Betelgeuse at it's faintest for 25 years!

[Merlin66]

An interesting time to be practising "Spectroscopy 101"
Report states:

Currently this is the faintest the star has been during our 25+ years of continuous monitoring and 50 years of photoelectric V-band observations. The light variations are complicated and arise from pulsations as well from the waxing and waning of large super-granules on the star's convective surface.

http://www.astronomerstelegram.org/?read=13341

[skysurfer]

Visually it appears also faint to me, I just saw it barely brighter than Bellatrix.
Upcoming supernova ? Probably not in our lifetimes.


When it does happen, it should look like this (when supernova, the temperature is much higher so it will appear blue) with Uluru on the foreground.

[ngcles]

Hi Ken & All,

Yes it has been interesting to follow -- when the sky is clear enough. For the last six weeks here it has either been smoke or dust. Often sufficient to obscure all stars down to second magnitude.

I did get a chance to finally get a look with a relatively clear sky on 22nd December at about 2.30am. My estimate was magnitude +1.3 -- the faintest certainly I've ever seen it. It was notably fainter than Aldebaran, (+0.9) (but variable) and a bit fainter that Pollux (+1.14) and a bit brighter than Bellatrix (+1.62).

Tonight the comparison stars were Adhara (Epsilon Canis Majoris +1.53) and Bellatrix (+1.62) and it was brighter than both these and I arrived at a similar magnitude for Betelgeuse (+1.3). The sky is still somewhat smoke affected but these three stars are all about the same height above the horizon and so, similarly affected by haze.

Recent (about a week old) photometric measures from different observatories have yielded: V = +1.273, +1.294 and +1.286. This is the faintest it has ever been photometrically measured.

The current thinking is this dip in brightness is a superimposition of two different minima within two of Betelgeuse's roughly cyclic pulsations -- 495 days and 2100 days. Call it a resonant super-dip if you like.

The latest update is in ATel #13365 that reads:

As reported earlier in ATel #13341, the luminous red supergiant (a core-collapse SN II progenitor) Betelgeuse (alpha Ori) has become unusually faint with a V ~+1.125 mag (measured on 2019 December 07.25 UT). Since that report Betelgeuse has continued to decrease further in brightness. The most recent measurements made on 2019 December 19.3 UT, 20.2 UT and 22.25 UT are V = +1.273, +1.294 and +1.286 mag, respectively. This appears to be the faintest the star has been measured since photoelectric observations have been carried out of the star. However, photoelectric photometry carried out during late-1926 / early-1927 by Joel Stebbins (1931: Pub. Washburn Obs., 15, 177) indicates that Betelgeuse declined to V’ ~+1.25 mag. At its average maximum brightness light (V ~ 0.3 - 0.4 mag), Betelgeuse is the 6 - 7th brightest star. But by 2019 mid-December the star has slipped to the ~21st brightest star. The red supergiant is now closer in brightness to Bellatrix (V =+1.64 mag) than to Rigel (V =+0.13 mag). Wing three-band Near-IR and TiO photometry carried out at Wasatonic Observatory shows that Betelgeuse is also cooler with an inferred spectral-type near ~M3.5 Iab (Teff ~ 3,545 K from TiO-photometry). This is about 150 K cooler than measured near maximum light. Analysis of the last 25-yrs of V-band and Wing TiO and Near-IR photometry shows a dominant ~425+/-10 day period as well as a long-term ~5.9+/-0.5 year period. The current faintness of Betelgeuse appears to arise from the coincidence of the star being near the minimum light of the ~5.9-yr light-cycle as well as near, the deeper than usual, minimum of the ~425-d period. We plan to continue to monitor the star. If the star continues to follow above periods, light minimum should occur soon. But this needs to be checked. This continues to be an opportune time to carry out complementary measures of Betelgeuse while it is in its current low state and is unusually cool and faint.



For those of you hoping for an imminent core-collapse supernova, you're probably going to be disappointed -- a mundane explanation is more likely. One to keep an eye on certainly so we can gain a better understanding of the late evolution of high-mass stars.

Best,

L.

[skysurfer]

Here a CNN article:


https://edition.cnn.com/2019/12/26/world/betelgeuse-may-explode-scn-trnd/index.html


But I don't expect an explosion in our lifetimes.


And I have my doubts about the 'red giant' nature. Well, probably I am saying nonsense, but it is just a theory.

Eta Carinae also appears red, but it is actually a very hot bluish star, but duct clouds around Eta make it red, just like the bushfire smoke makes the Sun appear red in NSW.
In this not also the case with Betelgeuse, that it is actally a hot Rigel like star embedded in a shroud of dust ?

