Perspective acceleration and gravitational redshift. Measuring masses of individual white dwarfs using Gaia + SIM astrometry

According to current plans, the SIM/NASA mission will be launched just after the end of operations for the Gaia/ESA mission. This is a new situation which enables long term astrometric projects that could not be achieved by either mission alone. Using the well-known perspective acceleration effect on astrometric measurements, the true heliocentric radial velocity of a nearby star can be measured with great precision if the time baseline of the astrometric measurements is long enough. Since white dwarfs are compact objects, the gravitational redshift can be quite large (40-80 km/s), and is the predominant source of any shift in wavelength. The mismatch of the true radial velocity with the spectroscopic shift thus leads to a direct measure of the Mass--Radius relation for such objects. Using available catalog information about the known nearby white dwarfs, we estimate how many masses/gravitational redshift measurements can be obtained with an accuracy better than 2%. Nearby white dwarfs are relatively faint objects (10 < V < 15), which can be easily observed by both missions. We also briefly discuss how the presence of a long period planet can mask the astrometric signal of perspective acceleration.Comment: 3 pages, 2 Figures. Proceedings of the IAU Symposium 261 : Relativity in Fundamental Astronomy. 27 April - 1 May 2009, Virginia Beach, VA, USA. refereed and accepted versio

A planetary system with gas giants and super-Earths around the nearby M dwarf GJ676A : Optimizing data analysis techniques for the detection of multi-planetary systems

G. Anglada-Escude and M. Tuomi, 'A planetary system via gas giants and super-Earths around the nearby M dwarf GJ 676A: Optimizing data analysis techniques for the detection of multi-planetary systems', Astronomy & Astrophysics, Vol. 548, A58 (2012). The version of record is available online at DOI: 10.1051/0004-6361/201219910 © ESO 2012 Published by EDP SciencesContext. Several M dwarfs are targets of systematical monitoring in searches for Doppler signals caused by low-mass exoplanet companions. As a result, an emerging population of high-multiplicity planetary systems around low-mass stars are being detected as well. Aims. We optimize classic data analysis methods and develop new ones to enhance the sensitivity towards lower amplitude planets in high-multiplicity systems. We apply these methods to the public HARPS observations of GJ≠676A, a nearby and relatively quiet M dwarf with one reported gas giant companion. Methods. We rederived Doppler measurements from public HARPS spectra using the recently developed template matching method (HARPS-TERRA software). We used refined versions of periodograms to assess the presence of additional low-mass companions. We also analysed the same dataset with Bayesian statistics tools and compared the performance of both approaches. Results. We confirm the already reported massive gas giant candidate and a long period trend in the Doppler measurements. In addition to that, we find very secure evidence in favour of two new candidates in close-in orbits and masses in the super-Earth mass regime. Also, the increased time-span of the observations allows the detection of curvature in the long-period trend. suggesting the presence of a massive outer companion whose nature is still unclear. Conclusions. Despite the increased sensitivity of our new periodogram tools, we find that Bayesian methods are significantly more sensitive and reliable in the early detection of candidate signals, but more work is needed to quantify their robustness against false positives. While hardware development is important in increasing the Doppler precision, development of data analysis techniques can help to reveal new results from existing data sets with significantly fewer resources. This new system holds the record of minimum-mass range (from Msini ~ 4.5 M⊕ to 5 Mjup) and period range (from P ~ 3.6 days to more than 10 years). Although all planet candidates are substantially more massive, it is the first exoplanetary system with a general architecture similar to our solar system. GJ 676A can be happily added to the family of high-multiplicity planetary systems around M dwarfs.Peer reviewe

Experiments i models relativistes per a l'astrometria òptica des de l'espai. Aplicació a la missió Gaia.

[spa] Gaia es un proyecto de la agencia espacial Europea (ESA) que pretende hacer un censo galáctico catalogando más de 1000 millones de objetos con una precisión astrometrica sin precedentes. La astrometria es la parte de la astronomia dedicada a la medida y al estudio del movimiento de los astros y ha sido uno de los principales motores de la física y las matemáticas de los últimos 2000 años. La precisión astrometrica de Gaia se estima en unos 10 microsegundos de arco, que es el tamaño angular de una moneda de dos euros en la superficie de la Luna vista desde la Tierra. A tal precisión, un montón de efectos en la propagación de la luz y la definición de los observables astrometricos entran en juego. Por ejemplo, la deflexión de la luz por el Sol pero también de los planetas del sistema solar, efectos de aberración en las imágenes adquiridas por la sonda debido a su rotación, o nuevos efectos astrométricos de segundo orden en el movimiento de las fuentes previamente indetectables. Este trabajo estudia estos aspectos desde un punto de vista relativista. Contiene tres partes. La primera se dedica a los efectos en la adquisición de datos astrometricos debidos a la propagación pro el interior de un sistema óptico en rotación (tipo Gaia). La segunda parte versa sobre la relaicón entre el intervalo de tiempo de emisión y de recepción, que causa movimiento aparente adicional sobre todo el movimiento de la sonda es no-lineal. La tercera parte estudia la deflexión dela luz relativista por parte de los planetas del sistema solar y se estudia la calidad así como el método de extracción de parámetros físicos a partir de la observaciones

