HIRES 2014: "Astronomy at high angular resolution – a cross-disciplinary approach"

Poster Abstracts

The interferometry's view on Symbiotic Stars

Henri Boffin (European Southern Observatory - Chile)

A fundamental question posed by symbiotic binaries, but with very wide application to a whole set of different kind of binary systems, is the process of mass transfer at play: Roche-lobe overflow (RLOF), stellar wind, or something in between, such as "wind RLOF"? Moreover, radiation pressure may also change the Roche lobe geometry, complicating things even further. To address this, it is crucial to get a good handle on the size of giants in symbiotic systems, and explain the apparent discrepancy between radius obtained by assuming synchronisation and those deduced from ellipsoidal variability. Optical interferometry is currently the only available technique which can probe directly the deformation of interacting stars. It allows to determine the size and the distortion of the giant star, as well as the orbital parameters of the systems, without any a priori on their characteristics. Here, I will show the amazing results we have already obtained thanks to interferometry and how they are fundamentally changing the game.


Post-adaptive optics speckle imaging in the visible

Marcel Carbillet (Université de Nice/Observatoire de la Côte d'Azur)

In the visible domain, turbulence is very fast and strong, and adaptive optics (AO) systems cannot provide full correction. In this context one can wonder whether deconvolution techniques are still that relevant, or whether it would be more interesting to work directly on short-exposure images by means of speckle methods used on partially corrected images. The purpose of this work is hence to make a first comparison, by means of numerical simulations of binary star post-AO images, between: (i) deconvolution methods applied to a long-exposure image, and (ii) speckle methods applied to a set of short-exposure images.


On the high resolution gravitational lens model

Leonid Chechin (V.G. Fessenkov Astrophysical Institute)

In report it was forwarded the new model of gravitational lens – high resolution gravitational lens. It based on the metric of gravitational field produced by N moving and rotating bodies of finite sizes. The application to the case of double galaxies’ gravitational lens is given. It was underlined that previous searching on the gravitational lensing in double systems was related to the eclipsing binaries and examined the luminosity changing in them. In contrary to these well-known results we found the additives to refracting angle produced by bodies’ movement and rotation. Beside we shown that galaxies’ movement accounting decreases the positions of lensing object’s images and this effect may be detectable by the modern astronomical observations.

Measurement of stellar diameters with Intensity Interferometry on cherenkov telescope arrays

Daniele Gardiol (Istituto Nazionale di Astrofisica - Osservatorio Astrofisico di Torino)

We will show the results of simulations of stellar diameters measurements made with Intensity Interferometry technique applied to future cherenkov telescope arrays


Differential rotation of the long-period RS CVn-type σ Gem revisited

Zsolt Kovari (Konkoly Observatory)

Spot migration pattern is analysed to derive surface differential rotation on the active K1-giant component of the long-period RS CVn-type binary system σ Gem. From a set of high-resolution spectra taken with STELLA-I SES in 2006/07, three subsequent Doppler images were obtained using our advanced surface reconstruction code iMap. The time-evolution of the spotted surface suggests antisolar-type differential rotation with α of -0.04 shear parameter, thus supporting the former detection on this star.


Contstraining Orbital Parameters with Doppler Tomography

Penelope Longa Pena (Warwick University)

In close binary stars, the evolution of one star affects its companion. Evolutionary expansion of stars allows for a mass exchange between the components. In most cases, the material from the less massive star forms an accretion disc around the heavier companion that has evolved faster to a compact stellar remnant, the final state of stellar evolution. We call these systems compact binary stars (CBs). Statistical information on CBs can be deduced by extracting common properties and characteristic system parameter distributions from observed data. But, despite been fundamental for a wide range of astronomical phenomena, our comprehension of their formation and evolution is still poor, mainly because of the lack of statistically significant CB''s parameter samples. The lack of reliable orbital parameters estimation for CBs is mainly due to observational handicaps, namely, the accretion disc outshines the system components. When this happens, even if any lines from the secondary are present, its weakness makes impossible to use a Gaussian fit on each spectrum to calculate the component's radial velocities. As Doppler tomography makes use of all data at once, some features that are too weak to be separated in individual spectrum can be detected. Doppler tomography can also provide an excellent tool for identifying the kinematics and the origin of the various emission components. We use time-series spectroscopy of short period CBs to test the efficiency of Doppler tomography based methods in constraining orbital parameters of short period cataclysmic variables. We find that the Ca II triplet lines offer superior diagnostics, revealing emission components from the mass donors and sharp images of the accretion discs. Furthermore, we use bootstrap to estimate the uncertainties from the Doppler maps. We compare our new methods against traditional radial velocity methods and show that they offer a valid route towards system parameter determination.


