Estimation of the XUV radiation onto close planets and their evaporation

Context: The current distribution of planet mass vs. incident stellar X-ray flux supports the idea that photoevaporation of the atmosphere may take place in close-in planets. Integrated effects have to be accounted for. A proper calculation of the mass loss rate due to photoevaporation requires to estimate the total irradiation from the whole XUV range. Aims: The purpose of this paper is to extend the analysis of the photoevaporation in planetary atmospheres from the accessible X-rays to the mostly unobserved EUV range by using the coronal models of stars to calculate the EUV contribution to the stellar spectra. The mass evolution of planets can be traced assuming that thermal losses dominate the mass loss of their atmospheres. Methods: We determine coronal models for 82 stars with exoplanets that have X-ray observations available. Then a synthetic spectrum is produced for the whole XUV range (~1-912 {\AA}). The determination of the EUV stellar flux, calibrated with real EUV data, allows us to calculate the accumulated effects of the XUV irradiation on the planet atmosphere with time, as well as the mass evolution for planets with known density. Results: We calibrate for the first time a relation of the EUV luminosity with stellar age valid for late-type stars. In a sample of 109 exoplanets, few planets with masses larger than ~1.5 Mj receive high XUV flux, suggesting that intense photoevaporation takes place in a short period of time, as previously found in X-rays. The scenario is also consistent with the observed distribution of planet masses with density. The accumulated effects of photoevaporation over time indicate that HD 209458b may have lost 0.2 Mj since an age of 20 Myr. Conclusions: Coronal radiation produces rapid photoevaporation of the atmospheres of planets close to young late-type stars. More complex models are needed to explain fully the observations.Comment: Accepted by A&A. 10 pages, 8 figures, 7 Tables (2 online). Additional online material includes 7 pages, 6 figures and 6 tables, all include

Active cool stars and He I 10830 \AA: the coronal connection

The mechanism of formation of the He I 10830 A triplet in cool stars has been subject of debate for the last 30 years. A relation between the X-ray luminosity and the He I 10830 A flux was found in cool stars, but the dominant mechanism of formation in these stars (photoionization by coronal radiation followed by recombination and cascade, or collisional excitation in the chromosphere), has not yet been established. We use modern instrumentation (NOT/SOFIN) and a direct measurement of the EUV flux, which photoionizes He I, to investigate the formation mechanism of the line for the most active stars which are frequently excluded from analysis. We have observed with an unprecedented resolution (R~170,000) the He I 10830 A triplet in a set of 15 stars that were also observed with the Extreme Ultraviolet Explorer (EUVE) in order to compare the line strengths with their EUV and X-ray fluxes. Active dwarf and subgiant stars do not exhibit a relation between the EUV flux and the equivalent width of the He I 10830 A line. Giant stars however, show a positive correlation between the strength of the He I 10830 A absorption and the EUV and X-ray fluxes. The strength of the C IV 1550 A emission does not correlate with coronal fluxes in this sample of 15 stars. Active dwarf stars may have high chromospheric densities thus allowing collisional excitation to dominate photoionization/recombination processes in forming the He I 10830 A line. Active giant stars possess lower gravities, and lower chromospheric densities than dwarfs, allowing for photoexcitation processes to become important. Moreover, their extended chromospheres allowfor scattering of infrared continuum radiation, producing strong absorption in He I and tracing wind dynamics.Comment: 9 pages, 12 figures. Accepted by A&A (June 2008

A scenario of planet erosion by coronal radiation

Context: According to theory, high-energy emission from the coronae of cool stars can severely erode the atmospheres of orbiting planets. No observational tests of the long term effects of erosion have yet been made. Aims: To analyze the current distribution of planetary mass with X-ray irradiation of the atmospheres in order to make an observational assessment of the effects of erosion by coronal radiation. Methods: We study a large sample of planet-hosting stars with XMM-Newton, Chandra and ROSAT; make a careful identification of X-ray counterparts; and fit their spectra to make accurately measurements of the stellar X-ray flux. Results: The distribution of the planetary masses with X-ray flux suggests that erosion has taken place: most surviving massive planets, (M_p sin i >1.5 M_J), have been exposed to lower accumulated irradiation. Heavy erosion during the initial stages of stellar evolution is followed by a phase of much weaker erosion. A line dividing these two phases could be present, showing a strong dependence on planet mass. Although a larger sample will be required to establish a well-defined erosion line, the distribution found is very suggestive. Conclusions: The distribution of planetary mass with X-ray flux is consistent with a scenario in which planet atmospheres have suffered the effects of erosion by coronal X-ray and EUV emission. The erosion line is an observational constraint to models of atmospheric erosion.Comment: A&A 511, L8 (2010). 4 pages, 3 figures, 1 online table (included). Language edited; corrected a wrong unit conversion (g/s -> M_J/Gyr); corrected values in column 12 of Table 1 (slightly underestimated in first version), and Figure 2 updated accordingl

