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| Upper Scorpius | |
|---|---|
| Name | Upper Scorpius |
| Type | Stellar association |
| Epoch | J2000 |
| Constellation | Scorpius |
| Distance | ~145 pc |
| Age | ~5–11 Myr |
| Members | ~1000+ |
Upper Scorpius is a nearby young stellar association in the constellation Scorpius that forms the northern part of the Scorpius–Centaurus OB association, associated with the larger Sco–Cen complex and located near the star Antares. It is a benchmark region for studies of pre–main-sequence evolution, brown dwarfs, protoplanetary disks, and early planetary evolution, and has been observed by instruments and missions such as Hubble Space Telescope, Spitzer Space Telescope, Gaia, Chandra X-ray Observatory, and ALMA.
Upper Scorpius lies within the larger Scorpius–Centaurus association and neighbors the subgroups Upper Centaurus–Lupus and Lower Centaurus–Crux, occupying a region near Antares and the Rho Ophiuchi cloud complex, at a mean distance of ~145 parsecs measured by Hipparcos and refined by Gaia. The association contains a mixture of OB stars, T Tauri stars, weak-lined T Tauri stars, and brown dwarfs discovered in surveys by teams associated with 2MASS, WISE, and the Sloan Digital Sky Survey. Upper Scorpius is a primary target for studies by observatories including ALMA, Spitzer, Keck Observatory, Very Large Telescope, and Subaru Telescope.
Recognition of an OB subgroup in Scorpius dates to early spectral surveys and proper motion studies by astronomers using catalogs such as the Henry Draper Catalogue and proper motion work preceding the Hipparcos mission, with detailed membership and age studies advanced by teams led by researchers from institutions like Harvard–Smithsonian Center for Astrophysics, University of Arizona, Max Planck Institute for Astronomy, University of Cambridge, and California Institute of Technology. Subsequent infrared excess discoveries with IRAS and follow-up with Spitzer Space Telescope revealed disk-bearing members, while X-ray surveys with ROSAT and Chandra X-ray Observatory identified young low-mass members. The advent of precision astrometry from Gaia Data Release 1 and later releases dramatically refined kinematic membership and distances, enabling follow-up spectroscopic studies at facilities such as Keck Observatory and Very Large Telescope.
The stellar content includes massive OB stars like members classified in catalogs compiled by Blaauw-era surveys, intermediate-mass Herbig Ae/Be analogs studied in works by groups at University College London and University of Vienna, and a rich population of T Tauri stars cataloged using spectrographs on Anglo-Australian Telescope and Magellan Observatory. Brown dwarf populations were identified through collaborations involving Calar Alto Observatory, Gemini Observatory, and UKIRT Wide Field Camera teams, while multiplicity and binaries have been characterized using adaptive optics at Keck Observatory and interferometry with CHARA Array. Spectroscopic classifications reference type standards similar to those in the Morgan–Keenan system with lithium absorption measurements obtained by instruments at ESO and McDonald Observatory.
Age estimates for Upper Scorpius have been debated, with isochrone fitting using models from groups such as Baraffe and Siess yielding ages around 5–11 million years, while lithium depletion boundary analyses by teams at Institute for Astronomy, University of Hawaii and University of Exeter provide independent constraints. Studies comparing pre–main-sequence tracks from D'Antona & Mazzitelli and Pisa models, and incorporating kinematic ages from Gaia data, have been employed to reconcile ages across spectral types. Triggered star formation scenarios involving feedback from massive stars cataloged in Scorpius–Centaurus and possible supernova events discussed in work by researchers associated with Max Planck Institute for Radio Astronomy and University of Chicago have been proposed to explain the star formation history.
Disk surveys in Upper Scorpius with Spitzer Space Telescope and WISE revealed a declining fraction of primordial disks compared with younger regions such as Taurus Molecular Cloud and Rho Ophiuchi, while ALMA continuum and CO line studies led by groups at Harvard–Smithsonian Center for Astrophysics, Max Planck Institute for Astronomy, and University of Arizona have imaged dust and gas in transitional and debris disks. Observations of disk clearing, dust evolution, and planetesimal signatures have been reported in papers by teams using Subaru Telescope coronagraphy, HST imaging, and high-contrast instruments like VLT/SPHERE and GPI on Gemini South. Comparative studies referencing disk lifetimes in associations such as Beta Pictoris Moving Group and TW Hydrae Association place Upper Scorpius at a critical epoch for planet formation.
Membership identification uses proper motions and parallaxes from Gaia, radial velocities from high-resolution spectrographs on Keck Observatory and ESO, and statistical methods developed by groups at Jet Propulsion Laboratory and IPAC. Kinematic substructure analyses have been compared with models of cluster dissolution and stellar feedback studied at Institute of Astronomy, Cambridge and Max Planck Institute for Astrophysics, while moving-group membership algorithms similar to those used for TWA and Beta Pictoris have been applied to refine lists of candidate members. The association’s velocity dispersion and spatial distribution have been used to trace back potential expansion and to test links to nearby molecular clouds cataloged by CO surveys and surveys at APEX and IRAM.
Noteworthy members include early-type stars cataloged in the Hipparcos catalog, intermediate-mass objects analogous to Herbig Ae/Be stars studied in the literature from ESO and NOIRLab, and several directly imaged planetary-mass companions discovered using instruments at Keck Observatory, VLT, and Subaru Telescope. Brown dwarfs and planetary-mass candidates identified by surveys such as 2MASS, UKIDSS, and WISE have been followed up spectroscopically at Gemini Observatory and Magellan Observatory to measure properties like effective temperature and surface gravity, with notable comparative samples drawn from regions including IC 348 and Chamaeleon I. High-energy emitters revealed by Chandra X-ray Observatory and XMM-Newton complement ALMA disk detections to build a multiwavelength picture of early stellar and substellar evolution.
Category:Stellar associations