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Hi Robin,
The quick posts are just designed to be text. A nice idea but for that kind of featured post I suggest using the forum as you already do.
Best wishes,
Andy
Thanks for sharing this Robin. When I first looked on the AAVSO database there were no recent IR measurements, it is great these have been added.
I agree this implies a cooling rather than a change in total luminosity (bolometric).
It is possible the star may have expanded a little rather than contracted as I have seen some saying, to explain the cooling. Though that is pure speculation on my part. A more detailed analysis of the existing data and ideally additional spectra in the IR would help to tie down the change in bolometric luminosity and temperature, to then understand if it has changed size.
Cheers,
Andy
Betelgeuse is a cool red star with the majority of its flux in the red and infrared, while the majority of observations are visual or with a V filter. It occurred to me the widely discussed drop in luminosity is based on the assumption that what is happening in the visual represents the total luminosity of the star, and this might not be the case. I decided to do a little investigation using spectra from the BAA Spectroscopy Database and V filter magnitudes from the AAVSO International Database to do a rough flux calibration of the spectra.
My first plot shows what passes through a V filter using James Foster’s spectrum from 9th April 2018. You can see the V filter is most sensitive to wavelengths where Betelgeuse is not at its brightest. The V filter is approximately like human vision, not a perfect match but reasonable. You can also see how the flux continues to rise to shorter wavelengths towards the infrared.
Next I compared James Foster’s spectrum from 9th April 2018 to Robin Leadbeater’s recent spectrum from 30th December 2019. The approximate V magnitudes on these dates are 0.4 and 1.4, though due to difficulties with measuring the luminosity of Betelgeuse it is best to consider these with uncertainties of +/-0.1 magnitudes. A magnitude of 0.4 is fairly typical of Betelgeuse in recent years, noting it regularly varies by nearly a magnitude. I did a flux calibration using the V filter profile rather than any specific representative wavelength. This was to avoid any effects due to individual lines skewing the results. This shows a very marked drop in luminosity to longer wavelengths up to at least 7400 Angstroms.
Their aren’t spectra in the BAA database with longer wavelengths into the infrared due to the difficulty in making these measurements. So instead I then compared Pickles reference spectra for M2 and M4 (both at luminosity class III). These aren’t perfect matches to James and Robin’s spectra but they are good enough for a first approximation (M2 typical and M4 now). It can be seen that a drop in luminosity at shorter wavelengths in the visual region does not necessary continue to longer wavelengths, with the flux being about the same from about 8000 Angstroms. These spectra only go to 10,000 Angstroms, but give a hint of stronger flux deeper into the infrared for the cooler M4 spectrum. So I wonder whether the total luminosity has not dropped by as much as it appears. Perhaps some or most of the flux has shifted from the visual into the infrared?
Comments and criticism welcome 🙂
Congratulations Robin!
It is incredible what has become possible due to advances in technology, though it still requires great skill to reach such faint magnitudes. A very well deserved award.
Andy
Well spotted Ken. This error was pointed out in the early November eNewsletter.
A replacement page is available in the Handbook area of the website, and the online Handbook has the correct phases.
https://britastro.org/handbook
Best wishes,
Andy
Hi Robin,
It is possible and I must admit I have not checked. It would be a useful and interesting experiment.
Cheers,
AndyKevin,
I will just a bit of clarification.
Yes, you can submit clear photometry, though you should probably use CV. This means clear filter (or unfiltered) using V-band comparison stars. The important point here is that while your own observation might be made with a clear filter, the comparison star magnitudes will have been made through a V filter, or at least you should try to obtain V filter magnitudes from the BAA or AAVSO charts.
The full list of filters can be seen near the bottom of the review observations page of the BAA Photometry Database. Note as far as possible we try to stay in-line with the AAVSO on filters and filter codes. This makes life easier when combining data from different databases.
https://britastro.org/photdb/data.php
If you have a spare slot in the filter wheel, it might also be worth trying truly unfiltered observations, as for some targets a slightly higher signal may be preferable to a luminance filter.
Best wishes,
Andy
BAA Photometry Database Manager
I have created an page for the Armagh meeting in the Publications -> Downloads -> Past Talks area of the website.
https://britastro.org/downloads/19324
We have 3 talks thus far, and I shall upload anymore that I receive.
Andy
Hi Martin,
The auto-suggest does not come from the BAA website. It is actually your web browser remembering what you have previously entered into those fields and then suggesting options based on this historic input.
It would be difficult to auto-populate object name and location from the filename as we would need to agree a standard filename layout that everyone would need to use, and otherwise gibberish would appear in those fields. There would also be a reasonable amount of bespoke development by BAA volunteers to write code to extract this information from the filename and populate the fields, assuming it is possible.
Sorry it is not better news.
