HIRES 2014: "Astronomy at high angular resolution – a cross-disciplinary approach"
All presentations will be available via the following dropbox folder: http://bit.ly/1y4WR4W
Session 1. Techniques
Speaker: W. Brandner
Speaker: Craig Mackay (University of Cambridge - Institute for Astronomy)
Lucky Imaging combined with low order adaptive optics has given the highest resolution images ever taken of faint objects in the visible. Unfortunately this is often only achieved by discarding the vast majority of images. Recently, however, excellent progress has been made in refining selection procedures so that very much higher selection percentages may be achieved. A range of other techniques have already improved the image quality and isoplanatic patch size and other novel techniques are presently being developed. This paper will describe what has been achieved already and point towards future developments that are particularly promising. Images will be shown from a 5 m telescope in I band with 35 milliarcsecond resolution following 50% selection.
Speaker: J. Milli
Speaker: Benoit Neichel (Laboratoire d'Astrophysique de Marseille)
Over the 20 past-years, Adaptive Optics [AO] for astronomy went from a demonstration phase, to a well-proven and operational technique. Since the first astronomical AO systems were opened to the community in the early 1990s, numerous technical achievements have been accomplished, and it is now inconceivable to consider building a large telescope without AO. AO observations have brought some of the major discoveries in astronomy with, among others, detailed study of the massive black hole at the center of our Galaxy, detailed images of the surface of solar systems planets, or precise morphology and dynamics of very distant galaxies. We are today at the beginning of a new step forward, with the birth of a revolutionary generation of AO systems called Wide Field AO [WFAO]. By using multiple Laser Guide Stars [LGS], WFAO significantly increases the field of the AO corrected images, and the fraction of the sky that can benefit from such correction. Therefore, where the first AO systems were well suited for observations of bright and relatively small objects, the new generation of WFAO is opening the path for a multitude of new science cases. In this presentation, I will present GeMS, the Gemini Multi-Conjugate Adaptive Optics System, which is the first WFAO instrument offered to the community. After a brief review of the principles of AO and the extension to WFAO, we will see the first images and science results obtained by GeMS. Finally, we will see how instruments like GeMS are paving the way for the future generations of Extremely Large Telescopes [ELTs].
Speaker: Klaus Pontoppidan (Space Telescope Science Institute)
Speaker: Miwa Goto (Universitäts-Sternwarte München)
A disk of radius 10 AU subtends 0.1 arcsecond at 100 pc away. The angular size is about that of the PSF of an 8-m class telescope at the wavelength 4 um. The disks of nearby Herbig Ae/Be stars are therefore marginally resolved by a high resolution spectrograph such as CRIRES at the CO fundamental band in the line images (as opposed to the spectroastrometry of T Tauri stars). Adding kinematic information to the line images recorded with several different instrumental angles enables us to rigorously constrain the geometric parameters of the disks (strictly speaking, the shapes of the CO emitting surface) as immediate observables. We will use instructive examples to illustrate how sensitive the basic disk parameters, such as the inner and outer radii, and the thickness of the disk and its rim, change the appearance of the line images. We will also report how the technique is used not only to find the standard disk parameters, but also to spot an anomaly of a disk such as warping and the fast radial infall of the gas.
Speaker: Luca Pasquini (European Southern Observatory)
Spectra of composite systems (e.g. spectroscopic binaries) contain spatial information that can be retrieved by just measuring the radial velocities (Doppler shifts) of the components in four observations with the slit rotated by 90 degrees in the sky. The spatial resolution is determined by the precision with which differential radial velocities can be measured. We use the UVES spectrograph at the VLT to observe the known spectroscopic binary star HD188088 (HIP97944). We measure an astrometric signal in radial velocity of 276 m/s, that corresponds to a separation between the two components at the time of the observations of 18 ± 2 milli-arcseconds. The stars were aligned east-west. We describe a simple optical device to simultaneously record pair of spectra rotated by 180 degrees, thus reducing systematic effects.
Speaker: Jean-Baptiste Le Bouquin (Institut de Planétologie et d’Astrophysique de Grenoble)
Speaker: Jean-Philippe Berger (European Southern Observatory)
I will present how GRAVITY and the four VLTI telescopes could in principle be used to detected and spectrally analyse massive planets.
