The low level of debris disk activity at the time of the Late Heavy Bombardment: a Spitzer study of Praesepe

We present 24 micron photometry of the intermediate-age open cluster Praesepe. We assemble a catalog of 193 probable cluster members that are detected in optical databases, the Two Micron All Sky Survey (2MASS), and at 24 micron, within an area of ~ 2.47 square degrees. Mid-IR excesses indicating debris disks are found for one early-type and for three solar-type stars. Corrections for sampling statistics yield a 24 micron excess fraction (debris disk fraction) of 6.5 +- 4.1% for luminous and 1.9 +- 1.2% for solar-type stars. The incidence of excesses is in agreement with the decay trend of debris disks as a function of age observed for other cluster and field stars. The values also agree with those for older stars, indicating that debris generation in the zones that emit at 24 micron falls to the older 1-10 Gyr field star sample value by roughly 750 Myr. We discuss our results in the context of previous observations of excess fractions for early- and solar-type stars. We show that solar-type stars lose their debris disk 24 micron excesses on a shorter timescale than early-type stars. Simplistic Monte Carlo models suggest that, during the first Gyr of their evolution, up to 15-30% of solar-type stars might undergo an orbital realignment of giant planets such as the one thought to have led to the Late Heavy Bombardment, if the length of the bombardment episode is similar to the one thought to have happened in our Solar System. In the Appendix, we determine the cluster's parameters via boostrap Monte Carlo isochrone fitting, yielding an age of 757 Myr (+- 36 Myr at 1 sigma confidence) and a distance of 179 pc (+- 2 pc at 1 sigma confidence), not allowing for systematic errors.Comment: 22 pages, 14 figures, 9 tables, emulateapj format; Accepted for publication in The Astrophysical Journa

Monitoreo de ecosistemas con estrategias geoestadísticas, una aplicación de gran escala en Jalisco, México

Abstract The Inventory and Monitoring of Natural Resources of Jalisco, Mexico (IMRENAT), is an innovative process suggesting a practical application for geospatial statistical modeling to credibly report the condition of land resources. Taking advantage of interconnections among terrain attributes, vegetation, human activities and multispectral remote sensing information, it is possible to develop statistically valid models depicting land resources spatial attributes and dynamic trends. These types of models enable us to create geoinformation products of greater practical utility than regular cartographic products, or geographic information derived from imagery interpretation. Geospatial products have the capability to describe different scales and resolution levels.Resumen El proyecto de Inventario y Monitoreo de los Recursos Naturales de Jalisco, México (IMRENAT), es un proceso innovador que propone una aplicación práctica de las herramientas de modelado estadístico geoespacial para reportar creíblemente la condición del territorio. Aprovechando las interconexiones que existen entre atributos del terreno, la vegetación, las actividades humanas y lo detectable con sensores remotos multiespectrales, se pueden construir modelos estadísticamente válidos que reflejan las relaciones espaciales y las tendencias dinámicas de los atributos del territorio. Este tipo de modelos permiten generar productos de geoinformación de mayor utilidad que la información geográfica de naturaleza cartográfica, y que la información pictórica proveniente de interpretar imágenes de sensores remotos. Estos productos geoespaciales tienen la capacidad de describir distintos niveles de resolución y de escala

Valoración de recursos naturales y ganadería en la zona centro de Veracruz, México

Abstract: Willingness to pay (WTP) for environmental services from a cattle ranching region encompasing Veracruz, La Antigua, and Boca del Río, Veracruz State, Mexico, is reported. A survey questionnaire, randomly applied to a stratified sample of 199 individuals, about regional demographic attributes, natural resources, wildlands condition, environmental quality and animal husbandry was administered. Contingent valuation techniques were applied, and supplemented with interviews and anthropologic field work. Results revealed that 83,42% of the sampled individuals have a positive WTP for an improved environment, and 84,42% of respondents will accept increases in taxation as the venue to that end; 85,93% of the public in the sample will rather see that cattle ranchers should be compensated by government for the extra cost of an environmentally conscious management. WTP through increased taxation has statistically significant influences (p<0,05) from household income, severity of regulations, and restrictions to ranching practices. Direct payment resulted acceptable, as well as additional government regulations mandating best ranching practices. Hence, these results led to support that public opinion favors a variety of payment mechanisms. Approval of additional environmental legislation, as well as strict enforcement of existing cattle raising regulations was also noticed.Resumen: Se estudió en Veracruz, La Antigua y Boca del Río, Veracruz, México, la disposición a pagar (DAP) por servicios ambientales generados en una zona ganadera. Se aplicó un cuestionario al azar estratificado a 199 personas de áreas rurales y urbanas, preguntando sobre temas sociodemográficos, naturaleza, recursos naturales, ambiente y ganadería. Usando valoración contingente, complementado con entrevistas y trabajo de campo antropológico, se encontró que 83,42% del público en la muestra está dispuesto a pagar por un incremento de calidad ambiental. Un 85,93% cree que el medio ideal sería que los ganaderos usen prácticas ambientalmente eficientes, y ser compensados por ello por parte del Estado, que según la mayoría (84,42%), podría venir de mayor carga impositiva. En esta DAP, por la vía tributaria fueron significativas (p <0,05) las influencias del nivel de ingresos, y la disposición a aceptar un incremento de la normatividad ambiental aplicable a actividades pecuarias, y reducción de actividades en terrenos ganaderos. Otros mecanismos de pago aceptables para los entrevistados fueron un pago directo y único, y el apoyo económico promoviendo el desarrollo de la ganadería bovina. De ahí que estos resultados lleven a suponer que la opinión pública apoya una variedad de mecanismos de pago. También se detectó que el público apoya la emisión de normas ambientales complementarias, así como una estricta aplicación de la legislación ganadera vigente