[ngcles]

Hi All,

For those still interested in the Betelgeuse ... thang, under a somewhat smoke affected sky, not completely dark (very deep twilight) to my eye it has dipped a bit further and is now no better than marginally brighter than Bellatrix (Gamma Orionis) -- magnitude +1.62. It seems equally bright to me as Epsilon Canis Majoris (Adhara) -- magnitude +1.53. Estimate of magnitude +1.4 to +1.5.

Betelgeuse and the two other stars were approximately similar in altitude and therefore should be equally affected by the smoke-haze.

Best,

L.

[billdan]

Our ABC published an article about Betelgeuse magnitude variations yesterday.

https://www.abc.net.au/news/2019-12-27/is-betelgeuse-about-to-explode3f/11828624

[JA]

Thanks Bill. I saw that earlier and was going to repost the same chart from Dr Stella Kafka, I think.

It is quite interesting when you look at the variation over say some 30 years of data mostly varying in Magnitude between 0.2 and 1, with infrequent outliers as high as nearly 0 and as low as 1.3 (now-ish), and the very consistent period of one year.

EDIT: given the one year periodicity I'd be interested to know if the maxima/minima were in any way related to our orbital parameters/ position around The Sun and whether it coincided with perihelion / aphelion or .... ?

EDIT #2:OK I just checked ROUGHLY from the graph data (and using a bit of visual interpolation over the years) which shows minimum apparent intensity around the start of each calender year, the same time as closest solar approach: perihelion, or close enough. Who Knows, perhaps it's something on the star itself (logically more likely) rather than something "in between" that accounts for the one year period in the intensity / magnitude data?



Best
JA

[skysurfer]

The embedded video is indeed spectacular.


Interesting ....




Betelgeuse is so close to the equator (7 degrees North) that it is visible from all over the world except most of Antarctica. In the regions above the polar circle in summer, it is daylight 24/7 inhibiting seeing the star with the naked eye.


But Australia lies between 12 and 43 S (Tasmania included) which allows viewing the star everywhere, so what 'almost' means I don't know.

[billdan]

They would have to be allowing for Australia's holdings in Antarctica.

According to Google :-
Eighty years ago Australia received from Great Britain its largest ever gift: six million square kilometres of Antarctica. Three years later it became the Australian Antarctic Territory (AAT). 42% of the Antarctic continent is Australia's.

[Terry B]

The spectrum of eta Car and Betelgeuse are very different. The red colour is not from the same thing. The 2 images below are of the 2 stars.
The Betelgeuse spectrum is not mine as I have not taken a low resolution image. It shows that the stars spectrum is predominately in the red with strong absorption features and hence a cool star.

The eta Car is mine from some years ago. It shows very strong Ha emission that makes it look red as well as lots of other emission lines.

Bushfire smoke will not create the same thing. It will just filter out the blue end of the spectrum generally and not cause absorption lines.
Cheers :)

[N1]

As I stepped outside tonight and looked at Orion, I thought Betelgeuse was slightly fainter than Bellatrix. Last observation was a week ago and it was the opposite then. Took a quick picture and the camera still sees Betelgeuse a little brighter but not by much.

[bojan]

Orion from 1967.... taken from balcony of our flat in Zagreb...
On this image, Betelgeuse is brighter than Rigel (film was EFKE 20DIN, panchromatic...)
Camera was SMENA8....

[N1]

Nice images. Certainly a big difference in brightness. What was the sky like in general, light pollution wise? Is that the Milky way upper left?

[bojan]

Mirko,

Light pollution there was bad even then, so Milky way was not visible from that location.

I took them whn I bought that camera (my second one :-) )...

[JohnF]

In ancient times Betelgeuse was yellow, not Red. Quoting Wikipedia:--

"By contrast, three centuries before Ptolemy, Chinese astronomers observed Betelgeuse as having a yellow coloration."

[N1]

I suspect the idea of what is a "red" star has shifted more since these observations than B's actual spectrum. I too would not consider B's colour red if I saw it anywhere else. If I ordered tomato soup and it came in that colour, I'd return it. The carbon star in Crux, now that's red.

[JohnF]

I did read somewhere that 50 stars just disappeared, that is these Stars just went out as if a light switch switched them off leaving no trace of these.

[bojan]

John,

"Yellow" Betelgeuse is probably just perception.. BTW, some people are partly colour blind ( protanomaly, see here (http://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/)) , and what they may see as "yellow" could be more red to the rest.. In science, we want confirmation of claims from couple of sources... if there is only one source, it could be considered as not reliable.