Best wishes,
Andy
Hi Eric,
I am sorry to read that you are unhappy about your posts being publicly visible. While only BAA members can post to the forum, in common with most internet fora and other astronomy fora the posts are visible to all, e.g. SPA, AAVSO, cloudy nights, stargazers lounge, astrobin, etc. This means internet search engines like Google have access to the content, and this can be helpful when searching on a particular topic.
I would draw your attention to the BAA forum terms of use, in particular:
“We strongly advise that you do not disclose personal information to others. Do remember that the Forum and Member Pages are visible not just to BAA members, but to the whole world. If you wish to exchange contact details with other members, the Forum and Member Pages are not an appropriate place to do it.”
https://britastro.org/forum-terms
Kind regards,
Andy Wilson
BAA Systems Administrator & Web Content Editor
Alex & Nick,
You can send me the pdf’s if you want. I can create an Armagh 2019 meeting page in the Publications -> Downloads -> Past Talks area of the website.
Best wishes,
Andy
Hi Dave,
Roger has decided to step down after 20 years of excellent service as Director of the VSS. A long service for any Section Director!
It is all explained in the past few VSS Circulars where Roger announced he would be standing down. We are very fortunate that Jeremy Shears agreed to take over from 1st September.
https://britastro.org/downloads/14108
Also note that Roger is not disappearing from the VSS as he will continue on as Assistant Director. From personal experience I know how busy the VSS can be so I am sure Jeremy will appreciate the help.
Best wishes,
Andy
A tweak has been made to that webpage, so the Photometry forum is now included. It was due to an oddity in how Drupal works, meaning this forum had to be manually added.
Andy
Well spotted Eliot!
I have done a quick test moving the post between forums and I think you are correct as to the cause. I have notified the BAA Website Developer so he can investigate.
Cheers,
Andy
I understand the following eBulletin on John Wall’s cremation was not received by everyone who knew him, so I repeat it below.
I’ve just been advised by Joyce Porritt, John Wall’s partner of many
years standing, that he is being cremated next Thursday (27th June) at
12.15 and she thought some of you might like to raise a glass in his
memory?Although, John died in January 2018, he donated his body to Leicester
University and they have only just finished with it! The cremation
will be a small, private affair, organised by the University.Roger Pickard
Hi Martin,
Apologies for the time it has taken to respond. I wanted to run my own tests before replying to be sure I was giving you accurate information.
The quick answer is the enlarge button will show a larger image if the image has been made smaller to fit webpage that shows the image and associated information. Also, large images are not recorded at the original resolution in the website.
The BAA website is built using Drupal. When images are uploaded Drupal will sometimes shrink images and may also reduce the image quality to make the image file smaller. We do not consider the member pages a formal image archive for storing images, rather a place to share observations and other interesting astronomical images. A formal image archive would not compress images, but would be a large project and probably not use Drupal.
I’ve run some tests by uploading a fairly large image of the Astronomical Clock at Exeter Cathedral.
https://britastro.org/node/18461
I created both jpg and png versions of the image, though I have only left the jpg version on the website. The original image is 2008 x 2443 pixels, with the jpg version 1.28 MB and the png 5.66 MB.
After I had uploading both versions I clicked ‘expand image’ and downloaded the new image. Both jpg and png had been resized by Drupal to 1355 x 1648 pixels, with the jpg image being 246 KB and the png 2.61 MB. However, I uploaded the same jpg image twice during this process and the first time Drupal retained the original size of 2008 x 2443 pixels but reduced the image quality so it was only 530 KB.
Note, while I think this is mostly due to how Drupal works, it is possible that different browsers will give different results. I used Google Chrome on a Windows 10 computer for these tests.
Andy (member of the Website Operations Team)
Hi John,
Thanks for pointing this out.
The message about needing to login is a generic message in the ‘Downloads’ area as a lot of the content is only available when BAA members are logged in, for example the full Journal archive dating back to the first Journal in 1890. However, there is some content like the slides from this workshop where the restriction has been lifted.
I’ll add this issue to the list of development items for the website, though I am not sure if it will be possible to remove the message where the restriction has been lifted.
Best wishes,
Andy
P.S. This old message jumped to the top of the list yesterday as it was being used for some website development testing.
In case any spectroscopists have missed the announcements elsewhere, the BAA is holding a 1 day Spectroscopy Software Training Workshop on Saturday 24th August 2019 in Birmingham, UK. It will cover the 2 software packages ISIS and BASS Project. The BASS Project by John Paraskeva (author of the software) and ISIS session will be run by David Boyd.
Thanks to the generous support from both the Equipment & Techniques and Variable Star Sections of the BAA, the cost is only £5 for members of the BAA and £7 for non-members.
More details can be found at the following link:
https://britastro.org/spectro2019
Online bookings can be made at:
https://www.britastro.org/spectro2019booking
To get the most out of the session attendees should bring along a laptop with BASS Project and ISIS installed.
If there is sufficient interest then we hope to run future spectroscopy workshops on other software and topics.
Clear skies!
Andy Wilson (Workshop Organiser)
