YRP PhD Projekte

Supervisors: Torsten Mayer-Gürr (TU Graz), Michael Steindorfer (IWF)
Groups: Theoretical Geodesy and Satellite Geodesy (TU Graz),  Satellite Laser Ranging (IWF)
Keywords: space debris, laser ranging, orbit determination, image analysis

In 2020 [1] first results were achieved performing space debris laser ranging measurements during daylight by visualizing the reflected sunlight from objects against the blue sky background. Improving this technique will be the main objective of this PhD.

The success rate of space debris laser ranging is directly related to the quality of existing predictions, which can be inaccurate up to several hundred meters. To overcome this issue during high-noise conditions at daylight, lateral offsets can be corrected by optically displaying the reflected sunlight of space debris. The successful identification of returns within daylight noise presupposes to time the detector as close as possible to the predicted arrival time. Three potential topics shall be investigated: (1) daylight noise reduction, (2) novel satellite imaging techniques, (3) orbit determination improvement. Polarization filtering aims at reducing the sky background noise based on the degree and direction of the skylight polarization. Event-based sensor technology should be investigated operating at low light conditions. Orbit determination will be performed using the GROOPS software [2]. Improvements using pointing angles (e.g. via plate solving) in addition to space debris laser ranging data should be tackled. Furthermore, the utilization of MHz lasers for space debris laser ranging during daylight shall be investigated.

[1] Steindorfer, M.A., Kirchner, G., Koidl, F., Wang, P., Jilete, B., Flohrer, T. (2020). Daylight space debris laser ranging. Nature Communications, https://doi.org/10.1038/s41467-020-17332-z

[2] Mayer-Gürr, T., Behzadpour, S., Eicker, A., Ellmer, M., Koch, B., Krauss, S., Pock, C., Rieser, D., Strasser, S., Suesser-Rechberger, B., Zehentner, N., Kvas, A. (2021). GROOPS: A software toolkit for gravity field recovery and GNSS processing. Computers & Geosciences, 104864. https://doi.org/10.1016/j.cageo.2021.104864

Supervisors: Birgitta Schultze-Bernhardt (TU Graz) & Luca Fossati (IWF/Uni Graz)
Groups: Coherent Sensing (TU Graz),  Exoplanet Characterisation and Evolution (IWF)
Keywords: experimental physics, laser spectroscopy, atmosphere physics, trace gas detection

The precise knowledge of molecular transitions of species found in exoplanetary atmospheres is of key importance for most astrophysical analysis. For this, absorption strengths and line positions of those molecular gases have been determined for decades from laboratory measurements aiming at an accuracy as high as possible. The spectral resolution achieved so far has not yet been sufficient for all relevant molecular species such as CO, N₂O, C₂H₄, CH₂O, HNO₃.

This PhD project applies dual comb spectroscopy with its broad spectral coverage and its elevated spectral resolution to study molecular gasses of exoplanetary relevance in order to improve the spectral resolution of up to three orders magnitude when compared to state-of-the-art laboratory astrophysical measurements. Depending on the science case, different spectral regions (near infrared, visible, ultraviolet) will be explored. In particular, the accuracy of the line positions will be improved by combining UV dual comb spectroscopy with ultralow temperature measurements for Doppler width reduced measurements. Additionally, a pump probe scheme can be used to study photo-chemical processes in gas species of exoplanetary relevance in real time with femtosecond temporal resolution.

[1] Bernhardt, B., Ozawa, A., Jacquet, P. et al. Cavity-enhanced dual-comb spectroscopy. Nature Photon 4, 55–57 (2010). https://doi.org/10.1038/nphoton.2009.217

[2] Tennyson, J., and Yurchenko, S. N. High Accuracy Molecular Line Lists for Studies of Exoplanets and Other Hot Atmospheres. Front. Astron. Space Sci. 8:795040. https://doi.org/10.3389/fspas.2021.795040

Supervisors: Astrid Veronig (Uni Graz) & Helmut Lammer (IWF/Uni Graz)
Groups: Solar and Heliospheric Physics (Uni Graz),  Solar system planetary physics (IWF)
Keywords: astrophysics, solar physics, programming, data analysis

What can we learn from the Sun about coronal mass ejections on solar-type stars?

