Tue, 12/24/2019 - 11:25
Surely, you have noticed that Betelgeuse is fainting. Although this is not unusual for this irregular star, this seems to be a deeper "dip" than in previous years. Spectra are strongly encouraged, all resolutions and all wavelength ranges, as we try to follow the phenomenon with all means possible...
Thank you in advance for your consideration!
Best wishes - clear skies,
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
Based on low resolution spectra (ALPY600 R~520) the change in the visible spectrum appears to be quite subtle (equivalent to a change in spectral class from M2 to M3.5 say based on the increase in TiO absorption band depth, much in line with Atel#13365)
Also nothing obvious in high resolution R~11000 echelle spectra
Spectra available from the BAA database
IR band measurements where most of the flux is could be interesting.
I see there is now a recent H,J point in the AAVSO database (The first for over a year)
It shows that Betelgeuse is not fading in the IR where most of the flux is so I would venture to suggest there has not been any significant drop in bolometric luminosity, just a small drop in temperature which has produced an exaggerated effect at V mag, a region sensitive to changes in the depth of the molecular absorption bands.
I grabbed another spectrum last night using the ALPY200 faint object spectrograph (Not the best target for this instument but that was the setup I was using at the time. It saturated in just 0.3 sec so I had to average about 50 exposures beat down the scintillation ! ) There has been no change in the visible region at low (R~130) resolution over the past 10 days. (Yes there really are two spectra in the graphic, they overlay almost exactly) Spectra in the BAA database.
Thanks for taking the data. I would appreciate it if you could also upload them to the AAVSO spectroscopic database, as this is where data are being retrieved by the professional astronomers who are interested in the star, and would be gret if they would use your spectra too.
I am attaching a screenshot of the latest light curve. Betelgeuse seems to be dimming more ... maybe?
Please keep observing!
Best wishes - clear skies,
All my spectra are uploaded to the BAA database as it started up before the AAVSO database and is also accessible by professionals and amateurs. Perhaps you could point interested parties there
I would prefer not duplicating the uploading of data. Perhaps the AAVSO could mirror the BAA data as is done for the variable star data ? Since both conform to the BeSS standard perhaps this should not be too difficult ?
We are not taking data from the BAA database to include in ours, as they ar enot validated. Indeed, it wouldn't be diffucult if we all had the same standards...
Best wishes - clear skies,
The BAA moderate new observers and mentor to achieve good quality and then trust observers to produce good quality data. This is the same as BAA and AAVSO do with variable star photometry/visual brightness data for decades. As far as I can see there is no published specification for spectra to "pass" the AAVSO standard (SNR, wavelength calibration accuracy, artifacts?) so it is not obvious what validation actually means. I dont understand why AAVSO have decided to take a different approach with spectra.
(Too many threads on the same subject !)
This is part of out new internal policies we have on new databases - same with exoplanet: validate every single data point that is being submitted (in line with BESS). Advertised when the databases opened. Photometry is a little mroe complicated b/c of long history...
I am certainly open to relevant discussions with the BAA leadership, but this is not the point of this forum conversation...
Best wishes - clear skies,
Here is my Betelgeuse spectra from 22 & 24 January 2020, shot with the Alpy600(22Jan20) and the LISA-IR(24Jan20):
All identified spectral lines are tentative. (These were uploaded as Visual and IR spectra to the AASVO spectra database).
Photo by L.A.R. Araujo (no. 2590) (2020/01/25/02/46)
I separated the 2 images (Bellat and Betelg ) of the same photo (2590) and put them side by side on a program (Frontpage)...for I can compare the images of 2 stars.
It seems me that here Bellatrix is more brilliant than Betelgeuse!
This is the combined image!.
The low resolution spectrum has continued to evolve further since 2020-01-18, following the same trend noticeable in the red around 7400A (The spectra are in relative flux, scaled to 1 in the V passband)
I was alerted by James Foster on the ARAS forum to possible changes in the strength of the H alpha absorption line. Comparing my medium resolution ( R~5500 ) spectra for this region for 2019-12-28 and 2020-02-04, there has indeed been a reduction in the line strength between the two dates.
