Presentation and Poster Abstracts
NOTE: Posters will be on display during the whole workshop.
In alphabetical order (by last name):
"Probing Stellar Photospheres for Fundamental Parameters"
Long-baseline interferometry at optical and near-IR bands provides not only the angular sizes and mean effective temperatures of stars but also the means to probe temperature variations across and within stellar photospheres. Such measurements are critical for testing models of stellar atmospheres and interiors. Spatially resolving the brightness distribution over a slowly-rotating star measures limb darkening, key to determining vertical temperature gradients within the photosphere. These measurements constrain, for example, state-of-the-art stellar atmosphere codes with 3-D convection, those responsible for the recent substantial revision in the Sun’s oxygen abundance. In the case of a rapidly-rotating star, measurements of the star's shape in principle constrain the underlying interior structure, while the brightness distribution of the projected disk yields a combination of limb- and gravity-darkening which testifies to the strong surface temperature gradients between their hotter, higher gravity poles and cooler, lower-gravity equators. Recent interferometric images of rapid rotators like Altair attest to the short-comings of standard models of rotating stars. In low-gravity photospheres, where changes in optical depth correspond to physical depths which are a significant fraction of a star's radius, interferometry at high-spectral resolution uniquely probes the angular size of a star through individual spectral bands. Such measurements enable the ability to map out the extended vertical structures of these photospheres and reveal the limitations of hydrostatic stellar atmosphere models.
"Inverse methods for interferometric imaging: new advances"
With the advent of new instruments (MIRC-6T at CHARA, PIONEER at VLTI, and VISION at NPOI) as well as the construction of MROI, the focus in optical and infrared interferometry has shifted toward imaging. However examining the current "model-independent" image reconstruction packages proves they are often inadequate to reconstruct even simple objects. This talk will illustrate with practical examples how the application of new theoretical frameworks brings significant improvements in image quality over the conventional approaches. We will demonstrate how the compressed sensing framework, prescribing the use of spatial bases in which the object is sparse, informs us on the use of wavelets for image reconstruction, and how it benefits the reconstruction of spotted stars. We will explain how the application of the Bayesian evidence framework allows to discriminate between physical models in imaging. We will also discuss direct image reconstruction on a sphere for rapid rotators, and new regularizers in development for the reconstruction of YSOs. Finally we will present the new techniques of Markov Chain exploration and GPU acceleration for interferometry.
"AGN observations at the smallest scales – Infall and Obscuration"
I will discuss recent observations of nearby Active Galactic Nuclei in the optical and near-IT which explore the smallest resolvable scales with present instrumentation. These observations include imaging and spectroscopy obtained with instruments aboard the Hubble Space Telescope as well as Integral Field Spectroscopy with large (8m) telescopes. I discuss in particular recent results based on observations with NIFS -- the Gemini Near-Infrared Integral Field Spectrometer -- used with the adaptative optics systems ALTAIR, which reveal compact structures (pc to 10 pc scales) in molecular hydrogen. The kinematics of such structures is dominated by rotation or inflow, suggesting that they are the source of fuel to the supermassive black hole. Unresolved at the nucleus (scales < 5pc), there is usually a near-IR warm (1000K) source, which can be attributed to dust heated by the AGN (the inner part of the dusty torus). Sources with temperatures of ~300K (probably the outer parts of a dusty torus) are beginning to be resolved with recent interferometric observations in the near and mid infrared.
Paul Boley - poster
"Numerical modeling of the MYSO AFGL 4176 with the VLTI/MIDI"
This poster is dedicated to the study of the Becklin-Neugebauer object AFGL 4176. Such objects are characterized by a large luminosity (10^2 – 10^5 Lsun) in the infrared and by a complete absence of any corresponding source at optical wavelengths, which is generally interpreted as a cocoon of absorbing material surrounding an embedded massive (proto)star. Making use of a large collection of interferometric data taken at 10 microns, we present the results of simultaneous numerical modeling of visibilities and the spectral energy distribution at near-infrared through millimeter wavelengths.
Tabetha Boyajian - poster
"Cool Dwarf Diameters"
We present measurements of fundamental astrophysical properties of nearby, low-mass, K- and M-dwarfs from our extensive interferometric survey carried out with the CHARA Array. The principal goal of our study is the determination of linear radii and effective temperatures for these stars. We calculate their radii and effective surface temperatures by combining our CHARA Array angular diameter measurements with Hipparcos distances and bolometric fluxes based on literature photometry. Thus far, we have doubled the number of measurements for these types of stars.
"Global-scale structures from simulations of stellar convection"
Stars on the lower main sequence have substantial convection zones just beneath their photospheres. Convection in these regions can couple with rotation to build global-scale thermal, velocity and magnetic structures which may be observable by interferometers that can resolve stellar disks. Here I talk about predictions emerging from 3-D magnetohydrodynamic (MHD) simulations of global-scale convection for stars on the lower main sequence with the anelastic spherical harmonic (ASH) code and about how these predictions may be observationally tested. Generally, we find that differential rotation is an important feature of these stars and probably plays a crucial role in the convective stellar dynamos that build the magnetic fields seen in these stars.
