About me

Hi! I am an ETH fellow working on direct imaging observations and atmospheric characterization of exoplanets and substellar companions in the Exoplanets and Habitability group of the Institute for Particle Physics and Astrophysics at ETH Zurich. Before, I was a PhD student at the University of Amsterdam where I mostly worked with VLT/SPHERE to map out the circumstellar environments of young stars in scattered light. Find more details on my research interests and ongoing projects below.

Research

High-contrast imaging observations & data analysis

Most of the work that I do involves high-contrast, high-resolution imaging observations with the Very Large Telescope in Chile to detect faint light coming from low-mass companions and circumstellar disks. I use various image processing techniques to reduce and analyze the data. For this purpose, I helped developing a generic, end-to-end pipeline called PynPoint which provides dedicated modules for processing and analyzing high-contrast imaging data.

Mid-infrared atmospheric characterization

MIRACLES is a mid-infrared direct imaging survey to systematically characterize the atmospheres of self-luminous gas giants and substellar companions. I use VLT/NACO to complement the spectral energy distributions of these objects with broad- and narrow-band photometry in the 4-5 micron range. In this way, I hope to provide better constraints on their physical and chemical properties such as temperature, surface gravity, and metallicity.

Substructures and dust in protoplanetary disks

Planet formation occurs in the dusty realms of young stars. I use high-contrast polarimetric imaging to reveal substructures these circumstellar environments which may trace down any forming planets. The scattered light is also affected by shadowing effects and the properties of the dust grains. An interesting case is HD 135344B which shows variable shadowing on a timescale of days to weeks due to changes in the disk structure close to the central star (see movie).

Cloud inhomogeneities in substellar atmospheres

PICCA is a polarimetric investigation to study cloud inhomogeneities in substellar companion atmospheres. Light scattering of dusty particles high in the atmosphere gets imprinted with a polarimetric signature. I use the high-contrast capabilities of VLT/SPHERE to measure the polarized signal from substellar objects to place empirical constraints on the horizontal distribution of clouds and rotationally-induced flattening of their atmospheres.

Software

species - A toolkit for analyzing spectral and photometric data of self-luminous exoplanets and brown dwarfs (see Stolker et al. 2020). The package provides a user friendly and coherent framework to analyze data from directly imaged objects by profiting from publicly available data such as spectral libraries, atmospheric models, and photometry of field dwarfs and low-mass companions. The package has been released on PyPI and is also available on Github. Several examples are included in the documentation.

PynPoint - A generic, end-to-end pipeline for processing and analysis of high-contrast imaging data of exoplanets and circumstellar disks (see Stolker et al. 2019). The modular architecture, with a separation of the core functionalities and pipeline modules, provides a highly robust environment which allows for an easy implementation of new pipeline modules. A variety of modules are included, for example for centering, PSF subtraction, estimation of detection limits, and photometric and astrometric analysis. The package is available on PyPI and Github. Have a look at the documentation for installation instructions, details on the architecture of PynPoint, and a description of the various pipeline modules and input parameters. An end-to-end example is available here of a SPHERE/ZIMPOL H-alpha dataset of HD 142527. This Herbig star is orbited by an accreting M dwarf companion at a separation of only 60 mas. The analysis includes a measurement of the companion's flux and position and a computation of detection limits.

ARTES - A three-dimensional Monte Carlo radiative transfer code specifically designed for (polarized) scattered light simulations of planetary atmospheres (see Stolker et al. 2017). Computations of both reflected stellar light and thermal emission from the planet are possible for an arbitrary 3D atmospheric structure and distribution of opacity sources. Multiple scattering, absorption, and polarization are fully treated and the output includes an image, spectrum, or phase curve. Several tools are included to create opacities and scattering matrices for molecules and clouds. The code can be found on Github. Have a look at the documentation for installation instructions, a description of the required input files, and several examples.

diskmap - A Python tool for scattered light mapping of protoplanetary disk (see Stolker et al. 2017). For a given parametrization of the scattering surface (e.g. a power law profile), the exact distance from the star and scattering angle are computed for each pixel. From this, a deprojected image, a stellar irradiation corrected image, and a´ scattering phase function can be extracted. The tool can be installed from the PyPI repository and is available on Github. Installation instructions and a tutorial are available in the documentation.

Selected publications

T. Stolker, S. P. Quanz, K. O. Todorov, J. Kühn, P. Mollière, M. R. Meyer, T. Currie, S. Daemgen, and B. Lavie
MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4-5 μm. II. Evidence that PDS 70 b is enshrouded by an extended dusty environment
2020, Astronomy & Astrophysics, submitted

T. Stolker, S. P. Quanz, K. O. Todorov, J. Kühn, P. Mollière, M. R. Meyer, T. Currie, S. Daemgen, and B. Lavie
MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4-5 μm. I. Photometric analysis of β Pic b, HIP 65426 b, PZ Tel B and HD 206893 B
2020, Astronomy & Astrophysics, 635, A182

T. Stolker, M. J. Bonse, S. P. Quanz, A. Amara, G. Cugno, A. J. Bohn, and A. Boehle
PynPoint: a modular pipeline architecture for processing and analysis of high-contrast imaging data
2019, Astronomy & Astrophysics, 621, A59

