Calar Alto Observatory Research Articles

Broad-line Region of the Quasar PG 2130+099. II. Doubling the Size Over Four Years?

Over the past three decades, multiple reverberation mapping (RM) campaigns conducted for the quasar PG 2130+099 have exhibited inconsistent findings with time delays ranging from ∼10 to ∼200 days. To achieve a comprehensive understanding of the geometry and dynamics of the broad-line region (BLR) in PG 2130+099, we continued an ongoing high-cadence RM monitoring campaign using the Calar Alto Observatory 2.2 m optical telescope for an extra four years from 2019 to 2022. We measured the time lags of several broad emission lines (including He ii, He i, Hβ, and Fe ii) with respect to the 5100 Å continuum, and their time lags continuously vary through the years. Especially, the Hβ time lags exhibited approximately a factor of 2 increase in the last two years. Additionally, the velocity-resolved time delays of the broad Hβ emission line reveal a back-and-forth change between signs of virial motion and inflow in the BLR. The combination of negligible (∼10%) continuum change and substantial time-lag variation (over 2 times) results in a significant scatter in the intrinsic R Hβ –L 5100 relationship for PG 2130+099. Taking the consistent changes in the continuum variability time scale and the size of the BLR into account, we tentatively propose that the changes in the measurement of the BLR size may be affected by “geometric dilution”

CAVITY: Calar Alto Void Integral-field Treasury surve. I. First public data release

The Calar Alto Void Integral-field Treasury surveY (CAVITY) is a legacy project aimed at characterising the population of galaxies inhabiting voids, which are the most under-dense regions of the cosmic web, located in the Local Universe. This paper describes the first public data release (DR1) of CAVITY, comprising science-grade optical data cubes for the initial 100 out of a total of sim 300 galaxies in the Local Universe ($0.005 < z < 0.050$). These data were acquired using the integral-field spectrograph PMAS/PPak mounted on the 3.5m telescope at the Calar Alto observatory. The DR1 galaxy sample encompasses diverse characteristics in the color–magnitude space, morphological type, stellar mass, and gas ionisation conditions, providing a rich resource for addressing key questions in galaxy evolution through spatially resolved spectroscopy. The galaxies in this study were observed with the low-resolution V500 set-up, spanning the wavelength range 3745–7500 with a spectral resolution of 6.0 (FWHM). Here, we describe the data reduction and characteristics and data structure of the CAVITY datasets essential for their scientific utilisation, highlighting such concerns as vignetting effects, as well as the identification of bad pixels and management of spatially correlated noise. We also provide instructions for accessing the CAVITY datasets and associated ancillary data through the project's dedicated database.

The CARMENES search for exoplanets around M dwarfs

We present the abundances of magnesium (Mg) and silicon (Si) for 314 dwarf stars with spectral types in the interval K7.0–M5.5 (Teff range ≈ 4200–3050 K) observed with the CARMENES high-resolution spectrograph at the 3.5 m telescope at the Calar Alto Observatory. Our analysis employs the BT-Settl model atmospheres, the radiative transfer code Turbospectrum, and a state-of-the-art selection of atomic and molecular data. These Mg and Si abundances are critical for understanding both the chemical evolution and assembly of the Milky Way and the formation and composition of rocky planets. Our chemical abundances show a line-to-line scatter at the level of 0.1 dex for all studied spectral types. The typical error bar of our chemical abundance measurements is ± 0.11 dex (Mg) and ± 0.16 dex (Si) for all spectral types based on the comparison of the results obtained for stellar components of multiple systems. The derived abundances are consistent with the galactic evolution trends and observed chemical abundance distribution of earlier FGK-type stars in the solar neighbourhood. Besides, our analysis provides compatible abundances for stars in multiple systems. In addition, we studied the abundances of different galactic stellar populations. In this paper, we also explore the relation of the Mg and Si abundances of stars with and without known planets.

