Asymptotic Giant Branch Stars (Astronomy and Astrophysics Library)

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Rubidium and zirconium abundances in massive Galactic asymptotic giant branch stars revisited

These libraries do not cover the ultraviolet UV , which is of keen interest especially for stellar population analysis of distant galaxies. Line lists in the UV are less mature than in the optical, and hence synthetic spectra do a worse job in predicting the flux there Edvardsson Wu et al.

Pulsars, Magnetars, Black Holes (Oh My!): The Wickedly Cool Stellar Undead

More stars have been observed since. Normal O stars are the dominant component of the integrated light of star forming galaxies. The NGSL also lacks late-stage stellar types. HST time was requested to observe these stellar groups, with the intent to add the reduced spectra to the NGSL, broadening its scientific applicability. The observations and data reduction, including correction for line of sight dust extinction, are described in Sect. The results for 40 of a total of 70 proposed stars are given in Sect.

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Conclusions and future work appearin Sect. NGSLstars and our sample in a log T eff , log g diagram. Hot star library candidate stars are marked with circles. The circles are filled for stars that were observed and included in this paper. To guide the eye, an approximate Eddington stability line is drawn, and approximate spectral type boundaries.

Stars were selected from the literature to cover a range of temperatures in each category with a preference for brighter stars to decrease exposure times. Vacca et al. In this mode, targets are chosen by the HST scheduling program from a list provided by the observer, in our case, 70 objects. Over time, targets are selected from the list and observed, but not all targets in the list. After being scheduled, the telescope points to the target star for somewhat less than half an orbit.

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Exposures are cosmic-ray split, and a fringe flat taken for the GL grating after each observation. All science images were cleaned for cosmic rays with a pass through L. Cosmic van Dokkum Occasionally, L.

Dust‐enshrouded asymptotic giant branch stars in the solar neighbourhood

Cosmic was destructive to our data. In that case, we relaxed parameters and iterated. In all cases, the L. The GL fringe flats of all visits were averaged. These tasks shifted the average fringe flat in wavelength and rescaled the correction, case by case. Grating-internal scattered light is an issue for GLB. It is obvious in very cool stars. The red scattered light calculation required integration over the whole spectrum, not just the UV portion.

We used the redder spectra to provide these count rates, but first we converted GL and GL count rates to GLB count rates using prelaunch throughput estimates. We subtracted Eq. Thus corrected, the GLB spectrum was multiplied by the post-launch sensitivity curve to obtain a final spectrophotometric flux. No wavelength calibration exposures were obtained during observations in order to save time on spacecraft overhead.

Wavelength jitter is introduced by 1 the wheel that carries the gratings Mode Selection Mechanism Biretta et al.

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Each exposure was cross-correlated with template stars to shift them to a zero velocity. Templates were drawn from banks of synthetic stellar spectra and the Calspec database Bohlin et al. Wavelengths are in vacuum. For stars with low extinction, we held all parameters constant except A V see Appendix B. To estimate the dust extinction, dust-free templates were needed.

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Both programs produced very similar continua for the same set of atmospheric parameters. Exact matches were not attempted because our goal was limited to fitting dust extinction parameters. The empirical curve was then fit with the model described above.

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The RMS value was calculated to obtain a rough goodness of fit, but most of the work of retrying templates and tweaking smoothing parameters was done judiciously by eye. Our main result is to present spectra of 40 stars. The SNAP program is still active at low priority, so a few more stars may enter the library in the future.

As best as can be contrived, the spectra are free of cosmic rays, red fringing in the GL, and scattered light in the case of our coolest stars. Cross-correlation was used to bring the spectra to a zero velocity wavelength scale. Finally, a five-parameter dust extinction model, or one-parameter in the case of low-extinction stars, was fit using synthetic spectra as zero-extinction templates.

Three examples are illustrated in Fig. The spectra are available online 2.

Cited article:

Origin of Pluto and Charon: the fission hypothesis revisited. Galactic cosmic rays in a finite solar cavity , Webb, G. Energy losses and modulation of galactic cosmic rays. L Rotating polytropes in the post-Newtonian approximation , Sudbury, A. The evolution of a horizontal scale for oscillatory magnetoconvection , Murphy, J.

After the observations were reduced, we discovered a duplication. They arrived in the target list via different literature paths, with temperatures 12 K apart. Despite this, their separately-derived extinctions are only 0. In the process of fitting extinction curves with synthetic templates, the central star in NGC object 21 in our list was difficultto match. The match improved, but was not good near H continuum breaks.

Published , p. Perturbations of vacuum Kerr-Schild spaces. Further studies of a fragmentation problem , Monaghan, J. Leaky and non-leaky oscillations in magnetic flux tubes , Cally, P. Uranus: Predicted origin and composition of its atmosphere, moons and rings , Prentice, A. Uranus after Voyager 2 and the origin of the solar system , Prentice, A. Preferred horizontal scale for thermal convection , Fiedler, R. A nonlinear bifurcation in cellular convection theory , Yannios, N.

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