Optical flares from the faint mid‐dM star 2MASS J00453912+4140395

We present B and V light curves of a large stellar flare obtained with the Wide Field Camera at the Isaac Newton 2.5‐m telescope (La Palma). The source object is a faint (m_V = 21.38) foreground star in the field of the Andromeda galaxy, with its most probable spectral type being dM4. We provide an estimate of the total flare energy in the optical range and find it to be of the order of 1035 erg. The cooling phase of the large flare shows three additional weak flare‐like events, which we interpret as results of a triggering mechanism also observed on the Sun during large coronal mass ejections. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Barranco de Arás flood of 7 August 1996 (Biescas, Central Pyrenees, Spain)

Geomorphic effects observed in the Barranco (creek) de Arás basin are used to characterize the flood. Sediment features allow to qualify the flood as essentially a water flow. Using the critical section method, the peak flood discharge is estimated to be between 400 and 600 m³ s⁻¹. Similar results were obtained using a paleohydraulic formula based on the size of the largest mobilized clasts. Using the rational method with available rainfall data, the discharge for a recurrence interval of 500 years is estimated to be between 150 and 200 m³ s⁻¹. These results agree with predictions obtained using curves of peak discharge versus basin area based on regional data. Several trenches dug on the fan showed that the size of boulders mobilized by the event is larger that those left by previous floods at the same place. When the estimated peak flood discharge is related to the basin area, values between 20 and 30 m³ s⁻¹ km⁻² are obtained, demonstrating that the Barranco de Arás flood was most unusual.     

Surface Synoptic Circulation and Daily Precipitation in Catalonia

Summary Catalonian daily precipitation patterns were obtained by means of S-mode Principal Component Analysis (PCA) applied to subsets built up according to synoptic surface airflow. Daily data from November to April 1990–1994 from 45 raingauge sites in Catalonia without missing data were used. Eight circulation classes for days in this period were considered. A Precipitation Activity Index (PAI) was calculated for each station and class, leading to the determination of the highest activity regions for each subset. In addition, we determined which circulation type produced most precipitation at each station of the network. Separate PCAs were performed for each of the eight classes considered and the first four Varimax rotated solutions were interpreted for each circulation type. The physical meaning of the rest of the factors were omitted as they were associated with local behaviour. Finally, some concluding remarks on the cyclogenic properties of the Western Mediterranean Basin and the diversity of the extracted patterns are presented and supported by the authors experience in forecasting in Catalonia. Received February, 11, 1997 Revised May 23, 1997     

Rainfall intensity patterns derived from the urban network of Barcelona (NE Spain)

Theoretical and Applied Climatology - An analysis of the normalised rainfall intensity curves in Barcelona (NE Spain) has been undertaken from 41 selected rain rate episodes recorded by an urban...     

The effects of organic acids on the dissolution of silicate minerals: A case study of oxalate catalysis of kaolinite dissolution

Most studies agree that the dissolution rate of aluminosilicates in the presence of oxalic and other simple carboxylic acids is faster than the rate with non-organic acid under the same pH. However, the mechanisms by which organic ligands enhance the dissolution of minerals are in debate. The main goal of this paper was to study the mechanism that controls the dissolution rate of kaolinite in the presence of oxalate under far from equilibrium conditions (−29 < ΔG_r < −18 kcal mol⁻¹). Two types of experiments were performed: non-stirred flow-through dissolution experiments and batch type adsorption isotherms. All the experiments were conducted at pH 2.5-3.5 in a thermostatic water-bath held at a constant temperature of 25.0, 50.0 or 70.0 ± 0.1 °C. Kaolinite dissolution rates were obtained based on the release of silicon and aluminum at steady state. The results show good agreement between these two estimates of kaolinite dissolution rate. At constant temperature, there is a general trend of increase in the overall dissolution rate as a function of the total concentration of oxalate in solution. The overall kaolinite dissolution rates in the presence of oxalate was up to 30 times faster than the dissolution rate of kaolinite at the same temperature and pH without oxalate as was observed in our previous study. Therefore, these rate differences are related to differences in oxalate and aluminum concentrations. Within the experimental variability, the oxalate adsorption at 25, 50, and 70 °C showed the same dependence on the sum of the activities of oxalate and bioxalate in solution. The change of oxalate concentration on the kaolinite surface (C_s,ox) as a function of the sum of the activities of the oxalate and bioxalate in solution may be described by the general adsorption isotherm:

     

Testing fundamental physics with distant star clusters: theoretical models for pressure-supported stellar systems

We investigate the mean velocity dispersion and the velocity dispersion profile of stellar systems in modified Newtonian dynamics (MOND), using the N -body code n-mody , which is a particle-mesh-based code with a numerical MOND potential solver developed by Ciotti, Londrillo & Nipoti. We have calculated mean velocity dispersions for stellar systems following Plummer density distributions with masses in the range of 10⁴ to  10⁹ M_⊙  and which are either isolated or immersed in an external field. Our integrations reproduce previous analytic estimates for stellar velocities in systems in the deep MOND regime  ( a _i, a _e≪ a ₀)  , where the motion of stars is either dominated by internal accelerations  ( a _i≫ a _e)  or constant external accelerations  ( a _e≫ a _i)  . In addition, we derive for the first time analytic formulae for the line-of-sight velocity dispersion in the intermediate regime  ( a _i∼ a _e∼ a ₀)  . This allows for a much-improved comparison of MOND with observed velocity dispersions of stellar systems. We finally derive the velocity dispersion of the globular cluster Pal 14 as one of the outer Milky Way halo globular clusters that have recently been proposed as a differentiator between Newtonian and MONDian dynamics.     

Statistics of hot and cold events in Catalonia (NE Spain) for the recording period 1950–2004

Spatial patterns and statistical models for hot and cold events affecting Catalonia (NE Spain) are obtained from series of daily maximum and minimum temperatures recorded at 65 meteorological stations throughout the period 1950–2004. The study is based on the crossing theory, taking care that daily temperatures are normally distributed and previous data treatments (removal of trends and periodicities) assure their stationary character. With the aim of facilitating comparisons among different thermometric records, hot and cold events are defined as large departures, given in standard deviations, of daily temperatures from daily averages. From the statistical point of view, the assumption of a normal distribution of the initial date of the events is questionable and a simple assignment of hot events to summer and cold events to winter must be discarded according to the averaged initial dates and their standard deviations. The event magnitudes, defined as the absolute value of their maximum departures, follow an exponential distribution and event lengths can be modelled by an autoregressive Markov process with a Gaussian noise component. The number of events per year fits a Poisson distribution well only for high departures and the whole number of hot and cold events decays exponentially with the increasing departure for every temperature series. This property permits an estimation of the expected maximum departure for every thermometric station during the recording period. Even though spatial features observed for the number of events, their mean initial date, average event magnitude and average event length depict quite complex patterns due to the orography of the country and the vicinity to the Mediterranean Sea, the results obtained improve the knowledge on the hot and cold events in Catalonia.