arXiv subjects

Anna B. T. Penzlin

Publications and source records attributed to Anna B. T. Penzlin.

23 records · Page 2Linked to original sources

arXiv2022

The morphology of CSCha circumbinary disk suggesting the existence of a Saturn-mass planet

Planets have been detected in circumbinary orbits in several different systems, despite the additional challenges faced during their formation in such an environment. We investigate the possibility of planetary formation in the spectroscopic binary CS Cha by analyzing its circumbinary disk. The system was studied with high angular resolution ALMA observations at 0.87mm. Visibilities modeling and Keplerian fitting are used to constrain the physical properties of CS Cha, and the observations were compared to hydrodynamic simulations. Our observations are able to resolve the disk cavity in the dust continuum emission and the 12CO J:3-2 transition. We find the dust continuum disk to be azimuthally axisymmetric (less than 9% of intensity variation along the ring) and of low eccentricity (of 0.039 at the peak brightness of the ring). Under certain conditions, low eccentricities can be achieved in simulated disks without the need of a planet, however, the combination of low eccentricity and axisymmetry is consistent with the presence of a Saturn-like planet orbiting near the edge of the cavity.

astro-ph.EP↗

arXiv2022

Binary orbital evolution driven by a circumbinary disc

The question whether the interaction of a circumbinary disc with the central binary system leads to shrinking or expansion of the binary orbit has attracted considerable interest as it impacts the evolution of binary black holes and stellar binary stars in their formation phase. We performed two-dimensional hydrodynamical simulations of circumbinary discs for a large parameter set of disc viscosities and thicknesses and two different binary mass ratios for binaries on circular orbits. For those we measured carefully the net angular momentum and mass transfer between disc and binary system, and evaluate the normalised specific angular momentum accretion, $j_\mathrm{s}$ . This is compared to the theoretical, critical specific angular momentum change $j_\mathrm{s,crit}$ that separates contracting from expanding cases which depends on the the binary's mass ratio and the relative accretion onto the two stars. Using finite and infinite disc models we show that the inferred binary evolution is very similar for both setups and confirm that $j_\mathrm{s}$ can be measured accurately with cylindrical simulations that do not include the central binary. However, to obtain the relative accretion onto the stars for non-equal mass binaries, simulations that cover the whole domain including the binary are required. We find that for thick discs with aspect ratio $h = 0.1$ the binaries expand for all viscosities, while discs with $h = 0.05$ lead to an expansion only for larger viscosities with $α$ exceeding $\sim 0.005$. Overall, the regime of binary expansion extends to a much wider parameter space than previously anticipated, but for thin, low viscosity discs the orbits shrink.

astro-ph.SR↗

arXiv2021

On moving shadows and pressure bumps in HD 169142

The search for young planets had its first breakthrough with the detection of the accreting planet PDS70b. In this study, we aim to broaden our understanding towards the formation of multi-planet systems such as HR8799 or the Solar System. Our previous study on HD169142, one of the closest Herbig stars, points towards a shadow-casting protoplanetary candidate. Here, we present follow-up observations to test our previously proposed hypothesis. We set our new data into context with previous observations to follow structural changes in the disk over the course of 6 years. We find spatially resolved systematic changes in the position of the previously described surface brightness dip in the inner ring. We further find changes in the brightness structure in azimuthal direction along the ring. And finally, a comparison of our SPHERE data with recent ALMA observations reveals a wavelength dependent radial profile of the bright ring. The time-scale on which the changes in the ring's surface brightness occur suggest that they are caused by a shadow cast by a 1-10Mj planet surrounded by dust, an orbit comparable to those of the giant planets in our own Solar System. Additionally, we find the first indications for temperature-induced instabilities in the ring. And finally, we trace a pressure maxima, for the first time spatially resolved, with a width of 4.5au. The density distribution of the ring at mm wavelengths around the pressure maxima could further indicate effects from snow lines or even the dynamics and feedback of the larger grains.

astro-ph.EP↗

arXiv2019

1:1 orbital resonance of circumbinary planets

The recent detection of the third planet in Kepler-47 has shown that binary stars can host several planets in circumbinary orbits. To understand the evolution of such systems we have performed two-dimensional hydrodynamic simulations of the circumbinary disc with two embedded planets for several Kepler systems. In two cases, Kepler-47 and -413, the planets are captured in a 1:1 mean-motion resonance at the planet parking position near the inner edge of the disc. The orbits are fully aligned, have mean eccentricities of about 0.25 to 0.30, and the planets are entangled in a horseshoe type of motion. Subsequent n-body simulations without the disc show that the configurations are stable. Our results point to the existence of a new class of stable resonant orbits around binary stars. It remains to be seen if such orbits exist in reality.

astro-ph.EP↗

arXiv2019

Circumbinary discs with radiative cooling and embedded planets

As of today ten circumbinary planets orbiting solar type main sequence stars have been discovered. Nearly all of them orbit around the central binary very closely to the region of instability where it is difficult to form them in situ. It is assumed that they formed further out and migrated to their observed position. We extend previous studies to a more realistic thermal disc structure and determine what parameter influence the final parking location of a planet around a binary star. We perform two-dimensional numerical simulations of viscous accretion discs around a central binary that include viscous heating and radiative cooling from the disc surfaces. We vary the binary eccentricity as well as disc viscosity and mass. Concerning the disc evolution we find that it can take well over 100000 binary orbits until an equilibrium state is reached. As seen previously, we find that the central cavity opened by the binary becomes eccentric and precesses slowly in a prograde sense. Embedded planets migrate to the inner edge of the disc. In cases of lower disc viscosity they migrate further in maintaining a circular orbit, while for high viscosity they are parked further out on an eccentric orbit. The final location of an embedded planet is linked to its ability to open a gap in the disc. Gap opening planets separate inner from outer disc, preventing eccentricity excitation in the latter and making it more circular. This allows embedded planets to migrate closer to the binary, in agreement with the observations. The necessary condition for gap opening and the final planet position depend on the planet mass and disc viscosity.

astro-ph.EP↗