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The evolution is discussed of gravitational waves spectra produced by binary stars, supernova explosions, and coalescences of binary compact stars in outer galaxies. These spectra are integrated over a simple model of the universe to give an estimate of the stochastic gravitational wave background due to astrophysical sources.
Proposed Netherlands satellite program launchings for solar and stellar radiation observations
Slit spectra, spectrophotometric scans and infrared broad band observations are presented. Eight of the program galaxies can be classified as Seyfert galaxies. Arguments are given that thermal, nonthermal and stellar radiation components were present. One group of Seyfert galaxies was characterized both by the presence of a high density region of gas and by a continuum dominated by nonthermal radiation. The continua of the remaining program Seyferts, which did not have a high density region of gas, were dominated by thermal radiation from dust and a stellar continuum. Ten of the galaxies, which are not Seyfert galaxies, are shown to be examples of extragalactic H 2 regions.
Slit spectra, spectrophotometric scans, and infrared broad-band observations are presented for 18 Markarian galaxies with emission lines. Eight of the program galaxies can be classified as Seyfert galaxies. Arguments are given that thermal, nonthermal, and stellar radiation components are present. Broadly speaking, one group of Seyfert galaxies is characterized both by the presence of a high-density region of gas and by a continuum dominated by nonthermal radiation. The continua of the remaining program Seyferts, which do not have a high-density region of gas, are dominated by thermal radiation from dust and a stellar continuum. The 10 galaxies which are not Seyfert galaxies are shown to be examples of extragalactic H II regions; there is evidence for thermal emission from dust being present at 10 microns in four of these galaxies.
When stellar radiation interacts with a molecular cloud, the cloud's fate depends on the strength of the incident radiation and the radiation's mean-free-path within the cloud [F. Bertoldi, Astrophys. J. 346, 735–755 (1989)]. Under the right conditions, the radiation compresses the cloud and a star formation may occur. Where and when the stellar formation occurs in the cloud's collapse are open questions. Direct observation of the complete star–cloud lifecycle is nearly impossible due to the immense timescales and distances over which the interaction occurs. Laboratory astrophysics offers a way to investigate such a system by scaling the important astrophysical parameters to the laboratory. This work describes laboratory experiments to study the radiation-driven implosion of clouds, using x rays from a laser-irradiated, thin, gold foil as a surrogate star and a carbon-foam sphere as a surrogate cloud. An optically thick system, theoretically corresponding to a star-forming regime, was selected by choice of the foam density. Gold foil and sphere motions were imaged by x-ray radiography. Radiographic images show the formation of an interface between rarefied gold and carbon plasmas, a shock moving into the sphere, and a blunting of the initial sphere's shape. Measurements show that the shock moved linearly around 64 μm/ns into the sphere, and the gold–carbon interface formed by 2 ns at the sphere edge remained stationary. The deformation of the sphere was driven by the incident radiation and not by mechanical pressures applied by gold plasma. The blunting of the sphere was likely due to the geometric reduction of flux near the sphere's poles. Higher x-ray flux near the sphere's equator caused high compression and a faster shock, which flattened the sphere. We will discuss the results and implications of our observations.
IR line intensity of planetary nebula NGC 7027, noting presence of measurable continuum flux of stellar radiation
In this contribution, we review our efforts toward understanding the typical mass-scale of primordial stars. Our direct numerical simulations show that, in both of Population III.1 and III.2 cases, strong UV stellar radiative feedback terminatesmass accretion onto a protostar.AnHII region formed around the protostar very dynamically expands throughout the gas accreting envelope, which cuts off the gas supply to a circumstellar disk. The disk is exposed to the stellar UV radiation and loses its mass by photoevaporation. The derived final masses are 43 Stellar Mass and 17 Stellar Mass in our fiducial Population III.1 and III.2 cases. Much more massive stars should form in other exceptional conditions. In atomic-cooling halos where H2 molecules are dissociated, for instance, a protostar grows via very rapid mass accretion with the rates M* approx. 0.1 - 1 Stellar Mass/yr. Our newstellar evolution calculations show that the protostar significantly inflates and never contracts to reach the ZAMS stage in this case. Such the "supergiant protostars" have very low UV luminosity, which results in weak radiative feedback against the accretion flow. In the early universe, supermassive stars formed through this process might provide massive seeds of supermassive black holes.
