Retrieving leaf area index from multi-angular airborne data

This work is aimed to demonstrate the feasibility of a methodology for retrieving bio-geophysical variables whilst at the same time fully accounting for additional information on directional anisotropy. A model-based approach has been developed to deconvolve the angular reflectance into single landcovers reflectances, attempting to solve the inconsistencies of 1D models and linear mixture approaches. The model combines the geometric optics of large scale canopy structure with principles of radiative transfer for volume scattering within individual crowns. The reliability of the model approach to retrieve LAI has been demonstrated using data from DAISEX- 99 campaign at Barrax, Spain. Airborne data include POLDER and HyMap data in which various field plots were observed under varying viewing/illumination angles. Nearly simultaneously, a comprehensive field data set was acquired on specific crop plots. The inversions provided accurate LAI values, revealing the model potential to combine spectral and directional information to increase the likely accuracy of the retrievals. In addition, the sensitivity of retrievals with the angular and spectral subset of observations was analysed, showing a high consistency between results. This study has contributed to assess the uncertainties with products derived from satellite data like SEVIRI/MSG

In Vivo Confirmation of the Role of Statins in Reducing Nitric Oxide and C-Reactive Protein Levels in Peripheral Arterial Disease

AbstractObjectivesInflammatory and other processes mediating impairment of endothelial function, where there are increased levels of C-reactive protein (CRP) and plasma nitrites, have a part to play in the early stages of peripheral arterial disease (PAD). Our objective was to analyse the effect of statins on the plasma nitrite and CRP levels in PAD.Material and methodsA prospective study of 30 patients with PAD Fontaine stage II, with no prior treatment with statins, determined high sensitivity (hs)-CRP and lipid profile in the patients. Plasma nitrite levels were determined by colourimetric assay based on the Griess reaction, at baseline and after 1 month of treatment with atorvastatin 40mgday−1.ResultsA significant reduction in plasma nitrite levels was detected after the treatment with statins (11.88±7.8μM vs. 5.7±1.8μM, p=0.0001). There was also a significant reduction in hs-CRP levels (13.58±24.00 vs. 3.93±3.19, p=0.02).When the patients were stratified according to claudication stage, a significant reduction in nitrite levels was obtained, both in patients with PAD Fontaine stage IIA (9.5±3.3μM vs. 5.3±1.7μM, p=0.0001) and in stage IIB (16.6±11.6μM vs. 6.7±1.8μM, p=0.032).ConclusionsTreatment with statins lowers plasma nitrite and CRP levels in patients with PAD. Our data support the effects of statins in vivo that have been demonstrated on the endothelium ex vivo, suggesting a beneficial effect by acting on the initial processes that trigger the disease, reducing oxidative stress (increase in the bioavailability of nitric oxide as peroxynitrite levels decrease) and curtailing the inflammatory processes which perpetuate the disease

Adaptación metabólica del ciclo de las pentosas fosfato de corteza renal de rata. II. Efecto de diferentes situaciones patológicas sobre el comportamiento cinético de la glucosa-6-fosfato deshidrogenasa y 6-fosfogluconato deshidrogenasa

The long-term and short-term effects of chronic metabolic acidosis and experimental diabetes on the PPC dehidrogenases activities have been investigated. The ingestion of 0.28 M ammonium chloride solution produced and increase in the G6PDH y 6PGDH activities about 90% and 60%, at day seven, either saturate or subsaturate substrate concentration. The alloxan induce diabetes (200 mg/Kg body weight) produced a significant increase of G6PDH and 6PGDH around 100 and 40% respectively, at both saturating or subsaturating substrate concentrations. Nevertheless, no significant changes were found during the short time periods. Also, during these pathological situations not significant variations were found in the Km values for G6PDH and 6PGDH. The nature of these increases and its relationship with the renal hipertrophy and cellular proliferation have been discussed.Se ha investigado el efecto de la acidosis crónica y diabetes experimental, a corto y largo plazo, sobre las actividades deshidrogenasas del ciclo de las pentosas fosfato de corteza renal de rata. A los 7 días de tratamiento, la ingestión de una solución de CINH4 0.28 M provoca un incremento en la actividad glucosa 6-fosfato deshidrogenasa y 6-fosfogluconato deshidrogenasa del orden del 90 y 60% respectivamente; tanto a concentración saturante de sustrato como subsaturante. La diabetes experimental provocada por la inyección intraperitoneal de alloxan (200 mg/Kg peso) induce, a los dos días, un incremento del 100% en la actividad G/PDH y del 40% en la 6PGDH tanto a concentración saturan te como subsaturante de sustrato. A corto plazo, no se detecta ningún cambio en el comportamiento cinético de este enzima. Las Kms para la glucosa 6-fosfato deshidrogenasa y 6-fosfogluconato deshidrogenasa en las distintas situaciones se mantienen sin variaciones apreciables. Se discute la naturaleza de los cambios observados, así como su relación con procesos de crecimiento y proliferación celular

