Modelling early-type stars in eclipsing binaries of open clusters: a new method for age determination from ratio of radii

Binary systems, in particular eclipsing binaries, are essential sources of our knowledge of the fundamental properties of stars. The ages of binaries, members of open clusters, are constrained by their own fundamental properties and by those of the hosting cluster. The ages of eleven open clusters are here found by constructing models for the components of twelve eclipsing binaries. The difference between the ages we found and the ages of the clusters derived from isochrone fitting is up to 40%. For the binary system V497 Cep in NGC 7160, the difference is about 100%. Binary systems whose primary component is aboutto complete main-sequence life time, such as V453 Cyg and V906 Sco, are the most suitable systems for age determination. Using model results for these stars, we derive an expression for sensitive and uncomplicated relative age determination of binary systems (age divided by the main-sequence life time of the primary star). The expression is given as logarithm of radii ratio divided by a logarithm of mass ratio. Two advantages of this expression are that (i) it is nearly independent of assumed chemical composition of the models because of the appearance of the ratio of radii, and (ii) the ratios of radii and masses are observationally much more precise than their absolute values. We also derive another expression using luminosities rather than radii and compare results.Comment: 12 pages, 6 figures, accepted by PAS

Grids of stellar models including second harmonic and colours: Solar composition

Grids of stellar evolution are required in many fields of astronomy/astrophysics, such as planet hosting stars, binaries, clusters, chemically peculiar stars, etc. In this study, a grid of stellar evolution models with updated ingredients and {recently determined solar abundaces} is presented. The solar values for the initial abundances of hydrogen, heavy elements and mixing-length parameter are 0.0172, 0.7024 and 1.98, respectively. The mass step is small enough (0.01 M$_\odot$) that interpolation for a given star mass is not required. The range of stellar mass is 0.74 to 10.00 M$_\odot$. We present results in different forms of tables for easy and general application. The second stellar harmonic, required for analysis of apsidal motion of eclipsing binaries, is also listed. We also construct rotating models to determine effect of rotation on stellar structure and derive fitting formula for luminosity, radius and the second stellar harmonic as a function of rotational parameter. We also compute and list colours and bolometric corrections of models required for transformation between theoretical and observational results. The results are tested for the Sun, the Hyades cluster, the slowly rotating chemically peculiar Am stars and the eclipsing binaries with apsidal motion. The theoretical and observational results along isochrones are in good agreement. The grids are also applicable to rotating stars provided that equatorial velocity is given.Comment: 13 Figures 21 pages. Accepted by RA

Intergenerational Mobility of Immigrants in Germany: Moving with Natives or Stuck in their Neighborhoods?

In this paper, I analyze intergenerational mobility of immigrants and natives in Germany. Using the German Socioeconomic Panel (GSOEP), I find intergenerational elasticities that range from 0.19 to 0.26 for natives and from 0.37 to 0.40 for immigrants. These elasticity estimates are lower than typically found for the U.S. and imply higher mobility in Germany than in the U.S. However, as in the U.S., I find greater mobility among German natives than among immigrants. Moreover, I investigate to what extent the lower mobility among immigrants in Germany is due to “ethnic capital” as suggested by Borjas (1992). I find that the impact of father’s earnings on son’s earnings remains virtually unchanged when including a measure of ethnic capital, suggesting that the higher father-son correlation found among immigrants is not due to omitting ethnic capital. However, I do find a large independent effect of ethnic capital on sons’ earnings (the coefficient is 0.81 as opposed to 0.25 found by Borjas (1992)). These results are consistent with estimates from Microcensus data, where the combined effect of parents’ and ethnic capital is close to unity. Thus, contrary to the U.S. results which suggest convergence of immigrants’ earnings towards natives’ earnings, the German results suggest divergence of immigrant earnings.immigration, intergenerational mobility, natives, ethnic capital

Intergenerational Transfer of Human Capital under Post-War Distress: The Displaced and the Roma in the Former Yugoslavia

In this chapter, we investigate the effects of vulnerability on income and employment in Bosnia and Herzegovina, Croatia, Montenegro and Serbia using a unique 2004 UNDP dataset. Treating the collapse of the former Yugoslavia as a natural experiment, we compare three groups that have been differently affected by the wars and post-war distress: the majority as the benchmark, the ex-ante and ex-post vulnerable Roma people, and the ex-ante equal but ex-post vulnerable refugees and internally displaced people (RIDPs). Our findings reveal significant negative effects of vulnerability on income and employment. RIDPs seem to be about as negatively affected as Roma across the four states, which indicate that vulnerability inflicted by relatively recent displacement may have similar effects as vulnerability rooted deep in the past. When we look at education as one of the key determinants of socio-economic outcomes, both groups exhibit similarly substandard educational outcomes of children and significant inertia in intergenerational transfer of human capital. Our findings highlight the need for policies that not only tackle vulnerability as such, but address the spillover effects of current vulnerability on future educational attainment.vulnerability, labor market, education, Roma, refugees, internally displaced people, discrimination, integration

Effects of Low-Skilled Immigration on U.S. Natives: Evidence from Hurricane Mitch

In the 1980s the composition of immigrants to the U.S. shifted towards less-skilled workers. Around this time, real wages and employment of younger and lesseducated U.S. workers fell. Some blame recent immigration shifts for the misfortunes of unskilled workers in the U.S. OLS estimates using Census data show instead that native wages are positively related to the recent influx of Latin Americans. However, these estimates are biased if demand shocks are positively related to immigration. An IV strategy, which deals with the endogeneity of immigration by exploiting a large influx of Central American immigrants towards U.S. Southern ports of entry after Hurricane Mitch, also generates positive wage effects but only for more educated native men. Yet, ignoring the flows of native and earlier immigrants in response to this exogeneous immigration is likely to generate upward biases in these estimates too. Native wage effects disappear and less-skilled employment of previous Latin American immigrants falls when controlling for outmigration. This highlights the importance of controlling for out-migration not only of natives but also of previous immigrants in regional studies of immigration.Immigration, Imperfect Substitution, Disemployment Effects, Natural Experiments, Outmigration

Capital-Skill Complimentarity: Evidence from Manufacturing Industries in Ghana

Using U.S. manufacturing data, Griliches (1969) found evidence suggesting that capital equipment was more substitutable for unskilled than skilled labor. Griliches formulated this finding as the capital-skill complementarity hypothesis. The purpose of this study is to determine whether the capital-skill complementarity framework holds for Ghana manufacturing plants in industry and aggregate level. We use an unbalanced panel of plant-level data for manufacturing firms in Ghana during the 1991 and 1997 in four industries (food-bakery, textiles-garments, wood-furniture and metal-machinery). Our findings suggest that capital-skill complimentarity holds in aggregate level and wood-furniture sector in Ghana. However, we reject the capital-skill complementarity hypothesis for food-bakery, textile-garment and metal-machinery sectors.capital-skill complementarity, elasticity of substitution, translog cost function