Starship Asterisk*

[quote=bystander post_id=329546 time=1677778238 user_id=112005]
[quote=johnnydeep post_id=329544 time=1677773918 user_id=132061]
Thanks. So all main sequence stars are "dwarfs". Wikipedia points out other uses - https://en.wikipedia.org/wiki/Dwarf_star#Current_uses_of_the_term_%22dwarf%22
[/quote]
If they are less than approximately 2 Solar masses ([i]M[sub]☉[/sub][/i]) and/or 2 Solar radii ([i]R[sub]☉[/sub][/i]), they may be considered dwarfs. However, I wouldn't consider O and B stars to be dwarfs. There are also two stellar classes not on the main sequence that are considered dwarfs, brown dwarfs and white dwarfs. (There are also black and blue dwarfs, but the universe isn't old enough for them.)
[/quote]

I have definitely seen hydrogen-fusing O and B stars being referred to as blue dwarfs. This is what Wikipedia says about the astronomical term "blue dwarf":

[quote][url=https://en.wikipedia.org/wiki/Blue_dwarf]Wikipedia[/url] wrote:
The term blue dwarf may refer to:

[b][size=110]Astronomical objects[/size][/b]

A blue compact dwarf galaxy
An early-type main-sequence star
B-type main-sequence star
O-type main sequence star
Blue dwarf (red-dwarf stage), a hypothetical stage in red dwarf interstellar evolution[/quote]

But I agree with you, bystander. It is not a good idea to call O- and B-type hydrogen-fusing stars "blue dwarfs". There is nothing dwarf-like about these stars, which are much bigger than the Sun (except in a few cases, where stars really [i]are[/i] hot and blue because they have lost much of their outer atmospheres and therefore are quite small.)

Overall, though, I think we should reserve the term "dwarfs" for M-type hydrogen-fusing stars. The term "red dwarf" is very well-established, and the hydrogen-fusing M-type stars really are tiny (compared with the Sun).

But I see no reason to call hydrogen-fusing K-type stars orange dwarfs, or the Sun a yellow dwarf, or F-type hydrogen-fusing stars yellow-white dwarfs, or A-type hydrogen-fusing stars white dwarfs ([b][i]absolutely[/i][/b] not!!!), or B- and O-type hydrogen-fusing stars blue dwarfs.

So let's keep the red dwarfs and chuck the rest of the dwarfs, shall we?

Ann

[quote=johnnydeep post_id=329544 time=1677773918 user_id=132061]
Thanks. So all main sequence stars are "dwarfs". Wikipedia points out other uses - https://en.wikipedia.org/wiki/Dwarf_star#Current_uses_of_the_term_%22dwarf%22
[/quote]
If they are less than approximately 2 Solar masses ([i]M[sub]☉[/sub][/i]) and/or 2 Solar radii ([i]R[sub]☉[/sub][/i]), they may be considered dwarfs. However, I wouldn't consider O and B stars to be dwarfs. There are also two stellar classes not on the main sequence that are considered dwarfs, brown dwarfs and white dwarfs. (There are also black and blue dwarfs, but the universe isn't old enough for them.)

[quote=Ann post_id=329529 time=1677734616 user_id=129702]
[quote=johnnydeep post_id=329522 time=1677707322 user_id=132061]
Wikipedia says that [url=https://en.wikipedia.org/wiki/AE_Aurigae]AE Aurigae[/url] is a "main sequence dwarf" with these stats:

Mass- 23 M☉
Radius - 7.47 R☉
Luminosity - 59,000 L☉

That's quite an impressive "dwarf"!
[/quote]

Stars that are on the main sequence, so that they support themselves by fusing hydrogen to helium in their cores, have traditionally been called dwarfs. I get the impression that this term is getting a lot less popular. For example, the Sun, which is defined as yellow (although it's arguable if it is, see [url=https://asterisk.apod.com/viewtopic.php?p=329504#p329504]here[/url],) is a yellow dwarf, if we are using the dwarf terminology. But what about hydrogen-fusing stars of spectral A, which have traditionally been called white (although they definitely are not), would they be called "white dwarfs"? So that, for example, Sirius would be called a white dwarf with a white dwarf companion?


