Faint signals from bright sources: identifying high-frequency waves in the Sun

Background

The Sun is the brightest object in the sky, and hence one would imagine it is straightforward to obtain very high quality solar observations, in terms of signal-to-noise. However, this is not the case. Although the Sun appears to be constant in the sky, it is highly dynamic in nature, with various processes (such as mass and wave motions) occurring over very small areas and time periods. Given this, very high spatial and temporal resolution observations are often required, particularly to fully investigate highly dynamic processes. Such data are provided by, for example, the Rapid Oscillations in the Solar Atmosphere (ROSA) instrument, which can observe simultaneously in 7 wavebands at a time resolution of up to 33 milliseconds and spatial resolution (following image reconstruction) of up to 0.11 arcseconds (85 km on the solar surface). The Hydrogen-Alpha Rapid Dynamics camera (HARDcam) can achieve a temporal resolution of up to 5 milliseconds at a spatial resolution of 160 km. Both of these instruments were developed by the PhD project supervisor (Dr David Jess) and are situated at the Dunn Solar Telescope (DST) in New Mexico. However, as the instruments observe a very small fraction of the solar surface (typically smaller than 10-8 of the total) at high cadence, the resulting signals are faint.

Some regions of the solar atmosphere are also intrinsically faint, specifically the solar corona, which is only visible to the naked eye during total solar eclipses as a halo of white light surrounding the Sun. The corona is extremely hot (several million K), while the solar surface only has a temperature of ~6000 K. Clearly, some heating mechanism is in place which continuously deposits energy in the corona, so that it can maintain its high temperature. However, investigations of possible mechanisms are limited by the faint signals obtained from the coronal plasma. This is the topic of the PhD project – using new computer algorithms, specifically designed to analyse faint solar signals, to investigate the heating mechanisms for the corona.

Project

What is the physical mechanism responsible for heating the solar corona? has been a major unanswered question in science since the 1930's when its high temperature was discovered. However, it is believed to involve high-frequency waves (specifically, those which occur more often than every 2 seconds), with the wave motion transporting energy from the surface of the Sun to the corona. These waves are predicted to be observed as changes in the intensity of the light emitted from solar material, and/or the speed at which the material is moving. However, these variations would also occur over relatively small distances (a few thousand km) on the surface. Hence to detect these waves one must observe the Sun at both high time and spatial resolution. Consequently, as previously noted the signals we measure in such solar observations are very weak, in particular for the corona itself which is intrinsically faint.

Techniques previously employed to analyse these observations are not suitable for dealing with faint signals, and hence unsurprisingly no high-frequency waves have been detected to date. The PhD student will apply new analysis techniques to faint solar data, particularly for total eclipses, to search for and identify high-frequency waves and hence definitively address the long-standing problem of how the corona is heated. Specifically, the student will:

  • Obtain high time and spatial resolution solar observations suitable for searching for wave motions that heat the corona. The time resolution of the data will be at least 0.3 seconds, and up to 0.03 seconds, and the spatial resolution at least 3000 km on the solar surface, and down to only 16 km using the new 4-m diameter Daniel K Inouye Solar Telescope in Hawaii that will have first-light in early 2020. Observations of total solar eclipses are particularly important. We already have data in hand for the 21 August 2017 eclipse in the USA, plus earlier events in 1999 and 2001, obtained with our instruments. Observations will also be obtained by the student for the total eclipses of 14 December 2020 in South America and 20 April 2023 in Indonesia.
  • Apply new computer algorithms, specifically aimed at reliably detecting high-frequency waves in faint signals, to the range of solar observations discussed above. The aim is to search for and identify variations in the intensity of light emitted from the solar material, and/or the speed at which the material is moving, indicative of high-frequency waves capable of heating the solar corona. In particular, we seek to identify those waves occurring more often than every 2 seconds.

Funding is provided within the PhD studentship for travel to, and participation in, eclipse campaigns in 2020 and 2023, as well as key astrophysics conferences. It is envisaged that the student will actively engage in both national and international meetings and workshops, where they will disseminate their cutting-edge research to a global audience. As a result, the ability to travel and work within a team environment is a crucial component of the research objectives.

Studentship details

We will normally only consider applicants holding, or expecting to obtain in 2020, a UK MSci (or equivalent) degree in physics, astronomy or a related scientific discipline with 2.1 or higher classification (or international equivalent). It is essential that you read and follow the appropriate application instructions, which can be found here: https://star.pst.qub.ac.uk/wiki/doku.php/public/phds2020

The deadline for applications is Friday 14th February 2020. All applications received by then will be reviewed immediately, with interviews to be held shortly thereafter. It is expected that the successful PhD applicant will commence their study at QUB in October 2020, although an earlier start is also possible.

Note that this 4-year studentship, funded by the Leverhulme Trust, will pay full fees and living expenses for EU citizens.

If you have any questions, please contact Dr David Jess (email address below).

Contact

Lead supervisor (QUB): Dr David Jess d.jess@qub.ac.uk

Co-supervisor (QUB): Prof Mihalis Mathioudakis m.mathioudakis@qub.ac.uk

public/phds2020/2020_jess.txt · Last modified: 2019/12/11 12:24 by Stuart Sim

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