Super stellar clusters with a bimodal hydrodynamic solution: an Approximate Analytic Approach

We look for a simple analytic model to distinguish between stellar clusters undergoing a bimodal hydrodynamic solution from those able to drive only a stationary wind. Clusters in the bimodal regime undergo strong radiative cooling within their densest inner regions, which results in the accumulation of the matter injected by supernovae and stellar winds and eventually in the formation of further stellar generations, while their outer regions sustain a stationary wind. The analytic formulae are derived from the basic hydrodynamic equations. Our main assumption, that the density at the star cluster surface scales almost linearly with that at the stagnation radius, is based on results from semi-analytic and full numerical calculations. The analytic formulation allows for the determination of the threshold mechanical luminosity that separates clusters evolving in either of the two solutions. It is possible to fix the stagnation radius by simple analytic expressions and thus to determine the fractions of the deposited matter that clusters evolving in the bimodal regime blow out as a wind or recycle into further stellar generations.Comment: 5 pages, 4 figures, accepted by A&

Borrowing Constraints and Credit Demand

This paper investigates the determinants of credit demand in the presence of borrowing constraints for the Chilean economy using a recently collected detailed and innovative data set, the Households Financial Survey. The estimation procedure employed allows for the observed debt to be a function of multiple selection rules and incorporates the endogeneity of income and assets into the debt equation. The paper provides compelling evidence that the relationship between household income and debt, both secured and non secured, is highly non linear. This result has clear implications for the level of household debt in the face of financial deregulation.

Complex gas kinematics in compact, rapidly assembling star-forming galaxies

Deep, high resolution spectroscopic observations have been obtained for six compact, strongly star-forming galaxies at redshift z~0.1-0.3, most of them also known as Green Peas. Remarkably, these galaxies show complex emission-line profiles in the spectral region including H\alpha, [NII]$\lambda\lambda 6548, 6584$ and [SII]$\lambda\lambda 6717, 6731$, consisting of the superposition of different kinematical components on a spatial extent of few kpc: a very broad line emission underlying more than one narrower component. For at least two of the observed galaxies some of these multiple components are resolved spatially in their 2D-spectra, whereas for another one a faint detached H\alpha\ blob lacking stellar continuum is detected at the same recessional velocity ~7 kpc away from the galaxy. The individual narrower H\alpha\ components show high intrinsic velocity dispersion (\sigma ~30-80 km s$^{-1}$), suggesting together with unsharped masking HST images that star formation proceeds in an ensemble of several compact and turbulent clumps, with relative velocities of up to ~500 km s$^{-1}$. The broad underlying H\alpha\ components indicate in all cases large expansion velocities (full width zero intensity FWZI $\ge$ 1000 km s$^{-1}$) and very high luminosities (up to ~10$^{42}$ erg s$^{-1}$), probably showing the imprint of energetic outflows from SNe. These intriguing results underline the importance of Green Peas for studying the assembly of low-mass galaxies near and far.Comment: 11 pages, 3 figures, and 1 Table. Accepted for publication in ApJ Letter

Chandra view of Kes 79: a nearly isothermal SNR with rich spatial structure

A 30 ks \chandra ACIS-I observation of Kes 79 reveals rich spatial structures, including many filaments, three partial shells, a loop and a ``protrusion''. Most of them have corresponding radio features. Regardless of the different results from two non-equilibrium ionization (NEI) codes, temperatures of different parts of the remnant are all around 0.7 keV, which is surprisingly constant for a remnant with such rich structure. If thermal conduction is responsible for smoothing the temperature gradient, a lower limit on the thermal conductivity of $\sim$ 1/10 of the Spitzer value can be derived. Thus, thermal conduction may play an important role in the evolution of at least some SNRs. No spectral signature of the ejecta is found, which suggests the ejecta material has been well mixed with the ambient medium. From the morphology and the spectral properties, we suggest the bright inner shell is a wind-driven shell (WDS) overtaken by the blast wave (the outer shell) and estimate the age of the remnant to be $\sim$ 6 kyr for the assumed dynamics. Projection is also required to explain the complicated morphology of Kes 79.Comment: 12 pages, 6 figures (3 in color), ApJ, in press, April 20, 200

Métodos de búsqueda y resultados en países en desarrollo: el caso de Venezuela

(Disponible en idioma inglés únicamente) En este trabajo se emplean datos de panel de Venezuela recabados recientemente correspondientes al período de 1994 a 2002 para analizar tres cuestiones básicas: la primera tiene que ver con la influencia de las características individuales y la experiencia previa en el mercado laboral en la elección de métodos de búsqueda distintos. La segunda se refiere a la eficacia de diversos métodos de búsqueda para salir del desempleo y se controlan las características individuales y de los empleos anteriores. Por último, la tercera cuestión se relaciona con la situación laboral previa, mediante el análisis de la importancia relativa del método de búsqueda y la situación laboral anterior, para determinar la probabilidad de conseguir empleo o quedar fuera de la fuerza laboral. Concluimos que la situación laboral anterior es un factor principal que determina si se pasa a una situación de empleo y que el uso de agencias de empleo hace aumentar la probabilidad de ese paso en cada situación laboral.

Choosing Health Insurance in a Dual Health Care System: The Chilean Case

In Chile there is a public insurance system where people contribute a fixed percentage of their income, and also a private system where people pay a premium based on their personal characteristics. Using a large survey for 1996, we study the determinants of the decision to buy a private health plan. We find that the probability of buying a private health plan is positively correlated with income and living in areas with private health services providers. This probability decreases as families become older, and with a larger proportion of fertile age females. We also find that people who are more likely to demand health services prefer to buy a private health plan, and that people enrolled in a private health plan increase their use of health services. The segmentation observed in the health sector relates with the way private insurers and the public insurance system set their premiums.health insurance; health services; income segmentation