The Pistol Star

Astronomy and Astrophysics – Astronomy

Scientific paper

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Scientific paper

We present near-infrared spectra, photometry (JHK(') nbL), and Keck K-band speckle images of the ``Pistol Star.'' We also present HST/NICMOS Paschen-alpha images and near-infrared spectra of the surrounding HII region (G0.15-0.05), the ``Pistol.'' The stellar spectra cover the J, H, and K bands at low resolution, and between 1.80 to 1.96 \micron, 2.10 to 2.26 \micron, and 4.02 to 4.08 \micron\ at moderate resolution. The spectra of the Pistol cover the K-band at low resolution and 1.80 to 1.96 \micron\ at moderate resolution. The stellar data are fit with wind/atmosphere models to find that the star is extraordinarily luminous, having L = 10(6.7({+0.5}_{-0.5})) L_sun, making it one of the most luminous stars known; the range in luminosity is primarily due to uncertainties in extinction and intrinsic spectral energy distribution of the star. Coupled with the relatively cool temperature, T_eff = 10(4.17({+0.19}_{-0.06})) K, the star is clearly in violation of the Humphreys-Davidson limit. The line of sight velocity of the star is confirmed to be ~ 130 kms(-1) , assuring membership in the Quintuplet cluster. This, along with the inferred extinction, places the star at the Galactic Center. The spectra of the Pistol confirm that the ionized gas has smoothly varying velocity gradients superposed on a bulk velocity of 130 kms(-1) . Radio and near-infrared hydrogen-to-helium line ratios suggest that the Pistol may have extrasolar helium abundance and that it must be excited, in part, by a star which is hotter than the Pistol Star. The morphology of the gas, the velocities in the gas, and the location of the star in the HR diagram suggest that the gas in G0.15-0.05 is matter which was ejected from the star.

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