Questions tagged [spectra]

Questions about the observed frequency range of the electromagnetic radiation of a celestial object.

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20
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2answers
2k views

Why are wavelengths shorter than visible light neglected by new telescopes?

The diagram below, which I stole from this post by @HDE226868, shows that angular resolution as a function of wavelength suddenly drops by three orders of magnitudes from visible to UV-light. The ...
17
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2answers
881 views

Problem regarding the absorption lines of the sun

Some of the wavelengths of light that are emitted from the sun will be absorbed by atoms in the outer layer of the sun and also the atmosphere of the sun, and we see this as absorption lines in the ...
15
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1answer
851 views

What is the Lyman Alpha forest Used For?

The Lyman-alpha forest is an interesting feature found in the spectra of sufficiently distant objects. This series of absorption lines extends over a range of frequencies, and are a result of the ...
13
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3answers
1k views

How to detect emission lines in optical spectra?

Is there any handy module to detect emission lines in a spectrum like one we get from the Sloan Digital Sky Survey (SDSS)? You can see there are many emission lines like Ha,OI in the spectrum below. ...
11
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1answer
896 views

Recording Spectral Lines at Home

I was wondering if it would be possible to record the emission/absorption spectra of stars without expensive spectroscopy equipment. Would it be possible to somehow utilize diffraction grating? I own ...
9
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1answer
868 views

Why does the Sun deviate from a typical blackbody spectrum in the S band?

This is sort of a follow-up to this question, and my answer to it. The graph I see here details the radio (and other frequencies) emission of the sun. What's most notable and interesting to me is the ...
9
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2answers
456 views

Typical wavelength of solar flare

I read that solar flares are customarily viewed in H-alpha light, as a temporary brightening of a small portion of chromosphere. What all can be interpreted from this? Is it because, energy of the ...
8
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2answers
731 views

How exactly will DESI simultaneously capture individual spectra from 5,000 galaxies using optical fibers?

The BBC News article Telescope tracks 35 million galaxies in Dark Energy hunt says: The aim of the five-year programme is to shed light on Dark Energy - the mysterious force thought to drive an ...
7
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1answer
549 views

Why does higher surface gravity broaden spectral lines?

It's always made intuitive sense to me that a higher surface gravity leads to broader spectral lines from a star, but yesterday I realized that I don't have a physical explanation for why this is so. ...
6
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1answer
421 views

Where can I find a database of galactic spectra?

I was wondering where spectra of galaxies at various redshifts are to be found. I'm looking for ones that can be used to find the recessional velocity of the galaxy and eventually the Hubble Constant. ...
6
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2answers
462 views

Temperature gradient in stars

It is a well known fact that in stars, there exists a temperature gradiënt. The observational reason is because we perceived spectral lines in the otherwise continuous spectrum of a star. If this ...
6
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1answer
210 views

How does the black hole at the center of M87 look like in the visible spectrum?

I learned here that the picture of the black hole we saw all over the news was a false color image, based on the radio spectrum emissions. How would the black hole at the center of M87 look like when ...
6
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1answer
1k views

Why are O III lines so prominent in the spectra of emission nebulae when the amount of oxygen relative to hydrogen is a million times smaller?

Looking at spectra of emission nebulae like the Lagoon Nebula, the $[\text{O III}]$ lines are prominent in intensity. However, the abundance of oxygen is minuscule compared to hydrogen. How then are ...
6
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1answer
784 views

How do you estimate the error on the height/width of a Gaussian?

I'm trying to fit Gaussians to several lines in a spectrum that I have. Some of them overlap with one another, causing the fitting program that I'm using to not be able to give reasonable estimates ...
5
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2answers
268 views

Which measurements have shown that 2014 MU69 is red? (New Horizons' next target)

The recent NASA feature article New Horizons: Possible Clouds on Pluto, Next Target is Reddish MU69 is actually the smallest KBO to have its color measured – and scientists have used that data to ...
5
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1answer
353 views

Why is the flux density and amplitude different for galaxies than stars?

This might be a simple question, but I'm having a hard time answering it myself - or at least answer it correctly, I think. I'm sitting with different spectrals; many for stars and one for a galaxy. ...
5
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1answer
85 views

Is there evidence of super-heavy elements in the x-ray and gamma-ray spectrums of neutron stars?