Speaker: Christian Hummel (European Southern Observatory)
We developed a new imaging algorithm allowing the combination of multi-channel interferometric data in a single image. The method is applicable to sources emitting optically thick radiation where the dependence of the source structure on wavelength can therefore be described by a single parameter, i.e. the effective temperature. Stellar atmospheres described by both effective temperature and surface gravity could also be used. The result of the imaging process is an intensity map as well as a map of the effective temperature across the source. The advantage of this method over the independent imaging of data in each channel is the benefit of a much better PSF ("dirty beam") when combining the aperture coverage of each channel over a wide range of wavelengths. We present results from applications to composite spectrum binaries and stellar surfaces of rotating stars based on simulated data. We will also try to present results from actual interferometric data on Altair from the Navy Precision Optical Interferometer.
Speaker: Sridharan Rengaswamy (European Southern Observatory)
Speckle imaging is one of the high resolution imaging techniques immune to the atmospheric turbulence. It involves reconstructing an high resolution image of an object from a series of short exposure images obtained from a filled-aperture telescope. The short exposure images are processed in the Fourier domain to recover the Fourier amplitude and phase information. I will present an overview of image reconstruction software and provide examples of reconstructed images of binary stars, extended objects (solar surface and near earth objects).
Speaker: R. Baptista
Speaker: Oleg Kochukhov (Uppsala University)
Doppler imaging is a powerful indirect remote sensing method that uses information contained in the distortions and variability of spectral line profiles to reconstruct distribution of spots on the stellar surfaces. An extension of this technique to line polarisation - Magnetic (Zeeman) Doppler imaging - is capable of inferring vector topology of stellar magnetic fields. Both techniques are currently playing a key role in the studies of stellar magnetism and surface activity. In this talk I review basic foundations of Doppler and Magnetic imaging and discuss strengths and intrinsic limitations of these inversion techniques. I also present examples of application of surface mapping to both early- and late-type active stars, highlighting some interesting recent discoveries made with the help of Doppler imaging.
Speaker: M. Ireland
Aperture-mask interferometry has a long history in the speckle regime - in principle equalling the performance of speckle interferometry in the low-flux, zero read-noise regime and offering superior calibration in the bright regime. Since adaptive optics has become commonplace on large telescopes, the key advantage of aperture-mask interferometry is in calibration, particularly of low spatial-frequency phase aberrations that cause quasi-static speckles. I will describe the principles of quasi-static speckle limited imaging in the Fourier plane, where bispectral phase (or Kernel-phase) and Fourier power are the primary observables, and will show that where Strehls are low or moderate, a non-redundant aperture can offer superior imaging performance. Finally, I will demonstrate the applicability of aperture-masking imaging both to laser-guide star imaging of faint (K~14) star systems and bright transition disk stars (e.g. LkCa 15) surrounded by faint (1000:1 dynamic range) structures.
Speaker: Makoto Uemura (Hiroshima University - Hiroshima Astrophysical Science Center)
Recently, the modeling methods that utilize the sparsity of information has received attention in the field of information science and machine learning. This new technique enables us to reconstruct images or other kinds of information with a high quality even in the case that the data is small. Here, I introduce our recent results in which the sparse modeling is applied to image reconstruction problems in Astronomy. The topics are: the reconstruction of VLBI image using l1-minimization, Doppler tomography using total variation minimization, and bin-mode estimation of gamma-ray Compton camera imaging.
Speaker: Jaeho Choi (Dankook University)
Non-interferometer phase-differential imaging method for direct imaging of the astronomical objects will be presented. The feasibility of non-interferometry method to retrieve the phase information at optical wavelengths is demonstrated in the laboratory experiments using the two-dimensional Foucault knife-edge filtering setup. The proposed method has a feature of render phase images as well as compensates atmospheric turbulence.
Speaker: Rainer Schoedel (Instituto de Astrofísica de Andalucía - CSIC)
I present a method for holographic image deconvolution that is optimized for crowded fields. Its two key features are an iterative improvement of the instantaneous point spread functions (PSFs) extracted from each image and the (optional) simultaneous use of multiple reference stars. High S/N ratio and accuracy can thus be achieved on the PSFs for each frame, which results in sensitive, high-Strehl reconstructed images. Image reconstruction a posteriori, the possibility to use multiple reference stars and the fact that these reference stars can be rather faint means that holographic imaging offers a simple way to image large, dense stellar fields near the diffraction limit of large telescopes, similar to, but much less technologically demanding than, the capabilities of a multiconjugate AO system. The method can be used with a large range of already existing imaging instruments and can also be combined with AO. To illustrate the power of the technique, I present 8.1'' x 2.7'' JHK images of the Galactic Centre with a homogeneous 0.2" PSF that were obtained with HAWK-I/VLT.
