Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · astro-ph/9602057

Constraints on the Horizontal-Branch Morphology of the Globular Cluster M79 (NGC 1904) from Optical and Far-UV Observations

W. Van Dyke Dixon·Arthur F. Davidsen·Ben Dorman·Harry Ferguson
View original source ↗Read source document ↗Export metadata ↓

Abstract

The globular cluster M79 was observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-1 space shuttle mission in 1990 December. The cluster's far-UV integrated spectrum shows strong absorption in the Lyman lines of atomic hydrogen. We seek to use this spectrum, together with optical photometry, to constrain the stellar mass distribution along its zero-age horizontal branch (ZAHB). We find that a Gaussian distribution of ZAHB masses, with a mean of 0.59 Msun and standard deviation 0.05 Msun, is able to reproduce the cluster's (B,V) color-magnitude diagram when subsequent stellar evolution is taken into account, but cannot reproduce the cluster's far-UV spectrum. Model stellar spectra fit directly to the HUT data indicate a surprising distribution of atmospheric parameters, with surface gravities (and thus implied masses) significantly lower than are predicted by canonical HB evolutionary models. This result is consistent with the findings of Moehler et al. [A&A, 294, 65 (1995)] for individual HB stars in M15. Further progress in understanding the mass distribution of the HB must await resolution of the inconsistencies between the derived stellar atmospheric parameters and the predictions of HB evolutionary models. Improved stellar spectral models, with higher spectral resolution and non-solar abundance ratios, may prove useful in this endeavor.

Explore related subjects

astro-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

W. Van Dyke Dixon, Arthur F. Davidsen, Ben Dorman, Harry Ferguson. 1996-02-12. Constraints on the Horizontal-Branch Morphology of the Globular Cluster M79 (NGC 1904) from Optical and Far-UV Observations. https://doi.org/10.1086/117931

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Frame covariance of CMBR lensing in the exact 1+3 covariant radiation hierarchy

The exact $1+3$ covariant Boltzmann hierarchy for the cosmic microwave background contains acceleration, shear and vorticity couplings whose coefficients grow linearly in $\ell$. We show that all are the multipole form of the aberration operator in the photon Liouville equation. Under a change of threading, this operator shifts by the along-ray generator of a Lorentz boost. The acceleration coupling of $\ell$ to $\ell\pm1$ and the shear coupling of $\ell$ to $\ell\pm2$ are therefore frame-covariant descriptions of the same operator, related by an algebraic, pointwise relabelling of direction. With emitter and observer frames fixed, the observed sky is independent of the intermediate threading at every $\ell$. We derive this in $1+3$ covariant and gauge-invariant variables without constructing second-order gauge-invariant variables. The $O(ε^2\ell)$ content is gravitational lensing, as known in metric variables. Linearisation about a Friedmann--Lemaître--Robertson--Walker background removes these couplings, requiring lensing to be reinstated from the geodesic equation. Keeping the threading arbitrary makes frame covariance explicit and places observer aberration in the same operator. In the Newtonian threading we compute both halves of the deflection: the equivalence-principle contribution enters through aberration, while the spatial-curvature contribution arises from free streaming on perturbed spatial sections and reduces to the same operator. The lensing efficiency follows from the direction derivative. The angular-power-spectrum contribution is quartic in the potential: for a deflection statistically independent of the source, the two fourth-order terms carrying $\ell^2$ cancel where the spectrum is smooth on the deflection scale, and lensing redistributes power without adding ensemble variance.

astro-ph↗
arXiv2026

Cosmic Conundrums with Quantum Corrections

Darh energy was discovered over 25 years ago and we do not have an explanation of it. Dark matter comprises 95% of matter in the universe and we still don't know what it is. The Webb telescope has been finding fully formed galaxies with massive black holes millions of times the mass of the sun in the early universe and we don't have any explanation. A quantum density limitation will be used to solve these and other outstanding problems.

astro-ph↗
arXiv2026

On binary pulsars and the force of gravity

The energy-momentum budget of the astrophysical systems can be studied by the exact local conservation equation derived by Landau and Lifshitz. We show that a similar equation is valid for the Einstein-Cartan gravity. We reanalyze a binary pulsar system using the Landau-Lifshitz conservation equation and show that the orbital period change rate can be completely understood as a curvature backreaction process. Taking into account the detailed theoretical and observational research of relativistic binary pulsar systems, especially the system of Hulse and Taylor, we conclude that general relativity and astrophysical observations rule out the existence of gravitational radiation. We comment upon the LIGO GW events and their alternative explanation, as well as the recent pulsar timing arrays data.

astro-ph↗