Questions tagged [spectra]

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

33 questions with no upvoted or accepted answers
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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 ...
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0answers
178 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). ...
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126 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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21 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 ...
3
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0answers
51 views

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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44 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 ...
2
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0answers
25 views

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 ...
2
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22 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 ...
2
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0answers
76 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 ...
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0answers
38 views

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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10 views

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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41 views

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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42 views

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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48 views

Is there any synthetic spectrum software for neutron star?

Is there any software that can calculate the emergent spectrum of a neutron star photosphere, for Teff is about 1e7K, density is above 1e21-1e22 cm^-3 ? Output line wavelength is about 0-100A is ...
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238 views

What is the spectral energy distribution (SED)?

I see the SED being referred to as several different things and now I am confused about what it actually is and what are its units. In particular, I find the SED Wikipedia page not understandable. ...
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63 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?
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97 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 ...
2
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0answers
130 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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19 views

How to calculate S/N in galaxy absorption spectra?

I want to calculate the S/N of an galaxy absorption spectrum. I therefore chose a part of the spectrum which contains very little to none absorption features and should be only made up of noise and ...
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42 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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26 views

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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36 views

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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37 views

Absorption line in quasar spectrum

I have quasar spectrum which includes emission and absorption lines. I need to find absorption lines in between 2 wavelength. How can I do it with coding?
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214 views

How to calculate Equivalent Width of a spectrum with continuum at 0

I am trying to calculate the Equivalent Width of emission lines of a spectrum whose continuum is at 0, making the calculation of the EW impossible. I have the spectrum of a transient in a galaxy, so ...
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44 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 ...
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22 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 ...
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214 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 ...
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328 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 ...
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30 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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58 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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22 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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26 views

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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156 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 ...