Session 2. Planets, disks and brown dwarfs
Speaker: Hans Ulrich Kaeufl (European Southern Observatory)
After its upgrade ESO's 10/20micron camera/spectrometer at the VLT, VISIR will feature highly competitive high spatial resolution observing capabilities. Beyond the "normal" diffraction limited imaging and long slit capabilities, VISIR has been equipped with specialized techniques such as sparse aperture masking and coronagraphy employing phase-shifting masks. With the overall enhancement of the spectroscopic modes, spectroastrometry at low and high spectral resolution will also provide for unique capabilites to address astrophysical problems at the milli-arcsec scale. Examples from past technical runs and from re-commissioning - planned for early Nov. 2014 - will be shown. And outlook as to the potential of such instrumentation at the E-ELT will be given.
Speaker: Leonid Chechin (V.G.Fessenkov Astrophysical institute - Perspective astrophysical research)
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.
Speaker: Andrew Cameron (University of St Andrews - School of Physics and Astronomy)
A planet transiting a rotating star behaves somewhat like a starspot, in that it obscures a section of the stellar photosphere whose Doppler shift changes as the planet moves across the face of the star. The area of the planet''s silhouette varies with slant optical depth, revealing the wavelength dependence of the atmospheric opacity. I this talk I will review how time-resolved, high resolution spectroscopy is used to determine the spin rates of the host stars, to measure the projected misalignment of the planetary orbit and the stellar spin axis, and to detect the spectral signatures of common molecules in planetary atmospheres.
Speaker: Craig Mackay (Institute of Astronomy, 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.
Speaker: Gergely Csépány (European Southern Observatory)
Examining young multiple stellar systems with lucky imaging and adaptive optics observations
Oral abstract: Lucky imaging was one of the earliest high resolution techniques to be used at ground-based telescopes. Its foremost strength is that it can achieve diffraction limited imaging at small to medium sized telescopes. In addition, the large database of existing lucky imaging data on selected systems allows studies of variability to be carried out at high spatial resolution and over long periods of time. However, reducing lucky images can have some pitfalls due to the special method of image selection. Using data from our on-going survey of 30 T Tauri multiple systems employing the AstraLux Norte system at Calar Alto, we discuss the major contributors to the error budget in astrometry and photometry present in lucky imaging and adaptive optics data, and we identify possible improvements for subsequent observations. We show that our long time-line of more than 20 years gives us an opportunity to detect the orbital motion of the companion. In some of the systems, it is also possible to determine the orbital parameters, yielding model-independent stellar masses. The masses accompanied with spectral data enables us to characterize the systems and examine the influence of multiplicity on the evolution of planet-forming disks.
Speaker: Tobias Schmidt (Hamburger Sternwarte)
We are currently working on high-resolution direct imaging data, i.e. astrometry and photometry in different bands in combination with integral spectroscopy of a likely planetary companion to a very young host star. The object itself shows unusual properties and we would like to show why high-resolution imaging was necessary for its detection and only photometry and integral field spectroscopy together could clarify the nature of the object. For this study two high-resolution AO instruments were used in combination with several dedicated reduction techniques.
Speaker: Sasha Hinkley (University of Exeter)
I will give a overview of our efforts devoted to high resolution imaging of planetary mass companions on large ground based telescopes. I will present our progress on the largest current Adaptive Optics survey dedicated to imaging planetary mass companions orbiting stars with newly identified debris disks, using Adaptive Optics (AO) at VLT and Keck. I will also focus on how this work can be extended with the resources of ESO. In addition, I will highlight recent progress and lessons learned with Project 1640: a coronagraph and integral field spectrograph coupled to the new extreme AO system at Palomar Observatory. The information gathered from all of these projects will be particularly important for obtaining imaging and spectrscopy of planetary mass companions with new instrumentation at VLT as well as on the upcoming 30m-class E-ELT telescope.
Speaker: Steve Ertel (European Southern Observatory - Chile)
Exozodiacal dust around main sequence stars is expected to be the analog of the zodiacal dust in our own Solar system. Detecting this hot dust close to other main sequence stars remained elusive until the FLUOR instrument at the CHARA interferometer detected for the first time a 1% excess in the near-infrared around the prominent debris disk host star Vega in 2006. Studying exozodiacal dust can give insights into the dynamics and evolution of the innermost regions of planetary systems, close to the habitable zone. First studies revealed the extreme nature of the systems detected, being more massive and hotter than our own zodiacal dust. On the other hand, the presence of such dust around other stars may represent a major obstacle for future terrestrial planet finding missions. The possible presence of diffuse emission adds uncertainty to the observations and clumpy structures in the dust distribution may point toward dynamical interaction with planets but a clump may also be misinterpreted as an actual planet. We are carrying out the first large, statistical survey for exozodiacal dust in the near-infrared using CHARA/FLUOR in the northern and VLTI/PIONIER in the southern hemisphere. We observed 134 stars in total so far, the majority of targets observed as a magnitude limited sample with PIONIER. We will present the strategy our survey with special emphasis of the challenges of our high accuracy measurements of the squared visibilities with PIONIER, including a specific calibration strategy and additional characterization of systematics from the instrument. We draw statistical conclusions on the incidence of exozodiacal dust with different parameters of the system and by that on the potential mechanisms being responsible for the dust production. For the excesses detected with PIONIER, we also present the first spectrally dispersed observations allowing us to constrain the dust properties and to distinguish between thermal emission and scattered light as the dominant emission process. Fina!lly, based on our results we discuss the impact of the presence of exozodiacal dust on future earth-like planet finding missions using direct imaging.
Speaker: Christian Ginski (Sterrewacht Leiden)
The formation of massive planetary or brown dwarf companions at large projected separations from their host star is not yet well understood. In order to put constraints on formation scenarios we search for signatures in the orbit dynamics of the systems. We show for the first time that the GQ Lup system shows significant change in both separation and position angle. Our analysis yields best fitting orbits for this system, which are eccentric, with an eccentricity between 0.21 and 0.69 and semi-major axes below 1 arcsec. Given our astrometry we discuss formation scenarios of the GQ Lup system.
Speaker: S. Kraus
Among the most fascinating and hotly-debated areas in contemporary astrophysics are the means by which planetary systems are assembled from the large rotating disks of gas and dust which attend a stellar birth. Although important work is being done both in theory and observation, a full understanding of the physics of planet formation can only be achieved by opening observational windows able to directly witness the process in action. The key requirement is then to probe planet-forming systems at the natural spatial scales over which material is being assembled. By definition, this is the so-called Hill Sphere which delineates the region of influence of a gravitating body within its surrounding environment. The Planet Formation Imager project has crystallized around this challenging goal: to deliver resolved images of Hill-Sphere-sized structures within candidate planet-hosting disks in the nearest star-forming regions.
In this contribution we outline the primary science case of PFI and discuss how PFI could significantly advance our understanding of the architecture and potential habitability of planetary systems. We present radiation-hydrodynamics simulations from which we derive preliminary specifications that guide the design of the facility. Finally, we give an overview about the interferometric and non-interferometric technologies that we are investigating in order to meet the specifications.
Session 3. Stars
Speaker: F. Baron
Speaker: Jason Grunhut (European Southern Observatory)
Many hot, massive stars that host primordial magnetic fields (such as the archetypical B2V star $\sigma$ Ori E) exhibit variable emission in hydrogen Balmer lines, photometric brightness variations, variable ultraviolet resonance lines, non-thermal radio emission and X-ray emission. It is now well understood that these phenomena are the result of the confinement of the highly ionized, radiatively driven stellar wind by a large-scale magnetic field. Furthermore, it is now well established that in the case of rapidly-rotating magnetic stars, the magnetically-confined stellar wind is centrifugally-supported beyond the Kepler radius, forming an approximately steady-state, co-rotating circumstellar structure. I will presents the first results of a new study to infer the detailed 2D plasma distribution of the magnetospheres of rapidly-rotating magnetic massive stars from high-resolution spectroscopy obtained in the context of the MiMeS Large Program. The indirect images (the first of their kind for massive star magnetospheres) are reconstructed using tomographic imaging techniques that have largely been discussed in the context of studies of cataclysmic variables and Algol type systems (e.g. Marsh & Horne 1989).
Speaker: Thomas Rivinius (European Southern Observatory - Chile)
I will present the results from our studies of Be star disk. We employ the Monte-Carlo code HDUST to compute model observables from the structure of a viscous decretion disk to compare to observational data. These data include, but are not restricted to, AMBER, MIDI, and PIONIER interferometric observations. Further constraints can be delivered by applying tomographic reconstruction to spectral observations of the disk, using both binarity but as well long-term V/R variationsas a phase-locking clock. The latter which are due to a precessing density waves in the circumstellar disk and have precession periods of several years, in which the structure of the disk does not change, but only the angle under which we observe it.
Speaker: Claudia Paladini (Université Libre de Bruxelles - Institut d'Astronomie et d'Astrophysique)
In this contribution I will present for the first time the "true face" of a carbon rich Mira star. In December 2012 we successfully observed the surface of R Fornacis with VLTI/PIONIER. The observations were carried in three spectral channels across the H-band. The images shows strong departure from spherical symmetry in all the spectral channels, being more pronounced in the short wavelengths where CO and possibly C2H2 are the major contributors. This is in contrast with all the images so far obtained with optical interferometry for AGB stars that show a roundish onion-like shape. On the other hand all the aforementioned images are from oxygen-rich Miras. I will discuss this result in connection with the fact that RFor is the archetype of carbon AGB stars with reported dust obscuration event. I will conclude discussing what the next generation of VLTI imaging instruments will bring to the AGB field.
