Alpha ori

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

CS

HB

This thread in Twitter analyzes alpha Ori's AAVSO data, rejecting outliers. In doing so, the user says that this dimming is unprecedented. This is the direct link to processed the light curve.

http://www.astronomerstelegram.org/?read=13365

CS

HBE

Friends,

Looking at the visual data from the AAVSO database, Betelgeuse reached 2nd mag in 1985, so this current event is not unique. However, we have the chance to observe it in unprecedented detail ... so I would like to request as many observations (in as many bands) possible!

Thank you in advance for your time and consideration!

Best wishes - clear skies,

Stella.

I have V=1.281  B=3.082  on JD=2458841.7.  My data for this season show a trend of ~10mmag/day fading.

The visual~=2.0 magnitudes in 1985 are from two particular observers and are considerably outside the norm.

Brian Skiff pointed me at the attached MNRAS from 1911.  It has long-term visual estimates from two 19th century observers, Baxendell and Argelander.  I also attach VStar-compatible csv files if people want to play around with the data.  I have re-reduced (almost) all of Baxendell's data with modern V magnitudes for the comparison stars.  They show a pretty good 460-day phase plot.  Argelander's estimates cannot be re-reduced with the information provided, and his data seem messy in comparison.

The fading of Betelgeuse appears to be slowing in UBV.

Tom

AAVSO Alert Notice 690 requests photometry and spectroscopy of alpha Ori (alf Ori, Betelgeuse) during and beyond its current minimum. Please see the notice for details and observing instructions.

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ

Dear all,

Thanks a lot for this observing campaign. We got Betelgeuse data on VLT/SPHERE and soon on VLTI/GRAVITY. We are currently looking at the possibility of observations with other instruments. I would like to emphasize the necessity of monitoring at other wavelengths than V (most interesting would be R, J, H and K).

Clear skies to all !

Miguel

See attached.

Tom

Dear observers,

even when Betelgeuse seems to be already rising now, due to all the attention it has been receiving, we considered it a good time to update the 10 Star Tutorial charts.
Since comparison stars are widespread over a large area, observers in the different hemispheres may find it useful to have comparison stars higher in their skies so there are two version of the charts, one for the Southern hemisphere (including eps CMa which at V= 1.50 is very useful now) and another one for the Northern hemisphere (which also works to estimate eta Geminorum).
You can download them from here:

https://www.aavso.org/10-star-training

VSP is not useful to create charts for Betelgeuse due to its limited field of view so these charts are recommended.
A list of accurate V magnitudes for the comparison stars follows:

01 bet Ori  V= 0.13* (Rigel)
04 alp CMi V= 0.36  (Procyon)
09 alf Tau V= 0.87*  (Aldebaran)
11 bet Gem V= 1.14 (Pollux)
15 eps CMa V= 1.50 (Adhara)
16 alp Gem V= 1.58 (Castor)
16 gam Ori V= 1.64 (Bellatrix)
18 zet Ori V= 1.76* (Alnitak)
19 gam Gem V= 1.93 (Alhena)
21 kap Ori V= 2.06* (Saiph)

* only for visual use. Small amplitude variables:

bet Ori - ACYG V= 0.08 - 0.20
alf Tau - LB: V= 0.86 - 0.89
zet Ori (NSV 2553) - VAR V= 1.74 - 1.77
kap Ori (NSV 2641) - ACYG V= 2.04 - 2.09

Remember this chart is only for visual use.

Unfortunately we don't have stars with the same colours of the variable, we have to use what is available.

Good observing and keep an eye to see if Betelgeuse is going to recover smoothly or not from this fading!

What about Betelgeuse chart ID? Robert Stalnaker (thanks Bob!) called our attention regarding this.
People using the 10 Star Tutorial chart have been providing the chart ID "10 Star" or "10 Star Tutorial". That's fine but now that a slight change has been made, it would be a good idea to call the new chart something like "10 Star 2020" so we know the new version is in use.

Another interesting question came up when talking about the rounded labels provided in visuals charts like this one.
For decades visual observers have been using the rounded values provided in the charts to make their estimates. We did not have photometry tables back then (and we don't have one for special charts like these, that's why I provided V values here) . It's been only a few years since photometry tables have been implemented through VSP.
Is there a reason not to use the photometry table values to perform estimates? I don't think so. I would encourage people to do it.
This chart showcases a couple of examples.
Elnath (bet Tau) was removed as a comparison star because it has V= 1.66 while Bellatrix has V= 1.64. They are placed towards the same side of the variable and were thus redundant. Their magnitude difference was 0.02 mag. instead of the 0.1 mag. implied by their rounded values.
Another example: Alnitak (18) has V= 1.76 while Bellatrix (16) has V= 1.64 as mentioned above. The difference is 0.12 and not 0.2 mag.
So rounding off values -as I see it- is just a useful practice for labelling and not filling up the charts with numbers. Also useful to identify comparison stars*. But there is no reason I can think of not to use the accurate V values to reduce the estimates. We haven't talked about using the photometry table values to reduce the visual estimates. Maybe it's time to do it.

*This chart also shows a situation that we have solved in the past by adding an uppercase letter to the lable: when we have two stars with the same rounded magnitude in the sequence.
In this case, especially for Northern observers, having Castor and Pollux so close to each other may make it useful to use Castor when the star is between 1.1 and 1.6. For Southern observers, Adhara and Bellatrix will be much better when the star is 1.5-1.6 (like right now!). So we have two "16" stars.
For now, the solution is labelling Castor as 16N and Bellatrix as 16W.
Some time in the future maybe we could think about giving two decimal places for chart reports to avoid this. But do not complicate things unnecessary right now!

Several AAVSO contributors have posted an ATel in the last few hours suggesting that Betelgeuse has gone through a shallow minimum in recent weeks, and is brightening again:

http://www.astronomerstelegram.org/?read=13982

The AAVSO record is rather sparse and scattered.  It seems that reliable photoelectric or other properly-calibrated photometry against similarly red stars is necessary at this point.

\Brian