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Questions tagged [spectroscopy]

Questions about the measurement of light waves whereby the wavelength is classified by its position in the electromagnetic spectrum.

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Why do linear velocity redshifts correspond to linear pixel shifts when the spectra are binned in constant log wavelength?

In Tonry & Davis (1979), they describe spectroscopic redshift measurement via correlating with templates at known redshift. In Section IIIa, they say "Because the spectra are binned linearly with ...
Tim's user avatar
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6 votes
1 answer
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What is a pupil slicer, and how does it work with anamorphic optics in VLT's ESPRESSO Echelle spectrograph?

This excellent answer points to ESPRESSO, - Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations. From there I looked at the Instrument Description and Performance page. ...
uhoh's user avatar
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5 votes
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Why does titanium oxide around Betelgeuse produce this particular sawtooth-shaped absorption spectrum?

Betelgeuse Just Isn’t That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse suggests that the recent dimming might be caused by increased optical absorption by dust ...
uhoh's user avatar
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19 votes
2 answers
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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 ...
User3141's user avatar
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9 votes
3 answers
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Why does Gaia use only calcium NIR lines for stellar radial velocity measurements?

I was reading this overview article about the Gaia spacecraft and I saw the following statement: These spectra provide radial velocity information that are used to study the kinematic and dynamic ...
uhoh's user avatar
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7 votes
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Did the late 2019 "fainting" of Betelgeuse show any spectral trends that differ from it's normal variability?

update: (August 2020) With all the newest news about including what the Dr. Becky video discusses as linked in How do magnetic fields mess with astronomers' observations? I'll bet this question ...
uhoh's user avatar
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4 votes
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Why does X-shooter use double passes through prisms for Echelle cross-dispersion instead of gratings?

The catchy title Down-the-barrel observations of a multiphase quasar outflow at high redshift: VLT/X-shooter spectroscopy of the proximate molecular absorber at z=2.631 towards SDSS J001514+184212 ...
uhoh's user avatar
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How do I apply a velocity shift to a wavelength array with uniform logarithmic spacing?

Suppose I have a wavelength array for a spectrum in units of Angstroms. Suppose further that the wavelength has "uniform logarithmic spacing" such that if I just take the difference in Angstroms ...
quantumflash's user avatar
3 votes
1 answer
185 views

What is the dimensions of the smallest object detectable by an optical fiber from a specific distance?

Optical fibers are well-known to observe astronomical objects, say, galaxies, to generate massive spectroscopic surveys. The galaxies are often very far from the optical fibers of a telescope. However,...
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8 votes
2 answers
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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 ...
uhoh's user avatar
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What are the pros and cons of different types of echelle spectrograph cross-dispersers?

Echelle spectrographs, operating at high resolving power, typically consist of an echelle grating with a low numbers of lines/mm, used with high diffraction orders (often $n=$50-100). To separate the ...
ProfRob's user avatar
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4 votes
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Stellar electromagnetic signatures

By using only the electromagnetic signature of a star, could a star be distinguished with reliable accuracy from any other star? To elaborate a little, say we have a collection of about 200,000 stars. ...
BenjaminF's user avatar
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4 votes
1 answer
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How will microshutter arrays be used in the James Webb and future space telescopes?

Question: How will microshutter arrays be used in the James Webb and future space telescopes? Are they acting as a sort of moving pinhole or slit, or is the pattern more complicated, like a coded ...
uhoh's user avatar
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How does the ESPRESSO Echelle spectrograph fold the spectrum so nicely?

The CBC News Technology and Science Q&A This ESPRESSO machine doesn't make coffee but scans the skies for habitable planets includes a nice description of ESPRESSO (Echelle SPectrograph for Rocky ...
uhoh's user avatar
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3 votes
0 answers
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How were "microshutters" or other multiplexed or multi-object techniques first used in Astronomical spectroscopy?

This answer to How will microshutter arrays be used in the James Webb and future space telescopes? explains how multiple objects can be selected so that the throughput of a spectrometer can be ...
uhoh's user avatar
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3 votes
1 answer
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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 ...
Pranay's user avatar
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Are the dispersion directions of the prism and the grating in Hubble WFC3 UVIS G280 perpendicular? Can we call this a "grism"? With cross-disparsion?

Prologue From Into the UV: A precise transmission spectrum of HAT-P-41b using Hubble's WFC3/UVIS G280 grism: The UVIS grism, however, comes with several quirks that make it difficult to observe with ...
uhoh's user avatar
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2 votes
1 answer
413 views

How can I calculate the luminosity and mass of a star only knowing it's peak wavelength and it's subtended angle?

