Author Information

Joseph HammillFollow

Is this project an undergraduate, graduate, or faculty project?

Undergraduate

individual

Daytona Beach

Poster Session; 5-minute Oral Presentation

Authors' Class Standing

Joseph Hammill, Senior in credits (3rd year)

Lead Presenter's Name

Joseph Hammill

Faculty Mentor Name

Jason Aufdenberg

Streaming Media

Abstract

Understanding the three-dimensional structure of the interstellar medium surrounding stars will always be a challenge due to our single vantage point from the Earth. This situation is aided in the case of an interstellar cloud surrounding a central hot star, where the cloud’s properties can be constrained by an analysis of its spectral-line emission. It is known, from observations by the Wisconsin Hα Mapper (WHAM, Haffner et al. 2003), that such a cloud exists around the star α Virginis (Spica), a concentration of ionized hydrogen with a surface brightness in Hα of roughly 5 Rayleighs (Reynolds 1985). Follow-up observations (Reynolds 1988). provided additional line-brightness ratios, with respect to Hα, including an ionized Sulphur line, [S II] at 671.6 nm. Our goal is to use the photoionization modelling software Cloudy (Ferland et al. 2017) to constrain the geometry of this region by simulating the ionization of a model cloud using realistic stellar atmospheres (Aufdenberg et al. 2020), adjusting model parameters to match Reynolds’ observations. We vary the star’s intensity on the cloud, as well as the hydrogen number density and the filling factor, a measure of the cloud’s “clumpiness.” Thus far, we have matched the observed Hα surface brightness and determined an ionizing flux from α Virginis slightly below Reynolds’ 1985 lower-limit estimate. The research is still ongoing, and the current problem we are facing is the [S II] line is unusually high relative to the primary hydrogen line, Hα. Finding a set of parameters which fits this observation is the next goal for this project.

Did this research project receive funding support (Spark, SURF, Research Abroad, Student Internal Grants, or Ignite Grants) from the Office of Undergraduate Research?

No

Share

COinS
 

Modelling the Interstellar Medium Around α Virginis Using Cloudy

Understanding the three-dimensional structure of the interstellar medium surrounding stars will always be a challenge due to our single vantage point from the Earth. This situation is aided in the case of an interstellar cloud surrounding a central hot star, where the cloud’s properties can be constrained by an analysis of its spectral-line emission. It is known, from observations by the Wisconsin Hα Mapper (WHAM, Haffner et al. 2003), that such a cloud exists around the star α Virginis (Spica), a concentration of ionized hydrogen with a surface brightness in Hα of roughly 5 Rayleighs (Reynolds 1985). Follow-up observations (Reynolds 1988). provided additional line-brightness ratios, with respect to Hα, including an ionized Sulphur line, [S II] at 671.6 nm. Our goal is to use the photoionization modelling software Cloudy (Ferland et al. 2017) to constrain the geometry of this region by simulating the ionization of a model cloud using realistic stellar atmospheres (Aufdenberg et al. 2020), adjusting model parameters to match Reynolds’ observations. We vary the star’s intensity on the cloud, as well as the hydrogen number density and the filling factor, a measure of the cloud’s “clumpiness.” Thus far, we have matched the observed Hα surface brightness and determined an ionizing flux from α Virginis slightly below Reynolds’ 1985 lower-limit estimate. The research is still ongoing, and the current problem we are facing is the [S II] line is unusually high relative to the primary hydrogen line, Hα. Finding a set of parameters which fits this observation is the next goal for this project.

 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.