On the Interferometric Sizes of Young Stellar Objects

Long-baseline optical interferometers can now detect and resolve hot dust emission thought to arise at the inner edge of circumstellar disks around young stellar objects (YSOs). We argue that the near-infrared sizes being measured are closely related to the radius at which dust is sublimated by the stellar radiation field. We consider how realistic dust optical properties and gas opacity dramatically affect the predicted location of this dust destruction radius, an exercise routinely done in other contexts but so far neglected in the analysis of near-infrared sizes of YSOs. We also present the accumulated literature of near-infrared YSO sizes in the form of a ``size-luminosity diagram'' and compare with theoretical expectations. We find evidence that large (>~ 1 micron) dust grains predominate in the inner disks of T Tauri and Herbig Ae/Be stars, under the assumption that the inner-most gaseous disks are optically-thin at visible wavelengths.Comment: Accepted by Astrophysical Journa

JouFLU: upgrades to the Fiber Linked Unit for Optical Recombination (FLUOR) interferometric beam combiner

The Fiber Linked Unit for Optical Recombination (FLUOR) is a precision interferometric beam combiner operating at the CHARA Array on Mt. Wilson, CA. It has recently been upgraded as part of a mission known as “Jouvence of FLUOR” or JouFLU. As part of this program JouFLU has new mechanic stages and optical payloads, new alignment systems, and new command/control software. Furthermore, new capabilities have been implemented such as a Fourier Transform Spectrograph (FTS) mode and spectral dispersion mode. These upgrades provide new capabilities to JouFLU as well as improving statistical precision and increasing observing efficiency. With these new systems, measurements of interferometric visibility to the level of 0.1% precision are expected on targets as faint as 6th magnitude in the K band. Here we detail the upgrades of JouFLU and report on its current status

Study of molecular layers in the atmosphere of the supergiant star µ Cep by interferometry in the K band

Infrared interferometry of supergiant and Mira stars has recently been reinterpreted as revealing the presence of deep molecular layers. Empirical models for a photosphere surrounded by a simple molecular layer or envelope have led to a consistent interpretation of previously inconsistent data. The stellar photospheres are found to be smaller than previously understood, and the molecular layer is much higher and denser than predicted by hydrostatic equilibrium. However, the analysis was based on spatial observations with medium-band optical filters, which mixed the visibilities of different spatial structures. This paper reports spatial interferometry with narrow spectral bands, isolating near-continuum and strong molecular features, obtained for the supergiant µ Cep. The measurements confirm strong variation of apparent diameter across the K-band. A layer model shows that a stellar photosphere of angular diameter 14.11±0.60 mas is surrounded by a molecular layer of diameter 18.56±0.26 mas, with an optical thickness varying from nearly zero at 2.15 µm to >1 at 2.39 µm. Although µ Cep and α Ori have a similar spectral type, interferometry shows that they differ in their radiative properties. Comparison with previous broad-band measurements shows the importance of narrow spectral bands. The molecular layer or envelope appears to be a common feature of cool supergiants

Probing the close environment of young stellar objects with interferometry

The study of Young Stellar Objects (YSOs) is one of the most exciting topics that can be undertaken by long baseline optical interferometry. The magnitudes of these objects are at the edge of capabilities of current optical interferometers, limiting the studies to a few dozen, but are well within the capability of coming large aperture interferometers like the VLT Interferometer, the Keck Interferometer, the Large Binocular Telescope or 'OHANA. The milli-arcsecond spatial resolution reached by interferometry probes the very close environment of young stars, down to a tenth of an astronomical unit. In this paper, I review the different aspects of star formation that can be tackled by interferometry: circumstellar disks, multiplicity, jets. I present recent observations performed with operational infrared interferometers, IOTA, PTI and ISI, and I show why in the next future one will extend these studies with large aperture interferometers.Comment: Review to be published in JENAM'2002 proceedings "The Very Large Telescope Interferometer Challenges for the future

Co-phasing the Large Binocular Telescope: status and performance of LBTI/PHASECam

The Large Binocular Telescope Interferometer is a NASA-funded nulling and imaging instrument designed to coherently combine the two 8.4-m primary mirrors of the LBT for high-sensitivity, high-contrast, and high-resolution infrared imaging (1.5-13 um). PHASECam is LBTI's near-infrared camera used to measure tip-tilt and phase variations between the two AO-corrected apertures and provide high-angular resolution observations. We report on the status of the system and describe its on-sky performance measured during the first semester of 2014. With a spatial resolution equivalent to that of a 22.8-meter telescope and the light-gathering power of single 11.8-meter mirror, the co-phased LBT can be considered to be a forerunner of the next-generation extremely large telescopes (ELT).Comment: 8 pages, 5 figures, SPIE Conference proceeding

Study of molecular layers in the atmosphere of the supergiant star mu Cep by interferometry in the K band

