The calculated [Fe II] 7155/8617 intensity ratios may be too high

[Hiro Takami]

Dear Madam/Sir,

Many thanks for developing this excellent software.

I have recently found pyneb, and my student, postdoc and myself are enjoying to use it.

My postdoc is now analyzing [Fe II] 7155/8617 intensity ratios in her data.

We are concerned that pyneb may yield too large intensity ratios.

Please see the attached pdf.

I suspect that the problem may be due to A coefficients used in the software.

I have made simple investigation using those in pyneb and NIST data base,

respectively. In the attached jupyter notebooks, I made simple comparisons for the LTE values for these cases. (You can just have a look at them; please do not execute

as these also require chianti and a module I developed.)

It would be good to investigate this issue sooner or later.

Thank you,

Hiro Takami

=====================================================
Michihiro Takami
Institute of Astronomy and Astrophysics, Academia Sinica
11F of Astronomy-Mathematics Building
No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, R.O.C.
Tel: +886-2-2366-5402
Fax: +886-2-2367-7849
e-mail: hi...@asiaa.sinica.edu.tw
=====================================================

[Christophe Morisset]

Hi Hiro,

We treat some aspects of the complex FeII and FeIII ions in a recent paper: https://ui.adsabs.harvard.edu/abs/2023Atoms..11...63M

PyNeb is able to use the Chianti atomic data, you only need to define the XUVTOP environment variable pointing to the directory where the Chianti database is located, and it will include Chianti as available data (BTW, different version of Chianti database can be used, starting from 7.0 I think, current version being 10.1). You can then explore all the combinations of As and Collision strengths and plot the line ratios. 

The philosophy of PyNeb is that it allows the user to choose between different atomic data (it also provides a default set of values). So it is up to you to choose any atomic data to compute the line ratio.

In the case of high density limit for the 7155/8617 ratio, the Chianti data (v 10.1) leads to a value of 26.3, very high compared to the value of 12.4 obtained using the default As in PyNeb (from Tayal & Zatsarinny, 2018, PhRvA, 98).

You can also use PyNeb to obtain the different values of the As for different sets of atomic data, to compare to NIST (which is not always the best value...).

We can for example print out the values of As for different atomic data (using getA(17,6) and getA(14,6) for 7155 and 8617 resp):

Chianti: 0.37    0.0190 

B15     :  0.156 0.0319

DH11  :  0.190 0.0273

TZ18   :  0.169 0.0194

From your notebooks, I see that the NIST values you are considering for the As of 7155 and 8617 are respectively 0.19 and 0.019 or 0.169 and 0.032, depending on the notebook. Those values seem to be a mixture from different sources. But one thing is that the very high values of 7155/8617 is obtained when A(7155)=0.37 is used, which does not correspond to any of the other sources. If you want to use so high value of A(7155), you may need to justify it.

I include the notebook I used to obtain these results, as well as a plot of the line ratios.

Hope it helps,

Best regards,

Christophe