GravityCam: the Detection of Large Numbers of Earth-Mass Planets

Craig Mackay (University of Cambridge)

The only technique that allows the detection of Earth (and smaller)-mass planets is gravitational microlensing.  Even in very dense star fields the probability of detecting one microlensing event is small.  However a new instrumental proposal involving a wide field Lucky Imaging camera on the NTT in La Silla will allow 20 million stars in the galactic bulge to be surveyed with 0.2 arcsec angular and 40 ms time resolution.  We predict 20-50 new microlensing events per night and a few small-planet detections in a week.  This paper will describe the instrument and it predicted performance.  In addition to microlensing studies it will allow high-speed photometry of large numbers of stars of many spectral types enabling high time resolution variability and astro seismology studies to be carried out.  Further GravityCam may be used for weak shear gravitational lens studies away from the bulge.


Double Periodic Variables as laboratories for high angular resolution studies

Ronald Cid Mennickent (Universidad de Concepción)

I review the phenomenon of Double Periodic Variables showing the potential of this class of interacting binaries for studies of mass transfer and mass loss with high angular resolution.


AMBER/VLTI Snapshot Survey on Circumstellar Environments (2 poster places)

Thomas Rivinius (European Southern Observatory - Chile)

OHANA - the Observatory survey at High ANgular resolution of Active OB stars - is an interferometric snapshot survey of the gaseous circumstellar environments of hot stars, carried out by the VLTI group at the Paranal observatory. It aims to characterize the mass-loss dynamics (winds/disks) at unexplored spatial scales for many stars. The survey employs the unique combination of AMBER high spectral resolution with the unmatched spatial resolution provided by the VLTI. Because of the spatially unresolved central OBA-type star, with roughly neutral colour terms, their gaseous environments are among the easiest objects to be observed with AMBER, yet the extent and kinematics of the line emission regions are of high astrophysical interest. The raw data has become public immediately, an here we report on the results of the final reduction, which we will make available as well as soon as quality tests have been passed. The survey targets included bright 12 Be stars, ranging from equator-on to pole-on stars. Nearly 100 observations were obtained. They all show the typical rotating disk kinematic features, sometimes with asymmetries, and the largest disks are fully resolved at the longest baselines. This poster is to advertise the data and to encourage all interested researches to make use of it in their studies.


The Potential η Car like Binarity of the LBV HR Car

Thomas Rivinius (European Southern Observatory - Chile)

VLTI/AMBER observations taken by the OHANA project (see other posters) showed a signature in the interferometric phase of the Br-gamma line that could not possibly have been explained by an extended wind, more or less symmetrically distributed around a single object. Instead, the blue part of the wind emission seemed offset in the North-East/South-West axis. Follow-up observations with PIONIER, probing the H-band continuum, are best explained by two point sources (or alternatively one point source and one slightly extended source) at about 2mas separation and a contrast ratio of about 1:5. These PIONIER observations establish that HR Car is a binary, but further interpretation will only be possible with future observations (currently applied for) to constrain the orbit. However, under the assumption that the current separation is close to the maximum one, we estimate an orbital period of the order of 5 years, similar as in the η Car binary. This would make HR Car the second such LBV binary, and a determination of the orbit will enable to correlate orbital phases with observed features of the last S Dor phase of HR Car, about 25 years ago.


Doppler tomography studies of the dwarf nova QZ Lib

Linda Schmidtobreick (European Southern Observatory - Vitacura)



Spatially Resolving the Kinematics of the <~0.1 mas Quasar Broad Line Region Using Spectroastrometry

Jonathan Stern (Max Planck Institute for Astronomy)

The broad line region (BLR) in luminous quasars is both a useful tool to measure black hole masses over cosmic history, and the most prominent observational signature of the accretion flow at ~10^4 gravitational radii. However, the BLR is not directly resolvable, due to its <~0.1 mas angular size. This shortcoming has inhibited constraining even the most basic kinematic and geometric properties of the BLR, despite four decades of research. We present the possibility to constrain the BLR size and kinematic structure in luminous quasars using spectroastrometry, where one measures the position centroid of photons as a function of wavelength. In principle, this technique can spatially resolve kinematics on scales which are a factor of Nphotons(1/2) below the scale of the telescope point spread function. We demonstrate that resolving the BLR with spectroastrometry is feasible with existing 8m, Adaptive-Optics assisted telescopes, and offers a compelling science case for next generation 30m-class telescopes.


Constraining the Structure of V1247 Orionis Using Multi Wavelength Interferometry and Radiative Transfer SED Modelling

Matthew Willson (Exeter University)

Here we present multiple wavelength and epoch spanning interferometric observations of the pre-transitional disk, V1247 Orionis. Previous observations of this object indicated the presence of significant amounts of dusty material within the disk gap potentially indicating a previously unseen stage of protoplanetary disk evolution. We use a combination of SED radiative transfer modelling using the TORUS radiative transfer code and masking & long baseline interferometry observations to constrain the structure of the disk. Our modelling process produces a more physically consistent result while our multiple wavelength interferometric observations result in tighter constrains on the density and temperature structure than the more commonly used single-wavelength band interferometry.