K2-399 b is not a planet

Context. The transit technique has been very efficient over the past decades in detecting planet-candidate signals. The so-called statistical validation approach has become a popular way of verifying a candidate’s planetary nature. However, the incomplete consideration of false-positive scenarios and data quality can lead to misinterpretation of the results. Aims. In this work, we revise the planetary status of K2-399 b, a validated planet with an estimated false-positive probability of 0.078% located in the middle of the so-called Neptunian desert, and hence a potential key target for atmospheric prospects. Methods. We used radial velocity data from the CARMENES, HARPS, and TRES spectrographs, as well as ground-based multiband transit photometry provided by LCOGT MuSCAT3 and broad band photometry to test the planetary scenario. Results. Our analysis of the available data does not support the existence of this (otherwise key) planet, and instead points to a scenario composed of an early G-dwarf orbited –with a period of a 846.62−0.28+0.22 days– by a pair of eclipsing M-dwarfs (hence a hierarchical eclipsing binary) likely in the mid-type domain. We thus demote K2-399 b as a planet. Conclusions. We conclude that the validation process, while very useful to prioritize follow-up efforts, must always be conducted with careful attention to data quality while ensuring that all possible scenarios have been properly tested to get reliable results. We also encourage developers of validation algorithms to ensure the accuracy of a priori probabilities for different stellar scenarios that can lead to this kind of false validation. We further encourage the use of follow-up observations when possible (such as radial velocity and/or multiband light curves) to confirm the planetary nature of detected transiting signals rather than only relying on validation tools.

Evidence of Water Vapor in the Atmosphere of a Metal-rich Hot Saturn with High-resolution Transmission Spectroscopy

Transmission spectroscopy presents one of the most successful approaches for investigating the atmospheres of exoplanets. We analyzed the near-infrared high-resolution transmission spectrum of a hot Saturn, HD 149026 b, taken using CARMENES spectrograph ( R∼80,400 ). We found evidence of H2O at a signal-to-noise ratio (S/N) of ∼4.8. We also performed grid search using a Bayesian framework and constrained the orbital velocity K p and rest velocity V rest to 158.17−7.90+8.31 km s−1 and 2.57−0.57+0.54 km s−1, respectively. While the retrieved K p value is consistent with theoretical prediction, the retrieved V rest value is highly redshifted (>3σ). This might be an indication of either anomalous atmospheric dynamics at play or an orbit with nonzero eccentricity. Additionally, we searched for HCN but no successful detection has been made, possibly due to the relatively low-S/N data set. The detection of H2O and subsequent retrieval of its abundance, coupled with analysis of other species such as CO in the K band, for example, might help us to get some information about the atmospheric C/O ratio and metallicity, which in turn could give us some insight into the planet’s formation scenario.

An Earth-sized Planet on the Verge of Tidal Disruption

TOI-6255 b (GJ 4256) is an Earth-sized planet (1.079 ± 0.065 R ⊕) with an orbital period of only 5.7 hr. With the newly commissioned Keck Planet Finder and CARMENES spectrographs, we determine the planet’s mass to be 1.44 ± 0.14 M ⊕. The planet is just outside the Roche limit, with P orb/P Roche = 1.13 ± 0.10. The strong tidal force likely deforms the planet into a triaxial ellipsoid with a long axis that is ∼10% longer than the short axis. Assuming a reduced stellar tidal quality factor Q⋆′≈107 , we predict that tidal orbital decay will cause TOI-6255 to reach the Roche limit in roughly 400 Myr. Such tidal disruptions may produce the possible signatures of planet engulfment that have been seen on stars with anomalously high refractory elemental abundances compared to their conatal binary companions. TOI-6255 b is also a favorable target for searching for star–planet magnetic interactions, which might cause interior melting and hasten orbital decay. TOI-6255 b is a top target (with an Emission Spectroscopy Metric of about 24) for phase-curve observations with the James Webb Space Telescope.

The CAVITY project: The spatially resolved stellar population properties of galaxies in voids

