{"id":551,"date":"2018-08-14T19:08:48","date_gmt":"2018-08-14T19:08:48","guid":{"rendered":"https:\/\/astronomia.bedigital.cl\/sphere-performance-permits-many-kinds-of-challenges-from-measuring-astrometric-microlensing-to-image-very-faint-planets\/"},"modified":"2024-11-12T17:46:50","modified_gmt":"2024-11-12T17:46:50","slug":"sphere-performance-permits-many-kinds-of-challenges-from-measuring-astrometric-microlensing-to-image-very-faint-planets","status":"publish","type":"post","link":"https:\/\/astronomia.udp.cl\/en\/sphere-performance-permits-many-kinds-of-challenges-from-measuring-astrometric-microlensing-to-image-very-faint-planets\/","title":{"rendered":"SPHERE performance permits many kinds of challenges, from measuring astrometric microlensing to image very faint planets"},"content":{"rendered":"

Alice Zurlo from the Astronomy Nucleus of UDP shows how with\u00a0 SPHERE we can learn more about exoplanets.<\/em><\/p>\n

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<\/a> on-sky movement of Proxima Centauri with respect to background stars<\/div>\n
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The gravitational mass of Proxima Centauri measured with SPHERE from a microlensing event<\/h1>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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Proxima Centauri<\/strong>, our closest stellar neighbor, is the subject of many attentions since the discovery of a telluric planet in 2016 by the technique of radial velocity. This planet would have a mass of 1.27 Earth masses and orbits the star in 11.2 days. Since the central star is a cool M dwarf the planet resides in the zone where water, if present at the surface of a rocky planet, can be potentially liquid, that is the so called habitable zone. However, the mass of the planet is not completely determined, because radial velocity measures in fact a mass ratio between the star and the planet. Therefore, the determination of the star\u2019s mass is of the outmost importance to reveal the actual nature of the planet. So far this mass (0.12 solar mass) was inferred indirectly using a model linking the luminosity of a star to its mass, but this can be subject to large uncertainties especially at young ages and low masses. However, the gravitational mass of the star can be determined using the micro-lensing effect which causes the light of background stars to be deflected by a foreground object. Because Proxima Centauri is very close to the Solar System it moves significantly with respect to the background stars increasing the chance of line of sight alignements with other stars. Such an event occurred in 2016, and a team led by Alice Zurlo\u00a0 have used SPHERE to monitor precisely the astrometric position of one particular source at 9 epochs between 2015 and 2017. The figure shows the motion of Proxima as measured by SPHERE with respect to background stars. With this experiment the team was able to set a gravitational mass of 0.15\u00a0 solar mass (with an accuracy of about 0.06 solar mass) shifting the mass of the planet to a slightly more massive value: 1.56 Earth masses. In this range of mass we can still expect the planet to be rocky. Another micro-lensing event caused by Proxima Cen happened last month and has been observed with SPHERE, which will allow us to refine even more the mass measurement.\u00a0<\/span><\/div>\n<\/div>\n<\/div>\n<\/div>\n

Paper published in Monthly Notices of the Astronomical Royal Society<\/a>,\u00a0 Zurlo et al, 2018<\/p>\n

Imaging radial velocity planets with SPHERE<\/h1>\n


Radial Velocity<\/strong>\u00a0(RV) is one of the most productive technique to detect planets orbiting around other stars.\u00a0 A lot has been learned from RV surveys on the ground about exoplanets demography. However, the mass of the planet that is inferred from this technique is a lower limit. Because the inclination of the orbit is unknown and\u00a0\u00a0 since RV measures the velocity along the line of sight, in some cases these planets could be larger and massier. Of interest is the possibility to obtain an upper limit of this mass by other means and other techniques, like for instance direct imaging. But planets detected by RV are usually old and cool and may not emit enough light to be directly observed… unless they are bigger than expected (meaning their orbital plane is far from edge one).\u00a0\u00a0
The team led by Alice Zurlo\u00a0 have selected 5 stars with known planets conveniently located (far enough from the host star) and massive enough too (5 to 10 masses of Jupiter) for expecting a detection with SPHERE. None of these planets were detected although the contrast in the images reached very large values. These stars turned out to be too old (>1 billion years), such that the achieved contrasts are corresponding in fact to masses of 25 to 28 Jupiter masses. These estimates allow to derive limits on the orbital plane inclinations of 10 to 20 degrees depending on systems. Overall, all these systems likely harbor actual planets below 13 Jupiter masses, the standard mass for an object to be a planet. The next generation of extremely large telescopes while increasing the angular resolution will definitely be more efficient for this type of study.<\/p>\n

