The Possible Identification of Promethium in S Stars

Davis, Dorothy N.

doi:10.1086/151034

Cited by 14 publications

(14 citation statements)

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“…These choices broadly bracket the values reported by Andrews et al (2010; see also e.g. Kuchner 2004;Davis 2005) for observed circumstellar disks. While the plots show that the dependence on the disk temperature normalization is very small, the dependence on the surface density normalization is larger, the critical metallicity varying by a factor of ≃ 3 between the plots.…”

Section: Appendix Dependence On Disk Parameterssupporting

confidence: 84%

The First Planets: The Critical Metallicity for Planet Formation

Johnson

2012

ApJ

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A rapidly growing body of observational results suggests that planet formation takes place preferentially at high metallicity. In the core accretion model of planet formation this is expected because heavy elements are needed to form the dust grains which settle into the midplane of the protoplanetary disk and coagulate to form the planetesimals from which planetary cores are assembled. As well, there is observational evidence that the lifetimes of circumstellar disks are shorter at lower metallicities, likely due to greater susceptibility to photoevaporation. Here we estimate the minimum metallicity for planet formation, by comparing the timescale for dust grain growth and settling to that for disk photoevaporation. For a wide range of circumstellar disk models and dust grain properties, we find that the critical metallicity above which planets can form is a function of the distance r at which the planet orbits its host star. With the iron abundance relative to that of the Sun [Fe/H] as a proxy for the metallicity, we estimate a lower limit for the critical abundance for planet formation of [Fe/H] crit ≃ -1.5 + log(r/1 AU), where an astronomical unit (AU) is the distance between the Earth and the Sun. This prediction is in agreement with the available observational data, and carries implications for the properties of the first planets and for the emergence of life in the early Universe. In particular, it implies that the first Earth-like planets likely formed from circumstellar disks with metallicities Z 0.1 Z ⊙ . If planets are found to orbit stars with metallicities below the critical metallicity, this may be a strong challenge to the core accretion model.

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Section: Appendix Dependence On Disk Parameterssupporting

confidence: 84%

The First Planets: The Critical Metallicity for Planet Formation

Johnson

2012

ApJ

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“…The matched catalog of WFPC2 and GMOS sources contains 10 3 stars. We calibrate the g ′ and r ′ magnitudes to HST F 555W and F 814W (hereafter called V and I) using derived transformations for the common stars in the space-and ground-based systems (see Davis et al 2009 for details on the transformations). These offsets are then applied to the entire GMOS catalog.…”

Section: Gemini/gmos Photometry and Astrometrymentioning

confidence: 99%

“…The impact of this measurement for bettering our knowledge of stellar structure and evolution, and for dating halo globular clusters through white dwarf cooling theory, are discussed. An analysis of the remaining M4 spectra that did not yield masses, e.g., to define the spectral types of population II white dwarfs, is presented in the companion paper by Davis et al (2009).…”

Section: Introductionmentioning

confidence: 99%

The Masses of Population Ii White Dwarfs

Kalirai¹,

Davis²,

Richer³

et al. 2009

ApJ

131

160

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Globular star clusters are among the first stellar populations to have formed in the Milky Way, and thus only a small sliver of their initial spectrum of stellar types are still burning hydrogen on the main-sequence today. Almost all of the stars born with more mass than 0.8 M ⊙ have evolved to form the white dwarf cooling sequence of these systems, and the distribution and properties of these remnants uniquely holds clues related to the nature of the now evolved progenitor stars. With ultra-deep HST imaging observations, rich white dwarf populations of four nearby Milky Way globular clusters have recently been uncovered, and are found to extend an impressive 5 -8 magnitudes in the faint-blue region of the H-R diagram. In this paper, we characterize the properties of these population II remnants by presenting the first direct mass measurements of individual white dwarfs near the tip of the cooling sequence in the nearest of the Milky Way globulars, M4. Based on Gemini/GMOS and Keck/LRIS multiobject spectroscopic observations, our results indicate that 0.8 M ⊙ population II main-sequence stars evolving today form 0.53 ± 0.01 M ⊙ white dwarfs. We discuss the implications of this result as it relates to our understanding of stellar structure and evolution of population II stars and for the age of the Galactic halo, as measured with white dwarf cooling theory.

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“…We close this section by addressing briefly the issue of WDs that have an atmosphere of helium rather than hydrogen. For the temperature range of the NGC 2158 cooling sequence, the typical number ratio of He-to H-atmosphere WDs in the field is of the order of 1:4 (e.g., Tremblay & Bergeron 2008), but it is not clear whether there is a dearth of He-atmosphere WDs in star clusters compared to the field (see, e.g., Strickler et al 2009, Davis et al 2009). In spite of this uncertainty, at the luminosities of the NGC 2158 WDs the He-atmosphere models have cooling ages very similar to those of H-atmosphere models at the same mass (see, e.g., Hansen 1999, Salaris 2009).…”

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confidence: 99%

The Bottom of the White Dwarf Cooling Sequence in the Old Open Cluster NGC 2158

Bedin

Salaris

King

et al. 2009

ApJ

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We use 10 orbits of Advanced Camera for Surveys observations to reach the end of the white dwarf cooling sequence in the solar-metallicity open cluster NGC 2158. Our photometry and completeness tests show that the end falls at magnitude m F606W = 27.5 ± 0.15, which implies an age between ∼1.8 and ∼2.0 Gyr, consistent with the age of 1.9 ± 0.2 Gyr obtained from fits to the main-sequence turn-off. The faintest white dwarfs show a clear turn toward bluer colors, as predicted by theoretical isochrones.Subject headings: open clusters and associations: individual (NGC 2158) -Hertzsprung-Russell diagram -white dwarfs

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The Possible Identification of Promethium in S Stars

Cited by 14 publications

References 0 publications

The First Planets: The Critical Metallicity for Planet Formation

The First Planets: The Critical Metallicity for Planet Formation

The Masses of Population Ii White Dwarfs

The Bottom of the White Dwarf Cooling Sequence in the Old Open Cluster NGC 2158

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