The Universe is shaped as a web-like structure, formed by clusters, filaments, and walls that leave large low number-density volumes in between named voids. Galaxies in voids have been found to be of a later type, bluer, less massive, and to have a slower evolution than galaxies in denser environments (filaments and walls). However, the effect of the void environment on their stellar population properties is still unclear. We aim to address this question using 118 optical integral field unit datacubes from the Calar Alto Void Integral-field Treasury surveY (CAVITY), observed with the PMAS/PPaK spectrograph at the 3.5 m telescope at the Calar Alto Observatory (Almería, Spain). We fitted their spectra from 3750 Å to 7000 Å with the non-parametric full spectral fitting code STARLIGHT to estimate their stellar population properties: stellar mass, stellar mass surface density, age, star formation rate (SFR), and specific star formation rate (sSFR). We analysed the results through the global properties, assessing the behaviour of the whole galaxy, and the spatially resolved information, by obtaining the radial profiles from the 2D maps up to the 2 half-light radius of each stellar population property. The results were examined with respect to their morphological type and stellar mass. Then, we compared them with a control sample of galaxies in filaments and walls, selected from the CALIFA survey and analysed following the same procedure. To make a fair comparison between the samples, we selected a twin filament galaxy for each void galaxy of the same morphological type and closest stellar mass, to match the void galaxy sample as much as possible in morphology and mass. Key findings from our global and spatially resolved analysis include void galaxies having a slightly higher half-light radius (HLR), lower stellar mass surface density, and younger ages across all morphological types, and slightly elevated SFR and sSFR (only significant enough for Sas). Many of these differences appear in the outer parts of spiral galaxies (HLR > 1), where discs are younger and exhibit a higher sSFR compared to galaxies in filaments and walls, indicative of less evolved discs. This trend is also found for early-type spirals, suggesting a slower transition from star-forming to quiescent states in voids. Our analysis indicates that void galaxies, influenced by their surroundings, undergo a more gradual evolution, especially in their outer regions, with a more pronounced effect for low-mass galaxies. We find that below a certain mass threshold, environmental processes play a more influential role in galactic evolution.

CAVITY, Calar Alto Void Integral-field Treasury surveY and project extension

We have learnt in the last decades that the majority of galaxies belong to high density regions interconnected in a sponge-like fashion. This large-scale structure is characterised by clusters, filaments, and walls, where most galaxies concentrate, but also under-dense regions called voids. The void regions and the galaxies within represent an ideal place for the study of galaxy formation and evolution, as they are largely unaffected by the complex physical processes that transform galaxies in high-density environments. The void galaxies may hold the key to answer current challenges to the Lambda CDM paradigm as well. The CAVITY survey is a Legacy project approved by the Calar Alto Observatory to obtain spatially resolved spectroscopic information of $ void galaxies in the Local Universe (0.005 < z < 0.050), covering -17.0 to -21.5 in $ r$ band absolute magnitude. It officially started in January 2021 and has been awarded 110 useful dark observing nights at the 3.5 m telescope using the PMAS spectrograph. Complementary follow-up projects, including deep optical imaging, integrated as well as resolved CO data, and integrated HI spectra, have joined the PMAS observations and naturally complete the scientific aim of characterising galaxies in cosmic voids. The extension data has been named CAVITY+. The data will be available to the whole community in different data releases, the first of which is planned for July 2024, and it will provide the community with PMAS datacubes for around 100 void galaxies through a user friendly and well documented database platform. Here, we present the survey, sample selection, data reduction, quality control schemes, science goals, and some examples of the scientific power of the CAVITY and CAVITY+ data.

The AstraLux-TESS high spatial resolution imaging survey

Context. Chance-aligned sources or blended companions can cause false positives in planetary transit detections or simply bias the determination of the candidate properties. In the era of high-precision space-based photometers, the need for high spatial resolution images has been demonstrated to be critical for validating and confirming transit signals. This already applied to theKeplermission, is now applicable to the TESS survey, and will be critical for the PLATO mission.Aims. In this paper we present the results of the AstraLux-TESS survey, a catalog of high spatial resolution images obtained with the AstraLux instrument at the Calar Alto observatory (Almería, Spain) in the context of the TESS Follow-up Observing Program.Methods. We used the lucky imaging technique to obtain high spatial resolution images from planet candidate hosts included mostly in two relevant regimes: exoplanet candidates belonging to the level one requirement of the TESS mission (planets with radiiR <4R⊕) and TESS planet candidates around intermediate-mass main-sequence stars.Results. Among the 185 planet host candidate stars observed, we found 13 (7%) to be accompanied by additional sources within a separation of 2.2 arcsec. Among them, six are not associated with sources in theGaiaDR3 catalog, thus contaminating the TESS light curve. Even if no contaminants have been detected, we can provide upper limits and probabilities to the possible existence of field contaminants through the sensitivity limits of our images. Among the isolated hosts, we can discard hazardous companions (bright enough to mimic a planetary transit signals) with an accuracy below 1% for all their planets.Conclusions. The results from this catalog are key to the statistical validation of small planets (prime targets of the TESS mission) and planets around intermediate-mass stars in the main sequence. These two populations of planets are difficult to confirm with the radial velocity technique because of the shallow amplitude of small planets and the high rotational velocities and low number of available spectral lines in the intermediate stellar mass regime. Our results also demonstrate the importance of this type of follow-up observation for future transit missions such as PLATO, even in theGaiaera.