[img3="Artist's impression of Sirius A and B. Sirius A at left and Sirius B at right. Copyright: NASA, ESA and G. Bacon (STScI)"]https://cdn.sci.esa.int/documents/34247/35306/1567213719061-heic0516b_625.jpg[/img3]


Would Sirius A, which is happily fusing hydrogen to helium in its core and is twinkling so brightly in our night skies, be the same kind of star as its tiny dead companion, which has cast off its outer atmosphere and is now radiating its remaining heat out into space? I think not!!!


Anyway. I think Wikipedia is overestimating AE Aurigae a little. According to Wikipedia, the distance to AE Aur is 1,320 ± 40 light-years, but according to the star's Gaia parallax of 2.574 ± 0.034 milliarcseconds, the distance to it would be between (roughly) 1,250 and 1,280 light-years. So according to Gaia, Ae Aur is a little closer to us than Wikipedia thought, and therefore it would be a little less bright, large and powerful.

Ann
[/quote]

Thanks. So all main sequence stars are "dwarfs". Wikipedia points out other uses - https://en.wikipedia.org/wiki/Dwarf_star#Current_uses_of_the_term_%22dwarf%22

[ I still haven't figured out how to use the ordered/unordered list tags or I'd try to quote what Wikipedia has to say. ]

[quote=johnnydeep post_id=329522 time=1677707322 user_id=132061]
Wikipedia says that [url=https://en.wikipedia.org/wiki/AE_Aurigae]AE Aurigae[/url] is a "main sequence dwarf" with these stats:

Mass- 23 M☉
Radius - 7.47 R☉
Luminosity - 59,000 L☉

That's quite an impressive "dwarf"!
[/quote]

Stars that are on the main sequence, so that they support themselves by fusing hydrogen to helium in their cores, have traditionally been called dwarfs. I get the impression that this term is getting a lot less popular. For example, the Sun, which is defined as yellow (although it's arguable if it is, see [url=https://asterisk.apod.com/viewtopic.php?p=329504#p329504]here[/url],) is a yellow dwarf, if we are using the dwarf terminology. But what about hydrogen-fusing stars of spectral A, which have traditionally been called white (although they definitely are not), would they be called "white dwarfs"? So that, for example, Sirius would be called a white dwarf with a white dwarf companion?


[img3="Artist's impression of Sirius A and B. Sirius A at left and Sirius B at right. Copyright: NASA, ESA and G. Bacon (STScI)"]https://cdn.sci.esa.int/documents/34247/35306/1567213719061-heic0516b_625.jpg[/img3]


Would Sirius A, which is happily fusing hydrogen to helium in its core and is twinkling so brightly in our night skies, be the same kind of star as its tiny dead companion, which has cast off its outer atmosphere and is now radiating its remaining heat out into space? I think not!!!


Anyway. I think Wikipedia is overestimating AE Aurigae a little. According to Wikipedia, the distance to AE Aur is 1,320 ± 40 light-years, but according to the star's Gaia parallax of 2.574 ± 0.034 milliarcseconds, the distance to it would be between (roughly) 1,250 and 1,280 light-years. So according to Gaia, Ae Aur is a little closer to us than Wikipedia thought, and therefore it would be a little less bright, large and powerful.

Ann

[attachment=0]FlamingStarComet_Roell_1080_annotated.jpg[/attachment]
!I like Ann's selexsion ! :mrgreen:

Wikipedia says that [url=https://en.wikipedia.org/wiki/AE_Aurigae]AE Aurigae[/url] is a "main sequence dwarf" with these stats:

Mass- 23 M☉
Radius - 7.47 R☉
Luminosity - 59,000 L☉

That's quite an impressive "dwarf"!

[quote="Paulo Carvalho" post_id=329518 time=1677667955]
Hello,
The "<" link is broken. It points to March, 28th instead of Feb, 28th. Certainly a typo.
thanks and keep up with this outstanding job,
Paulo
[/quote]

Thanks! Fixed it on the main NASA APOD.
- RJN

As someone has already pointed out, the backward link [u]in the APOD of March 1[/u], is in error. It points to a date that has not yet occurred!

