1,059 research outputs found
Surface Brightness and Stellar Populations at the Outer Edge of the Large Magellanic Cloud: No Stellar Halo Yet
We present a high quality CMD for a 36'x 36' field located 8 degrees (7 kpc)
from the LMC center, as well as a precise determination of the LMC surface
brightness derived from the resolved stellar population out to this large
galactocentric radius. This deep CMD shows for the first time the detailed age
distribution at this position, where the surface brightness is V=26.5 mag/sq".
At a radius R=474' the main sequence is well populated from the oldest turnoff
at I=21.5 to the 2.5 Gyr turnoff at I=19.5. Beyond this radius, a relatively
strong gradient in the density of stars with ages in the 2.5-4 Gyr range is
apparent. There are some stars brighter and bluer than the main population,
quite uniformly distributed over the whole area surveyed, which are well
matched by a 1.5 Gyr isochrone and may be indicative of a relatively recent
star formation, or merger, event. The surface brightness profile of the LMC
remains exponential to this large galactocentric radius and shows no evidence
of disk truncation. Combining the information on surface brightness and stellar
population we conclude that the LMC disk extends (and dominates over a possible
stellar halo) out to a distance of at least 7 kpc. These results confirm that
the absence of blue stars in the relatively shallow off-center CMDs of dIrr
galaxies is not necessarily evidence for an exclusively old stellar population
resembling the halo of the Milky Way.Comment: ApJLett, in press 13 pages including 3 color figure
Smart grid architecture for rural distribution networks: application to a Spanish pilot network
This paper presents a novel architecture for rural distribution grids. This architecture is designed to modernize traditional rural networks into new Smart Grid ones. The architecture tackles innovation actions on both the power plane and the management plane of the system. In the power plane, the architecture focuses on exploiting the synergies between telecommunications and innovative technologies based on power electronics managing low scale electrical storage. In the management plane, a decentralized management system is proposed based on the addition of two new agents assisting the typical Supervisory Control And Data Acquisition (SCADA) system of distribution system operators. Altogether, the proposed architecture enables operators to use more effectivelyâin an automated and decentralized wayâweak rural distribution systems, increasing the capability to integrate new distributed energy resources. This architecture is being implemented in a real Pilot Network located in Spain, in the frame of the European Smart Rural Grid project. The paper also includes a study case showing one of the potentialities of one of the principal technologies developed in the project and underpinning the realization of the new architecture: the so-called Intelligent Distribution Power Router.Postprint (published version
Transpiration of montane <I>Pinus sylvestris</I> L. and <I>Quercus pubescens</I> Willd. forest stands measured with sap flow sensors in NE Spain
International audienceStand transpiration was measured during the 2003 and 2004 growing seasons using heat dissipation sap flow sensors in a Scots pine (Pinus sylvestris L.) and a pubescent oak (Quercus pubescens Willd.) forest located in a montane area of the Eastern Pyrenees (NE Spain). The first aim of the study was to assess the differences in quantitative estimates of transpiration (Ec) and the response to evaporative demand of the two stands. Over the studied period of 2003, characterised by a severe drought episode during the summer, the oak stand Ec was only 110mm compared to the 239 mm transpired by the Scots pine stand, although the ratio of transpiration to reference evapotranspiration (Ec/ET0) in the oak stand compares well with the expected values predicted for low leaf area index (LAI) oak forests in southern Europe. Scots pine showed a strong reduction in Ec/ET0 as the drought developed, whereas pubescent oak was less affected by soil moisture deficits in the upper