# Questions tagged [spectra]

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

135 questions
Filter by
Sorted by
Tagged with
42 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 ...
1k views

### 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 ...
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?
88 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, ...
54 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?
23 views

### H alpha - double peak (Be star)

What is the double peak in this case, please? What does the third mean? Many thanks
100 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 ...
651 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$_\alpha$? ...
17 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 ...
55 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 "...
32 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
19 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 ...
55 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 ...
32 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 ...
37 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 ...
43 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 ...
58 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 ...
47 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 (...
86 views

### 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 ...
9 views

43 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 ...
195 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 ...
39 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 ...
319 views

### How to shift an AGN X-ray spectrum to rest frame

I have limited information to shift a spectrum (in the X-ray 0.5-10 keV bandpass) from redshift $z=2$ to the rest frame. I have a plot of normalized (photon) counts s$^{−1}$ keV$^{−1}$ as a function ...
40 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 (...
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. ...
850 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 ...
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 ...
41 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 ...
24 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 ...
168 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 transform ...
175 views

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 (...
886 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 ...