Analyzing the Magnetic Field in the Solar Atmosphere
It greatly influences the processes of energy transport within the solar atmosphere, and dominates the morphology of the solar chromosphere and corona. Kinetic energy from convective motions in the Sun can be efficiently stored in magnetic fields and subsequently released - to heat the solar corona to several million degrees or to blast off coronal mass ejections.
The determination of the conditions in the lower layers of the solar atmosphere (photosphere - chromosphere), including the three-dimensional structure of the magnetic field therein, is the main task within this PhD project. Knowing these accurately is essential for many things, understanding turbulent magnetoconvection, finding out how energy is loaded onto the magnetic field lines that is then transported up to the corona and deposited there, uncovering the secrets of how heavy prominences can stay suspended in the thin corona, or gaining new insights into the solar cycle and solar irradiance variations.
MPS has access to world leading facilities to measure these conditions: the largest available solar telescopes, such as the GREGOR telescope on Tenerife, the Swedish Solar Telescope on La Palma (Spain), or the balloon-borne Sunrise observatory, deliver maps of the emitted solar radiation, displaying details down to scales of about 70 km. Access to data from space borne observatories such as the Japanese Hinode spacecraft extends these rich data sets. For the ground-based observatories SLAM group members have recently built or are building our own, often highly novel instruments, which provide us with outstanding and unique data.
'Freezing' the Earth's Atmosphere with the Fast Solar Polarimeter
Turbulences in the Earth atmosphere cause rapid fluctuations in the quality of the images observed with ground-based telescopes. Observations at extremely high frame rates allow to freeze these seeing fluctuations to deliver polarimetric observations of the solar atmosphere at the theoretical resolution limit of the used telescope.
The Fast Solar Polarimeter (FSP) instrument, developed by MPS in collaboration with the MPG semiconductor lab, allows to perform such measurements. It is based on a dedicated fast and low-noise sensor. The high frame rate of FSP allows to suppress measurement errors caused by e.g. atmospheric turbulence above the telescope (i.e., 'freezing' the atmospheric conditions), and to recover the finest details in solar images.
Solar magnetic fields play a crucial role in driving solar activity, so that their investigation holds a particularly important position in solar physics. As in most branches of astrophysics, we are relying on light as main information carrier also when studying the Sun. Magnetic fields influence the polarization of light through various mechanisms, e.g. through the interaction with atomic momentum (Zeeman effect), or in the context of coherent scattering processes (Hanle effect). The data obtained with FSP will contribute to science questions addressing for example, the total amount of magnetic flux on the Sun, the existence and magnitude of a small-scale turbulent dynamo, or the contribution of small-scale magnetic processes to the energy transfer in the solar atmosphere.
After a successful prototype phase, the final science-ready instrument will be commissioned early 2017 at the GREGOR solar telescope, one of the World’s leading ground-based solar observatories on the island of Tenerife, Spain. In this PhD project you will carry out observations with FSP, and work on the scientific data analysis.
Digging deep: peering into the deepest observable layers of the Sun
The rapid increase of the particle density with depth impedes the escape of photons from deep layers of the solar atmosphere, making the measurement of the physical conditions in these layers extremely difficult. Observations in a spectral region around the opacity minimum, located in the near-infrared region of the solar spectrum, are essential to improve our understanding about the convective processes in the near-surface layers.
The challenge of this PhD project is to first convert high-resolution observations of photospheric spectral lines in the visible and the infrared into reliable, 3D maps of the solar atmospheric conditions, and second to deepen the understanding of the physical mechanisms working in the giant natural plasma physics laboratory, the Sun. Very often comparisons to state-of-the-art magneto-hydrodynamic simulations, performed within the solar group at the MPS, are used to gain insight into these mechanisms.
Unique data from the largest European solar telescope GREGOR, with two major upgrades to perform infrared observations of unprecedented quality in 2018 (IR-FSP and GRIS+), will deliver the information about the conditions in the solar atmosphere in the deepest accessible layers. Complemented with observations from space-based observatories (Hinode, SDO) the 3-dimensional stratification of the solar atmospehre can be reconstructed.
The applicant should have basic knowledge in the fields of spectral line formation (atomic physics, Zeeman effect, radiative transfer), very good programming skills (Python or IDL, C/C++ or Fortran), and should have a good understanding of observational data (e.g. measurement and statistical errors).
Mapping the Sun's mysterious chromosphere and its driver, the magnetic field
Between the photosphere, where most of the solar energy escapes, and the hot Corona, the outer atmosphere of the Sun where the temperature reaches millions of degrees, sits the chromosphere, a layer above the solar surface in which the temperature reaches a minimum before rising again. The chromosphere is characterized by magnetically dominated, highly dynamic structures, but is visible only in a small number of the strongest atomic lines in the solar spectrum. Due to their strength, these lines form in conditions far away from thermal equilibrium, making the interpretation of their line profiles in terms of physical quantities very challenging. Several codes for the interpretation of such spectral lines are currently available for general use, and we are currently developing a new code to extend our capabilities.
Data from the largest European solar telescope GREGOR, and instruments like GRIS+ or the infrared-FSP, will allow the key chromospheric magnetic field to be observed as never before. Obtaining your own data set during one or two observing campaigns on Tenerife will be part of this project.
In this PhD project you observe and record data in a chromospheric line, with the focus on the He 10830 triplet. You will reduce and analyze the data using available interpretation tools or by writing new analysis software. The focus of the project is on the physics and dynamics of solar magnetic structures on and above the solar surface.
Unlocking the Sun's secrets with unique data from the balloon-borne observatory Sunrise
Sunrise is a balloon-borne solar observatory developed under the leadership of MPS. The 1-meter telescope is the largest solar telescope ever to leave the ground, allowing for highest spatial resolution measurements (~70 km on the Sun) in UV wavelength bands not accessible with ground-based observatories.
Two successful flights at an altitude of 37 km around the north pole have delivered a wealth of high-quality data sets. The analysis of these unique data sets has already resulted in numerous high-impact scientific publications, but is far from complete. Large chunks of the data have never been properly looked at so far and likely contain many surprises and discoveries to be made.