# Tag Info

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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 ...

12

The photosphere of the sun does produce an emission spectrum (a Planck spectrum according to its temperature of about 6000K). It is only that the atmosphere above the photosphere (the chromosphere) scatters light out of the line of sight at those frequencies where the scattering cross section is very high (i.e. at the atomic resonance frequencies of a given ...

8

Essentially what they did was assume that normally when observing with their telescope the spectral absorptions they see are due to the Earth's atmosphere. Which is a pretty good assumption. They then normalize the data to those absorption, so if there was any phosphine gas within the package of atmosphere they are looking through, it will be taken into ...

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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 ...

7

The hotter layers above the solar photosphere do have an emission spectrum. The emission spectrum is much fainter than the visible photosphere and so is not easily seen through broadband filters in the optical spectrum, though it can be observed through very narrow filters centred on the emission lines (e.g. H$\alpha$ from the chromosphere) in question. The ...

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,...

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There is the NIST Atomic Spectra Database where you could browse by elements. This the reverse approach, meaning that you have to first query element by element and then see which of the lines you find in the spectrum - that's how we used to do it in our labs during studies: Then, there is another NIST site where you can enter up to 4 spectral lines in ...

5

The science that studies the problem you described, is called "spectroscopy". Every element absorbs some of the wavelengths. Same is with molecules. The spectrum is like the footprint of the molecule. When you observe the light from emitted from some object, you see the continuous spectrum, emited from the light sources (stars, etc.). But it has ...

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 ...

5

I have read that the reason why the sun produces an absorption spectrum is because the temperature drops as you go away from the center, such that as the various layers of the atmosphere of the sun absorb certain wavelengths, the re-emitted light will have a smaller intensity than the absorbed one, causing a dip in the spectrum (ie an absorption spectrum). ...

4

Surely the sun possesses calcium in its atmosphere, as well as in its bulk volume. This plot, based on the data published in Asplund et al.,(2009), shows what elements can be found in the solar atmosphere: And we can read off that the abundance [Ca]/[Si] = 0.1 for example. Elements in stellar atmospheres can occur both in absorption and emission in stellar ...

4

Here is another alternative/supplement to NIST. The VALD atomic line database, which is specifically for astrophysical applications. I believe this database does contain some molecular data too.

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 ...

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 ...

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 ...

3

The picture is a mocked-up fake and is not an actual picture of the solar spectrum. You can easily see this because the black "Fraunhofer lines" extend beyond the spectrum and H alpha should have an appreciable width. The table is massively incomplete. It list only a tiny fraction (the strongest) absorption lines in the solar spectrum. There are ...

3

I'm not a spectroscopist, but, I know a fair bit about spacecraft data reduction. CRISM is a spectrometer that's very sensitive, but it needs more light than it can get by just riding along with the spacecraft, so it slews in the reverse direction of motion (that's why CRISM images have that hourglass shape). Despite that, it STILL has some light issues ...

3

This figure is from the paper "Phosphine as a bio signature gas in exoplanet atmospheres". It shows the absorption cross section of Phosphine compared to other molecules. We can see that Phosphine has a distinct enough profile from the others molecules in the 7.8-11.5 microns range, with the exception of NH3. Probing from 2-11.5 microns should ...

2

Visualizing a cross-dispersed echelle spectrum directly is a nice experiment to do (I do it with my upper-level astronomy students when I teach about this) but it's a little tricky because your intuition from other types of gratings can lead you astray in terms of how to arrange things for viewing. The key is to realize that the blaze angle of an echelle ...

2

You are doing it incorrectly if you are trying to cross-disperse your Fig.2. You should be cross-dispersing your Fig.1. A "cross-dispersed" spectrum requires requires the dispersive elements to be at right angles. Your Fig.1 shows the dispersed spectrum from the echelle with overlapping orders. To separate the orders you view Fig.1 with the cross-...

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The answer turned out to be that I was pushing the models package too far with the data that I was giving it. More careful background subtraction and much more localised fitting helped greatly.

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Sure, but it is not straightforward. There's a lot of degeneracies involved, such as many molecules sharing similar absorption bands, the presence of clouds, scattering, absorption happening at many different pressure ranges, solving the chemical equilibirum equations of the species and the temperature-profile modifying the overall spectrum as well. There's ...

2

This is not exclusive to spectroscopy applied to astronomy but general. Matter can interact with electromagnetic waves spanning a very wide range of frequency (energy). Also matter can emit electromagnetic radiation when in a kind of excited state. Due to the internal mechanism of absorption/emission it happens that the spectral characteristics can be ...

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On the sky at night programme on bbc 4 yesterday, the scientists explained how they were able to detect different levels of phosphine at the equator vs the poles of Venus. For me this indicates that the gas isn’t being detected locally

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A source cannot coherently vary on timescales shorter than the source size divided by the speed of light. That is because there is no way that different points on the source could "communicate" with each other and arrange for a coordinated increase or decrease in brightness. Therefore the shortest timescale of variability gives an upper limit to ...

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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 ...

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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 ...

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The three common techniques used for aquiring the spectra of exoplanets and their atmosphereseres are: Transmission: The brightness of a star decreases as the subject planet moves in front of it. If the planet has an atmosphere, it absorbs the suns emitted light. By measuring the brightness decrease at different wavelengths, the wavelength dependent ...

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