Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Betelgeuse is faint (for it)

  • Please log in to reply
119 replies to this topic

#51 Jure Atanackov

Jure Atanackov

    Vostok 1

  • -----
  • Posts: 160
  • Joined: 04 May 2010

Posted 02 January 2020 - 02:40 AM

A really impressive sight over the past several nights - on Dec 30.92UT I estimated it at ~+1.4 (+1.37). Very noticeably fainter than Pollux, still slightly brighter than Bellatrix. It had faded slightly since my previous estimate, on Dec 25.92UT, when I made it ~+1.3 (+1.32).


  • giorgio_ne, Aquarellia, kdenny2 and 1 other like this

#52 Waddensky

Waddensky

    Mariner 2

  • -----
  • Vendors
  • Posts: 263
  • Joined: 18 Sep 2017
  • Loc: The Netherlands

Posted 02 January 2020 - 05:42 AM

A carefully flux calibrated ALPY 600 spectrum from last night (using two reference stars and repeat spectra) shows a small increase in depth of the molecular bands compared with the MILES reference spectrum taken when the brightness was more typical.  Considering the current brightness is probably around half what it was then the changes in the spectrum are rather subtle. The spectrum has been added to the BAA database.

 

Cheers

Robin

 

attachicon.gifbetelgeuse_telrem_20191230_949_Leadbeater.png

Can you enlighten us a bit about what we see here? What molecular bands have changed the most? I'm sure this chart contains lots of interesting information.



#53 robin_astro

robin_astro

    Viking 1

  • -----
  • Posts: 867
  • Joined: 18 Dec 2005

Posted 02 January 2020 - 07:07 AM

Can you enlighten us a bit about what we see here? What molecular bands have changed the most? I'm sure this chart contains lots of interesting information.

The spectra of cool stars are dominated by broad absorption bands from molecules which are able to form in the cool (~3500K) atmosphere. The most obvious ones in M giant stars like Betelegeuse are from Titanium Oxide (TiO)  You can see their positions marked on the spectrum up the thread here

https://www.cloudyni...r-it/?p=9829536

 

In my graphic the pink line shows  the current spectrum divided by one from the MILES library of spectra taken around 2000/2001 by a professional team using the Issac Newton telescope (INT) so it shows any changes more clearly.

 

You can see how the broad molecular bands have increased in magnitude peak to peak by around 10-20% which indicates a drop in temperature.  The luminosity of a star is quite sensitive to temperature (luminosity ~T^4) so even a modest change in temperature can produce a dimming but there are other possibilities for dimming. For example the star may have also contracted in radius or there may have been dust formation in the star's atmosphere, though that would be expected to preferentially affect the blue end.

What we are seeing is most likely the normal variations of the star due to pulsations with different periods which have happened to coincide but if it keeps dropping something else might be going on  

 

Betelegeuse is thought most likely to be in its Helium burning stage. eg

https://iopscience.i...04-637X/819/1/7

If the theories of core collapse supernovae is correct it would need to move to Carbon burning and even then would likely last for at least another thousand year after that so it is probably not going to go bang any day now. Since we have never seen a red giant before it went supernovae though, what happens as the star nears that stage is  mainly just conjecture. (We knew something about Sanduleak -69 202, the progenitor of SN 1987A  which was a core collapse supernova, but it unexpectedly turned out to be  a blue supergiant)

 

Cheers

Robin


  • giorgio_ne, quality guy, smithrrlyr and 2 others like this

#54 Waddensky

Waddensky

    Mariner 2

  • -----
  • Vendors
  • Posts: 263
  • Joined: 18 Sep 2017
  • Loc: The Netherlands

Posted 02 January 2020 - 09:33 AM

The spectra of cool stars are dominated by broad absorption bands from molecules which are able to form in the cool (~3500K) atmosphere. The most obvious ones in M giant stars like Betelegeuse are from Titanium Oxide (TiO)  You can see their positions marked on the spectrum up the thread here

https://www.cloudyni...r-it/?p=9829536

 

[...]

 

Cheers

Robin

Thanks for sharing this, Robin! Extremely interesting what can be inferred from spectra like this.



