Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

Beryllium Abundances in Halo Stars from Keck/HIRES Observations

We have determined the abundance of Be in stars with an array of metal abundances in order to enhance our understanding of the chemical evolution of the Galaxy, cosmic-ray theory, and cosmology. Observations of the Be II resonance lines at λ3130 and λ3131 were made at the Keck telescope with the HIRES spectrometer at a resolution of 46,000 and signal-to-noise ratios of 60–110 (per pixel) typically. Our sample includes 22 halo dwarfs and five disk stars (including the Sun). We have taken special care in determining the stellar parameters for these stars in a consistent manner. The Be abundances were found (1) from the measured equivalent width of the relatively unblended Be II line at 3131.065 Å with an analysis that included 11 weak atomic and molecular lines near that wavelength and (2) from spectrum synthesis that included newly derived enhanced O (relative to Fe) in the synthesis calculations. The two methods are in excellent agreement. We find straight-line fits between Be and Fe: log N(Be/H) = 0.96(±0.04)[Fe/H] − 10.59(±0.03) ; and between Be and O: log N(Be/H) = 1.45(±0.04)[O/H] − 10.69(±0.04) . It seems that Be and Fe increase at the same rate during the course of the evolution of the Galaxy. But as O increases by a factor of 100, Be increases more rapidly, by a factor of 800. Traditional models in which energetic cosmic rays interact with ambient CNO nuclei in the interstellar medium to produce Be are consistent with this finding, as long as certain chemical evolution effects (such as mass outflow from the halo) are taken into account. However, models predicting a linear relationship between Be and O, such as those producing Be in the vicinity of Type II supernovae, are less consistent with our result. There is some evidence for an intrinsic spread in Be at a given [Fe/H] or [O/H]. There is currently no evidence of a primordial plateau level of Be down to log N(Be/H) = -13.5

Optimal Distinctiveness: The Role of Platform Size and Identity

Recent theoretical advances hold that platforms comprise a second strategic dimension next to size, called identity, which describes the platform's technological and market scope. Letting go of platform size as the main criterion for platform value opens the possibility for platforms to pursue differentiation strategies with a distinct market positioning. The concept of optimal distinctiveness (OD) implies that differentiation can be optimized so that it maximizes performance. In this paper, we draw on recent OD research in and outside of the field of platforms and elaborate on the role of platform size within the distinctiveness framework. We discuss platform size and identity in the context of OD and suggest propositions for future research. The paper contributes to the management of platforms and OD in platform markets by showing how a platform's distinctiveness strategy may depend on its size. We contribute to platform management across various platform sizes and to research on OD in platform markets

The effect of internal and external technology sourcing on firm performance throughout the technology life cycle

In studies about the impact of technology sourcing on firm performance, the impact of the technology life cycle has thus far received scant attention. This paper investigates this topic from the knowledge-based perspective. Data was gathered from 22 PLD (Programmable Logic Device) manufacturers in the integrated circuit industry between 1986 and 2005, and used to test two hypotheses based on panel analysis: (1) that strategic alliance networks, as a mode of external technology sourcing, have a positive effect on a firm's innovative and market performance early in the technology life cycle, and (2) that internal development as a mode of internal technology sourcing has a positive effect on a firm's innovative and market performance later in the technology life cycle. Although both hypotheses are supported as far as market performance is concerned, neither is supported when it comes to innovative performance