The structure of neutron stars is considered from theoretical and observational perspectives We demonstrate an important aspect of neutron star structure: the neutron star radius is primarily determined by the behavior of the pressure of matter in the vicinity of nuclear matter equilibrium density In the event that extreme softening does not occur at these densities, the radius is virtually independent of the mass and is determined by the magnitude of the pressure For equations of state with extreme softening or those that are self-bound, the radius is more sensitive to the mass Our results show that in the absence of extreme softening, a measurement of the radius of a neutron star more accurate than about 1 km will usefully constrain the equation of state We also show that the pressure near nuclear matter density is primarily a function of the density dependence of the nuclear symmetry energy, while the nuclear incompressibility and skewness parameters play secondary roles In addition, we show that the moment of inertia and the binding energy of neutron stars, for a large class of equations of state, are nearly universal functions of the star's compactness These features can be understood by considering two analytic, yet realistic, solutions of Einstein's equations, by, respectively, Buchdahl and Tolman We deduce useful approximations for the fraction of the moment of inertia residing in the crust, which is a function of the stellar compactness and, in addition, the pressure at the core-crust interface

https://iopscience.iop.org/article/10.1086/319702/pdf

Neutron Star Structure and the Equation of State

Neutron Stars 1: Equation of State and Structure

We present the results of a speckle interferometric survey made with the CHARA speckle camera and 4 m–class telescopes of Galactic O-type stars with V 59% have a visual or spectroscopic companion) but less so among field and especially runaway stars. There are many triple systems among the speckle binaries, and we discuss their possible role in the ejection of stars from clusters. The period distribution of the binaries is bimodal in log P, but we suggest that binaries with periods of years and decades may eventually be found to fill the gap. The mass ratio distribution of the visual binaries increases toward lower mass ratios, but low mass ratio companions are rare among close, spectroscopic binaries (probably because of the difficulty of spectroscopic detection rather than a real deficit). We present distributions of the eccentricity and longitude of periastron for spectroscopic binaries with elliptical orbits, and we find strong evidence of a bias in the longitude of periastron distribution (the Barr effect), which is probably caused by line distortions introduced by circumstellar gas.

https://iopscience.iop.org/article/10.1086/300234/pdf

ICCD Speckle Observations of Binary Stars. XIX. An Astrometric/Spectroscopic Survey of O Stars

The paper describes the general design, instrumentation, and ground control system of the International Ultraviolet Explorer (IUE) satellite, which will serve as an astronomical observatory providing both high and low resolution UV spectra of sources other than the sun. Basic data are given on the telescope, the UV-visible converter, the spectrograph optics, the camera response, and the communications systems.

The IUE spacecraft and instrumentation

Extreme ultraviolet astronomy

During the commissioning phase of IUE observations were made of a selection of hot stars: the white dwarf HZ43, the hot subdwarf BD + 75°325, the nucleus of the planetary nebula NGC6826, the dwarf nova SS Cygni, and the peculiar object η Carinae. The observations were made in the low dispersion mode and the data have been reduced using a preliminary calibration. The results are presented and discussed for each object.

IUE observations of hot stars: HZ43, BD + 75°325, NGC6826, SS Cygni, η Carinae

Coordinated optical, ultraviolet, radio and X-ray observations of SN 1979c in M 100.

/pdf/the-orbit-of-the-supergiant-component-of-vela-x-1-derived-26dsxw759y.pdf

The orbit of the supergiant component of Vela X-1 derived from IUE radial velocities

The system IK Peg has been known to be a binary for over 60 years but the secondary has never been identified. The detection of this system in the British Wide Field Camera All-Sky Survey in the EUV has enabled the secondary to be positively identified as a white dwarf. Fits to EUV survey data, the first IUE spectrum, and archival X-ray data indicate that the system contains a high-mass (∼ 1 M ○ .) white dwarf and that it is very close to edge-on. The evolutionary status of this system is discussed; it is shown to be the result of a common-envelope phase, and it is expected to evolve into a Type I supernova or a cataclysmic variable

/pdf/ik-peg-a-nearby-short-period-sirius-like-system-1whh0a6956.pdf

IK Peg – a nearby, short-period, Sirius-like system

A detailed abundance analysis of the bright A-type star {3 Crt is presented. It is found that most of the abundances are essentially solar, indicating that the star is not a hot Am star. The only prominent anomalies are an under abundance of AI and overabundances of S, Sr and Ba. The barium overabundance is the most prominent and has important implications for the past history of this supposed binary system. The presence of the ROSAT-discovered white dwarf companion could indicate that the A-type star may have accreted material from the white dwarf progenitor. There are indications in the literature that the system is a relatively short -period binary. However, the radial velocity measurements presented in this paper show no apparent velocity changes, and do not support this hypothesis. It may be that the system is a wide long-period binary, or not even physically associated. Additional radial velocity measurements are required to investigate the orbit of this

D. J. Stickland

Papers

IUE observations of hot stars: HZ43, BD + 75°325, NGC6826, SS Cygni, η Carinae

Coordinated optical, ultraviolet, radio and X-ray observations of SN 1979c in M 100.

The orbit of the supergiant component of Vela X-1 derived from IUE radial velocities

IK Peg – a nearby, short-period, Sirius-like system

The chemical composition and binarity of β Crateris