Questions tagged [luminosity]
Questions regarding the amount of energy produced by an object per unit of time.
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Estimating Sun luminosity from first principles
In a lecture, it was claimed that luminosity can be estimated by dividing how much energy there is in the Sun with the typical time it takes for a photon to get out from the centre of the Sun to its ...
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0answers
19 views
Equilibrium Temperature for Extremely Cold Planets: Incorporating the CMB and Intrinsic Radiation
I want to check if I'm doing this right. I'm computing the equilibrium temperature for planets where the CMB and/or the planet's intrinsic radiation (as in weakly radiating jovians) matters.
I start ...
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1answer
30 views
Does photon capture in a black hole (or any other “very compact” object) reduce the luminosity/photon flux from its self isotropic emission?
I don't know if this is even a feasible question or if I have a point in asking so.
Let's say we can model the radiation coming from a very compact object, such as a BH with an accretion disc or any ...
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1answer
44 views
How to obtain a luminosity from an SED
I have a spectral energy distribution (flux densities measured at several frequencies), and have fitted a 'greybody' model to these points.
I am confused about how I use this information to determine ...
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1answer
97 views
What units are used for the Stefan-Boltzmann law?
I have a star with given temperature in Kelvin and radius in solar radii. I tried to calculate the luminosity of the star using Stefan Boltzmann's law, and got an absurd number (over 1 million). What ...
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1answer
541 views
Increase in Luminosity of the star
The Luminosity of a star is proportional to the 4 th power of its temperature and square of its radius. Also the mass-luminosity relationship says that the luminosity of star is proportional to ...
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1answer
63 views
Luminosity of Neowise
So, I have been trying to figure out the bolometric luminosity of the comet C/2020 F3 (Neowise) on the 22nd of June, 2020. At that time, Neowise was $1.4$ AU away from Earth and had an apparent ...
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31 views
Samples from the double Schechter luminosity funcion
I want to produce samples from a double Schechter luminosity function.
Ideally, I am looking for a python implementation of this problem but am open to other tools if necessary.
Do you know of any ...
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3answers
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What is meant by the notation $A^{\times{B}}_{\div{C}}$; where A,B,C are real numbers?
I have come across a few papers using the notation $A^{\times{B}}_{\div{C}}$; where A,B,C are real number. For example, $3000^{\times{3}}_{\div{4}}$.
An example can be Eqn (4) in Stern & Laor (...
2
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1answer
61 views
Converting Light curve to Luminosity
So I'm currently working around a specific variable star, Ī± Ori and I want to determine it's luminosity...I do only have the light curve (driven from V-optical photometric band - Johnson V from AAVSO)....
2
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1answer
45 views
Strip Brightness in a Spherical System
My question concerns the following problem, published in Galactic Dynamics by Binney and Tremaine and based on a work by Schwarzschild.
Specifically, I am having difficulties in deriving the given ...
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0answers
63 views
How do I calculate the surface temperature of a star from luminosity? [duplicate]
How do I calculate the surface temperature of a star from luminosity? I've been trying to delve into speculative solar systems for a bit, and I've heard the surface temperature of a star can be ...
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1answer
65 views
How does the Eddington limit make the gravitational field of stars asymmetric?
This answer to Is the gravitational field of the sun uniform? says:
Very large stars are asymmetric due to being close to the Eddington limit. The Sun is too small of a star to have the kind of ...
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1answer
124 views
Is there a relation between mass, radius, and luminosity in deuterium-burning brown dwarfs?
I'm a worldbuilder and my setting has a lot of brown dwarfs.
While I'm trying to keep my setting as science-compliant as possible, I can't seem to find any resources for brown dwarfs like there are ...
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0answers
18 views
Total luminosity of total population of galaxies!
I'm trying to get the total luminosity of a total population of galaxies.
I have the Schechter Function like
$$\Phi(L) = \frac{\Phi^{*}}{L^{*}} \left(\frac{L}{L^{*}}\right)^{\alpha} \exp \left(\frac{...
