MWC 349

Did You Know?

• The main component, MWC 349A, is assumed to have been born with 40 solar masses but now has 20–25 solar masses due to stellar evolution.
• Mass loss from MWC 349A may have destabilized the system, causing MWC 349B to no longer be gravitationally bound.

MWC 349A and B and a third star

MWC 349 is a resolved double star with components separated by 2.4 arc seconds. The primary, MWC 349A, is a B[e] star with a variable spectrum classified as B0-1.5 and a supergiant luminosity class, lacking absorption features. The secondary, MWC 349B, is a B0III giant. A third, lower-mass star may orbit MWC 349A at 12–13 AU with a 9-year period, though it has not been observed.

Features

MWC 349B appears to be a conventional hot giant star, yet the system is very unusual. MWC 349A is a supergiant B[e] star, indicating high mass loss and a surrounding disc, traits shared by both pre-main-sequence and evolved very massive stars; its category remains unclear. The system is one of the brightest radio sources in the sky, with 2 cm observations revealing a prominent hourglass nebula. A very faint infrared nebula shares the same orientation and geometry but is 400 times larger, spanning 5 parsecs. The system is extremely unusual in showing hydrogen recombination masers and lasers, interpreted as originating in the disc. One theory holds that MWC 349A is a highly luminous evolved star similar to a luminous blue variable (LBV), with an absolute magnitude between −6.7 and −7.3 and a bolometric luminosity several hundred thousand times that of the Sun. It is listed as an S Doradus variable due to erratic brightness and spectral changes. The distant association with MWC 349B and its remoteness from dense star-forming regions is unusual; the system may have been ejected from Cygnus OB2, with the components becoming unbound due to mass loss from MWC 349A. Alternatively, MWC 349A may still be condensing onto the main sequence, surrounded by a disc of material not ejected from the star, with lower luminosity than a more massive evolved star; the compact nature of the absorbing and re-radiating material suggests it is unlikely to be extremely luminous.