Solving the Ubiquitous Problem of Stellar Radii

Lead Research Organisation: University of Exeter
Department Name: Physics


The student will primarily use optical and infrared data to study populations of recently formed stars in the Milky Way to better understand the physics of star formation and to study the planet-forming discs which surround them. We will use GAIA to study the medium-term variability of the stars, in addition to follow-up ground-based studies. We will use wide-field survey data to study population statistics.


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publication icon
Hillenbrand Lynne A. (2018) Gaia 17bpi: An FU Ori-type Outburst in The Astrophysical Journal

Studentship Projects

Project Reference Relationship Related To Start End Student Name
ST/N504063/1 01/10/2015 30/09/2020
1635907 Studentship ST/N504063/1 01/10/2015 31/03/2019 Samuel Arthur Morrell
Title Spectroscopic and photometric observations of M dwarf stars in the Pleiades and Praesepe 
Description This dataset contains spectroscopic and photometric observations of a sample of stars within the Pleiades and Praesepe open clusters. This dataset has contributed a large amount to our research on the evolution of low-mass stars within the clusters. This dataset is notable for robust flux calibration, meaning that we can compare directly to models of stars. Because of this, we have been provided insight into the physics of M dwarf stars that has lead to the genesis of two publications that are currently in preparation. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? No  
Impact This dataset has allowed us to make direct comparisons to models of stars and note the differences between them. From this we have been able to study the differences in physics between real observations and the model simulations of the same stars. From these studies we have been able to determine and confirm that these kind of stars are larger than model predictions, which has a large impact on many areas of astronomy, such as stellar and plentary evolution, exoplanet discovery and characterisation, and exoclimatology. 
Title Stellar radii for late-K and early-M dwarf stars 
Description Using optical / near-infrared / mid infrared photometry and gemetric distances from Gaia DR2, we have been able to assemble a catalogue of 15 365 stars for which we have determined the radii using a method and piece of software that we developed for this project. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? No  
Impact This catalogue of stars has allowed us to perform extensive studies of the properties of main sequence stars. First we have been able to study the correlations between both radius and activity to help determine what physics is driving the radius inflation of main sequence M-dwarfs. This can then feedback on and inform the next generation of stellar models - which are crucial for many different fields of astronomy. In the more short term, this database can be used by exoplanet scientists to determine the radii of their exoplanet host stars, and hence the exoplanets which orbit them. As the stellar models under perform in this respect, accurate radii are invaludable to the current slew of exoplanet characterisation surveys that are currently hunting for Earth-like planets around this type of star. 
Title Photgrid 
Description This software is a suite of tools that was written for this project and facilitaties the fitting of photometry in order to yield the radius and temperature of a star. This works with distances, which are now provided in abundance by the geometric distances from Gaia Data Release 2. Using this software we have been able to accurately fit the radii of between M and A spectral types. The technique generalises well to many distances and is tollerant to poor quality photometry, as well lacking photometry in one or several of the fit bands. Othe pieces of software in the package have been developed to pre-process stellar atmosphere models to produce grids of synthetic photometry with which to fit, as well as tools to help post-process and analyse results files output by the code. 
Type Of Technology Software 
Year Produced 2018 
Impact Based on our testing, this software is able to accurately determine the radii of relatively faint stars, inaccessible to other methods of radius determination. This permits us characterisation of large samples of stars, given accurate stellar atmospheres. In this case, the software has been applied to studying the M-dwarf inflation problem. We have also applied to characterising exoplanet host stars with great success. We have shown that this software can be used to obtain accurate radii M-dwarf, which are the prime targets for the next generation of exoplanet hunting and characterisation campaigns. This software or technique could be applied to this in order to make exoplanet host parameters more accurate than current means. In addition, the software has permitted us to better understand M-dwarf stars which will feedback into and inform the work of the stellar modelling community when developing the next generation of models.