10
votes
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Determining the extinction by counting stars?
The general idea is that the more extinction there is, the less you'll be able to see stars. So there is a direct relation between the decrease in flux observed for any individual star and the number ...
- 17.7k
6
votes
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How to evaluate the fit of an isochrone to a stellar population?
Finding the best-fitting isochrone, a.k.a. isochrone fitting, is a standard approach to determine the age of globular clusters. This problem can be solved with a least-square method, where the data to ...
- 430
5
votes
At what wavelengths can black hole Sagittarius A* be observed from Earth?
From Genzel et al. (2010), here's part of Fig. 7.7.1:
This is part of the spectral energy distribution of Sagittarius A*, a flot of $\nu$ (frequency) vs. $\nu L_{\nu}$ (frequency times luminosity). ...
- 37.4k
5
votes
Accepted
Extinction Level Event (Asteroid Impact Hypothesis) Likelihood Equation
Knowing that there are X asteroids that could threaten is not in itself useful. What you want to get is a event rate, the probability of something happening per year.
One oversimplified way is to ...
- 15.7k
4
votes
Accepted
Distance to star using color index
There is a relationship between $E(B-V)$ and the reddening in any other colour. The exact value depends on the type of dust, the extinction value itself and the intrinsic spectrum of the star (as does ...
- 162k
4
votes
What object(s) are furthest above/below the galactic plane?
Bochanski et al. (2014; "The Most Distant Stars in the Milky Way") reported the discovery of two stars -- ULAS J001535.72+015549.6 and ULAS J074417.48+253233.0 -- found to be M giants at ...
- 18.4k
3
votes
What object(s) are furthest above/below the galactic plane?
Globular clusters orbit in the Galactic halo, and so are good candidates for being far above the disc. The globular cluster PSO J174.0675-10.8774 is the furthest, 470,000 light years distant, well ...
- 129k
3
votes
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Clarification on calculating IR Dust Extinction $A_K$/$A_V$
The extinction $A$ of a medium (e.g. dust) is defined as the number of magnitudes an object is increased (because higher magnitude means less light), as the light from that object travels through the ...
- 39.6k
3
votes
Difference in observing hot stars that have been reddened and stars that are cool and red
Reddening does not change the details of the spectrum of a star. The differences in absorption lines that are present in a hot star vs a cool star are still there after reddening. So if you have a ...
- 162k
2
votes
How to obtain distance modulus and Total extinction from Isochrone fitting to CMD?
The isochrones are not straight lines in the CMD. Extinction moves the stars both redward (right) as well as fainter (down) in the CMD. The vertical shift (the extinction $A$) is calculated from the ...
- 162k
2
votes
Accepted
Why does infrared pass through clouds of gas and dust with minimal extinction?
but why is this? My thinking is that it is because there are minimum energy transitions of infrared, causing less light to be absorbed, but when I look at the hydrogen Bohr model there are clearly ...
- 30.7k
1
vote
Accepted
How to compute extinction for XP GAIA spectra?
This is just a unitless number by which the flux is multiplied. The conversion from magnitudes to a factor is handled by the $10^{-0.4}$ bit. Note you should be using $A'(\lambda)$ in the exponent.
...
- 162k
1
vote
Accepted
How to count observable number of galaxies at a given latitude considering interstellar extinction?
When accounting for extinction, the number you count will be the number you would have seen at a brighter (numerically smaller) magnitude given by $m - \Delta m$ if there were no extinction, where $\...
- 162k
1
vote
Color index B-V of the dimming Betelgeuse
The changes in Jupiter's B-V index are not compatible with the expected properties of circumstellar dust. Circumstellar disks cause Infrared excess, which would cause reddening, not a shortening of ...
- 1,097
1
vote
Accepted
Extinction and reddening dataset
Note that they are related via the reddening law, i.e.
\begin{equation*}R_\lambda = \frac{A_\lambda}{E(B-V)}\end{equation*}
where $A_\lambda$ is the extinction at wavelenght $\lambda$, and $E(B-V)$ is ...
- 430
1
vote
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Quesions about extinction power law
The value is $\beta \simeq -1$ (e.g. see Cardelli et al. 1988). The extinction would not be well fitted by a power law, except over a very narrow wavelength range.
- 162k
1
vote
Accepted
Absolute magnitudes with dust extinction
Check this lecture note. I believe there is everything you need to understand how to proceed. In brief, you should have extra information about the relative absorption, shown in the table on p.18. ...
- 1,434
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