This is such a bad process of this image, 0 integrity of the real data. Poor denoising + horrible masking + no usage of sigma clipping in poor staking which causes hot pixel trails of RGB through the whole image... clipped background to a blue hue with no denoising on the comet making it appear as a rainbow tail .. poor usage of combining mosaic causing line artefacts and extremely elongated stars due to poor tracking and stacking. Just a good idea and poor execution.

Hello,
The "<" link is broken. It points to March, 28th instead of Feb, 28th. Certainly a typo.
thanks and keep up with this outstanding job,
Paulo

[float=left][img3="The Flaming Star Nebula
Image Credit & Copyright: Thomas Röell"]https://apod.nasa.gov/apod/image/2303/FlamingStarComet_Roell_1080_annotated.jpg[/img3][/float][float=right][img3="AE Aurigae and the Flaming Star Nebula
Image Credit & Copyright: Amir Abolfath (TWAN)"]https://www.nasachina.cn/wp-content/uploads/2019/03/IC405_Abolfath_960.jpg[/img3][/float]
[clear][/clear]
Today's APOD uses the same caption that was used for [url=http://www.star.ucl.ac.uk/~apod/apod/ap190326.html]the APOD of March 26, 2019[/url]. But the APOD of March 26, 2019 was really a closeup portrait of AE Aurigae and the Flaming Star Nebula, whereas today's APOD is a composite showing us other important deep-sky objects too. Still,today’s caption refers only to the Flaming Star Nebula and AE Aurigae.

There are definitely things that I admire about today's APOD. Most of all, I admire the portrait of the comet, the green and brilliantly white coma, the broad sweeping yellow dust tail and the narrow blue bifurcated IOM tail. Bravo!

I'm a lot less enthusiastic about the portrait of the nebulas at left. First of all, the portrait of them was made using narrowband photography, which I'm normally not too happy about (since I usually don't find such images very aesthetically pleasing or "true" color). Okay, so how can we tell that the portrait of the nebulas was made using narrowband filters?


[float=left][img3="A broadband image of Flaming Star Nebula, Tadpole Nebula IC405 IC410 IC417 & NGC1931. Credit: Keesscherer"]https://upload.wikimedia.org/wikipedia/commons/thumb/1/16/The_Flaming_Star_Nebula%2C_Tadpole_Nebula_IC405_IC410_IC417_%26_NGC1931.jpg/1024px-The_Flaming_Star_Nebula%2C_Tadpole_Nebula_IC405_IC410_IC417_%26_NGC1931.jpg[/img3][/float][float=right][img3="A narrowband image of the Flaming Star Nebula and the Tadpole Nebula. Credit: u/amajed172"]https://preview.redd.it/pv4vkxm3qr361.jpg?width=960&crop=smart&auto=webp&v=enabled&s=a3f6d65c512aaa7505971a7060500e64a04074bf[/img3][/float]
[clear][/clear]


In the broadband image by Keesscherer at left, you can see how the the blue light of star AE Aurigae reflects off dust in the in the Flaming Star Nebula, making the dust shine softly blue. (The rest of the Flaming Star Nebula is red from the glow of ionized hydrogen). The Tadpole Nebula, by contrast, looks non-blue in the broadband image.

But in the narrowband image by u/amajed172 (Anas Almajed), the blue color disappears from the Flame Nebula, but it appears in the Tadpole Nebula instead. The Tadpole Nebula is a site of star formation, unlike the Flaming Star Nebula, which is just a gas cloud being lit up by a passing star, O9.5V-type AE Aurigae. And while AE Aurigae is hot, certainly hot enough to ionize hydrogen and make it glow red, that's nothing compared with HD 242908, the main ionizing star of the Tadpole Nebula. HD 242908 is spectral class O4.5V, and [b][i]that's[/i][/b] hot! Therefore, there is a lot of ionized oxygen in the Tadpole Nebula, which is detected by OIII filters and mapped as blue in narrowband images.

