Hubble Space Telescope spectroscopy of massive hot stars in the Magellanic Clouds and M31

Using the Hubble Space Telescope (HST) and the Faint Object Spectrograph (FOS) high signal to noise spectrograms were obtained for 15 OB stars in the Magellanic Clouds^***, three of which are of spectral type O3. The data cover the spectral region from 1150 A – 2300 A with a resolution of /1 A. One O8.5 supergiant, OB78#231, in M31is also included in this work. These data are a substantial improvement on previous high resolution IUE observations in the Magellanic Clouds (Walborn et al. 1985 and references therein) because of the smaller aperture and the much better signal to noise ratio, while no high resolution UV spectra of O stars in M31 have been obtained before. In this paper we discuss various morphological aspects of the spectra, concerning metallicity and the stellar winds, compared to galactic analogues.     

Cosmological variability of fundamental physical constants

Gamow was one of the pioneers who studied the possible variability of fundamental physical constants. Some versions of modern Grand Unification theories do predict such variability. The paper is concerned with three of the constants: the fine-structure constant , the ratio of the proton massm _p to the electron massm _e, and the ratio of the neutron massm _n tom _e. It is shown on the basis of the quasar spectra analysis, that all the three constants revealed no statistically significant variation over the last 90% of the life time of the Universe. At the 2 significance level, the following upper bounds are obtained for the epoch corresponding to the cosmological redshiftsz2–3: /<1.5×10^–3, m _p/m _p<2×10^–3, and m/m<3×10^–4, where x is a possible deviation of a quantityx from its present value,m=m _p+m _n, and the nucleon masses are in units ofm _e. (According to new observational data which became known most recently, m _p/m _p<2×10^–4) In addition a possible anisotropy of the high-redshift fine splitting over the celestial sphere is checked. Within the relative statistical error 3 < 1% the values of turned out to be the same in various quadrants of the celestial sphere, which corresponds to their equality in causally disconnected areas. However, at the 2 level a tentative anisotropy of estimated / values is found in directions that approximately coincide with the direction of the relic microwave background anisotropy.The revealed constraints serve as criteria for selection of those theoretical models which predict variation of ,m _p orm _n with the cosmological time.     

Observed Densities in the Universe

Baryons observed in Ly absorbers contribute to the density parameter 0 by bar 0.06 in close agreement with the value of 0.06 from primordial nucleosynthesis (H0=55 km s-1 Mpc-1, = 0 assumed throughout). A number of methods are known to measure 0 from density fluctuations; bound structures tend to yield lower values (m 0.2-0.4), field galaxies over large scales higher, but still undercritical values (m 0.6 ± 0.2). The best compromise value is 0 0.5, but the present methods are blind to diffusely distributed, exotic matter which still could make 0 = 1. A satisfactory solution of 0 (and ) will only come from a fundamental cosmological test (e.g. the Hubble diagram of [evolution-corrected] supernovae type Ia) in combination with the CMB fluctuation spectrum.     

Non-BBN Constraints on the Key Cosmological Parameters

Since the baryon-to-photon ratio 10 is in some doubt at present, we ignore the constraints on 10 from big bang nucleosynthesis (BBN) and fit the three key cosmological parameters (h, M, 10) to four other observational constraints: Hubble parameter (ho), age of the universe (to), cluster gas (baryon) fraction (fo fGh3/2), and effective shape parameter (o). We consider open and flat CDM models and flat CDM models, testing goodness of fit and drawing confidence regions by the 2 method. CDM models with M = 1 (SCDM models) are accepted only because we allow a large error on ho, permitting h < 0.5. Open CDM models are accepted only for _M 0.4. CDM models give similar results. In all of these models, large 10 ( 6) is favored strongly over small 10 ( 2), supporting reports of low deuterium abundances on some QSO lines of sight, and suggesting that observational determinations of primordial 4He may be contaminated by systematic errors. Only if we drop the crucial o constraint are much lower values of M and 10 permitted.     