Aerobee rocket experiment for detecting X-ray sources in Cygnus constellation - stellar radiation
The ionization structure of hydrogen in a cloud-containing low-density gas surrounding an O star is calculated, emphasizing how UV photons cause the ionization of hydrogen in regions which are totally obscured from the star by neutral clouds. Particular consideration is given to the ionization of such obscured regions by diffuse Lyman continuum radiation produced when H(+) recombines directly to the ground state. The assumed physical structure of the cloud-containing neighborhood of an O star is discussed, a method is outlined for expressing the emission and absorption properties of the neutral clouds and their shadows in terms of effective volume emissivities and absorption coefficients on a line of sight, and equations of radiative transfer are derived for diffuse and stellar radiation in a cloud-containing H II region. Reradiation of Lyman continuum photons from the ionized boundary layer of a neutral cloud or shadow is analyzed. The expected emission measure across a large cloud-containing H II region is determined and found to compare well with that obtained from observations of H-alpha emission around runaway O stars. It is shown that the hydrogen in cloud shadows may be completely ionized by diffuse radiation within approximately half the Stroemgren radius, depending on the extent of that radius, the average frequency of the Lyman continuum radiation from the star, and the average cloud size.
Objectives of orbiting astronomical observatory satellites - continuous ultraviolet & infrared measurement of celestial radiation, stellar map
Stellar atmosphere radiation field quantity vs quality, deriving electron temperature as function of tau
Some stars, in particular, T Tauri stars, have substantial IR excesses at 10 microns. It is now understood that the long wavelength radiation comes from a shell of dust which surrounds the star and absorbs the stellar radiation. Part of the mass which is lost from supergiants is condensed into solid particles which remain in the stellar environment and provide the excess IR radiation. The most intense far-infrared object outside the solar system is the galactic center. Diffuse galactic IR objects include extended regions of gas and dust surrounding very hot young stars and regions of gas and dust surrounding cooler stars. Other subjects considered include IR galaxies and cosmic radiation.
Observations of the (O III) 52 and 88 micron lines and the (N III) 57 micron line have been made at 6 positions and the (Ne III) 36 micron line at 4 positions in the Orion Nebula to probe its ionization structure. The measurements, made with a -40" diameter beam, were spaced every 45" in a line south from and including the Trapezium. The wavelength of the (Ne III) line was measured to be 36.013 + or - 0.004 micron. Electron densities and abundance ratios of N(++)/O(++) have been calculated and compared to other radio and optical observations. Detailed one component and two component (bar plus halo) spherical models were calculated for exciting stars with effective temperatures of 37 to 40,000K and log g = 4.0 and 4.5. Both the new infrared observations and the visible line measurements of oxygen and nitrogen require T sub eff approx less than 37,000K. However, the double ionized neon requires a model with T sub eff more than or equal to 39,000K, which is more consistent with that inferred from the radio flux or spectral type. These differences in T sub eff are not due to effects of dust on the stellar radiation field, but are probably due to inaccuracies in the assumed stellar spectrum. The observed N(++)/O(++) ratio is almost twice the N(+)/O(+) ratio. The best fit models give N/H = 8.4 x 10 to the -5 power, O/H = 4.0 x 10 to the -4 power, and Ne/H = 1.3 x 10 to the -4 power. Thus neon and nitrogen are approximately solar, but oxygen is half solar in abundance. From the infrared O(++) lines it is concluded that the ionization bar results from an increase in column depth rather than from a local density enhancement.
