Circumstellar Disks

Circumstellar disks provide key insights into the physics inherent in star and planet formation. As the earliest stage of planet formation, massive, optically thick, and gas rich protoplanetary disks give information about the distribution and composition of the dust grains that will eventually coalesce into planetesimal bodies. Debris disks, the remnants of planet formation (our own Kuiper Belt for example), serve as signposts for the dynamical history of the circumstellar system.
Disks also provide the environment, literally the birthplaces, for planets to form! The question is HOW? More specifically, are the disk masses and densities large enough to grow planets? How and where in the disks do grains grow to form planets? On what timescales? At the Leiden Observatory, our team seeks to address these and other questions using a wide variety of observational tools and modelling efforts. 
 

Recent advances in instrumentation have allowed for detailed images of circumstellar environments. With the advent of ground-based adaptive optics (AO) systems and most recently, dedicated ExtremeAO systems (e.g. SPHERE, GPI, SCExAO), these disks can now be characterized with great detail in scattered optical and near-infrared starlight.  Complementary to these observations, radio (sub)millimeter aperture synthesis images (e.g. ALMA) provide information about the larger dust grains in the disk; the total dust mass and the radial surface density distribution. Additionally, observations of various molecular species can be used to trace the disks’ gas content, as well as the velocity and temperature profiles.  Members of our circumstellar disks group are involved with both the SPHERE and GPI consortia, and have expertise in all current high contrast instruments. 
The Leiden Observatory Disks Team works with state of the art instrumentation in high contrast imaging (e.g. VLT/SPHERE, Gemini-S/GPI) and millimeter synthesis imaging (e.g. ALMA). Image of Gemini South above courtesy of Gemini Observatory/Association of Universities for Research in Astronomy.
The Leiden Observatory Disks Team works with state of the art instrumentation in high contrast imaging (e.g. VLT/SPHERE, Gemini-S/GPI) and millimeter synthesis imaging (e.g. ALMA). Image of Gemini South above courtesy of Gemini Observatory/Association of Universities for Research in Astronomy.
The Leiden Observatory Disks Team works with state of the art instrumentation in high contrast imaging (e.g. VLT/SPHERE, Gemini-S/GPI) and millimeter synthesis imaging (e.g. ALMA). VLT Image above courtesy of ESO/A.
The Leiden Observatory Disks Team works with state of the art instrumentation in high contrast imaging (e.g. VLT/SPHERE, Gemini-S/GPI) and millimeter synthesis imaging (e.g. ALMA). VLT Image above courtesy of ESO/A.
The Leiden Observatory Disks Team works with state of the art instrumentation in high contrast imaging (e.g. VLT/SPHERE, Gemini-S/GPI) and millimeter synthesis imaging (e.g. ALMA). ALMA Image above courtesy of ESO/A.
The Leiden Observatory Disks Team works with state of the art instrumentation in high contrast imaging (e.g. VLT/SPHERE, Gemini-S/GPI) and millimeter synthesis imaging (e.g. ALMA). ALMA Image above courtesy of ESO/A.

Research Highlights

Synergies with Scattered Light and Millimeter Continuum

Scattered light and millimeter continuum observations probe different disk properties. In scattered light, we are more sensitive to the smaller dust grains on the disk surface, while longer wavelengths show the larger dust grains in the midplane. Both provide valuable clues to disk physics. The image above provides an example scattered light image with the ALMA continuum observations overplotted with contours.

Unique Disk Shadowing and Morphologies

Current observations of circumstellar disks show a wide variety of morphologies. Offset rings, spiral arms, and shadows both narrow and wide offer valuable insight into the presence of planets embedded in these systems. In this case, a young, thick disk is seen at an angle, where offset rings point to the disk inclination. Could these rings be shepherded by unseen planets?

Circumstellar Disks and Planetary Companions

Gaps and spiral structures in disks can point to unseen planetary companions hidden beneath the surface of the disk. More rare, are cases when the planets can be seen in the process of carving the disk structures. One exciting system, PDS 70, shows a bright, young disk alongside an accreting protoplanet. Credit: ESO/A.

Radiative Transfer Modeling

We are entering an era where workhorse high contrast instruments are providing diverse galleries of circumstellar disks observations. In order to link disk morphologies with the underlying physics, we require comprehensive modeling efforts. In the example above, we model an optically thick protoplanetary disks observed with the Hubble Space Telescope along with a spectral energy distribution, and were able to determine the temperature structure and dust mass in the disks.

Current Student Projects

Dust grains in planet forming (or protoplanetary) disks grow with time to form
pebbles, comets and eventually planets. An outstanding problem in the field is
how fast these grains grow with time and across the surface of the disk
(perhaps faster or slower close to the star than further out). To answer this
problem we first need to be able to accurately characterize dust grains in
different areas of these disks. The degree of polarization of starlight that is
scattered by the disk surface will depend on the grain size and shape of the
scattering particles.
We are working with SPHERE, the state of the art high-contrast imager at the
ESO Very Large Telescope in Chile to image protoplanetary disks. We ask
the student to work on mapping the degree of polarization of these disks using
new and innovative data reduction and analysis methods.