SWE,a comprehensive plasma instrument for the WIND spacecraft

The Solar Wind Experiment (SWE) on the WIND spacecraft is a comprehensive, integrated set of sensors which is designed to investigate outstanding problems in solar wind physics. It consists of two Faraday cup (FC) sensors; a vector electron and ion spectrometer (VEIS); a strahl sensor, which is especially configured to study the electron strahl close to the magnetic field direction; and an on-board calibration system. The energy/charge range of the Faraday cups is 150 V to 8 kV, and that of the VEIS is 7 V to 24.8 kV. The time resolution depends on the operational mode used, but can be of the order of a few seconds for 3-D measurements. Key parameters which broadly characterize the solar wind positive ion velocity distribution function will be made available rapidly from the GGS Central Data Handling Facility.     

Gamma-ray line production in astronomical objects

This review focuses on the conditions for -ray line production in the most interesting astronomical objects, in light of the planned experiments: Gamma-1, GRO, Sigma, GRASP, and others. Among these objects are the Sun, the galactic center region, molecular and dust clouds, accreting and exploding stars.     

Primordial Helium and ΔY/ΔZ from H II Regions and from Fine Structure in the Main Sequence Based on Hipparcos Parallaxes

The primordial helium abundance YP is important for cosmology and the ratio Y/Z of the changes relative to primordial abundances constrains models of stellar evolution. While the most accurate estimates of YP come from emission lines in extragalactic H II regions, they involve an extrapolation to zero metallicity which itself is closely tied up with the slope Y/Z. Recently certain systematic effects have come to light in this exercise which make it useful to have an independent estimate of Y/Z from fine structure in the main sequence of nearby stars. We derive such an estimate from Hipparcos data for stars with Z Z and find values between 2 and 3, which are consistent with stellar models, but still have a large uncertainty.     

Solar wind charge states measured by ULYSSES/SWICS in the south polar hole

The Ulysses mission now has an extensive data base covering several passes of the south polar coronal hole as the spacecraft proceeds to higher latitudes. Using composition measurements from the SWICS experiment on the Ulysses spacecraft, we have obtained charge state distributions, and hence inferred coronal ionization temperatures, for several solar wind species. In particular, we present an overview of Oxygen ionization temperature measurements, based on the O⁷⁺/O⁶⁺ ratio, for the period January 1993 until April 1994 (23°S to 61°S heliographic latitude), and detailed Oxygen, Silicon and Iron charge state distributions of the south polar hole during a two month period of nearly continuous hole coverage, Dec 1993–Jan 1994 (45°S to 52°S heliographic latitude).     

The Freja F3C Cold Plasma Analyzer

The F3C Cold Plasma Analyzer (CPA) instrument on theFreja spacecraft is designed to measure the energy per unit charge (E/Q) of ions oe electrons in the range 0<E/Q<200 V and complements the observations made by the F3H Hot Plasma Experiment. The CPA sensor, which is deployed on a boom, is an electrostatic analyzer which produces angle/energy images of particles incident on the sensor in a plane perpendicular to the boom axis. Charged particles incident normal to the CPA sensor housing axis of symmetry, which coincides with the boom axis, pass through collimators and enter a semi-spherical electrostatic analyzer which disperses particles in energy and azimuthal angle of arrival onto an imaging MCP detector thus producing images of the particle distributions in a plane perpendicular to the boom axis. Measurements are transmitted either as discrete 16×16 (angle/energy) images or as parameters related to the incident particle distribution function. Pixels in the discrete images are separated approximately equally in azimuthal angle while the 16 energy bins are separated approximately geometrically in energy. The ratio of the maximum to minimum energy imaged is programmable up to a maximum of more than a factor of ten, and the energy range itself is also under the control of the processor and can be varied by more than an order of magnitude. The density dynamic range of the sensor is increased by the introduction of an electrostatic gating system between the entrance aperture and the analyzer which can be used to duty-cycle low-energy electrons into the sensor thus keeping the count rate within appropriate levels. To reduce the effects of spacecraft induced perturbations on the lower-energy particle distributions, the sensor portion of the instrument is deployed on a 2 m long boom, perpendicular to the spacecraft spin axis. Spacecraft rotation is used to recover complete (4) angle/energy distributions every half spin period. In addition, the sensor skin may be biased with respect to the spacecraft ground to offset effects due to spacecraft charging. Current to the skin is monitored, making the exterior of the sensor equivalent to a large cylindrical Langmuir probe. Two separate processing paths for signals from the MCP anode may be chosen; slow and rast. The slow pulse processing path provides discrete angle/energy images at a nominal rate of 10 images per second and a peak burst mode rate of 100 images per second. The fast analog or current mode path provides crude parameterized estimates of densities, temperatures and drift velocities at nominal rates of up to 1000 parameters per second with a burst rate near 6000 parameters per second. Observations of cold ions and electrons in an unperturbed ionospheric plasma are presented which demonstrate the functionality of the instrument. Suprathermal ion observations in a transverse ion energization or acceleration region are also shown which demonstrate many of the small-scale features of these events.The Canadian Government's right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledge.     

