The canonical Luminous Blue Variable AG Car and its neighbor Hen 3-519 are much closer than previously assumed

The strong mass loss of Luminous Blue Variables (LBVs) is thought to play a critical role in massive-star evolution, but their place in the evolutionary sequence remains debated. A key to understanding their peculiar instability is their high observed luminosities, which often depends on uncertain distances. Here we report direct distances and space motions of four canonical Milky Way LBVs---AG~Car, HR~Car, HD~168607, and (candidate) Hen~3-519---from the Gaia first data release. Whereas the distances of HR~Car and HD~168607 are consistent with previous literature estimates within the considerable uncertainties, Hen~3-519 and AG~Car, both at $\sim$2~kpc, are much closer than the 6--8~kpc distances previously assumed. As a result, Hen~3-519 moves far from the locus of LBVs on the HR Diagram, making it a much less luminous object. For AG~Car, considered a defining example of a classical LBV, its lower luminosity would also move it off the S~Dor instability strip. Lower luminosities allow both AG~Car and Hen~3-519 to have passed through a previous red supergiant phase, lower the mass estimates for their shell nebulae, and imply that binary evolution is needed to account for their peculiarities. These results may also impact our understanding of LBVs as potential supernova progenitors and their isolated environments. Improved distances will be provided in the Gaia second data release, which will include additional LBVs. AG~Car and Hen~3-519 hint that this new information may alter our traditional view of LBVs.Comment: 15 pages, 2 figures, 1 table. Accepted by Astronomical Journa

Angular Momentum Evolution of Young Stars: Toward a Synthesis of Observations, Theory, and Modeling

The aim of this AAS Topical Session was to update the community on the current state of knowledge about the angular momentum evolution of young stars. For newcomers to the subject, the session was intended to provide an introduction and general overview and to highlight emerging issues. For experienced workers in this field, the session provided an opportunity for synthesizing recent developments in observations, theory, and modeling of rotation of young stars and for identifying promising new research directions.Comment: 10 pages, conference summary, to appear in April PAS

Magnetic Accretion and Photopolarimetric Variability in Classical T Tauri Stars

We employ a Monte Carlo radiation transfer code to investigate the multi- wavelength photopolarimetric variability arising from a spotted T Tauri star surrounded by a dusty circumstellar disk. Our aim is to assess the ability of the magnetic accretion model to explain the observed photopolarimetric variability of classical T Tauri stars, and to identify potentially useful observational diagnostics of T Tauri star/disk/spot parameters. We model a range of spot sizes, spot latitudes, inner disk truncation radii, and system inclination angles, as well as multiple disk and spot geometries. We find that the amplitude, morphology, and wavelength dependence of the photopolarimetric variability predicted by our models are generally consistent with existing observations; a flared disk geometry is required to reproduce the largest observed polarization levels and variations. Our models can further explain stochastic polarimetric variability if unsteady accretion is invoked, in which case irregular -- but correlated -- photometric variability is predicted, in agreement with observations. Potentially useful observational diagnostics of system parameters of interest are discussed. We also investigate the reliability of modeling spot parameters via analytic fits to multi-band photometric variations.Comment: 25 pages, 8 figures To be published in ApJ, 1999, 51