Theo ten Brummelaar - poster
"Recent Results from the CHARA Array"
The CHARA Array is a six 1-m telescope optical and near infrared > interferometer located at the Mount Wilson Observatory in southern California and operated by the Center for High Angular Resolution Astronomy of Georgia State University. The CHARA Array has been in regular scientific operation since 2005 and now has over 50 publications in the refereed literature, including two in Science and one in Nature. The Array now supports seven beam combiners ranging from 0.5 microns up to 2.3 microns and combing from 2 to 4 beams at a time. An upgrade to a full 6 beam combiner is now underway. Here we present a brief overview of recent results including images of rotating stars, images of interacting binary stars, images of the recent eclipse event of Eps Aur, studies of exoplanet host stars, YSOs, Be stars, and the astrometry of binary stars.
"Dissecting the sub-parsec-scale mid-infrared emission of Centaurus A"
Interferometric observations with MIDI/VLTI in the mid-infrared made studies of the central dusty tori of Active Galactic Nuclei (AGNs) possible and proved their existence in a number of nearby AGNs. Both type 2 and type 1 galaxies showed parsec-scale structures whose properties were comparable, thus confirming the unifying model for Seyfert galaxies. Among the few extragalactic targets that are bright enough to be studied with MIDI, is also the nearest radio galaxy, Centaurus A (NGC 5128). The first results on this galaxy showed that nuclear dust also exists in the innermost parsec of a radio galaxy and that about half of the emission is non-thermal (Meisenheimer et al., 2007). From new observations with an improved (u,v)-coverage and resolution, it is now possible to model the geometry of the mid-infrared emission. We find a visibility pattern that defies an explanation with simple model geometries. A possible scenario built on multi-wavelength observations of Cen A will be presented.
"Radio and IR Observations of the Envelopes of AGB Stars"
Asymptotic Giant Branch Stars (AGB) are evolved red giants with tenuous molecular envelopes which have been the subject of much recent study using infrared and radio interferometers. In oxygen rich stars, radio SiO masers form in the outer regions of the molecular envelopes and are powerful probes of the extent and dynamics of these envelopes. I will discuss recent IR and radio measurements which are providing a wealth of information on these systems.
"Interferometric observations of solar system minor bodies"
I will present results of the first long-baseline interferometric observations of asteroids from the ground.
In particular, I will describe the analysis of observations of asteroids that we have obtained with the MIDI instruments of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory.
I will also discuss some of the current limitations of this technique and how we hope to overcome them using the second-generation instruments of the VLTI. I will show how these latter technological advances in high spatial resolution astronomy will offer a unique opportunity to study the densities and internal structures of asteroids in unprecedented detail.
'The Inner AU of Protoplanetary Disks: From Visibilities to Spectra to Images"
I will review infrared interferometric observations of young stars and their circumstellar material. Even simple, single-baseline measurements caused substantial revision of standard ideas about protoplanetary disks. We have now moved beyond this early era, and are now able to use multiple baselines, high spectral dispersion, and even basic image reconstruction to probe young stellar objects. I will discuss the physical insights enabled by these instrumental improvements, and indicate areas where I think future interferometers will advance our understanding of star and planet formation.
Nick Elias - poster
"Full-Stokes Interferometric Imaging of Stars"
Long-baseline optical interferometry and classical polarimetry have provided key insights in the fields of stellar atmospheres, stellar disks, and interacting binary stars. We present scientific justfications for "full-Stokes" polarization observations of these objects with optical interferometers. We also discuss: 1) instrument requirements; 2) a design for a simple and inexpensive polarizing beam combiner (including feed optics and detector) that can be integrated into existing instruments; 3) systems engineering simulations for coherent averaging, Stokes vector inversion, and instrumental polarization calibration; 4) full-Stokes images of Be stars created with the python-based radio interferometry software CASA; 5) a brief list of tasks to be completed; and 6) how the knowledge gained from full-Stokes interferometer design and observations can be used in other fields, such as exoplanet atmospheres.
Paul Gabor - poster
"Heterodyne interferometry with a supercontinuum local oscillator"
A fundamental limitation of optical heterodyne interferometry is the narrow spectral band of the local oscillator. Studies are under way to overcome this issue, e.g., by using tunable set-ups. The present paper proposes to inspect the potential of a broadband local oscillator constituted by a supercontinuum source, i.e., a "white" laser. These non-linear optical devices have been commercially available in the last ten years and their application in interferometry is yet to be explored.
"The Galactic Center and GRAVITY"
Over the last decade the Center of the Milky Way has become a laboratory for studying a massive central black hole and the physical processes in its immediate vicinity. I will summarize the current status of testing the black hole paradigm, and discuss current and future questions on the distribution and evolution of the nuclear star cluster and accretion. I will then describe the goals and status of the astrometric imager GRAVITY for the 4-telescope VLTI.
James Gordon - poster
"Multiplicity of pre-main-sequence stars at AU and sub-AU separations"
To understand star formation one must understand the formation of multiple systems. The statistical properties of pre-main-sequence binary and higher order systems are direct indicators of the mechanisms and initial conditions influential in their formation. We advocate the use of long-baseline optical interferometry to determine the multiplicity fraction of pre-main-sequence stars on AU scales to distinguish between competing formation models. We present the feasibility, statistical considerations, and scientific value of an interferometric multiplicity survey.
