| 1. |
- Ringqvist, Simon C., 1983-
(författare)
-
Unveiling the Accretion Process at Planetary Masses
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Giant planets have had a long history of radically overturning our expectations of how they form and where they are likely to be found around other stars. In 1995, the first exoplanet detected around a Sun-like star was not found further out from the star, as expected from the locations of Jupiter and Saturn and then current formation theories, but rather on a 4-day orbit with a surface temperature just above the melting point of silver and a radius nearly twice that of Jupiter. Since then we have detected thousands of exoplanets, which have shown remarkable diversity, and imaged the discs around young stars where baby planets are being born. Although there are many common characteristics of these exoplanets and discs, some stand out as outliers. There are systems that are thought ‘too old’ to form planets, or planetary-mass companions that are ‘too big’ in relation to their host stars or should not have had the time to grow that massive to begin with. These are some of the (many) outstanding questions on the frontier of research into planet formation, and in just the past few years we have finally been able to directly observe a few planets that are in the process of forming. In an almost parallel development to the rapid expansion of research into exoplanets, we have also come to realise that brown dwarfs can be excellent analogues to giant planets and contribute significantly to our understanding of both the atmospheres and the formation process of giant planets.This thesis explores several aspects of the dynamics of substellar atmospheres and the accretion process at planetary masses. It discusses the observing methods, which provide the foundations of the photometric and spectroscopic observations that produced the data for the included papers. This is followed by a chapter on star and planet formation and one discussing the variability of substellar atmospheres. The final chapter delves more directly into the observational features of accretion and the tracers and diagnostics which enable us to start qualitatively characterise the accretion process at planetary masses.The first paper presents a NOT/NOTCam photometric survey of ten brown dwarfs, where the goal was to identify new high-amplitude variables that could be suitable for deeper studies. A large fraction was found to be variable, significantly adding to the number of known variable brown dwarfs.In the second paper, integral field spectroscopy obtained with VLT/MUSE of the planetary-mass companion Delorme 1 (AB)b and its host binary star is presented. Very strong hydrogen line emission was detected from the companion, indicative of active accretion in this 40-myr-old system. In the third paper, Delorme 1 (AB)b was further studied by VLT/UVES and R = 50000 spectroscopy. As a result, near-UV hydrogen emission lines were resolved in a planetary-mass companion for the first time. The analysis of these lines strengthened the case for active accretion in the companion.
|
|
| 2. |
- Calissendorff, Per, 1989-
(författare)
-
Characterising Emblematic Binaries at the Lowest Stellar and Substellar Masses
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stars are involved in most research fields of astronomy, ranging from studies of faraway galaxies, exploding supernovae, to more nearby exoplanets and even our own Sun. As such, it is paramount that our physical interpretation of stars is accurate. By observing stars at different epochs, we can fashion evolutionary models to predict important events that occur at different phases during their life-cycle. Thus, exemplary stars where properties including mass, age and luminosity can be observed become increasingly valuable as benchmarks for calibrating said models with. Sometimes, all of these essential properties can be measured for a single system. For instance, for a binary star which circles a common centre of mass we can from its orbital motion calculate the dynamical mass of the system. If the stellar system also has a well-determined age we may use it as a benchmark for our models, and hence refer to it as an emblematic binary system.In this thesis we are searching for exactly these emblematic binaries, both among lowmass stars and substellar brown dwarfs. We also show how to measure the different characteristics that make the systems into exemplary touchstones. We provide an overview over the different types of stellar binaries, how mass and age estimates are performed, as well as discuss the implications multiplicity has for the formation and evolution of stars and brown dwarfs. In Paper I we present the results from an orbital fit we constrained for a low-mass binary with a known age, making into a valuable and relatively rare benchmark. We also show in Paper II how long baseline astrometry can be exploited in order to place better constraints for orbital fits and dynamical masses for low-mass companions to stars by measuring the perturbation in proper motion over time. The dynamical masses are sequentially tested against evolutionary models, which at these low masses display several discrepancies compared to the observables, and are thus questioned. We explore more uncharted mass-regimes in Paper III, where we employ laser guide star assisted adaptive optics to search for multiplicity among faint substellar objects in young moving groups, detecting 3 new young brown dwarf binary systems. These new binaries will prove to be highly valuable systems for future research of brown dwarfs, and will be able to be studied further with for instance the Extremely Large Telescope or James Webb Space Telescope, which also makes them into prominent benchmarks for substellar evolutionary models. Furthermore, age estimation typically dominates the error budget for low-mass stars and brown dwarfs, requiring several different approaches for a robust assessment. In Paper IV we test and compare different techniques for age determination of 7 low-mass binary stars. These binaries have had their orbital motion monitored for a longer time, and will soon be constrained well enough that dynamical masses may be procured. As such, these low-mass binaries will extend the so far scarce number of exemplary systems where both mass, luminosity and age can be determined, to later be used to calibrate theoretical evolutionary models.