Adaptación metabólica del ciclo de las pentosas fosfato de corteza renal de rata. II. Efecto de diferentes situaciones patológicas sobre el comportamiento cinético de la glucosa-6-fosfato deshidrogenasa y 6-fosfogluconato deshidrogenasa

Se ha investigado el efecto de la acidosis crónica y diabetes experimental, a corto y largo plazo, sobre las actividades deshidrogenasas del ciclo de las pentosas fosfato de corteza renal de rata. A los 7 días de tratamiento, la ingestión de una solución de CINH4 0.28 M provoca un incremento en la actividad glucosa 6-fosfato deshidrogenasa y 6-fosfogluconato deshidrogenasa del orden del 90 y 60% respectivamente; tanto a concentración saturante de sustrato como subsaturante. La diabetes experimental provocada por la inyección intraperitoneal de alloxan (200 mg/Kg peso) induce, a los dos días, un incremento del 100% en la actividad G/PDH y del 40% en la 6PGDH tanto a concentración saturan te como subsaturante de sustrato. A corto plazo, no se detecta ningún cambio en el comportamiento cinético de este enzima. Las Kms para la glucosa 6-fosfato deshidrogenasa y 6-fosfogluconato deshidrogenasa en las distintas situaciones se mantienen sin variaciones apreciables. Se discute la naturaleza de los cambios observados, así como su relación con procesos de crecimiento y proliferación celular.The long-term and short-term effects of chronic metabolic acidosis and experi mental diabetes on the PPC dehidrogenases activities have been investigated. The ingestion of 0.28 M ammonium chloride solution produced and increase in the G6PDH y 6PGDH activities about 90% and 60%, at day seven, either saturate or subsaturate substrate concentration. The alloxan induce diabetes (200 mg/Kg body weight) produced a significant increase of G6PDH and 6PGDH around lOO and 40% respectively, at both saturating or subsaturating substrate concentrations. Nevertheless, no significant changes were found during the short time periods. Also, during these pathological situations not significant variations were found in the Km values for G6PDH and 6PGDH. The nature of these increases and its relationship with the renal hipertrophy and cellular proliferation have been discussed

The knee prosthesis constraint dilemma: Biomechanical comparison between varus-valgus constrained implants and rotating hinge prosthesis. A cadaver study

The real degree of constriction of rotating hinge knee (RHK) and condylar constrained prostheses (CCK) is a matter of discussion in revision knee arthroplasty. The objectives of this study are to compare the tibial rotation of both implants and validate the use of inertial sensors with optical tracking system as movement measurement tools. A total of 16 cadaver knees were used. Eight knees were replaced using a RHK (Endomodel LINK), and the remaining eight received a CCK prosthesis (LCCK, Zimmer). Tibial rotation range of motion was measured in full extension and at 30°, 60°, and 90° of flexion, with four continuous waveforms for each measurement. Measurements were made using two inertial sensors with specific software and compared with measurements obtained using the gold standard technique - the motion capture camera. The comparison of the accuracy of both measurement methods showed no statistically significant differences between inertial sensors and motion capture cameras, with p > .1; the mean error for tibial rotation was 0.21°. Tibial rotation in the RHK was significantly greater than in the CCK (5.25° vs. 2.28°, respectively), p < .05. We have shown that RHK permit greater tibial rotation, being closer to physiological values than CCKs. Inertial sensors have been validated as an effective and accurate method of measuring knee movement. The clinical significance: RHK appears to represent a lower constriction degree than CCK systems.This study wassupported by Ministerio de Ciencia, Innovación y Universidades, Instituto de Salud Carlos III and European Regional Development Fund "Una manera de hacer Europa" (grant number PI18/01625

Capability assessment of the SEVIRI/MSG GPP product for the detection of areas affected by water stress

