Multi-wavelength observations of planet forming disks: Constraints on planet formation processes

Our understanding of protoplanetary disks has greatly improved over the last decade due to a wealth of data from new facilities. Unbiased dust surveys with Spitzer leave us with good constraints on the dust dispersal timescale of small grains in the terrestrial planet forming region. In the ALMA era, this can be confronted for the first time also with evolutionary timescales of mm grains in the outer disk. Gas surveys in the context of the existing multi-wavelength dust surveys will be a key in large statistical studies of disk gas evolution. Unbiased gas surveys are limited to ALMA CO submm surveys, where the quantitative interpretation is still debated. Herschel gas surveys have been largely biased, but [OI] 63 mic surveys and also accretion tracers agree qualitatively with the evolutionary timescale of small grains in the inner disk. Recent advances achieved by means of consistent multi-wavelength studies of gas AND dust in planet forming disks reveal the subtleties of the quantitative interpretation of gas surveys. Observational methods to determine disk masses e.g. from CO submm lines require the knowledge of the dust properties in the disk. Understanding not only the gas evolution, but also its chemical composition will provide crucial input for planet formation models. Kinetic chemical results give profoundly different answers than thermodynamic equilibrium in terms of the C/O ratios as well as the water ice/rock ratios. Again, dust has a key impact on the chemical evolution and composition of the gas. Grain growth for example affects freeze-out processes and strongly increases the cosmic ray induced UV field.Comment: appears in the proceedings of the conference "The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life", October 17-20, 2017, Tokyo, Japa

Dust radiative transfer in protoplanetary disks with PHOENIX/3D

Scheiben um junge Sterne im niedrigen/mittleren Massenbereich werden oft protoplanetare Scheiben genannt, da sie als die Geburtsstätte von Planeten gelten. Für das Verständnis der komplexen Struktur dieser Scheiben und deren Zusammensetzung sind aufwendige und genaue Strahlungstransportmodelle notwendig. Diese Arbeit ist Teil eines größeren Projektes das sich eine möglichst umfassende Modellierung von „statischen", bestrahlten protoplanetaren Scheiben mit Hilfe des 3D Strahlungstransportcodes PHOENIX/3D zum Ziel gesetzt hat. Diese Arbeit beschränkt sich auf den 3D Staubstrahlungstransport und die Bestimmung der Temperaturstruktur der protoplanetaren Scheibe. Wir präsentieren eine neues Verfahren für die Bestimmung der Temperaturstruktur unter der Annahme von Strahlungsgleichgewicht. Die Implementierung des Verfahrens basiert auf der Benutzung des „Approximate Lambda"-Operators der in PHOENIX/3D für das Strahlungstransportproblem verwendet wird. Für die Überprüfung der Korrektheit unserer Methode wurde der Benchmark Test von Pinte et al. 2009 gewählt. Das neue Verfahren zeigt gute Konvergenzeigenschaften und konvergiert für alle vier Testfälle des Benchmarktests. Für den Großteil der Scheibe wurde eine gute Übereinstimmung der Resultate festgestellt. In den tiefen inneren Regionen der Scheibe, in die die Strahlung des Sternes nicht vordringen kann, sind die von PHOENIX/3D ermittelten Temperaturen aber zu hoch. Die Abweichungen liegen, abhängig von der Masse der Scheibe, im Bereich von +20% bis +65%. Momentan kann die Abweichung nur mit einer größeren Anzahl von räumlichen Gitterpunkten verringert werden. Das erfordert aber eine großen Rechenaufwand. Für die praktische Anwendung des Verfahrens ist deshalb eine Verbesserung der Genauigkeit und der Performance notwendig.Disks around young low/intermediate mass stars are often called protoplanetary disks as they are considered to be the birthplaces of planets. To understand their complex structure and composition accurate radiative transfer modelling is necessary. This thesis is part of a larger project for modelling of passive, irradiated protoplanetary disks with the stellar atmosphere code PHOENIX/3D. This work is limited to the 3D dust continuum radiative transfer including the calculation of the disk temperature structure. We present a new method for solving the radiative equilibrium equation based on the Approximate Lambda-Operator technique used in PHOENIX/3D for the radiative transfer problem. To test our implementations we use the benchmark problem defined in Pinte et al. 2009. The new temperature correction scheme shows good convergence properties and converges for all four test cases defined in the benchmark. For large areas of the disk the results of the new scheme are in good agreement with the results of the benchmark. However, in the deep inner region of the disk, where the stellar radiation does not penetrate, the estimated temperature is always too high. The deviations depend on the optical depth, ranging from +20%, for the lowest optical depth test case to +65% for the highest optical depth test case. To overcome this problem large spatial grids are necessary, which increases the computational needs, and therefore, becomes unreasonable at least for the highest optical depth test cases. So, further improvements concerning the accuracy and the performance are required

Spatially selecting single cell for lysis using light induced electric fields

An optoelectronic tweezing (OET) device, within an integrated microfluidic channel, is used to precisely select single cells for lysis among dense populations. Cells to be lysed are exposed to higher electrical fields than their neighbours by illuminating a photoconductive film underneath them. Using beam spot sizes as low as 2.5 μm, 100% lysis efficiency is reached in <1 min allowing the targeted lysis of cells

