11

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 of stars you can see in that general direction. So the surface distribution of star counts is an excellent tracer of optical extinction, and $\Delta m = 2.5 \...


6

You can find a neat description and some examples of the effect here. This is known as the pulsar dispersion measure. As you correctly say, waves with longer wavelength (lower energy photons) are delayed with respect to shorter wavelength radiation from the same phenomenon. When electromagnetic waves travel through a plasma, they excite currents in the free ...


5

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). For comparison, visible light is in wavelengths from $\sim4\times10^{14}\text{ Hz}$ to $\sim8\times10^{14}\text{ Hz}$, which happens to be around the bottom of ...


3

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 spectrum then distinguishing the two scenarios is easy. If you don't have a spectrum but have two colours then it is still possible to distinguish the scenarios ...


3

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 the 3.0 coefficient mentioned in your question). However, for the purposes of estimation, the canonical relationship is $E(U-B) = 0.72 E(B-V)$ (e.g. Pandey et ...


3

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 be fitted are the points on the color-magnitude diagram and the fitting curve is the isochrone. Since there are many ways to apply this method, I will first ...


3

The quantity you want is basically the extinction law, and is usually called $k(\lambda)$. An extinction law is a fit to several measurements of the extinction $A_\lambda$ in some direction (or an average of several directions). Cardelli et al. (1989) provides different functional forms for the mean extinction law, parametrized in their Eq. 1 as $$ \frac{A_\...


3

If your sources are within 100pc then the best thing to do is assume the extinction is zero, unless you are looking for absolute magnitudes that are a lot more precise than say +/- 0.1 mag. I think you would be very unfortunate if the extinction was any more than about ~0.1 mag in the V-band (and less than that at R and I). Beyond that you are really ...


2

Puppis Window? (Neutral hydrogen observations towards the Puppis Window of the Milky Way)


2

The Lockman hole? http://en.wikipedia.org/wiki/Lockman_Hole It has a column density of neutral hydrogen of $6\times10^{19}$ cm$^{-2}$, which will correspond to very little dust. Two others I've heard of towards the Galactic bulge are known as the Sgr I and Sgr II windows. Finally, I offer "Stanek's window" towards the bulge, which has been referred to in ...


1

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 the color excess for $B-V$. In literature is commonly used $E(B-V)$, while in practice is usually needed $A_\lambda$, to switch back and forth from apparent ...


1

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 horizontal shift (the reddening) using an extinction law. (e.g. $A_V = 3.1 E(B-V)$). The effects of extinction and distance (which only moves the stars ...


1

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.


1

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. Given the correction in one band (which you already have $A_V = 1)$, you can find the correction in other bands using the table. Note that the relative absorption ...


1

You might want to have a look to the GALExtin models. The official site is still not finished (not even sure if it's still being developed), but you can access the original article here, and download the models here. Here's a poster that provides a quick introduction. Basically this is composed of two models of the Galaxy (one with spiral arms and one ...


1

I think you are talking about Plaut's window, which is located at l=0° and b=-8°. It has a reddening of E(B-V)=0.25 magnitudes. HTH, Germán.


Only top voted, non community-wiki answers of a minimum length are eligible