TOI-1135 b: A young hot Saturn-size planet orbiting a solar-type star

Despite the thousands of planets in orbit around stars known to date, the mechanisms of planetary formation, migration, and atmospheric loss remain unresolved. In this work, we confirm the planetary nature of a young Saturn-size planet transiting a solar-type star every 8.03 d, TOI-1135 b. The age of the parent star is estimated to be in the interval of 125-1000 Myr based on various activity and age indicators, including its stellar rotation period of 5.13 ± 0.27 days and the intensity of photospheric lithium. We obtained follow-up photometry and spectroscopy, including precise radial velocity measurements using the CARMENES spectrograph, which together with the TESS data allowed us to fully characterise the parent star and its planet. As expected for its youth, the star is rather active and shows strong photometric and spectroscopic variability correlating with its rotation period. We modelled the stellar variability using Gaussian process regression. We measured the planetary radius at 9.02 ± 0.23 R⊕ (0.81 ± 0.02 RJup) and determined a 3σ upper limit of < 51.4 M⊕ (< 0.16 MJup) on the planetary mass by adopting a circular orbit. Our results indicate that TOI-1135 b is an inflated planet less massive than Saturn or Jupiter but with a similar radius, which could be in the process of losing its atmosphere by photoevaporation. This new young planet occupies a region of the mass-radius diagram where older planets are scarse, and it could be very helpful to understanding the lower frequency of planets with sizes between Neptune and Saturn.

TOI-4438 b: a transiting mini-Neptune amenable to atmospheric characterization

We report the confirmation and mass determination of a mini-Neptune transiting the M3.5\,V star TOI-4438 (G 182-34) every 7.44 days. A transit signal was detected with NASA's TESS space mission in the sectors 40, 52, and 53. In order to validate the planet TOI-4438\,b and to determine the system properties, we combined TESS data with high-precision radial velocity measurements from the CARMENES spectrograph, spanning almost one year, and ground-based transit photometry. We found that TOI-4438\,b has a radius of $R_ b $\,=\,2.52\,pm \,0.13 R$_ (5<!PCT!> precision), which together with a mass of $M_ b $\,=\,5.4\,pm \,1.1 M$_ (20<!PCT!> precision), results in a bulk density of $ b $ (sim 28<!PCT!> precision), aligning the discovery with a volatile-rich planet. Our interior structure retrieval with a pure water envelope yields a minimum water mass fraction of 46<!PCT!> (1sigma ). TOI-4438\,b is a volatile-rich mini-Neptune with likely H/He mixed with molecules, such as water, CO$_2$, and CH$_4$. The primary star has a $J$-band magnitude of 9.7, and the planet has a high transmission spectroscopy metric (TSM) of 136\,pm \,13. Taking into account the relatively warm equilibrium temperature of $T_ eq $\,=\,435\,pm \,15 K, and the low activity level of its host star, TOI-4438\,b is one of the most promising mini-Neptunes around an M dwarf for transmission spectroscopy studies.

The CARMENES search for exoplanets around M dwarfs

Light from celestial objects interacts with the molecules of the Earth’s atmosphere, resulting in the production of telluric absorption lines in ground-based spectral data. Correcting for these lines, which strongly affect red and infrared wavelengths, is often needed in a wide variety of scientific applications. Here, we present the template division telluric modeling (TDTM) technique, a method for accurately removing telluric absorption lines in stars that exhibit numerous intrinsic features. Based on the Earth’s barycentric motion throughout the year, our approach is suited for disentangling telluric and stellar spectral components. By fitting a synthetic transmission model, telluric-free spectra are derived. We demonstrate the performance of the TDTM technique in correcting telluric contamination using a high-resolution optical spectral time series of the feature-rich M3.0 dwarf star Wolf 294 that was obtained with the CARMENES spectrograph. We apply the TDTM approach to the CARMENES survey sample, which consists of 382 targets encompassing 22 357 optical and 20 314 near-infrared spectra, to correct for telluric absorption. The corrected spectra are coadded to construct template spectra for each of our targets. This library of telluric-free, high signal-to-noise ratio, high-resolution (ℛ > 80 000) templates comprises the most comprehensive collection of spectral M-dwarf data available to date, both in terms of quantity and quality, and is available at the project website.