The low resolution spectrum looks to have returned to how it was at the start of the year
...and here is the 4-day binned AAVSO V light curve. Spot on!
I notice a steady string of visual observations in the database for Betelgeuse since May. Presumably these must daytime observations. With something like a single-channel photometer accurate measurements would be possible with some care. Complete phase coverage for Mercury and Venus were obtained this way in the 1950s. But how would you do them visually?
I believe the observer lives in Victoria, Australia (S.E. of Melbourne). For his observation of Betelgeuse on 2020 June 12th at 07:50 UT, Betelgeuse is 6.4 degrees high and the Sun is 9.5 degrees below the horizon.
I had only a passing interest in Betelgeuse until it was suggested for inclusion in the revent LPV webinar. Its reappearance in the form area led me to look at the spectra and comments here. The comment that it has not faded in H and J is incoreect - both these show it is fainter than in the past two declines with approximately the amplitude normal at these wavelengths. The phase of minimum matches well. Allen's AAQ suggests a peak temperatur for an M2 supergiant at about 8000 Angstoms but Foster's spectrum suggests it might be a lower temperature at a longer wavelength. But I know little about the interpretation of spectra exept that I would imagine it's best to examine the region of the peak radiation wavelength. I note that each of the last four minima have been deeper than the previous one.
I made a casual comment about the B-V colour curve in that webinar as being, perhaps, indicative of a hotter companion and was rather startled when Tom Calderwood drew my attention to papera by Karovska and others postulating at least one companion. At three of four magnitudes fainter the light would only be 2% to 6% so it would be difficult to see in a spectrum but those shown in this forum seem to have a brighter short wavelength tail than I would naively expect.
There were a few U measures as well and when combined with B to produce a B-V curve they also supported the idea of a companion. So for those of you with conventional PEP UBV equipment, SSP3 or SSP5, measures in UBV to provide V, B-V and U-B over a couple of cycles might show something.
"The comment that it has not faded in H and J is incoreect - both these show it is fainter than in the past two declines with approximately the amplitude normal at these wavelengths."
The comment was correct at the time for this fading. It was based on the first measurement published in these bands for this fading (as there were none for that season up to then) and it showed that the unusually deep fade seen in V was much less pronounced in the IR. (I did not comment on if that was typical or not of previous fades as the data for those bands appeared to be too sparse to be sure.) The subsequent coverage during the recovery does indeed show that there was a likely a fading of ~0.1 magnitudes in H,J, less than 1/10 of that in V. The point I was making at the time was that V magnitude is not a good indicator of total luminosity in cool stars and the claims in the popular press around that time that Betelgeuse had become less than half as luminous as normal were a gross exaggeration.
RE:".... The point I was making at the time was that V magnitude is not a good indicator of total luminosity in cool stars and the claims in the popular press around that time that Betelgeuse had become less than half as luminous as normal were a gross exaggeration. "
I concurr, many of the M and Carbon stars I observe with the Alpy600 are rather inconspicuious, but very prominent in my LISA-IR spectra; sometimes the carbon stars have almost no continuum shorter than 5500A!
RE:" The phase of minimum matches well. Allen's AAQ suggests a peak temperatur for an M2 supergiant at about 8000 Angstoms but Foster's spectrum suggests it might be a lower temperature at a longer wavelength. But I know little about the interpretation of spectra exept that I would imagine it's best to examine the region of the peak radiation wavelength."
I frequently combine Vis+IR spectra, spanning 3800-9600A. I wonder if it would be trivial to derrive the planck black-body temperature and equivalent stellar spectral type; abiet with +/- values due to intersterllar and stellar dust.
I managed to get up to have a quick look for Beteleuse in the morning twilight (July 19.48 UT). About all I would say is that it is 'bright', brighter than Aldebaran, but also clearly brighter than Mercury (V = 0.67 per JPL Horizons), which was at similar airmass. If I had to make an estimate, I'd say mv = 0.3 or 0.4. Also a very pretty crescent Moon, which made it worth getting out of bed!