#55 Dave Mitsky

Dave Mitsky

    ISS

  • *****
  • Moderators
  • Posts: 87,713
  • Joined: 08 Apr 2002
  • Loc: PA, USA, Planet Earth

Posted 02 January 2020 - 03:34 PM

Here are some additional articles on the increasing-in-publicity but decreasing-in-brightness star Alpha Orionis, better known as Betelgeuse.  
 

https://www.skyandte...ing-betelgeuse/

 

http://www.astronomy...ing-their-heads

 

http://www.astronomy...mes-a-supernova

 

Betelgeuse is a semi-irregular variable M1–M2 Ia–ab star with an apparent magnitude that usually varies between magnitude +0.0 and +1.3. This is the widest magnitude range of any first-magnitude star.


  • DHEB, Aquarellia and flt158 like this

#56 Forward Scatter

Forward Scatter

    Mariner 2

  • -----
  • Posts: 210
  • Joined: 22 Jul 2018
  • Loc: Wandering the PNW

Posted 02 January 2020 - 04:38 PM

Could the Big B be dimming due to interstallar dust or ejected and cooling mass? I'm sure folks have been already turning their spectrographs to it.



#57 robin_astro

robin_astro

    Viking 1

  • -----
  • Posts: 867
  • Joined: 18 Dec 2005

Posted 02 January 2020 - 05:33 PM

Could the Big B be dimming due to interstallar dust or ejected and cooling mass? I'm sure folks have been already turning their spectrographs to it.

It doesn't look like dust (or anything else dramatically different) from the spectrum. Dust would be expected to preferentially affect the blue end but the dimming appears to be similar at all visible wavelengths with some sign of a small (perhaps~200-300K) drop in temperature from the TiO band strength.

https://www.cloudyni...r-it/?p=9877412


  • kdenny2 likes this

#58 kdenny2

kdenny2

    Mariner 2

  • *****
  • Posts: 234
  • Joined: 18 Dec 2013

Posted 02 January 2020 - 08:58 PM

Not to get ahead of myself, but I wonder what type of changes we'd start to notice if Betelgeuse actually was about to undergo a supernova? Be interesting to ponder. The only example of a star that we've been able to observe before a supernova was Sanduleak 69 202. Would the star just start dimming to a ridiculous level as it undergoes core collapse? 


Edited by kdenny2, 02 January 2020 - 09:01 PM.


#59 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 7,462
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, Arkansas

Posted 02 January 2020 - 09:18 PM

Not to get ahead of myself, but I wonder what type of changes we'd start to notice if Betelgeuse actually was about to undergo a supernova? Be interesting to ponder. The only example of a star that we've been able to observe before a supernova was Sanduleak 69 202. Would the star just start dimming to a ridiculous level as it undergoes core collapse? 

What's ridiculously low?  Maybe if Betelgeuse dimmed to 3rd or 4th magnitude, that might be a warning something bigger was going to happen.  We really do not know............



#60 earlyriser

earlyriser

    Surveyor 1

  • *****
  • Posts: 1,799
  • Joined: 08 Nov 2016
  • Loc: Cincinnati

Posted 03 January 2020 - 09:01 AM

It doesn't look like dust (or anything else dramatically different) from the spectrum. Dust would be expected to preferentially affect the blue end but the dimming appears to be similar at all visible wavelengths with some sign of a small (perhaps~200-300K) drop in temperature from the TiO band strength.

https://www.cloudyni...r-it/?p=9877412

Dimming at all wavelengths would seem to indicate that the dimming is primarily from a contraction in size. 



#61 earlyriser

earlyriser

    Surveyor 1

  • *****
  • Posts: 1,799
  • Joined: 08 Nov 2016
  • Loc: Cincinnati

Posted 03 January 2020 - 09:09 AM

Not to get ahead of myself, but I wonder what type of changes we'd start to notice if Betelgeuse actually was about to undergo a supernova? Be interesting to ponder. The only example of a star that we've been able to observe before a supernova was Sanduleak 69 202. Would the star just start dimming to a ridiculous level as it undergoes core collapse? 

The core collapse happens in seconds once the mass of the iron core exceeds the Chandrasekhar limit. What we would need to look for are changes in visible output due to fusion in the core transitioning from carbon to neon, neon to oxygen, or oxygen to silicon burning. I'm not sure if this would cause visible changes. I would guess brightening from expansion of the outer layers due to increased core temperatures, but I really don't know. 


  • GalaxyPiper likes this

#62 robin_astro

robin_astro

    Viking 1

  • -----
  • Posts: 867
  • Joined: 18 Dec 2005

Posted 03 January 2020 - 11:29 AM

Dimming at all wavelengths would seem to indicate that the dimming is primarily from a contraction in size. 