"Observational Constraints, Stellar Models, and Kepler Data for 13 Cyg"
13 Cyg (theta Cyg) is an F4V star that, at visual magnitude V=4.48, is the brightest star observable by the Kepler spacecraft. Short (59 s) and long (29.4 min) cadence photometric data were obtained for this star between June and September 2010. The target was not well-captured by the dedicated mask for 50% of the quarter, so data quality is degraded during those two windows. The data is now publicly available at
In preparation for interpreting this data and motivating further observations, we use observational constraints from the literature to construct stellar evolution and pulsation models of this star. We will discuss the expectations for solar-like oscillations or gamma Doradus-like g-mode pulsations given these constraints. 13 Cyg has been the subject of interferometric observations (Van Belle et al. 2008) giving an angular diameter of 0.760 ± 0.021 mas. Combined with Hipparcos parallax measurements, the diameter of 13 Cyg is measured to be 1.39 ± 0.04 Rsun. We will also discuss the value of the angular diameter measurements (vs. doing without them) in informing the stellar models and pulsation predictions.
"Introductory talk: Concepts, Terminology, The state of the art (Part I & Part II)
The use of optical/infrared interferometric methods by non-interferometric specialists is becoming more commonplace, and offers many opportunities for novel studies at high angular resolution. In this talk I will present an overview of current optical/infrared interferometric methods for non-experts, with particular emphasis on the basic terminology and concepts. I will also outline the capabilities of current and planned interferometers, and review their broad capabilities, for example, their spatial and spectral resolution, limiting sensitivity, imaging fidelity and dynamic range. My goal will be to provide the background needed for a non-expert audience to assess the utility of interferometry for potential scientific studies, and to help identify those capabilities of existing arrays that offer the best prospects for future science exploitation.
"Answering Fundamental Questions about Cataclysmic Variables and Classical Novae"
Cataclysmic variables (CVs) are interacting binaries consisting of a white dwarf primary, and a non-degenerate secondary star. There are numerous subclasses of CVs (any of which could become a Classical Nova), but broadly, these classifications are believed to arise from either differing values of the mass accretion rate, or whether the white dwarf primary is magnetic. There continue to be numerous questions about the origin, and evolution of these systems. We will review some of the outstanding issues, and address how advances in interferometry might be used to resolve them.
Jennifer Hoffman - poster
"Reflections and Fringes: How Can We Link Polarimetry with Interferometry to Illuminate Circumstellar Material?"
The circumstellar material created by mass loss from an evolved star leaves its imprint on the resulting supernova. Thus, studying the CSM distributions around evolved stars may help link core-collapse supernovae with specific progenitor types. Interferometric methods can image the immediate environments of nearby stars, whereas polarimetric observations can distinguish aspherical structures at great distances in unresolved systems. By combining the two, can we create a CSM "distance ladder" of sorts that will enable us to identify specific circumstellar structures surrounding faraway supernovae?
Elliot Horch - poster
"Single- and Dual-Aperture Interferometry at Southern Connecticut State University"
Two instruments for astronomical interferometry built Southern Connecticut State University (SCSU) will be discussed. The first is the Differential Speckle Survey Instrument (DSSI), which is speckle camera built in 2008 and currently in operation at the WIYN 3.5-m Telescope at Kitt Peak. It is a two-channel speckle imaging system that utilizes electron-multiplying CCD cameras to capture speckle images in two colors simultaneously. The information in two colors gives leverage on residual atmospheric dispersion that may be present in an observation. This allows reliable differential astrometry of binaries to be obtained on systems with separations smaller than one-quarter of the diffraction limit of the telescope, or under 10 mas at WIYN. A summary of the current observational projects being pursued with this system will be given, including a survey of spectroscopic binaries from the Geneva-Copenhagen Catalogue. The second instrument, still being assembled and tested in the laboratory at SCSU, is a new intensity interferometer that utilizes a Picoquant Picoharp timing module for real-time correlation of the photon signals received. The instrument and plans for observing with it will be described.
"The brief lifes of massive stars as witnessed by interferometry"
Massive stars present the newest and perhaps most challenging opportunity for long baseline interferometry to excel. Large distances require high angular resolution both to study the means of accreting enough mass in a short time and to split new-born multiples into their components for the determination of their fundamental parameters. Dust obscuration of young stellar objects require interferometry in the mid-infrared, while post-main sequence stellar phases require high-precision measurements to challenge stellar evolution models. I will summarize my recent work on modeling mid-IR observations of a massive YSO in NGC 3603, and on the derivation of masses and luminosities of a massive hot supergiant star in another star forming region in Orion. Challenges presented themselves when constraining the geometry of a hypothetical accretion disk, as well as obtaining spectroscopy matching the interferometric precision when working with only a few photospheric lines. As a rapidly evolving application of interferometry, massive stars have a bright future.
