M-Band Spectra of Dust Embedded Sources at the Galactic Center

Abstract

The goal of the present paper is to investigate the circumstellar material around the brightest dust-enshrouded sources in the central stellar cluster of the Milky Way. Observations have been carried out at the European Southern Observatory's Very Large Telescope on Paranal, Chile. We have used the long wavelength (LWS3) low resolution (LR) spectroscopic mode of the ISAAC camera at the VLT in the spectral range of the M filter from 4.4micron to 5.1micron. The use of a slit width of 0.6" implied a spectral resolution of R=l/Dl=800 (Dv=375 km/s). These observations resulted in M-band spectra of 15 bright sources in the central stellar cluster of the Milky Way. In addition to gaseous 12^CO (4.666 micron) and 13^CO (4.77 micron) vibration-rotational absorptions, we detect a strong absorption due to a mixture of polar and apolar CO ice (centered at 4.675 micron). In the shorter wavelength absorption wing there is an absorption feature due to XCN at 4.62 micron. The XCN absorption is strongest toward the M2 supergiant IRS7. We find that the extinctions due to material traced by the CO ice and the CO gas absorptions may be of comparable importance. Using the spectra of IRS2L and IRS16C we perform a first order correction of the line of sight absorption due to CO-ice and 13^CO gas. In combination with published hydrogen number density estimates from sub-mm CO(7-6) and FIR [OI] line data we obtain gas masses of the circumstellar shells of the order of 10^-3 and 10^-2 solar masses. This implies that in future spectra taken at high spectral and angular resolution the bright and dust embedded Galactic Center sources should show a substantial line absorption due to source intrinsic absorption.

23 pages, 9 figures, Accepted for publication in ApJ

References in corpus (10)

• The Two Young Star Disks in the Central Parsec of the Galaxy: Properties, Dynamics and Formation
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• Direct Measurement of the Ratio of Carbon Monoxide to Molecular Hydrogen in the Diffuse Interstellar Medium
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Cited by in corpus (12)

• Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W
• Monitoring dusty sources in the vicinity of Sgr A*
• First observed interaction of the circumstellar envelope of an S-star with the environment of Sgr A*
• JWST reveals widespread CO ice and gas absorption in the Galactic Center cloud G0.253+0.016
• The Evaporating Massive Embedded Stellar Cluster IRS 13 Close to Sgr A*. II. Kinematic structure
• The Interstellar Medium toward the Galactic Center Source 2MASS J17470898-2829561
• Mapping the aliphatic hydrocarbon content of interstellar dust in the Galactic plane
• Candidate Young Stellar Objects in the S-cluster: The Kinematic Analysis of a Sub-population of the Low-mass G-objects close to Sgr A*
• High-spectral resolution M-band observations of CO Rot-Vib absorption lines towards the Galactic center
• Ices in the Galactic Centre : solid ice and gaseous CO in the central parsec
• The JWST-NIRCam View of Sagittarius C. III. The Extinction Curve
• The Discovery of an Active Wind from the Milky Way's Black Hole