Yes this was my original thought. A combination of a small drop in temperature (from spectral class M2i to M3-4i as seen by the increased TiO absorption bands) plus a contraction combining to produce a halving of luminosity.  However as has recently been pointed out on the BAA forum, we are considering here just what is happening in a relatively narrow band (V mag or visual range) whereas most of the flux from Betelgeuse is in the IR. Without knowing what is happening there it is difficult to make a judgement of exactly how much the total luminosity has dropped. 


  • earlyriser and smithrrlyr like this

#63 TonyChestnut

TonyChestnut

    Lift Off

  • -----
  • Posts: 11
  • Joined: 04 Jan 2020

Posted 04 January 2020 - 04:08 PM

This is my first post, so bear with me please. I plotted the brightness of Betelgeuse at https://www.aavso.org/LCGv2/ and tried to post the chart below. Not sure if it will work.
 
The dimmest value for the period of record was 1.5 magnitude on December 30, 2019. The latest reading was 1.407 on January 1, 2020. I plotted on the "V" values.
 
It appears that its brightness has been fainting precipitously since about late October of 2019. 
 
I haven't been able to view Betelgeuse for the past few weeks, ever since its behavior made the news because of the constant overcast conditions where I live. I'm hoping for the skies to clear so I can get out and make some observations and take some photos. 
 
I don't know if this if the "end" for Betelgeuse - but maybe it's the beginning of the end (?). 
 
One question: has Betelgeuse ever had a recorded magnitude of greater than (dimmer than) 1.5?
 
Thanks!
 
 
Betelgeuse brightness 1985 2020   1.5 dimmest 30Dec2019a
Album: Betelgeuse
8 images
1 comments


Edited by TonyChestnut, 04 January 2020 - 04:16 PM.

  • flt158 and Forward Scatter like this

#64 kdenny2

kdenny2

    Mariner 2

  • *****
  • Posts: 234
  • Joined: 18 Dec 2013

Posted 04 January 2020 - 06:39 PM

I observed Betelgeuse last night and I estimated its apparent magnitude to be about +1.45. I used Regulus and Adhara as my reference. Adhara is slightly dimmer than Betelgeuse, but the difference was only noticeable through a telescope. 


  • TonyChestnut likes this

#65 DHEB

DHEB

    Viking 1

  • -----
  • Posts: 716
  • Joined: 12 Sep 2010
  • Loc: Sweden

Posted 05 January 2020 - 06:44 AM

One must be very careful when estimating Betelgeuse visually. Betelgeuse is a very difficult star to estimate visually because it is bright, its reddish color (Purkinje red flag!), it's normally small variability range (normally less than a magnitude), comparison stars are relatively far and are of different color than Betelgeuse, and also lies normally pretty low over the horizon which brings atmospheric absorption effects (that affect stars at different altitudes and different colors differently). It is fun to estimate Betelgeuse in such fun times, but as a rule stars like it are best left to photometric methods.

 

As a visual variable star observer I rejoice in the fact that Betelgeuse has brought the attention of many other observers to variable stars. I nevertheless will like to remind any new variable star observers out there that there are limits and pitfalls in visual observation. For example, reports of visual estimates with two significant digits are unrealistic. Please, read AAVSO's manual for visual observers, it is full of interesting material and guidelines.


  • Shine, Rich (RLTYS) and Astrolog like this

#66 flt158

flt158

    Apollo

  • -----
  • Posts: 1,210
  • Joined: 11 Aug 2014
  • Loc: Dublin, Republic of Ireland

Posted 05 January 2020 - 09:38 AM

One must be very careful when estimating Betelgeuse visually. Betelgeuse is a very difficult star to estimate visually because it is bright, its reddish color (Purkinje red flag!), it's normally small variability range (normally less than a magnitude), comparison stars are relatively far and are of different color than Betelgeuse, and also lies normally pretty low over the horizon which brings atmospheric absorption effects (that affect stars at different altitudes and different colors differently). It is fun to estimate Betelgeuse in such fun times, but as a rule stars like it are best left to photometric methods.

 

As a visual variable star observer I rejoice in the fact that Betelgeuse has brought the attention of many other observers to variable stars. I nevertheless will like to remind any new variable star observers out there that there are limits and pitfalls in visual observation. For example, reports of visual estimates with two significant digits are unrealistic. Please, read AAVSO's manual for visual observers, it is full of interesting material and guidelines.