Paper published by the Monthly Notices of the Astornomical Royal Society<\/a>, Zurlo et al, 2018<\/p>\n

A continuaci\u00f3n,\u00a0una entrevista de Media INAF (Instituto Nacional de Astrof\u00edsica (Italia)) \u00a0a la investigadora<\/p>\n

Entrevista<\/h3>\n

La masa de Proxima Centauri se hab\u00eda estimado previamente utilizando un m\u00e9todo indirecto. \u00bfQu\u00e9 cambia con este nuevo enfoque?<\/p>\n

\\\\\\”Nuestra medida es un m\u00e9todo completamente independiente de las estimaciones de la relaci\u00f3n masa-luminosidad, que para estrellas poco masivas puede tener un gran rango de incertidumbre. Lo que medimos es la masa gravitacional de la estrella, que hasta ahora s\u00f3lo se pudo medir para otra estrella distinta al Sol, la enana blanca Stein 2051 B. Encontramos valores compatibles con las estimaciones previas, y agregando mediciones a Pr\u00f3xima Centauri, la incertidumbre en la masa de esta estrella disminuy\u00f3 sustancialmente\\\\\\”.<\/p>\n

\"\\\\\\"\\\\\\"\" Imagen de campo de SPHERE para las mediciones de abril de 2016. Se indican las estrellas de fondo consideradas para la microlente gravitacional. Cr\u00e9ditos: A. Zurlo et al. 2018<\/p>\n

Para su estimaci\u00f3n, se ha utilizado una\u00a0microlente gravitacional<\/strong>. \u00bfC\u00f3mo funciona?<\/p>\n

\\\\\\”La microlente es un fen\u00f3meno predicho por la relatividad general, y se produce cuando un objeto masivo, en este caso una estrella, Proxima Centauri, se interpone entre el observador y un objeto m\u00e1s lejano (en nuestro caso una estrella de fondo). El objeto m\u00e1s cercano crea un fen\u00f3meno de desviaci\u00f3n de luz del objeto de fondo cuando se acerca a la l\u00ednea de visi\u00f3n. La deformaci\u00f3n que se crea se parece a lo que se puede ver a trav\u00e9s de una lente \u00f3ptica. El evento de microlente para Pr\u00f3xima Centauri fue predicho en el 2014 por un grupo liderado por Kailash Sahu. Se utilizaron im\u00e1genes del Telescopio espacial Hubble para este trabajo\\\\\\”.<\/p>\n

En 2016, se detect\u00f3 un exoplaneta \\\\\\”terrestre\\\\\\” en \u00f3rbita alrededor de Proxima Centauri utilizando el m\u00e9todo de velocidades radiales. \u00bfLo observaste\u00a0con tu m\u00e9todo, u obtuviste alguna informaci\u00f3n nueva?<\/p>\n

\\\\\\”El planeta que rodea a Pr\u00f3xima Centauri es demasiado peque\u00f1o para ser visto con nuestro m\u00e9todo. Dado que la medici\u00f3n de su masa depende de la masa de la estrella central, hemos obtenido esta informaci\u00f3n para el planeta. Nuestras mediciones son obviamente compatibles con las encontradas anteriormente de una masa terrestre aproximadamente, ya que la masa de la estrella en s\u00ed misma es muy similar a la determinada por las estimaciones de la masa-luminosidad\\\\\\”.<\/p>\n

\"\\\\\\"prox_key-1\\\\\\"\"<\/a> Representaci\u00f3n del movimiento de Pr\u00f3xima Centauri con respecto al fondo durante el per\u00edodo de observaci\u00f3n. Las posiciones de Pr\u00f3xima Centauri est\u00e1n indicadas con la estrella azul, mientras que las verdes y rojas indican las dos estrellas con respecto a las cuales se midi\u00f3 la microlente gravitacional. Cr\u00e9ditos: A. Zurlo et al.<\/p>\n

\u00bfC\u00f3mo se desarroll\u00f3 el estudio? \u00bfHas encontrado alguna dificultad?<\/p>\n

