Recent content by vladivostok

Great, thanks !

Thanks a lot and sorry for the late reply. Do you have any reference for the formula that you give? I'd like to see how it is derived. Thanks again.

In celestial coordinate system (right ascension/declination), how to check if an object with position RA and dec is within a given circular field of view of radius R (in arcminutes) and centred at (0,0)? R is small in this case so I assumed that I could compute the distance d of the object from...

Hi, Here is an info I don't manage to obtain from anywhere so far ! What is the "best-estimate" of the Helium abundance (the He/H ratio) in the interstellar medium of galaxies in the nearby Universe and at high redshift? I know the primordial He abundance is Y = 0.24 but what is the...

Yep, sure. Thanks for replying. The questions would be: - what is your definition of a resonant transition line? - what is your definition of resonant scattering? When you calculate a "resonant scattering" cross section, what differs from a the calculation of a "NON-resonant...

No idea? :)

some lines are called "resonant" Hi, I would like some explanation on a topic for which I do not find detailed literature online or in books. In photon absorption/emission processes by atoms, some lines are called "resonant" (for example, the 2P1/2 (or 2P3/2) to 1S1/2 transition of...