Don Hutter - poster
"Recent Science Results from the NPOI"
The latest science results from the Navy Prototype Optical Interferometer (NPOI) are summarized. Major areas reviewed include: 1) Recent results on NPOI imaging and orbits of radio star systems, with emphasis on the delineation of the Algol triple system; 2) NPOI observations that complement speckle interferometry programs by measurement of those portions of the orbits inaccessible at the resolution of speckle; 3) Revised orbits for systems of particular astrophysical interest such as delta Sco; and 4) Applications of advanced coherent integration techniques to the determination of ultra-precise stellar angular diameters in exoplanet and other systems.
Jeremy Jones - poster
"Interferometric Study to determine A-star Ages using CHARA"
Observational studies of A-type stars continue to shape our basic understanding of circumstellar disks and extrasolar planets. The first directly imaged circumstellar disks and extrasolar planets were discovered around A-type stars, and they still harbor the best studied of these systems. Nevertheless, our understanding of the temporal evolution of disks and planets is in many ways limited by the poorly known ages of A stars; mostly are known only to 50-200%. The CHARA Array has the unique ability to overcome this limitation by measuring the sizes of A stars. A stars evolve significantly in size while on the main sequence, so this straight-forward measurement can constrain the age to within a remarkable 10-20%! We plan to use CHARA to determine such ages for all single, northern A stars within 50 pc. Extrasolar disk and planet studies will undoubtedly continue to focus on the A-type stars over the next decade, so precisely determining the sizes and ages of the nearest of these will help ensure the long-term legacy of long-baseline interferometry.
Anders Jorgensen - poster
"Fundamental Stellar Parameters with Extreme Precision: Theory
and Practice of Coherent Integration of Optical Interferometric Data"
In the near future coherent integration will likely be one of the most tools in achieving high SNR on optical interferometric observations of faint and resolved targets. There are two basic ways to perform coherent integration, both of which are used today. Real time coherent integration stabilizes fringes using one detector while integrating for a long time on a separate detector. Post-processing coherent integration involves recording short snapshots and performing the coherent integration later in software. While coherent integration can greatly increase the visibility SNR (or decrease the observing time), sometimes by orders of magnitudes. For some applications (but not all) fringe smearing due to imperfect fringe tracking may require a different calibration strategy. In this presentation we will discuss the theory of coherent integration, practical approaches to coherent integration, related calibration, and show some specific examples of how it can be used to achieve extremely high precision.
Jaroslaw Kijak - poster
"A Binary system:Be star SS 2883 and spectrum evolution of pulsar B1259-63 - the Gigahertz-Peaked Spectrum"
We report the evidence for Gigahertz-Peaked Spectrum (GPS) in a pulsar. The binary pulsar system PSR B1259-63/SS2883 shows radio spectrum changes seemingly correlated with the orbital phase, with a maximum flux in the spectrum above 1 GHz appearing close to the periastron passage. This could suggest that in case of pulsars the GPS phenomenon is associated with the environmental conditions around the neutron star - in this case the Be-star companion envelope.
"Can interferometry resolve the mass ratio in all single line spectroscopic eclipsing binary stars?"
If radial velocity and astrometric data are combined, they can yield a full 3D orbital solution for most binary stars. In the case of single line spectroscopic binaries this approach fails to result in a solution. We report on a modification to these methods which combined astrometry, radial velocity, and interferometry of eclipsing systems that yield full 3D orbital solutions. This method is particularly applicable to single line eclipsing binaries, whose secondary is hidden from view, or for planets that transit the face of their host stars.
Rainer Koehler - poster
"Software for Astrometry with PRIMA at the VLTI"
PRIMA (Phase-Referenced Imaging and Microarcsecond Astrometry) is an ESO/VLTI instrument designed for phase-referenced imaging and narrow-angle astrometry, dedicated to exoplanet detection. Astrometric detection of planets requires a precision of 10-30 micro-arcsec. For an interferometer with a baseline of 100 m, this corresponds to measuring the (differential) optical path difference with a precision of 5-15 nanometers. This precision can only be achieved with careful calibration of the instrument, including effects that are irrelevant for almost any other scientific application. PRIMA is currently being commissioned on Paranal, its first full (and uninterrupted) astrometric observations have been achieved in January. I will report on the results of the first tests of the data reduction pipeline with real data, and the challenges encountered on the way.
Yitping Kok - poster
"Narrow-angle astrometry with SUSI"
The Sydney University Stellar Interferometer (SUSI) is currently being fitted with a 2nd beam combiner, MUSCA (Micro-arcsecond University of Sydney Companion Astrometry) for the purpose of narrow-angle astrometry. With an aim to achieve ~10 micro-arcseconds of angular resolution at its best, MUSCA allows SUSI to search for planets around bright binary stars, which are its primary targets. While the first beam combiner will be used to track stellar fringes during an observation, MUSCA will be used to measure separations of binary stars. MUSCA is a Michelson interferometer and its setup at SUSI will be described in the poster.
