Upper Scorpius OB association

Upper Scorpius OB association
Name	Upper Scorpius OB association
Type	OB association
Epoch	J2000
Constellation	Scorpius
Distance	~145 pc
Mass	~3,000–6,000 M☉
Age	~5–11 Myr

Upper Scorpius OB association is a young, nearby OB association notable for its concentration of massive stars, pre-main-sequence objects, and protoplanetary disks. It is a prominent component of the larger Scorpius–Centaurus complex and has been central to studies by observatories and missions such as European Southern Observatory, Hubble Space Telescope, Spitzer Space Telescope, Chandra X-ray Observatory, and Gaia (spacecraft). Surveys from facilities including Two Micron All Sky Survey, Sloan Digital Sky Survey, and ALMA have mapped its stellar content and circumstellar environments.

Overview

Upper Scorpius is identified as an OB association containing numerous O-type, B-type, A-type, F-type, G-type, K-type, and M-type stars cataloged by projects like Hipparcos, Tycho Catalog, and Gaia DR2. It has been targeted by campaigns led by institutions such as Max Planck Institute for Astronomy, Harvard–Smithsonian Center for Astrophysics, California Institute of Technology, and University of Cambridge to study pre-main-sequence evolution, disk dispersal, and early planet formation. Key individual members include stars observed with instruments on Keck Observatory, Very Large Telescope, and Subaru Telescope.

Location and Structure

Upper Scorpius lies within the constellation Scorpius and forms the northernmost subregion of the Scorpius–Centaurus OB complex, adjacent to the Lower Centaurus–Crux subgroup studied by teams at University of Pennsylvania and University of Michigan. Its spatial extent was refined using astrometry from Hipparcos and Gaia (spacecraft), and its three-dimensional structure has been modeled employing methods developed by groups at Princeton University and Massachusetts Institute of Technology. The association spans tens of parsecs with filamentary substructures traced in surveys by Planck (spacecraft) and mapped in molecular gas by James Clerk Maxwell Telescope and Atacama Pathfinder Experiment.

Stellar Population and Properties

The stellar census of Upper Scorpius includes early-type stars cataloged in lists associated with Bright Star Catalogue and faint members identified via X-ray emission in observations by ROSAT and XMM-Newton. Brown dwarfs and very low-mass stars were detected through programs at UK Infrared Telescope and Subaru Telescope using techniques from researchers at University of Hawaii and University of Tokyo. Spectroscopic follow-up from teams at European Southern Observatory and Keck Observatory provided spectral classification standards tied to systems used by Morgan–Keenan (MK) system proponents. Elemental abundances and lithium depletion patterns were analyzed by groups from University of California, Berkeley and University of Geneva to constrain pre-main-sequence models by theorists at University of Cambridge and Yale University.

Star Formation History and Age

Age estimates for Upper Scorpius, derived through isochrone fitting with models from MESA (software), Baraffe et al., and Siess et al., cluster around ~5–11 million years, with seminal age analyses published by researchers at Harvard University and University of Exeter. Star formation episodes have been linked to triggers discussed in studies involving feedback from massive stars in nearby associations such as Orion OB1, with supernova-driven scenarios considered by teams at Max Planck Institute for Astrophysics and Institut d'Astrophysique de Paris. Chronologies constructed using photometry from Two Micron All Sky Survey and astrometry from Gaia (spacecraft) are consistent with sequential star formation across the Scorpius–Centaurus complex.

Kinematics and Dynamics

Kinematic properties of Upper Scorpius were measured via proper motions and parallaxes from Hipparcos and Gaia (spacecraft)],] with radial velocities contributed by spectrographs on Anglo-Australian Telescope, ESO 3.6 m Telescope, and Keck Observatory. Dynamical analyses have been conducted using N-body codes developed by research groups at University of Cambridge and University of Edinburgh, and velocity dispersions have been compared to theoretical expectations from studies at Institute for Advanced Study and Princeton University. The association displays bulk motion relative to the Local Standard of Rest studied in context with moving groups cataloged by BANYAN Σ and membership algorithms from SACY survey teams.

Protoplanetary Disks and Planet Formation

Upper Scorpius hosts a diverse array of circumstellar disks characterized by multiwavelength observations from Spitzer Space Telescope, Herschel Space Observatory, and ALMA. Transitional disks, debris disks, and gas-rich protoplanetary systems were reported in papers from investigators at Carnegie Institution for Science, Max Planck Institute for Astronomy, and University of Arizona. Disk fraction studies leveraging mid-infrared surveys by Spitzer Space Telescope and millimeter imaging by ALMA constrain disk lifetimes and planetesimal formation theories developed by researchers at California Institute of Technology and University of California, Berkeley. Direct-imaging searches for young giant planets around Upper Scorpius members used instruments like Gemini Planet Imager and SPHERE on Very Large Telescope, engaging teams from ETH Zurich and Leiden University.

Relationship to the Scorpius–Centaurus OB Association and Nearby Regions

Upper Scorpius is a principal subgroup of the Scorpius–Centaurus OB Association, a structure whose other major subgroups—Upper Centaurus–Lupus and Lower Centaurus–Crux—have been mapped and analyzed by collaborations including Gaia Collaboration, European Southern Observatory, and Max Planck Institute for Astronomy. The spatial and temporal relation between these subgroups informs models of hierarchical star formation advanced by theorists at University of California, Santa Cruz and Columbia University. Upper Scorpius interacts with nearby star-forming regions such as ρ Ophiuchi and Lupus (constellation) through large-scale flows observed in CO surveys by Mopra Observatory and NANTEN2, with feedback processes discussed in work from CITA and Space Telescope Science Institute.

Category:Star clusters