Are apochromatic refractors better at estimating magnitudes of red and orange carbon stars, DHEB?

Do they lessen the severity of the Purkinje Effect?

I would be delighted to know your opinion on that.

 

Clear skies, 

 

Aubrey.  



#67 DHEB

DHEB

    Viking 1

  • -----
  • Posts: 716
  • Joined: 12 Sep 2010
  • Loc: Sweden

Posted 05 January 2020 - 10:05 AM

Are apochromatic refractors better at estimating magnitudes of red and orange carbon stars, DHEB?

Do they lessen the severity of the Purkinje Effect?

I would be delighted to know your opinion on that.

 

Clear skies, 

 

Aubrey.  

Interesting question, Aubrey. Honestly, I do not know.

 

I normally use the method of defocusing stars when in doubt, particularly for red/orange stars, and compare the relative brightness of the resulting star blobs. I do this in both refractor and reflector. When using my refractor (achromatic) I defocus on both ends since one end is logically redder than the other. I find this to help.

 

However, I admit I fall pray of Purkinje every now and then and over the years had to delete about a dozen reported estimates that where obviously off. I suspect a lot of people suffer from this effect as well, as one can easily see in the spread of light curves of very red stars like U Cygni and T Lyrae.

 

One must be very careful. The Purkinje effect is possibly the main problem and the bane of visual variable star observing.

 

Good luck and clear skies!


  • Rich (RLTYS) and flt158 like this

#68 flt158

flt158

    Apollo

  • -----
  • Posts: 1,210
  • Joined: 11 Aug 2014
  • Loc: Dublin, Republic of Ireland

Posted 05 January 2020 - 10:43 AM

That's an utterly acceptable answer, DHEB!

 

You probably know that I am one of the very privileged owners of a William Optics 158 mm F/7 apochromatic refractor.

It doesn't always kill false colours - I'm sure of that. 

And it has been a long time since I used a Newtonian reflector on a carbon star. 

I used to have one; but I did not know the Purkinje word during those times. 

And I didn't estimate magnitudes during those days of yore.

I simply admired such carbon stars such as T Lyrae which actually was my very first carbon star in December 2000. 

But now I do try and estimate the magnitudes of these stars. 

And I do inform www.aavso.org when I do so. 

 

Please keep up the good work on Betelgeuse, 

 

Very kind regards, 

 

Aubrey. 


  • DHEB and GalaxyPiper like this

#69 DHEB

DHEB

    Viking 1

  • -----
  • Posts: 716
  • Joined: 12 Sep 2010
  • Loc: Sweden

Posted 05 January 2020 - 10:50 AM

That's an utterly acceptable answer, DHEB!

 

You probably know that I am one of the very privileged owners of a William Optics 158 mm F/7 apochromatic refractor.

It doesn't always kill false colours - I'm sure of that. 

And it has been a long time since I used a Newtonian reflector on a carbon star. 

I used to have one; but I did not know the Purkinje word during those times. 

And I didn't estimate magnitudes during those days of yore.

I simply admired such carbon stars such as T Lyrae which actually was my very first carbon star in December 2000. 

But now I do try and estimate the magnitudes of these stars. 

And I do inform www.aavso.org when I do so. 

 

Please keep up the good work on Betelgeuse, 

 

Very kind regards, 

 

Aubrey. 

Interesting! You are then the one in a position to judge whether an apochromatic makes a better instrument for visual variable star estimates.

 

Keep observing and estimating, but you already know: it's addictive lol.gif


  • flt158 likes this

#70 Rich (RLTYS)

Rich (RLTYS)

    Fly Me to the Moon

  • *****
  • Posts: 7,001
  • Joined: 18 Dec 2004
  • Loc: Mayo (Maryland)

Posted 05 January 2020 - 11:43 AM

DHEB, read your numerous replies and total agree with you.waytogo.gif Usually light curves of very red stars show a lot of scatter.


  • DHEB, flt158 and Astrolog like this

#71 flt158

flt158

    Apollo

  • -----
  • Posts: 1,210
  • Joined: 11 Aug 2014
  • Loc: Dublin, Republic of Ireland

Posted 05 January 2020 - 12:10 PM

Hi DHEB and Rich. 

 

Can I just encourage everyone not to live in fear regarding estimating the magnitudes of any variable star?