Some results of ionospheric investigations by means of coherent radiowaves emitted by satellites

In this paper we discuss theoretical expressions, determining the difference of Doppler shifts of various coherent radiowave frequencies emitted by a radiator moving in the ionosphere or interplanetary medium. The rotating Doppler effect (Faraday effect) caused by the Doppler shifts ±H of the ordinary and extraordinary waves is also considered. In a three-dimensional inhomogeneous ionosphere, stationary in time (N/t = 0), is determined in the general case, by an equation with three variables. The equation for proper depends only on the local value of the electron concentration N _c around the radiator and on integral values, determining, by means of additional calculations, the angle of refraction or its components, the horizontal gradients of electron concentration N/x and N/y, and in some cases, the integral electron concentration ₀ ^zcN dz. We describe the analysis of the measurements, made with the satellites Cosmos I, II and partially XI, assuming that N/t = N/y = 0, with a two variables equation. The expected errors are considered. The results coincide well for different points (Moscow, The Crimea, Sverdlovsk) and thus agree with the measurements of _H and with height-frequency ionospheric characteristics. The curve giving electron concentration versus height N (z) in the outer ionosphere (above the maximum of F2), shows a new maximum higher than the main maximum of the ionosphere N _MF2 at 120–140 km. At this maximum the value of N (z) is (0.9–0.95) N _MF2. The new data on the large-scale horizontal inhomogeneities of the ionosphere, exceed the previous ones by about a factor 10. By means of the irregular variations of the spectrum W() of the inhomogenous formation is determined. Three unknown constant maxima with values 16 to 18 km, 28 to 32 km and 100 to 120 km are found. The spectrum W () mainly characterizes the local properties of the ionosphere along the orbit of the satellite.     

Concerning the interpretation of the ultraviolet radiation from B stars

Measurements of the shape of the ultraviolet spectrum from B stars are compared with the theoretical spectra predicted from a homogeneous series of eight model atmospheres which are known to be close to a state of radiative equilibrium and to give a good representation of the ordinarily observed spectral region. The broad-band photometer measurements of Byram, Chubb, and Friedman in the region 1314 indicate that the stars become brighter in the ultraviolet as their temperature increases. The theoretical spectra reproduce this trend. However, the theoretical spectra are about three times as bright at 1314 relative to their brightness at 5560 as is observed.The spectral observations at 50Å resolution of Stecher and Milligan of six absorption-line stars are compared in detail with theoretical spectra. The observed shape of the spectrum is reproduced well by the models from 2600 to longer wavelengths. At wavelengths shorter than 2600 Å, the observed fluxes from B stars are less than the predicted fluxes. At 2000 the deficiency is between a factor two and a factor four. The spectrum of Canis Majoris is observed to have a different shape from that found for four other early-type stars. In the case of Canis Majoris the deficiency at 2000 is about a factor 13.The proper manner in which to compare theory and observation is discussed and some astrophysical terminology is explained. Theoretical fluxes, , are given in Table 1 for eight early B type model atmospheres at wavelengths between the Lyman limit and 6251. These fluxes have been computed without consideration of the opacity due to line blanketing. It is shown that line blanketing can probably account for the differences noted between predicted and observed ultra-violet spectra of B stars. It is not necessary at present to invoke unusual sources of opacity in the stellar atmosphere or in the space between the star and the earth in order to explain the observations. Spectra of B stars in the 2000 region at sufficient resolution to show the line spectrum would clarify the problem.     

