Questions tagged [flux]
The flux tag has no usage guidance.
26
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What do the negative values in FITS images mean?
I am using FITS images, and noticed negative values in value matrix. What they mean? For example, for one of the images, the minimum value is -0.34472656 and the maximum = 552.0. The data type(format) ...
- 51
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28
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Magnitude cuts in different bands/surveys
I have data on around 142,000 galaxies. Some of these galaxies have apparent magnitude data in different bands. For example, many of my galaxies have SDSS PSF data in ugriz bands,GALEX FUV, GALEX NUV, ...
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32
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Effective radius from astropy sersic profile
I would like to integrate the 2d Sérsic profile of the astropy library to check the half light radius, but I have some issues.
First, I create a simple profile:
...
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2
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36
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What is the Chołoniewski method of estimating galaxy luminosity functions?
This paper describes a method to estimate the reddening of AGN using various methods, mostly to do with the intensity ratios of different absorption lines. It also mentions the Chołoniewski method, ...
- 2,394
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Source flux in Jy + noise computation, radio astronomy
I have an image of an extended source obtained with an interferometer (after imaging the uv-data). The image consist of a certain number of pixels, with unit of Jy/beam. Somewhere on the image is a ...
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2
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What do the flux letters mean? (U, B, V, R, I, G, J, H, K, u, g, r, i, z)
For any object on Simbad so lets take a random one,
http://simbad.u-strasbg.fr/simbad/sim-id?Ident=ton%20618 (Ton 618)
I'm trying to get a layman's explanation of Flux.
What do the letters stand for,
...
- 1,271
1
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1
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102
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Is the flux density independent of source-observer distance?
A particular observatory is providing the flux density of an astronomical source and only from this information, is it implicated that this particular parameter is unaffected by the distance between ...
- 11
4
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36
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Total scattered flux and polarization for a ring of dust particles close to a star
I have an important problem and maybe some of you can help me with the following question:
I have a mathematical expression for the total scattered flux in Jansky and the total linear polarized flux (...
- 41
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3
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304
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Calculating the luminosity of a comet
Assuming a 9-km comet is heading towards the Earth and it is at distance 5.2 AU away from the Sun, what is its luminosity? Assume that it has an albedo of 0.5?
For now, I have calculated the Sun's ...
- 21
1
vote
1
answer
473
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How to access the raw time-series dataset of GOES X-Ray Flux?
I would like to access the time-series dataset of X-Ray Flux obtained by GOES. I expect that the flux units to be Watts / square-meter; this is because of the figure below (obtained from this Nature ...
- 13
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2
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137
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Is there a way to convert a list of stellar fluxes to a star type?
If I look up a star on Simbad, (for instance this one), a list of fluxes in different bands might be given.
Star classes (O, B, A, F, G, K or M) depend on the color of the star. The color of a star ...
- 17.1k
2
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0
answers
50
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 ...
- 51
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74
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Flux Density Unit Conversion [closed]
I am confused how to convert from ${\rm cm^{-2}\,s^{-1}\,Å^{-1}}$ to ${\rm erg\,cm^{-2}\,s^{-1}\,Å^{-1}}$. How do I do that?
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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?
2
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0
answers
165
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How to calculate rest-frame luminosity in a specific wavelength band?
For instance, I have a set of templates whose y is in Jy and x is in Angstroms. I have both of their rest-frame and obs-frame wavelength (i.e. redshift). I want to know their luminosity in one ...
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How is the difference of bolometric magnitudes not dependent on the stars' radii?
The difference of 2 bolometric magnitudes is given by:
$$M_{bol, ★} - M_{bol, ☉} = -2.5 \cdot \log \left( \frac{L_★}{L_☉} \right)$$
But Pogson's equation is:
$$M_{bol, ★} - M_{bol, ☉} = -2.5 \cdot \...
5
votes
1
answer
262
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How do you carry errors for brightness magnitudes [duplicate]
I have a value for the relative flux $F_2/F_1$. With some uncertainty value $a$.
If I use the equation to get relative magnitude: $m_1 - m_2 = 2.5 \log_{10}(F_2/F_1)$
How do you now calculate the ...
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49
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How to calculate the flux of a galaxy merger? [closed]
Say three galaxies, with equal fluxes, $f_1$, merge. How could I calculate their combined flux?
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1
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119
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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 $W = \int_{-\infty}^{\infty} \bigg(\frac{1-F_{\nu}}{F_c}\bigg) ...
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2
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1
answer
69
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Using SDSS data / finding a catalog
I am looking for a catalog of low redshift galaxies (preferably SDSS) with information on line fluxes and stellar mass. My Google searches keep pointing me to work by the Portsmouth group, so I ...
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1
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168
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Determining needed exposure time given SNR
I need help on how to estimate an exposure time for a desirable signal to noise ratio (SNR). For example, given the magnitude and a desired SNR of a star we want to achieve, how long should the ...
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43
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What is the O[III]/H$\alpha$ line ratio for Active Galactic Nuclei?
I have the H$\alpha$ line flux of an AGN and I am trying to calculate the Bolometric luminosity using it. Bolometric luminosity can be calculated from O[III] fluxes by $L_{\rm Bol} = 3500 L_{\rm O[III]...
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1
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156
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Flux density from brightness map
This is a naive question. I have a temperature map of radio emission at 1420 MHz, in Kelvin. I want to extract the flux density (in Janskys) from an extended region of this map.
Is the flux density ($...
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427
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Conversion of Magnitude to flux using zero point in AB Magnitude
I want to calculate the flux of the 5 sigma limited magnitude. It is given that the zero point magnitude of NB964 is 28.77 and 5sigma magnitude is 25.45.
The following example is from A large, deep ...
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247
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Units confusion while calculating flux of a star using distance and luminosity, Python
I am trying to calculate the flux of various stars in Python. I am using the information from a database containing all stars in Hipparcos, Yale Bright Star, and Gliese catalogs (almost 120,000 stars)....
user30617
2
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0
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67
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How to calculate the light energy of a supernova? [closed]
I have been given a distance, an average flux, and a time period. How do I find the light energy emitted of a supernova over that time period?
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