Solar, stellar and planetary astrophysics in DAMTP

Lead Research Organisation: University of Cambridge
Department Name: Applied Maths and Theoretical Physics

Abstract

The Sun's magnetic field can be seen at the surface through the appearance of sunspots, which are also associated with solar flares and prominences. Sunspot activity is not constant, but waxes and wanes on an 11-year timescale. Disordered magnetic fields can be maintained by the turbulent motions of the plasma making up the outer part of the Sun, but the cyclical behaviour shows coherence between the two hemispheres and is clearly a global process operating throughout this convective zone. It is not clearly understood how the magnetic field organizes itself to produce such large-scale cyclical behaviour. A natural large-scale effect is provided by the internal rotation of the Sun, which varies rapidly near the base of the convection zone about two-thirds of the distance to the surface. Our work is devoted to producing a model of cyclical activity that draws its energy from this shearing motion and produces the rising magnetic field structures that eventually emerge as sunspots through the mechanism of magnetic buoyancy. Together with a simplified description of the effect of the convection, this model, which will be solved numerically, is expected to lead to a self-sustaining magnetic field with large-scale features that can be compared with solar behaviour.

Discs of matter orbiting around a central mass are found in numerous astronomical settings, including protoplanetary discs of dusty gas surrounding young stars, where planets are formed, high-energy plasma accretion discs around black holes, and more familiar examples such as Saturn's rings and spiral galaxies. A great variety of planets and planetary systems continue to be discovered around other stars. We propose to investigate several aspects of the dynamics of astrophysical discs, the physics of planet formation and the dynamics of extrasolar planetary systems. We will study the properties of turbulence, magnetic fields and vortices in discs, and the behaviour of discs that are not circular and flat. We will investigate the tidal interaction between extrasolar planets and their host stars, which can strongly heat or even destroy the planets, and the interaction of planets and discs, which can greatly modify the size and shape of the planets' orbits. All this work is related to current observations.

One of the outstanding problems in solar physics is to understand how the solar corona is heated. We know that the magnetic field plays a key role in transporting and transferring energy from beneath the solar surface into the solar atmosphere. This happens on many scales from nanoflares to microflares, major flares, prominence eruptions and coronal mass ejections. However, we do not yet fully understand how magnetic energy is converted into thermal and kinetic energy. Recent observations show that the solar atmosphere is highly dynamic; imaging instruments (SoHO/EIT, TRACE, Stereo, Hinode/XRT and more recently SDO/AIA) have provided spectacular high-spatial-resolution images and high-cadence movies. These suggest that equilibrium models may not be appropriate and non-equilibrium effects may need to be revisited, for example transient ionization and recombination and non-Maxwellian electron distributions.

EUV (and X-ray) spectroscopy, combined with atomic physics calculations, is playing a major role in the field of solar physics. It is enabling the physical parameters of the plasma (temperature and electron density distributions, flows, elemental abundances and non-thermal broadening) to be determined and constraints to be placed on the various heating models. For the first time, we have spectroscopic observations from the SOHO, Hinode and SDO satellites detailed enough that we can directly compare observable quantities with those predicted by theoretical modelling, at least for coronal loops and flares. Also, for the first time, we can link the coronal properties with the evolution of the magnetic field as is observed in the photosphere while emerging.

Planned Impact

Theme 1. A detailed understanding of solar processes is essential in predicting magnetic events on the Sun, which in turn have very significant consequences for the Earth's magnetosphere, affecting the weather and electronic communications. The construction of a solar dynamo model with realistic features will enable detailed prediction of the relationship between solar activity and sunspot numbers and shed new light on modulations of the cycle, as exemplified by the anomalous behaviour of the current cycle 24. The expected reduction in solar activity is expected to have a small but significant cooling effect on the Earth's climate, though this will not counteract global warming caused by burning fossil fuels.

Theme 2. The study of extrasolar planetary systems and of planet formation has a significant cultural impact. It broadens our horizons, illuminates our origins and helps to define our place in the Universe.

Theme 3. Some of the atomic data and diagnostics techniques that we will make available will be used by magnetic fusion laboratories around the world, by research laboratories and industry.

All of our research is regularly communicated to the general public through DAMTP Open Days and the University of Cambridge Science Festival. Dr Helen Mason is especially involved in outreach activities, through public lectures and the Sun|trek project (www.suntrek.org), to which Dr Giulio Del Zanna has also contributed. This is a major educational website about the Sun and its effect on the Earth, aimed at students aged 11-16.

Publications

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Barker A (2014) THEORY AND SIMULATIONS OF ROTATING CONVECTION in The Astrophysical Journal

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Barker A (2016) Non-linear tides in a homogeneous rotating planet or star: global modes and elliptical instability in Monthly Notices of the Royal Astronomical Society

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Barker A (2014) Hydrodynamic instability in eccentric astrophysical discs in Monthly Notices of the Royal Astronomical Society

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Barker A (2015) On the vertical-shear instability in astrophysical discs in Monthly Notices of the Royal Astronomical Society

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BenMoussa A (2013) On-Orbit Degradation of Solar Instruments in Solar Physics

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Braviner H (2015) Tidal interactions of a Maclaurin spheroid - II. Resonant excitation of modes by a close, misaligned orbit in Monthly Notices of the Royal Astronomical Society

 
Description We have significantly improved the CHIANTI atomic database with new atomic data, much of which has been calculated by us. We have shown that the completeness and accuracy of atomic data significantly affect the scientific return of current space missions. We have also carried out several new studies on non-equilibrium effects on plasma.

