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The structure of the interstellar gas towards stars in the globular cluster M 55
Observations are presented of high resolution interstellar Na D lineprofiles towards 10 stars in the globular cluster M 55 and 6 foregroundstars which lie within 3 deg from the cluster. The spectral regioncontaining the K I (lambda 7699 A) line is simultaneously recorded butthis line is detected only towards one of the foreground stars as acomponent having a relatively high K I/Na I abundance ratio. Twoprincipal components are observed towards the cluster stars atvelocities of approximately +1 and +15 km/s and weaker higher velocitygas is detected at approximately -21, +33 and +55 km/s. The +1 km/scomponent is at a distance of approximately less than 100 pc and wesuggest that this is part of an extensive region of diffuse gas whichconnects the molecular and dark clouds observed closer to the galacticplane. The +15 km/s component lies at a distance between 130 to 300 pcand is identified with an anomalous velocity arc observed in HI. Thehigher velocity gas components are at a distance approximately greaterthan 700 pc. From a comparison with our previous observations in thegeneral direction of the Carina-Sagittarius arm we suggest that thesefeatures have an origin in spiral arm gas, in which case their detectiontowards M 55 places them some 600 to 800 pc from the galactic plane.
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Osservazione e dati astrometrici
| Costellazione: | Sagittario |
| Ascensione retta: | 19h38m52.16s |
| Declinazione: | -30°16'51.9" |
| Magnitudine apparente: | 7.79 |
| Distanza: | 3448.276 parsec |
| Moto proprio RA: | 1.2 |
| Moto proprio Dec: | -7.2 |
| B-T magnitude: | 7.911 |
| V-T magnitude: | 7.8 |
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