Karl H. Hofmann

ON THE NATURE OF THE HERBIG B[e] STAR BINARY SYSTEM V921 SCORPII: GEOMETRY AND KINEMATICS OF THE CIRCUMPRIMARY DISK ON SUB-AU SCALES*

V921 Scorpii is a close binary system (separation 0025) showing the B[e]-phenomenon. The system is surrounded by an enigmatic bipolar nebula, which might have been shaped by episodic mass-loss events, possibly triggered by dynamical interactions between the companion and the circumprimary disk. In this paper, we investigate the spatial structure and kinematics of the circumprimary disk, with the aim to obtain new insights into the still strongly debated evolutionary stage. For this purpose, we combine, for the first time, infrared spectro-interferometry (VLTI/AMBER, λ/Δλ = 12, 000) and spectro-astrometry (VLT/CRIRES, λ/Δλ = 100, 000), which allows us to study the AU-scale distribution of circumstellar gas and dust with an unprecedented velocity resolution of 3 km s–1. Using a model-independent photocenter analysis technique, we find that the Brγ-line-emitting gas rotates in the same plane as the dust disk. We can reproduce the wavelength-differential visibilities and phases and the double-peaked line profile using a Keplerian-rotating disk model. The derived mass of the central star is 5.4 ± 0.4 M ☉ (d/1150 pc), which is considerably lower than expected from the spectral classification, suggesting that V921 Sco might be more distant (d ~ 2 kpc) than commonly assumed. Using the geometric information provided by our Brγ spectro-interferometric data and Paschen, Brackett, and Pfund line decrement measurements in 61 hydrogen recombination line transitions, we derive the density of the line-emitting gas (Ne = (2-6) × 1019 m–3). Given that our measurements can be reproduced with a Keplerian velocity field without an outflowing velocity component and the non-detection of age-indicating spectroscopic diagnostics, our study provides new evidence for the pre-main-sequence nature of V921 Sco.

Gliese 569b: a young multiple brown dwarf system?

The nearby late M star Gliese 569B was recently found by adaptive optics imaging to be a double with separation ~1 AU. To explore the orbital motion and masses, we have undertaken a high-resolution (~005) astrometric study. Images were obtained over 1.5 yr with bispectrum speckle interferometry at the 6.5 m Multiple Mirror Telescope (MMT) and 6 m Special Astrophysical Observatory telescope. Our data show motion corresponding to more than half the orbital period and constrain the total mass to be greater than 0.115 M☉, with a most probable value of 0.145 M☉. Higher masses cannot be excluded without more extended observations, but from statistical analysis we find an 80% probability that the total mass is less than 0.21 M☉. An infrared spectrum of the blended B double obtained with the MMT has been modeled as a blend of two different spectral types, chosen to be consistent with the measured J- and K-band brightness difference of a factor of ~2. The blended fit is not nearly as good as that to a pure M8.5+ template. Therefore, we hypothesize that the brighter component likely has two unresolved components with near equal masses, each the same as the fainter component. If Gl 569B is a triple, our dynamical limits suggest each component has a mass of 50 MJup. We infer an age for the system of 300 Myr from its kinematic motion, which places it as a member of the Ursa Major moving group. All the above parameters are consistent with the latest DUSTY evolution models for brown dwarfs.

The LEECH Exoplanet Imaging Survey: Characterization of the Coldest Directly Imaged Exoplanet, GJ 504 b, and Evidence for Superstellar Metallicity

As gas giant planets and brown dwarfs radiate away the residual heat from their formation, they cool through a spectral type transition from L to T, which encompasses the dissipation of cloud opacity and the appearance of strong methane absorption. While there are hundreds of known T-type brown dwarfs, the first generation of directly imaged exoplanets were all Luf0a0type. Recently, Kuzuhara et al. announced the discovery of GJ 504 b, the first T dwarf exoplanet. GJ 504 b provides a unique opportunity to study the atmosphere of a new type of exoplanet with a ∼500 K temperature that bridges the gap between the first directly imaged planets (∼1000 K) and our own solar systemʼs Jupiter (∼130 K). We observed GJ 504 b in three narrow L-band filters (3.71, 3.88, and 4.00 μm), spanning the red end of the broad methane fundamental absorption feature (3.3 μm) as part of the LBTI Exozodi Exoplanet Common Hunt (LEECH) exoplanet imaging survey. By comparing our new photometry and literature photometry with a grid of custom model atmospheres, we were able to fit GJ 504 bʼs unusual spectral energy distribution for the first time. We find that GJ 504 b is welluf0a0fit by models with the following parameters: Teffuf0a0=uf0a0544uf0a0±uf0a010 K, guf0a0<uf0a0600 m s �2 , [M/H]uf0a0=uf0a00.60uf0a0±uf0a00.12, cloud opacity parameter of fseduf0a0=uf0a02–5, Ruf0a0=uf0a00.96uf0a0±uf0a00.07RJup, and log(L)uf0a0=uf0a0�6.13uf0a0±uf0a00.03 Le, implying a hot start mass of 3–30 Mjup for a conservative age range of 0.1–6.5 Gyr. Of particular interest, our model fits suggest that GJ 504 b has a superstellar metallicity. Since planet formation can create objects with nonstellar metallicities, while binary star formation cannot, this result suggests that GJ 504 b formed like a planet, not like a binary companion.

