Topics

Total ionization rate of oxygen suddenly drops to zero before the Stromgren radius

Gary Ferland
 

I didn't try to run your model but have some suggestions.  We do not solve for the ionization of elements with trivial abundances - that ion stage is turned off.  that may be what you are seeing.

some suggestions follow - let me know what happens.
Gary

to check, make a plot showing the abundances of the first three ion stages of O by looking at the output from
save element oxygen ionization "name" - see Hazy 1 for more details

you can change the threshold for "turning off" an ion stage with the command

19.14.51 Set trimming -9 [upper lower, off] [old, new]

The code saves execution time by not computing the population of stages of ionization with trivial

abundances. The thresholds for excluding an ionization stage are chosen with photoionization

equilibrium in mind. These may not be appropriate for some other conditions or if your definition

of trivial is different from mine.

This command changes the limit for the smallest fractional abundance, n(A+x)=n(A), to

consider. The smallest relative abundance to be considered for a stage of ionization higher than

the ionization peak is changed with the upper keyword. The command set trimming upper off

will turn off trimming of the highest stage of ionization. The smallest relative abundance of ions

below the peak is changed with the lower keyword. The default relative ionization fractions are

10􀀀6 and 10􀀀10 respectively. If no keyword appears then both are changed to the number entered.

The argument is the log of the lowest or highest ionization fraction to consider.

Generally, line excitation energies for atoms with stages of ionization higher than the peak

ionization will strongly exceed the ambient temperature so these ions will have little influence on

the calculated temperature or spectrum. This is not true for lines formed by ions below the peak

distribution. The keyword off sets the smallest abundance to just above the machine’s floating

precision limit.

The keyword new switches the algorithm used for trimming to an experimental revised

approach; the keyword old resets the approach to the default legacy algorithm.


On Wed, May 20, 2020 at 11:53 PM Shengqi Yang <sy1823@...> wrote:
Hi all,
I am studying the radial density profile of OIII in the closed spherical geometry. As a simplest case I set up a hydrogen and oxygen only environment. I assume the stellar radiation at the center of the cloud is the only radiation source. The input file I am using is attached below as '0.5_0.2_50_test.in'. The stellar radiation spectrum is from starburst99 with SFR=1 M_sun/yr, Salpeter IMF, Z=0.004, age=1 Myr. You can see a lot of this radiation spectrum here: https://www.stsci.edu/science/starburst99/figs/fig2.html 

From the CLOUDY output file '0.5_0.2_50_test.ionrate_O' column 13 and 14 I get the total recombination and ionization rate of OIII, plotted in the 'profile1.png'. I find the total ionization rate suddenly drops to 0 at radius r=0.8Rs, but the OIII abundance profile given by column 12 of '0.5_0.2_50_test.ionrate_O' decreases continuously (which I don't understand... I thought the OIII abundance should also drops to zero following the ionization rate). Do you know what causes this discontinuous behavior of the total ionization rate of OIII? How can I avoid this? I already set the age of the cloud to 10^17s but the sudden drop is still there, so the limited cloud age shouldn't be the cause...

Thank you very much for your help and time!
Best,
Shengqi



--
Gary J. Ferland
Physics, Univ of Kentucky
Lexington KY 40506 USA
Tel: 859 257-8795
https://pa.as.uky.edu/users/gary

Shengqi Yang
 

Hi Gary,
Thank you very much for the reply! I later found out that since I care about OIII radial profile, what I should check is the OII recombination rate, which is actually smooth throughout the HII region. The sudden drop down for OIII recombination rate at R=0.8*R_HII could be that OIIII abundance gets too low there. 
Thanks again! 

Best,
Shengqi

On Wed, May 27, 2020 at 9:50 PM Gary Ferland <gary@g.uky.edu> wrote:
I didn't try to run your model but have some suggestions.  We do not solve for the ionization of elements with trivial abundances - that ion stage is turned off.  that may be what you are seeing.

some suggestions follow - let me know what happens.
Gary

to check, make a plot showing the abundances of the first three ion stages of O by looking at the output from
save element oxygen ionization "name" - see Hazy 1 for more details

you can change the threshold for "turning off" an ion stage with the command

19.14.51 Set trimming -9 [upper lower, off] [old, new]

The code saves execution time by not computing the population of stages of ionization with trivial

abundances. The thresholds for excluding an ionization stage are chosen with photoionization

equilibrium in mind. These may not be appropriate for some other conditions or if your definition

of trivial is different from mine.

This command changes the limit for the smallest fractional abundance, n(A+x)=n(A), to

consider. The smallest relative abundance to be considered for a stage of ionization higher than

the ionization peak is changed with the upper keyword. The command set trimming upper off

will turn off trimming of the highest stage of ionization. The smallest relative abundance of ions

below the peak is changed with the lower keyword. The default relative ionization fractions are

10􀀀6 and 10􀀀10 respectively. If no keyword appears then both are changed to the number entered.

The argument is the log of the lowest or highest ionization fraction to consider.

Generally, line excitation energies for atoms with stages of ionization higher than the peak

ionization will strongly exceed the ambient temperature so these ions will have little influence on

the calculated temperature or spectrum. This is not true for lines formed by ions below the peak

distribution. The keyword off sets the smallest abundance to just above the machine’s floating

precision limit.

The keyword new switches the algorithm used for trimming to an experimental revised

approach; the keyword old resets the approach to the default legacy algorithm.


On Wed, May 20, 2020 at 11:53 PM Shengqi Yang <sy1823@...> wrote:
Hi all,
I am studying the radial density profile of OIII in the closed spherical geometry. As a simplest case I set up a hydrogen and oxygen only environment. I assume the stellar radiation at the center of the cloud is the only radiation source. The input file I am using is attached below as '0.5_0.2_50_test.in'. The stellar radiation spectrum is from starburst99 with SFR=1 M_sun/yr, Salpeter IMF, Z=0.004, age=1 Myr. You can see a lot of this radiation spectrum here: https://www.stsci.edu/science/starburst99/figs/fig2.html 

From the CLOUDY output file '0.5_0.2_50_test.ionrate_O' column 13 and 14 I get the total recombination and ionization rate of OIII, plotted in the 'profile1.png'. I find the total ionization rate suddenly drops to 0 at radius r=0.8Rs, but the OIII abundance profile given by column 12 of '0.5_0.2_50_test.ionrate_O' decreases continuously (which I don't understand... I thought the OIII abundance should also drops to zero following the ionization rate). Do you know what causes this discontinuous behavior of the total ionization rate of OIII? How can I avoid this? I already set the age of the cloud to 10^17s but the sudden drop is still there, so the limited cloud age shouldn't be the cause...

Thank you very much for your help and time!
Best,
Shengqi



--
Gary J. Ferland
Physics, Univ of Kentucky
Lexington KY 40506 USA
Tel: 859 257-8795
https://pa.as.uky.edu/users/gary