Betelgeuse

Re: Betelgeuse

Postby Robin Leadbeater » Thu Jan 02, 2020 7:24 pm

Simon de Visscher wrote:Hi,


Olivier and I did some comparisons with his own measurement (see before), and the agreement is generally ok-ish although not perfect. Now no clue if that may come a change of the continuum global shape in 1-2 days time.


Cheers,

Simon


Hi Simon,

I suggest dividing one spectrum by the other as I did. Differences due to flux calibration errors (chromatism, focus change, extinction etc) will be a smooth curve. Real changes,for example changes in TiO absorption band depth will be obvious

You can also compare with my spectrum for 20191230 which can be downloaded from the BAA datbase
https://britastro.org/specdb/


Cheers
Robin
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Re:

Postby Robin Leadbeater » Thu Jan 02, 2020 7:50 pm

Francois Teyssier wrote:Toujours utiliser la même étoile de référence, comme tu le notes dans ton message.


With the ALPY I compared two reference stars HD38545 (A MILES Star) and HD36777 (A low B-V A2v star) and took two separate (~1min total) spectra of Beteleuse. There were small (<+-4%) differences between the two instrument responses and no measurable difference between the two Betelgeuse spectra. This gives me confidence in the accuracy of the spectrum

Cheers
Robin

_hd38545_HD36777_instresp.png
_hd38545_HD36777_instresp.png (9.65 KiB) Viewed 2388 times


_betelgeuse_telrem_20191230_969-949_leadbeater.png
_betelgeuse_telrem_20191230_969-949_leadbeater.png (7.49 KiB) Viewed 2388 times
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Re: Betelgeuse

Postby Simon de Visscher » Thu Jan 02, 2020 8:33 pm

Robin Leadbeater wrote:
Simon de Visscher wrote:Hi,


Olivier and I did some comparisons with his own measurement (see before), and the agreement is generally ok-ish although not perfect. Now no clue if that may come a change of the continuum global shape in 1-2 days time.


Cheers,

Simon


Hi Simon,

I suggest dividing one spectrum by the other as I did. Differences due to flux calibration errors (chromatism, focus change, extinction etc) will be a smooth curve. Real changes,for example changes in TiO absorption band depth will be obvious

You can also compare with my spectrum for 20191230 which can be downloaded from the BAA datbase
https://britastro.org/specdb/


Cheers
Robin



Hi Robin,

As far as I understand you are comparing spectra having the same resolution, right? In our case we were just comparing the global shape of ALPY and echelle-made spectra. Beside the average resolution difference, I suspect that the resolution changes across the spectra, if not fully under control, may lead to fake peaks/dips where slopes are steepier. I mean, it would be easier to compare to ALPYs :-)

Cheers
Simon
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Re: Betelgeuse

Postby Robin Leadbeater » Thu Jan 02, 2020 10:54 pm

Simon de Visscher wrote:
As far as I understand you are comparing spectra having the same resolution, right? In our case we were just comparing the global shape of ALPY and echelle-made spectra. Beside the average resolution difference, I suspect that the resolution changes across the spectra, if not fully under control, may lead to fake peaks/dips where slopes are steepier. I mean, it would be easier to compare to ALPYs :-)


Hi Simon,

That is why I suggested comparing with my ALPY 600 spectrum from 20191230 in the BAA database. That is very accurately flux calibrated and will be a direct comparison with your spectra. I have attached it as a zipped fits file.

The comparison of my ALPY spectrum with the MILES spectrum from 2000/2001 at slightly higher resolution than the ALPY is reliable I believe and shows a decrease in effective temperature of ~200-300K from the strength of the TiO bands ( ~1.5 points from say M2 to M3.5) That is also consistent with the results from my high resolution LHIRES spectrum and with the findings reported from 20191219 in ATel #13365 when the drop in brightness was less than it is now.
http://www.astronomerstelegram.org/?read=13365
The drop in temperature is enough to explain approximately half the drop in brightness but the radius may also have reduced due to the lower temperature so that might explain the total brightness drop seen. There is no sign of dust production in the spectrum as that would be expected to produce preferential dimming in the blue. I expect the brightness drop is just an exaggerated example of the normal pulsations but it will be interesting to see how low it goes.

The

Cheers
Robin
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Re: Betelgeuse

Postby Robin Leadbeater » Thu Jan 02, 2020 11:09 pm

Here are my ALPY600 spectrum from 20191230 (version with telluric bands removed) and the MILES reference spectrum, filtered to match the ALPY resolution

_betelgeuse_telrem_20191230_949_Leadbeater.zip
(29.22 KiB) Downloaded 108 times

betelgeuse.zip
(26.04 KiB) Downloaded 116 times
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Re: Betelgeuse

Postby Robin Leadbeater » Thu Jan 02, 2020 11:19 pm

Here for comparison is the change in Pickles spectra from M2iii to M3iii . Note the similarity to the change between my spectrum and the MILES spectrum from 2000/2001
download/file.php?id=6488
Betelgeuse_pickles.png
Betelgeuse_pickles.png (12.97 KiB) Viewed 2375 times
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Re: Betelgeuse

Postby Simon de Visscher » Fri Jan 03, 2020 9:38 pm

Hi Robin,

Ok now I got it! I'll do the exercise, thanks a bunch for the suggestion!

Cheers,

Simon
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Re: Betelgeuse

Postby James Foster » Wed Jan 08, 2020 7:52 pm

Here is my stitched spectra data of a ORI from my Alpy600(Atik414ex), 01Jan20 & LISA-IR(Atik460ex) on 06Jan20:
Image
I see a couple of dips in the IR CaII bands. I've been dodging the storms here in SoCalif, so my spectra have much
more H2O vapors than when I shoot from hifgh and dry Mt. Pinos, CA.

James
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Re: Betelgeuse

Postby Robin Leadbeater » Wed Jan 08, 2020 8:29 pm

It is interesting to see that far into the IR. There have just been a pair of H,J magnitude values added to the AAVSO database (The first for over a year)

Betelgeuse_HJ.png
Betelgeuse_HJ.png (38.89 KiB) Viewed 2255 times


It shows that Betelgeuse is not fading in those IR bands where Betelgeuse is much brighter
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Re: Betelgeuse

Postby James Foster » Wed Jan 08, 2020 11:04 pm

To: Robin,

RE:"It is interesting to see that far into the IR."

Yes that why I like the LISA in IR mode and probably won't reconfigure back to Visual mode for the foreseeable future. LPV stars I used
to ignore getting spectra for get more interesting in the 7400-9600A band. T-Tauri and other young stars show nice IR CaII triplet lines as well.
I'm going to collect my 1800/2400 l/mm GRAT spectrum in UV Cak & Ha I've been taking every 5-7 months on alpha Ori and see if there any drastic
changes there as well.

James
James Foster
eShel2 (under development-1/3)
Lhires III (2400/1800/600 ln/mm Grat) Spectroscope,
LISA IR/Visual Spectroscope (IR Configured Presently)
Alpy 600 with Guide/Calibration modules and Photometric slit
Star Analyzer 200
James Foster
 
Posts: 390
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