Lupus Clouds

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Lupus Cloud

Nebula
Image of Lupus 3 part of Lupus cloud
Observation data: J2000.0 epoch
Right ascension	16h 03m
Declination	−38° ′ ″
Apparent dimensions (V)	10°
Constellation	Lupus
Notable features	Associated with the Scorpius–Centaurus association

The Lupus Cloud is a complex system of dark nebulae, apparently distinct but physically connected to one another, visible in the direction of the constellation Lupus.

It is a heavily studied region because it represents one of the nearest nebular regions to the Solar System, where significant star formation processes are taking place, producing low-mass stars. A large proportion of these stars form a numerous population of T Tauri stars extending throughout the nebular filaments of the region, particularly in the northern components. Among them are several especially well-known and studied stars, such as EX Lupi, the prototype of the EXor class of variable stars.

According to dynamical models of the region, star formation was favoured by the expansion of a large stellar wind bubble generated by the most massive stars of the Upper Scorpius subgroup, the northernmost part of the Scorpius–Centaurus association; its physical position, intermediate between Upper Scorpius and the central region of this large association, would support this theory.

Observation

Map of the Lupus Cloud.

The Lupus Cloud appears as a series of dark filaments of varying length and density visible in the northern and central regions of the constellation Lupus. Because these clouds are almost entirely unilluminated, they cannot be observed directly with either binoculars or an amateur telescope. Their presence can be detected in long-exposure or composite photographs because the clouds obscure the background star fields. The longest filament is also the northernmost and lies between the stars Template:STL and Template:STL, closer to the latter. In this region part of the gas becomes visible because it is directly illuminated by nearby blue stars. The other filaments extend southward and southeastward from this region, reaching into the neighbouring constellations of Scorpius and Norma.

Because the constellation Lupus has a relatively southern declination, observation from the Northern Hemisphere is considerably restricted, especially from locations north of the 50th parallel north. From the Southern Hemisphere, however, Lupus is visible for most nights of the year and appears high above the horizon. The ideal period for evening observation is between May and September.

Relationship with the Scorpius–Centaurus association

See also: Scorpius–Centaurus association

Dynamics of the possible star-formation processes that led to the birth of the Scorpius–Centaurus association. Red indicates regions where star formation has ceased, green indicates active regions, and grey indicates inactive clouds.

The Lupus Cloud lies physically close to the large Scorpius–Centaurus association, the nearest OB association to the Solar System. It is easily visible to the naked eye because it includes the blue stars that form the constellations of Lupus, Centaurus, and Crux. The Lupus Cloud occupies a transitional position between two of the association's principal subgroups: Upper Scorpius (US), which includes the so-called Antares association (Scorpius OB2), and Upper Centaurus–Lupus (UCL), which forms the central section of the association. The ages of these two subgroups are approximately 5–6 million years and 14 million years, respectively. Understanding the dynamics that led to the formation and evolution of this large association is essential to understanding the origin of the Lupus Cloud.

According to some simplified models, the star-formation processes that gave rise to the Scorpius–Centaurus association initially occurred in the northern part of the Upper Centaurus–Lupus group about 17 million years ago and subsequently propagated southward to the Lower Centaurus–Crux subgroup, reaching a peak around 12 million years ago. The newly formed stars were initially concentrated in small clusters and filaments surrounded by gas and containing dozens or hundreds of stars. The residual gas from the progenitor molecular cloud was later swept away by the combined action of stellar winds and the possible explosion of several supernovae. Around 6 million years ago these star-forming processes extended to clouds south of the galactic equator, particularly in the region of the Chamaeleon molecular cloud complex.

Beginning about 12 million years ago, the stellar wind bubble produced by the young stars of Upper Centaurus–Lupus began to expand, perhaps further accelerated by later supernova explosions. These supernovae were the result of the rapid stellar evolution of the most massive members of the newly formed stellar group. Around 5 million years ago, the high pressure generated by the expanding bubble compressed the molecular cloud located where the stars forming the head of Scorpius are now found, producing the youngest part of the association, Upper Scorpius, or Scorpius OB2.

The wave of star formation that affected the northern Scorpius cloud produced approximately 2,500 stars, including several particularly massive supergiant stars with masses greater than 10 solar masses (M_⊙). These stars later exploded as supernovae, and the resulting powerful shock wave almost completely swept away the remaining gas of the ancient molecular cloud. During the last million years it impacted the adjacent Rho Ophiuchi cloud complex, stimulating the intense star-forming activity that can still be observed there today. The same shock wave may also have reached the region now occupied by the Lupus Cloud, compressing its gas and thereby triggering star formation.

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