Episodic excursions of low-mass protostars on the Hertzsprung-Russell diagram

Following our recent work devoted to the effect of accretion on the pre-main-sequence evolution of low-mass stars, we perform a detailed analysis of episodic excursions of low-mass protostars in the Hertzsprung-Russell (H-R) diagram triggered by strong mass accretion bursts typical of FU Orionis-type objects (FUors). These excursions reveal themselves as sharp increases in the stellar total luminosity and/or effective temperature of the protostar and can last from hundreds to a few thousands of years, depending on the burst strength and characteristics of the protostar. During the excursions, low-mass protostars occupy the same part of the H-R diagram as young intermediate-mass protostars in the quiescent phase of accretion. Moreover, the time spent by low-mass protostars in these regions is on average a factor of several longer than that spent by the intermediate-mass stars in quiescence. During the excursions, low-mass protostars pass close to the position of most known FUors in the H-R diagram, but owing to intrinsic ambiguity the model stellar evolutionary tracks are unreliable in determining the FUor properties. We find that the photospheric luminosity in the outburst state may dominate the accretion luminosity already after a few years after the onset of the outburst, meaning that the mass accretion rates of known FUors inferred from the bolometric luminosity may be systematically overestimated, especially in the fading phase.Comment: 15 pages, 12 figure

The effect of metallicity on the abundances of molecules in protoplanetary disks

We study the influence of different metallicities on the physical, thermal, and chemical properties of protoplanetary disks, and in particular on the formation and destruction of carbon-based molecules. With the thermo-chemical code ProoDIMO we investigate the impact of lower metallicities on the radiation field, disk temperature, and the abundance of different molecules (H$_2$O, CH$_4$, CO, CO$_2$, HCN, CN, HCO$^+$ and N$_2$H$^+$). We use a fiducial disk model as a reference model and produce two models with lower metallicity. The resulting influence on different chemical species is studied by analyzing their abundance distribution throughout the disk and their vertical column density. Furthermore, the formation and destruction reactions of the chemical species are studied. The results show a relation between the metallicity of the disk and the strength of the stellar radiation field inside the disk. As the metallicity decreases the radiation field is able to penetrate deeper regions of the disk. As a result, there is a stronger radiation field overall in the disk with lower metallicity which also heats up the disk. This triggers a series of changes in the chemical formation and destruction efficiencies for different chemical species. In most cases, the available species abundances change and have greater values compared to scaled-down abundances by constant factors. Metallicity has a clear impact on the snowline of the molecules studied here as well. As metallicity decreases the snowlines are pushed further out and existing snow rings shrink in size.Comment: 19 pages, 18 figure

Spectroscopy of the circumplanetary disk around the young planet-mass companion CT Cha b

Several planet-mass companions (PMCs) on wide-orbits have been imaged around young stars (1-10 Myr). Their estimated mass is just around the brown dwarf to giant planet transition (~13 Jupiter masses), which makes them especially interesting for both star and planet formation theories. Several formation scenarios exist, but none of them can explain all properties of the currently known PMCs. There are strong theoretical reasons to expect disks around PMCs, and indirect evidence for disks around PMCs from optical and near-infrared emission exists. However, attempts to detect the dust and gas emission of the disk directly have been unsuccessful. The high sensitivity of JWST MIRI will allow detecting disks with sizes smaller than one au, masses as low 1/10000 of a Jupiter mass and will provide first constraints on the solid and gas composition of disks around PMCs. We propose to observe the PMC CT Cha b with the MIRI spectrograph to detect the dust and gas emission (water lines) of its disk. Those results allow for a comparison to the composition of the primary disk of CT Cha, which is observed simultaneously, and to observations of protoplanetary disks, providing new constraints for possible differences in disk evolution. Those observations, together with forthcoming complementary ALMA observations, will put stringent limits on the mass and size of the companion's disk; quantities most relevant for PMC formation theories and spin-evolution studies. The proposed program will be a big step forward for our understanding of the mysterious nature of wide-orbit planet-mass companions and will serve as a pioneering study for future JWST surveys of PMCs

JWST/MIRI Spectroscopy of the Disk of the Young Eruptive Star EX Lup in Quiescence

EX Lup is a low-mass pre-main sequence star that occasionally shows accretion-related outbursts. Here, we present JWST/MIRI medium resolution spectroscopy obtained for EX Lup fourteen years after its powerful outburst. EX Lup is now in quiescence and displays a Class II spectrum. We detect a forest of emission lines from molecules previously identified in infrared spectra of classical T Tauri disks: H2O, OH, H2, HCN, C2H2, and CO2. The detection of organic molecules demonstrates that they are back after disappearing during the large outburst. Spectral lines from water and OH are for the first time de-blended and will provide a much improved characterization of their distribution and density in the inner disk. The spectrum also shows broad emission bands from warm, sub-micron size amorphous silicate grains at 10 and 18 um. During the outburst, in 2008, crystalline forsterite grains were annealed in the inner disk within 1 au, but their spectral signatures in the 10 um silicate band later disappeared. With JWST we re-discovered these crystals via their 19.0, 20.0, and 23.5 um emission, whose strength implies that the particles are at ~3 au from the star. This suggests that crystalline grains formed in 2008 were transported outwards and now approach the water snowline, where they may be incorporated into planetesimals. Containing several key tracers of planetesimal and planet formation, EX Lup is an ideal laboratory to study the effects of variable luminosity on the planet-forming material and may provide explanation for the observed high crystalline fraction in solar system comets.Comment: 9 pages, 4 figures, accepted for publication in ApJL. JWST/MIRI spectrum is available for download at https://tinyurl.com/spexodisksJWS