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Papers by Enrique Covarrubias
Astronomy and Astrophysics Supplement Series, 1996
A catalogue of uvby-β photometry for 87 of the turn-off and subgiant stars from the HK survey of ... more A catalogue of uvby-β photometry for 87 of the turn-off and subgiant stars from the HK survey of is given. Most of these stars have [Fe/H]≤ −2.5. These photometric data have been taken and reduced using the same techniques as in our previous two uvby-β catalogues. An error analysis has been made; typical mean observational errors for a star with V = 14. m 2 are 0.008, 0.007, 0.011, 0.010 and 0.012 in V , (b − y), m1, c1 and β, respectively. Our photometric data are also compared to the UBV photometry and spectral indices from the HK survey; satisfactory agreement is found indicating good quality for the two data sets. The stars are classified in reddening-free diagrams of the uvby-β system; several of the stars are found to have been mis-classified in the HK survey. Two metal-poor supergiants, three (possibly four) horizontal branch stars, one blue subluminous star and two stars with ambiguous photometry have been identified. Stellar parameters, such as E(b − y), MV , δMV , and Teff, plus error estimates for these parameters, are provided using our photometric calibrations. Although all stars have galactic latitudes |b| ≥ 30 • many of them are significantly reddened with E(b − y) ranging from 0.02 to 0.15. The average reddening towards the South Galactic Pole region, b < −60 • , is E(b − y) = 0.027 ± 0.004 corresponding to E(B − V ) = 0.036 ± 0.005 in contrast to the low value of E(B − V ) 0.01 derived from the maps. The stars are analyzed in the (b − y)0, [Fe/H] diagram, and individual ages estimated using the isochrones of and of . These very metal-poor stars are found to be coeval, within 1−2 Gyr, with the halo and thick-disk stars studied previously, with a mean age in excess of 18 Gyr. Several blue "thick-disk" stars, which are perhaps analogous to the "blue metal-poor" stars of , have been identified.
Rev Bras Neurol, Sep 1, 2010
Journal of Cognition and Culture, 2009
... Joshua Glasgowa,* Julie L. Shulmanb Enrique G. Covarrubiasc a Philosophy Program, Victoria Un... more ... Joshua Glasgowa,* Julie L. Shulmanb Enrique G. Covarrubiasc a Philosophy Program, Victoria University of Wellington, Wellington, New Zealand b ... the ethnic groups 'Asians' and 'Hispanics' (which some might argue are actually racial groups; Alcoff, 2003; Haney López, 2005 ...
Abstract and Applied Analysis, 2006
We derive necessary and sufficient conditions for global-in-time existence of solutions of ordina... more We derive necessary and sufficient conditions for global-in-time existence of solutions of ordinary differential, stochastic differential, and parabolic equations. The conditions are formulated in terms of complete Riemannian metrics on extended phase spaces (conditions with two-sided estimates) or in terms of derivatives of proper functions on extended phase spaces (conditions with one-sided estimates).
Astronomy and Astrophysics Supplement Series, 1996
A catalogue of uvby-β photometry for 87 of the turn-off and subgiant stars from the HK survey of ... more A catalogue of uvby-β photometry for 87 of the turn-off and subgiant stars from the HK survey of is given. Most of these stars have [Fe/H]≤ −2.5. These photometric data have been taken and reduced using the same techniques as in our previous two uvby-β catalogues. An error analysis has been made; typical mean observational errors for a star with V = 14. m 2 are 0.008, 0.007, 0.011, 0.010 and 0.012 in V , (b − y), m1, c1 and β, respectively. Our photometric data are also compared to the UBV photometry and spectral indices from the HK survey; satisfactory agreement is found indicating good quality for the two data sets. The stars are classified in reddening-free diagrams of the uvby-β system; several of the stars are found to have been mis-classified in the HK survey. Two metal-poor supergiants, three (possibly four) horizontal branch stars, one blue subluminous star and two stars with ambiguous photometry have been identified. Stellar parameters, such as E(b − y), MV , δMV , and Teff, plus error estimates for these parameters, are provided using our photometric calibrations. Although all stars have galactic latitudes |b| ≥ 30 • many of them are significantly reddened with E(b − y) ranging from 0.02 to 0.15. The average reddening towards the South Galactic Pole region, b < −60 • , is E(b − y) = 0.027 ± 0.004 corresponding to E(B − V ) = 0.036 ± 0.005 in contrast to the low value of E(B − V ) 0.01 derived from the maps. The stars are analyzed in the (b − y)0, [Fe/H] diagram, and individual ages estimated using the isochrones of and of . These very metal-poor stars are found to be coeval, within 1−2 Gyr, with the halo and thick-disk stars studied previously, with a mean age in excess of 18 Gyr. Several blue "thick-disk" stars, which are perhaps analogous to the "blue metal-poor" stars of , have been identified.
Rev Bras Neurol, Sep 1, 2010
Journal of Cognition and Culture, 2009
... Joshua Glasgowa,* Julie L. Shulmanb Enrique G. Covarrubiasc a Philosophy Program, Victoria Un... more ... Joshua Glasgowa,* Julie L. Shulmanb Enrique G. Covarrubiasc a Philosophy Program, Victoria University of Wellington, Wellington, New Zealand b ... the ethnic groups 'Asians' and 'Hispanics' (which some might argue are actually racial groups; Alcoff, 2003; Haney López, 2005 ...
Abstract and Applied Analysis, 2006
We derive necessary and sufficient conditions for global-in-time existence of solutions of ordina... more We derive necessary and sufficient conditions for global-in-time existence of solutions of ordinary differential, stochastic differential, and parabolic equations. The conditions are formulated in terms of complete Riemannian metrics on extended phase spaces (conditions with two-sided estimates) or in terms of derivatives of proper functions on extended phase spaces (conditions with one-sided estimates).