Fernando Pérez Hernández
Antonio Jiménez Mancebo, Roi Alonso Sobrino, Pere L. Pallé Manzano, Clara Régulo Rodríguez, Teodoro Roca Cortés, David López Fernández-Nespral, Paul Beck, Savita Mathur, Juan Antonio Belmonte Avilés, Peter Klagyivik, Hans J. Deeg
IAC Collaborators: Antonio Eff-Darwich, Jesús Patrón Recio
R. García,, S. Mathis, D. Salabert (IRFU/DSM/CEA Saclay, Francia); Mads F. Anderson; J. Christensen-Dalsgaard, F. Grundahl, H. Kjeldsen (Univ. Aarhus, Dinamarca); Enrico Corsaro (INAF Osservatorio Astrofisico di Catania); M. Cunha (CAUP, Portugal); G. Davies (Univ. Birmingham, RU); T. Metcalfe; T. Bedding (Univ. Sydney, Australia); D. Chou, J. Fernández (National Tsing Hua Univ., Taiwan);F. Hill (GONG-NSO, EEUU); J.C. Suárez, R. Garrido (IAA, Granada); S. Korzennik (Harvard-Smithsonian Center for Astrophysics, EEUU); R.; M. Deleuil (LAM Marseille, Francia); D. Gandolfi, (U. Torino, Italia); M. Fridlund (Onsala, Suecia); L. Doyle (SETI, EEUU); H. Rauer, J. Cabrera, Sz. Csizmadia (DLR, Alemania); V. Kozhevnikov (Ural State Univ., Rusia); D. Pollacco (Queens Univ. Belfast, RU); E. Günther, A. Hatzes (Tautenburg Obs, Alemania); T. Mazeh (Tel Aviv Univ., Israel); D. Queloz (Obs. Ginebra); J. Ballot (CNRS, Université de Toulouse, Francia); O. Creevey (Laboratoire Lagrange. Univ, Nice Sophia-Antipolis. Francia); T. Boyajian (Yale, EEUU); B. Tingley (Aarhus U., Dinamarca); D. Martin (U. Ginebra), A. Triaud (Cambridge); D. Fabrycky (U. Chicago)
The principal objectives of this project are: 1) to study the structure and dynamics of the solar interior, 2) to extend this study to other stars, 3) to search for extrasolar planets using photometric methods (primarily by transits of their host stars) and their characterization (using radial velocity information) and 4) the study of the planetary atmospheres.
To reach our first objective, we use Global Helioseismology (analysis of the solar oscillation eigenmodes) and Local Helioseismology (that uses travel waves). Through the detection and investigation of the solar oscillation mode spectrum it is possible to accurately infer information about its interior structure and dynamics, that is, the determination of the most important physical profiles from the centre to the surface of the Sun. This project covers the various necessary aspects to attain the aforementioned objectives: a) Instrumental, which has been previously a strong component of our work and we continue to be involved in new space-based and ground-based projects; b) Observational, we work with continuous uninterrupted data from various global helioseismological networks (BiSON and GONG), as well as data from GOLF and VIRGO on-board SOHO; c) Techniques of reduction, analysis and interpretation of data; d) Theoretical developments of inversion techniques of data and development of solar stellar and structure models. Results have shown that we can understand the details of the Sun with a precision of the order of 0.1%.
On the other hand, the Astroseismology or Stellar seismology aims to obtain a similar knowledge of other stars. This branch of Astrophysics is currently experiencing a golden age thanks to the huge number of stars observed by CoRoT and Kepler space missions. With the data obtained by these missions (already finished) it is possible to extract seismic global parameters of hundreds of stars; both solar type stars and red giants, as well as stars belonging to clusters. With these averaged seismic parameters it is possible to derive scale relationships that allow us to estimate global stellar parameters in a wide range of evolutionary stages covering the HR diagram. In addition, for many of these stars, the excellent quality of the photometry provided by these instruments allow to measure individual acoustic and mixed modes. Furthermore, the recent deployment and beginning of observations with the high precision spectrographs of the SONG (Stellar Observations Network Group) ground-based telescopes will substantially improve the characterization of the eigenmodes spectrum in bright stars. With this extra information, a very precise modelling of the structure of the stars can be performed.
The strategy of using planetary transits to discover new planets around other stars consists of the photometric detection of the dimming of the light of the star when one of its planets passes, or ‘transits’ in front of it. Currently this method is the preferred one for the study of small planets, not only due to its sensitivity, but also because this method allows a more detailed investigation of the planets found (e.g. Planetary atmospheres). This technique is similar to the one that is used for helio- and asteroseismology and so some of its methods are a logical extension from that. However, it is also important to develop new algorithms and observing methods for the unequivocal detection and analysis of planets and to be able to distinguish them from false alarms.
When an exoplanet transits its host star, a variety of follow-up observations are feasible thanks to the special geometry of the orbit. Most of the observational knowledge about the atmospheres of these planets was obtained in the last decade with transiting exoplanets. While many of the results were made possible thanks to space telescopes such as HST and Spitzer, in the last four years several ground-based instruments have reached the precision to start providing useful inputs to the field. We intend to push the ground-based techniques to study physical characteristics of the Hot Jupiter exoplanets. This can be reached with transmission spectroscopy techniques (measuring the radius of the exoplanet at different wavelengths while transiting) or with occultation techniques (the measurement of the depth of the secondary eclipse or occultation of the planet provides a direct probe of its day-side emission).
The current horizon for studies of exoplanets with space missions involves new missions, beginning with the launch of CHEOPS, followed by TESS, JWST and in 2024, PLATO. Thus, there is presently a window of opportunity for ground-based facilities, and we are pursuing observations using mainly TNG, NOT y GTC.
A new methodology of analysis of nearly 17 years of integral sunlight velocity measurements obtained with GOLF on SoHO has allowed the detection of the solar g-modes signature in the asymptotic regime. Such modes are confined in the solar radiative interior and modulate the acoustic p-modes, more precisely the inverse of the acoustic round-trip travel time of the sun. In the frequency range between 9 and 48 hours almost a hundred l=1 g-modes can be found and some more of th l=2 type. They cannot be detected individually above noise however we could find and measure their signature (their period spacing Po) and their rotational splittings. A value of 34 minutes and 1 second (1 second uncertainty) is measured for Po while the averaged core solar rotation is found to be 1644 ± 23 nHz (nearly one week). Such rotation results in 3.8 times faster than the one measured in the radiative layers. Such measurements, pending independent confirmation, is the most solid evidence for solar g-modes to date.
Spectrophotometric observations of Boyajian's star taken with GTC showed that dips in brightness of this object are deeper in red than in blue wavelengths. This implies that occulters with an extended dusty envelope are a likeley origin of this object's brightness variations. Published in two papers in early 2018 (Boyajian et al.; Deeg et al.)
Figure: Measured dip-depths Dn in five wavelenghts (vertical axis), versus the white (average) depths Dw (horizontal axis), during several dips of Boyajian's star observed by GTC. The straight lines indicate a joint fit to all bands, which implies absorption by dust. The lower panel shows the residuals on the same scale. Figure from Deeg et al. (2018, A&A, in print).