|
|
| 3. |
- Viswanath, Gayathri, 1992-
(författare)
-
A Window into the Cradle of Planets : Direct detection and characterisation of young sub-stellar objects using high-contrast tools
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ever since we first laid eyes on the twinkling lights in the night sky, our species began its age-old quest to understand how we came into existence as a planet and what the future holds for it. Most of the traditional formation theories of planets were anchored on the examples drawn from our own solar system. With the surprising and emerging trends among the yet incomplete exoplanet demographics, we are at the wake of a rigorous revision of our theoretical understanding of how planets form and evolve. To form accurate theories however, it is necessary to base them on a planet population that spans the complete range of parameter space not only in terms of its physical properties like mass and orbital separation, but also with respect to the type of stars that host these planets and their age. In this regard, direct detection, whereby you measure photons coming from the planet, helps one get closer to the whole picture since the ideal target population for this technique are young, giant planets in wide orbits that are generally difficult to observe with other detection techniques. Over the last few years, the sensitivity reached by direct imaging observations has seen tremendous improvement owing to the use of high-contrast tools like coronagraphy and adaptive optics. The development of high-resolution spectrographs together with advanced post-processing techniques have recently, for the first time, enabled witnessing planets while in the process of being born, helping us understand how they grow by devouring material from the planetary nursery — a mechanism known as accretion. This is an exciting era for planetary science, with many ongoing as well as planned future surveys with both ground and space-based telescopes dedicated to unravelling the mysteries surrounding the origin of planets. In this thesis, I provide an overview of direct detection as a tool to study sub-stellar objects – a categorisation that includes both planets and brown dwarfs, and whose blurred lines of distinction is a point of contention in astronomy today. I concentrate my discussion on two techniques, high-contrast imaging and high-resolution spectroscopy, both of which have proven significant in the race for planet detection and characterisation. Three scientific research works are carried out as a part of this thesis, using which I highlight the benefits of these techniques in constraining the physical properties of planets and brown dwarfs, as well as obtaining clues to their formation mechanism. In Paper I, I search for a Jupiter-like planet around a nearby Sun-like star that has long eluded imaging surveys, revealing its presence only via its influence on the parent star. I show how the brightness constraints at various separations and multiple wavelengths from the parent star help set a lower limit on the vaguely defined age of the system, in the absence of detection of the planet in our observations. In Paper II, I report the discovery of two low-mass companions to a massive, bright, young star, infer their orbital dynamics from multi-epoch imaging data, and constrain their physical properties using simultaneous low-resolution spectroscopy. In Paper III, I use a high-resolution spectrograph to observe for the first time, resolved Hydrogen and Helium emission lines from a young, isolated planetary-mass object in the midst of formation. Based on analysis of these line profiles, I obtain clues to the possible accretion mechanism at play in this nebulous cosmic phenomenon.
|
|