The Calar Alto Legacy Integral Field Area survey: extended and remastered data release

ABSTRACT This paper describes the extended data release (eDR) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. It comprises science-grade quality data for 895 galaxies obtained with the Potsdam Multi Aperture Spectograph/PPak instrument at the 3.5-m telescope at the Calar Alto Observatory along the last 12 yr, using the V500 setup [3700–7500 Å, 6 Å/full-width at half-maximum (FWHM)] and the CALIFA observing strategy. It includes galaxies of any morphological type, star formation stage, a wide range of stellar masses (∼107–1012 M⊙), at an average redshift of ∼0.015 (90 per cent within 0.005 < z < 0.05). Primarily selected based on the projected size and apparent magnitude, we demonstrate that it can be volume corrected resulting in a statistically limited but representative sample of the population of galaxies in the nearby Universe. All the data were homogeneous re-reduced, introducing a set of modifications to the previous reduction. The most relevant is the development and implementation of a new cube-reconstruction algorithm that provides with an (almost) seeing-limited spatial resolution (FWHMPSF ∼ 1.0 arcsec). To illustrate the usability and quality of the data, we extracted two aperture spectra for each galaxy (central 1.5 arcsec and fully integrated), and analyse them using pyFIT3D. We obtain a set of observational and physical properties of both the stellar populations and the ionized gas, that have been compared for the two apertures, exploring their distributions as a function of the stellar masses and morphologies of the galaxies, comparing with recent results in the literature.

The CARMENES search for exoplanets around M dwarfs

The hydrogen Paschen lines are known activity indicators, but studies of them in M dwarfs during quiescence are as rare as their reports in flare studies. This situation is mostly caused by a lack of observations, owing to their location in the near-infrared regime, which is covered by few high-resolution spectrographs. We study the Paβ line, using a sample of 360 M dwarfs observed by the CARMENES spectrograph. Descending the spectral sequence of inactive M stars in quiescence, we find the Paβ line to get shallower until about spectral type M3.5 V, after which a slight re-deepening is observed. Looking at the whole sample, for stars with Hα in absorption, we find a loose anti-correlation between the (median) pseudo-equivalent widths (pEWs) of Hα and Paβ for stars of similar effective temperature. Looking instead at time series of individual stars, we often find correlation between pEW(Hα) and pEW(Paβ) for stars with Hα in emission and an anti-correlation for stars with Hα in absorption. Regarding flaring activity, we report the automatic detection of 35 Paschen line flares in 20 stars. Additionally we found visually six faint Paschen line flares in these stars plus 16 faint Paschen line flares in another 12 stars. In strong flares, Paschen lines can be observed up to Pa 14. Moreover, we find that Paschen line emission is almost always coupled to symmetric Hα line broadening, which we ascribe to Stark broadening, indicating high pressure in the chromosphere. Finally we report a few Paβ line asymmetries for flares that also exhibit strong Hα line asymmetries.

Two sub-Neptunes around the M dwarf TOI-1470

Aims. A transiting planet candidate with a sub-Neptune radius orbiting the nearby (d = 51.9 ± 0.07 pc) M1.5 V star TOI-1470 with a period of ~2.5 d was announced by the NASA Transiting Exoplanet Survey Satellite (TESS), which observed the field of TOI-1470 in four different sectors. We aim to validate its planetary nature using precise radial velocities (RVs) taken with the CARMENES spectrograph. Methods. We obtained 44 RV measurements with CARMENES spanning eight months between 3 June 2020 and 17 January 2021. For a better characterization of the parent star activity, we also collected contemporaneous optical photometric observations at the Joan Oró and Sierra Nevada Observatories, and we retrieved archival photometry from the literature. We used ground-based photometric observations from MuSCAT and also from MuSCAT2 and MuSCAT3 to confirm the planetary transit signals. We performed a combined photometric and spectroscopic analysis by including Gaussian processes and Keplerian orbits to simultaneously account for the stellar activity and planetary signals. Results. We estimate that TOI-1470 has a rotation period of 29 ± 3d based on photometric and spectroscopic data. The combined analysis confirms the discovery of the announced transiting planet, TOI-1470 b, with an orbital period of 2.527093 ± 0.000003 d, a mass of 7.32-1.24+1.21M⊕, and a radius of 2.18-0.04+0.04R⊕. We also discover a second transiting planet that was not announced previously by TESS, TOI-1470 c, with an orbital period of 18.08816 ± 0.00006 d, a mass of 7.24-2.77+2.87M⊕, and a radius of 2.47-0.02+0.02R⊕ . The two planets are placed on the same side of the radius valley of M dwarfs and lie between TOI-1470 and the inner border of its habitable zone.