Some amateurs have sleepless nights wondering and even worrying that they may made a fool of themselves. 

Life has enough pressures as things stand!  

We must live and learn. 

Recently I estimated a carbon star and gave a magnitude of 9.6. 

Then someone a a few days later gave the same star a magnitude of 10.5. 

 

If we make a mess of doing this task, we can always make it right the next time. 

Let's keep printing off the maps from www.aavso.org 

So let's chill out and have fun!

 

And I do agree with you, DHEB, it is all seriously addictive. 

 

Very kind regards from Aubrey. 


  • gregj888, John Gauvreau, DHEB and 2 others like this

#72 DHEB

DHEB

    Viking 1

  • -----
  • Posts: 716
  • Joined: 12 Sep 2010
  • Loc: Sweden

Posted 05 January 2020 - 12:37 PM

Hi DHEB and Rich. 

 

Can I just encourage everyone not to live in fear regarding estimating the magnitudes of any variable star?

Some amateurs have sleepless nights wondering and even worrying that they may made a fool of themselves. 

Life has enough pressures as things stand!  

We must live and learn. 

Recently I estimated a carbon star and gave a magnitude of 9.6. 

Then someone a a few days later gave the same star a magnitude of 10.5. 

 

If we make a mess of doing this task, we can always make it right the next time. 

Let's keep printing off the maps from www.aavso.org 

So let's chill out and have fun!

 

And I do agree with you, DHEB, it is all seriously addictive. 

 

Very kind regards from Aubrey. 

Ahh writing can be a difficult art too. I did not mean to be so serious. You are right, Aubrey: one must have fun above everything else. Its a hobby after all! smile.gif


  • flt158 likes this

#73 Rich (RLTYS)

Rich (RLTYS)

    Fly Me to the Moon

  • *****
  • Posts: 7,001
  • Joined: 18 Dec 2004
  • Loc: Mayo (Maryland)

Posted 06 January 2020 - 09:51 AM

I've been VSOing for almost 50 years and it's still fun!


  • Jure Atanackov, DHEB, Aquarellia and 4 others like this

#74 robin_astro

robin_astro

    Viking 1

  • -----
  • Posts: 867
  • Joined: 18 Dec 2005

Posted 08 January 2020 - 09:16 AM

As Mark Twain might have said. "The reports of Betelgeuse's death may have been greatly exaggerated". While it is true that the Visual magnitude has been dropping, the latest point in the AAVSO database in the HJ bands from 7 Jan shows it is shining as brightly as ever in the IR where most of the radiation is produced.

 

Betelgeuse_HJ.png

 

I suspect there has been a small drop in temperature of the photosphere which has produced an exaggerated effect at V mag, a region of the spectrum sensitive to temperature dependent changes in the depth of the molecular absorption bands.

 

Cheers

Robin


Edited by robin_astro, 08 January 2020 - 09:17 AM.

  • CPellier, DHEB, Aquarellia and 5 others like this

#75 CPellier

CPellier

    Apollo

  • -----
  • Posts: 1,389
  • Joined: 07 Aug 2010

Posted 09 January 2020 - 05:00 PM

Hi guys,

Here are my results using my experimental method of spectro-photometry using the Star Analyzer, 2019 (when in the winter the star was at its mean V mag) vs. 2020. Observation from January 4th shows a V magnitude of +1,51 and B mag +3,13, in coherence with the AAVSO measurements.

The first graph is a comparison between two dates in a pseudo-flux processing using Phi2 Orionis as a reference. Pseudo, because the spectrum of that star is not calibrated relating to its own true spectrum, but to the theoretical K0III spectrum. If this is not a real flux processing, none the less the evolution pretends to be correct. 

The second graph describes the BVRI magnitudes of the star using synthetic Johnson bands. 

Both graphs are showing a important decrease in emission centered in the V band, and less important toward red and IR wavelengths. If correctly measured, the difference in the I band is only half a magnitude, where in V it's slightly more than one, and this is not incoherent with the star remaining steady in brightness in the longest J and H IR bands, as Robin says.

If the photometry is correct, the star is now at a positive magnitude in the Rc band, which is probably a first!

Attached Thumbnails

  • spectro_betelgeuse_flux_20200104.png
  • spectro_betelgeuse_photo_20200104.png

Edited by CPellier, 09 January 2020 - 05:04 PM.

  • robin_astro, DHEB, Aquarellia and 1 other like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics