Further Results from the Galactic O-Star Spectroscopic Survey: Rapidly Rotating Late ON Giants
Nolan R. Walborn$^1$, Jesús Maíz Apellániz$^2$, Alfredo Sota$^2$, Emilio J. Alfaro$^2$, Nidia I. Morrell$^3$, Rodolfo H. Barbá$^4$, Julia I. Arias$^4$, and Roberto C. Gamen$^5$
1 - STScI, Baltimore, USA; 2 - IAA-CSIC, Granada, Spain; 3 - Carnegie Observatories, La Serena, Chile; 4 - Universidad de La Serena, La Serena, Chile; 5 - IALP-CONICET, La Plata, Argentina
With new data from the Galactic O-Star Spectroscopic Survey, we confirm and expand the ONn category of late-O, nitrogen-enriched (N), rapidly rotating (n) giants. In particular, we have discovered two ``clones'' (HD 102 415 and HD 117 490) of one of the most rapidly rotating O stars previously known (HD 191 423, ``Howarth’s Star''). We compare the locations of these objects in the theoretical HR Diagram to those of slowly rotating ON dwarfs and supergiants. All ON giants known to date are rapid rotators, whereas no ON dwarf or supergiant is; but all ON stars are small fractions of their respective spectral- type/luminosity-class/rotational subcategories. The ONn giants, displaying both substantial processed material and high rotation at an intermediate evolutionary stage, may provide significant information about the development of those prop- erties. They may have preserved high initial rotational velocities or been spun up by TAMS core contraction; but alternatively and perhaps more likely, they may be products of binary mass transfer. At least some of them are also runaway stars.
Reference: To appear in the November 2011 issue of AJ
Status: Manuscript has been accepted