The Mantis Network

Cross-correlation spectroscopy is an invaluable tool in the study of exoplanets. However, aliasing between spectral lines makes it vulnerable to systematic biases. This work strives to constrain the aliases of the cross-correlation function to provide increased confidence in the detections of elements in the atmospheres of ultra-hot Jupiters (UHJs) observed with high-resolution spectrographs. We use a combination of archival transit observations of the UHJ KELT-9 b obtained with the HARPS-N and CARMENES spectrographs and show that it is possible to leverage each instrument’s strengths to produce robust detections at a substantially reduced signal-to-noise. Aliases that become present at low signal-to-noise regimes are constrained through a linear regression model. We confirm previous detections of H I, Na I, Mg I, Ca II, Sc II, Ti II, Cr II, Fe I, and Fe II, and detect eight new species, Ca I, Cr I, Ni I, Sr II, and Tb II, at the 5σ level, and Ti I, V I, and Ba II above the 3σ level. Ionised terbium (Tb II) has never before been seen in an exoplanet atmosphere. We further conclude that a 5σ threshold may not provide a reliable measure of confidence when used to claim detections, unless the systematics in the cross-correlation function caused by aliases are taken into account.

Robustness measures for molecular detections using high-resolution transmission spectroscopy of exoplanets

ABSTRACT Ground-based high-resolution transmission spectroscopy has emerged as a promising technique for detecting chemicals in transiting exoplanetary atmospheres. Despite chemical inferences in several exoplanets and previous robustness studies, a robust and consistent detrending method to remove telluric and stellar features from transmission spectra has yet to be agreed upon. In this work, we investigate the robustness of metrics used to optimize principle component analysis (PCA)-based detrending for high-resolution transmission spectra of exoplanets in the near-infrared. As a case study, we consider observations of the hot Jupiter HD 189733 b obtained using the CARMENES spectrograph on the 3.5 m CAHA telescope. We confirm that optimizing the detrending parameters to maximize the signal-to-noise ratio (S/N) of a cross-correlation signal in the presence of noise has the potential to bias the detection significance at the planetary velocity of optimization. However, we find that optimization using the difference between a signal-injected cross-correlation function and the direct cross-correlation function (CCF) is more robust against over-optimization of noise and spurious signals. We additionally examine the robustness of weighting the contribution of each order to the final CCF, and of S/N calculations. Using a prescribed robust methodology, we confirm H2O in the atmosphere of HD 189733 b (S/N = 6.1). We then investigate two further case studies, of exoplanets HD 209458 b and WASP-76 b, confirming OH in the atmosphere of WASP-76 b (S/N = 4.7), and demonstrating how non-robust methods may induce false positive or inflated detections. Our findings pave the way towards a robust framework for homogeneous characterization of exoplanetary atmospheres using high-resolution transmission spectroscopy in the near-infrared.

The CARMENES search for exoplanets around M dwarfs

It is clearly established that the Sun has an 11-yr cycle that is caused by its internal magnetic field. Such a cycle is also observed in a sample of M dwarfs. In the framework of exoplanet detection or atmospheric characterisation of exoplanets, the activity status of the host star plays a crucial role, and inactive states are preferable for such studies. This means that it is important to know the activity cycles of these stars. We study systematic long-term variability in a sample of 211 M dwarfs observed with CARMENES, the high-resolution optical and near-infrared spectrograph at Calar Alto Observatory. In an automatic search using time series of different activity indicators, we identified 26 stars with linear or quadratic trends or with potentially cyclic behaviour. Additionally, we performed an independent search in archival R′HK data collected from different instruments whose time baselines were usually much longer. These data are available for a subset of 186 of our sample stars. Our search revealed 22 cycle candidates in the data. We found that the percentage of stars showing long-term variations drops dramatically to the latest M dwarfs. Moreover, we found that the pseudo-equivalent width (pEW) of the Hα and Ca II infrared triplet more often triggers automatic detections of long-term variations than the TiO index, differential line width, chromatic index, or radial velocity. This is in line with our comparison of the median relative amplitudes of the different indicators. For stars that trigger our automatic detection, this leads to the highest amplitude variation in R′HK, followed by pEW(Hα), pEW(CaII IRT), and the TiO index.

