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Interstellar NaI and CaII absorption observed towards the Cygnus Loop SNR
We present high resolution spectra (R ~ 5 km s-1) of theinterstellar NaI and CaII absorption lines observed towards 9 early-typestars with distances ranging from 250 to 2300 pc in the line-of-sighttowards the Cygnus Loop Supernova Remnant (SNR). All but one of theseabsorption profiles can be fit using a combination of one or more ofthree absorption components with average best-fit (lsr) velocities ofV1 = + 0.8 km s-1, V2 = +9.0 kms-1 and V3 = +19.7 km s-1. Anadditional velocity component at V4 = +29.7 km s-1is required in order to fit the NaI profile recorded towards the star HD198946, whose distance of 794 pc places it well in excess of the nominal440 pc distance to the SNR. The NaI/CaII column density ratios for thethree higher velocity components are typically <1.0, which aresimilar to values found for high-velocity gas components detectedtowards other evolved SNRs. Even though we have detected the threehigher velocity components solely along the sight-lines towards starswith distance estimates greater than that of the Cygnus Loop, we areunable to definitely associate these components with an interactionbetween the expansion of the SN shock wave and the ambient interstellarmedium. We suggest a more likely origin for these absorption componentsis that of an old pre-cursor SN neutral gas shell, within whoseinterstellar cavity the Cygnus Loop supernova explosion occured some 20000 years ago.
| A kinematic and proper-motion survey of the Cygnus Loop
H-alpha radial velocities, line widths, and line intensities based on 71Fabry-Perot interferometer scans of 61 fields in the Cygnus Loopsupernova remnant SNR are reported. Also, measurements of proper motionsat 39 locations within the Cygnus Loop are summarized. These resultsshow that the remnant is expanding asymmetrically into the ambientinterstellar medium, with rest-frame velocities as high as 380 km/s inthe near half and 150 km/s in the far half. This can plausibly beinterpreted as the result of the progenitor's evolution near a densitydiscontinuity, the consequent formation of a cavity and partial shell,and the SN's interaction with that shell. The remnant's opticallyobserved filamentary structure results from line-of-sight effects asshock waves advance into the irregular inner surface of the shell. Inthis context, the derived expansion velocities and proper motions give aformal distance to the Cygnus Loop of roughly 600 pc, with 1-sigmalimits of 300 and 1200 pc.
| Meridian observations made in Brorfelde (Copenhagen University Observatory) 1975-76.
This catalogue presents positions for selected faint stars mainly fromAGK3 observed with the 7" transit circle at Brorfelde. The stars aredistributed in 43 selected areas around radio sources and are suitableas reference stars for measuring the optical counterparts to the radiosources. The obscr 'itioi cre carried out from 1975.16 to 1976.04, andevery star was observed at least two times giving a m.s.e. of "13 forthe catalogue positions given in the FK4 system. These positions usedtogether with AGK3 proper motions will in the period 1975 to 1980 have am.s.e. at the epoch ranging from `:13 to `:15, which is less than halfof what is expected when using AGK3 positions. Key words: transit circle- catalogue of positions
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Observation and Astrometry data
| Constellation: | Cygnus |
| Right ascension: | 20h47m43.74s |
| Declination: | +31°54'46.1" |
| Apparent magnitude: | 8.133 |
| Distance: | 657.895 parsecs |
| Proper motion RA: | -5 |
| Proper motion Dec: | -6 |
| B-T magnitude: | 8.265 |
| V-T magnitude: | 8.144 |
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