It occurs to me, that between the surface and interior of neutron stars, gravitational pressure might produce super-heavy elements and that signatures of such elements might be detectable in the star'...
5
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1answer
65 views

What is the physical interpretation of the derivative of the emitted and observed wavelength?

The flux F of an event at redshift $z$ is related to its luminosity L as $$F=\dfrac{L}{4\pi d_L^2}\,,$$ where $d_L\equiv d_L(z)$ is the luminosity distance between us (the observer) and the event (...
5
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1answer
146 views

Do narrow lines in the spectra of O- and B- type stars always indicate magnetic fields?

I was reading a paper on the differential emission measures of a set of hot O- and B- type stars. As the authors discuss in Section 3 (page 959), two stars, $\tau$ Sco and $\theta^1$ Ori C, have ...
4
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1answer
223 views

Identifying common galaxy spectral lines

How does one identify the common galaxy absorption lines (e.g. Na, Mg, K, etc.) and emission lines (H-alpha, O III, S II, etc.) by just looking at a galaxy spectrum (like the one below)? I need to ...
4
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2answers
573 views

Why don't we see purple stars

I know that we don't see green stars because in blackbody radiation star doesn't produce one spectrum. The stars that have peaks in the green spectrum produce other spectrum in nearly same amout. ...
4
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1answer
48 views

How to model and subtract nebular emission lines from stellar spectrum

I have optical stellar spectra from a star forming region with spatially varying nebular background. I want to subtract the nebular lines from the stellar spectra (which are varying in intensity from ...
4
votes
1answer
690 views

What is an “arc” spectrum ?

I sometimes hear about astronomers using an arc spectrum to calibrate observations. For example a "He-Ar arc spectrum". What is an "arc" in this context? I assume it's nothing got to do with angles (...
4
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2answers
278 views

Why isn't everything yellow(ish)?

I understand that - although appearing yellow - the sun is white. And that this is because the other light colours are scattered by the atmosphere. For example: Google image search for "The Sun from ...
4
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1answer
545 views

In galaxy optical spectra, why are Hbeta and Hdelta sometimes absorption lines?

I've heard that $\mathrm{H\beta}$ and $\mathrm{H\delta}$ lines in galaxy spectra might be either emission lines or absorption lines, is that correct? From Wikipedia, Balmer lines are usually emission ...
3
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3answers
143 views

Is there a far away probe that has recorded the light spectrum from Earth as if it were an exoplanet?

We analyze the light spectrum of stars and distant planets to know characteristics like: chemical composition, temperature, mass, etc. Starting from the same principle, a probe at the border of the ...
3
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2answers
182 views

How to disentangle a very distant star's relative velocity vs. redshift distance

We measure a star's relative velocity towards or away from us via its Doppler-shifted spectrum. This is also how we measure the distance of very distant stars: measuring the shifts in the spectrum ...
3
votes
2answers
923 views

How do we know which elements are in a galaxy spectra?

I know that each element has it's own distinct spectra (this is a good site that lists them: Periodic Table) but when looking at a spectra of a galaxy (or even a star) how do we match those elements ...
3
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2answers
2k views

How to measure distances to stars by means of spectroscopic parallaxes?

How to measure distances to stars by means of spectroscopic parallaxes on practice? What is the accuracy of measuring distances using this method compared with distances based on HIPPARCOS ...
3
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2answers
170 views

Broadband spectrum of Sun

Broadband spectrum is one which is inclusive of all the observed wavelength ranges. In the case of the BB spectra of our Sun, there is a sharp (non-differentiable) kink in the curve in the UV-range (...
3
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1answer
66 views

Nebula and its colors

A Nebula has bright awesome colors that include red, blue, green, orange, white, etc? They're result of excitation of electrons. Is there a clear explanation as to which color is attributed to an ...
3
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1answer
35 views

What does the “a” at the end of a spectral type mean?

Looking at the chart for spectral type peculiarities (here), I noticed that the letter a was missing from the chart. This seems to be an error, as the star Vega has spectral type A0Va, with the a ...
3
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2answers
144 views

How does a cross dispersed spectrum look like in a reality (from echelle spectrographs)?

I am an analytical chemist with some interest in amateur spectroscopy. Since astronomers use echelle spectrographs to study the high resolution spectrum of the stars, someone suggested to post the ...
3
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1answer
467 views

Why the forbidden lines of [OIII],[NII] and [SII],[OII] are sensitive to electron temperature and electron density, respectively?