Hendrik Linz - poster
- "MIDI/VLTI interferometry of massive YSOs: Resolving the SED-fit ambiguities"
Information about the inner structure of young stellar objects is crucial for understanding how the central forming stars gain their mass. However, especially for observations of (usually further away) high-mass YSOs, conventional imaging has limitations in spatial resolution. By means of mid-infrared interferometry, we can peek deeply into the strongly extinguished central 100 AU of such objects. Here, we report on recent results we obtained within our GTO program using MIDI at the VLTI. In particular, we describe how the MIDI results can resolve ambiguities of simple SED fitting, and how quantities like differential phases give additional geometrical structure information. In addition, we show how the synergy with facilities at different wavelength regimes can lead to a more complete picture of the nature of such YSOs.
Sean Lockwood - poster
"Recent Results from the ISI"
Infrared Spatial Interferometer observations of Betelgeuse over the last 5 years show a variation in size, shape and intensity. The ISI is also building a new high-speed digital spectrometer-correlator and recent test results will be presented.
"The Dynamic Duo: Interferometry and Asteroseismology"
Over the past decade, asteroseismology and interferometry have emerged as important new tools to improve our understanding of stellar structure and evolution. By providing direct measurements of fundamental properties for large samples of relatively nearby stars, these complementary techniques are now being used to calibrate more traditional indirect methods. I will give an overview of asteroseismology in the Kepler era, with a focus on solar-like oscillations and the power of interferometric constraints to leverage the full potential of stellar pulsations.
"Imaging Rapid Rotators"
O/IR interferometers can now image the oblate and gravity-darkened photospheres of rapidly rotating stars. I will review recent progress and summarize results that have revealed severe weaknesses in current theories. New spectro-interferometric capabilities promise to soon measure differential rotation and test hydrodynamical simulations with unprecedented precision, offering a chance to calibrate/validate crucial aspects of massive star evolution.
"1-D imaging of the red supergiant Betelgeuse in the CO first overtone lines with VLTI/AMBER"
We present high-spatial and high-spectral resolution observations of the red supergiant Betelgeuse in the CO lines near 2.3 micron with VLTI/AMBER. For the first time, we have reconstructed 1-D images in the individual CO lines with an angular resolution of 9.8 mas and a spectral resolution of 6000 by applying the self-calibration technique. The reconstructed 1-D images reveal that the star appears different in the blue and red wing of the individual CO lines. In the blue wing, the star shows a pronounced, asymmetric extended component up to 1.3 stellar radii, while such a component does not appear in the red wing. This can be explained by a model, in which the CO gas clump roughly half as large as the star is moving downward with 0--10 km/s, while the gas in the remaining region is infalling much faster with 30--40 km/s. Comparison between the CO line data taken in 2008 and 2009 shows a significant change in the dynamics of the atmosphere. However, the 1-D images in the continuum show only a slight deviation from a limb-darkened disk. Moreover, the continuum data taken in 2008 and 2009 reveal no or only marginal time variations, much smaller than the maximum variation predicted by the current 3-D convection simulations.
James Parks - poster
"Can CHARA Image Cool Starspots?"
We present H band interferometric images of cool starspots on the chromospherically active giant Lambda Andromedae. Images span roughly 75% of the rotational period with a cadence of ~1 week. The data were obtained using all six telescopes in the CHARA array with the MIRC beam combiner. Model solutions provide direct measurements of cool starspot properties. Images are constructed with MACIM implementing a new gradient suppressing regularizer. We obtained consistent results between model solutions and MACIM reconstructions. The results of simulations testing model fidelity based on u,v sampling are presented. In addition, we present evidence interferometrically measured diameters are insensitive to cool starspot presence at an ~2.5% confidence level.
Jayadev Rajagopal - poster
"Near-IR Sizes of Circumbinary Disks"
We report the diameters in the near-IR of purported disks around post-AGB binaries, measured using the CHARA array. These are amongst the first measurements of these objects. Various characteristics of these systems including the large IR excess, and refractory-deficient stellar photospheres, have been linked to the possible existence of stable Keplerian dust disks, probably formed during the evolution of the binary pair. These systems are also of interest as bright precursors of Planetary Nebulae and can be studied to probe the origins of the asymmetry seen in PNe. Our sample includes confirmed post-AGB binaries as well as RV Tauri stars that have previously been included in the same class (as hosting circumbinary disks). We have used long (200 m) baselines to determine the stellar contribution to the coherent flux, thereby removing a source of large uncertainty in the disk sizes. For the post-AGB stars, the disk sizes are consistent with the “wall” models which are similar to the Herbig Ae/Be disk models in many aspects. The data provides the first direct measurements of disk sizes and are the first step to further development of this type of model. For the RV Tauris, the sizes are consistent with simple shell models, raising some doubt about the generalization that they have the same class of dust disks as the binary post-ABG stars.
Alexander Rea - poster
"Impact of Fast Tip Tilt Systems on the Scientific Performance of Optical Interferometers"
Enhancing the limiting sensitivity of optical/infrared interferometers is a major task for today's array designers. In many cases this can be compromised by the inability of other critical sub-systems - in particular the fast tip tilt (FTT) systems associated with each unit telescope - to match the sensitivity of the interferometric beam combiner. This can be especially problematic for dusty targets, where optical extinction may be high. Here we investigate how the FTT sensitivity of an array can limit its scientific potential with particular reference to AGN, YSO and evolved stellar targets, and outline how the MROI FTT design aims to mitigate losses in capability through matching its performance to that of the MROI beam combiners.
