Exoplanet research at the
Thüringer Landessternwarte Tautenburg

News: Heavy Metal Planet Discovered

More information about the discovery can be found in the ESO Science BLOG, and in the Press releases of the Thüringer Landessternware Tautenburg (English, Deutsch) <

Team members: Artie Hatzes, Eike W. Guenther, Silvia Sabotta, David Wöckel, Michael Hartmann, Michaela Döllinger


Although the detection of extrasolar planets was impossible until the end of the 20th century, the idea that such objects exist was discussed since the dawn of modern astronomy. For example, the book 'Entretiens sur la pluralite des mondes' (Dialogue about the plurality of the worlds) written by Bernhard le Bovier de Fontenelle in 1686 became very popular. Also, Isaac Newton (1643-1727) and Immanuel Kant (1724-1804) discussed the idea of extrasolar planets.

Since the discovery of the first extrasolar planets at the end of the 20th century there has been a tremendous increase in both observational discoveries and theoretical work in this field of research. Although many of the extrasolar planets found up to now are gas-giants, the number of planets with masses below 10 MEarth is growing rapidly. Particularly exciting was in 2009 the discovery of CoRoT-7b the first rocky exoplanet outside the solar-system. The Thüringer Landessternwarte Tautenburg is engaged in two large surveys that are particularly focusing on the detection of low-mass planets, and new planets are routinely found. Particularly interesting are the transiting ones, for which mass and radius can be determined. The determination of the mass and radius is currently the best way to find out what the composition of these planets are. Do rocky planets have an Earth-like composition, or are they very different. Thanks to the new discoveries and new instruments, it also now becomes possible to study the atmospheres of planets, certainly an exciting field of research.

The space telescopes CoRoT (operating from December 27, 2006 to November 2, 2012) and Kepler (operating since March 7, 2009) with their very high photometric precision revolutionized our knowledge of exoplanets. We are now looking forward to the next missions: CHEOPS (launch 2018), TESS (launch 2018), JWST (launch 2018). The golden era of exoplanet research will come with the ELT and PLATO in 2024/2026.


CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a new instrument for the 3.5m telescope at the Calar Alto Observatory, that was built by a consortium of eleven Spanish and German institutions including the Thüringer Landessternwarte Tautenburg.

The CARMENES instrument consists of two separate echelle spectrographs covering the wavelength range from 550nm to 1700nm at a spectral resolution of R = 82,000. This instrument is fed by fibers from the Cassegrain focus of the telescope. Both spectrographs are housed in temperature-stabilized vacuum tanks, to enable a long-term 1 m/s radial velocity precision employing a simultaneous calibration with two Fabry-Perots that are calibrated with ThAr, Th-Ne and U-Ne emission line lamps. The contribution of the Thüringer Landessternwarte Tautenburg to the project was building the two calibration units. CARMENES has been optimized for a search for terrestrial planets in the habitable zones (HZs) of low-mass stars, which may well provide our first chance to study environments capable of supporting the development of life outside the Solar System. With its unique combination of optical and near-infrared echelle spectrographs, CARMENES will provide better sensitivity for the detection of low-mass planets than any comparable instrument, and a powerful tool for discriminating between genuine planet detections and false positives caused by stellar activity. The CARMENES survey of 300 M dwarfs has started in January 2017.

CARMENES has now made its first discoveries. New planet was found in the GJ1148-system and it was found that the claimed planet of GJ15A with a period of 11.4 days does not exist. See scientific article for more details. Previously discovered planets in GJ176, GJ436, GJ536, GJ1148, GJ581 and GJ876 were confirmed. See also this press release, and this one.


Transiting exoplanets are benchmark objects. Like an eclipsing binary star, a transiting exoplanet offers unique opportunities for a rich variety of follow-up studies due to its favourable orbital geometry. It is possible to measure a planet's fundamental bulk properties like mass and radius, study its atmosphere photometrically or spectroscopically, and measure the alignment between the planet's orbit and the host star's spin axis. More so than eclipsing binary stars, transiting exoplanets are difficult to detect. Wide-field ground-based transit surveys have detected hundreds of hot Jupiters, but the sensitivity of these surveys falls off quickly at longer orbital periods and smaller planet radii. Space telescopes like CoRoT and Kepler with their very high photometric precision revolutionized our knowledge of exoplanets. The survey with the Kepler telescope is now extended K2 mission.

The KESPRINT team is analysing the light-curves, and carrying follow-up observations with ground-based telescopes in order to determine the stellar parameters and to measure the masses of the planets. The KESPRINT teams has made already many discoveries, a particularly exciting one was the discovery of the planets of HD3167. HD3167 is a bright (V=8.9 mag) K0V star. HD3167b, an ultra-short-period (0.96 days) super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit (29.85 days). With a mass of 5.7 MEarth, a radius of 1.6 REarth, and a mean density of 8 gcm-3, HD3167b joins the small group of ultra-short-period planets known to have rocky terrestrial compositions. This planet thus resembles CoRoT-7b but the star is much brighter, allowing very detailed studies. HD3167c has a mass of 8 MEarth and a radius of 2.7 REarth, yielding a mean density of 2.2 gcm-3, indicative of a planet with a composition comprising a solid core surrounded by a thick atmospheric envelope. The rather large pressure scale height (350 km) and the brightness of the host star makes HD3167c an ideal target for atmospheric characterization via transmission spectroscopy across a broad range of wavelengths.

Our main work-horses are the FIES, HARPS, HAPS-N and the CARMENES spectrographs. FIES is at the 2.6m Nordic Optical Telescope (NOT), HARPS-N at the 3.5m Telescopio Nazionale "Galileo" (TNG), both telescopes are at the Observatorio del Roque de los Muchachos. HARPS at the 3.6m telescope at La Silla, and CARMENES at the 3.5m telescope at Calar Alto.

Dome of the NOT at the Observatorio del Roque de los Muchachos.
That is where FIES is.

Dome of the TNG at the Observatorio del Roque de los Muchachos.
That is where HARPS-N is.

Dome of the 3.6m telescope at La Silla.
That is where HARPS is.

Dome of the 3.5m telescope at Calar Alto observatory.
That is where CARMENES is.

Seeing monitor at Calar Alto observatory.


The Thüringer Landessternwarte Tautenburg is involved in upgrading the near-infrared spectrograph CRIRES on the VLT to CRIRES+. The upgrade project CRIRES+, transforms this VLT instrument into a cross-dispersed spectrograph to increase the wavelength range that is covered simultaneously by a factor of ten. In addition, a new detector focal plane array of three Hawaii 2RG detectors with a 5.3 mum cut-off wavelength will replace the existing detectors, a new spectroparimetric unit will be added and the calibration system will be enhanced.

This instrument will have great potentials for the studies of planets orbiting cool stars and studies of the atmospheres of planets.