* Astronomy

Title: The observed spiral structure of the Milky Way
Author: L. G. Hou, J. L. Han

The spiral structure of the Milky Way is not yet well determined. The keys to understanding this structure are to increase the number of reliable spiral tracers and to determine their distances as accurately as possible. HII regions, giant molecular clouds (GMCs), and 6.7-GHz methanol masers are closely related to high mass star formation, and hence they are excellent spiral tracers. We update the catalogs of Galactic HII regions, GMCs, and 6.7-GHz methanol masers, and then outline the spiral structure of the Milky Way. We collected data for more than 2500 known HII regions, 1300 GMCs, and 900 6.7-GHz methanol masers. If the photometric or trigonometric distance was not yet available, we determined the kinematic distance using a Galaxy rotation curve with the current IAU standard, R_0 = 8.5 kpc and Theta_0 = 220 km s^-1, and the most recent updated values of R_0 = 8.3 kpc and Theta_0 = 239 km s^-1, after we modified the velocities of tracers with the adopted solar motions. With the weight factors based on the excitation parameters of HII regions or the masses of GMCs, we get the distributions of these spiral tracers. The distribution of tracers shows at least four segments of arms in the first Galactic quadrant, and three segments in the fourth quadrant. The Perseus Arm and the Local Arm are also delineated by many bright HII regions. The arm segments traced by massive star forming regions and GMCs are able to match the HI arms in the outer Galaxy. We found that the models of three-arm and four-arm logarithmic spirals are able to connect most spiral tracers. The four-arm model provides a better match to the observed tangential directions of spiral arms, and is consistent with the two-fold symmetry of the Galaxy structure. A model of polynomial-logarithmic spirals not only delineates the tracer distribution but also matches the observed tangential directions.

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Title: The starbursts in the Milky Way
Author: Ignacio Negueruela (Alicante)

High-mass stars are major players in the chemical and dynamical evolution of galaxies, and young massive clusters are the natural laboratories to study their evolution and their impact on star formation processes. Only in recent years have we become aware of the existence of numerous massive (M_cl > 10000M_sun) clusters in our Galaxy. Here I give a review, rather biased towards my own research interests, of the observational and theoretical efforts that have led to a description of their properties, and present an overview of the two (perhaps three) starburst regions known outside the Galactic Centre neighbourhood: the Scutum Complex, its putative counterpart on the far side of the Long Bar, and the starburst cluster Westerlund 1.

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Massive stars mark out Milky Way's 'missing' arms

A 12-year study of massive stars has reaffirmed that our Galaxy has four spiral arms, following years of debate sparked by images taken by NASAs Spitzer Space Telescope that only showed two arms.
The new research, which is published online today [17 December] in the Monthly Notices of the Royal Astronomical Society, is part of the RMS Survey, which was launched by academics at the University of Leeds.
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Milky Way's 'Local Arm' larger than thought

Our home in the Milky Way galaxy could be much larger than previously thought, a new study suggests.
Earth resides between two major spiral arms of our home galaxy, in a structure called the Local Arm.
New research using the ultra-sharp radio vision of the National Science Foundation's Very Long Baseline Array (VLBA) indicates that the Local Arm, previously thought to be only a small spur, instead is much more like the adjacent major arms, and is likely a significant branch of one of them.
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