Questions tagged [luminosity]

Questions regarding the amount of energy produced by an object per unit of time.

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Is luminosity distance related to both heliocentric redshift and CMB restframe redshift?

The luminosity distance $d_l=(1+z)r(z)$, where $r(z)$ is given by $r(z)=cH^{-1}_0\int_{0}^{z}\frac{dz'}{E(z')}$. When I use SN dataset Pantheon, I find there are two redshift $z_{cmb}$ and $z_{hel}$. ...
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On finding the magnitude of Stars

I am wondering how I would be able to predict the Magnitude of fictional stars, given we know enough about them. As the formulae I can find online are mostly getting overly high values that don't seem ...
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2 votes
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DIY Sky Quality Meter: Conversion between Illuminance and Luminance

I am trying to create a homemade Sky Quality Meter (SQM) using a TSL2591 light sensor. This sensor measures Illumination (lux), but SQMs measure Luminance (mpsas). I have seen that there are many ...
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How luminous does a brown dwarf have to be to illuminate an Earth-sized planet with 0.5 lux at 2,000,000 kilometers away?

A brown dwarf is a deuterium-fusing substellar object, and, in the cases of the larger ones, a lithium-fusing one. They often emit electromagnetic radiation in frequencies that humans cannot see. ...
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1 vote
2 answers
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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 ...
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2 votes
2 answers
71 views

Finding stellar radii

Is apparent magnitude of star, distance(in pc) and effective temperature enough to calculate its stellar radii or we need some extra information?
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7 votes
1 answer
110 views

Measuring the mass of the luminous matter in a galaxy

The mass of total matter in a galaxy can be measured using the rotation curve of the galaxy. However, how do people determine the mass of luminous matter in the galaxy, as a function of the distance ...
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2 votes
1 answer
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Brightness and flux density

The alpha star in a constellation has the highest brightness, but does that mean it has the highest flux density among the other stars in the constellation?
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-1 votes
1 answer
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How to find luminosity from a light curve? [closed]

I am currently trying to find the luminosity from the light curve. I have the data about the distance, counts/sec and the energy range in which it is measured for an object. What equation can be used ...
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5 votes
3 answers
677 views

Could a black hole's accretion disk be bright through natural means?

This question is based on this description of the Cormoran Supermassive Black Hole in the Orion Arm's website: Surrounding this event horizon is an (apparently artificial) accretion disk about 4AU in ...
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5 votes
1 answer
112 views

What does a + (plus) mean in stellar classification?

I've noticed some stellar classifications might look like this: A0IV+G: (HD 70003) F3IV+F0IV (HD 82434) ...
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12 votes
1 answer
983 views

Spectral class and luminosity of hydrogen bomb explosions?

Since hydrogen bombs detonating are like tiny little stars, I wonder what luminosity and spectral classification they would get if one were to categorize them like this. E.g. Starfish Prime and the ...
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2 votes
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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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4 votes
1 answer
122 views

Is it dangerous to look at an L-type brown dwarf from too close?

Are some L-type brown dwarves bright enough so that it would be dangerous to the eyes if one looked at them from habitable distance or closer? If not, are the weakest M-type stars undangerous to look ...
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3 votes
1 answer
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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 \...
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1 vote
1 answer
87 views

HR diagram x-axis (color) and redshift?

I've read several articles and watched some videos on the HR diagram, but no-one seems to mention the effect of redshift on the color of a star. Is there some calibration step that needs to be applied ...
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1 answer
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Is something wrong with my luminosity calculation?

A few million years after a white dwarf forms, its surface temperature reaches $100000\text{K}$, while its radius is $0.01R_\odot$. Would this mean that its luminosity is $\Big(\dfrac{100000}{5778}\...
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1 answer
109 views

How to calculate galaxy bolometric luminosity?

I am a bit confused by bolometric corrections. If I have an x-ray luminosity in the 2-10 keV band, how does one convert that to $L_{bol}$? From Netzer's book The Physics and Evolution of Active ...
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1 vote
0 answers
313 views

Schechter Luminosity Function fitting plot of galaxies

I would like to plot the Schechter Luminosity function of galaxies. Here is my data(I have the Luminosity L[Ha] in erg/s). I would like to plot like this figure from this paper. In this paper, they ...
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1 vote
1 answer
59 views

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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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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0 votes
1 answer
52 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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1 vote
1 answer
149 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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1 vote
1 answer
267 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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9 votes
1 answer
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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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3 votes
1 answer
73 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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0 votes
0 answers
51 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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8 votes
3 answers
160 views

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 (...
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2 votes
1 answer
111 views

Converting Light curve to Luminosity

So I'm currently working around a specific variable star, α 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)....
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2 votes
1 answer
87 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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2 votes
0 answers
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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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1 answer
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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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11 votes
1 answer
275 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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2 votes
1 answer
54 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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1 vote
0 answers
176 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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3 votes
1 answer
2k 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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8 votes
4 answers
2k 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 ...
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7 votes
1 answer
640 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 ...
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3 votes
1 answer
446 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 ...
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2 votes
0 answers
410 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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4 votes
1 answer
271 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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1 vote
1 answer
152 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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0 votes
0 answers
24 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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2 votes
1 answer
1k 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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-2 votes
1 answer
214 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 ...
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4 votes
1 answer
750 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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1 vote
1 answer
89 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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0 votes
1 answer
568 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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1 vote
0 answers
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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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1 vote
1 answer
449 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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