Homework 2025 Lexington

2025 July 21:

This page is being updatd and is not complete. Our YouTube channel on using Cloudy is complete through running the homework assignment.

We will use release candidate 2 for the upcoming c25.00 at the workshop. The release candidate is available on our downloads page.

You are welcome to do the following homework to prepare for the workshop

Join our discussion group

Join the Cloudy2025 groups.io forum. There will be announcements posted on the group, and it is a good place for you to ask questions.

Bookmark the class web share

Please bookmark the class web share. We will place documents, PDFs of the lectures, and models, in folders below this site.

Cloudy

We have a YouTube channel on installing and using Cloudy! It goes into how to navigate our wiki, download Cloudy, build it, run models, and some of the physics. Please have a look. Feedback is most welcome.

Have a laptop to compute models and plot results during the workshop

We want to spend our time thinking about astronomy rather than computer science. You need a working copy of Cloudy to participate. You should be able to create an input deck using a text editor, run Cloudy, and make plots of the predictions as we go along. The first dozen videos on the Cloudy YouTube channel would be a great place to start.

We are approaching the final release of Version 25.00 of Cloudy and expect to have it available for our workshop. Its release will be announced on our forum. To get started before then, use the release candidate of C25, available now and named c25rc1 on our downloads page.

Problems?? Search our group.io user group to see if others have solved it, and post a question on the workshop forum if you don't find help.

Have access to the code's documentation. These are PDF files are located in the docs directory of the Cloudy download, and are also posted in the docs directory of the web share. You should be able to view the Cloudy Quick Start Guide Hazy1 and Hazy2, the documentation files, on your laptop. Please don't print them. Important chapters in Osterbrock and Ferland are posted under the AGN3 folder.

Typos?? If you notice any please let me know by posting to the user forum.

Read the Cloudy Quick Start Guide

This is a short introduction to all of Cloudy. Read it to get an overview of what we will be discussing.

Run the "M16.in" model and plot some results. Due Friday Aug 1 2025

You should have an Cloudy executable that can successfully pass its smoke test (run the code with the input having the single command "test"). You should have a script "run" that will read input from "name.in" and produce the "name.out" output file. And you should be able to create plots of predictions.

We will be considering the famous HST image of M16 throughout the workshop. Here is a recent paper describing the optical spectrum. We will start by making a model the ionized layer.

Run the model

You will find the input script M16.in in the homework directory of the web share. Several files will be created when you compute the model. The most important is the main output, named "M16.out" if you use our recommended "run" script. Look at the last lines in that file. They should say "Cloudy exited OK". If they don't you have problems and should investigate.

Plot the temperature and ionization structure

We will make lots of plots showing predicted quantities during the workshop. You will need to compute models and create plots while in the class. I use Jeremy Sanders' Veusz program, which is GUI based and very Cloudy friendly. The appendix of the Quick Start Guide explains how we use Veusz and I strongly recommend it.

The file "M16.ovr" is the "overview" file that was created when you ran Cloudy. It has lots of information about the physical conditions in the cloud. The first row gives column headers. The remaining rows give properties of the cloud as a function of depth into the cloud. They are tab delimited fields meaning that a tab character separates columns.

Make a plot in which the depth into the cloud is the x-axis and the gas kinetic temperature is the y-axis. The depth in cm is the first column in the overview file. Both axis should be linear. The temperature is the second. Save a copy of the plot in PDF format. Post the plot on our forum.

Next plot the atomic and ionized hydrogen ionizations as a function of depth into the cloud. The depth in cm is the first column, the fraction of hydrogen that is atomic is the seventh column, and the fraction that is ionized is the eighth column. Include both ionization fractions on the same plot. Both axis should be linear.

Plot the entire spectrum of the star and the cloud

This is contained in the file M16.con. The first column is the wavelength in microns. This is the x-axis and the plot should be a base 10 log and have a range from 0.01 to 1000 microns. The spectrum of the incident radiation field, the star, is in column 2. Add this to the pole. Column 7 gives the spectrum of the cloud. Add this to the cloud. Both spectra are specific luminosities in ergs/s and should be plotted as a base 10 log y-axis. Make the axis have a maximum of 1e40 erg/s and minimum of 1e35 erg/s. This gives the emission from the M 16 cloud. Add the spectrum of the star to the plot. This is in column 2.

Plot the optical spectrum of the star and cloud

This is the same as the previous spectrum but change the x-axis to range from 0.35 microns to 0.8 microns.

Plot the emissivity of some strong lines

This emissivity, the emission in various lines, is stored in the M16.ems file. The first column gives the depth into the cloud while the rest give the emissivity, erg cm-3 s-1, in various lines. Plot these as a function of depth. Make both axis linear to better predict what the image shows.

Introduce yourself

We will break up into small teams to apply Cloudy to research projects of mutual interest. This introduction will help us get to know one another and identify participants with similar interests.

Help prepare the list of participants - due Friday July 25

We will create a handout giving name, institution, a small photo, and research interests of all participants. Please post a small passport-style photo (mainly your face), your affiliation, a brief statement of research interests, and how you might use Cloudy, to the forum.

Prepare a 4-minute introductory talk - due Friday July 25

We will all give 4-minute introductory presentations on our research interests and a project you might do during the workshop. Please prepare a one-page landscape format (to fit the projector screen) PDF of your talk with your surname as the title and post it to the forum. These will be saved in the participants folder on the class web share and projected when you give your talk.

Astrophysics of Gaseous Nebulae (AGN3)

We will refer to Osterbrock & Ferland 2006. Don always called this AGN3 since it is the third version of the book. Bring your copy if you have one. PDFs of the chapters we will use are in the docs folder of the web share.