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0answers
94 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)....
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1answer
212 views
Does the luminosity of a star on its main sequence increase or remain approximately constant?
From my understanding, the luminosity of a main sequence star should increase because, in its core, hydrogen is being burnt into helium which means that the number density of hydrogen decreases and ...
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4answers
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Visible Stars in Andromeda Galaxy
So when I look at images taken of Andromeda, I see a lot of individual stars.
Image by AndrƩ van der Hoeven
It seems to me that the actual individual stars that far away would be too small to ...
7
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1answer
589 views
What is the most appropriate way to estimate the helium composition of a star?
Say we have to estimate the helium content in Proxima Centauri.
We begin by calculating the content of helium in the Sun (source): $24.85$% of $2.10^{30}$ kg.
Mostly all the energy is generated due ...
2
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1answer
218 views
How to convert luminosity at rest frame wavelength of 1450 A to absolute magnitude at 1450 A?
How do I convert the luminosity (erg sec$^{-1}$ Hz$^{-1}$) of a quasar at a rest frame wavelength of 1450 Angstroms to absolute magnitude at the same wavelength?
I know that the bolometric ...
2
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0answers
103 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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1answer
135 views
Convolve a SED with a filter. Is convoluting the mathematical operation?
I know that in order to get the Flux of a star (or something else) in a particular filter from its SED (luminosity per unit wavelength), I need to convolve the spectrum (SED) with the filter response. ...
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1answer
65 views
Can a star emit a larger fraction of its total light in the visual range than the Sun does
If one sets both the bolometric and visual luminosity of the Sun to 1 (and use a linear scale), can a star then have a higher visual than bolometric luminosity?
It makes sense that this will not be ...
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0answers
22 views
Relationship between IMF and time spent during an evolutionary phase
I was reading a little about stellar evolution and was wondering whether there was any relationship between the lifetime of an evolutionary phase and the IMF, I searched on google but all I found were ...
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1answer
303 views
Formula to calculate B-V index? [duplicate]
Is there a formlua or equation to calculate a star's B-V index based on it's observed frequencies in the B and V spectrums ? I have unfortunately not been able to find anything...
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1answer
67 views
Finding the solar radius from temperature and luminosity
This question has eluded me for days; I can't seem to solve it.
A certain star has a temperature twice that of the Sun and a luminosity 55 times greater than the solar value. What is its radius, in ...
2
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1answer
274 views
Estimating a star's radius, temperature, and luminosity based on its mass
(See updated figure and description below.)
I've been trying to generate ballpark estimates for the radius, temperature and luminosity of stars in the main sequence based solely on their masses (...
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1answer
69 views
How Wide Would the Habitable Zone Be in a Singular Red Giant System?
Astrobiologists looking for signs of life outside Earth usually take excitement over planets orbiting red giant stars because a larger, brighter star usually means a farther-away but still wider ...
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1answer
373 views
Why is the Sun's Luminosity not equal to the Zero Point Luminosity?
I was doing some research and found that the zero-point luminosity was $L_\odot = 3.75\times 10^{28} $, while the sun's reported luminosity was $L_{Sun} = 3.828\times 10^{26}$, according to Wikipedia. ...
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0answers
28 views
How to convert magnitude to spectral luminosity? [duplicate]
In the Gaia catalogue I have the magnitude of several stars in the G band. I also have the distances to these stars (parallax is known). Additionally, I oftentimes have the effective temperature in ...
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1answer
188 views
Converting the log (Stellar Luminosity/Solar Luminosity) and the log of the plus and minus variation
There are some stars in the NASA Exoplanet Archive that I am interested in but I am confused by the physical meaning of the terms.
For example, there's a star BD+15 2940 with a log10 of Solar ...
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153 views
Q: Calculating the luminosity of a galaxy
I am currently working on a project on which I am calculating the luminosity of galaxies by using the SDSS data. They use a system of asinh magnitudes, and according to their website they use a system ...