(Also, fascinatingly, the Flaming Star Nebula is "only" some 1,300 light-years away, while the Tadpole Nebula resides at a whopping distance of some 11,000 light-years. Wowzers! That's also why the Tadpole Nebula is more dust-reddened than the Flaming Star Nebula and looks more orange than the Flaming Star Nebula, which looks a bit more magenta.)

In today's APOD, you can see that the inner part of the Tadpole Nebula is blue, whereas the Flaming Star Nebula is non-blue. This is a dead giveaway that these nebulas have been photographed using narrowband filters. (Admittedly, if you look at the full size of today's APOD, which I highly recommend, you can actually make out the bluish dust lanes of the Flaming Star Nebula, where they are a faint shade of gray.)

Okay, here's my main complaint. Today's APOD is a composite where the right side of the image was made using broadband photography (the comet) and the left side was made primarily using narrowband filters (the nebulas). This makes my head spin a little.

But do note the lovely cluster, M38, in the upper left corner of the APOD! This sure looks like a broadband portrait of the cluster.


[attachment=0]M38 detail in APOD1 March 2023.png[/attachment]


Ann

[url=https://apod.nasa.gov/apod/ap230301.html] [img]https://apod.nasa.gov/apod/calendar/S_230301.jpg[/img] [size=150]The Flaming Star Nebula[/size][/url]

[b] Explanation: [/b] Is star AE Aurigae on fire? No. Even though [url=https://en.wikipedia.org/wiki/AE_Aurigae]AE Aurigae[/url] is named the Flaming Star and the surrounding nebula [url=https://apod.nasa.gov/apod/ap200107.html]IC 405[/url] is named the [url=https://www.daviddarling.info/encyclopedia/F/Flaming_Star_Nebula.html]Flaming Star Nebula[/url], and even though the nebula appears to some like a swirling [url=https://apod.nasa.gov/apod/ap180826.html]flame[/url], there is [url=https://www.nfpa.org/News-and-Research/News-and-media/Press-Room/Reporters-Guide-to-Fire-and-NFPA/Key-Fire-Safety-Tips]no fire[/url]. [url=https://en.wikipedia.org/wiki/Fire]Fire[/url], typically defined as the rapid molecular acquisition of [url=https://periodic.lanl.gov/8.shtml]oxygen[/url], happens only when sufficient oxygen is present and is [url=https://media.istockphoto.com/id/509119713/photo/weimaraner-with-head-cocked.jpg?s=612x612&w=0&k=20&c=FMXNT4yye2_I5n5Z8ZGJZxlYnosXXw9xPcUQ1FtATdM=]not important[/url] in such high-energy, low-oxygen environments such as stars. The bright star [url=https://www.nsf.gov/news/mmg/mmg_disp.jsp?med_id=57052]AE Aurigae[/url] occurs near the center of the Flaming Star Nebula and is [url=https://www.youtube.com/watch?v=igDZ8CMWq1k]so hot it glows blue[/url], emitting light so energetic it knocks [url=https://history.aip.org/exhibits/electron/]electrons[/url] away from surrounding gas. When a [url=https://en.wikipedia.org/wiki/Proton]proton[/url] recaptures an electron, light is emitted, as seen in the surrounding [url=https://apod.nasa.gov/apod/emission_nebulae.html]emission nebula[/url]. [url=https://www.instagram.com/p/Cou3cnzs6zV/]Captured here[/url] three weeks ago, the [url=https://ui.adsabs.harvard.edu/abs/2004ApJ...616..257F/abstract]Flaming Star Nebula[/url] is visible near the composite image's center, between the red [url=https://apod.nasa.gov/apod/ap221219.html]Tadpole Nebula[/url] on the left and blue-tailed [url=https://apod.nasa.gov/apod/ap230221.html]Comet ZTF[/url] on the right. The Flaming Star Nebula lies about 1,500 [url=http://chandra.harvard.edu/photo/cosmic_distance.html]light years[/url] distant, spans about 5 [url=https://spaceplace.nasa.gov/light-year/]light years[/url], and is visible with a small telescope toward the [url=https://spaceplace.nasa.gov/constellations/]constellation[/url] of [url=https://en.wikipedia.org/wiki/Auriga_(constellation)]the Charioteer[/url] (Auriga).


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