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تسجيل مستخدم جديدA comparison of the local spiral structure from Gaia DR2 and VLBI maser parallaxes
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Context. The Gaia mission has released the second data set (Gaia DR2), which contains parallaxes and proper motions for a large number of massive, young stars. Aims. We investigate the spiral structure in the solar neighborhood revealed by Gaia DR2 and compare it with that depicted by VLBI maser parallaxes. Methods. We examined three samples with different constraints on parallax uncertainty and distance errors and stellar spectral types: (1) all OB stars with parallax errors of less than 10%; (2) only O-type stars with 0.1 mas errors imposed and with parallax distance errors of less than 0.2 kpc; and (3) only O-type stars with 0.05 mas errors imposed and with parallax distance errors of less than 0.3 kpc. Results. In spite of the significant distance uncertainties for stars in DR2 beyond 1.4 kpc, the spiral structure in the solar neighborhood demonstrated by Gaia agrees well with that illustrated by VLBI maser results. The O-type stars available from DR2 extend the spiral arm models determined from VLBI maser parallaxes into the fourth Galactic quadrant, and suggest the existence of a new spur between the Local and Sagittarius arms.
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Context. The astrometric satellite Gaia is expected to significantly increase our knowledge as to the properties of the Milky Way. The Gaia Early Data Release 3 (Gaia EDR3) provides the most precise parallaxes for many OB stars, which can be used to
delineate the Galactic spiral structure. Aims. We investigate the local spiral structure with the largest sample of spectroscopically confirmed young OB stars available to date, and we compare it with what was traced by the parallax measurements of masers. Methods. A sample consisting of three different groups of massive young stars, including O-B2 stars, O-B0 stars and O-type stars with parallax accuracies better than 10% was compiled and used in our analysis. Results. The local spiral structures in all four Galactic quadrants within $approx$5 kpc of the Sun are clearly delineated in detail. The revealed Galactic spiral pattern outlines a clear sketch of nearby spiral arms, especially in the third and fourth quadrants where the maser parallax data are still absent. These O-type stars densify and extend the spiral structure constructed by using the Very Long Baseline Interferometry (VLBI) maser data alone. The clumped distribution of O-type stars also indicates that the Galaxy spiral structure is inhomogeneous.
We compare the distribution in position and velocity of nearby stars from the Gaia DR2 radial velocity sample with predictions of current theories for spirals in disc galaxies. Although the rich substructure in velocity space contains the same inform
ation, we find it more revealing to reproject the data into action-angle variables, and we describe why resonant scattering would be more readily identifiable in these variables. We compute the predicted changes to the phase space density, in multiple different projections, that would be caused by a simplified isolated spiral pattern, finding widely differing predictions from each theory. We conclude that the phase space structure present in the Gaia data shares many of the qualitative features expected in the transient spiral mode model. We argue that the popular picture of apparently swing-amplified spirals results from the superposition of a few underlying spiral modes.
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We develop a novel method to simultaneously determine the vertical potential, force and stellar $z-v_z$ phase space distribution function (DF) in our local patch of the Galaxy. We assume that the Solar Neighborhood can be treated as a one-dimensional
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Classical Cepheids (CCs) are at the heart of the empirical extragalactic distance ladder. Milky Way CCs are the only stars of this class accessible to trigonometric parallax measurements. Until recently, the most accurate trigonometric parallaxes of
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