For example if a certain star subtends an angle of 32 arcminutes at the Earth’s orbit and it's light has a peak wavelength of 500 nm, how can I find the luminosity and mass of that star?
R-802's user avatar
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2 votes
1 answer
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Vacuum and air wavelengths in spectroscopy

In the SDSS page https://classic.sdss.org/dr7/products/spectra/vacwavelength.html, it is written Because the SDSS observes many quasars at rest-frame ultraviolet wavelengths, the data are stored in ...
Lekha's user avatar
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14 votes
2 answers
335 views

Strange bump in solar spectrum taken with home-made spectrograph

I am an astronomy teacher, and made some kind of spectrograph with a difraction grating, a 3D printed slit, water pipes and a reflex camera. With a group of students we got this picture of the solar ...
Luis López's user avatar
13 votes
2 answers
7k views

How does one determine the effective temperature of a star from its spectrum?

Determining effective temperature of a star is in general a non-trivial task. Simple reason for this is that we can only study the electromagnetic radiation from a star, but not the temperature ...
Alexey Bobrick's user avatar
8 votes
1 answer
512 views

Why is $H_\delta$ prominent in type A stars?

I understand factually that H$\delta$ lines are most prominent in type A stars and less so in more extreme types of stars on the H-R diagram. However I was wondering the reason for why they are not ...
QuantumPanda's user avatar
7 votes
1 answer
135 views

Is it conceivable that the presence of chlorophyll (or similar) could be distinguishable from other chemicals on an exoplanet?

If an Earth-like exoplanet had a sufficiently extensive plant biosphere (i.e large forests, aquatic algal mats etc), is it at all conceivable that scientists could spectroscopically detect the ...
user avatar
7 votes
1 answer
142 views

Have we detected spectra of exotic atoms in stars?

I was reading this wikipedia article on positronium (a type of exotic atom) and noticed it mentioned that positronium has a spectra (of course). So naturally this makes me wonder, have we looked at ...
Sidharth Ghoshal's user avatar
7 votes
3 answers
2k views

Solar visible light spectrum

So the visible light from stars can be used to identify the elements in that star by looking at the spectral emission lines and comparing those lines to emission lines of various elements (and their ...
Milwrdfan's user avatar
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6 votes
1 answer
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What is the temperature of the solar atmosphere (the corona) and how is it measured?

The temperature of the Sun's atmosphere, also referred to as the solar corona, is known to be hot even hotter than the Sun's surface. What is its temperature and how is it measured? How does it ...
ehsteve's user avatar
  • 1,154
5 votes
2 answers
380 views

How spectrographs that measure radial velocities manage to translate variations in the stars' spectrum lines into the orbital speed of the star?

Like ESPRESSO or CARMENES, for example. I just don't understand the process or the way these spectrographs manage to obtain the line-of-sight velocity of the "wobble" of the star (due to ...
Carlos Vázquez Monzón's user avatar
4 votes
2 answers
174 views

How to interpret this spectrum of the "new DESI Quasar at z = 6.53"; what causes the big edge at about 9150 Angstroms?

I'm not exacty sure why but Scitech Daily's Seeing Dark Energy’s True Colors: DESI Creates Largest 3D Map of the Cosmos includes the graphic and caption below. It indicates a quasar in a Hubble image ...
uhoh's user avatar
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4 votes
2 answers
243 views

Formation of spacecraft instrumentation [closed]

List of spacecraft instruments are selected to meet a mission's science goals. Let's take New Horizons as an example and study the composition of Pluto's atmosphere, the shape and geological ...
ayr's user avatar
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4 votes
1 answer
130 views

Can visible wavelength spectroscopy study an exoplanet's chemical composition directly?

I know spectroscopy of light in visible wavelengths is very effective for studying and determining the chemical composition of bodies within the solar system and bright objects outside of it. However, ...
NotSoSN's user avatar
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4 votes
2 answers
1k views

When examining an exoplanet's atmosphere is the star's emission spectra or planet's light used?

My understanding of the main method we use to figure out an exoplanet atmosphere composition is that when a exoplanet transits their sun, visible light passes through the planet's atmosphere, and ...
Hash's user avatar
  • 503
3 votes
1 answer
370 views

Estimate upper limits on flux values in the case of a non-detection?

I have ALMA data which are non-detections of some spectral lines in a protoplanetary disk. The data is in the form of spectral cubes. I am hoping to estimate an upper limit on the flux of each of the ...
lucas's user avatar
  • 1,386
3 votes
2 answers
775 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 ...
ACR's user avatar
  • 178
3 votes
2 answers
343 views

What is an "Off Rowland-circle Telescope"? Are there "On Rowland-circle Telescope" as well?

