Evidence of Deep Mixing in IRS 7, a Cool Massive Supergiant Member of the Galactic Nuclear Star Cluster

Abstract

The center of the Milky Way contains stellar populations spanning a range in age and metallicity, with a recent star formation burst producing young and massive stars. Chemical abundances in the most luminous stellar member of the Nuclear Star Cluster (NSC), IRS 7, are presented for ${}^{19}$F, ${}^{12}$C, ${}^{13}$C, ${}^{14}$N, ${}^{16}$O, ${}^{17}$O, and Fe from an LTE analysis based on spherical modeling and radiative transfer with a 25M${}_{\odot }$ model atmosphere, whose chemistry was tailored to the derived photospheric abundances. We find IRS 7 to be depleted heavily in both ${}^{12}$C (~-0.8 dex) and ${}^{16}$O (~-0.4 dex), while exhibiting an extremely enhanced ${}^{14}$N abundance (~+1.1 dex), which are isotopic signatures of the deep mixing of CNO-cycled material to the stellar surface. The ${}^{19}$F abundance is also heavily depleted by ~1 dex relative to the baseline fluorine of the Nuclear Star Cluster, providing evidence that fluorine along with carbon constrain the nature of the deep mixing in this very luminous supergiant. The abundances of the minor isotopes ${}^{13}$C and ${}^{17}$O are also derived, with ratios of ${}^{12}$C/${}^{13}$C~5.3 and ${}^{16}$O/${}^{17}$O~525. The derived abundances for IRS 7, in conjunction with previous abundance results for massive stars in the NSC, are compared with rotating and non-rotating models of massive stars and it is found that the IRS 7 abundances overall follow the behavior predicted by stellar models. The depleted fluorine abundance in IRS 7 illustrates, for the first time, the potential of using the ${}^{19}$F abundance as a mixing probe in luminous red giants.

11 pages, 6 figures, 2 tables

References in corpus (22)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The Two Young Star Disks in the Central Parsec of the Galaxy: Properties, Dynamics and Formation
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Line lists for the A2PI-X2Sigma+ (red) and {B2Sigma+-X2Sigma} (violet) Systems of CN, 13C14N, and 12C15N, and Application to Astronomical Spectra
• The APOGEE Data Release 16 Spectral Line List
• Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy
• New H-band Stellar Spectral Libraries for the SDSS-III/APOGEE survey
• Neon Abundances in B-Stars of the Orion Association: Solving the Solar Model Problem?
• The Milky Way's nuclear star cluster: Old, metal-rich, and cuspy
• KMOS view of the Galactic Centre - II. Metallicity distribution of late-type stars
• New constraints on the structure of the nuclear stellar cluster of the Milky Way from star counts and MIR imaging
• Detailed Abundances for the Old Population near the Galactic Center: I. Metallicity distribution of the Nuclear Star Cluster
• Grids of stellar models with rotation VII: Models from 0.8 to 300 M${}_{\odot }$ at super-solar metallicity (Z = 0.020)
• Jeans modelling of the Milky Way's nuclear stellar disc
• Detailed abundances in the Galactic center: Evidence of a metal-rich alpha-enhanced stellar population
• The Chemical Evolution of Fluorine in the Bulge - High-resolution K-band spectra of giants in three fields
• A new solar fluorine abundance and a fluorine determination in the two open clusters M 67 and NGC 6404
• Oxygen isotopic ratios in intermediate-mass red giants
• The nuclear star cluster and nuclear stellar disc of the Milky Way: Different stellar population and star formation history
• Fluorine Abundances in the Galactic Nuclear Star Cluster
• Measuring the alpha-abundance of subsolar-metallicity stars in the Milky Way's central half-parsec: testing globular cluster and dwarf galaxy infall scenarios
• Sub-millimeter Detection of a Galactic Center Cool Star IRS 7 by ALMA

Cited by in corpus (4)

• Synthesizing Spectra from 3D Radiation Hydrodynamic Models of Massive Stars Using Monte Carlo Radiation Transport
• MAGIS (Measuring Abundances of red super Giants with Infrared Spectroscopy) project I. Establishment of an abundance analysis procedure for red supergiants and its evaluation with nearby stars
• A Near-Infrared and Optical Study of NGC 5822: An Open Cluster Hosting Barium-stars and Lithium-Enriched Giant Stars
• Supergiant GCIRS 22 in the Milky Way Nuclear Star Cluster: Revised alpha abundances