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

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

Detection of the nearest Jupiter analog in radial velocity and astrometry data

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.The presence of Jupiter is crucial to the architecture of the Solar System and models underline this to be a generic feature of planetary systems. We find the detection of the difference between the position and motion recorded by the contemporary astrometric satellite Gaia and its precursor Hipparcos can be used to discover Jupiter-like planets. We illustrate how observations of the nearby star $\varepsilon$ Indi A giving astrometric and radial velocity data can be used to independently find the orbit of its suspected companion. The radial velocity and astrometric data provide complementary detections which allow for a much stronger solution than either technique would provide individually. We quantify $\varepsilon$ Indi A b as the closest Jupiter-like exoplanet with a mass of 3 $M_{Jup}$ on a slightly eccentric orbit with an orbital period of 45 yr. While other long-period exoplanets have been discovered, $\varepsilon$ Indi A b provides a well constrained mass and along with the well-studied brown dwarf binary in orbit around $\varepsilon$ Indi A means that the system provides a benchmark case for our understanding of the formation of gas giant planets and brown dwarfs.Peer reviewe

Hypergravity induces changes in physiology, gene expression and epigenetics in zebrafish

All living organisms that inhabit Earth have evolved under a common value of gravity, which amounts to an acceleration of 9.81 m/s2 at mean sea level. Changes on it could cause important alterations that affect vital biological functions. The crescent interest in spatial exploration has opened the question of how exactly these changes in gravity would affect Earth life forms on space environments. This work is the result of a collaborative co-supervision of a master thesis between experts in the area of space sciences and biology, and it can serve as a case study for training experts in such interdisciplinary environments. In particular, we focus on the effect of gravity as a pressure factor in the development of zebrafish (Danio rerio) in the larval stage as a model organism using up-to-date (genomic and epigenetic) techniques. Given the high cost of any experiment in true low gravity (which would require a space launch), we performed an initial experiment in hypergravity to develop the methodologies and identify good (epi)genetic markers of the effect of gravity in our model organism. Previous studies in zebrafish have shown how alteration in gravity effects the development and the gene expression of important regulatory genes. For this study, we firstly customized a small laboratory scale centrifuge to study changes in fish physiology together with changes at molecular levels. We exposed zebrafish larvae from 0 to 6 days post fertilization to the simulated hypergravity (SHG) (100 rpm 3g). After 6 days of hypergravity exposition the larvae showed changes in their swimming and flotation patterns, and presented corporal alterations. Then, we assessed gene expression of genes implicated in important biological processes, (e.g., epigenetics), and an upregulation were observed when compared to the control. Taken together, these preliminary findings show how gravity alterations could affect some basic biological responses, and illustrate the potential of developing new science cases to be developed by students at postgraduate level (MSc and beyond) in a multidisciplinary environmen

Epigenetic and physiological alterations in zebrafish subjected to hypergravity [Dataset]

1 dataset, 16 videosVideos exhibiting every morphological characteristic observed in both the control and hypergravity groups of zebrafish larvaWith the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)Characteristic, Abbreviation, Number of the video file control group, Number of the video file hypergravity group / Position, Movement frequency, Swimming behaviorPeer reviewe