Coronal mass ejections (CMEs) are huge expulsions of magnetized plasma observed from our Sun. They are often accompanied by solar flares, i.e. intense flashes of high-energy emission. Solar CMEs are regularly observed by space-based coronagraphs, with an occurrence frequency of several per day. CMEs are the main source of severe disturbances of our outer atmosphere and magnetosphere. On late-type stars, CMEs may be even more massive and frequent, and endager the habitability of their exo-planets – however, their exist hardly any observations. CMEs from the Sun typically cause so-called “coronal dimmings”, i.e. sudden decreases of the coronal emission at EUV and X-ray wavelengths due to the CME mass loss. Recently, coronal dimmings have been also detected on late-type stars.

In this PhD project, a systematic study of the occurrence and recovery of solar coronal dimmings in association with CMEs will be performed. The study will use the wealth of observations from EUV and SXR imagers along with coronagraphs available over almost 3 decades. Using additionally Sun-as-a-star observations from the Extreme-ultraviolet Variability Experiment (EVE) onboard NASA’s SDO, one can also derive the full-Sun Differential Emission Measure in order to infer on the different plasma components. The derived knowledge will be used to better constrain the properties of the underlying CME.   

[1] Veronig, A.M., Odert, P., Leitzinger, M. et al. Indications of stellar coronal mass ejections through coronal dimmings. Nat Astron 5, 697–706 (2021). https://doi.org/10.1038/s41550-021-01345-9

[2] Lammer, H., Lichtenegger, H. I. M., Kulikov, Y. N. et al. Coronal Mass Ejection (CME) Activity of Low Mass M Stars as An Important Factor for The Habitability of Terrestrial Exoplanets. II. CME-Induced Ion Pick Up of Earth-like Exoplanets in Close-In Habitable Zones. Astrobiology 7, 185–207 (2007). https://doi.org/10.1089/ast.2006.0128

Supervisors: Christiane Helling (IWF/TU Graz), Ludmila Carone (IWF), Rumi Nakamura (IWF/Uni Graz)
Groups: Astronomy and Space Science (TU Graz), Exoplanet Weather and Climate (IWF), Space Plasma Physics (IWF)
Keywords: astrophysics, atmosphere physics, programming, multi-lingual

How is the global weather cycle in exoplanets affected by magnetic coupling of their atmosphere?

CHEOPS observations in the optical spectral range have supported early findings of SPITZER observations in the IR that suggest that exoplanet weather and climate cycles may be affected by the presence of a global planetary magnetic field. Our 3D global circulation models show that the equatorial jet can be substantially slowed down and the global weather patterns homogenised in the presence of a magnetic field. Consequently, the whole thermodynamic fluid field of the atmosphere will be affected, and hence, the local chemistry and cloud coverage by magnetic coupling of the atmosphere.  This project aims to explore the link magnetic coupling - atmosphere dynamics - cloud coverage in support of the scientific data interpretation for present (CHEOPS, JWST) and future (PLATO, ATHENA) space missions.

[1] Helling, Ch., Worters, M., Samra, D. et al. Understanding the atmospheric properties and chemical composition of the ultra-hot Jupiter HAT-P-7b. III. Changing ionisation and the emergence of an ionosphere. A&A 648, A80 (2021). https://doi.org/10.1051/0004-6361/202039699

[2] Carone, L., Baeyens, R., Mollière, P. et al. Equatorial retrograde flow in WASP-43b elicited by deep wind jets? MNRAS 496, 3582–3614 (2020). https://doi.org/10.1093/mnras/staa1733