by BDanielMayfield » Mon Sep 28, 2020 12:33 pm
Glad to see that GAIA is now providing results that are clearing up distance questions. This is from the Wikipedia article Cygnus Loop:
Distance
Until 1999, the most often-quoted distance to the supernova remnant was a 1958 estimate made by R. Minkowski, combining his radial velocity measurements with E. Hubble's proper motion study of the remnant's optical filaments to calculate a distance of 770 parsecs or 2500 light-years.[13][14] However, in 1999, William Blair, assuming that the shock wave should be expanding at the same rate in all directions, compared the angular expansion along the sides of the bubble (visible in Hubble Space Telescope images) with direct line-of-sight measurements of the radial expansion towards the Earth and concluded that the actual size of the bubble was about 40% smaller than the conventional value, leading to a distance of about 1470 ly.[13][14]
A larger revised value of 540 pc (1760 ly) appeared to be corroborated by Blair's later discovery, via the Far Ultraviolet Spectroscopic Explorer (FUSE), of a star seemingly behind the Veil. A UV spectrum of this star, KPD 2055+3111 of spectral type sdOB, showed absorption lines in its spectrum indicate that its light is partially intercepted by the supernova remnant. With an estimated (but uncertain) distance of about 1860 ly away, this star seemed to support the revised estimate of 1760 ly.[14]
A more recent investigation of the Cygnus Loop's distance using Gaia parallax measurements of several stars seen toward the Cygnus Loop has led to a more accurate distance estimate.[15] One of these stars, a 9.6 magnitude B8 star (BD+31 4224) located near the remnant's northwestern rim shows evidence of interactions of its stellar wind with the Cygnus Loop's shock wave, thereby indicating it is located actually inside the remnant. This star's Gaia estimated distance of around 770 ± 30 pc, along with two other stars both at 735 ± 30 pc which exhibit spectral features indicating they must lie behind the remnant, leads to new distance of 735 ± 25 pc or around 2400 light-years. (Note: The Gaia estimated distance to the sdOB star KPD 2055+3111 is 793 pc (2600 ly). This new distance, surprisingly close to the value estimated some 60 yrs ago by Minkowski, means the Cygnus Loop is physically some 40 pc (130 ly) in diameter and has an age of around 21,000 years.[15]
Glad to see that GAIA is now providing results that are clearing up distance questions. This is from the Wikipedia article Cygnus Loop:
[quote][b]Distance[/b]
Until 1999, the most often-quoted distance to the supernova remnant was a 1958 estimate made by R. Minkowski, combining his radial velocity measurements with E. Hubble's proper motion study of the remnant's optical filaments to calculate a distance of 770 parsecs or 2500 light-years.[13][14] However, in 1999, William Blair, assuming that the shock wave should be expanding at the same rate in all directions, compared the angular expansion along the sides of the bubble (visible in Hubble Space Telescope images) with direct line-of-sight measurements of the radial expansion towards the Earth and concluded that the actual size of the bubble was about 40% smaller than the conventional value, leading to a distance of about 1470 ly.[13][14]
A larger revised value of 540 pc (1760 ly) appeared to be corroborated by Blair's later discovery, via the Far Ultraviolet Spectroscopic Explorer (FUSE), of a star seemingly behind the Veil. A UV spectrum of this star, KPD 2055+3111 of spectral type sdOB, showed absorption lines in its spectrum indicate that its light is partially intercepted by the supernova remnant. With an estimated (but uncertain) distance of about 1860 ly away, this star seemed to support the revised estimate of 1760 ly.[14]
[color=#0000FF]A more recent investigation of the Cygnus Loop's distance using Gaia parallax measurements of several stars seen toward the Cygnus Loop has led to a more accurate distance estimate.[15] One of these stars, a 9.6 magnitude B8 star (BD+31 4224) located near the remnant's northwestern rim shows evidence of interactions of its stellar wind with the Cygnus Loop's shock wave, thereby indicating it is located actually inside the remnant. This star's Gaia estimated distance of around 770 ± 30 pc, along with two other stars both at 735 ± 30 pc which exhibit spectral features indicating they must lie behind the remnant, leads to new distance of 735 ± 25 pc or around 2400 light-years. (Note: The Gaia estimated distance to the sdOB star KPD 2055+3111 is 793 pc (2600 ly). This new distance, surprisingly close to the value estimated some 60 yrs ago by Minkowski, means the Cygnus Loop is physically some 40 pc (130 ly) in diameter and has an age of around 21,000 years.[15][/color][/quote]