The CARMENES search for exoplanets around M dwarfs

We present the discovery of an Earth-mass planet (Mb sin i = 1.26 ± 0.21 M⊕) on a 15.6 d orbit of a relatively nearby (d ~ 9.6 pc) and low-mass (0.167 ± 0.011 M⊙) M5.0 V star, Wolf 1069. Sitting at a separation of 0.0672 ± 0.0014 au away from the host star puts Wolf 1069 b in the habitable zone (HZ), receiving an incident flux of S = 0.652 ± 0.029 S⊕. The planetary signal was detected using telluric-corrected radial-velocity (RV) data from the CARMENES spectrograph, amounting to a total of 262 spectroscopic observations covering almost four years. There are additional long-period signals in the RVs, one of which we attribute to the stellar rotation period. This is possible thanks to our photometric analysis including new, well-sampled monitoring campaigns undergone with the OSN and TJO facilities that supplement archival photometry (i.e., from MEarth and SuperWASP), and this yielded an updated rotational period range of Prot = 150–170 d, with a likely value at 169.3−3.6+3.7. The stellar activity indicators provided by the CARMENES spectra likewise demonstrate evidence for the slow rotation period, though not as accurately due to possible factors such as signal aliasing or spot evolution. Our detectability limits indicate that additional planets more massive than one Earth mass with orbital periods of less than 10 days can be ruled out, suggesting that perhaps Wolf 1069 b had a violent formation history. This planet is also the sixth closest Earth-mass planet situated in the conservative HZ, after Proxima Centauri b, GJ 1061 d, Teegarden’s Star c, and GJ 1002 b and c. Despite not transiting, Wolf 1069 b is nonetheless a very promising target for future three-dimensional climate models to investigate various habitability cases as well as for sub-m s−1 RV campaigns to search for potential inner sub-Earth-mass planets in order to test planet formation theories.

The CARMENES search for exoplanets around M dwarfs

Context. The CARMENES instrument, installed at the 3.5 m telescope of the Calar Alto Observatory in Almería, Spain, was conceived to deliver high-accuracy radial velocity (RV) measurements with long-term stability to search for temperate rocky planets around a sample of nearby cool stars. Moreover, the broad wavelength coverage was designed to provide a range of stellar activity indicators to assess the nature of potential RV signals and to provide valuable spectral information to help characterise the stellar targets. Aims. We describe the CARMENES guaranteed time observations (GTO), spanning from 2016 to 2020, during which 19 633 spectra for a sample of 362 targets were collected. We present the CARMENES Data Release 1 (DR1), which makes public all observations obtained during the GTO of the CARMENES survey. Methods. The CARMENES survey target selection was aimed at minimising biases, and about 70% of all known M dwarfs within 10 pc and accessible from Calar Alto were included. The data were pipeline-processed, and high-level data products, including 18 642 precise RVs for 345 targets, were derived. Time series data of spectroscopic activity indicators were also obtained. Results. We discuss the characteristics of the CARMENES data, the statistical properties of the stellar sample, and the spectroscopic measurements. We show examples of the use of CARMENES data and provide a contextual view of the exoplanet population revealed by the survey, including 33 new planets, 17 re-analysed planets, and 26 confirmed planets from transiting candidate follow-up. A subsample of 238 targets was used to derive updated planet occurrence rates, yielding an overall average of 1.44 ± 0.20 planets with 1 M⊕ < Mpl sin i < 1000 M⊕ and 1 day < Porb < 1000 days per star, and indicating that nearly every M dwarf hosts at least one planet. All the DR1 raw data, pipeline-processed data, and high-level data products are publicly available online. Conclusions. CARMENES data have proven very useful for identifying and measuring planetary companions. They are also suitable for a variety of additional applications, such as the determination of stellar fundamental and atmospheric properties, the characterisation of stellar activity, and the study of exoplanet atmospheres.