Helium atmospheric abundance

An element may be abundant but the dominant stages of ionization in the atmosphere do not provide detectable lines. Helium stands as the quintessential example. In normal cool stars, helium is abundant (n(He)/n(H) 0.1) but no photospheric lines are seen. Helium is present in the atmosphere as neutral atoms. The He I leading resonance line is inaccessible at 304 A. Lines from excited states do occur at accessible wavelengths but these states are very thinly populated. First excited states are at about 21 eV above the ground state with a population 1O-X0 = 1O 210 of the total He abundance, where 0 = 5040/T. For the Sun, 6 1, and a Hei line strength is governed by not the abundance of 0.1 but an effective abundance of 10-22, which is a factor of 1010 less than required to provide a detectable photospheric line. 

To see whether the abundance of phases of similar stabilities is due to the influence of air on clathrate formation or not, the investigation of the systems has been undertaken in helium atmosphere. The results, obtained in helium and air atmosphere, are in agreement (Fig. 1). 

There appears to be a correlation between the mass of the planets and the mass and composition of their atmospheres. Generally, only those planets of high mass were able to retain much of their atmospheres. Nitrogen, hydrogen, and helium are probably abundant, though not yet detected, on the heavier planets. Table 25-V also reveals a considerable range in the surface temperatures of the planets. The higher temperatures on the terrestrial planets also contributed to the loss of their atmospheres. 

Helium is not plentiful on Earth and is only the sixth most abundant gas in the atmo-sph ere. It does not accumulate in the atmosphere because it is lighter than air. Some amount of helium continually escapes into space from the outer atmosphere of the Earth. 

Argon is a colorless, odorless, tasteless, chemically inert noble gas that makes up about 0.93% of the Earths atmosphere. It is the third most abundant gas in the atmosphere, meaning it is more common than carbon dioxide, helium, methane, and hydrogen. 

Why are elemental hydrogen and helium, the two most abundant elements in the universe, not present in significant amounts in the Earth s atmosphere ... 

We know today that hydrogen and helium are overwhelmingly the most abundant species in the atmospheres of the outer planets, but direct evidence for their presence was virtually absent prior to the work mentioned [145]. Supermolecular spectroscopy had to be discovered before such evidence could be understood and it comes as no surprise that soon after Welsh s discovery many other uses of collision-induced absorption were pointed out in various astrophysical studies. Supermolecular absorption and emission have become the spectroscopy of the neutral, dense regions, especially where non-polar gases prevail. 

Supermolecular absorption determines significant features of the atmospheres of the planets and their large moons, such as the vertical temperature profile and the high-altitude haze distribution, and offers opportunities for the determination of abundance ratios of helium and hydrogen, ortho- and para-H2, etc. [390, 396]. In certain spectral bands the spectra may sometimes be obtained by Earth-based observations. More commonly, the spectra will be obtained in space missions, such as IRIS of Voyager I and II future missions (Infrared Space Observatory) will doubtlessly enhance the available information significantly. 

It is remarkable that He-rich stars appear to have a higher rate of mass loss than stars with solar-type atmospheres with the same Teff and L-values The Wolf-Rayet stars have, on the average, Al-values that are 140 times larger than the values for corresponding 0 and B type stars (De Jager et al., 1987). This may be due to the fact that WR stars, with their large Helium abundance, are relatively closer to their Eddington limit than the most luminous 0-type stars. 

ASTROCHEMISTRY. Application of radioastronomy (microwave spectroscopy) to determination of the existence of chemical entities in the gas clouds of interstellar space and of elements and compounds in celestial bodies, including their atmospheres. Such data aie obtained from spectrographic study of the light from the sun and stars, from analysis of meteorites, and from actual samples from the moon. Hydrogen is by far the most abundant element in interstellar space, with helium a distant second. 

Helium, the second most abundant element in the universe after hydrogen, is rare on Earth because its atoms are so light that a large proportion of them reach high speeds and escape from the atmosphere. However, it is found as a component of natural gases trapped under rock formations (notably in Texas), where it has collected as a result of the emission of a particles by radioactive elements. An a particle is a helium nucleus (4He2+), and an atom of the element forms when the particle picks up two electrons from its surroundings. 

Tritium (tm = 12.3 y) is used to date relatively recent samples in a technique similar to carbon-14 dating. For example, tritium is used to determine the age of groundwater. The ratio of and 3H abundances in rain and snow is stable over time. However, once the water seeps into the ground, it cannot mix with the water in the atmosphere, and the tritium nuclei that decay are not replaced. To determine the age of groundwater, we can measure the concentrations of both tritium and its daughter nuclide, helium-3. The age of the groundwater can help determine properties such as the depth of its source. 

The chemical composition of the Universe is primarily estimated from models of the Big Bang (Delsemme, 1998, 19-42) and spectrographic analyses of nebulas and the atmospheres of stars (Krauskopf and Bird, 1995, 563-564). Currently, hydrogen and helium are the most abundant elements, representing 71% and 28%, respectively, of all known matter in the Universe (Delsemme, 1998, 22). Arsenic has been ranked as the 39th most common element in the Universe with an average concentration of 0.008 mg kg-1 (Matschullat, 2000, 299 Table 3.1). 

The first, second and third periods are short periods. There are two elements in the first period and eight elements in both the second and the third periods. The elements in the short periods constitute almost 97% of the earth s crust, oceans and atmosphere. Among these elements, helium (He) and neon (Ne) gases occur only in trace amounts in the atmosphere but argon (Ar) makes up about 1 % of the atmsophere. The other elements are abundant. 

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