Modelling the photosphere of active stars for planet detection and characterizaton

Context. Stellar activity patterns are responsible for jitter effects that are observed at different timescales and amplitudes in the measurements obtained from photometric and spectroscopic time series observations. These effects are currently in the focus of many exoplanet search projects, since the lack of a well-defined characterization and correction strategy hampers the detection of the signals associated with small exoplanets. Aims. Accurate simulations of the stellar photosphere based on the most recent available models for main-sequence stars can provide synthetic photometric and spectroscopic time series data. These may help to investigate the relation between activity jitter and stellar parameters when considering different active region patterns. Moreover, jitters can be analysed at different wavelength scales (defined by the passbands of given instruments or space missions) to design strategies to remove or minimize them. Methods. We present the StarSim tool, which is based on a model for a spotted rotating photosphere built from the integration of the spectral contribution of a fine grid of surface elements. The model includes all significant effects affecting the flux intensities and the wavelength of spectral features produced by active regions and planets. The resulting synthetic time series data generated with this simulator were used to characterize the effects of activity jitter in extrasolar planet measurements from photometric and spectroscopic observations. Results. Several cases of synthetic data series for Sun-like stars are presented to illustrate the capabilities of the methodology. A specific application for characterizing and modelling the spectral signature of active regions is considered, showing that the chromatic effects of faculae are dominant for low-temperature contrasts of spots. Synthetic multi-band photometry and radial velocity time series are modelled for HD 189733 by adopting the known system parameters and fitting for the map of active regions with StarSim. Our algorithm reproduces both the photometry and the radial velocity (RV) curves to good precision, generally better than the studies published to date. We evaluate the RV signature of the activity in HD 189733 by exploring a grid of solutions from the photometry. We find that the use of RV data in the inverse problem could break degeneracies and allow for a better determination of some stellar and activity parameters, for example, the configuration of active regions, the temperature contrast of spots, and the amount of faculae. In addition, the effects of spots are studied for a set of simulated transit photometry, showing that these can introduce variations in Rp/R∗ measurements with a spectral signature and amplitude that are very similar to the signal of an atmosphere dominated by dust

The K2-ESPRINT Project II: Spectroscopic follow-up of three exoplanet systems from Campaign 1 of K2

We report on Doppler observations of three transiting planet candidates that were detected during Campaign 1 of the K2 mission. The Doppler observations were conducted with FIES, HARPS-N, and HARPS. We measure the mass of EPIC 201546283b, and provide constraints and upper limits for EPIC 201295312b and EPIC 201577035b. EPIC 201546283b is a warm Neptune orbiting its host star in 6.77 days and has a radius of 4.45_(-0.33)^(+0.33)R_⊕ and a mass of 29.1_(-7.4)^(+7.5)M_⊕, which leads to a mean density of 1.80_(-0.55)^(+0.70) cm^(-3). EPIC 201295312b is smaller than Neptune with an orbital period of 5.66 days, a radius of 2.75_(-0.22^)(0.24)R_⊕, and we constrain the mass to be below 12 M_⊕ at 95% confidence. We also find a long-term trend indicative of another body in the system. EPIC 201577035b, which was previously confirmed as the planet K2-10b, is smaller than Neptune, orbiting its host star in 19.3 days, with a radius of 3.84_(-0.34)^(+0.35)R_⊕. We determine its mass to be 27_(-16)^(+17)M_⊕, with a 95% confidence upper limit at 57M_⊕, and a mean density of 2.6_(-1.6)^(+2.1)g cm^(-3). These measurements join the relatively small collection of planets smaller than Neptune with measurements or constraints of the mean density. Our code for performing K2 photometry and detecting planetary transits is now publicly available

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

Enabling planetary science across light-years. Ariel Definition Study Report

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution

The CARMENES search for exoplanets around M dwarfs Guaranteed time observations Data Release 1 (2016-2020)