La alfabetización visual en el aula de español como lengua extranjera

Treball Final de Master en Comunicació Intercultural i d'Ensenyament de Llengües. Codi: SAN014. Curs: 2013/2014Este trabajo defiende la necesidad de incluir la alfabetización visual en el proceso de enseñanza/aprendizaje de segundas lenguas, y en concreto del español como lengua extranjera. El trabajo sigue dos líneas principales de argumentación. Por un lado, a través de varios autores de referencia en el campo de la educación, de las nuevas tecnologías y de la alfabetización visual, veremos que el desarrollo de la destreza de la lectura de imágenes es imprescindible para preparar a los futuros ciudadanos en un mundo digital. Por el otro, demostraremos que la lectura de imágenes no es una habilidad universal ya que está determinada por la formación, el entorno educativo y, en definitiva, por la cultura. Resultará, pues, muy productivo incluir el análisis iconográfico e ideológico de imágenes en el aula de segundas lenguas ya que no solo ayudará a los aprendientes a comprender mejor los diferentes puntos de vista de la lengua meta, sino que también facilitará la generación y ampliación de lo que Roland Barthes denomina registros o repertorios sígnicos. Tras esto ofreceremos, usando como punto de partida las teorías de autores como Erwin Panofsky o Roland Barthes, algunas herramientas y ejemplos de análisis crítico de imágenes útiles para el aula de español como lengua extranjera

Up to four planets around the M dwarf GJ 163 : Sensitivity of Bayesian planet detection criteria to prior choice

M. Tuomi and G. Anglada-Escude, 'Up to four planes around the M dwarf GJ 163: Sensitivity of Bayesian planet detection criteria to prior choice', Astronomy & Astrophysics, Vol. 556, A111 (2013), available online at DOI: 10.1051/0004-6361/201321174 © ESO 2013 Published by EDP SciencesContext. Exoplanet Doppler surveys are currently the most efficient means to detect low-mass companions to nearby stars. Among these stars, the light M dwarfs provide the highest sensitivity to detect low-mass exoplanet candidates. Evidence is accumulating that a substantial fraction of these low-mass planets are found in high-multiplicity planetary systems. GJ 163 is a nearby inactive M dwarf with abundant public observations obtained using the HARPS spectrograph. Aims. We obtain and analyse radial velocities from the HARPS public spectra of GJ 163 and investigate the presence of a planetary companions orbiting it. The number of planet candidates detected might depend on some prior assumptions. Since the impact of prior choice has not been investigated throughly previously, we study the effects of different prior densities on the detectability of planet candidates around GJ 163. Methods. We use Bayesian tools, i.e. posterior samplings and model comparisons, when analysing the GJ 163 velocities. We consider models accounting for the possible correlations of subsequent measurements. We also search for activity-related counterparts of the signals we observe and test the dynamical stability of the planetary systems corresponding to our solutions using direct numerical integrations of the orbits. Results. We find that there are at least three planet candidates orbiting GJ 163. The existence of a fourth planet is supported by the data but the evidence in favor of the corresponding model is not yet conclusive. The second innermost planet candidate in the system with an orbital period of 25.6 days and a minimum mass of 8.7 M· is inside the liquid-water habitable zone of the star. Conclusions. The architecture of GJ 163 system resembles a scaled-down Solar System in the sense that there are two low-mass planets on orbital periods of 8.7 and 25.6 days in the inner system, a possible slightly more massive companion on an intermediate orbit, and an outer sub-Saturnian companion at roughly 1 AU. The discovery of (yet) another planetary system with several low-mass companions around a nearby M-dwarf indicates that the high-multiplicity planetary systems found by the NASA Kepler mission around G and K dwarfs is also present (possibly even reinforced) around low-mass stars. © 2013 ESO.Peer reviewe