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Abstract: The goal of the present paper is to investigate the circumstellar materialaround the brightest dust-enshrouded sources in the central stellar cluster ofthe Milky Way. Observations have been carried out at the European SouthernObservatory-s Very Large Telescope on Paranal, Chile. We have used the longwavelength LWS3 low resolution LR spectroscopic mode of the ISAAC camera atthe VLT in the spectral range of the M filter from 4.4micron to 5.1micron. Theuse of a slit width of 0.6- implied a spectral resolution of R=l-Dl=800 Dv=375km-s. These observations resulted in M-band spectra of 15 bright sources inthe central stellar cluster of the Milky Way. In addition to gaseous 12^CO4.666 micron and 13^CO 4.77 micron vibration-rotational absorptions, wedetect a strong absorption due to a mixture of polar and apolar CO icecentered at 4.675 micron. In the shorter wavelength absorption wing there isan absorption feature due to XCN at 4.62 micron. The XCN absorption isstrongest toward the M2 supergiant IRS7. We find that the extinctions due tomaterial traced by the CO ice and the CO gas absorptions may be of comparableimportance. Using the spectra of IRS2L and IRS16C we perform a first ordercorrection of the line of sight absorption due to CO-ice and 13^CO gas. Incombination with published hydrogen number density estimates from sub-mmCO7-6 and FIR OI line data we obtain gas masses of the circumstellar shellsof the order of 10^-3 and 10^-2 solar masses. This implies that in futurespectra taken at high spectral and angular resolution the bright and dustembedded Galactic Center sources should show a substantial line absorption dueto source intrinsic absorption.

Author: J. Moultaka, A. Eckart, R. Schödel

Source: https://arxiv.org/

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