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147 views
Stars that don't fit $L=4\pi R^{2}\sigma T^{4}$?
When calculating luminosity/radius/temperature for several stars, I've noticed that while the majority of stars conform to the luminosity relationship $L=4\pi R^{2}\sigma T^{4}$, there are a few that ...
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46 views
How to calculate the distance to galaxies with standard candles?
I was wondering how the distance in Mpc could be calculated between Earth and a galaxy using the luminosity provided? Do not be shy to use all math necessary :)
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1answer
128 views
How actively is Deep Learning being used in exoplanet identification?
Papers, like this one from Google, show that Deep Learning and Machine Learning are effective in detecting exoplanets from luminosity data provided by telescopes like TESS or Kepler.
These models ...
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1answer
119 views
Eddington luminosity in various plasmas
So I know that the Eddington luminosity is given by:
$L_{Eddington} = 4\pi GMc/\kappa$.
I want to calculate this luminosity for a plasma of purely ionized helium, as well as for an electron-...
2
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2answers
312 views
Radiative Flux, Irradiance and Luminosity confusion
First of all I know there is a similar question here, but I feel is wasn't answered at all.
My question is that I have seen many texts which says that Radiative Flux is equal to the Irradiance of a ...
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1answer
707 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 ...
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60 views
Luminosity of the Milky Way compared to Seyfert galaxies
This page lists the total luminosity of the Milky Way Galaxy to be $4\times10^{10}$ $L_{sol}$, and $L_{sol}=3.86 \times10^{33}$ ergs.sec$^{-1}$; this gives a total luminosity for the MW of $1.54\...
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0answers
191 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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1answer
89 views
What area of Proxima Centauri would need to be occluded for the effect to be observable on Earth?
One of ideas of how Breakthrough Starshot could communicate data from Proxima Centauri is to have a massive swarm of the solar sail powered craft to pivot (with their sails) synchronously, taking ...
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1answer
81 views
How can I estimate the M/L ratio from a fitted SED on a galaxy?
This answer (here in the forum) provides background to my question: https://astronomy.stackexchange.com/a/5953
I am trying to understand the process in which a stellar population synthesis (SPS) is ...
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1answer
108 views
H-R diagram, Double stars
Can someone help me? I have a case, like, we have H-R diagram and two stars on it. One of them is a blue star on main sequence, another is a red giant. They have equal luminosity. If they are in a ...
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2answers
267 views
What does this figure imply about the luminosity of pre-main-sequence stars?
Check out Figure 1 in http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1955PASP...67..154H&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf .
It seems to ...
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1answer
3k views
How to calculate luminosity in g-band from absolute AB magnitude and luminosity distance?
How can I calculate the (non-bolometric) luminosity $L$ of a galaxy (or a star for that matter) over a given band from its AB apparent magnitude $m_{AB}$ over that band and its luminosity distance $...
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1answer
101 views
Is it possible that quasars are not powered by black holes but some other kind of compact, massive object?
AFAIK, objects in the universe thought to be black holes show evidence of radiatively inefficient accretion flow. But is this the case with Quasars? If not, is there a possibility that the core of a ...
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1answer
2k views
How bright would it be on the “face” of Titan
If you were planing a maned mission to Titan and wanted to find a landing site that would get the most visible light for the longest amount of time, your first logical choice would be the dark side of ...
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1answer
63 views
Two lights roughly 5 minutes apart about as bright as Mars or maybe Saturn
I'm in the Minneapolis/St. Paul area and around 9:30 on August 4th 2017 I saw a bright light that got dimmer moving from the tree line to the east up and to my left fairly slowly, and steadily getting ...
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1answer
316 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$^{ā1}$ keV$^{ā1}$ as a function ...
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1answer
213 views
What is the radiant intensity of the celestial sphere?
Specifically, excluding the Sun and the Moon:
How much energy, as light and other frequencies reaches a point in space on the average, if you add up all the sources like distant stars, the Milky Way, ...
