Dr. Jens Hoeijmakers

Exoplanet astronomer at Lund Observatory, Sweden

Research Profile

I observe exoplanet atmospheres using high-resolution ground-based echelle spectrographs. Using advanced, open-source chemical and radiate transfer models I constrain atmospheric properties such as temperatures, chemical composition and processes, atmospheric dynamics (winds) and atmospheric structure. My recent research has centered on observations of gaseous metals such as iron, titanium, sodium and magnesium in the atmospheres of Ultra-hot Jupiters.

Besides hunting for vaporised metals in extra-solar planets, I am involved in projects to place Earth-observing polarimeters aboard the ISS and on the surface of the Moon to map and characterize polarimetric biosignatures of Earth as a living planet.

I obtained my Ph.D. in the Exoplanets group of Ignas Snellen at Leiden Observatory, and am employed at Lund Observatory as of October 2020. I enjoy collaborative research projects, helping students or collaborators on their way through the wonderous worlds of exoplanet astronomy and astro-spectroscopy, and value a professional, inclusive, diverse and respectful work environment.

Metals in KELT-9 b

KELT-9 b is the hottest exoplanet around a main-sequence star known to date. With a day-side temperature of over 4,000 K, the chemistry in its atmosphere was expected to be unique, and is almost exlusively atomic. Observations obtained with the HARPS-N spectrograph showed that the optical transmission spectrum of KELT-9 b is rich, allowing me and my collaborators to identify a multitude of atoms and ions.

Ti/V chemistry in WASP-121 b

UV, optical and NIR spectroscopy of WASP-121 b shows strong variability, mainly attributed to metal oxide absorption. We studied the high-resolution transmission spectrum with the HARPS spectrograph, and found absorption by various metals, including vanadium and nickel. These observations shed light on the structure of the atmosphere, chemistry and condensation processes of gas-phase metals.

Machine Learning for high-resolution spectroscopy

Classical statistical inference methods do not perform well on high-resolution exoplanet spectra due to their size, the high model dimensionality and the prevalence of random noise. We developed a retrieval technique based on the random forest algorithm that can robustly and rapidly retrieve fundamental parameters from high-resolution transit spectroscopy.

The Cross correlation technique

Explanation of the basic concepts behind the cross-correlation technique.

Codes and Resources

For obtaining, analyzing and understanding exoplanet observations, I make use of public resources and open-source software packages. In particular, I collaborate with the developers of the Exoclimes Simulations Platform, a collection of codes designed for modeling exoplanet atmospheres. In addition, I maintain a github page where my own analysis codes are hosted for public use and scrutiny.

Get in touch

Please feel free to contact me if you would like to engage with my science or need help / pointers.

  • Visiting Address

    Sölvegatan 27
  • Postal Address

    Jens Hoeijmakers
    Box 43
    SE-221 00 Lund