Steve Gottlieb
July 31st, 2013, 07:43 PM
2) Quadrant Arc
The "Quadrant" (of a circle) is a unique feature of the LMC -- an arching collection of associations (LH 65, 77 and 84), extending roughly 40' E-W and 15' N-S, bowed out to the south. It is sometimes incorrectly referred to as Shapley's "Constellation III", though that name applies to the NGC 1955/1968/1974 complex -- also known as the "Sextant". This group of associations is nearly centered with a huge supergiant loop HII region complex designated as LMC 4. The Quadrant Arc region is visible in binoculars as an elongated glow (seen in 10x30's). The following clusters are within this region:
NGC 2002 (24"): at 200x this cluster is extremely bright but small. It is sharply concentrated with a small, brilliant core surrounded by a much fainter 30" halo. At 346x, the core diameter is ~15" diameter and three interior stars are resolved, the brightest on the SE side. Sharing the same field 8' SE is the double cluster NGC 2006 and S-L 538. NGC 2002 is within the OB association LH 65, at the west end of a huge, arcing string of associations (bowed to the south) referred to as LH 77 or the "Quadrant", which extends nearly 40' to the east beyond NGC 2041.
NGC 2006/S-L 538 (24"): NGC 2006 forms the southern member of a close pair of small clusters (a double cluster!) with SL-538 less than 1' N. At 346x it appeared fairly bright, fairly small, ~30" diameter, brighter core, with no evident resolution. Forms a small triangle with two stars on the east side. Located 8' SE of NGC 2002. Just 0.9' N is SL-538, a small, moderately bright glow that was sandwiched between a brighter star at the east edge and a fainter star off the west side. At 346x the shape appeared irregular and ~25" diameter.
NGC 2027 (13"): at the west end of an interesting, elongated cluster or association (NGC 2034 = LH 84) extending ~4'x2' E-W in a crescent shape. At 105x, this condensed portion of the cloud contains a couple of dozen mag 12-13 star and a wide pair of mag 10 stars on the NW side.
NGC 2034 (13"): at 105x this is an interesting, elongated cluster or association (LH 84), situated NW of the compact cluster NGC 2041 and at the east end of a very large cloud of stars, known as the "Quadrant", looping 30' W to NGC 2002 and including the OB associations LH 77 and LH 84. This condensed portion of LH 84 contains a couple of dozen mag 12-13 star and a wide pair of mag 10 stars on the NW side. The resolved stars are embedded in an unresolved glow of fainter stars, ~4'x2', extended E-W in a crescent shape, concave towards the north (arching north on the south side).
The "Quadrant" (of a circle) is a unique feature of the LMC -- an arching collection of associations (LH 65, 77 and 84), extending roughly 40' E-W and 15' N-S, bowed out to the south. It is sometimes incorrectly referred to as Shapley's "Constellation III", though that name applies to the NGC 1955/1968/1974 complex -- also known as the "Sextant". This group of associations is nearly centered with a huge supergiant loop HII region complex designated as LMC 4. The Quadrant Arc region is visible in binoculars as an elongated glow (seen in 10x30's). The following clusters are within this region:
NGC 2002 (24"): at 200x this cluster is extremely bright but small. It is sharply concentrated with a small, brilliant core surrounded by a much fainter 30" halo. At 346x, the core diameter is ~15" diameter and three interior stars are resolved, the brightest on the SE side. Sharing the same field 8' SE is the double cluster NGC 2006 and S-L 538. NGC 2002 is within the OB association LH 65, at the west end of a huge, arcing string of associations (bowed to the south) referred to as LH 77 or the "Quadrant", which extends nearly 40' to the east beyond NGC 2041.
NGC 2006/S-L 538 (24"): NGC 2006 forms the southern member of a close pair of small clusters (a double cluster!) with SL-538 less than 1' N. At 346x it appeared fairly bright, fairly small, ~30" diameter, brighter core, with no evident resolution. Forms a small triangle with two stars on the east side. Located 8' SE of NGC 2002. Just 0.9' N is SL-538, a small, moderately bright glow that was sandwiched between a brighter star at the east edge and a fainter star off the west side. At 346x the shape appeared irregular and ~25" diameter.
NGC 2027 (13"): at the west end of an interesting, elongated cluster or association (NGC 2034 = LH 84) extending ~4'x2' E-W in a crescent shape. At 105x, this condensed portion of the cloud contains a couple of dozen mag 12-13 star and a wide pair of mag 10 stars on the NW side.
NGC 2034 (13"): at 105x this is an interesting, elongated cluster or association (LH 84), situated NW of the compact cluster NGC 2041 and at the east end of a very large cloud of stars, known as the "Quadrant", looping 30' W to NGC 2002 and including the OB associations LH 77 and LH 84. This condensed portion of LH 84 contains a couple of dozen mag 12-13 star and a wide pair of mag 10 stars on the NW side. The resolved stars are embedded in an unresolved glow of fainter stars, ~4'x2', extended E-W in a crescent shape, concave towards the north (arching north on the south side).