Robert de Rosa - poster
"Two B's or Not Two B's - An NPOI Survey of Massive Stars"
Surveys of massive O- and B-type stars suggest a significantly higher multiplicity fraction than for Solar-type primaries, but coverage over a critical separation range is missing. Understanding the distribution of the separation of these companions is important when considering the formation and survivability of disks and proto-planetary systems around these massive stars. We present preliminary findings from a volume-limited multiplicity survey of B-type stars covering this important separation range between 1 and 15AU. The angular resolution provided by the Navy Prototype Optical Interferometer (NPOI) allows for the detection of close (5--250mas) binaries with a magnitude difference reaching ΔR of ~3. With our large, unbiased volume-limited sample of 69 targets, these observations will allow for a robust constraint on the multiplicity of these massive stars within this separation range. This survey will be complementary to both previous spectroscopic surveys, and speckle interferometry observations. Newly resolved companions within this study will make ideal targets for follow-up interferometric observations to detect orbital motion and determine their orbital parameters. Future interferometers will extend this work to closer, fainter companions around both these targets, and intrinsically fainter A-type stars.
Benjamin Sargent - poster
"Probing Dust Formation around Evolved Stars with Near-Infrared Interferometry"
Near-infrared interferometry holds great promise for advancing our understanding of the formation of dust around evolved stars. For example, the Magdalena Ridge Observatory Interferometer (MROI), which will be an optical/near-infrared interferometer with down to submilliarcsecond resolution, includes studying stellar mass loss as being of interest to its Key Science Mission. With facilities like MROI, many questions relating to the formation of dust around evolved stars may be probed. How close to an evolved star such as an asymptotic giant branch (AGB) or red supergiant (RSG) star does a dust grain form? Over what temperature ranges will such dust form? How does dust formation temperature and distance from star change as a function of the dust composition (carbonaceous versus oxygen-rich)? What are the ranges of evolved star dust shell geometries, and does dust shell geometry for AGB and RSG stars correlate with dust composition, similar to the correlation seen for planetary nebula outflows? At what point does the AGB star become a post-AGB star, when dust formation ends and the dust shell detaches? Currently we are conducting studies of evolved star mass loss in the Large Magellanic Cloud using photometry from the Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) Spitzer Space Telescope Legacy program. We model this mass loss using the radiative transfer program 2Dust to create our Grid of Red supergiant and Asymptotic giant branch ModelS (GRAMS). For simplicity, we assume spherical symmetry, but 2Dust does have the capability to model axisymmetric, non-spherically-symmetric dust shell geometries. 2Dust can also generate images of models at specified wavelengths. We discuss possible connections of our GRAMS modeling using 2Dust of SAGE data of evolved stars in the LMC and also other data on evolved stars in the Milky Way's Galactic Bulge to near-infrared interferometric studies of such stars. By understanding the origins of dust around evolved stars, we may learn more about the later parts of the life of stardust; e.g., its residence in the interstellar medium, its time spent in molecular clouds, and its inclusion into solid bodies in future planetary systems.
"Fundamental Properties of Young Binary Stars"
Spatially resolving the orbits of double-lined spectroscopic binaries allows us to measure the dynamical masses of the component stars. At the distances to the nearest star forming regions, high angular resolution techniques are required to resolve these short period systems. In this presentation, I provide an overview of the few pre-main sequence spectroscopic binaries that have been resolved thus far using long-baseline optical/infrared interferometers. I also compiled a list of known spectroscopic binaries in nearby star forming regions (Taurus, Orion, Ophiuchus, Scorpius Centaurus, etc) and show that with modest improvements in the sensitivity of interferometers with 200-300 meter baselines, we can begin building a statistically significant set of pre-main sequence stars with precise mass determinations. This is important for validating and distinguishing among the theoretical calculations of pre-main sequence evolution. Additionally, the distances to the binaries determined from their orbital parallaxes provides a way to map the three-dimensional structure of nearby star forming regions.
"Extrasolar Planetary Systems"
"Stellar Diameters in the Beta Pic Moving Group"
Members of the BPMG are young enough (10-20 MY) and near enough ($< 50$ pc) that some are resolvable with the CHARA Array in the H and K bands. We used the interferometer with the CLASSIC beam combiner, in an allocation granted through the NOAO allotment, to measure the angular diameters of the F spectral type stars HIP 560 and HIP 21547 at $0.47\pm 0.04$ and $0.53\pm0.04$ mas, respectively, at H and K. These values are the result of a quick, first-look processing of the visibilities applied to uniform disk models. We expect to improve the precision and accuracy as we reprocess the data and apply it to limb-darkened models. The immediate result is that these stars are truly pre-main sequence between 10 and 20 MY old. The PMS evolutionary tracks of stars more massive than ~1 solar mass, hence F spectral type stars, are relatively non-controversial unlike the situation for less massive stars. We expect therefore to improve the estimate of their ages as we improve the precision of their diameter measurements. The measured radius will also provide a direct determination of the effective temperature through L= 4 π R2 σ Teff4 for comparison with theoretical calculations. Measuring the radius as the star contracts to the main sequence provides a new means of estimating age accurately by reference to models of their evolution. In the coming year we plan to use the VEGA visible light spectrometer at the CHARA Array to measure the limb darkening of these stars. Inversion to a distribution of temperature as function of optical depth in the photosphere will provide a test of the temperature distributions used in the theoretical calculations of their stellar atmospheres. Measured limb darkening of the F and G stars will also provide empirical tests of the theoretical occultation profiles that will be used to interpret exoplanet transits detected by the Kepler spacecraft.
