by AVAO » Fri Sep 27, 2024 5:13 am
Ann wrote: ↑Fri Sep 27, 2024 4:16 am
Chris Peterson wrote: ↑Thu Sep 26, 2024 7:55 pm
Randall Rathbun wrote: ↑Thu Sep 26, 2024 7:29 pm
I would like to see a post on UV bright star Barnard 29 (not to be confused with a dark nebula of the same name) with some discussion on the unique place it has on the Hertzsprung-Russell diagram. Thanks. How was this star found in the first place? Did someone have UV film and the star was ultra-bright?
I doubt the UV is detectable from the ground. The star appears very blue, and by measuring its intensity at two or more wavelengths the shape of the blackbody can be inferred, and therefore the temperature. At something like 21,000 K, the peak output will be around 140 nm, in the UV... even if that can't be measured directly through the atmosphere.
How did the two of you, Randall and Chris, find out about this star? I asked Simbad Astronomical database about Barnard 29, and all it would give me was the dark cloud. The only source I could find that would talk about this star at all was
messier.seds.org., and it gave me the designation NGC 6205 222, which was accepted by Simbad. (Simbad itself called the star 2MASS J16413368+3626077, which is a mouthful.)
Unfortunately, Simbad has no information on the U magnitude of this star. It does tell us that the B magnitude of the star is 12.98, the V magnitude is 13.14, and the J, K and H magnitudes are progressively (but slowly) fainter. According to Simbad, the spectral class of this star is B2p D ~. I don't know what D ~ means, but B2p should mean that the star is spectral class B2, but peculiar. Of course, since it is a post-AGB star, it will indeed be peculiar compared to stars of spectral class B2 that are supporting themselves through fusion.
My point, however, is that this star is spectral class B2 and not O. A main sequence star of spectral class B2 will have a temperature of ~21,000 K, according to
University of Northern Iowa. Some central stars of planetary nebulas are known to be much, much hotter. And yes, I know that you know that. And all that it really means is that the star is in the process of removing its outer layers, but it has most certainly not finished that process or cast off all of its outer atmosphere.
The Gaia parallax of this star is 0.0775 ± 0.0298 milliarcseconds. A parallax of 0.0775 mas corresponds to a distance of 12,900 parsecs or 42,000 light-years. That's too far away for M13, whose accepted distance is 22,000-25.000 light-years. If we use the uncertainty of the Gaia measurement to make the parallax as large as possible, we get a parallax of 0.1073, corresponding to a distance of about 30,000 light-years, which still seems a bit far away. Using that distance, however, and the star's B and V magnitudes, gives an absolute B magnitude of some 440 solar luminosities and a V magnitude of some 380 solar luminosities. That sounds reasonable for a star of spectral class B2.
I tried to find a reasonably good color photo of a star of spectral class B2, to show it here as a proxy for Barnard 29. Well, you wouldn't believe how hard it was to find a star of spectral class B2 that is well-known enough to have had its portrait taken. Finally I found Alpha Musca, which gets photographed only because it is located next to the Dark Doodad.
Still, I have to ask, how did you, Randall, hear of Barnard 29?
Ann
In the UV, Barnard 29 actually shows a slight
halo around the star.
But the star still poses several mysteries, such as why it is practically invisible in the IR.
"A post-AGB star (pAGB, abbreviation of post-asymptotic giant branch) like Barnard 29* (or L2 Puppis, RV Tauri, R Scuti od U Monocerotis) is a type of luminous supergiant star of intermediate mass in a very late phase of stellar evolution. The post-AGB stage occurs after the asymptotic giant branch (AGB or second-ascent red giant) has ended. The stage sees the dying star, initially very cool and large, shrink and heat up.The duration of the post-AGB stage varies based on the star's initial mass, and can range from 100,000 years for a solar-mass star to just over 1,000 years for more massive stars. The timescale gets slightly shorter with lower metallicity.
Towards the end of this stage, post-AGB stars
also tend to produce protoplanetary nebulae as they shed their outer layers, and this creates
a large infrared excess and obscures the stars in visible light. After reaching an effective temperature of about 30,000 K, the star is able to ionise its surrounding nebula, producing a true planetary nebula.
Properties
Post-AGB stars span a large range of temperatures, as they are in the process of heating up from very cool temperatures (3,000 K or less) up to about 30,000 K. Technically, the post-AGB stage only ends when the star reaches its maximum temperature of 100-200,000 K,[2] but beyond 30,000 K, the star ionises the surrounding gas and would be considered a central star of a planetary nebula more often than a post-AGB star.
On the other hand, the luminosity of post-AGB stars is usually constant throughout the post-AGB stage, and slightly dependent on the star’s core mass, and getting slightly brighter with lower metallicity."
https://en.wikipedia.org/wiki/Post-AGB_star and "Iron abundances of B-type post-Asymptotic Giant Branch stars in globular clusters: Barnard 29 in M 13 and ROA 5701 in omega Cen" H. M. A. Thompson, F. P. Keenan, P. L. Dufton, R. S. I. Ryans, J. V. Smoker, D. L. Lambert, A. A. Zijlstra
XMM-Newton-UV and SDSS9-opt jac berne (flickr)
ALLWISE-MidIR and XMM-Newton-UV jac berne (flickr)[quote=Ann post_id=341445 time=1727410590 user_id=129702]
[quote="Chris Peterson" post_id=341442 time=1727380518 user_id=117706]
[quote="Randall Rathbun" post_id=341441 time=1727378977]
I would like to see a post on UV bright star Barnard 29 (not to be confused with a dark nebula of the same name) with some discussion on the unique place it has on the Hertzsprung-Russell diagram. Thanks. How was this star found in the first place? Did someone have UV film and the star was ultra-bright?