I. Ribas et al.[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.CARMENES is an instrument at the Centro Astronómico Hispano en Andalucía (CAHA) at Calar Alto (Almería, Spain), operated jointly by the Junta de Andalucía and the Instituto de Astrofísica de Andalucía (CSIC). CARMENES was funded by the Max-Planck-Gesellschaft (MPG), the Consejo Superior de Investigaciones Científicas (CSIC), the Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through projects FICTS-2011-02, ICTS-2017-07-CAHA-4, and CAHA16-CE-3978, and the members of the CARMENES Consortium (Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Königstuhl, Institut de Ciències de l’Espai, Institut für Astrophysik Göttingen, Universidad Complutense de Madrid, Thüringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología and Centro Astronómico Hispano-Alemán), with additional contributions by the MINECO, the Deutsche Forschungsgemeinschaft (DFG) through the Major Research Instrumentation Programme and Research Unit FOR2544 “Blue Planets around Red Stars”, the Klaus Tschira Stiftung, the states of Baden-Württemberg and Niedersachsen, and by the Junta de Andalucía. We acknowledge financial support from the Spanish Agencia Estatal de Investigación of the Ministerio de Ciencia e Innovación (AEI-MCIN) and the ERDF “A way of making Europe” through projects PID2020-117493GB-I00, PID2019-109522GB-C5[1:4], PID2019-110689RB-I00, PID2019-107061GB-C61, PID2019-107061GB-C64, PGC2018-098153-B-C33, PID2021-125627OB-C31/AEI/10.13039/501100011033, and the Centre of Excellence “Severo Ochoa” and “María de Maeztu” awards to the Institut de Ciències de l’Espai (CEX2020-001058-M), Instituto de Astrofísica de Canarias (CEX2019-000920-S), Instituto de Astrofísica de Andalucía (SEV-2017-0709), and Centro de Astrobiología (MDM-2017-0737). We also benefited from additional funding from: the Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya and the Agència de Gestió d’Ajuts Universitaris i de Recerca of the Generalitat de Catalunya, with additional funding from the European FEDER/ERDF funds, and from the Generalitat de Catalunya/CERCA programme; the DFG through the Major Research Instrumentation Programme and Research Unit FOR2544 “Blue Planets around Red Stars” (RE 2694/8-1); the University of La Laguna through the Margarita Salas Fellowship from the Spanish Ministerio de Universidades ref. UNI/551/2021-May-26, and under the EU Next Generation funds; the Gobierno de Canarias through projects ProID2021010128 and ProID2020010129; the Spanish MICINN under Ramón y Cajal programme RYC-2013-14875; the “Fondi di Ricerca Scientifica d’Ateneo 2021” of the University of Rome “Tor Vergata”; and the programme “Alien Earths” supported by the National Aeronautics and Space Administration (NASA) under agreement No. 80NSSC21K0593. TPeer reviewe

A search for low-mass objects in young star-forming regions

The object of this thesis is find new low-mass objects in Taurus in order to get new insights on its mass function. The investigated area in this work is located 5 deg north of the main clouds and covers around 25 sq:deg. Thus, we also contribute to answer the question whether the low-mass objects have moved from their birth sites or not.La mejor herramienta para caracterizar la formación de estrellas es la función de masas. Muchas estrellas de baja masa faltarían en la región de formación estelar de Toro para que pudiera encajar la forma universal de la función. Así pues, los miembros de esta joven y próxima región representan una excepción a dicha forma universal. Nuestro objetivo fue encontrar nuevos miembros de Toro. Para ello, investigamos la región localizada 5 deg al norte de las nubes principales. Para estudiar la relación entre la diferencia de la función de masa de Toro y su baja densidad, también estudiamos la región Orion. Se utilizó el registro fotométrico de campo amplio e infrarrojo cercano UKIDSS GCS como base de datos para nuestra búsqueda. Asimismo, investigamos las características fotométricas de los 351 miembros de Toro ya conocidos. En total se aplicaron 40 criterios de selección. Para confirmar la pertenencia a una de las regiones de todas las fuentes selecionadas, los candidatos se observaron mediante espectroscopia óptica de baja resolución. En estos rangos de longitud de onda, múltiples características de las líneas pueden revelar la juventud de una fuente. Para comparar dichas fuentes se observaron unos miembros de Toro ya conocidos y unas estrellas enanas de campo. En Toro fueron observados 47 de 272 candidatos y 7 de 55 en Orion. El análisis fotométrico y espectral completo pudo identificar 7 y 4 de ellos como posibles nuevos miembros WTTS. Los nuevos miembros de Toro no están conectados a ninguna nube molecular y se han movido desde su sitio de nacimiento a su sitio actual. Su existencia indica una significante población todavía desconocida de miembros de Toro lejos de las nubes principales. Por tanto podemos concluir que los objetos de Toro de baja masa que faltaban están localizados lejos de las nubes principales de la región. Si esta región joven y cercana de formación estelar es única o no, se puede estudiar en sus partes externas. Toro es sin lugar a dudas de menor densidad y está más extendida a como se había asumido previamente

MCDF calculations of the specific mass shift in helium-like ions

An extension of the GRASP92 (Parpia F A, Froese Fischer C and Grant I P 1996 Comput. Phys. Commun. 94 249) multi-configuration Dirac-Fock (MCDF) program described previously (Perger W F and Idrees M 1995 Phys. Commun. 85 389-97) is used for the calculation of the specific mass shift (SMS) of the helium 1S ground state isoelectronic sequence. We also employ a multi-configuration Hartree-Fock (MCHF) method to calculate the ground state SMS for comparison with MCDF results. The SMS matrix elements for two-electron systems obtained from the relativistic program are shown to exhibit a trend: the larger the atomic number Z, the larger the relativistic contributions to the SMS matrix elements for the ions. The SMS matrix elements approximately vary as Z3 along the isoelectronic sequence from Z = 2 to 92. In addition, it is shown that the relativistic effects increase approximately as Z3/A2 in the SMS values for all the ions considered confirming some previous observations (Parpia F A, Tong M and Froese Fischer C 1992 Phys. Rev. A 46 3717-24). Excellent agreement is found between the present ab initio calculations and the available semi-relativistic calculations for the small values of Z along the helium-like ions. Furthermore, a large set of configuration state functions used in the calculations has revealed larger disagreements for high-Z ions between both relativistic (MCDF-optimized-level) and nonrelativistic (MCHF) calculations suggesting that the SMS for helium-like ions with Z \u3e 40 relativistic and correlation effects are increasingly important