"Evolved Stars, pulsation and mass loss – understanding the link between variability and evolution of intermediate mass stars"
Low and intermediate mass stars (1-8 solar masses) are very important contributors of material to the interstellar medium. However, the mechanisms by which this matter is expelled remain a mystery. Moreover, the evolutionary effects of dust formation are poorly understood. Low and intermediate mass stars eventually evolve into asymptotic giant branch (AGB) stars, which subsequently evolve further to become planetary nebulae (PNe). The formation of dust shells during the AGB phase is believed to be driven by the pulsation of these stars. During this phase the dust shell is expected to increase in depth both optically and geometrically as mass-loss rate increases. At the end of the AGB phase, the mass loss virtually stops and the circumstellar shell begins to drift away from the star. At the same time, the central star begins to shrink and heat up from~3000K until it is hot enough to ionize the surrounding gas, at which point the object becomes a planetary nebula (PN). The short-lived post-AGB phase, as the star evolves toward to the PN phase, is also known as the proto- or pre-planetary nebula (PPN) phase. Whereas observations suggest that the AGB phase has mostly spherically-symmetric mass loss, there is clearly a deviation from spherical symmetry somewhere in the evolution of these stars and their mass loss, since PNe are rarely spherical. By studying the distribution of matter in these AGB and post-AGB circumstellar shells we can gain a better understanding of the mass-loss processes involved in the evolution of these stars. I will discuss how interferometry plays a role in studying the interplay between pulsation, mass loss, dust formation and evolution of these stars.
Stanislav Stefl - poster
"AMBER spectro-interferometry of Be Stars"
Since the high-resolution (R=12000) mode of the VLT/Amber interferometer was introduced two years ago, unique spectro-interferometric data were obtained for several classical Be stars. Preliminary analysis of interferometric observables for six of them is presented here. The observations bring new challenges for modelling of Be star disks. Br gamma visibilities, phases and closure phases of all Be stars show complicated profiles which were not seen in previous lower resolution observations. One example is the shape of the phase curve, which departs significantly from the simple S-shaped curve obtained previously.
Robert Stencel - poster
"A look inside the disk of the epsilon Aurigae system"
Interferometric imaging combined with spectroscopy is providing to be a powerful way to unlock the long kept secrets of this enigmatic eclipsing system that has puzzled astronomers for many decades. In this presentation, we combine a sequence of H band images obtained at the CHARA Array during the 2010 eclipse, with spectra of ours and others obtained from a worldwide network of observers participating in the eclipse campaign. The MIRC images confirm the hypothesized dark disk, revealing it to have dimensions of ~8AU long by ~0.7AU thick, that occults the southern hemisphere of the 135Ro F star primary – but these dimensions are dependent on the assumed distance, still not settled. Spectra reveal a wealth of changes caused by facets of the disk that can be associated with substructure, including possible rings, a central ionized region and evidence for accretion onto a hot embedded object. We acknowledge the help of numerous observers, and support for this effort that was derived in part from a bequest of William Herschel Womble in support of astronomy at the University of Denver, from NSF grant 1016678 and from JPL RSA 1414715 to the University of Denver.
Ramarao Tata - poster
"VLTI/AMBER Observations of an exoplanet host star"
As a first attempt to obtain the true mass and inclination of a radial velocity detected companion using optical interferometry, we observed HD33636 (Kmag = 5.57) using AMBER+FINITO with the UTs. A radial velocity (RV) companion msin(i)= 9.28Mj was detected around HD33636 (Vogt et. al. 2002) . Studies using HST astrometry revealed the true mass of the companion to be 142Mj (Bean et. al. 2007). Using interferometry, we will verify the true mass of this companion and also demonstrate a method for using AMBER+FINITO to provide either the true mass or an upper limit on the true mass (if no signal detected) of the RV-detected exoplanet companions. We can also use this data to get a radius estimate of the host star. Once established, this technique can be used to quickly and effectively filter out radial velocity exoplanets for follow-up astrometric studies (PRIMA, SIM, etc.) to determine the true mass. In this poster, we present some of our preliminary results.
"Fundamental properties of binary stars and dynamical masses"
For many decades the determination of accurate fundamental parameters for stars (masses, radii, temperatures, luminosities, etc.) has mostly been the domain of eclipsing binary systems. That has begun to change as long-baseline interferometric techniques have improved significantly, and powerful new instruments have come online. I will review the status of the field, and in particular how the knowledge of precise stellar properties helps us understand stars. Main-sequence stars similar to the Sun are by far the best studied, but much remains to be done for other kinds of objects such as early-type and late-type stars including brown dwarfs, evolved stars, metal-poor stars, and pre-main sequence stars. I will illustrate progress with several examples of how interferometry has contributed significantly in some of these areas.