Optical identification of X-ray sources in the Einstein observatory medium and deep surveys

Methods are discussed for establishing the optical identification of X ray sources in the medium and deep X-ray surveys of the Einstein Observatory. Of the 63 X-ray sources with a statistical significance of 5 in the medium survey (Maccacaro et al. 1981), optical identification work is summarized for 51, of which identifications have been made with 30 active galactic nuclei. The optical properties of some of these X-ray selected objects are briefly discussed.The Einstein deep survey of Pavo (Griffiths et al. 1981) is used to illustrate the problems and methods used for securing optical identifications for X-ray sources in the deep survey fields. Identifications have been made with 4 QSOs at the bright end of the optical candidate distribution (together with 3 G stars) and it is shown that a further 7 fainter objects are also likely to be QSOs.     

The magnetogram inversion technique: Applications to the problem of magnetospheric substorms

The magnetogram inversion technique (MIT) is based upon recordings of geomagnetic variations at the worldwide network of ground-based magnetometers. MIT ensures a calculation of a global spatial distribution of the electric field, currents and Joule heating in the ionosphere. Variant MIT-2 provides, additionally, continuous monitoring of the following parameters: Poynting vector flux from the solar wind into the magnetosphere (); power, both dissipated and accumulated in the magnetosphere; magnetic flux in the open tail; and the magnetotail length (l _T) (distance between the dayside and nightside neutral points in the Dungey model). Using MIT-2 and data of direct measurements in the solar wind, an analysis is made of a number of substorms, and a new scenario of substorms is suggested. The scenario includes the convection model, the model with a neutral line and the model of magnetosphere-ionosphere coupling (outside the current sheet), i.e., the three known models. A brief review is given of these and some other substorms models. A new element in the scenario is the strong positive feedback in the primary generator circuit, which ensures growth of the ratio = / _Aby an order of magnitude or more during the substorms. Here _Ais the Pointing vector flux in the Akasofu-Perrault approximation, i.e., without the feedback taken into account. The growth of during the substorm is caused only by the feedback effect. It is assumed that the feedback arises due to an elongation of the magnetotail, i.e., a growth of l _Tby a factor of (23) during the substorm.In the active phase of substorm, a part (the first active phase) has been identified, where the principal role in the energetics is played by the feedback mechanism and the external energy source (although the internal source plus reconnection inside the plasma sheet make a marked contribution). In the second active phase (expansion) the external generator (solar wind) is switched off, and the main role is now played by the internal energy source (the tail magnetic field and ionospheric wind energy).Models of DP-2 DP-1 transitions are also considered, as well as the magnetospheric substorm-solar flare analogy.     

Temperature Fluctuations,H II Region Abundances,and Primordial Helium

There is evidence for temperature fluctuations in Planetary Nebulae and in some Galactic H II regions. If such fluctuations occur in the low metallicity, extragalactic H II regions used to probe the primordial helium abundance, the derived 4He mass fraction, YP, could be systematically different from the true primordial value. Although this effect could be large, there are no data which allow us to estimate the size of the temperature fluctuations for the extragalactic H II regions. Therefore, we have explored this effect via Monte Carlo simulations of the data in which the abundances derived from a fiducial data set are modified by T chosen from a distribution with 0 T Tmax where Tmax is varied from 500 K to 4000 K.     

A high-resolution Ge spectrometer for Gamma-Ray burst astronomy

The Transient Gamma-Ray Spectrometer (TGRS) to be flown aboard the WIND spacecraft is primarily designed to perform high resolution spectroscopy of transient -ray events, such as cosmic -ray bursts and solar flares over the energy range 25 keV to 8.2 MeV with an expected spectroscopic resolution of 3 keV at 1 MeV. The detector itself consists of a 215 cm³ high purityn-type Ge crystal kept at cryogenic temperatures by a passive radiative cooler. The geometric field of view defined by the cooler is 1.8 steradian. To avoid continuous triggers by soft solar events, a thin BeCu Sun-shield around the sides of the cooler has been provided. A passive Mo/Pb occulter, which modulates signals from within ±5° of the ecliptic plane at the spacecraft spin frequency, is used to identify and study solar flares, as well as emission from the galactic plane and center. Thus, in addition to transient event measurements, the instrument will allow the search for possible diffuse background lines and monitor the 511 keV positron annihilation radiation from the galactic center. In order to handle the typically large burst count rates, which can be in excess of 100 kHz, burst data are stored directly in an onboard 2.75 Mbit burst memory with an absolute timing accuracy of ±1.5 ms after ground processing. The memory is capable of storing the entire spectral data set of all but the largest bursts. WIND is scheduled to be launched on a Delta II launch vehicle from Cape Canaveral on November 1, 1994. After injection into a phasing orbit, the spacecraft will execute a double lunar swing-by before being moved into a controlled halo orbit about theL1 Lagrangian point (250R _e towards the Sun). This will provide a 5 light-second light travel time with which to triangulate gamma-ray burst sources with Earth-orbiting systems, such as those on-board the Gamma-Ray Observatory (GRO). The response of instrument to transient -ray events such as GRB's and solar flares will be presented as well as the expected response to steady state point sources and galactic center line emission.     