Observations of the forbidden O III 52 and 88 microns lines and the forbidden N III 57 microns line have been made at six positions and the forbidden Ne III 36 microns line at four positions in the Orion Nebula to probe its ionization structure. The wavelength of the forbidden Ne III line was measured to be 36.009-36.017 microns. Electron densities and abundance ratios of N(++)/O(++) have been calculated and compared to other radio and optical observations. Detailed one-component and two-component (bar plus halo) spherical models were calculated for exciting stars with effective temperatures of 37,000-40,000 K and log g = 4.0 and 4.5. Both the new IR observations and the visible line measurements of oxygen and nitrogen require Teff of no more than 37,000 K. However, the doubly ionized neon requires a model with Teff of at least 39,000 K, which is more consistent with that inferred from the radio flux or spectral type. These differences in Teff are not due to effects of dust on the stellar radiation field but are probably due to inaccuracies in the assumed stellar spectrum. Neon and nitrogen are approximately solar, but oxygen is half-solar in abundance. From the IR O(++) lines, it is concluded that the ionization bar results from an increase in column depth rather than from a local density enhancement.
M-dwarf stars are prime targets for exoplanet searches because of their close proximity and favorable properties for both planet detection and characterization. However, the potential habitability and atmospheric characterization of these exoplanetary systems depends critically on the history of high-energy stellar radiation from X-rays to NUV, which drive atmospheric mass loss and photochemistry in the planetary atmospheres. With the Far Ultraviolet M-dwarf Evolution Survey, we have assessed the evolution of the FUV radiation, specifically eight prominent emission lines, including Lyα, of M-dwarf stars with stellar rotation period and age. We demonstrate tight power-law correlations between the spectroscopic FUV features, and measure the intrinsic scatter of the quiescent FUV emissions. The luminosity evolution with rotation of these spectroscopic features is well-described by a broken power law, saturated for fast rotators, and decays with increasing Rossby number, with a typical power-law slope of −2, although likely shallower for Lyα. Our regression fits enable FUV emission-line luminosity estimates relative to bolometric from known rotation periods to within ∼0.3 dex, across eight distinct UV emission lines, with possible trends in the fit parameters as a function of source layer in the stellar atmosphere. Our detailed analysis of the UV luminosity evolution with age further shows that habitable-zone planets orbiting lower-mass stars experience much greater high-energy radiative exposure relative the same planets orbiting more massive hosts. Around early- to mid-M dwarfs, these exoplanets, at field ages, accumulate up to 10–20× more EUV energy, relative to modern Earth. Moreover, the bulk of this UV exposure likely takes place within the first Gyr of the stellar lifetime.
Continuous optical conversion to IR and directional stellar radiation flow conversion to diffused radiation fields in circumstellar dust envelopes
An objective grating spectrometer covering the wavelength range of 500 to 1700 A with a 10-A resolution is employed for the Voyager ultraviolet spectrometer experiment. In determining the composition and structure of the atmospheres of Saturn, Jupiter and several satellites, the ultraviolet spectrometer will rely on airglow mode observations to measure radiation from the atmospheres due to resonant scattering of solar flux, and the occultation mode for assessments of the atmospheric extinction of solar or stellar radiation as the spacecraft enters shadow zones. Since it is capable of prolonged stellar observations in the 500 to 1000 A wavelength range, the spectrometer is expected to make important contributions to exploratory studies of UV sources.
The radio and IR observations of the H II region G333.6-0.2 are matched with a detailed spherical model with a density distribution which has a uniform-density core of radius 0.05 pc, a power-law intermediate zone, and a uniform-density halo. A stellar radiation field is required that is somewhat different from those predicted by available model atmospheres. Of the stellar models of Kurucz, the Teff = 34,000 K and log g = 3.5 model best fits the observed ratio of helium to hydrogen recombination lines. A good fit to all the observations in obtained with an S(2+) ionizing flux which is a factor of 20 times less than predicted by the Kurucz atmosphere. Current model atmospheres may not be appropriate because a single stable star with Teff = 34,000 K fails by at least an order of magnitude to produce the ionizing luminosity. The small radius of the constant-density core implies a short dynamical lifetime of approximately 5000 years for this spherical model; this may indicate that a nonspherical blister geometry is more appropriate for this H II region.