Speaker: Michel Hillen (KU Leuven)
In this contribution I will show why combining various high-resolution techniques is essential to understand the enigmatic, but significant, population of post-AGB binaries. Although ~40% of all optically bright post-AGB stars reside in a binary system, these objects are puzzling: their circumstellar material is trapped in discs which are very reminiscent of protoplanetary discs around young stellar objects. The binary interaction processes that led to the disc formation is not understood, neither is the final evolutionary outcome of these systems. We are currently conducting a large multi-technique and multi-wavelength program to characterize the circumstellar environment of these stars, and to put them in a (binary) evolutionary context. We use different techniques to probe the systems in a wide range of scales. Our time series of high-resolution optical spectra allow us to study the complex gas streams in the very inner regions of these systems. Many systems
show indications for the presence of a jet emanating from the neighborhood of the secondary, possibly originating in an inner accretion disk. Our near- and mid-IR, as well as optical, interferometric data probe the dust''s thermal emission and scattered light from the inner regions of the circumbinary disk. Finally, with ALMA we have an ongoing program to probe the large scales, i.e. the outer disk and any cold outflow from the system. Here I will mainly focus on our most exciting and recent interferometric results (from Hillen et al. 2014, and Hillen et al., in prep.), but I will also touch upon the need for Doppler techniques to extract the full potential out of our rich spectroscopic time series.
Speaker: Pierre Cruzalebes (Observatoire de la Côte d’Azur - Lagrange)
Departure for centrosymmetry is suspected to be the rule for evolved stars. We present the results of a long-term collaborative program led over 5 years to observe some 20 giants and supergiants with VLTI-AMBER. Although the uv-plane coverage was not full enough to proceed reliable image reconstruction, we show evidence for global deviation for centrosymmetry, using a new parameter, called CSP and derived from the measured triple product integrated over the wavelength range. We observe that CSP increases along the evolution track on the asymptotic giant branch. The tendency of CSP to increase with the atmospheric pressure scale height supports the hypothesis that the observed deviations from centrosymmetry are somehow related to convective cells, whose size depends upon the atmospheric pressure scale height.
Speaker: Julien Morin (Laboratoire Univers et Particules de Montpellier - Université Montpellier 2)
During the past few years, magnetic fields have been detected and studied on stars throughout the Hertzsprung-Russell diagram. Spectropolarimetric techniques and their analysis by means of Zeeman Doppler Imaging have played a key role in this exploration. In this talk I will briefly summarize the theorerical puzzles we want to address in the field of cool stars magnetism, discuss issues specific to stellar spectropolarimetry and Zeeman Doppler Imaging, and present recent results obtained with spectropolarimetry alone or coupled to other techniques. Finally, I will present how future instruments operating in the near infrared will contribute to the next advances in the field, especially for M type dwarfs and brown dwarfs.
Speaker: Ulli Käufl (European Southern Observatory)
The shaping mechanism of asymmetrical planetary nebulae (PNe) involves processes that defy the standard formation models of PNe. Among the high-resolution observational techniques used nowadays, interferometry has demonstrated that their usage is a valuable tool to reveal evidences of disks at the cores of PNe. However, the use of VLTI may impose constraints in the sensitivity and in the spatial coverage, limiting the targets that can be investigated with this technique. Regarding high-resolution spectroscopy, the spectro-astrometry technique has proven its efficiency revealing the existence of protoplanetary disks. Inspired by these results, we have applied for the first time the spectro-astrometry technique to CRIRES-VLT data of sources in transition to the PN phase. Our main goal was to prove the capabilities of this technique in the search of disks and compact structures at the innermost regions of these objects, environments that are wealthy in dust and molecules and thus often obscured at optical wavelengths. We have used CRIRES commissioning data of two post-AGB sources (IRAS 17516-2525 and SwSt 1) to develop the methodology and the tools to apply spectro-astrometry to these type of sources. In previous studies, the morphology of the young PN SwSt 1 was barely resolved and remains unresolved for the proto-PN IRAS 17516-2525. Our exploratory study revealed compact structures thanks to the spectro-astrometric analysis. In the case of SwSt 1 we have investigated the [Fe III] line at 2.145 microns and Brackett gamma line at 2.160 microns. We detected two small structures with a size of 230 mas and 130 mas, respectively. As for IRAS 17516-252, the spectro-astrometric signature revealed suggests the presence of a bipolar structure of 12 mas in size. Additionally, we have obtained CRIRES spectra in the near infrared M-band to investigate the emission of the CO fundamental band in the circumstellar region of the axisymmetric proto-PN AFGL 915 (a.k.a. "The Red Rectangle"). We have found the spectro-astrometric signature of the Keplerian disk detected in previous studies at radio wavelengths, but with a considerably smaller size (>100 mas), tracing inner and hotter zones of this equatorial structure. These results are promising, they open a new observational window to study the shaping agents of the more complex morphologies of PNe.
Speaker: Julián David Alvarado Gómez (European Southern Observatory)
Zeeman Doppler Imaging (ZDI) has proven to be a powerful technique to extract magnetic field information in a wide range of stellar types. This technique applies the principles behind the Doppler Imaging (DI) to time-series of circularly polarised (Stokes V) signatures in order to reconstruct the large scale magnetic fields on the surfaces of magnetically active stars. The spatial resolution of the magnetic field maps obtained with ZDI depends, in principle, on the vsin(i) of the star, the spectroscopic resolution and the phase coverage obtained, leading to be applied with caution in slow rotating stars. Additionally as with all Doppler imaging techniques, the solutions obtained are non-unique (in terms of the map distribution/goodness of fit recovered), so is necessary to employ a regularising function, which enables a unique robust solution to be obtained. We revisit the spatial resolution and entropy content of magnetic field maps recovered with ZDI for a slow-rotating magnetically active star (HD1237) and propose a robust systematic criteria for balancing the optimal resolution/goodness of fit to be applied in these type of stars.
Session 4. Binaries
Speaker: Thomas Marsh (University of Warwick)
I will describe the principles and practice of Doppler Tomography, a method of imaging binary stars using spectroscopy which is particularly suited to those containing complex accretion flows. Limitations of the method will be covered along with how they can be circumvented in some cirsumstances. I will also present examples of real applications to illustrate the chief areas that Doppler Tomography has had most impact upon.
Speaker: Axel Schwope (Leibniz-Institut für Astrophysik Potsdam)
Speaker: Jan Cechura (Astronomical Institute of the Academy of Sciences of the Czech Republic)
We present a novel observation interpreting method for the high-mass X-ray binaries (HMXBs) based on a combination of spectroscopic data and numerical results of a radiation hydrodynamic model of stellar wind in HMXBs. We calculate synthetic Doppler tomograms of a predicted emission in Low/Hard and High/Soft X-ray states and compare them with Doppler tomograms produced using spectra of Cygnus X-1, a prototype of HMXBs. The emissions of HMXBs are determined by the local conditions within the circumstellar medium - namely by local density, temperature, and ionization parameter. These quantities are computed by the radiation hydrodynamic code and strongly depend on the X-ray state of such systems. By increasing intensity of an X-ray emission produced by the compact companion in the HMXB-model, we achieved a complete redistribution of the circumstellar medium in the vicinity of the modelled system. These changes (which simulate the transitions between two major spectral states) are also apparent in the synthetic Doppler tomograms which are in a good agreement with the observational data.
Speaker: Christopher Watson (Queen's University Belfast - Astrophysics Research Centre)
The mass-donating stars in interacting binaries such as cataclysmic variables (CVs) and low-mass X-ray binaries are the principal drivers of the evolution and behaviour of these enigmatic objects. In turn, magnetic activity on the cool donor stars is often invoked to explain the observed characteristics of both single systems (e.g. outburst durations and intervals), and as an ensemble (e.g. the period distribution of CVs). Understanding magnetic activity in these systems is therefore of great importance. Roche tomography is an indirect imaging technique used to map surface features (such as starspots and irradiation patterns) on the Roche-lobe filling donor stars in interacting binaries. I will begin by reviewing the methodology and axioms under-pinning Roche tomography, before moving on to look at some of the early results that arose from this technique. I will then highlight some of the most recent successes, including the first measurement of differential rotation on a CV donor, and the first indirect image of a starspot on an X-ray binary. I will then finish by reflecting on some possible future directions for this technique.