[ES] Se presenta el nuevo producto de producción primaria bruta (GPP) de EUMETSAT derivado a partir de datos del satélite geoestacionario SEVIRI/MSG (MGPP LSA-411) y se evalúa su potencial para detectar zonas afectadas por estrés hídrico (hot spots). El producto GPP se basa en la aproximación de Monteith, que modela la GPP de la vegetación como el producto de la radiación fotosintéticamente activa (PAR) incidente, la fracción de PAR absorbida (fAPAR) y un factor de eficiencia de uso de la radiación (ε). El potencial del producto MGPP para detectar hot spots se evalúa, utilizando un periodo corto de tres años, a escala local y regional, comparando con datos in situ derivados de medidas en torres eddy covariance (EC) y con datos GPP derivados de satélite (producto de 8 días MOD17A2H.v6 a 500 m y producto de 10 días GDMP a 1 km). Los resultados preliminares sobre el uso del producto MGPP en la evaluación de la respuesta del ecosistema a posibles eventos de déficit de agua ponen de manifiesto que este producto, calculado íntegramente a partir de datos MSG (EUMETSAT), ofrece una alternativa prometedora para detectar y caracterizar zonas afectadas por sequía a través de la incorporación de un coeficiente de estrés hídrico.[EN] This study aims to introduce a completely new and recently launched 10-day GPP product based on data from the geostationary MSG satellite (MGPP LSA-411) and to assess its capability to detect areas affected by water stress (hot spots). The GPP product is based on Monteith’s concept, which models GPP as the product of the incoming photosynthetically active radiation (PAR), the fractional absorption of that flux (fAPAR) and a lightuse efficiency factor (ε). Preliminary results on the use of the MGPP product in the assessment of ecosystem response to rainfall deficit events are presented in this work for a short period of three years. The robustness of this product is evaluated at both site and regional scales across the MSG disk using eddy covariance (EC) GPP measurements and Earth Observing (EO)-based GPP products, respectively. The EO-based products belong to the 8-day MOD17A2H v6 at 500 m and the 10-day GDMP at 1 km. The results reveal the MGPP product, derived entirely from MSG (EUMETSAT) products, as an efficient alternative to detect and characterize areas under water scarcity by means of a coefficient of water stress.Trabajo financiado por los proyectos LSA SAF (EUMETSAT) y ESCENARIOS (CGL2012–35831). Agradecemos a los responsables de las torres EC la cesión de los datos de GPP.Martínez, B.; Sánchez-Ruiz, S.; Campos-Taberner, M.; García-Haro, FJ.; Gilabert, MA. (2020). Potencial del producto SEVIRI/MSG GPP en la detección de zonas afectadas por estrés hídrico. Revista de Teledetección. 0(55):17-29. https://doi.org/10.4995/raet.2020.13285OJS1729055Anyamba, A., Glennie, E., Small, J. 2018. Teleconnections and Interannual Transitions as Observed in African Vegetation: 2015-2017. Remote Sensing, 10, 1038. https://doi.org/10.3390/rs10071038Bahta, Y.T., Jordaan, A., Muyambo, F. 2016. Communal Farmers' perception of drought in South Africa: policy implication for drought risk reduction. International Journal of Disaster Risk Reduction, 20, 39-50. https://doi.org/10.1016/j.ijdrr.2016.10.007Bartholome, E. Belward, A.S. 2005. GLC2000: a new approach to global land cover mapping from Earth observation data. International Journal of Remote Sensing, 26(9), 1959-1977. https://doi.org/10.1080/01431160412331291297Bojinski, S., Verstraete, M., Peterson, T.C., Richter, C., Simmons, A., Zemp, M. 2014. The concept of essential climate variables in support of climate research, applications, and policy. American Meteorologial Society, 95(9), 1431-1443. https://doi.org/10.1175/BAMS-D-13-00047.1CGLOPS1. 2018. Copernicus Global Land Operations 'Vegetation and Energy' Product User Manual for Dry Matter Productivity (DMP) and Gross Dry Matter Productivity (GDMP). Collection 1 km, version 2- CGLOPS1_PUM_DMP1km-V2, February 2018, 47 pp.Chamaillé-Jammes, S. Fritz, H. 2009. Precipitation-NDVI relationships in eastern and southern African savannas vary along a precipitation gradient. International Journal of Remote Sensing, 30(13), 3409-3422. https://doi.org/10.1080/01431160802562206Flaming, G.M. 2004. Measurement of global precipitation. In: International Geoscience and Remote Sensing Symposium. 