Questions tagged [spectra]

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

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3
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0answers
16 views

How to find x-values of fourier-transformed correlation functions in velocity space?

I am trying to extract the kinematic parameters (rotation velocity, velocity dispersion, ...) of an elliptical galaxy by extracting the kinematical broadening function using the FCQ-Algortihm first ...
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1answer
38 views

Are there any SuperCam spectra available?

A lot of pictures from the SuperCam, the NavCam or the Mastcam onboard the Perseverance rover are available online (for instance on the NASA and JPL websites). Have any SuperCam spectra been made ...
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How to remove redshift from galaxy spectra in Python?

Hello I extracted a spectrum from the central region of the 2D spectrum of the major axis from NGC 4697 (I just took a central row in the 2D data set, see this question for more information: How to ...
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39 views

How far can a star's visual colour deviate from black body radiation?

The primary driver of a star's colour is its temperature, by way of black-body radiation. Black body radiation restricts stellar colour to a narrow slice of the full RGB spectrum. However, all stars ...
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starting from SSP spectra to evaluate galaxy spectrum and observed mag

I know that the galaxy spectrum, namely the flux per unit wavelength versus the wavelength, is the sum of the Simple Stellar Population (SSP) spectra at a fixed redshift (e.g. similar to eq. 1 in ...
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1answer
82 views

Spectra of different stellar classes?

I'm beyond an amateur, but I've been failing to find this information and it makes me think I'm missing something. Anyway: I am trying to write a procedurally generated simulation that includes ...
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1answer
86 views

Spectral lines of the Sun?

If I remember correctly, the pp chain and (partially) the CNO cycle are the dominating set of reactions in our Sun. On the other hand, the composition of the Sun has many more elements/isotopes than ...
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1answer
89 views

How to extract galaxy spectra for different radii in Python for spectra taken by long slit spectrograph?

I am trying to extract the kinematics from the elliptical galaxy NGC 4697 using the Fourier Correlation Quotient (FCQ) algorithm described by Bender (http://adsabs.harvard.edu/full/1990A%26A...229.....
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1answer
49 views

What type of spectrum does the Wolf-Rayet star WR137 have?

Is it an Emission Spectra or an Absorption Spectra? I think that it's an absorption spectrum, but then why is the light intensity curve focused on elements that should not be in the star in this case, ...
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29 views

Young galaxies VS. old galaxies spectra differences

What are the main (UV/optical) spectral differences between a young star-forming galaxy and an old galaxy with no ongoing star formation?
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1answer
93 views

Question regards to Kirchhoff’s Laws (of spectroscopy)

In the book "Horizons: exploring the universe-Cengage learning (2018)", page 210, it states that: Observational evidence can tell you how nova explosions occur. As the explosion begins, ...
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1answer
53 views

Derive LOSVD from galaxy spectrum, using fourier method

I am trying to implement a programm, that derives the kinematics (specifically the kinematic parameters: mean rotation velocity, velocity, dispersion, hermite coefficients h3 and h4) from an ...
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4answers
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Why doesn't the Sun produce an emission spectrum?

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 ...
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57 views

Astronomical data bases express spectra in flux density, e.g. ergs/s/cm2/Angstrom( or Hz) how can I calculate the flux, i.e. ergs/s/cm2?

I have light spectral data from astronomy data bases in flux density (flux/Angstrom or flux/Hz) and would like to calculate the flux. How can I calculate the flux from the flux density?
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21 views

How to create synthetic galaxy spectrum by broadening stellar spectra with a gaussian

I am trying to create a synthetic galaxy spectrum, by convolving a gaussian-velocity-distribution f(v) with my stellar spectra S. I have already logarithmically rebinned the spectrum and removed the ...
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1answer
39 views

Why is He I 6678.151 line used for investigating variations in Be stars?

Why is He I 6678.151 line used for investigating variations in Be stars? I mean, for instance, asymmetry and radial velocity. Many thanks
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H alpha - double peak (Be star)

What is the double peak in this case, please? What does the third mean? Many thanks
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21 views

Cosmic variance - Fourier Transform - a few precisions

I have posted initially on physics exchange but none answer, so I try my chance here (I am going to delete the physics exchange one) : I cite an original report of a colleague : If we are interested ...
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72 views

Logarithmic rebinning and continuum removal of stellar spectra

I am trying to learn how to derive the line of sight velocity distributions from galaxy spectrum to extract kinematical parameters like rotational velocity and velocity dispersion. Therefore I need to ...
2
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1answer
33 views

Flux vs. Velocity representation of spectra?

I'm looking for a basic explanation of the flux vs. velocity representation of a spectrum and how it's obtained from the regular flux vs. wavelength representation. A good example of this is in Arav ...
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0answers
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How to determine the temperature of a star according to the strength of the line in the spectra?

Based on the comments, I have changed some things. Below is a graph showing the relative strength of $H_\gamma$ and Fe I lines of two stars. Which star is hotter? This is a question from the book:An ...
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1answer
73 views

How would one estimate the rotation period of a star from its spectrum?

The figure is shown; the measurements were taken on two consecutive observing nights. The Ordinate is the flux normalized to continuum and the abscissa is the wavelength scale. You can see the "...
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1answer
56 views

Finding galaxy spectra in SDSS Catalog by object name

I am looking to find galaxy spectra of early type elliptical galaxies in the SDSS catalog by the objects name. See: https://dr12.sdss.org/advancedSearch. I dont know how to find out the PLATEID of my ...
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1answer
60 views

Spectra: What is that Supposed to Mean?