Speaker: Colin Hill (Queen's University Belfast - Astrophysics Research Centre)
Cataclysmic variables (CVs) are semi-detached binaries consisting of a (typically) lower main-sequence star transferring mass to a white dwarf primary via Roche-lobe overflow. With several hundred systems known, typical orbital periods of several hours and binary separations of a few solar radii, CVs form the foundation of our understanding of a wide range of accretion driven phenomena. In turn, the donor stars are key to our understanding of the origin, evolution and behaviour of this class of interacting binary. In particular, magnetic activity on the donor has been invoked to explain many of the observed characteristics of CVs. Studies of such activity provide unique tests of dynamo theories, allowing the impact of tidal forces (raised by the nearby companion) on the stellar dynamo to be assessed. Roche tomography is an indirect imaging technique which allows surface features (such as starspots and irradiation) to be mapped on the donor star in CVs. I will discuss how this technique has been used to provide the first measurement of differential rotation on AE Aqr, and the implications of this discovery for this and other CVs. In addition, I will present preliminary results of a long term study of AE Aqr spanning 8 years.
Speaker: Enrico Kotze (South African Astronomical Observatory)
We present preliminary results obtained from combining multiple tomographic techniques in order to gain new more detailed insights into the three dimensional view of the spatial and velocity structure of polars.
Speaker: Petr Hadrava (Astronomical Institute, Czech Academy of Sciences)
The method of disentangling of stellar spectra and its applications will be briefly reviewed and its complementarity with interpretation of other observations like photometry and interferometry discussed. An attention will also be devoted to comparison with Doppler tomography of interacting binaries.
Speaker: Stephen Potter (South African Astronomical Observatory)
Stokes imaging is an indirect imaging technique that maps accretion regions on the surface of the white dwarf in magnetic Cataclysmic Variables (mCVs). Specifically location, shape, and size are mapped by modelling photo-polarimetric observations of mCVs. I will review the technique, present some new results and demonstrate how Stokes imaging can be combined with other techniques such as Doppler tomography.
Session 5. Large scale phenomena
Speaker: Stefan Gillesen (Max-Planck-Institut für extraterrestrische Physik)
Speaker: Misty Bentz (Georgia State University - Department of Physics and Astronomy)
Reverberation mapping is a technique that substitutes time resolution for spatial resolution in order to probe structures on the size of ~0.01pc in the nuclei of active galaxies. I will describe the technique and basic implementation, and the major results to date, including a focus on the determination of black hole masses from reverberation results. I will also discuss the results from more advanced analysis methods that are designed to deconvolve the information as a function of both velocity and time, thereby providing a full map of the broad emission line regions in active galaxies, simultaneously constraining the geometry and kinematics of the gas on unresolved spatial scales.
Speaker: Sebastian Hoenig (University of Southampton - School of Physics & Astronomy)
This year marks the 10th anniversary of the first VLTI publication of an AGN. While initial sensitivity limits put strong restrictions on the number of targets, we are now approaching 50 AGN with interferometric constraints in the near- or mid-infrared. Those observations allowed us to test the standard picture of the mass distribution around accreting black holes. In this review talk I will discuss the state of the field and the challenges that interferometry made to our understanding of "dusty tori."
Speaker: Noel Lopez Gonzaga (Leiden University)
The high resolution achieved with the VLT interferometer, together with the instrument MIDI, can help us to get information about the geometry and structure of the nuclear mid-infrared emission of AGNs. In order to interpret the MIDI data, we have develop a statistical test that allows to make a comparison between the interferometric data and clumpy torus models. Our test includes the effects caused by the randomness of the clouds and the uncertainty of the true position angle on the sky. The results from this comparison can be used as a test for the Unified Model for AGN.
Speaker: Suvendu Rakshit (Observatoire de la Côte d’Azur)
Reverberation mapping (RM) size-luminosity and mass-luminosity laws could allow QSOs to be used as standard cosmological candles and evolution mass tags if they could be checked, calibrated and based on better confirmed models. After our first successful resolution of the BLR of 3C273 by optical long baseline differential interferometry (DI) we investigate the general constraints that DI can yield on BLRs by developing a 3D BLR model to explain the both RM and DI observables. Our Bayesian analysis of simulated OI data suggests that DI, under RM constraints, can constrain the fundamental model parameters, such as BH mass, BLR size, radial distribution, inclination, thickness, local micro or macro turbulence versus global velocity and cloud optical depth, and provide higher accuracy (<0.15 dex. uncertainty) on BH mass measurement than traditional cross-correlation technique. A SNR analysis of DI updated and calibrated on our actual 3C273 data, to evaluate the number of targets accessible to current (AMBER+), upcoming (GRAVITY and MATISSE) and possible VLTI instruments. We show that GRAVITY should give high quality data and accurate mass and distance estimates on a dozen of targets and that the full potential of the VLTI exceeds 60 targets with known improvements of instruments and fringe trackers. The combination of DI and RM on such a target set, that covers 4 to 5 decades of luminosity range, should allow a decisive improvement in RM mass-luminosity and size-luminosity laws and permit to evaluate a larger unification scheme relating the main BLR characteristics to the luminosity of the central source.
