Questions tagged [spectra]

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

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147 views

What (actually) does “peculiar periodic spectral modulations” refer to in this preprint?

I saw this ArXiv preprint after reading about it in the popular media. I can not even understand the beginning of the introduction (much less the whole paper): INTRODUCTION A Fourier ...
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2answers
241 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 ...
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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 ...
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152 views

Extraction of error spectrum in Sloan Digital Sky Survey

I need to know does SDSS spectrum contains error spectrum as well? http://www.sdss.org/dr12/spectro/spectro_basics/#AbouttheSpectra The above link says, further HDU's contain error spectrum and than ...
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1answer
642 views

Converting ångström spectral dimension to galaxy speed (km/s)

I have a spectral cube (in FITS format) whose spectral dimension is in ångströms. The sampling along the spectral dimension is 0.28A (CDELT=0.28). The observation in the cube is Ha emission of a ...
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129 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 ...
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1answer
126 views

In what manner is the spectrum of a black body really a continuum?

Usually they say the spectrum of a black body is a continuum and emits radiation at every frequency. Is it really a continuum like a line or are there (small) intervals? For example, can a body emit ...
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87 views

Reference for broader spectral lines?

I'm looking for some reference listing spectral lines outside the visible spectrum. (In particular, I'm looking for an element or compound that emits strongly in the 700-900nm range.)
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263 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 ...
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1answer
604 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 ...
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564 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 (...
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113 views

Why does spectral class and U-V colour correlate slightly differently for main sequence, giant and supergiant stars?

In this diagram the $x$-axis is spectral type for stars and the $y$-axis is B-V colour. Taking Series 1 as the Main Sequence, Series 2 as Giants and Series 3 as Super-giants. Why the spectral class ...
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641 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 ...
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164 views

Are hot stars like O-type stars entirely composed of helium?

Hot stars like O-type stars show no hydrogen in their spectra. Does this mean they are made entirely of helium? Any explanation would be really helpful.
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152 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 ...
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547 views

Definition question: continuum-subtracted spectrum

What is the exact definition of a "continuum-subtracted spectrum", such that one finds in SDSS spectra? http://classic.sdss.org/dr7/dm/flatFiles/spSpec.html#specmask Is there a definition somewhere?...
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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 ...
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555 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$_\alpha$? ...
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113 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 ...
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2answers
234 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?
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319 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 ...
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1answer
71 views

In Chromoscope, what is the X-ray source between Ophiuchus, Libra and Scorpius?

Chromoscope is a nice toy. Pressing 'L' shows the constellations as guide. There's a bright X-ray source between Ophiuchus, Libra and Scorpius. In Hydrogen-Alpha there are two circular formations to ...
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1answer
109 views

What is this graph showing?

This is from the NED What do these three titles mean? log fb (Jy) MRK 1014 Log v (HZ) Why is there LINE,LINE,...
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1answer
99 views

Invisible in visible light but visible in non-visible light?

This may be a stupid question, but I've been wondering this for a while and haven't yet found a solid answer. I'm worried the answer will be something along the lines of "of course not, you dummy" but ...
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1answer
134 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 (...
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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 ...
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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. ...
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736 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 ...