\\\\\\”La primera dificultad fue la cobertura temporal del evento. Seguimos a Pr\u00f3xima Centauri desde un observatorio terrestre: VLT en Cerro Paranal, Chile, y con el\u00a0instrumento SPHERE, muy solicitado. Tuvimos que obtener muchas\u00a0observaciones en un corto per\u00edodo, los meses de febrero a marzo, cuando se produjo el evento de microlente gravitacional. Afortunadamente pudimos obtener el tiempo necesario y buenas condiciones de observaci\u00f3n. Entonces la dificultad principal fue la precisi\u00f3n astrom\u00e9trica. El efecto de la microlente crea una desviaci\u00f3n de la luz de la estrella de fondo de aproximadamente un mili-arcosegundo, una cantidad muy peque\u00f1a. Para poder medirla, nuestros errores deben ser inferiores al milisegundo de arco, y efectivamente se\u00a0pudieron medir\u00a0con gran precisi\u00f3n la posici\u00f3n de todas las estrellas en el campo de visi\u00f3n del instrumento, las cuales utilizamos como una rejilla para mejorar nuestra medida de astrometr\u00eda. La precisi\u00f3n obtenida es la mejor que se ha logrado con este instrumento\\\\\\”.<\/p>\n

\u00bfCu\u00e1l fue tu papel en este estudio?<\/p>\n

\\\\\\”Fui investigadora principal de las observaciones de Pr\u00f3xima Centauri con el instrumento SPHERE, tomando parte en las observaciones de Paranal con otros colaboradores. Reduje los datos de alto contraste y obtuve con precisi\u00f3n las posiciones de las estrellas de fondo en las observaciones y la estrella de microlente. Entonces, con un m\u00e9todo de Markov Chain Monte Carlo, calcul\u00e9 los elementos del movimiento de Pr\u00f3xima Centauri en el cielo y la calibraci\u00f3n astrom\u00e9trica necesaria para obtener una precisi\u00f3n del sub-milisegundo de arco. La mayor parte del trabajo fue la redacci\u00f3n de la cadena de Markov Chain Monte Carlo, que dur\u00f3 varios meses. Este estudio fue particularmente complicado debido a la precisi\u00f3n requerida y los numerosos efectos astron\u00f3micos y f\u00edsicos en juego, y la ayuda de mis colaboradores fue decisiva para el \u00e9xito de este an\u00e1lisis\\\\\\”.<\/p>\n

Para saber m\u00e1s:<\/p>\n

Leer en Monthly Notices de la Royal Astronomical Society el art\u00edculo\u00a0\\\\\\”La masa gravitacional de Pr\u00f3xima Centauri medido con la esfera de un evento de microlente.\\\\\\”<\/a>, De A. Zurlo, R. Gratton, D. Mesa, S. Preferencias, A. Enia, K. Sahu, J.-M. Almenara, P. Kervella, H. Avenhaus, J. Girard, M. Janson, E. Lagadec, M. Langlois, J. Milli, C. Perrot, J.-E. Schlieder, C. Thalmann, A. Vigan, E. Giro, L. Gluck, J. Ramos y A. Roux<\/p>\n

FUENTE:\u00a0http:\/\/www.media.inaf.it\/2018\/07\/18\/proxima-centauri-lensing\/<\/a><\/p>\n

[:]<\/p>\n","protected":false},"excerpt":{"rendered":"

Alice Zurlo from the Astronomy Nucleus of UDP shows how with\u00a0 SPHERE we can learn more about exoplanets. on-sky movement of Proxima Centauri with respect to background stars The gravitational mass of Proxima Centauri measured with SPHERE from a microlensing event Proxima Centauri, our closest stellar neighbor, is the subject of many attentions since the …<\/p>\n

SPHERE performance permits many kinds of challenges, from measuring astrometric microlensing to image very faint planets<\/span> Read More »<\/a><\/p>\n","protected":false},"author":2,"featured_media":552,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"site-sidebar-layout":"default","site-content-layout":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":""},"categories":[13],"tags":[],"acf":[],"_links":{"self":[{"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/posts\/551"}],"collection":[{"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/comments?post=551"}],"version-history":[{"count":4,"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/posts\/551\/revisions"}],"predecessor-version":[{"id":4020,"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/posts\/551\/revisions\/4020"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/"}],"wp:attachment":[{"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/media?parent=551"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/categories?post=551"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/astronomia.udp.cl\/en\/wp-json\/wp\/v2\/tags?post=551"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}