2006 interferometry imaging beauty contest

We present a formal comparison of the performance of algorithms used for synthesis imaging with optical/infrared long-baseline interferometers. Five different algorithms are evaluated based on their performance with simulated test data. Each set of test data is formatted in the OI-FITS format. The data are calibrated power spectra and bispectra measured with an array intended to be typical of existing imaging interferometers. The strengths and limitations of each algorithm are discussed.

High contrast imaging at the LBT: the LEECH exoplanet imaging survey

In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its ~130-night campaign from the Large Binocular Telescope (LBT) atop Mt Graham, Arizona. This survey benefits from the many technological achievements of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual adaptive secondary mirrors for high Strehl performance, and a cold beam combiner to dramatically reduce the telescope’s overall background emissivity. LEECH neatly complements other high-contrast planet imaging efforts by observing stars at L’ (3.8 μm), as opposed to the shorter wavelength near-infrared bands (1-2.4 μm) of other surveys. This portion of the spectrum offers deep mass sensitivity, especially around nearby adolescent (~0.1-1 Gyr) stars. LEECH’s contrast is competitive with other extreme adaptive optics systems, while providing an alternative survey strategy. Additionally, LEECH is characterizing known exoplanetary systems with observations from 3-5μm in preparation for JWST.

ON THE NATURE OF THE HERBIG B[e] STAR BINARY SYSTEM V921 SCORPII: DISCOVERY OF A CLOSE COMPANION AND RELATION TO THE LARGE-SCALE BIPOLAR NEBULA

Belonging to the group of B[e] stars, V921 Scorpii is associated with a strong infrared excess and permitted and forbidden line emission, indicating the presence of low- and high-density circumstellar gas and dust. Many aspects of V921 Sco and other B[e] stars still remain mysterious, including their evolutionary state and the physical conditions resulting in the class-defining characteristics. In this Letter, we employ Very Large Telescope Interferometer/AMBER spectro-interferometry in order to reconstruct high-resolution (λ/2B = 0. 0013) model-independent interferometric images for three wavelength bands around 1.65, 2.0, and 2.3 μm. In our images, we discover a close (25.0 ± 0.8 mas, corresponding to ∼29 ± 0.9 AU at 1.15 kpc) companion around V921 Sco. Between two epochs in 2008 and 2009, we measure orbital motion of ∼7 ◦ , implying an orbital period of ∼35 years (for a circular orbit). Around the primary star, we detect a disk-like structure with indications for a radial temperature gradient. The polar axis of this AU-scale disk is aligned with the arcminute-scale bipolar nebula in which V921 Sco is embedded. Using Magellan/IMACS imaging, we detect multi-layered arc-shaped substructure in the nebula, suggesting episodic outflow activity from the system with a period of ∼25 years, roughly matching the estimated orbital period of the companion. Our study supports the hypothesis that the B[e] phenomenon is related to dynamical interaction in a close binary system.

2008 imaging beauty contest

We present the results of the third Optical/IR Interferometry Imaging Beauty Contest. A formal comparison is presented of the performance of algorithms used for imaging data from optical/infrared long-baseline interferometers. The contest consists of blind imaging of test data sets derived from model sources and distributed in the OI-FITS format. The test data consisted of datasets on two objects each observed in J, H, and K bands. The majority of the entries produced accurate reconstructions of the initial models. Each of the methods presented is discussed.

Spatially resolved m-band emission from io's Loki Patera-fizeau imaging at the 22.8 m LBT

The Large Binocular Telescope Interferometer mid-infrared camera, LMIRcam, imaged Io on the night of 2013 December 24 UT and detected strong M-band (4.8 μm) thermal emission arising from Loki Patera. The 22.8 m baseline of the Large Binocular Telescope provides an angular resolution of ∼32 mas (∼100 km at Io) resolving the Loki Patera emission into two distinct maxima originating from different regions within Loki’s horseshoe lava lake. This observation is consistent with the presence of a high-temperature source observed in previous studies combined with an independent peak arising from cooling crust from recent resurfacing. The deconvolved images also reveal 15 other emission sites on the visible hemisphere of Io including two previously unidentified hot spots.

THE LEECH EXOPLANET IMAGING SURVEY: ORBIT AND COMPONENT MASSES OF THE INTERMEDIATE-AGE, LATE-TYPE BINARY NO UMa* **

We present high-resolution Large Binocular Telescope LBTI/LMIRcam images of the spectroscopic and astrometric binary NO UMa obtained as part of the LBTI Exozodi Exoplanet Common Hunt (LEECH) exoplanet imaging survey. Our H, K

VLTI-AMBER observations of Eta Carinae with high spatial resolution and spectral resolutions of 1,500 and 10,000

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