[/quote]
I doubt the UV is detectable from the ground. The star appears very blue, and by measuring its intensity at two or more wavelengths the shape of the blackbody can be inferred, and therefore the temperature. At something like 21,000 K, the peak output will be around 140 nm, in the UV... even if that can't be measured directly through the atmosphere.
[/quote]
How did the two of you, Randall and Chris, find out about this star? I asked Simbad Astronomical database about Barnard 29, and all it would give me was the dark cloud. The only source I could find that would talk about this star at all was [url=http://www.messier.seds.org/more/m013_b29.html]messier.seds.org[/url]., and it gave me the designation NGC 6205 222, which was accepted by Simbad. (Simbad itself called the star 2MASS J16413368+3626077, which is a mouthful.)
Unfortunately, Simbad has no information on the U magnitude of this star. It does tell us that the B magnitude of the star is 12.98, the V magnitude is 13.14, and the J, K and H magnitudes are progressively (but slowly) fainter. According to Simbad, the spectral class of this star is B2p D ~. I don't know what D ~ means, but B2p should mean that the star is spectral class B2, but peculiar. Of course, since it is a post-AGB star, it will indeed be peculiar compared to stars of spectral class B2 that are supporting themselves through fusion.
My point, however, is that this star is spectral class B2 and not O. A main sequence star of spectral class B2 will have a temperature of ~21,000 K, according to [url=https://sites.uni.edu/morgans/astro/course/Notes/section2/spectraltemps.html]University of Northern Iowa[/url]. Some central stars of planetary nebulas are known to be much, much hotter. And yes, I know that you know that. And all that it really means is that the star is in the process of removing its outer layers, but it has most certainly not finished that process or cast off all of its outer atmosphere.
The Gaia parallax of this star is 0.0775 ± 0.0298 milliarcseconds. A parallax of 0.0775 mas corresponds to a distance of 12,900 parsecs or 42,000 light-years. That's too far away for M13, whose accepted distance is 22,000-25.000 light-years. If we use the uncertainty of the Gaia measurement to make the parallax as large as possible, we get a parallax of 0.1073, corresponding to a distance of about 30,000 light-years, which still seems a bit far away. Using that distance, however, and the star's B and V magnitudes, gives an absolute B magnitude of some 440 solar luminosities and a V magnitude of some 380 solar luminosities. That sounds reasonable for a star of spectral class B2.
I tried to find a reasonably good color photo of a star of spectral class B2, to show it here as a proxy for Barnard 29. Well, you wouldn't believe how hard it was to find a star of spectral class B2 that is well-known enough to have had its portrait taken. Finally I found Alpha Musca, which gets photographed only because it is located next to the Dark Doodad.
[img3="B2V-type blue star Alpha Musca is seen next to the Dark Doodad nebula. Globular cluster NGC 4372 is also in the picture. Post-AGB star Barnard 29 is similar in color to Alpha Musca. Credit: Andrey Oreshko"]https://apod.nasa.gov/apod/image/0812/doodad_oreshko.jpg[/img3]
Still, I have to ask, how did you, Randall, hear of Barnard 29?
Ann
[/quote]
In the UV, Barnard 29 actually shows a slight [b]halo[/b] around the star.
But the star still poses several mysteries, such as why it is practically invisible in the IR.
"A post-AGB star (pAGB, abbreviation of post-asymptotic giant branch) like Barnard 29* (or L2 Puppis, RV Tauri, R Scuti od U Monocerotis) is a type of luminous supergiant star of intermediate mass in a very late phase of stellar evolution. The post-AGB stage occurs after the asymptotic giant branch (AGB or second-ascent red giant) has ended. The stage sees the dying star, initially very cool and large, shrink and heat up.The duration of the post-AGB stage varies based on the star's initial mass, and can range from 100,000 years for a solar-mass star to just over 1,000 years for more massive stars. The timescale gets slightly shorter with lower metallicity.
Towards the end of this stage, post-AGB stars [b]also tend to produce protoplanetary nebulae as they shed their outer layers[/b], and this creates [b]a large infrared excess[/b] and obscures the stars in visible light. After reaching an effective temperature of about 30,000 K, the star is able to ionise its surrounding nebula, producing a true planetary nebula.
Properties
Post-AGB stars span a large range of temperatures, as they are in the process of heating up from very cool temperatures (3,000 K or less) up to about 30,000 K. Technically, the post-AGB stage only ends when the star reaches its maximum temperature of 100-200,000 K,[2] but beyond 30,000 K, the star ionises the surrounding gas and would be considered a central star of a planetary nebula more often than a post-AGB star.
On the other hand, the luminosity of post-AGB stars is usually constant throughout the post-AGB stage, and slightly dependent on the star’s core mass, and getting slightly brighter with lower metallicity." [size=75]https://en.wikipedia.org/wiki/Post-AGB_star and "Iron abundances of B-type post-Asymptotic Giant Branch stars in globular clusters: Barnard 29 in M 13 and ROA 5701 in omega Cen" H. M. A. Thompson, F. P. Keenan, P. L. Dufton, R. S. I. Ryans, J. V. Smoker, D. L. Lambert, A. A. Zijlstra [/size]
[imghover="https://live.staticflickr.com/65535/54024774828_c142cd6e50_b.jpg"]https://live.staticflickr.com/65535/54023645117_e88425b1fc_b.jpg[/imghover]
[size=75]XMM-Newton-UV and SDSS9-opt jac berne (flickr)[/size]
[imghover="https://live.staticflickr.com/65535/54024873849_21d6ee3264_b.jpg"]https://live.staticflickr.com/65535/54024774828_c142cd6e50_b.jpg[/imghover]
[size=75]ALLWISE-MidIR and XMM-Newton-UV jac berne (flickr)[/size]