved of either nitrate or silicate, and TAGs were extracted with hexane from lyophilized samples taken at various time intervals following starvation. The timing of TAG production and the relative abundance of TAGs were estimated by fluorescence spectroscopy using Nile red and the total yield per biomass determined by gravimetric assay. TAGs were analyzed using thin layer chromatography, gas chromatography-mass spectrometry, and electrospray ionization mass spectrometry to identify the major TAG species produced during the growth curve. Under our conditions, the TAG yield from T. pseudonana is about 14-18% of total dry weight. The TAG yield from P. tricornutum is about 14% of total dry weight. Silicate-starved T. pseudonana accumulated an average of 24% more TAGs than those starved for nitrate; however, the chemotypes of the TAGs produced were generally similar regardless of the starvation condition employed.
We report the discovery of WTS-2 b, an unusually close-in 1.02-d hot Jupiter (M
P
= 1.12M
J, R
P
= 1.30R
J) orbiting a K2V star, which has a possible gravitationally bound M-dwarf companion at 0.6 ...arcsec separation contributing ∼20 per cent of the total flux in the observed J-band light curve. The planet is only 1.5 times the separation from its host star at which it would be destroyed by Roche lobe overflow, and has a predicted remaining lifetime of just ∼40 Myr, assuming a tidal dissipation quality factor of
.
is a key factor in determining how frictional processes within a host star affect the orbital evolution of its companion giant planets, but it is currently poorly constrained by observations. We calculate that the orbital decay of WTS-2 b would correspond to a shift in its transit arrival time of T
shift ∼ 17 s after 15 yr assuming
. A shift less than this would place a direct observational constraint on the lower limit of
in this system. We also report a correction to the previously published expected T
shift for WASP-18 b, finding that T
shift = 356 s after 10 yr for
, which is much larger than the estimated 28 s quoted in WASP-18 b discovery paper. We attempted to constrain
via a study of the entire population of known transiting hot Jupiters, but our results were inconclusive, requiring a more detailed treatment of transit survey sensitivities at long periods. We conclude that the most informative and straightforward constraints on
will be obtained by direct observational measurements of the shift in transit arrival times in individual hot Jupiter systems. We show that this is achievable across the mass spectrum of exoplanet host stars within a decade, and will directly probe the effects of stellar interior structure on tidal dissipation.
Abstract
We report on the discovery of four ultra-short-period (P ≤ 0.18 d) eclipsing M-dwarf binaries in the Wide-Field Camera (WFCAM) Transit Survey. Their orbital periods are significantly shorter ...than that of any other known main-sequence binary system, and are all significantly below the sharp period cut-off at P ∼ 0.22 d as seen in binaries of earlier-type stars. The shortest-period binary consists of two M4-type stars in a P = 0.112 d orbit. The binaries are discovered as part of an extensive search for short-period eclipsing systems in over 260 000 stellar light curves, including over 10 000 M-dwarfs down to J = 18 mag, yielding 25 binaries with P ≤ 0.23 d. In a popular paradigm, the evolution of short-period binaries of cool main-sequence stars is driven by the loss of angular momentum through magnetized winds. In this scheme, the observed P ∼ 0.22 d period cut-off is explained as being due to time-scales that are too long for lower-mass binaries to decay into tighter orbits. Our discovery of low-mass binaries with significantly shorter orbits implies that either these time-scales have been overestimated for M-dwarfs, e.g. due to a higher effective magnetic activity, or the mechanism for forming these tight M-dwarf binaries is different from that of earlier-type main-sequence stars.
Algal biofuels are a growing interest worldwide due to their potential in terms of sustainable greenhouse gas displacement and energy production. This article describes a comparative survey of ...biodiesel production and conversion yields of biodiesel via alkaline transesterification of acylglycerols extracted from the microalgae Thalassiosira pseudonana and Phaeodactylum tricornutum, grown under silicate or nitrate limitation, and that of model vegetable oils: soybean, and rapeseed oil. Acylglycerols were extracted with n‐hexane and the total yield per biomass was determined by gravimetric assay. Under our conditions, the total acylglycerol yield from the microalgae studied was 13–18% of total dry weight. The biodiesel samples were analyzed using gas chromatography–flame ionization detector to determine quantitative information of residual glycerol, mono‐, di‐, and tri‐acylglycerol concentrations in the biodiesel. All of the algal‐based biodiesel demonstrated less mono‐, di‐, and tri‐acylglycerol concentrations than the vegetable‐based biodiesel under identical transesterification conditions. The fatty acid compositions of all the feedstock oils and their resultant biodiesel were also analyzed and reported. Based on the fatty acid methyl ester compositions of our samples we qualitatively assessed the suitability of the algal‐derived biodiesel in terms of cetane number (CN), cold‐flow properties, and oxidative stability. Biotechnol. Bioeng. 2012;109: 1146–1154. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.
This work presents the feasibility of producing biodiesel, at the bench‐scale, from extracted algal acylglycerols produced by Phaeodactylum tricornutum and Thalassiosira Pseudonana under targeted environmental conditions. Using GC‐FID the authors quantified the residual glycerol, MAGs, DAGs, TAGs, and total free glycerol within the resultant biodiesel. The fatty acid profiles for the feedstock oils and their resultant biodiesel methyl esters are also presented along with a qualitative assessment of the suitability of the diatom‐based biodiesel in terms of cetane number (CN), cold‐flow properties, and oxidative stability.
