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# Questions tagged [flux]

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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 ...
0 votes
0 answers
43 views

### Eddington-Barbier approximation next term for flux

When adding a term to E-B approx it should lead to this for the astronomical flux. $\frac{F}{\pi }\approx S\left(\tau =\frac{2}{3}\right)+\frac{5}{18}\frac{d^2S}{d\tau ^2}_{\tau =\frac{2}{3}}$ S is ...
0 votes
0 answers
18 views

### How to calculate 2-10keV Flux or Luminosity by Power Law from 0.2-12keV with known $\Gamma = 1.7$

I have $0.2-12$keV flux observations, distance observations and $\Gamma =1.7$. I want to apply power law to calculate 2-10keV flux. How can i do that?
• 77
3 votes
3 answers
704 views

### Integration of Plank curve of the Sun

Why I did not get the value of 1361 W m^{-2}, please? I am getting 2.0125538614437745e-47. ...
• 505
0 votes
0 answers
44 views

### converting rms to limit flux

My question is simple: if I have an RMS value (the standard deviation for my background) at 1 sigma, and I also have the zero point of my observation, how can I transform that value into the limiting ...
0 votes
0 answers
71 views

### How to convert flux to flux density for a synthetic spectrum?

I have several model SEDs generated by the CLOUDY spectral synthesis code. The data is formatted with one wavelength column and one flux column. I wish to perform Hubble synthetic photometry on these ...
0 votes
0 answers
47 views

### How to calculate flux at a specific frequency from another frequency and spectral index

First of all, I know spectral index is $\alpha=\frac{log\frac{S_1}{S_2}}{log\frac{v_1}{v_2}}$ where $s$ are the flux densities and $v$ is the frequencies. I wonder that If i can use spectral index and ...
• 77
1 vote
2 answers
215 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
1 answer
409 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
1 answer
417 views

### 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 ...
• 77
5 votes
1 answer
369 views

### 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) ...
1 vote
0 answers
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, ...
2 votes
0 answers
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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3 votes
0 answers
93 views

### 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
2 votes
2 answers
694 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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1 vote
1 answer
190 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
4 votes
0 answers
39 views

### 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
1 vote
3 answers
546 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 ...
2 votes
1 answer
1k views

### 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 ...
4 votes
2 answers
181 views

### 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 ...
• 17.5k
2 votes
0 answers
72 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 ...
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2 votes
0 answers
125 views

### 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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0 votes
0 answers
360 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?
2 votes
0 answers
277 views

### 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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3 votes
1 answer
134 views

### 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
451 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 ...
• 415
1 vote
0 answers
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?
• 61
3 votes
1 answer
153 views

4 votes
1 answer
240 views

### 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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3 votes
0 answers
741 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 ...
1 vote
0 answers
364 views

### 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)....
2 votes
0 answers
80 views

### 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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