9, Anchorage, AK, EUA.Fuster, B., Sánchez-Zapero, J., Camacho, F., García- Haro, F.J., Campos-Taberner, M. 2017. Validation of the Climate Data Record of EUMETSAT LSA SAF SEVIRI/MSG LAI, FAPAR and FVC products. Proceedings of the V RAQRS conference, Torrent, September 2017. pp. 191-196.Garbulsky, M.F., Peñuelas, J., Papale, D., Ardo, J., Goulden, M.L., Kiely, G., et al. 2010. Patterns and controls of the variability of radiation use efficiency and primary productivity across terrestrial ecosystems. Global Ecology and Biogeography, 19, 253-267. https://doi.org/10.1111/j.1466-8238.2009.00504.xGarcía-Haro, F.J., Campos-Taberner, M., Sabater, N., Belda, F., Moreno, A., Gilabert, M.A., Martínez, B., Pérez-Hoyos, A., Meliá, J. 2014. Vulnerabilidad de la vegetación a la sequía en España. Revista de Teledetección, 42, 29-37. https://doi.org/10.4995/raet.2014.2283García-Haro, F.J., Campos-Taberner, M., Muñoz- Mari, J., Laparra, V., Camacho, F., Sánchez- Zapero, J., Camps-Valls, G. 2018. Derivation of global vegetation biophysical parameters from EUMETSAT polar system. ISPRS Journal of Photogrammetry and Remote Sensing, 139, 57-74. https://doi.org/10.1016/j.isprsjprs.2018.03.005García-Haro, F.J., Camacho, F., Martínez, B., Campos- Taberner, M., Fuster, B., Sánchez-Zapero, J., Gilabert, M.A. 2019. Climate Data Records of Vegetation Variables from Geostationary SEVIRI/MSG Data: Products, Algorithms and Applications. Remote Sensing, 11, 2103. https://doi.org/10.3390/rs11182103Gilabert, M.A., Moreno, A., Maselli, F., Martínez, B., Chiesi, M., Sánchez-Ruíz, S., et al. 2015. Daily GPP estimates in Mediterranean ecosystems by combining remote sensing and meteorological data. ISPRS Journal of Photogrammetry and Remote Sensing, 102, 184- 197. https://doi.org/10.1016/j.isprsjprs.2015.01.017Jones, L.A., Kimball, J.S., Reichle, R.H., Madani, N., Glassy, J., Ardizzone, J.V., et al. 2017. The SMAP level 4 carbon product for monitoring ecosystem land-atmosphere CO2 exchange. IEEE Transactions on Geoscience and Remote Sensing, 55(11), 6517- 6532. https://doi.org/10.1109/TGRS.2017.2729343Kummerowa, C., Simpson, J., Thielea, O., Barnesa, W., Changa, A.T.C., Stockera, E., 2000. The Status of the Tropical Rainfall Measuring Mission (TRMM) after Two Years in Orbit. Journal of Applied Meteorology, 39, 1965-1982.Liu, Z., Ostrenga, D., Teng, W., Kempler, S. 2012. Tropical Rainfall Measuring Mission (TRMM) Precipitation Data and Services for Research and Applications. Bulletin of the American Meteorological Society, 93, 1317-1325. https://doi.org/10.1175/BAMS-D-11-00152.1Liu, N., Harper, R. J., Dell, B., Liu, S., Yu, Z. 2017. Vegetation dynamics and rainfall sensitivity for different vegetation types of the Australian continent in the dry period 2002-2010. International Journal of Remote Sensing, 17, 2761-2782. https://doi.org/10.1002/eco.1811Malo, A.R Nicholson, S.E. 1990. A study of rainfall and vegetation dynamics in the African Sahel using normalized difference vegetation index. Journal of Arid Environments, 19, 1-24. https://doi.org/10.1016/S0140-1963(18)30825-5Martínez, B., Sánchez-Ruiz, S., Gilabert, M.A., Moreno, A., Taberner, M.C., García-Haro, F.J., et al. 2018. Retrieval of daily gross primary production over Europe and Africa from an ensemble of SEVIRI/MSG products. International Journal of Applied Earth Observation and Geoinformation, 65, 124-136. https://doi.org/10.1016/j.jag.2017.10.011Martínez, B., Gilabert, M.A., Sánchez-Ruiz, S., Taberner, M.C., García-Haro, F.J. 2020. Evaluation of the LSA-SAF gross primary production product derived from SEVIRI/MSG data (MGPP). ISPRS Journal of Photogrammetry and Remote Sensing, 159, 220-236. https://doi.org/10.1016/j.isprsjprs.2019.11.010McKee, T.B., Doesken, N.J., Kleist, K. 1993. The relationship of drought frequency and duration to time scale. In: Proceedings of the Eighth Conference on Applied Climatology, Anaheim, California, 17- 22 January 1993. Boston, American Meteorological Society, 179-184.Monteith, J. L. 1972. Solar radiation and productivity in tropical ecosystems. Journal of Applied Ecology, 9, 747-766. https://doi.org/10.2307/2401901Running, S.W., Zhao, M. 2015. Daily GPP and Annual NPP (MOD17A2/A3) Products NASA Earth Observing System MODIS Land Algorithm. User's Guide. Version 3.0 For Collection 6.Sánchez-Ruiz, S., Moreno, A., Piles, M., Maselli, F., Carrara, A., Running, S., Gilabert, M.A. 2017. Quantifying water stress effect on daily light use efficiency in Mediterranean ecosystems using satellite data. International Journal of digital Earth, 10(6), 623-638. https://doi.org/10.1080/17538947.2016.1247301Simpson, J., Adler, R., North, G.A. 1988. Proposed tropical rainfall measuring mission (TRMM) satellite. 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Holography of AdS vacuum bubbles

