# Tag Info

7

Eric Jensen has already provided a nice link to a description of the basic structure of the ${\rm CO}_{2}$ spectrum, so I'll focus on the question of why there's a "spike" at 15.0 microns in the Earth spectrum, but not in the Venus or Mars spectra. If you look at the link in Eric's answer, the very first image shows a high-resolution version of the ...

5

This is caused by the internal structure of the CO2 molecule. When a molecule absorbs light, the energy of the photon goes into changing the internal energy of the molecule. Many bands that are strongly absorbing (especially at infrared and radio wavelengths) are related to changes in both the rotational and vibrational energy of the molecule. In this ...

4

Short version: velocity resolution is the smallest velocity difference you can measure between two moving objects, using a given spectrum. More details: As you probably know (based on your implicit use of the formula in your question), we can measure velocities by using the Doppler shift. To do that, we need to measure a feature (an absorption or emission ...

6

Collisional broadening - which includes van der Waals and Stark broadening - is more important in the higher gravity, higher pressure/density atmospheres of dwarf stars (a factor of 100-1000 higher for dwarfs vs giants of the same photospheric temperature). These collisional effects effectively "truncate" radiative emission and absorption processes,...

3

You seem to have all the ingredients apart from the variables of what size your detector pixels are (either physically or binned in software/hardware) and the angular extent of the object you are taking a spectrum of. The basic trade-off, as you say, is between flux and spectral resolution, but there are limits to that trade off. You should not reduce your ...

2

Imagine your line as a rectangle of width $w$ and depth $d$ relative to a normalised continuum. Without scattered light, the area blocked off by the line is $wd$ and if the continuum level is normalised to 1, then the equivalent width is $wd$. Now add 5% scattered light. The height of the continuum is 1.05 (but we're going to renormalise it) and the depth ...

-3

The act of fusion transfers part of atom into energy and the part left over is fused together with Hydrogen to make heavier and heavier elements. Heavier elements create more pressure in the middle of the star which creates more and more heavier elements fusing the many nuclei together. Once the sun starts making Iron(Fe), it dies and collapses which ...

28

The Sun is currently turning hydrogen into helium. There are no other nuclear reactions taking place at any significant rate in the Sun. The Sun will not start to make heavier elements until it reaches the tip of the red giant branch in about 7 billion years time. The elements heavier than helium that are present in the Sun were almost all made inside other ...

2

Pretty sure from my stellar nucleosynthesis days that the p-p I chain is the dominant form of nucleosynthesis in the sun, but the p-p II, p-p III, and p-p IV chains also occur, just to a much lesser extent. Those will make Be, B, Li. But, Na and Fe - and other heavier elements - mostly come from the sun not being a first-generation star: Previous supernovae ...

3

'Absorption' lines are caused by resonance scattering (scattering the radiation out of the line of sight, see illustration below), and resonance scattering has a very large cross section of roughly $10^{-12} cm^2$. This means that even for a thin layer of 10km ($10^6 cm$) you need only a density of >$10^6 /cm^3$ of an element for the layer to become ...

3

The strength of an absorption feature in the stellar spectrum is dependent on the amount of that element that is in the photosphere but it also depends on the atomic structure of the element and the conditions of temperature and density in the photosphere. For example the CaII lines need there to be singly ionised calcium ions in the photosphere. This ...

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