The Wide Field Camera Transit Survey is a pioneer program aiming at for searching extra-solar planets in the near-infrared. The images from the survey are processed by a data reduction pipeline, ...which uses aperture photometry to construct the light curves. We produce an alternative set of light curves using the difference-imaging method for the most complete field in the survey and carry out a quantitative comparison between the photometric precision achieved with both methods. The results show that difference-photometry light curves present an important improvement for stars with J > 16. We report an implementation on the box-fitting transit detection algorithm, which performs a trapezoid-fit to the folded light curve, providing more accurate results than the box-fitting model. We describe and optimize a set of selection criteria to search for transit candidates, including the V-shape parameter calculated by our detection algorithm. The optimized selection criteria are applied to the aperture photometry and difference-imaging light curves, resulting in the automatic detection of the best 200 transit candidates from a sample of ~475 000 sources. We carry out a detailed analysis in the 18 best detections and classify them as transiting planet and eclipsing binary candidates. We present one planet candidate orbiting a late G-type star. No planet candidate around M-stars has been found, confirming the null detection hypothesis and upper limits on the occurrence rate of short-period giant planets around M-dwarfs presented in a prior study. We extend the search for transiting planets to stars with J ≤ 18, which enables us to set a stricter upper limit of 1.1%. Furthermore, we present the detection of five faint extremely-short period eclipsing binaries and three M-dwarf/M-dwarf binary candidates. The detections demonstrate the benefits of using the difference-imaging light curves, especially when going to fainter magnitudes.
Reflexión sobre las especificidades teórico-metodológicas de Avatares de la antropología histórica (Kuri y Millán 2021), libro sobre los orígenes, particularidades y retos de la licenciatura en ...antropología histórica de la Universidad Veracruzana, a veinte años de su fundación. Ubico sus propuestas respecto de debates internacionales a fin de resaltar la relevancia de su énfasis crítico de esencializaciones culturales. Se han centrado en análisis relacionales e interpretativos sobre la producción de significaciones, referidos a vínculos entre prácticas cotidianas y sus condiciones socio-espaciales de realización, a fin de distanciarse de conceptos ontológicos, estructuralistas y estáticos de cultura e identidad, tradiciones, espacio y cuerpo, así como de nociones objetivistas de historia, archivos y memoria colectiva. Termino sobre oportunidades y retos teórico-metodológicos clave para que sigan enriqueciendo la orientación antropológico-histórica de su programa: sobre vínculos entre significación y poder, y sobre sus posicionamientos en debates sobre las especificidades de una antropología histórica.
A release of multicolor broadband (BVRI) photometry for a subsample of 44 isolated spirals drawn from the Catalogue of Isolated Galaxies is presented. Total magnitudes and colors at various circular ...apertures, as well as some global structural/morphological parameters, are estimated. Morphology is reevaluated through optical and sharp-filtered R-band images, (B - I) color index maps, and archived near-IR JHK images from the Two Micron All Sky Survey. The CAS structural parameters (concentration, asymmetry, and clumpiness) were calculated from the images in each of the bands. The fraction of galaxies with well-identified optical/near-IR bars (SB) is 63%, while another 17% show evidence of weak or suspected bars (SAB). The sample average value of the maximum bar ellipticity is max 0.4. Half of the galaxies in the sample show rings. We identify two candidates for isolated galaxies with disturbed morphology. The structural CAS parameters change with the observed band, and the tendencies they follow with morphological type and global color are more evident in the redder bands. In any band, the major difference between our isolated spirals and a sample of interacting spirals is revealed in the A-S plane. A deep and uniformly observed sample of isolated galaxies is intended for various purposes, including (1) comparative studies of environmental effects, (2) comparing model predictions of galaxy evolution, and (3) evaluating the change of galaxy properties with redshift.
We report the discovery of WTS-1b, the first extrasolar planet found by the WFCAM Transit Survey, which began observations at the 3.8-m United Kingdom Infrared Telescope (UKIRT) in 2007 August. Light ...curves comprising almost 1200 epochs with a photometric precision of better than 1per cent to J 16 were constructed for 60000 stars and searched for periodic transit signals. For one of the most promising transiting candidates, high-resolution spectra taken at the Hobby-Eberly Telescope (HET) allowed us to estimate the spectroscopic parameters of the host star, a late-F main-sequence dwarf (V = 16.13) with possibly slightly subsolar metallicity, and to measure its radial velocity variations. The combined analysis of the light curves and spectroscopic data resulted in an orbital period of the substellar companion of 3.35d, a planetary mass of 4.01 ± 0.35MJ and a planetary radius of RJ. WTS-1b has one of the largest radius anomalies among the known hot Jupiters in the mass range 3-5MJ. The high irradiation from the host star ranks the planet in the pM class. PUBLICATION ABSTRACT
Abstract
We report the discovery of WTS-1b, the first extrasolar planet found by the WFCAM Transit Survey, which began observations at the 3.8-m United Kingdom Infrared Telescope (UKIRT) in 2007 ...August. Light curves comprising almost 1200 epochs with a photometric precision of better than 1 per cent to J ∼ 16 were constructed for ∼60 000 stars and searched for periodic transit signals. For one of the most promising transiting candidates, high-resolution spectra taken at the Hobby-Eberly Telescope (HET) allowed us to estimate the spectroscopic parameters of the host star, a late-F main-sequence dwarf (V = 16.13) with possibly slightly subsolar metallicity, and to measure its radial velocity variations. The combined analysis of the light curves and spectroscopic data resulted in an orbital period of the substellar companion of 3.35 d, a planetary mass of 4.01 ± 0.35 M
J and a planetary radius of
R
J. WTS-1b has one of the largest radius anomalies among the known hot Jupiters in the mass range 3-5 M
J. The high irradiation from the host star ranks the planet in the pM class.
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