We have improved our understanding of flaring plasma, combining imaging with spectral data from current space missions (Hinode, SDO, IRIS), focusing on the chromospheric evaporation process but also on the plasma response to heating, with hydrodynamic simulations that took non-equilibrium ionisation into account.

We have developed new theoretical models of the local dynamics of astrophysical discs that are either warped or elliptical, so generalizing the very successful shearing-box model. We have shown that warped and elliptical discs are hydrodynamically unstable, presumably leading to turbulent motion.

We have studied the launching of jets and winds from magnetized astrophysical discs, and helped to elucidate the connection between the magnetorotational instability and the launching process.

We have used numerical simulations of turbulent magnetized discs to understand how thermal instability and accretion outbursts operate in the presence of turbulence.

We have used semi-analytical models of turbulent magnetized discs to determine how the rate of radial transport of magnetic flux in an accretion disc depends on the strength of the field.

We have studied the dynamical tides that are forced in short-period exoplanets and their host stars, taking into account their rotation and internal structure. We have computed the resulting dissipation rates, which determine the rate at which the orbits of exoplanets undergo circularization, alignment and decay.
Exploitation Route The atomic data that are calculated and benchmarked by the Atomic Astrophysics group at DAMTP have a wide distribution and are used not just within astrophysics, but also by fusion research via the ADAS consortium, the main diagnostic modelling package found at all major fusion laboratories in the world (including the European JET and ITER). The CHIANTI atomic data have been made available to VAMDC (www.vamdc.eu), a large European consortium of providers of atomic and molecular data. VAMDC data are used by a very wide community, including industries that are researching and developing new light sources.
Sectors Energy

 
Description The CHIANTI atomic data have been made available to VAMDC (www.vamdc.eu), a large European consortium of providers of atomic and molecular data. VAMDC data are used by a very wide community, including industries that are researching and developing new light sources. Given the possible consequences to the economy and society of "disruptive" space weather, there is a huge demand from industry to engage with academia to protect systems. Indeed space weather has received much attention in the UK in the past few years. Solar flares are the main sources of space weather events, so understanding them is of paramount importance.
First Year Of Impact 2015
Sector Energy
Impact Types Societal,Economic

 
Description BBC 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact BBC programmes featuring Helen Mason:
- Seven Ages of Starlight (BBC4), August 2013
- Science Britannica (with Brian Cox) (BBC2), October 2013
- Midweek (with Libby Purves) (Radio 4), April 2013


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Year(s) Of Engagement Activity 2013
 
Description Big Ball of Fire 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact iBook "Big Ball of Fire" launched in March 2014. Produced by students at Eastlea Community College, East London, with the help of Helen Mason.

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Year(s) Of Engagement Activity 2014
 
Description Helios Storm Scenario Report 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Dr Helen Mason acted as a consultant to the Helios Storm Scenario Report prepared by the Cambridge Centre for Risk Studies London Risk Briefing. The Centre's new stress test, Helios Solar Storm Scenario, examines the potential business and industry impacts of an extreme space weather event affecting Earth. The scenario's subsequent power-loss amongst value-added activities in the United States is estimated between $220 billion to $1.2 trillion across scenario variants. The study finds that the total direct after- shock of the storm may give rise to consequential market disruption with the manufacturing and financial insurance sectors most negatively impacted.
Year(s) Of Engagement Activity 2016
URL https://www.jbs.cam.ac.uk/faculty-research/centres/risk/news-events/events/2016/understanding-the-he...
 
Description IOP event "Taking control of your career as a female physicist" 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Undergraduate students
Results and Impact Dr Helen Mason gave a keynote speech at an event organized by the Institute of Physics to offer advice to female undergraduates, PhD students and very early-career academics. She described the early steps in her career, from undergraduate studies at Queen Mary College, London to a PhD and then a postdoc at University College London, which she transferred to the University of Cambridge when her husband's job moved to the city. About 60 female physics undergraduates from all over the UK attended the talk, which encouraged female physicists to look at a diversity of career options, including academia and beyond, when they complete their BSc. The students were very eager to talk to Dr Mason about different aspects of their careers.
Year(s) Of Engagement Activity 2016
URL http://www.iop.org/news/16/nov/page_68558.html
 
Description Royal Institution 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Friday Evening Discourse at the Royal Institution by Helen Mason: Our Dynamic Sun, 23rd April 2013

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Year(s) Of Engagement Activity 2013
 
Description Seven Ages of Starlight 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact Helen Mason featured in the BBC4 programme 'Seven Ages of Starlight', broadcast autumn 2012

The programme reached 795,000 viewers
Year(s) Of Engagement Activity 2012
 
Description Space to Earth Challenge 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Production of new resources for UK schools relating to solar research for the Space to Earth Challenge, linked to Tim Peake's flight on the ISS
Year(s) Of Engagement Activity 2015
URL http://www.spacetoearthchallenge.org.uk
 
Description Sun|trek classroom projects 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact A set of new projects for schools using real solar data by Helen Mason and Miriam Chaplin

http://www.suntrek.org/classroom-projects/Projects-for-schools-using-real-solar-data.shtml
Year(s) Of Engagement Activity 2012