BTW, couple of thousand of years is very short time in evolution of stars... that applies even to short-lived supergiants, like Betelgeuse),

So far Betelgeuse seems to be at the end of it's red supergiant phase.. which may last hundreds of thousand of years - so it is very unlikely it was yellow giant 2 thousands years ago. But, if this is actually the case (some people are currently working on such models), that means there will be no fireworks any time soon :-)

And, stars do not just dissapear.. so those 50 missing that you are mentioning are most likely still there (or someone just wrote a fake news somewhere).
Or there is much more to it than just dissaperance.
If a star explodes as supernova, it will be much fainter (in visible light that is) that progenitor once the fireworks is over..

[N1]

Ishihara says I'm probably not colour blind, and I say Betelgeuse is probably not red (orange, maybe)

[skysurfer]

I just saw that "Faintelgeuse" is not brighter than Bellatrix anymore.
I am curious how it will develop in the upcoming weeks.
But a supernova within our lifetimes is highly unlikely.


About the "yellow" Betelgeuse : actually the star *is* yellow, because the temperature and hence color is the same as a incandescent halogen bulb (3000 K). But because it is faint compared to much closer terrestal lights it appears 'red' to our eyes.
When you are a few kilometers from a 3000 K lamp (can also be a warm white LED), or even only a few hundred meters from small warm white garden decoration LEDs, it appears as red as Betelgeuse (or Antares or whatever M class star).

[N1]

Interesting stuff. Could that be because for the colour to register "correctly" (for that particular observer), the image on the retina must have a certain size and not just be a point? Like when you defocus a star in the telescope to better see its colour

[bojan]

There must be a bit of "spilling" of light over adjacent rods and cones... so precise focussing probably is not a big factor.. or not?

[JohnF]

https://www.sciencealert.com/a-look-through-past-star-catalogues-finds-scores-of-stars-that-have-mysteriously-vanished

[JohnF]

https://www.space.com/27844-missing-stars-globular-clusters-defy-theories.html

[JohnF]

Bojan, I am just quoting what others are saying about stars that have gone missing. Do not know myself, and m not attempting to explain this. And whether these websites are genuine do not know.

https://www.iflscience.com/space/missing-stars-confound-globular-cluster-formation-theories/

[Saturnine]

Had some clear sky last night and had a long look at Betelgeuse, comparing it to Bellatrix and it certainly looked a smigden ( technical term ) fainter . Whereas 2 weeks ago Alpha Orionis was definitely slightly brighter than Bellatrix.

[bojan]

John,

I had a look at all three links.

The first link is about records (catalogs, photographs), older and newer.
Two later ones are about discrepancies between theory and observation (chemical composition of stars in globular clusters can not be explained by current theories of clusters evolution).
The terms "missing" and "disappearance" of stars is applied in somewhat "plastic" manner.... Taken out of context, they could be misleading to "people from street".

[N1]

Absolutely. Deducting that stars that aren't observed have "gone missing" because a theory predicts their observation is turning science on its head.

Back on topic, I watched Orion appear in the evening twilight sky last night, and could detect Bellatrix before Betelgeuse. Watching the two in averted vision later (thereby reducing effects caused by their different colour) also gave Bellatrix a small but reproducible advantage.

[multiweb]

Some cool highres pics from the ESO.here (https://www.eso.org/public/news/eso2003/).

[sutekh]

The supernova watch is cancelled -- Betelgeuse is brightening again:

https://www.spaceweather.com/

--sutekh

[skysurfer]

Well, yesterday night I saw Faintelgeuse still slightly fainter than Bellatrix.

[N1]

The star looked just about reinstated to me tonight. 92% of its usual brightness I'm told. This return to normal looks as impressive as the fainting.

[bojan]

Same here, last night... (today it's raining)

[Saturnine]

Thought I would revive this thread for anyone who may be curious, have noticed over the previous 2 evenings that Betelgeuse has brightened considerably and is now almost as bright as Rigel, so that is a bit of a turn around from a few months ago.
Going by the plotted graphs on the AAVSO it is now back up to mag. 0.5, from the 1.6 at its faintest back in Jan / Feb.
Wouldn't have expected the star to brighten that quickly given its approximate 150 to 300 day period.

[N1]

Yes that was more rapid than the decline. Certainly an interesting object to watch, and no scope needed!

[cannon_gray]

Betelgeuse has reduced its brilliance to 38 percent of its normal brightness.
https://icdn.lenta.ru/images/2020/02/17/09/20200217095959745/pic_ca3a9eb604ef9b250768dddcd13e378 9.png
On the surface are huge convective cells, up to 60 percent of the star's diameter, creating bright and dim regions. The appearance of such a cell explains why some areas on the star's surface are bright, and most of the surface is dim.