The discovery of radio stars within 10″ of Sgr A* at 7 mm

Abstract

Very Large Array observations of the Galactic center at 7 mm have produced an image of the 30″ surrounding Sgr A* with a resolution of ∼82 × 42 milliarcseconds (mas). A comparison with IR images taken simultaneously with the Very Large Telescope identifies 41 radio sources with L-band (3.8 μm) stellar counterparts. The well-known young, massive stars in the central Sgr A* cluster (e.g., IRS 16C, IRS 16NE, IRS 16SE2, IRS 16NW, IRS 16SW, AF, AFNW, IRS 34W, and IRS 33E) are detected with peak flux densities between ∼0.2 and 1.3 mJy. The origin of the stellar radio emission in the central cluster is discussed in terms of ionized stellar winds with mass-loss rates in the range ∼0.8-5 × 10-5 Ṁ yr -1. Radio emission from eight massive stars is used as a tool for registration between the radio and infrared frames with mas precision within a few arcseconds of Sgr A* . This is similar to the established technique of aligning SiO masers and evolved stars except that radio stars lie within a few arcseconds of Sgr A*. Our data show a scatter of ∼6.5 mas in the positions of the eight radio sources that appear in both the L-band and 7 mm images. Last, we use the radio and IR data to argue that members of IRS 13N are young stellar objects rather than dust clumps, supporting the hypothesis that recent star formation has occurred near Sgr A*. © 2014. The American Astronomical Society. All rights reserved.