# Questions tagged [flux]

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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) ...
464 views

### 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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### 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 ...
• 1,105
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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 ...
• 61
759 views

### 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 ...
739 views

### 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, ...
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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 ...
47 views

### 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, ...
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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 ...
• 51
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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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### 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 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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1 vote
194 views

### 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 ...
• 111
1 vote
467 views

### Help converting Jansky/beam to erg s^-1

I have some radio observation data in jansky/beam from NVSS at 1.4GHZ, and I want to convert these values into luminosity values (erg/sec). I have the distance data and I made a formula to convert it: ...
• 77
1 vote
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### How to convert Flux Density to Flux?

I have a radio catalogue with flux density values. (Jy/bm) I'm confused converting this value to flux. Because I want to calculate luminosity, I need flux values. The unit made me confused. Since I ...
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1 vote
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### I need clarity on the units in this flux equation

I have the following equation used to calculate line flux from equivalent width. $F_{line}=EW \times F_{cont}$ If $EW$, the equivalent width of a line is in Angstroms, and $F_{cont}$, the continuum ...
1 vote
236 views

### How to get the flux from a synthetic spectrum in a bandpass, when only given specific luminosity times frequency?

I have some synthetic spectra of stars (M and K giants) with columns wavelength [Angstroms], continuum normalised flux and specific luminosity $\times$ frequency [ergs/s]; I also have some Euclid ...
• 11
1 vote
555 views

### 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 ...
1 vote
55 views

### 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, ...
1 vote
51 views

### 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 vote
323 views

### 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 ...
1 vote