Discovering rare brown dwarf companions to white dwarfs

Qualification: PhD

Department: School of Physics and Astronomy

Application deadline: 21 November 2019

Start date: 28th Septembeer 2020

Overview

Supervisors

Dr Sarah Casewell and Professor Graham Wynn

Project Description

Brown dwarfs are often thought of as failed stars. They form like stars, but never burn hydrogen into helium, and so are degenerate objects the size of Jupiter with masses of up to 70 times that of Jupiter and atmospheres dominated by dust clouds and molecules such as methane and carbon monoxide.  Brown dwarfs are rarely found in close orbits around main sequence stars – a phenomenon known as the brown dwarf desert. Those that are found here are rare, and difficult to study as the main sequence star is much larger and brighter than the brown dwarf companion. 

In order to understand brown dwarfs in these systems more deeply, we can look at their evolved forms - white dwarf-brown dwarf binaries. In these systems the main sequence star has evolved into a giant and engulfed the brown dwarf which has spiralled inwards inside the giant’s envelope. The envelope has then been ejected, leaving the brown dwarf orbiting the white dwarf remnant in a close orbit of a few hours.  

The proximity of the brown dwarf means it is tidally locked to the white dwarf and has a heated dayside and colder nightside – a situation we see in hot Jupiter exoplanets. Indeed, these systems can be used as proxies for heated exoplanets as their Jupiter-like atmospheres get heated in the same way. However, these systems are very rare, as only 8 are known. In order to explore the effects of heating on the brown dwarf atmosphere we need to find more systems with a wider range of white dwarf temperatures and more diversity in brown dwarf atmospheres.

In this PhD you will conduct a search for more white dwarf-brown dwarf systems using multi-waveband all sky surveys, and use imaging and spectroscopy from a wide range of telescopes to characterise and investigate the systems more fully.  At the end of your PhD you will have discovered some of the rarest systems in the universe and investigated their atmospheres, potentially discovering unique cloud systems, differences in day and night side temperatures of over 500 K and evenauroral-like emission caused by irradiation.

References: 

1. The first sub-70 min non-interacting WD–BD system: EPIC212235321, Casewell et al., 2018,MNRAS: http://dx.doi.org/10.1093/mnras/sty245 
2. The direct detection of the irradiated brown dwarf in the white dwarf-brown dwarf binary SDSS J141126.20+200911.1: Casewell et al., 2018, MNRAS: http://dx.doi.org/10.1093/mnras/sty2599 
3. Emission lines in the atmosphere of the irradiated brown dwarf WD0137−349B: Longstaff, Casewell et al., 2017, MNRAS: http://dx.doi.org/10.1093/mnras/stx1786



Funding

Funding

UK/EU applicants

This research project is eligible for a fully funded College of Science and Engineering studentship which includes:

• A full UK/EU fee waiver for 3.5 years
• An annual tax free stipend (For 2019/20 this is currently £15,009)
• Research Training Support Grant (RTSG)

International Applicants

This project is eligible for a partially funded College of Science and Engineering studentship which includes:

• A full UK/EU fee waiver for 3.5 years (applicants will need to provide evidence they can fund the difference between the UK/EU fee and International fee for the duration of their studies)
• An annual tax free stipend of £15,009 (2019/20)
• Research Training Support Grant (RTSG)

Entry requirements

Entry requirements

Applicants are required to hold/or expect to obtain a UK Bachelor Degree 2:1 or better in a relevant subject or overseas equivalent.
The University of Leicester English language requirements apply where applicable.

Informal enquiries

Informal enquiries

Project / Funding Enquiries: csepgr@le.ac.uk 
Application enquiries to pgradmissions@le.ac.uk

How to apply

How to apply

Please use the Apply button at the bottom of the page.  Select September 2020 entry.

Application Notes

We recommend you apply as early as possible so that any missing information can be obtained before the deadline.

In the funding section of the form state CSE2020 Casewell Studentship

In the research proposal section include the name of the supervisors and project title.  If you are applying for more than one project within Physics include details of each project.

In the personal statement section upload your completed CSE Studentship Form.  If you are applying for more than one Physics project complete a form for each project and email the additional forms to csepgr@le.ac.uk together with your application ID number.  If you are applying for projects in other subject areas please submit separate PhD applications online.

Upload a copy of your CV, copies of your degree certificates and transcripts if awarded and evidence of English language proficiency if applicable and available.

If you already have reference letters please upload these. If not enter the contact details of your referees in the reference section. Please ask your referees if they can submit their references as quickly as possible, ideally within two weeks of receipt of our reference request.

Application timetable

21st November Deadline for applications and all supporting documents 
9th December Interview invitations to be sent out by email
w/c 13th January 2020  Interviews
21st January 2020 Informal offers to be made
31st January 2020 Deadline for acceptable of informal offers 
The PGR Admissions Office will notify unsuccessful applicants once a decision has been made

Eligibility

Eligibility

UK/EU applicants

International applicants who can demonstrate that they can fund the difference in UK/EU and International fees