by Ann » Wed Oct 13, 2021 5:37 am
NGC 7822 is a nebula that I have always dismissed, because I haven't been able to make head or tail of it. Where are the stars ionizing it? Let's try to find them!
1)
SAO 21019, spectral class O7.5V
2)
BD+66 1673, spectral class O5.5V
3) A small cluster of hot stars
The hottest of these two O-type stars, BD+66 1673, is a lot hotter than than the hottest star of the Trapezium, Theta 1 C Orionis, and SAO 21019 is comparable with the luminary of the Trapezium.
Wikipedia wrote:
NGC 7822 is a young star forming complex in the constellation of Cepheus. The complex encompasses the emission region designated Sharpless 171, and the young cluster of stars named Berkeley 59. The complex is believed to be some 800–1000 pc distant, with the younger components aged no more than a few million years.
The complex also includes one of the hottest stars discovered within 1 kpc of the Sun, namely BD+66 1673, which is an eclipsing binary system consisting of an O5V that exhibits a surface temperature of nearly 45,000 K and a luminosity about 100,000 times that of the Sun. The star is one of the primary sources illuminating the nebula and shaping the complex's famed pillars of creation-type formations, the elephant trunks.
"an eclipsing binary system consisting of an O5V", that sounds a bit funny, doesn't it, Wikipedia?
The ionizing star inside the "dot" of the "question mark" is much easier to spot than the ionizing stars of NGC 7822 proper, and Yizhou Zhang has done a good job of bringing the "question mark dot star" out for us. This is a star of spectral class O9.5V, so it is much more modest than the two furious powerhouses of NGC 7822 proper. Still, the O9.5V star is hot enough to ionize a nebula. But the star itself has garnered so little interest that it has only one designation that I can make any sense of, TYC 4022-1649-1. It doesn't even have a Hipparcos or a Gaia number, can you imagine? Simbad calls it
LS I +64 11 -- Star. Yeah, right, sounds familiar.
Ann
NGC 7822 is a nebula that I have always dismissed, because I haven't been able to make head or tail of it. Where are the stars ionizing it? Let's try to find them!
[float=left][img3="NGC 7822: Cosmic Question Mark. Image Credit & Copyright: Yizhou Zhang"]https://apod.nasa.gov/apod/image/2110/NGC7822_Yizhou_960.jpg[/img3][/float][float=right][attachment=0]NGC 7822 ionizing stars Yizhou Zhang.png[/attachment][/float]
[clear][/clear]
1) [url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=SAO+21019&submit=SIMBAD+search]SAO 21019[/url], spectral class O7.5V
2) [url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=BD%2B66+1673&submit=SIMBAD+search]BD+66 1673[/url], spectral class O5.5V
3) A small cluster of hot stars
The hottest of these two O-type stars, BD+66 1673, is a lot hotter than than the hottest star of the Trapezium, Theta 1 C Orionis, and SAO 21019 is comparable with the luminary of the Trapezium.
[quote][url=https://en.wikipedia.org/wiki/NGC_7822]Wikipedia[/url] wrote:
NGC 7822 is a young star forming complex in the constellation of Cepheus. The complex encompasses the emission region designated Sharpless 171, and the young cluster of stars named Berkeley 59. The complex is believed to be some 800–1000 pc distant, with the younger components aged no more than a few million years. [b][size=110][color=#FF00FF]The complex also includes one of the hottest stars discovered within 1 kpc of the Sun[/color][/size], [size=120][color=#0080FF]namely BD+66 1673[/color][/size], which is an eclipsing binary system consisting of an O5V that exhibits [size=120][color=#0080FF]a surface temperature of nearly 45,000 K and a luminosity about 100,000 times that of the Sun[/color][/size].[/b] The star is one of the primary sources illuminating the nebula and shaping the complex's famed pillars of creation-type formations, the elephant trunks.[/quote]
[size=65]"an eclipsing binary system consisting of an O5V", that sounds a bit funny, doesn't it, Wikipedia?[/size]
The ionizing star inside the "dot" of the "question mark" is much easier to spot than the ionizing stars of NGC 7822 proper, and Yizhou Zhang has done a good job of bringing the "question mark dot star" out for us. This is a star of spectral class O9.5V, so it is much more modest than the two furious powerhouses of NGC 7822 proper. Still, the O9.5V star is hot enough to ionize a nebula. But the star itself has garnered so little interest that it has only one designation that I can make any sense of, TYC 4022-1649-1. It doesn't even have a Hipparcos or a Gaia number, can you imagine? Simbad calls it [url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=TYC+4022-1649-1&submit=SIMBAD+search]LS I +64 11 -- Star[/url]. Yeah, right, sounds familiar.
Ann