soil. As a second objective, and given the contrasting meteorological conditions between 2003 and 2004 summer periods, the interanual variability of transpiration was studied in the Scots pine plot. Rainfall during the summer months (June-September) in 2003 was almost 40% less than in the same interval in 2004. Accordingly, transpiration was also reduced about 25% in 2003. Finally, Scots pine data from 2003 and 2004 was used to calibrate a simple transpiration model using ET0 and soil moisture deficit (SMD) as input variables, and implicitly including stomatal responses to high vapour pressure deficits (D?) and soil water status
Smart grids for rural conditions and e-mobility - Applying power routers, batteries and virtual power plants
Significant reductions of greenhouse gas emission by use of renewable energy sources belong to the common targets of the European Union. Smart grids address intelligent use and integration of conventional and renewable generation in combination with controllable loads and storages. Two special aspects have also to be considered for smart grids in future: rural conditions and electric vehicles. Both, the increasing share of renewable energy sources and a rising demand for charging power by electrical vehicles lead to new challenges of network stability (congestion, voltage deviation), especially in rural distribution grids. This paper describes two lighthouse projects in Europe (âWell2Wheelâ and âSmart Rural Gridâ) dealing with these topics. The link between these projects is the implementation of the same virtual power plant technology and the approach of cellular grid cells. Starting with an approach for the average energy balance in 15 minutes intervals in several grid cells in the first project, the second project even allows the islanded operation of such cells as a microgrid. The integration of renewable energy sources into distribution grids primary takes place in rural areas. The lighthouse project âSmart Rural Gridâ, which is founded by the European Union, demonstrates possibilities to use the existing distribution system operator infrastructure more effectively by applying an optimised and scheduled operation of the assets and using intelligent distribution power routers, called IDPR. IDPR are active power electronic devices operating at low voltage in distribution grids aiming to reduce losses due to unbalanced loads and enabling active voltage and reactive power control. This allows a higher penetration of renewable energy sources in existing grids without investing in new lines and transformers. Integrated in a virtual power plant and combined with batteries, the IDPR also allows a temporary islanded mode of grid cells.
Both projects show the potential of avoiding or postponing investments in new primary infrastructure like cables, transformers and lines by using a forward-looking operation which controls generators, loads and batteries (mobile and stationary) by using new grid assets like power routers.
While primary driven by physical restrictions as voltage-band violations and energy balance, these cells also define and allow local smart markets. In consequence the distribution system operators could avoid direct control access by giving an incentive to the asset owners by local price signals according to the grid situation and forecasted congestions.Peer ReviewedPostprint (published version
Spatially resolved LMC star formation history: I. Outside in evolution of the outer LMC disk
We study the evolution of three fields in the outer LMC disk Rgc=3.5-6.2 Kpc.
Their star formation history indicates a stellar populations gradient such that
younger stellar populations are more centrally concentrated. We identify two
main star forming epochs, separated by a period of lower activity between ~7
and ~4 Gyr ago. Their relative importance varies from a similar amount of stars
formed in the two epochs in the innermost field, to only 40% of the stars
formed in the more recent epoch in the outermost field. The young star forming
epoch continues to the present time in the innermost field, but lasted only
till ~0.8 and 1.3 Gyr ago at Rgc=5.5 degrees and 7.1 degrees, respectively.
