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The Ca triplet in the near infrared are extremely strong resonance absorption lines. They are by far the strongest features in the near infrared spectra of cool G,K,M type dwarfs and giants, which will be the majority of the stars observed by the Gaia RVS. The Ca triplet lines are so strong that even in low metallicity halo stars, that have little Ca in ...


8

The gap appears because of pair instability supernovae. In short, as one looks at such massive stellar cores at increasing temperatures, an ever-larger fraction of the photons are sufficiently energetic to spontaneously form electron-positron pairs. True, they soon recombine, but there is nevertheless a loss in (radiation) pressure, which causes contraction, ...


7

The ESA states it pretty clearly (although their figure of 855.2 nm is incorrect; it should be 866.2 nm): The RVS wavelength range, 847-874 nm, has been selected to coincide with the energy-distribution peaks of G- and K-type stars which are the most abundant RVS targets. For these late-type stars, the RVS wavelength interval displays, besides numerous ...


7

It isn't true that elliptical (or early-type) galaxies are metal-poor. This sounds like a pop-sci myth being propagated. The first line of the abstract of Pipino & Matteucci (2006) states that "Elliptical galaxies probably host the most metal rich stellar populations in the Universe". Thus your suspicion of the idea that "ellipticals are metal-poor" is ...


6

The amount of metals locked up in planets is completely negligible compared to that of the interstellar medium (ISM). First, in a typical stellar system, the mass fraction of planets is less than 1%, and of this by far the most mass will be in gaseous planets, rather than rocky planets. For instance, in the Solar System, the mass fraction of all planets is ...


6

Context Iron has the highest nuclear binding energy of all the elements (not completely true, but sufficiently accurate in an astronomical context). So, fusion of light elements into iron or something lighter is an exothermic process - you gain energy doing it, allowing the star to function. This is what happens in the last stages of a type II supernova. ...


6

According to Cropper and Katz 2011 part 2.2, the RVS working group considered other bands, but the ~850 nm band is relatively unaffected by absorption in the Earth's atmosphere, facilitating ground-based preparation and follow-up. In addition to the strong Ca II triplet, this band is rich in lines enabling study of astrophysical quantities other than radial ...


4

Lithium, along with Hydrogen and Helium, was one of the 3 elements created in the Big Bang. Thus, it should exist to some part in any star that hasn't burnt all of it out, and as mentioned, it's not an easy thing to do. Population III stars are expected to contain Lithium, and Beryllium as well. The amount, however, is not particularly high.


4

The journal paper is Thorsbro et al. (2018). The facts are somewhat mundane. The atmospheres of cool M-giants are not well understood in detail. The infrared lines of neutral Scandium that had previously been used to claim massive overabundances in stars near the Galactic centre are problematic. The paper by Thorsbro et al. shows that the same "anomalies" ...


3

Finding the best-fitting isochrone, a.k.a. isochrone fitting, is a standard approach to determine the age of globular clusters. This problem can be solved with a least-square method, where the data to be fitted are the points on the color-magnitude diagram and the fitting curve is the isochrone. Since there are many ways to apply this method, I will first ...


2

Electron capture supernovae occur in a narrow regime where electron captures on to products such as Mg and Ne are happening at a rate that removes support of the core against collapse "faster" (or more efficiently than) the white dwarf will be able to explode via thermonuclear runaway as the white dwarf approaches the Chandrasekhar mass limit. Several ...


2

Your intuition is largely correct: the key is that the proto-bulge region had a deep enough potential well so that the supernovas couldn't expel the remaining gas, and so new stars could form out of the gas (enriched by the supernova ejecta) in a continuing cycle. In the low-mass, isolated protogalactic clouds which probably contributed to the halo, the ...


2

Forbidden lines like these arise in thin gases, where collisional de-excitation is unlikely. Forbidden lines become "quenched" by collisional de-excitation when the densities reach levels that depend on the detailed quantum physics of each transition (i.e. different for every line/transition). If you study the ratio of a pair of lines at densities well ...


2

I think the misunderstanding (which I've been asked about before) is because Population II stars are redder as a population, even though for a given mass, a main-sequence Pop II (i.e. metal-poor) star would be bluer. That is, if you compare representative samples of Pop I and Pop II stars, the Pop II stars will on average be redder. This because Pop II ...


1

Elliptical galaxies have no regions of high density, so they are not forming stars any more. So all the stars in an elliptical galaxy are old stars, and as you say, tend to have low metallicity (actually, as pointed out, that doesn't seem to be true-- they have higher metallicity, presumably from old star formation no longer occurring). You are right that ...


1

Metallicity and abundance Metallicity Without specifying a given metal, the term "metallicity" — abbreviated $Z$ — usually refers to the total metallicity of all elements, i.e. the mass fraction of all metals to the total mass of some ensemble of elements, e.g. a star, a cloud of gas, a galaxy, etc. (as usual, the term "metal" refers to all elements that ...


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