Gamma Rays From Molecular Clouds

High energy -rays from individual giant molecular clouds contain unique information about the hidden sites of acceleration of galactic cosmic rays, and provide a feasible method for study of propagation of cosmic rays in the galactic disk on scales 100 pc. I discuss the spectral features of ⁰-decay -radiation from clouds/targets located in proximity of relatively young proton accelerators, and speculate that such `accelerator+target systems in our Galaxy can be responsible for a subset of unidentified EGRET sources. Also, I argue that the recent observations of high energy -rays from the Orion complex contain evidence that the level of the `sea of galactic cosmic rays may differ significantly from the flux and the spectrum of local (directly detected) particles.     

Alfvenic fluctuations in the solar wind: A case study using Ulysses measurements

We present preliminary results of a study of solar wind Alfvénic fluctuations using magnetometer and plasma measurements from the spacecraft Ulysses. We focus on a particular case study, and use wave language to discuss the fluctuations. The observations are consistent with a mixture of convected structures and Alfvén wave trains. Furthermore, our results tend to suggest that the Alfvénic-fluctuations propagate in the radial direction.     

ULF waves: Conjugated ground-satellite relationships

We study the simultaneous occurrence of ULF waves observed on board GEOS and at two of its conjugated stations: Husafell (Iceland) and Skibotn (Norway). We try to deduce some properties of the regions in which these waves are generated. The few number of simultaneous observations of pearl events indicates that such structured oscillations can occur only in specific conditions which are not met generally at the geostationary altitude. We introduce a new method for measuring time delays between the satellite and the ground. We show that this time is much higher than it would be expected from a simple extrapolation of measurements done at lower latitudes on structured events.     

Nonlinear theory of the two-point correlation function

We consider the influence of the nonlinear stage of gravitational instability on the two-point correlation functions of gravitationally bound objects. Based on the theory of nonlinear gravitational contraction of a single density peak of dissipationless matter (Gurevich and Zybin, 1988a,b; 1990) we develop a method for calculating the two-point correlation functions of different objects of any mass. The method works good in the region of strong correlations and can be easily extended to calculate higher correlation functions. We show that the main contribution to the correlation function _i in the region of strong correlations _i 1 is made by pair systems located outside large clusters of objects. In this region the shape of _i is determined only by the nonlinear dynamics of gravitational contraction of dissipationless matter and has the form _i C ^–, where 1.8 is a universal parameter.     

High-resolution observations of Hα flare regions

This paper gives a review of the recent high-resolution H observations of solar flares and flare-productive active regions. From studies of the morphological and evolutional features of H flare emitting regions, two types of two-ribbon flares, which are termed separating two-ribbon flare and confined two-ribbon flare, are discussed. The former is characterized by conspicuous separating motions or expanding motions of the H two ribbons, whereas the latter shows only a short range of or no separating motions of the two ribbons. The explosive compact flares, which occur in some compact newly-emerging flux regions, are also discussed.Attention is paid to the successive and impulsive brightenings of H flare points which form the H flare kernels and the front lines of H two ribbons at the impulsive phases of flares. Temporal relationships between H line intensities or profiles and hard X-ray or microwave emissions are discussed to discriminate the energy transport mechanisms in the flare loops.H monochromatic image of high spatial resolution, at the present time, is the most sensitive detector for finding the first appearance of newly-emerging magnetic flux region and the developing features of sheared configuration of magnetic field, both of which are the key factors in flare energy build-up processes. It is suggested that the successive emergence of a twisted magnetic flux rope might be essential for the production of a major flare.Contributions from the Kwasan and Hida Observatories, Kyoto University, No. 292.