Questions tagged [luminosity]
Questions regarding the amount of energy produced by an object per unit of time.
76
questions
9
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1answer
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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 ...
1
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0answers
16 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{...
1
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0answers
70 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)....
3
votes
1answer
66 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 ...
5
votes
4answers
878 views
Visible Stars in Andromeda Galaxy
So when I look at images taken of Andromeda, I see a lot of individual stars.
Image by André van der Hoeven
It seems to me that the actual individual stars that far away would be too small to ...
7
votes
1answer
578 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
votes
1answer
92 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
votes
0answers
52 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.
...
2
votes
1answer
75 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. ...
1
vote
1answer
55 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 ...
0
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0answers
19 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 ...
2
votes
1answer
105 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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votes
1answer
42 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
votes
1answer
126 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 (...
1
vote
1answer
62 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 ...
0
votes
1answer
188 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
24 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 ...
0
votes
1answer
84 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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0answers
90 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 ...
2
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0answers
99 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 ...
0
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0answers
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 :)
10
votes
1answer
118 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 ...
1
vote
1answer
93 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
votes
2answers
172 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 ...
2
votes
1answer
419 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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0answers
50 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
165 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 ...
0
votes
1answer
88 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 ...
4
votes
1answer
73 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 ...
1
vote
1answer
97 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 ...
3
votes
2answers
253 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 ...
5
votes
1answer
2k 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 $...
4
votes
1answer
98 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 ...
4
votes
1answer
1k 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 ...
2
votes
1answer
61 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 ...
0
votes
1answer
302 views
How to shift AGN x-ray spectrum to rest frame from
I have limited information to shift a spectrum (in the x-ray 0.5-10 keV bandpass) at redshift z=2 to rest frame. I have a plot of normalized (photon) counts s$^{−1}$ keV$^{−1}$ by energy (keV), and so ...
7
votes
1answer
204 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, ...
2
votes
1answer
510 views
What does Eddington Limit (Eddington Luminosity) Show?
We know Eddington Limit (Eddington Luminosity) is calculated with this formula:
$$L_{Ed} \approx 3 * 10^4 * L_{sun} * \frac{M}{M_{sun}}$$
Example: For a black hole with $10^4 M_{sun}$, we get
$$L_{...
2
votes
1answer
3k views
How to convert magnitudes to bolometric luminosity? [duplicate]
If we know a star's magnitudes from several bands(say u,g,r,i,z,J,H,k) and the star's distance, how to calculate Lbol?
Let's suppose the star has a black body spectrum. Is there any manual about the ...
2
votes
2answers
298 views
Question about radiation pressure
A spaceship with mass $m = 25\:kg$ is moving toward a red giant with $M = M_{sun}$ and $L = 1000\:L_{sun}$ (L: Luminosity). It is moving on a line (so this is not an orbital question). When it gets ...
1
vote
1answer
200 views
Problem about finding distance with magnitude given
A star in Pleiades cluster has apparent magnitude of +12 ($m_{star} = +12$) determine it's distance from the sun? (We know the Sun properties such apparent and absolute magnitudes, distance from earth,...
1
vote
1answer
825 views
How to convert theoretical template spectrum from luminosity density to flux density units?
I'm working with galaxy spectral templates (e.g., Bruzual & Charlot 2003) which seem to always come with y-axis units of $L_{\odot}$/A and x-axis units of Angstroms. Thus the y-axis is a ...
3
votes
1answer
233 views
Why do different instrumental filters use different magnitude systems (Vega vs AB)?
Suppose I wanted to construct the spectral energy distribution (SED) of an object. Further suppose I observe this object through the 9 broad-band filters using the Subaru Suprimecam (just for an ...
3
votes
2answers
2k views
Difference between luminosity, luminous flux, and radiant flux?
I've looked this up, and was wondering the differences between them. Luminosity is the total energy emitted by a source, in watts. However, I'm confused about luminous flux and radiant flux. Since ...
1
vote
1answer
881 views
How to find a Cepheid's pulsation period using its graph?
Basically, I've been seeing these graphs that say: Cepheid Period-Luminosity Relation and the Period axis is supposed to be "logarithmic";
How does this graph work? Since the luminosity of a star ...
0
votes
3answers
1k views
Calculate Luminosity of Vega
I want to calculate the Luminosity of a star e.g. Vega but can be any star and came across the formula for Luminosity at the University of Oregon (http://pages.uoregon.edu/soper/Light/luminosity.html)....
4
votes
1answer
775 views
Finding luminosity of a star with magnitude
I'm working on my assessment for Physics in the IB, and I'm planning to investigate stars in spiral galaxies and determine their ages. For this I'm going to use data from the SDSS (Sloan digital sky ...
2
votes
0answers
350 views
What characteristics or patterns do galaxies have on color-luminosity chart? [closed]
For the following graph, I have some confusions:
How do galaxies rank by mass? We know that on main-sequence, more luminous stars are also more massive, so I guess it also applies to galaxies.
Do red ...
3
votes
0answers
136 views
What is the spectral power output of a typical galaxy?
I'm looking for a function which gives the typical isotropic spectral power of light emitted by an entire galaxy on the whole electromagnetic spectrum (in watts per frequency unit), as a function of ...
1
vote
1answer
920 views
Flux density to flux
The definition of flux and flux density is fairly straightforward. However, I'm musing over the practical usage of it.
For one thing, if you observe a source through a filter, how would one go from ...