Infrared interferometry of supergiant and Mira stars has recently been reinterpreted as revealing the presence of deep molecular layers. Empirical models for a photosphere surrounded by a simple molecular layer or envelope have led to a consistent interpretation of previously inconsistent data. The stellar photospheres are found to be smaller than previously understood, and the molecular layer is much higher and denser than predicted by hydrostatic equilibrium. However, the analysis was based on spatial observations with medium-band optical filters, which mixed the visibilities of different spatial structures. This paper reports spatial interferometry with narrow spectral bands, isolating near-continuum and strong molecular features, obtained for the supergiant mu Cep. The measurements confirm strong variation of apparent diameter across the K-band. A layer model shows that a stellar photosphere of angular diameter 14.11+/-0.60 mas is surrounded by a molecular layer of diameter 18.56+/-0.26 mas, with an optical thickness varying from nearly zero at 2.15 microns to >1 at 2.39 microns. Although mu Cep and alpha Ori have a similar spectral type, interferometry shows that they differ in their radiative properties. Comparison with previous broad-band measurements shows the importance of narrow spectral bands. The molecular layer or envelope appears to be a common feature of cool supergiants.Comment: 9 pages, 2 figures, to appear in A&

Aperture synthesis using multiple facilities: Keck aperture masking and the IOTA interferometer

As the number of optical interferometers increase, multi-facility observations become both feasible and scientifically interesting. For imaging of complex sources, the capability of increasing (u,v) coverage by using multiple arrays may be necessary for accurately interpreting the fringe visibility and closure phase data. Toward this end, coordinated observations with the IOTA interferometer and Keck aperture masking have been carried out to test techniques for synthesizing images using data from heterogeneous arrays with sparse (u,v) coverage. In particular, we will focus on how the image prior in the Maximum Entropy Method can be used to efficiently incorporate very high spatial frequency information with "low-resolution" data for imaging the generic prototype "Star + Dust Shell" image morphology. Preliminary results using real data for a few dusty evolved stars are presented

Exoplanet science with the LBTI: instrument status and plans

The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument of the LBT designed for high-sensitivity, high-contrast, and high-resolution infrared (1.5-13 $\mu$m) imaging of nearby planetary systems. To carry out a wide range of high-spatial resolution observations, it can combine the two AO-corrected 8.4-m apertures of the LBT in various ways including direct (non-interferometric) imaging, coronagraphy (APP and AGPM), Fizeau imaging, non-redundant aperture masking, and nulling interferometry. It also has broadband, narrowband, and spectrally dispersed capabilities. In this paper, we review the performance of these modes in terms of exoplanet science capabilities and describe recent instrumental milestones such as first-light Fizeau images (with the angular resolution of an equivalent 22.8-m telescope) and deep interferometric nulling observations.Comment: 12 pages, 6 figures, Proc. SPI

Recent science results with the two-telescope IOTA

The IOTA (Infrared Optical Telescope Array) has been routinely operating with two-telescopes since 1994, a mode destined to become obsolete following its recent conversion to a three-telescope array. In two-telescope mode, the IOTA has made numerous scientific and technical contributions, see e.g. our list of publications at http://cfa-www.harvard.edu/cfa/oir/IOTA/PUBLI/publications.html. We present preliminary results on three different topics using recent data from the two-telescope IOTA: (1) measurements of Mira star diameters simultaneously in three different near-infrared spectral bands, (2) measurement of the characteristic size and shape of the source of near-infared emission in the x-ray binary system CI Cam, and (3) aperture synthesis of the Carbon star V Hydrae combining data from the IOTA and from aperture masking at the Keck-I telescope

The physical conditions in Gomez's Hamburger (IRAS 18059-3211), a pre-MS rotating disk

We aim to study the structure, dynamics and physical conditions of Gomez's Hamburger (IRAS 18059-3211; GoHam). We confirm that GoHam essentially consists of a flaring disk in keplerian rotation around a young, probably pre-MS star. We present high resolution SMA maps of 12CO J=2-1, 13CO J=2-1, 12CO J=3-2, and C17O J=3-2, as well as data on 12CO J=6-5 and the continuum flux at these wavelengths. Spatial resolutions up to 1" are obtained. Except for the C17O data, the dynamical ranges are larger than 10. The maps are compared to a numerical model, which simulates the emission of a rotating disk with the expected general properties of such objects; a very satisfactory fitting of our maps is obtained. The meaning and reliability of our results are thoroughly discussed. Our observations allow measurement of the main properties of GoHam at scales between ~ 1" (~ 5 10^15 cm, for the assumed distance, 300 pc) and the total extent of the nebula, 14". We are able to measure the global structure of the gas-rich disk, which is found to be flaring, and its dynamics, which is clearly dominated by keplerian rotation, with a very small degree of turbulence. The combination of different lines, particularly showing different opacities, allows us to reasonably estimate the distributions of the gas temperature and density. We clearly find a significant and sharp increase in temperature at large distances from the equator, accompanied by a decrease in density of the same order. Finally, we identify and study a condensation in the southern part of the disk that has no counterparts in the rest of the nebula. This condensation is quite extended (about 5 10^15 cm), contains a significant amount of mass (roughly, ~ 6 10^-3 Mo), and seems to be associated with a detectable distortion of the global rotation kinematics.Comment: 16 pages, 12 figures, 1 pdflatex text file, goha.bbl file, aa.cls style fil