This gradient is correlated with the measured HI column density and implies an
outside-in quenching of the star formation, possibly related to a variation of
the size of the HI disk. This could either result from gas depletion due to
star formation or ram-pressure stripping, or from to the compression of the gas
disk as ram-pressure from the Milky Way halo acted on the LMC interstellar
medium. The latter two situations may have occurred when the LMC first
approached the Milky Way.Comment: 15 pages, 13 figures, 4 tables. MNRAS, in pres
Transpiration of montane Pinus sylvestris L. and Quercus pubescens Willd. forest stands measured with sap flow sensors in NE Spain
Stand transpiration was measured during the 2003 and 2004 growing seasons using heat dissipation sap flow sensors in a Scots pine (Pinus sylvestris L.) and a pubescent oak (Quercus pubescens Willd.) forests located in a montane area of the Eastern Pyrenees (NE Spain). The first aim of the study was to assess the differences in quantitative estimates of transpiration (Ec) and the response to evaporative demand of the two stands. Over the studied period of 2003, characterised by a severe drought episode during the summer, the oak stand E2 was only 110 turn compared to the 239 mm transpired by the Scots pine stand, although the ratio of transpiration to reference evapotranspiration (Ec/ET0) in the oak stand compares well with the expected values predicted for low leaf area index (LAI) oak forests in southern Europe. Scots pine showed a strong reduction in Ec/ET0) as the drought developed, whereas pubescent oak was less affected by soil moisture deficits in the upper soil. As a second objective, and given the contrasting meteorological conditions between 2003 and 2004 summer periods, the interannual variability of transpiration was studied in the Scots pine plot. Rainfall during the summer months (June-September) in 2003 was almost 40% less than in the same interval in 2004. Accordingly, transpiration was also reduced about 25% in 2003. Finally, Scots pine data from 2003 and 2004 was used to calibrate a simple transpiration model using ET0 and soil moisture deficit (SMD) as input variables, and implicitly including stomatal responses to high vapour pressure deficits (Dd) and soil water status. © 2005 Author(s). This work is licensed under a Creative Commons License.This research was supported by the projects PROHISEM (REN2001-2268-C02-01/HID), PIRIHEROS (REN2003-08768/HID) and CANOA (CGL2004-04919-C02- 01), funded by the Spanish Ministerio de Ciencia y TecnologĂa (MCYT)/Ministerio de EducaciĂłn y Ciencia (MEC). The Vallcebre research area also operates with support from the RESEL network through an agreement between the CSIC and DGCONA.Peer Reviewe
Remnants of Sagittarius Dwarf Spheroidal Galaxy around the young globular cluster Palomar 12
Photometry of a large field around the young globular cluster Palomar 12 has
revealed the main-sequence of a low surface-brightness stellar system. This
main-sequence is indicative of a stellar population that varies significantly
in metallicity and/or age, but in the mean is more metal poor than Pal 12.
Under different assumptions for the properties of this population, we find
distances from the Sun in the range 17-24 kpc, which encompasses the distance
to Pal 12, kpc. The stellar system is also detected in a field
2\arcdeg North of Pal 12, which indicates it has a minimum diameter of
kpc. The orbit of Pal 12 (Dinescu et al. 2000), the color-magnitude
diagram of the stellar system, their positions on the sky, and their distances
suggest that they are debris from the tidal disruption of the Sgr dSph galaxy.
We discuss briefly the implications for the evolution of Sgr and the Galactic
halo.Comment: 16 pages, 2 figures, accepted for ApJ Letters. Some importante
changes after revision, including a new figur
HST-NICMOS Observations of M31's Metal Rich Globular Clusters and Their Surrounding Fields: I. Techniques
We have obtained HST-NICMOS observations of five of M31's most metal rich
globular clusters. These data allow photometry of individual stars in the
clusters and their surrounding fields. However, to achieve our goals -- obtain
accurate luminosity functions to compare with their Galactic counterparts,
determine metallicities from the slope of the giant branch, identify long
period variables, and estimate ages from the AGB tip luminosity, we must be
able to disentangle the true properties of the population from the
observational effects associated with measurements made in very crowded fields.
In this paper we present a careful analysis of photometry in crowded regions,
and show how image blending affects the results and interpretation of such
data. Although this analysis is specifically for our NICMOS observations in
M31, the techniques we develop can be applied to any imaging data taken in
crowded fields; we show how the effects of image blending will even limit NGST.
We use three different techniques to analyze the effects of crowding on our
data, including the insertion of artificial stars (traditional completeness
tests) and the creation of completely artificial clusters. They are used to
derive threshold- and critical-blending radii for each cluster, which determine
how close to the cluster center reliable photometry can be achieved. The
simulations also allow us to quantify and correct for the effects of blending
on the slope and width of the RGB at different surface brightness levels.Comment: AAS LaTeX v5.0, 18 pages. Submitted to the A
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