Three years in the coronal life of AB Dor. I. Plasma emission measure distributions and abundances at different activity levels

The young active star AB Dor (K1 IV-V) has been observed 16 times in the last three years with the XMM-Newton and Chandra observatories, totalling 650 ks of high-resolution X-ray spectra. The XMM/RGS observations with the highest and lowest average emission levels have been selected to study the coronal properties of AB Dor in two different activity levels. We compare the results based on the XMM data with those obtained from a higher resolution Chandra/HETG spectrum, using the same line-based analysis technique. We have reconstructed the plasma Emission Measure Distribution vs. temperature (EMD) in the range log T(K) ~ 6.1-7.6, and we have determined the coronal abundances of AB Dor, obtaining consistent results between the two instruments.The overall shape of the EMD is also consistent with the one previously inferred from EUVE data. The EMD shows a steep increase up to the peak at log T (K) ~ 6.9 and a substantial amount of plasma in the range log T (K) ~ 6.9-7.3. The coronal abundances show a clear trend of increasing depletion with respect to solar photospheric values, for elements with increasing First Ionization Potential (FIP), down to the Fe value ([Fe/H]=-0.57), followed by a more gradual recovery of the photospheric values for elements with higher FIP. He-like triplets and Fe XXI and Fe XXII lines ratios indicate electron densities log ne~10.8 cm^-3 at log T(K) ~ 6.3 and log ne ~ 12.5 at log T(K) ~ 7, implying plasma pressures steeply increasing with temperature. These results are interpreted in the framework of a corona composed of different families of magnetic loop structures, shorter than the stellar radius and in isobaric conditions, having pressures increasing with the maximum plasma temperature, and which occupy a small fraction (f ~ 10^-4 - 10^-6) of the stellar surface.Comment: Accepted by A&

Status of marine protected areas in Egypt

Egypt has sought to protect its natural resources and marine biodiversity by establishing a network of six MPAs that are generally located in the Gulf of Aqaba and the Red Sea; most of them include interconnected marine and terrestrial sectors based on conserving coral reefs and accompanying systems. We assessed the present status of MPA networks that showed a set of important results manifested in some strengths (i.e. proper selection according to specific criteria, management plans, etc.), and also some weaknesses (i.e. a relatively small protected proportion of the Egyptian marine territorial waters, significant pressures mainly by tourism activities, etc.). Finally, some recommendations are proposed from this work (i.e. incorporate more habitats that are not well represented in the network, especially on the Mediterranean Sea; establishing a touristic carrying capacity of each area; etc.) to improve the current situation. Key words: Marine reserves, Fishing, Tourism, Conservation, Sustainable development, Egypt.Egipto ha establecido una red de seis áreas marinas protegidas (AMPs), situadas principalmente en el Golfo de Aqaba y el mar Rojo para proteger sus recursos naturales y su biodiversidad marina. La mayoría incluyen sectores terrestres y marinos interconectados con el fin de conservar los arrecifes de coral y otros sistemas acompañantes. El estado actual de la red de AMPs se manifiesta mediante algunos puntos fuertes (selección basada en criterios apropiados, existencia de planes de gestión, etc.) y también algunos puntos débiles (protección de una proporción relativamente pequeña de las aguas territoriales egipcias; presiones significativas de algunas actividades, principalmente el turismo, etc.). Finalmente, se proponen algunas recomendaciones (incorporación de más hábitats que no están bien representados en la red actual, particularmente en el Mediterráneo; establecimiento de una capacidad de carga turística para cada área; etc.) para mejorar la situación actual. Palabras clave: Reservas marinas, Pesca, Turismo, Conservación, Desarrollo sostenible, Egipto.Egypt has sought to protect its natural resources and marine biodiversity by establishing a network of six MPAs that are generally located in the Gulf of Aqaba and the Red Sea; most of them include interconnected marine and terrestrial sectors based on conserving coral reefs and accompanying systems. We assessed the present status of MPA networks that showed a set of important results manifested in some strengths (i.e. proper selection according to specific criteria, management plans, etc.), and also some weaknesses (i.e. a relatively small protected proportion of the Egyptian marine territorial waters, significant pressures mainly by tourism activities, etc.). Finally, some recommendations are proposed from this work (i.e. incorporate more habitats that are not well represented in the network, especially on the Mediterranean Sea; establishing a touristic carrying capacity of each area; etc.) to improve the current situation. Key words: Marine reserves, Fishing, Tourism, Conservation, Sustainable development, Egypt

Photospheric and coronal abundances in solar-type stars: the peculiar case of Tau Bootis