Speaker: Romain Petrov (Observatoire de la Côte d’Azur - Lagrange)
We have used the enhanced data processing mode on the VLTI/AMBER+ to observe successfully several times the QSO 3C273 in medium spectral resolution through its broad emission line Pa_alpha. We have measured and carefully calibrated the differential visibility and phase showing that the BLR is substantially larger than reverberation mapping (RM) estimates. We have reanalyzed RM data showing that for this specific object with a very large time lag, RM can give only a lower limit of the BLR size. This solved the apparent contradiction between VLTI and RM measures of the size of 3C273 that we confirm to be 1500 +-300 ld. We also see that the BLR of 3C273 extends beyond the inner rim of the dust torus. Its very small differential phase indicates that the BLR is quite far from any thin disk or bowl shape geometry. We use a global geometrical and kinematic model of BLR and a Markov chain Monte Carlo model fit to evaluate the parameters of the BLR (local/global velocity field, inclination, thickness...) and constrain the mass of the central super massive black hole.
Speaker: Daniel Asmus (European Southern Observatory - Chile)
The centers of active galaxies emit a large part of their energy in the mid-infrared (MIR), allowing us to study the responsible nuclear structures and processes in detail, and almost independent of obscuration. I will present the largest compilation of local active galactic nuclei (AGN) observed at sub-arcsec spatial scales in the MIR. It comprises all available ground-based high-angular resolution images obtained with 8-meter class telescopes, 895 photometric measurements for 253 objects in total. I will briefly discuss some scientific applications for this data set and also discuss important technical aspects like the online publication through the Virtual Observatory.
Speaker: Leonard Burtscher (Max-Planck-Institut für Extraterrestrische Physik)
Interferometric observations in the infrared have resolved dusty structures on parsec and sub-parsec scales in more than two dozen AGNs by now -- a giant leap when considering that the first infrared interferometric observation of an extragalactic object is only about 10 years old. Since then, studies have confirmed the existence of dust in AGNs at its sublimation radius and have clearly dismissed models of very extended tori. Individual, well studied sources have been instrumental to reveal the complexity of these parsec-scale structures and statistical studies have shown a perplexing diversity in the population as a whole. Surprisingly, the diversity does not seem to follow the expected bimodality between optical type 1 and type 2 AGNs -- which are thought to be just face-on and edge-on tori. This central premise of viewing-angle dependent unified models is challenged if not dismissed by interferometric observations. The next step in understanding the AGN phenomenon -- beyond unification aspects -- is now to combine multi-scale observations with multi-scale simulations to constrain the physical processes driving the feeding and feedback of AGNs.
Speaker: 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 N_photons^(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 ca
se for next generation 30m-class telescopes.
Session 6. Final session
Speaker: Suzanne Ramsay (European Southern Observatory)
Speaker: Jörg-Uwe Pott (Max-Planck Institut für Astronomie)
VLTI uniquely combines the power of adaptive optics and interferometry to open a scientific parameter space at mas-scale spatial resolution at NIR-MIR wavelengths. At this spatial scale many astrophysical processes are variable in easily observable periods (days to months). I will discuss how we use and benefit in this context from the technique of fringe tracking (FT aka adaptive optics for interferometry). The commissioning of the MIDI+FSU FT mode allowed as to demonstrate on sky that two new science cases are now in observational reach:
(i) subtle flux variations at the 100mJy level in the MIR (10um) in a massive Xray binary system. These variations trace directly the dust evolution in the stellar wind at the 20mas scale matching the orbital period of the system
(ii) observe planet-hosting stars in differential phase at a precision of 50-100mdeg which allows for direct light detection of a faint companions (flux ratio 10^2..3) in the N-band. Such flux ratios are typical for substellar companions, and reach down to the hot exoplanet flux ratios.
Both observed systems have an orbital time scale of about 10 days, so the required precision in absolute and wavelength-differential measurables needs to be achieved in a single night at best to avoid signal confusion due to source variability. We discuss how the MIDI+FSU mode at the VLTI helped to achieve these goals. Furthermore, the achieved results give credibility to the claim that an external fringe tracker will increase the imaging dynamic range of MATISSE by a factor of 10 for the majority of the targets.
The upcoming 4-telescope beam combiner MATISSE will open the window of model-independent closure phase imaging at MIR wavelengths. MATISSE is currently under construction, and expected to go to the telescope in only two years time.
Speaker: Keith Horne (University of St Andrews - School of Physics and Astronomy)