Observations of stars with the Hopkins Ultraviolet Telescope

The Hopkins Ultraviolet Telescope (HUT) was flown aboard the space shuttle Columbia as part of the Astro-1 mission during December 1990. During the nine-day flight, HUT carried out 3 Å resolution spectrophotometry of a wide variety of astronomical objects, including a number of stellar targets, in the 912–1860 Å range of the far ultraviolet. A few nearby stars were observed in the 415–912 Å range of the extreme ultraviolet as well. For nearly all of these targets, the spectra obtained by HUT are the first ever obtained in the spectroscopically rich region between Lyman (1216 Å) and the Lyman limit (912 Å). Here, we present highlights of the results obtained by HUT in a variety of areas of stellar astronomy.     

Improved bolometric corrections for WR stars

Evolutionary models allow an assignment of both a mass and a luminosity to a Wolf-Rayet (WR) star in a cluster, and hence allow a determination of the Bolometric Correction (B.C.). The B.C.'s derived for WN stars range from –4.0 to –6.0 with the expected trend of larger values (in absolute values) for stars with higher excitation spectra. For WC stars, there is little evidence for a similar trend; most observations presented here are consistent with B.C.=–4.5, as found by Smith and Maeder (1989). The convergence of B.C. values derived from evolutionary and atmospheric models is extremely satisfactory, giving increased confidence in both methods.     

Cardiovascular effects of simulated zero-gravity in humans

Head-down and head-up [correction of heat-up] tilted bedrest (5 degrees) and head out water immersion (HOWI) for 6 hr were compared. Parameters: Cardiac output (rebreathing method), blood pressure (arm cuff), forearm blood flow (venous occlusion plethysmography), total peripheral (TPR), and forearm vascular (FVR) resistances, Hct, Hb, relative plasma volume (PV) changes, and plasma catecholamines (single-isotope assay). During HOWI there was as expected a decrement in TPR, FVR, Mean arterial pressure (MAP, from 100 to 80 mmHg), Hct, and PV, and--as a new finding--catecholamines, which were 30-50% lower compared with both +5 and -5 degrees bedrest. During head down tilt, MAP was elevated (to 100-110 mmHg) and catecholamines did not fall, while TPR and EVR slowly decreased over 6 hr. HOWI is a stronger stimulus than -5 degrees bedrest, probably because HOWI elevates central venous pressure more markedly emptying the peripheral veins, while bedrest permits a distension of veins, which induces an increase in sympathetic nervous activity.     

Italy's contribution, from a medical standpoint, to the space safety of payload scientists, and perspectives for the future

In Italy, the selection of the Italian payload scientists has been performed according to the Spacelab Program of ESA. Twenty-four subjects underwent a screening performed by the Health Service of Italian Air Force. They were requested to pass an exercise test on treadmill and another ten-minute test on centrifuge, subject to the effect of +3 Gz. The authors briefly describe the results of the test. Noteworthy is the determination of Central Flicker Fusion Frequency. This parameter makes it possible to assess the endurance level of the subject, much earlier than other techniques (e.g. EKG). The importance of an accurate preliminary screening is emphasized as well as of successive training periods. Future studies will be undertaken to compare evoked cortical potentials with behaviour parameters of space safety, with a view to setting up a subtle tool of evaluation for both future candidates and payload scientists.     

The variable X-ray spectrum of Cyg XR-1

The variability of the X-ray spectrum of the discrete source Cyg XR-1 (α = 19^h 56^m δ = +35°.1) is reviewed. The variations observed in the energy region accessible to balloon borne detectors (energies greater than 20 keV) can be explained by assuming them to be caused by the eclipsing properties of a binary system. It is suggested that the system is composed of a source of small angular extent having a spectrum similar to that of a black body at approximately 1.5 × 10⁸ K (kT= 12.5 keV) and a non X-radiating companion which eclipses it at intervals of 2.9850 days. The system would be surrounded by an X-radiating plasma whose photon flux between 1 and 100 keV can be approximated by a power law spectrum whose exponent is — 1.7.     

X-ray scattering by intergalactic dust

The imaging capabilities of the Exosat and Einstein satellites at soft X-ray wavelengths have begun to show that suitable Galactic X-ray sources have extended ( 10 arcmin) haloes due to scattering of soft X-rays by interstellar dust. A simple argument suggests that similar haloes, due to scattering by intergalactic dust, should exist around distant (z 1) quasars and detailed analysis confirms this conclusion. A search for such haloes around suitable X-ray quasars could provide valuable, model-independent, constraints on the amount and origin of intergalactic dust.     

Experiments with injection of powerful plasma jet into the ionosphere

This paper describes two rocket experiments “Aelita” with high power lithium plasma injection. The results of onboard magnetometer, massspectrometer, photometer, plasma, corpuscular and ground radar measurements are given. Dynamics and structure of plasma formation are discussed.     

Space robotics in the '90s

This article describes the use of robots to perform work in space. In particular, telerobotics, which uses human operators to control the movement and operation of the robots, are explored. The relationship between the human operator and the robot is very complex but these systems are being used to explore planetary surfaces and will also be used in the construction of the space station. Research being conducted at NASA facilities is described, providing a picture of the future of space robotics.     

Induced abnormality in Mir- and Earth grown Super Dwarf wheat.

Super-dwarf wheat grown on the Mir space station using the Svet "Greenhouse" exhibited morphological, metabolic and reproductive abnormalities compared with Earth-grown wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of 'Super-Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen gains, however, contained only one nuclei, while normal viable pollen is tri-nucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was the presence of a high level of atmospheric ethylene (1,200 ppb). Ground studies conducted by exposing 'Super-Dwarf' wheat to ethylene just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples.     

Comment on estimating the solar proton environment that may affect Mars missions.

Estimates of the energetic proton environment for a Mars mission are generally extrapolated from the solar proton observations at 1 AU. We find that solar particle events may be divided into two general classes. Events dominated by a near-sun injection of particles onto interplanetary magnetic field lines leading to the spacecraft position represent the "classical" solar particle event associated with solar activity. This class of event will scale in radial distance by the classical power law extrapolation. The extended-interplanetary-shock source generates a maximum flux as the shock passes the detection location. This class of event typically generates maximum fluence, but in this case, the flux and fluence will not scale in the classical manner with radial distance.