I've found this website (click here for the link), the link leads you to a problem about the velocity Andromeda is going towards the Milky way galaxy, and you can try three approaches. I like to ...
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1answer
129 views

working with stellar spectra in fits format in python

Hey I am new to working with astronomical data in Python. I wanted to start working with stellar spectra and I am having trouble with the data. To get a first look I just wanted to plot a spectra (...
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0answers
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Is threre a relation between relative or absolute error and standard deviation for ratio of power spectra?

I have to compute the variance on this ratio, that is to say on the observable $O$ : $$O=\left(\frac{C_{\ell, \mathrm{gal}, \mathrm{sp}}^{\prime}}{C_{\ell, \mathrm{gal}, \mathrm{ph}}^{\prime}}\right)=\...
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1answer
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Understanding better the factors on $C_l$ in Angular power spectrum and Relation with Matter power spectrum

I am looking for an explanation on the angular power spectrum. I found this extract that is interesting but not fully understood for me (I will cite the step that I didn't understand) "what is ...
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1answer
424 views

Why are the wings of many strong lines, including hydrogen lines and most metal lines, stronger in Dwarfs than in Supergiants?

What is the reason? Is it because Dwarfs have higher surface gravity (log g), in turn related to pressure, than Supergiants so there is more contribution from van der Waals and Stark broadening?
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1answer
45 views

.mt file convert to .fits/.ascii/.dat

How to convert .mt file with a spectrum to a more convenient format, please? I am able to display that in fv: Fits Viewer, but I am lost in converting. Thank you
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1answer
43 views

What leads an observer to choose a narrow slit over a wide one (and vice-versa) when observing?

In spectroscopy, a wide slit will lead to lower spectral resolution while too narrow of a slit will reduce incoming flux from the object. From what I read, it appears as though there is always a ...
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Spectrograph Arrangement, Noise, and Fourier Domain [closed]

If the transform of a line profile extends out to the Nyquist frequency such that we cannot see the noise level, what could we change in our spectrograph arrangement that would allow us to see the ...
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1answer
54 views

How much does the equivalent width of a line change by the introduction of 5% scattered light?

How much does the equivalent width of a line change by the introduction of 5% scattered light? We know the equivalent width is defined as $W = \int_{-\infty}^{\infty} \bigg(\frac{1-F_{\nu}}{F_c}\bigg) ...
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3answers
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Formation of elements in the Sun other than helium

I just learned that the Fraunhofer lines of the Sun's spectrum indicate that the Sun contains various elements other than just hydrogen and helium (for example, Na and Fe) but don't the Sun's p-p ...
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3answers
200 views

Spectrum of stars

If some specific metal is shown in a star's spectrum, does it indicate that the star has that specific metal? For example, the Sun, a G2 star, shows medium strength of Ionised Calcium in its spectrum, ...
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2answers
494 views

What is the best database for identification of spectral lines?

What is the best database for the identification of spectral lines? For instance, I have a red spectrum of A0 star and I would like to recognize the most prominent lines, where to find them? Many ...
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2answers
151 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 ...
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2answers
97 views

How to accurately measure the temperature of red supergiants?

I just (February 28th, 2021) heard the news on progress how to measure the temperature of super giants: Red supergiants are a class of star that end their lives in supernova explosions. Their ...
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1answer
64 views

Demo to get Matter Power Spectrum in cosmology

I would like please to demonstrate the expression of Power spectrum in Cosmology : First, I have the relative contrast: $$\delta_{i}(\vec{x}, z) \equiv \rho_{i}(\vec{x}, z) / \bar{\rho}_{i}(z)-1\quad(...
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0answers
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How to algorithmically distinguish between different types of nebulae?

I remember that there are five types of nebulae: Planetary nebulae have not much to do with planets, but are emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red ...
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What is the gravitational wave spectrum of an ellipsoid neutron star like?

If the star is ellipsoid instead a sphere, the wave should be rich of harmonics, not only (2*orbital frequency). Can these harmonics behave the same way, i.e. they appear/disappear together and drift (...
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1answer
363 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. ...
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1answer
20 views

Where to find spectra from Las Campanas Redshift Survey?

I am interested in the optical spectrum of a galaxy. In SIMBAD the reference for the redshift of my galaxy is the Las Campanas Redshift Survey. Hence I am looking for the optical spectrum from which ...
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1answer
47 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 ...
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Where can I find galaxy spectra (in the form of FITS files)?

I know there's SDSS and I tried searching for the spectra through the navigate and explore tool under CAS as well as by using RA/Dec coordinates under SAS, but every single time it comes out with 0 ...
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1answer
890 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 ...
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0answers
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How to convert between spectra given in terms of velocity (km/s) to wavelength spectra?

I have H alpha spectra of H II regions in our galaxy. In the paper, the x-axis is in units of km/s and the corresponding line width as well. From this, how can I get equivalent width of the H alpha ...
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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 ...
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1answer
110 views

How to isolate H$_\alpha$ from Nitrogen doublet emission lines

I am trying to find out line intensity and FWHM of H$_\alpha$6565 emission line from a quasar spectrum obtained from SDSS DR-14Q. Visual inspection of spectrum shows H$_\alpha$ being contaminated with ...
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1answer
189 views

Converting from $\mathrm{W \: m^{-2}}$ to $\mathrm{Jy \: km \: s^{-1}}$

Suppose I observe a spectral line with rest frequency $\nu_0$ and integrated flux density $F = 10^{-26} \mathrm{W/m^2}$. Is the following line of reasoning correct? $1 \: \mathrm{Jy} = 10^{-26} \: \...
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1answer
91 views

How is spectroscopy used to deduce what an object is made of?

Spectroscopy is an analysis of light (or other EM wavelengths) that is often used by scientists to examine what an object is made from or contains. Apologies if this is a stupid question, but this ...