We consider the fate of AdS vacua connected by tunneling events. A precise holographic dual of thin-walled Coleman--de Luccia bounces is proposed in terms of Fubini instantons in an unstable CFT. This proposal is backed by several qualitative and quantitative checks, including the precise calculation of the instanton action appearing in evaluating the decay rate. Big crunches manifest themselves as time dependent processes which reach the boundary of field space in a finite time. The infinite energy difference involved is identified on the boundary and highlights the ill-defined nature of the bulk setup. We propose a qualitative scenario in which the crunch is resolved by stabilizing the CFT, so that all attempts at crunching always end up shielded from the boundary by the formation of black hole horizons. In all these well defined bulk processes the configurations have the same asymptotics and are finite energy excitations.Comment: version submitted to journal. Note added referring to previous work on holographic instantons

Vegetation vulnerability to drought in Spain

Revista oficial de la Asociación Española de Teledetección[EN] Frequency of climatic extremes like long duration droughts has increased in Spain over the last century.The use of remote sensing observations for monitoring and detecting drought is justified on the basis that vegetation vigor is closely related to moisture condition. We derive satellite estimates of bio-physical variables such as fractional vegetation cover (FVC) from MODIS/EOS and SEVIRI/MSG time series. The study evaluates the strength of temporal relationships between precipitation and vegetation condition at time-lag and cumulative rainfall intervals. From this analysis, it was observed that the climatic disturbances affected both the growing season and the total amount of vegetation. However, the impact of climate variability on the vegetation dynamics has shown to be highly dependent on the regional climate, vegetation community and growth stages. In general, they were more significant in arid and semiarid areas, since water availability most strongly limits vegetation growth in these environments.[EN] Los extremos climáticos se han incrementado en España a los largo del último siglo; por ello, su análisis se ha convertido en una línea prioritaria de conocimiento con objeto fundamental de diseñar planes para la gestión y mitigación de sus efectos. Los datos de satélite permiten analizar las variaciones en la actividad de la vegetación a varias escalas temporales y su respuesta a la variabilidad climática. En este trabajo se pone de manifiesto la vulnera-bilidad de la vegetación en España ante condiciones ambientales extremas a través de las correlaciones entre índices meteorológicos de sequía (SPI) y variables biofísicas extraídas de datos MODIS/EOS y SEVIRI/MSG. Las anomalías en la vegetación, como indicadores de las condiciones de humedad de la misma, pueden ayudar a cuantificar y gestionar episodios meteorológicos extremos y hacer un seguimiento de la misma. Las mayores correlaciones se han obtenido en las regiones áridas y semiáridas y durante los meses de máxima actividad de la vegetación, generalmente entre mayo y junio.Este trabajo se enmarca en los proyectos DULCINEA (CGL2005–04202), RESET CLIMATE (CGL2012–35831), LSA SAF (EUMETSAT) y ERMES (FP7-SPACE-2013, Contract 606983).García-Haro, F.; Campos-Taberner, M.; Sabater, N.; Belda, F.; Moreno, A.; Gilabert, M.; Martínez, B.... (2014). Vulnerabilidad de la vegetación a la sequía en España. Revista de Teledetección. (42):29-38. https://doi.org/10.4995/raet.2014.2283SWORD29384

