Questions tagged [spectra]
Questions about the observed frequency range of the electromagnetic radiation of a celestrial object.
76
questions
7
votes
2answers
654 views
+50
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 ...
2
votes
2answers
41 views
What does the opacity of a molecular transition mean?
In particular, what does it mean when a line (e.g, emission line in stellar wind) is optically thick or thin. I know what an optically think/thick medium is, but how does this concept compare to ...
4
votes
1answer
36 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 ...
2
votes
1answer
203 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
votes
1answer
122 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 ...
1
vote
0answers
27 views
Relation between oscillator strengths $\log{gf}$ and the Einstein $A$-coefficient, rotational quantum number,
I'm analyzing the spectra of M dwarfs. Some authors characterize the lines with the oscillator strengths $\log{gf}$ while others follow different paths with the Einstein $A$-coefficient. I would like ...
2
votes
1answer
33 views
Where can I find a good solar irradiance chart for the infrared?
I'm trying to understand the results of the ExoMars Trace Gas Orbiter vs the Mars Express in terms of their abilities to find methane on the surface of Mars. The solution that I'm coming to is that it ...
1
vote
1answer
46 views
Examples of absorption lines for main sequence stars
Where might I find a detailed table or figure containing the absorption lines and their corresponding wavelengths for each type of main sequence star?
I'm trying to get the chemical abundance of ...
5
votes
1answer
310 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. ...
2
votes
2answers
141 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 ...
11
votes
1answer
863 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 ...
3
votes
0answers
113 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).
...
1
vote
1answer
72 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 ...
1
vote
1answer
159 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?
1
vote
0answers
20 views
Polarization of an emission line
Say I have a flux density spectrum of a galaxy, as well as polarization spectra for the object in U, Q, and P. I want to find the polarization of some emission line in the spectrum. First, I can fit a ...
2
votes
3answers
109 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 ...
2
votes
0answers
109 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 ...
0
votes
0answers
59 views
Smoothing an SED with binning
I have an (observed) SED of a galaxy, and am attempting to match model SEDs to it. To do this I need to be able to see its shape better, which would involve some sort of smoothing of the spectrum. I ...
2
votes
0answers
31 views
Spectra from Temperature and Emission Measure [closed]
Having the solar flare fluxes on the two bands of GOES (0.05-0.4 nm and 0.1-0.8 nm) I need to calculate the flux between 0.05 and 0.2 nm.
3
votes
2answers
630 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 ...
1
vote
0answers
26 views
What could be observed with LOFAR in 230 MHz - 10.0 MHz wavelength?
Nuclear astrophysics greatly interests me and i was wondering if there is something that could be observed with the LOFAR project in this wavelength that would benefit the field?
Also some general ...
5
votes
1answer
82 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'...
1
vote
1answer
67 views
Was is the angle needed to see a glory (a rainbow-like effect) from space off the Earth? [closed]
What positions would the Earth, Sun and viewer need to be to see a glory (a rainbow-like effect) from space?
What position would they need to be in to reproduce this picture?
Source: Gizmodo (NASA ...
1
vote
0answers
135 views
Conversion factors for flux
I have a flux value in the infrared band of 8 mJy at a wavelength of 80 microns that I want to translate into X-ray conventional ...
0
votes
1answer
53 views
Spectra and star identification [duplicate]
Are stellar spectra unique enough that they could be used to identify particular stars? If so, has any attempt been made to use them for navigation or equipment alignment?
3
votes
1answer
279 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
2answers
178 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. ...
1
vote
1answer
48 views
Normalizing the supernova spectrum by photometry
I have a SN spectrum here (already reduced) that seems to have some artifacts. Professor tells me that I may have to normalize it using photometry.
As far as I understand, I just have to multiply it ...
5
votes
2answers
227 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 ...
1
vote
1answer
134 views
Why do we observe spectral lines of specific energy?
The basis of my confusion is that atomic orbitals, even when described accurately by quantum numbers, have definite energies, meaning they represent energy eigenstates of the wave function. They're ...
1
vote
0answers
126 views
Correctly scaling Power Spectrum and Correlation Function of Galaxies from Mock Catalogues
I'm currently writing a code to compute the two-point correlation function of a set of galaxies. As I work with a loooot of galaxies, it was suggested to me not to do it in real space, but to compute ...
5
votes
1answer
131 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 ...
2
votes
2answers
138 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 ...
-1
votes
1answer
123 views
Where can I find a database of elemental spectra? [closed]
I know that spectroscopy can be used to analyze the light of stars to determine the elements causing their emissions in the visible spectrum, but this requires knowing the emission spectra of the ...
2
votes
1answer
63 views
Spectrum of star
I constructed a telescope and fixed my mobile's camera to the eye lens. I then viewed the sky via the mobile and I captured this image.
This is the magnified version of it:
I'm not sure if this ...
2
votes
2answers
292 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 ...
4
votes
1answer
350 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 ...
2
votes
0answers
57 views
Who first used two lambdas to typeset the wavelengths of a spectra line doublet?
Also what is the accepted or most common way to typeset the wavelengths of a doublet? e.g. lambdalambda-3727,3729 with or without a hyphen? and without the Angstrom symbol?
1
vote
1answer
263 views
Are there clouds/clusters of gas in space that have red and blue color adjescent to one another?
In artistic renditions of space scenes, there were stunning depictions of gasses or galaxies with bold red and blue colors immediately adjacent to one another, in contact as water is with oil in a ...
2
votes
0answers
88 views
Source for Identification of Balmer Hydrogen Absorption Lines
I'm working on an assignment, where I have to classify stars using the raw data of the telescope. I'm now trying to calibrate the pixel to armstrong ratio, and for that I need to identify the ...
0
votes
1answer
290 views
How to shift AGN x-ray spectrum to rest frame from
I have limited information to shift a spectrum (in the x-ray 0.5-10 keV bandpass) at redshift z=2 to rest frame. I have a plot of normalized (photon) counts s$^{−1}$ keV$^{−1}$ by energy (keV), and so ...
11
votes
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. ...
5
votes
2answers
237 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 ...
7
votes
1answer
381 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. ...
1
vote
1answer
106 views
How did we differentiate lights from stars?
I got this question while watching the COSMOS TV series. I couldn't find the right answer in google.
I read about Stellar classification and it states that we can classify the stars based on their ...
1
vote
1answer
69 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 ...
0
votes
1answer
767 views
How to convert theoretical template spectrum from luminosity density to flux density units?
I'm working with galaxy spectral templates (e.g., Bruzual & Charlot 2003) which seem to always come with y-axis units of $L_{\odot}$/A and x-axis units of Angstroms. Thus the y-axis is a ...
2
votes
2answers
231 views
How to tell whether an optical spectrum is featureless or just with a low S/N?
A featureless spectrum and a spectrum low S/N are very similar.
Is there a way to tell the difference between them?
6
votes
1answer
812 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 ...
2
votes
1answer
111 views
wavelength-based IFU data cubes VS velocity-based IFU data cubes
I have 2 simulated IFU data cubes of the same observation, let's say A and B. The 3rd dimension of cube A is in wavelengths. In order to create cube B I just rebinned cube A in log-wavelengths and ...
