Link to the ADS page containing all of my published work
Below is a list of my first-authored publications, including some in preparation, and a brief description of their contents.
Some acronyms that may be helpful:
TESS reveals yet another Stochastic Low Frequency Variable— The Extreme Helium Stars
C. L. Crawford & C. S. Jeffery (2026, in prep)
This article showcases the TESS data for the Extreme Helium Stars, another type of HdC or post-merger star. We find for the first time that these stars are stochastic low frequency variables, which was previously thought to be exclusive to massive stars. We use gaussian process regression to characterize this variability and compare it to stellar parameters.
The highest mass Kepler red giants ─ II. Spectroscopic parameters, the amplitude─activity relation, and unexpected halo orbits
C. L. Crawford et al. (2025) ads link here
This is the second article in a series of work on the high-mass Kepler red giants. In this paper, we focus on the spectroscopic properties of these stars, including atmospheric parameters, select abundances, exotic lines (such as Li), and chromospheric activity indicators. Using this, we confirmed an anticorrelation between surface chromospheric activity and radial mode oscillation amplitudes, which indicates that strong surface magnetic fields weaken stellar oscillations. We also used the Gaia DR3 astrometric data to show that our sample of stars have orbits consistent with all three Galactic kinematic regions, which is interesting considering young stars such as these were not believed to be present in the Galactic Halo.
A comprehensive study of the dust declines in R Coronae Borealis stars
C. L. Crawford et al. (2025) ads link here
Due to the proliferation of known RCB stars in recent years, and the culmination of many years of large-field photometric surveys, there is an unprecedented amount of light curve data available for the RCB type variables that has heretofore not been studied. We have been studied the statistics and properties of the dust-decline events seen in the RCB light curves to characterize the dust formation properties of these stars. We find that the cooler RCB stars have more active dust production than the warmer members, which has been theorized previously using different data. We also find evidence for two distinct dust production mechanisms. This paper contains some work undergone by many undergraduate student projects over the years.
Modelling Hydrogen-deficient Carbon stars in MESA— The effects of total mass and mass ratio
C. L. Crawford, N. Nikultsev et al. (2024) ads link here
This article began as my student’s Honours thesis. This paper describes the generation and analysis of 35 new post-double-white-dwarf-merger models which represent the real, rare phenomenon of the HdC stars. These 35 models vary the initial merger parameters, specifically the total mass and mass ratio of the progenitor binary system. In doing so, we show evidence that the dLHdC stars are likely formed via lower mass mergers than the RCB stars.
The highest mass Kepler red giants - I. Global asteroseismic parameters of 48 stars
C. L. Crawford et al. (2024)
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This is the first of a series of papers I have been working on studying the highest mass red giants from the Kepler sample. These are interesting as they are rare and relatively unstudied. In this paper I define the sample as those stars with masses greater than 3 solar masses. I report their global asteroseismic parameters, and discuss various other asteroseismic measurements that can be made with the Kepler data. I show that these stars are most likely to be core helium burning, that the majority of them show weak or suppressed dipole modes, and that they have fairly large oscillation widths.
A spectral classification system for hydrogen-deficient carbon stars
Courtney L. Crawford et al. (2023)
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This is my doctoral thesis. In the same style as the MK stellar classification system we all know (e.g. OBAFGKM classifications), I’ve created a stellar classification system for RCB and HdC stars using modern techniques (principal component analysis for dimensionality reductuion and K-means clustering). The system classifies all known HdC stars which have been observed at maximum light on their temperature and carbon molecular strengths. I additionally provide commentary on many of the unique optical spectroscopic traits of HdC stars.
Peculiar R Coronae Borealis Stars: Strontium-Rich Stars and the s-Process
Courtney L. Crawford et al. (2022)
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In this work I looked at all of the spectra we have collected of the RCB and HdC stars and discovered a subclass of these stars which show strongly enhanced Strontium spectral features. Three of these stars have the strongest Strontium lines of any known stars. I also explored the potential reason behind the unique s-processing that would have had to occur in these stars.
Modelling R Coronae Borealis stars: effects of He-burning shell temperature and metallicity
Courtney L. Crawford et al. (2020)
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I created 18 MESA models of double white dwarf post-merger objects, where we varied the temperature of the helium burning shell and the metallicity of the star. Through this, we were able to explore how the parameters of a double white dwarf merger will effect the evolution of the resultant star. Additionally, I was able to figure out that the reason RCB stars show partial helium burning products on their surfaces was because of a unique pattern in the convection of the envelope of the star. This same result was shown later in a different type of model, implying that this is likely inherent to the evolution of the post-merger-object and not specific to the type of model that we created.