The design and construction of CARMENES has been presented at previous SPIE conferences. It is a next-generation radial-velocity instrument at the 3.5m telescope of the Calar Alto Observatory, which was built by a consortium of eleven Spanish and German institutions. CARMENES consists of two separate échelle spectrographs covering the wavelength range from 0.52 to 1.71μm at a spec-tral resolution of R < 80,000, fed by fibers from the Cassegrain focus of the telescope. CARMENES saw “First Light” on Nov 9, 2015.
During the commissioning and initial operation phases, we established basic performance data such as throughput and spectral resolution. We found that our hollow-cathode lamps are suitable for precise wavelength calibration, but their spectra contain a number of lines of neon or argon that are so bright that the lamps cannot be used in simultaneous exposures with stars. We have therefore adopted a calibration procedure that uses simultaneous star / Fabry Pérot etalon exposures in combination with a cross-calibration between the etalons and hollow-cathode lamps during daytime. With this strategy it has been possible to achieve 1-2 m/s precision in the visible and 5-10 m/s precision in the near-IR; further improvements are expected from ongoing work on temperature control, calibration procedures and data reduction. Comparing the RV precision achieved in different wavelength bands, we find a “sweet spot” between 0.7 and 0.8μm, where deep TiO bands provide rich RV information in mid-M dwarfs. This is in contrast to our pre-survey models, which predicted comparatively better performance in the near-IR around 1μm, and explains in part why our near-IR RVs do not reach the same precision level as those taken with the visible spectrograph.
We are now conducting a large survey of 340 nearby M dwarfs (with an average distance of only 12pc), with the goal of finding terrestrial planets in their habitable zones. We have detected the signatures of several previously known or suspected planets and also discovered several new planets. We find that the radial velocity periodograms of many M dwarfs show several significant peaks. The development of robust methods to distinguish planet signatures from activity-induced radial velocity jitter is therefore among our priorities.
Due to its large wavelength coverage, the CARMENES survey is generating a unique data set for studies of M star atmospheres, rotation, and activity. The spectra cover important diagnostic lines for activity (H alpha, Na I D1 and D2, and the Ca II infrared triplet), as well as FeH lines, from which the magnetic field can be inferred. Correlating the time series of these features with each other, and with wavelength-dependent radial velocities, provides excellent handles for the discrimination between planetary companions and stellar radial velocity jitter. These data are also generating new insight into the physical properties of M dwarf atmospheres, and the impact of activity and flares on the habitability of M star planets.
We present EclipseSim, a radiometric model for exoplanet transit spectroscopy that allows easy exploration of
the fundamental performance limits of any space-based facility aiming to perform such observations. It includes
a library of stellar model atmosphere spectra and can either approximate exoplanet spectra by simplified models,
or use any theoretical or observed spectrum, to simulate observations. All calculations are done in a spectrally
resolved fashion and the contributions of the various fundamental noise sources are budgeted separately, allowing
easy assessment of the dominant noise sources, as a function of wavelength. We apply <i>EclipseSim</i> to the Exoplanet
Characterization Observatory (EChO), a proposed mission dedicated to exoplanet transit spectroscopy that is
currently in competition for the M3 launch slot of ESA’s cosmic vision programme. We show several case studies
on planets with sizes in the super-Earth to Jupiter range, and temperatures ranging from the temperate to the
≈1500K regime, demonstrating the power and versatility of EChO. <i>EclipseSim</i> is publicly available.<sup>*</sup>
Well over 700 exoplanets have been detected to date. Only a handful of these have been observed directly. Direct observation is extremely challenging due to the small separation and very large contrast involved. Imaging polarimetry offers a way to decrease the contrast between the unpolarized starlight and the light that has become linearly polarized after scattering by circumstellar material. This material can be the dust and debris found in circumstellar disks, but also the atmosphere or surface of an exoplanet.
We present the design, calibration approach, polarimetric performance and sample observation results of the Extreme Polarimeter, an imaging polarimeter for the study of circumstellar environments in scattered light at visible wavelengths.
The polarimeter uses the beam-exchange technique, in which the two orthogonal polarization states are imaged simultaneously and a polarization modulator is swaps the polarization states of the two beams before the next image is taken. The instrument currently operates without the aid of Adaptive Optics. To reduce the effects of atmospheric seeing on the polarimetry, the images are taken at a frame rate of 35 fps, and large numbers of frames are combined to obtain the polarization images.
Four successful observing runs have been performed using this instrument at the 4.2 m William Herschel Telescope on La Palma, targeting young stars with protoplanetary disks as well as evolved stars surrounded by dusty envelopes. In terms of fractional polarization, the instrument sensitivity is better than 10<sup>−4</sup>. The contrast achieved between the central star and the circumstellar source is of the order 10<sup>−6</sup>. We show that our calibration approach yields absolute polarization errors below 1%.
We present the design of a compact module that converts the HARPS instrument at the 3.6-m telescope at
La Silla to a full-Stokes high-resolution spectropolarimeter. The polarimeter will replace the obsolete Iodine
cell inside the HARPS Cassegrain adapter. Utilizing the two fibers going into the spectrograph, two dual-beam
systems can be positioned in the beam: one with a rotating superachromatic quarter-wave plate for circular
polarimetry and one with a rotating superachromatic half-wave plate for linear polarimetry. A large polarimetric
precision is ensured by the beam-exchange technique and a minimal amount of instrumental polarization. The
polarimeter, in combination with the ultra-precise HARPS spectrograph, enables unprecedented observations of
stellar magnetic fields and circumstellar material without compromising the successful planet-finding program.
Research on extrasolar planets is one of the most rapidly advancing fields of astrophysics. In just over a decade
since the discovery of the first extra-solar planet orbiting around 51 Pegasi, 289 extrasolar planets have been
discovered. This breakthrough is the result of the development of a wide range of new observational techniques
and facilities for the detection and characterisation of extrasolar planets. In Utrecht we are building the Extreme
Polarimeter (ExPo) to image extra-solar planets and circumstellar environments using polarimetry at contrast
ratio of 10<sup>-9</sup>.
To test and calibrate ExPo, we have built a laboratory-based simulator that mimics a star with a Jupiter-like
exoplanet as seen by the 4.2m William Herschel Telescope. The star and planet are simulated using two single-mode
fibres in close proximity that are fed with a broadband arc lamp with a contrast ratio down to 10<sup>-9</sup>. The
planet is partially linearly polarized. The telescope is simulated with two lenses, and seeing can be included
with a rotating glass plate covered with hairspray. In this paper we present the scientific requirements and the
The Extreme Polarimeter (ExPo) is approaching its first deployment at the 4.2 m William Herschel Telescope at La
Palma. This imaging polarimeter, developed at the Astronomical Institute of Utrecht University, aims to study
circumstellar material at a contrast ratio with the central star of 10<sup>-9</sup>. Working at visible wavelengths, it will provide an
inner working angle down to 0.5 arcsec and a field of view of 20 arcsec diameter. ExPo employs a dual beam-exchange
technique based on polarimeter designs for solar studies. A partially transmitting coronagraph mask placed in the first
focus reduces the light of the star. The beam is modulated using three ferro-electric liquid crystals in a Pancharatnam
configuration, then split in a polarizing beamsplitter. Both beams are re-imaged onto the same Electron-Multiplying
We present the design of the ExPo instrument, highlighting the elements that are critical to the polarimetric performance.
Some prototype laboratory experiments demonstrating the instrument concept are discussed. These have been performed
using our realistic exoplanet laboratory simulator.