Modelling the photosphere of active stars for planet detection and characterization

International audienc

Modelling the photosphere of active stars for planet detection and characterizaton

Context. Stellar activity patterns are responsible for jitter effects that are observed at different timescales and amplitudes in the measurements obtained from photometric and spectroscopic time series observations. These effects are currently in the focus of many exoplanet search projects, since the lack of a well-defined characterization and correction strategy hampers the detection of the signals associated with small exoplanets. Aims. Accurate simulations of the stellar photosphere based on the most recent available models for main-sequence stars can provide synthetic photometric and spectroscopic time series data. These may help to investigate the relation between activity jitter and stellar parameters when considering different active region patterns. Moreover, jitters can be analysed at different wavelength scales (defined by the passbands of given instruments or space missions) to design strategies to remove or minimize them. Methods. We present the StarSim tool, which is based on a model for a spotted rotating photosphere built from the integration of the spectral contribution of a fine grid of surface elements. The model includes all significant effects affecting the flux intensities and the wavelength of spectral features produced by active regions and planets. The resulting synthetic time series data generated with this simulator were used to characterize the effects of activity jitter in extrasolar planet measurements from photometric and spectroscopic observations. Results. Several cases of synthetic data series for Sun-like stars are presented to illustrate the capabilities of the methodology. A specific application for characterizing and modelling the spectral signature of active regions is considered, showing that the chromatic effects of faculae are dominant for low-temperature contrasts of spots. Synthetic multi-band photometry and radial velocity time series are modelled for HD 189733 by adopting the known system parameters and fitting for the map of active regions with StarSim. Our algorithm reproduces both the photometry and the radial velocity (RV) curves to good precision, generally better than the studies published to date. We evaluate the RV signature of the activity in HD 189733 by exploring a grid of solutions from the photometry. We find that the use of RV data in the inverse problem could break degeneracies and allow for a better determination of some stellar and activity parameters, for example, the configuration of active regions, the temperature contrast of spots, and the amount of faculae. In addition, the effects of spots are studied for a set of simulated transit photometry, showing that these can introduce variations in Rp/R∗ measurements with a spectral signature and amplitude that are very similar to the signal of an atmosphere dominated by dust

Modelling the photosphere of active stars for planet detection and characterizaton

Context. Stellar activity patterns are responsible for jitter effects that are observed at different timescales and amplitudes in the measurements obtained from photometric and spectroscopic time series observations. These effects are currently in the focus of many exoplanet search projects, since the lack of a well-defined characterization and correction strategy hampers the detection of the signals associated with small exoplanets. Aims. Accurate simulations of the stellar photosphere based on the most recent available models for main-sequence stars can provide synthetic photometric and spectroscopic time series data. These may help to investigate the relation between activity jitter and stellar parameters when considering different active region patterns. Moreover, jitters can be analysed at different wavelength scales (defined by the passbands of given instruments or space missions) to design strategies to remove or minimize them. Methods. We present the StarSim tool, which is based on a model for a spotted rotating photosphere built from the integration of the spectral contribution of a fine grid of surface elements. The model includes all significant effects affecting the flux intensities and the wavelength of spectral features produced by active regions and planets. The resulting synthetic time series data generated with this simulator were used to characterize the effects of activity jitter in extrasolar planet measurements from photometric and spectroscopic observations. Results. Several cases of synthetic data series for Sun-like stars are presented to illustrate the capabilities of the methodology. A specific application for characterizing and modelling the spectral signature of active regions is considered, showing that the chromatic effects of faculae are dominant for low-temperature contrasts of spots. Synthetic multi-band photometry and radial velocity time series are modelled for HD 189733 by adopting the known system parameters and fitting for the map of active regions with StarSim. Our algorithm reproduces both the photometry and the radial velocity (RV) curves to good precision, generally better than the studies published to date. We evaluate the RV signature of the activity in HD 189733 by exploring a grid of solutions from the photometry. We find that the use of RV data in the inverse problem could break degeneracies and allow for a better determination of some stellar and activity parameters, for example, the configuration of active regions, the temperature contrast of spots, and the amount of faculae. In addition, the effects of spots are studied for a set of simulated transit photometry, showing that these can introduce variations in Rp/R∗ measurements with a spectral signature and amplitude that are very similar to the signal of an atmosphere dominated by dust