The PAU survey: classifying low-z SEDs using Machine Learning clustering

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Monthly Notices of the Royal Astronomical Society 524.3 (2023): 3569-3581 is available online at: https://academic.oup.com/mnras/article-abstract/524/3/3569/7225529?redirectedFrom=fulltextWe present an application of unsupervised Machine Learning clustering to the PAU survey of galaxy spectral energy distribution (SED) within the COSMOS field. The clustering algorithm is implemented and optimized to get the relevant groups in the data SEDs. We find 12 groups from a total number of 5234 targets in the survey at 0.01 < z < 0.28. Among the groups, 3545 galaxies (68 per cent) show emission lines in the SEDs. These groups also include 1689 old galaxies with no active star formation. We have fitted the SED to every single galaxy in each group with CIGALE. The mass, age, and specific star formation rates (sSFR) of the galaxies range from 0.15 < age/Gyr <11; 6 < log (M/M⊙) <11.26, and -14.67 < log (sSFR/yr-1) <-8. The groups are well-defined in their properties with galaxies having clear emission lines also having lower mass, are younger and have higher sSFR than those with elliptical like patterns. The characteristic values of galaxies showing clear emission lines are in agreement with the literature for starburst galaxies in COSMOS and GOODS-N fields at low redshift. The star-forming main sequence, sSFR versus stellar mass and UVJ diagram show clearly that different groups fall into different regions with some overlap among groups. Our main result is that the joint of low- resolution (R ∼50) photometric spectra provided by the PAU survey together with the unsupervised classification provides an excellent way to classify galaxies. Moreover, it helps to find and extend the analysis of extreme ELGs to lower masses and lower SFRs in the local UniverseThis work has been supported by the Ministry of Science and Innovation of Spain, project PID2019-107408GB-C43 (ESTALLIDOS), and the Government of the Canary Islands through EU FEDER funding, projects PID2020010050 and PID2021010077. This article is based on observations made in the Observatorios de Canarias of the Instituto de Astrofísica de Canarias (IAC) with the WHT operated on the island of La Palma by the Isaac Newton Group of Telescopes (ING) in the Observatorio del Roque de los Muchachos. The PAU Survey is partially supported by MINECO under grants CSD2007-00060, AYA2015-71825, ESP2017-89838, PGC2018-094773, PGC2018-102021, PID2019-111317GB, SEV-2016-0588, SEV-2016-0597, MDM-2015-0509 and Juan de la Cierva fellowship and LACEGAL and EWC Marie Sklodowska-Curie grant No 734374 and no.776247 with ERDF funds from the EU Horizon 2020 Programme, some of which include ERDF funds from the European Union. IEEC and IFAE are partially funded by the CERCA and Beatriu de Pinos program of the Generalitat de Catalunya. Funding for PAUS has also been provided by Durham Univer sity (via the ERC StG DEGAS-259586), ETH Zurich, Leiden University (via ERC StG ADULT-279396 and Netherlands Organisation for Scientific Research (NWO) Vici grant 639.043.512), University College London and from the European Union’s Horizon 2020 research and innovation programme under the grant agreement No 776247 EWC. The PAU data center is hosted by the Port d’Información Científica (PIC), maintained through a collaboration of CIEMAT and IFAE, with additional support from Universitat Autónoma de Barcelona and ERDF. We acknowledge the PIC services department team for their support and fruitful discussion

The weak-line T Tauri star V410Tau I. A multi-wavelength study of variability

We present the results of an intensive coordinated monitoring campaign in the optical and X-ray wavelength ranges of the low-mass, pre-main sequence star V410Tau carried out with the aim to study the relation between various indicators for magnetic activity that probe emission from different atmospheric layers: optical photometric star spot (rotation) cycle, chromospheric Halpha emission, and coronal X-rays. Two X-ray pointings were carried out with the Chandra satellite simultaneously with the optical observations, and centered near the maximum and minimum levels of the optical lightcurve. A relation of their different count levels to the rotation period of the dominating spot is not confirmed by a third Chandra observation carried out some months later, during another minimum of the 1.87d cycle. Similarly we find no indications for a correlation of the Halpha emission with the spots' rotational phase. The extraordinary stability of the largest spot is confirmed by long-term photometric and radial velocity measurements. Joining our optical photometry with previous data we provide a new estimate for the dominant periodicity of V410Tau. This updated value removes systematic offsets of the time of minimum observed in data taken over the last decade. Furthermore, the combination of the new data with published measurements taken during the last decade allows us to examine long-term changes in the mean light level of the photometry of V410Tau. A variation on the timescale of 5.4yr is suggested. Assuming that this behavior is truely cyclic V410Tau is the first pre-main sequence star on which an activity cycle is detected.Comment: 16 pages, accepted for publication in A&