Stromgren Radius

Hi All

Can someone please help.

I am trying to work out the Stromgren Radius for an active Galaxy that
is acting as a source of ionising photons. The nucleus of the Galaxy
has an ionising Luminosity L of 10^37 Watts. The mean energy of each
emmitted UV photon is 50eV. The nucleus of the Galaxy is surrounded by
an interstellar medium of pure hydrogen. The number density n(r)
varies with radial distance (r) from nucleus as n(r)=10^8(100parsecs /
r) per cubic metre. The recombination coefficient (alpha) has a value
of 10^-19 per cubic metre per sec.

The main problem is how to establish a value for n since it is a
function of radius - which is turn is a function of the Stromgren
radius - which is what I am trying to establish!!!!!!!!!!!!!!

Please can someone help.

All comments welcome,

Thank you














Hi All
Can someone please help.

I am trying to work out the Stromgren Radius for an active Galaxy that
is acting as a source of ionising photons. The nucleus of the Galaxy
has an ionising Luminosity L of 10^37 Watts. and the mean energy of
each emmitted UV photon is 50eV. The nucleus of the Galaxy is
surrounded by an interstellar medium of pure hydrogen. The number
density n(r) varies with radial distance (r) from nucleus as
n(r)=10^8(100parsecs / r) per cubic metre. The recombination
coefficient (alpha) has a value of 10^-19 per cubic metre per sec.
The main problem is how to establish a value for the particle density
n since it is a function of radius - which is turn is a function of
the Stromgren radius - which is what I am trying to
establish!!!!!!!!!!!!!!

Please can someone help.

All comments welcome,

Thank you

Harvey wrote:

I am trying to work out the Stromgren Radius for an active Galaxy
that
is acting as a source of ionising photons. The nucleus of the Galaxy
has an ionising Luminosity L of 10^37 Watts. The mean energy of each
emmitted UV photon is 50eV. The nucleus of the Galaxy is surrounded
by
an interstellar medium of pure hydrogen. The number density n(r)
varies with radial distance (r) from nucleus as n(r)=10^8(100parsecs
/
r) per cubic metre. The recombination coefficient (alpha) has a value
of 10^-19 per cubic metre per sec.

Sounds like you can start by using the same assumption Stromgren did
all those years ago: assume that in the steady state, the number of
ionizing
photons emitted per second from the source is equal to the number of
recombinations in the surrounding nebula. So, once you calculate N =
the number of ionizing photons emitted per second, you know the total
number of hydrogen atoms which make up the surrounding nebula: it's
the very same N.

Then it just becomes a simple problem of integrating the number
density
outwards to the radius which encompasses N atoms.
Have fun.

Michael Richmond