Research Projects

My scholarly interests revolve around stars -- specifically, stars that are significantly more massive than the Sun.

Below I share some of my favorite projects from over the years, beginning with ongoing work. A full list of publications can be found on the ADS.

Here is the key to text formatting for published works:


B-type Star Spectral Classification

My ongoing work is classifying optical spectra of bright B-type stars. This is actually a re-classification project, as the source catalogs I am drawing from (the Bright Star Catalog and Henry Draper Catalogue) made spectral classifications public years ago. However, the advent of digital spectra has made re-classifying stellar spectra necessary. Below are some highlights; n.b. some of the work presented in sections lower down started here.

  • The Sacramento Mountains Spectroscopy Workshops ended up being a fruitful opportunity to share spectroscopy with amateur astronomers. In my two talks, given in 2018 and 2019 respectively, I introduced attendees to some of the physics of stellar spectra, principles of spectral classification, and astrophysical rewards of studying spectra of stars.
  • We provided spectral classifications of Be stars for a more profound study (with students Amy Glazier, Sophie Anderson, and Anthoni Caravello ): Labadie-Bartz, Chojnowski, Whelan et al., 2018, AJ, 155, 53.


Binary and Multiple Star Systems

Spectra are particularly useful for revealing information about stars in orbit about one another. What may appear as one star to the naked eye, or through a telescope, can actually be made up of two or more stars. Knowledge of the Doppler Effect and the lines associated with different spectral types help us to reveal the truth.

  • I was curious if δ Scuti stars in close binary systems exhibited major differences from those without binary companions; honors student Brett Skinner demonstrated that there were no statistically significant differences between δ Scuti stars in and out of binaries.
  • I gave a couple of students a project to spectrally classify the three stars in Algol. There had been some question lingering in the literature about the nature of the third star in the system, Algol C. Having resolved the dispute to our satisfaction, one of the students went on to lead our publication of the result: Frank, Whelan, & Junginger, 2022, JAAVSO, 50, 123.
  • When we discovered that the A1V star HD 63021 exhibited Balmer line emission, making it an Ae star, we were happy at the discovery. When we further discovered that it was a source of X-ray emission, we were perplexed. After follow-up observations, we concluded that this bright star not known for anything in particular was a mass-transfering binary. Whelan, Chojnowski, Labadie-Bartz, et al., 2021, AJ, 161, 67 (with student Gary Casey).
  • Honors student Emma Page investigated how to discover binary stars using spectral energy distributions (SEDs), and then she quantified those SEDs based on each stars' known photometric variability type.
  • How many other secrets are waiting to be revealed in the bright sky?

The above animation is courtesy of Jessica Junginger.

Image credit: Figure 6 from Chojnowski et al. (2015)

Be, Bp/Ap, and Magnetic Stars

This is the miscellaneous collection of weird B-type stars. The emission-line B-type stars (Be) are generally fast-rotating and oftentimes spewing matter off their surfaces. The chemically peculiar stars (Bp/Ap) suffer from chemical anomalies resulting from specific physical traits interiorly. The magnetic stars are usually revealed by means of abnormally strong or weak helium lines.

  • I discovered a Be star using the Adams Observatory: Whelan & Baker, 2017, JAAVSO, 45, 60.
  • Honors student Amy Glazier tested whether a simple-seeming photometric method could be used to identify Be stars.
    • She won the 2017 Chambliss Award at the AAS meeting for her poster presentation.
  • Drew Chojnowski discovered a whole bunch of Be stars within the APOGEE dataset: Chojnowski, Whelan, Wisniewski, et al. 2015, AJ, 149, 7; Chojnowski, Wisniewski, Whelan, et al. 2017, AJ, 153, 174.
  • Drewski also lead a study on Bp stars observed with APOGEE, and discovered the rigidly-rotating magnetosphere stars discussed in Eikenberry et al. (2014) and Wisniewski et al. (2015).
  • Is it a massive Herbig Be star, or a B[e] supergiant? We discussed star Cl* NGC 346 KWBBE 200 as part of a wider study on the dust properties of stars in N66, Whelan et al. 2013, ApJ 771, 16 sections 4.1.2 and 4.3.
  • Modeling the molecular emission from the Herbig Be star 51 Ophiuchi's circumstellar disk: Berthoud, Keller, Herter, Richter, & Whelan 2007, ApJ, 660, 461.


Optics

Optics is a practical pursuit for me; though recently I have taken a deeper interest in the field for its own sake.

  • When we were studying photometric methods for detecting Be stars (see above), we strongly suspected that one of our filters was a bit wonky. Charles Rambo quantified the throughput of the suspect filter and discovered that the issue was a major one.
  • Spectrograph design: more soon
  • Optical properties of matter in unusual distributions: more soon


NGC 346 in the Small Magellanic Cloud. Image Credit: Webb Space Telescope

Gas and Dust in Star-Forming Regions

The Spitzer Space Telescope was good at detecting light originating between stars -- particularly light from interstellar dust grains. This, in turn, made it a seminal tool for studying the environments in which stars form. Many, but not all, of the following studies depended upon this telescope.

  • Modeling and Observations of Massive Star Cluster Formation: This dissertation theorizes the earliest stages of star formation in massive clusters, and studies some of these clusters' dust and gas emission properties.
  • NGC 346 is a massive cluster of stars in the Small Magellanic Cloud. Among the many things that we discovered, perhaps the most interesting is evidence for ongoing photoprocessing of the dust by the young, hot stars in the region: Whelan, Lebouteiller, Galliano, et al., 2013, 771, 16.
  • Dust grain radiative energy transfer models of the matter surrounding massive star clusters, with predictions for future observations: Whelan, Johnson, Whitney, et al. 2011, ApJ, 729, 111.
  • Comparative studies of massive star-forming regions in different environments, with foci of dust grain properties and elemental abundances respectively: Lebouteiller et al. 2011, ApJ, 728, 45; Lebouteiller et al. 2008, ApJ, 690, 398.
  • It turns out that young star-forming clusters exude just as much light from the gas between the stars as from the stars themselves: Reines, Nidever, Whelan & Johnson 2010, ApJ, 708, 26.


Galaxies

The only galaxies that have interested me to date are called starburst galaxies -- those that are actively forming large numbers of stars.

  • The Antennae galaxies are colliding, and in their overlap region they are actively creating millions upon millions of stars. The very youngest, hottest, brightest stars in the galaxy come from this overlap region: Brandl et al. 2009, ApJ, 699, 1982.
  • NGC 6052 also has an overlap region, and we conclusively showed that the brightest regions are where hot, new stars are forming, off of the galactic nuclei (which is usually the brightest place in a galaxy): Whelan et al. 2007, ApJ, 666, 896.

Different wavelengths of light reveal different bright spots in NGC 6052. Image credit: Figure 4 from Whelan et al. (2007)


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