I am trying to understand the topic of "Metallicity estimates", either HII regions or planetary nebula. For this latter, the electron temperature (and density) must be known. I am studying the ...
3
votes
1answer
2k views

How deep is the “A” Fraunhofer line in the solar spectrum? Is it from the Sun's or Earth's atmosphere?

Question: Where can I see - or even download - a fairly high resolution (~0.1 nm) solar spectrum at zero air mass - in other words from space without absorption and other features from the Earth's ...
3
votes
1answer
171 views

How long do hot X-ray sources last?

Some X-ray sources in nebulae are caused by hot materials in the millions of degrees that formed in supernovae. What's the cooling rate of this stuff? How long does it stay this hot? If we would take ...
3
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0answers
41 views

What can Jupiter's spectrograph tell us other than its rotational velocity?

I have data of a Jupiter's image and the spectra of each pixel in the image, and I am playing around to see what I can do with it. I have managed to find Jupiter's rotational velocity by finding the ...
3
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0answers
155 views

Strong orange line in wood fire spectrum?

I just built a DIY spectroscope using a CD and after making some tests, I noticed a really strong emission line located in the orange-yellowish zone of the fire spectrum (specifically, burning wood). ...
3
votes
1answer
635 views

How to correct observed flux densities for redshift

Say I have a spectrum of a galaxy at a redshift $z$, in flux density units of erg/s/cm^2/Angstrom. I'd like to recover the spectrum (in the same flux density units) at z=0, i.e. at its rest ...
3
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0answers
120 views

Spectral analysis of AGN (velocity dispersion of galaxy absorption, doppler shifts)

I was wondering what parameters I need to know/measure to calculate the velocity dispersion of a galaxy, specifically an AGN. Also, I have spectra where there are blueshifted and redshifted ...
2
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2answers
360 views

Can you identify a star's 'signature' from its spectroscopy?

I overheard a discussion between friends: If your spaceship was transported to a random location in our galaxy, you could identify nearby stars by their signature, and then triangulate your ...
2
votes
2answers
531 views

How do I understand a brown dwarf with a M-type spectrum?

There are a large fraction of M dwarfs which are claimed to be brown dwarfs. Why do we still use M-type and not create a new stellar type like L, T and Y? The main signature of M is TiO absorption ...
2
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2answers
188 views

Using emission lines to determine redshift of a quasar

I am attempting this past paper question and am not sure how to tackle this, this is not homework! :) The spectrum of a distant quasar shows two broad emission lines with observed wavelengths of ...
2
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1answer
795 views

How to differentiate elements that have same spectral lines in a star?

Suppose that iron and calcium have a spectral line with the same wavelength. How would you determine which element is present in the atmosphere of a star if you found this line in its spectrum?
2
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3answers
612 views

How to calculate the S/N of IFU or long-slit galaxy observations

I would like to calculate the Signal-to-Noise ratio (SNR) of long-slit or integral field unit (IFU) observations of H$\alpha$ emission. I can calculate the SNR or each individual spectrum, just fine. ...
2
votes
1answer
45 views

Radial velocity curves

When I measure RV in a program for more spectral lines, will it be equivalent? I mean I measure RVs of a line in blue spectral region, RVs of a line in red spectral region... Many thanks.
2
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1answer
72 views

How do elements with only one shell emit light? [closed]

Electrons move to higher energy levels and drop back (electron migration). When they drop levels, photons are emitted and the wavelength/frequency emitted is based on how many levels are dropped. My ...
2
votes
2answers
621 views

about H$_\alpha$ and H$_\beta$ lines in astronomical objects' spectra

Generally there may be some line ratio between the two lines. If H$\alpha$ is strong, it is quite possible we can see H$_\beta$ too. Is it possible we can see H$_\beta$, but can not see H$_\alpha$? ...
2
votes
1answer
75 views

What is “g-98” in plots of stellar spectra?

I was looking to find some example carbon star spectra and came across this page on the Harvard website which shows several plots of carbon star spectra. The horizontal axis is labelled as wavelength ...
2
votes
2answers
173 views

absorption line from the chromosphere

If I understand correctly, the H-alpha and Ca II K lines are absorption lines of the sun and allow to see the chromosphere. Following the Kirchhoff-Bunsen law, an absorption line is produced by a gas ...