24 research outputs found
Abundances of the elements in the solar system
A review of the abundances and condensation temperatures of the elements and
their nuclides in the solar nebula and in chondritic meteorites. Abundances of
the elements in some neighboring stars are also discussed.Comment: 42 pages, 11 tables, 8 figures, chapter, In Landolt- B\"ornstein, New
Series, Vol. VI/4B, Chap. 4.4, J.E. Tr\"umper (ed.), Berlin, Heidelberg, New
York: Springer-Verlag, p. 560-63
Star clusters near and far; tracing star formation across cosmic time
© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00690-x.Star clusters are fundamental units of stellar feedback and unique tracers of their host galactic properties. In this review, we will first focus on their constituents, i.e.\ detailed insight into their stellar populations and their surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond the Local Group to review star cluster populations at various evolutionary stages, and in diverse galactic environmental conditions accessible in the local Universe. At high redshift, where conditions for cluster formation and evolution are more extreme, we are only able to observe the integrated light of a handful of objects that we believe will become globular clusters. We therefore discuss how numerical and analytical methods, informed by the observed properties of cluster populations in the local Universe, are used to develop sophisticated simulations potentially capable of disentangling the genetic map of galaxy formation and assembly that is carried by globular cluster populations.Peer reviewedFinal Accepted Versio
Young stars in Galactic clusters and the Magellanic Clouds
SIGLEAvailable from British Library Document Supply Centre- DSC:DXN002675 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
The chemical composition towards the galactic anti-centre .1. Observations and model atmosphere analyses
High resolution spectra of six early B-type main-sequence
stars having galactocentric distances of between 10 and 18 kpc are
presented. We list the equivalent widths for the metal lines and illustrate
their hydrogen and helium line profiles. The stars are analysed using LTE
line-blanketed model atmosphere techniques to derive atmospheric parameters
and surface chemical compositions. All six stars have similar
effective temperatures and surface gravities, allowing a reliable comparison
of their metal abundances and distances. Significant variations
in the photospheric abundances are evident and we discuss the need for a more
detailed line-by-line differential analysis to exactly quantify the
differences. This will be presented in a companion paper (Smartt et al.
1996)
The present-day chemical composition of the LMC
High-resolution observations of five OB-type main-sequence stars in the
Large Magellanic Cloud (LMC) have been obtained with the UCL échelle
spectrograph on the 3.9-m Anglo-Australian Telescope. These spectra have
been analysed using LTE model-atmosphere techniques, to derive stellar
atmospheric parameters and chemical compositions. As these stars are located
within the hydrogen burning main-sequence band, their surface abundances
should reflect those of the present-day interstellar medium. Detailed
line-by-line differential analyses have been undertaken relative to Galactic
comparison stars. We conclude that there exists a general metal deficiency
of  dex within the LMC, and find no significant abundance
variations between cluster and field stars. There is also tentative evidence
to suggest a lower oxygen to iron abundance ratio, and an over-deficiency
of magnesium relative to the other α–elements. These are discussed
in terms of previous abundance analyses and models of discontinuous (or
bursting) star formation within the LMC. Finally, there is some evidence to
suggest a greater chemical enrichment of material within the \ion{H}{ii} region LH 104
A search for circumstellar material around B-type stars in the Galactic halo
19 B-type stars, selected from the Palomar-Green Survey, have been observed at infrared wavelengths to search for possible infrared excesses, as part of an ongoing programme to investigate the nature of early-type stars at high Galactic latitudes. The resulting infrared fluxes, along with Stromgren photometry, are compared with theoretical flux profiles to determine whether any of the targets show evidence of circumstellar material, which may be indicative of post-main- sequence evolution. Eighteen of the targets have flux distributions in good agreement with theoretical predictions. However, one star, PG 2120 + 062, shows a small near-infrared excess, which may be due either to a cool companion of spectral type F5-F7, or to circumstellar material, indicating that it may be an evolved object such as a post-asymptotic giant branch star, in the transition region between the asymptotic giant branch and planetary nebula phase, with the infrared excess due to recent mass loss during giant branch evolution