Recent content by vladivostok

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    Undergrad Object in or out of a circular field of view? (celestial coordinate system)

    Great, thanks !
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    Undergrad Object in or out of a circular field of view? (celestial coordinate system)

    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.
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    Undergrad Object in or out of a circular field of view? (celestial coordinate system)

    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...
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    Graduate Helium Abundance in ISM of Galaxies: Best-Estimate Value

    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...
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    Graduate Some lines are called resonant

    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...
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    Graduate Some lines are called resonant

    No idea? :)
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    Graduate Some lines are called resonant

    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...