by Ann » Tue Apr 11, 2023 6:52 am
Nice APOD and helpful links!
However...
APOD Robot wrote:
... as well as the
globular star cluster
NGC 188 on the far left.
Nope. NGC 188 is an open cluster, and the Wikipedia page that the caption links to says so, too. According to Wikipedia, NGC 188 is older than the Sun:
Wikipedia wrote:
NGC 188 lies far above the plane of the galaxy and is one of the most ancient of open clusters known, at approximately 6.8 billion years old.
High school student Abigail Bohl and and her advisor Mark Brooks Hedstrom wrote:
NGC 188, one of the oldest open clusters in the Milky Way, provides a unique insight into the history of the universe.
NGC 188 has been historically used as a reliable test subject for various methods of determining data about star clusters. Because of its importance in the field of astronomical study and due to its unique age, this paper serves to independently verify the data found by previous research and to determine the age, metallicity, distance, and mass of open cluster NGC 188. Methods involved color magnitude diagram creation, isochrone fitting, and mass determination using the virial theorem. This research verifies that NGC 188 has an age of 6 billion years, a metallicity of 0.2 [Fe/H], a distance of 1348 parsecs, and a mass of 1392 solar masses.
file:///C:/Users/Ann%20Sidbrant/Downloads/2436-Article%20Text-14314-1-10-20220423%20(1).pdf
I like this picture of Polaris, NGC 188 and the Integrated Flux Nebula (the IFN), taken by 14-year-old Kush Chandaria:
Note how blue Polaris looks in Kush Chandaria's image. I have seen this effect in other pictures of Polaris too. Below is a brilliant picture of a blue-looking Polaris and Comet C/2014 Q2 Lovejoy passing within a degree of the bright star:
Awesome picture, isn't it? But why does Polaris look blue? It is not a blue star, as it is spectral class F8Ib, which makes it just a tiny bit bluer than the Sun. I guess it is all the IFN near Polaris that acts as a reflection nebula.
The picture of a blue-looking Polaris surrounded by all that IFN reminds me of star HD 200775 inside the Iris Nebula, surrounded by a lot of brown dust clouds:
Well, fascinating! There is a lot more to say particularly about Polaris. I must add that as usual, there is a mistake at Wikipedia. The luminosity of the brightest component of Polaris (which totally dominates the light output of this triple star system) is said to be 1,260 L
☉. The source behind this figure is a
2005 paper. Well, the best available parallax for Polaris puts it at a distance of some 430 light-years, similar to the Pleiades, and coupled with its apparent luminosity, this translates to an absolute luminosity of some 2,000 L
☉.
Okay! I throw in the towel now.
Ann
[img3="North Star: Polaris and Surrounding Dust
Image Credit & Copyright: Javier Zayaz"]https://apod.nasa.gov/apod/image/2304/PolarisIfn_Zayaz_960.jpg[/img3]
Nice APOD and helpful links! :D
However...
[img3="NGC 188. Credit: Donald Pelletier."]https://upload.wikimedia.org/wikipedia/commons/7/70/NGC_188_PanS.jpg[/img3]
[quote]APOD Robot wrote:
... as well as the [url=https://en.wikipedia.org/wiki/Globular_cluster]globular[/url] star cluster [url=https://en.wikipedia.org/wiki/NGC_188]NGC 188[/url] on the far left.[/quote]
Nope. NGC 188 is an open cluster, and the Wikipedia page that the caption links to says so, too. According to Wikipedia, NGC 188 is older than the Sun:
[quote][url=https://en.wikipedia.org/wiki/NGC_188]Wikipedia[/url] wrote:
NGC 188 lies far above the plane of the galaxy and is one of the most ancient of open clusters known, at approximately 6.8 billion years old.[/quote]
[clear][/clear]
[quote]High school student Abigail Bohl and and her advisor Mark Brooks Hedstrom wrote:
NGC 188, one of the oldest open clusters in the Milky Way, provides a unique insight into the history of the universe.
NGC 188 has been historically used as a reliable test subject for various methods of determining data about star clusters. Because of its importance in the field of astronomical study and due to its unique age, this paper serves to independently verify the data found by previous research and to determine the age, metallicity, distance, and mass of open cluster NGC 188. Methods involved color magnitude diagram creation, isochrone fitting, and mass determination using the virial theorem. [b][size=110][color=#FF0000]This research verifies that NGC 188 has an age of 6 billion years, a metallicity of 0.2 [Fe/H], a distance of 1348 parsecs, and a mass of 1392 solar masses.[/color][/size][/b]
file:///C:/Users/Ann%20Sidbrant/Downloads/2436-Article%20Text-14314-1-10-20220423%20(1).pdf[/quote]
I like this picture of Polaris, NGC 188 and the Integrated Flux Nebula (the IFN), taken by 14-year-old Kush Chandaria:
[img3="Polaris and the Integrated Flux Nebula. NGC 188 is at upper left. Credit: Kush Chandaria."]https://upload.wikimedia.org/wikipedia/commons/thumb/1/10/Integrated_Flux_Nebula_Surrounding_Polaris_-_Kush_Chandaria.jpg/1280px-Integrated_Flux_Nebula_Surrounding_Polaris_-_Kush_Chandaria.jpg[/img3]
Note how blue Polaris looks in Kush Chandaria's image. I have seen this effect in other pictures of Polaris too. Below is a brilliant picture of a blue-looking Polaris and Comet C/2014 Q2 Lovejoy passing within a degree of the bright star:
[img3="Comet C/2014 Q2 Lovejoy passing within a degree of Polaris. Credit: Rogelio Bernal Andreo."]https://www.syfy.com/sites/syfy/files/styles/blog-post-embedded--tablet/public/rba_cometlovejoy_may292015_0.jpg[/img3]
Awesome picture, isn't it? But why does Polaris look blue? It is not a blue star, as it is spectral class F8Ib, which makes it just a tiny bit bluer than the Sun. I guess it is all the IFN near Polaris that acts as a reflection nebula.
The picture of a blue-looking Polaris surrounded by all that IFN reminds me of star HD 200775 inside the Iris Nebula, surrounded by a lot of brown dust clouds:
[img3="The Iris Nebula and surrounding dust clouds. Credit: Baerenstein Observatory and Marcel Drechsler."]https://www.sternwarte-baerenstein.de/assets/ngc_7023_kern.jpg[/img3]
Well, fascinating! There is a lot more to say particularly about Polaris. I must add that as usual, there is a mistake at Wikipedia. The luminosity of the brightest component of Polaris (which totally dominates the light output of this triple star system) is said to be 1,260 L[sub][size=85]☉[/size][/sub]. The source behind this figure is a [url=https://arxiv.org/abs/0708.0333]2005 paper[/url]. Well, the best available parallax for Polaris puts it at a distance of some 430 light-years, similar to the Pleiades, and coupled with its apparent luminosity, this translates to an absolute luminosity of some 2,000 L[sub][size=85]☉[/size][/sub].
Okay! I throw in the towel now.
Ann