Yamina Touhami - poster
"Long Baseline Interferometric Survey of Be stars made with the CHARA Array"
We present the first spatially resolved observations of circumstellar envelopes of 25 bright northern Be stars. The survey was performed with the CHARA Array interferometer in the K-band at intermediate and long baselines. The interferometric visibilities are well fitted by an optically thick disk model where the gas density steeply decreases with the radius. Physical and geometrical parameters such as the density profile, the inclination, and the position angle of the circumstellar disks are determined, and we find that the density exponent varies between n~ 2.4 - 3.2, which is consistent with previous IRAS measurements. In addition to the interferometric observations, we also obtained simultaneous optical and near-IR spectrophotometry data taken at Lowell observatory. We find that the thick disk model reproduces well the observed disk IR-continuum excess. By combining the projected rotational velocity of the Be star with the disk inclination derived from interferometry, we can estimate the equatorial rotational velocities of these Be stars.
Qian Wang and Lee Anne Willson - poster
"Spirals from the interaction of a small body with a pulsating AGB star wind"
We have been investigating the effects of a small body (~ 10 MJupiter) on the winds of pulsating, mass-losing AGB stars (Miras). For such low companion masses, the star is not spun up, and so the body creates a short-duration highly-localized gravitational impulse as it orbits. Using the Bowen code for the flow, we have looked at the effects of the extra impulse, and find that for very close orbits the result can be 2, 3 or 4-armed spiral patterns. Thus, observations of 3-armed symmetry – triangular stars – or 4-armed spirals would likely indicate the presence of such a close companion. This also has clear implications for the formation of planetary nebulae.
Russel White - poster
'Young Stars Sizes Measured with the CHARA Array"
We present results of a CHARA Array interferometric survey of adolescent-age stars in the AB Dor moving group. The motivation is to spatially resolve stars larger than ~0.4 milliarcseconds to help constrain the group's age, and to search for close binary systems from which dynamical masses may be determined. This survey spatially resolved 2 members, the F6 star GJ 159 (0.568 +/- 0.017 mas) and the M2 star GJ 393 (0.524 +/- 0.016 mas). GJ 393 is especially interesting as evolutionary models predict that it should be above the main sequence for approximately 70 million years, thereby providing a powerful constraint on the group's age. This survey also spatially resolved the known spectroscopic binary HD 113449. Continued observations of it, in combination with spectroscopic monitoring, will yield dynamical masses for a young sub-solar mass binary in a few years time.
Ed Wishnow - poster
"Recent Results from the ISI"
Infrared Spatial Interferometer observations of Betelgeuse over the last 5 years show a variation in size, shape and intensity.
The ISI is also building a new high-speed digital
spectrometer-correlator and recent test results will be presented.
John Young - poster
"Simulated MROI imaging of AGN dust tori and stellar surfaces"
We present simulated observations of surface features on Red Supergiant (RSG) stars and clumpy dust structures surrounding Active Galactic Nuclei (AGN) with the Magdalena Ridge Observatory Interferometer (MROI). These represent two of the classes of astrophysical targets enumerated in the MROI Key Science Mission that are typical of the types of complex astrophysical phenomena that the MROI has been designed to image. The simulations are based on source structures derived from recent theoretical models and include both random and systematic noise on the measured Fourier data (visibility amplitudes and closure phases) consistent with our expectations for typical such targets observed with the MROI. Image reconstructions, obtained using the BSMEM imaging package, are presented for 4-, 6- and 8-telescope implementations of the array. We discuss the utility of the reconstructions for discriminating between competing models such as smooth and clumpy dust distributions in AGN.
"Keeping Theorists Connected to Reality"
Stellar theory, despite its long history, still has outstanding problems in its more subtle physics. Interferometry offers precision observations that can constrain models of these important processes. I will discuss newly described stellar physics, particularly convection, that can be tested and elucidated by asteroseismology, measurements of stellar radii, and other interferometry-enabled measurements. The prospects for supernova progenitors and remnants with future higher sensitivity instruments will be briefly discussed.
"Toward Direct Detection of Hot Jupiters with Precision Closure Phase"
Direct detection of thermal emission from nearby hot Jupiters has greatly advanced our knowledge of extrasolar planets in recent years. Since hot Jupiter systems can be regarded as analogs of high contrast binaries, ground-based infrared long baseline interferometers have the potential to detect their thermal emission with precision closure phase. Here we present closure phase studies toward direct detection of nearby hot Jupiters using the CHARA array and the MIRC combiner. We conducted a large number of observations for the best candidate υ And, and find much larger systematic errors than expected, most likely caused by dispersion across different wavelengths. We also find that using higher spectral resolution modes (e.g., R=150) can significantly reduce the systematics. By combining all calibrators in an observing run together, we are able to roughly re-calibrate the lower spectral resolution data, allowing us to obtain upper limits of the star/planet contrast ratios of υ And b across the H band. Our best upper limit suggests that we are starting to have the ability to constrain atmospheric models of hot Jupiters with interferometry.