The NASA Goddard news item NASA to Demonstrate New Star-Watching Technology with Thousands of Tiny Shutters says: The technology, called the Next-Generation Microshutter Array (NGMSA), will fly for ...
uhoh's user avatar
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3 votes
2 answers
1k views

Why are helium resonance lines called "resonance lines"?

Examples of the use of the term: Formation of the helium extreme-UV resonance lines On the Formation of the Resonance Lines of Helium in the Sun (unpaywalled) Formation of the helium EUV resonance ...
uhoh's user avatar
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3 votes
1 answer
3k 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 ...
uhoh's user avatar
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2 votes
3 answers
959 views

Using optical fibers in astronomy

Why are optical fibers important in astronomy? I have read on the internet that they find applications in many fields including astronomy and this intrigued me and I would like to know what they are ...
Leonardo Fabbro's user avatar
2 votes
1 answer
89 views

Where do Astronomers usually get their wavelengths? Where do they turn to look up standard, accepted values for spectral features?

When identifying isolated observed spectral features or fitting complex observed spectra or even running complex numerical simulations, one needs a reliable, standard table of known wavelengths and ...
uhoh's user avatar
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2 votes
1 answer
573 views

How to specify SM libraries for MOOG

I am running MOOG on OS X Yosemite and with $MOOG running the abfind driver I can force fit elemental abundances with an appropriate input line list and model ...
user avatar
2 votes
1 answer
2k 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 ...
AstrOne's user avatar
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2 votes
2 answers
121 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 ...
S. Mas's user avatar
  • 69
2 votes
2 answers
127 views

First spectroscopic detection of Uranus' rotation?

As an undergraduate exercise quite a while ago, we placed the equator of Jupiter's disk across the slit of a high resolution grating spectrometer and then measured the tilt of the resulting line in ...
uhoh's user avatar
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1 vote
1 answer
115 views

How does an Echelle spectrograph put such a long, high resolution spectrum into a square-ish format?

In order to obtain a very high resolution spectrum to resolve closely spaced lines, or to measure doppler shits, spectrographs are operated with very high dispersion. But photographic plates and CCDs ...
uhoh's user avatar
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1 vote
2 answers
253 views

How is IR spectroscopy used to determine the composition of asteroids?

I am trying to understand how spectrometers or spectroscopy can be used to calculate the surface composition of asteroids for the purposes of asteroid mining.
Stuti Sharma's user avatar
1 vote
1 answer
42 views

How do they see BOTH "anomalously cool with a significant mid-IR excess" rather than one or the other? (SN 2023ixf progenitor)

The abstract of the arXiv preprint SN 2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova (itself recently "discovered" in the observatory) ...
uhoh's user avatar
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1 vote
1 answer
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What spectral feature was used to confirm that S0-2 is "single and available"? What is Brγ?

The Phys.org article Astronomers discover S0-2 star is single and ready for big Einstein test describes the results of a careful analysis of radial velocity measurements of the star S0-2, which orbits ...
uhoh's user avatar
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1 vote
1 answer
121 views

How to calculate the statistically significant level for a guassian line profile?

In some papers, they fit a line profile with gaussian model. For example, in this paper, fig 1 draw three gauss line profile, O VII, O VIII, and Ne IX. But the data seems noisy and the gaussian height ...
Chen's user avatar
  • 339
1 vote
1 answer
313 views

Why do space telescopes have GRISMS? Why a grating AND a prism for cross-dispersion in slitless spectroscopy?

https://hst-docs.stsci.edu/wfc3ihb lists the page 8.2 Slitless Spectroscopy with the UVIS G280 Grism which contains details of one of the GRISMs of the Hubble Space Telescope (GRISM = Grating + Prism)....
uhoh's user avatar
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1 vote
0 answers
42 views

Astrophysical particle spectroscopy; narrow-line particle sources (charged or uncharged) for things other than photons? Have any been detected?

Is Cosmic Ray Astronomy a thing? Is there an equivalent of the red shift effect for cosmic rays? have got me thinking and under this answer I've commented: That's a good point; there aren't as many ...
uhoh's user avatar
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1 vote
0 answers
36 views

Any examples of a gas object temperature from Doppler broadening along one axis turning out to be wrong because velocity spread was not isotropic?

Discussions under Mass of the stellar cluster (not the whole galaxy) lead me to mention that when an actual temperature is inferred from a Doppler-broadened line profile (rather than just a linewidth ...
uhoh's user avatar
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