ABSTRACT
The Milky Way's halo contains clouds of neutral hydrogen with high radial velocities which do not follow the general rotational motion of the Galaxy. Few distances to these high-velocity clouds are known, so even gross properties such as total mass are hard to determine. As a consequence, there is no generally accepted theory regarding their origin. One idea is that they result from gas that has cooled after being ejected from the Galaxy through fountain-like flows powered by supernovae; another is that they are composed of gas, poor in heavy elements, which is falling onto the disk of the Milky Way from intergalactic space. The presence of molecular hydrogen, whose formation generally requires the presence of dust (and therefore gas, enriched in heavy elements), could help to distinguish between these possibilities. Here we report the discovery of molecular hydrogen absorption in a high-velocity cloud along the line of sight to the Large Magellanic Cloud. We also derive for the same cloud an iron abundance which is half of the solar value. From these data, we conclude that gas in this cloud originated in the disk of the Milky Way.
Subject(s)
Astronomy , Hydrogen/analysis , Astronomical Phenomena , Extraterrestrial Environment , Gases , Spectrum AnalysisSubject(s)
Blood Pressure/physiology , Cardiac Pacing, Artificial , Coronary Artery Bypass , Heart Rate/physiology , Adult , Aged , Atrioventricular Node/physiology , Blood Pressure Determination , Electrocardiography, Ambulatory , Humans , Middle Aged , Signal Processing, Computer-Assisted , Systole/physiologySubject(s)
Anesthesia , Autonomic Nervous System/physiopathology , Coronary Artery Bypass , Coronary Disease/surgery , Heart Rate/physiology , Aged , Blood Pressure/physiology , Cardiac Pacing, Artificial , Coronary Disease/physiopathology , Electrocardiography , Heart Rate/drug effects , Humans , Middle Aged , Plethysmography , Postoperative Period , Respiration, Artificial , Signal Processing, Computer-Assisted , Systole/physiologyABSTRACT
We have performed theoretical determination and experimental calibrations of an objective grating designed for high resolution spectroscopy of astronomical faint sources in the EUV and far-UV wavelength ranges (500-1400 A). First through theoretical calculations we show the feasibility of the concept with an aspheric shape for the grating blank and determine its geometrical parameters. A grating of this large size has been manufactured and tested, associated with a photon counting detector, in a vacuum environment. Finally we demonstrate that a resolving power of 3 x 10(4), a total equivalent effective area of ~5-10 cm(2) can be achieved, together with a very low scattered light level (10(-4)-10(-5) of the peak value).