Chemical abundances in solar-type stars are a much debated topic. Planet-hosting stars are known to be metal-rich, but whether or not this peculiarity applies also to the chemical composition of the outer stellar atmospheres is still to be clarified. More in general, coronal and photospheric abundances in late-type stars appear to be different in many cases, but understanding how chemical stratification effects work in stellar atmospheres requires an observational base larger than currently available. We obtained XMM-Newton high-resolution X-ray spectra of Tau Bootis, a well known nearby star with a Jovian-mass close-in planet. We analyzed these data with the aim to perform a detailed line-based emission measure analysis and derive the abundances of individual elements in the corona with two different methods applied independently. We compared the coronal abundances of Tau Bootis with published photospheric abundances based on high-resolution optical spectra and with those of other late-type stars with different magnetic activity levels, including the Sun. We find that the two methods provide consistent results within the statistical uncertainties for both the emission measure distribution of the hot plasma and for the coronal abundances, with discrepancies at the 2-sigma level limited to the amount of plasma at temperatures of 3-4 MK and to the O and Ni abundances. In both cases, the elements for which both coronal and photospheric measurements are available (C, N, O, Si, Fe, and Ni) result systematically less abundant in the corona by a factor 3 or more, with the exception of the coronal Ni abundance, which is similar to the photospheric value. Comparison with other late-type stars of similar activity level shows that these coronal/photospheric abundance ratios are peculiar to Tau Bootis and possibly related to the characteristic over-metallicity of this planet-hosting star.Comment: 9 pages, 7 figures. A&A, in press. Language-edited version, one reference update

Lesiones de partes blandas por fricción

La lesión por fricción es una lesión de partes blandas que dentro de su rareza se encuentra más frecuentemente en el contexto de los accidentes de tráfico. Las fuerzas tangenciales se transmiten des del asfalto, ruedas de los vehículos a tejido celular subcutáneo conduciendo a un gran deslizamiento del mismo sobre la fascia muscular. El movimiento anormal provoca la rotura de vasos linfáticos y vasculares conduciendo una colección serohemática. Las situaciones más frecuentemente encontrada son aquellas las cuales contienen masas musculares grandes. Normalmente es una lesión de larga evolución e infradiagnosticada en sus estados iniciales. Se presenta como una tumoración fría, dolorosa e incapacitante con piel adyacente intacta o con petequías. Se diagnostica con exploración física y pruebas complementarias, como ecografía. El tratamiento teniendo en cuenta diferentes ítems puede consistir en medida conservadoras o llegar a procedimientos quirúrgicos. En la literatura no se pone de manifiesto variabilidad en los resultados de diferentes procedimientos terapéuticos.Injury by friction is an injury of soft parts that although not frequent it is not unusual in the context of the traffic accidents. The tangential forces are transmitted from the asphalt and the wheels of the vehicles to the cellular subcutaneous fabric, producing a big sliding on the muscular fascia. The abnormal movement breaks the lymphatic and vascular glasses leading to a serohematic collection. The most usual situations are that ones which contain muscular big masses. Normally it is an injury of long evolution and infradiagnosticated in its initial conditions. The skin appears as a cold, painful tumor and disabling with adjacent skin intact or with petechiae. It is diagnosed by physical exploration and with additional tests, like ultrasound scan. The treatment, considering different items, can consist on conservative measures or even surgical procedures. In the literature variability is not revealed in the results of different therapeutic procedures.Peer ReviewedAward-winnin

Auditory, Olfactory and Tactile Contact is not an Obstacle for Studies Involving Hormonal Interrelationships

Thirty-two ewes were used to determine whether individual housing, allowing contact with neighbours, induces a stress response. Ewes were housed in individual pens designed to allow the ewes to see, hear, smell and touch adjacent animals, and were distributed into four groups (n=8/group): ewes with subcutaneous implants containing melatonin and oestradiol (M+E), melatonin (M), oestradiol (E) and non-implanted control ewes (C). Heart rate, stress indicators (plasma cortisol, glucose, lactate and creatine kinase (CK) concentrations) and luteinizing hormone (LH) concentrations were measured hourly and compared with the resting values (before and after pen housing). Heart rate increased significantly during the introduction into the pen (P<0.001) in all groups, in comparison with the resting values. No significant differences between groups were observed for cortisol concentrations, with the exception of the M group, which showed the highest response (P<0.001) when ewes were introduced into the pens. Lactate, CK and glucose changes in comparison with the resting values were similar between groups. LH concentrations during pen housing decreased significantly in all groups in comparison with resting values. In conclusion, individual confinement of sheep allowing visual, auditory, olfactory and tactile contact with their neighbouring animals was not an obstacle for investigating particular hormonal interrelationships with multiple sampling procedures. However further investigations are required to determine if this conclusion applies to other hormone systems in sheep