T. Stolker, M. Sitko, B. Lazareff, M. Benisty, C. Dominik, R. Waters, M. Min, S. Perez, J. Milli, A. Garufi, J. de Boer, C. Ginski, S. Kraus, J.-P. Berger, and H. Avenhaus
Variable dynamics in the inner disk of HD 135344B revealed with multi-epoch scattered light imaging
2017, The Astrophysical Journal, 849, 143

T. Stolker, M. Min, C. Dominik, D. M. Stam, P. Mollière, and L. B. F. M. Waters
Polarized scattered light from self-luminous exoplanets. Three-dimensional scattering radiative transfer with ARTES
2017, Astronomy & Astrophysics, 607, A42

T. Stolker, C. Dominik, M. Min, A. Garufi, G. D. Mulders, and H. Avenhaus
Scattered light mapping of protoplanetary disks
2016, Astronomy & Astrophysics, 596, A70

T. Stolker, C. Dominik, H. Avenhaus, M. Min, J. de Boer, C. Ginski, H. M. Schmid, A. Juhasz, A. Bazzon, L. B. F. M. Waters, A. Garufi, J.-C. Augereau, M. Benisty, A. Boccaletti, T. Henning, M. Langlois, A.-L. Maire, F. Ménard, M. R. Meyer, C. Pinte, S. P. Quanz, C. Thalmann, J.-L. Beuzit, M. Carbillet, A. Costille, K. Dohlen, M. Feldt, D. Gisler, D. Mouillet, A. Pavlov, D. Perret, C. Petit, J. Pragt, S. Rochat, R. Roelfsema, B. Salasnich, C. Soenke, and F. Wildi
Shadows cast on the transition disk of HD 135344B. Multiwavelength VLT/SPHERE polarimetric differential imaging
2016, Astronomy & Astrophysics, 595, A113

P. Mollière, T. Stolker, S. Lacour, G. P. P. L. Otten, J. Shangguan, B. Charnay, T. Molyarova, M. Nowak, Th. Henning, G.-D. Marleau, D. A. Semenov, E. van Dishoeck, F. Eisenhauer, P. Garcia, R. Garcia Lopez, J. H. Girard, A. Z. Greenbaum, S. Hinkley, P. Kervella, L. Kreidberg, A.-L. Maire, E. Nasedkin, L. Pueyo, I. A. G. Snellen, A. Vigan, J. Wang, P. T. de Zeeuw, A. Zurlo
Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
2020, Astronomy & Astrophysics, in press.

M. Min, T. Stolker, C. Dominik, and M. Benisty
Connecting the shadows: probing inner disk geometries using shadows in transitional disks
Astronomy & Astrophysics, 2017, 604, L10

A.-L. Maire, T. Stolker, S. Messina, A. Müller, B. A. Biller, T. Currie, C. Dominik, C. A. Grady, A. Boccaletti, M. Bonnefoy, G. Chauvin, R. Galicher, M. Millward, A. Pohl, W. Brandner, T. Henning, A.-M. Lagrange, M. Langlois, M. R. Meyer, S. P. Quanz, A. Vigan. A. Zurlo, R. van Boekel, E. Buenzli, T. Buey, S. Desidera, M. Feldt, T. Fusco, C. Ginski, E. Giro, R. Gratton, N. Hubin, J. Lannier, D. Le Mignant, D. Mesa, S. Peretti, C. Perrot, J. R. Ramos, G. Salter, M. Samland, E. Sissa, E. Stadler, C. Thalmann, S. Udry, and L. Weber
Testing giant planet formation in the transitional disk of SAO 206462 (HD 135344B) using deep VLT/SPHERE imaging
2017, Astronomy & Astrophysics, 601, A134

M. Benisty, T. Stolker, A. Pohl, J. de Boer, G. Lesur, C. Dominik, C. P. Dullemond, M. Langlois, M. Min, K. Wagner, T. Henning, A. Juhasz, P. Pinilla, S. Facchini D. Apai, R. van Boekel, A. Garufi, C. Ginski, F. Ménard, C. Pinte, S. P. Quanz, A. Zurlo, A. Boccaletti, M. Bonnefoy, J. L. Beuzit, G. Chauvin, M. Cudel, S. Desidera, M. Feldt, C. Fontanive, R. Gratton, M. Kasper, A.-M. Lagrange, H. LeCoroller, D. Mouillet, D. Mesa, E. Sissa, A. Vigan, J. Antichi, T. Buey, T. Fusco, D. Gisler, M. Llored, Y. Magnard, O. Moeller-Nilsson, J. Pragt, R. Roelfsema, J.-F. Sauvage, and F. Wildi
Shadows and spirals in the protoplanetary disk HD 100453
2017, Astronomy & Astrophysics, 597, A42

C. Ginski, T. Stolker, P. Pinilla, C. Dominik, A. Boccaletti, J. de Boer, M. Benisty, B. Biller, M. Feldt, A. Garufi, C. U. Keller, M. Kenworthy, A. L. Maire, F. Ménard, D. Mesa, J. Milli, M. Min, C. Pinte, S. P. Quanz, R. van Boekel, M. Bonnefoy, G. Chauvin, S. Desidera, R. Gratton, J. H. V. Girard, M. Keppler, T. Kopytova, A.-M. Lagrange, M. Langlois, D. Rouan, and A. Vigan
Direct detection of scattered light gaps in the transitional disk around HD 97048 with VLT/SPHERE
2016, Astronomy & Astrophysics, 595, A112

Contact

tomas.stolker [at] phys.ethz.ch

Wolfgang-Pauli-Strasse 27
8093 Zurich

+41 44 633 6144