Skip to main content

alf Ori (Betelgeuse) - Dec 2016 spectra vs Jan 2020 spectra

16 posts / 0 new
Last post
JPM
alf Ori (Betelgeuse) - Dec 2016 spectra vs Jan 2020 spectra

Hi All, regarding the topic, I found one of my old low quality spectra of Betelgeuse, that I took back in Dec 2016. Was wondering if the spectra taken back then vs my current spectra, are able to contribute to the explanation of what is currently happening to the star. I myself can note a few differences, but don't quite understand what they are and the cause of these differences. If the spectra are useful, would appreciate if someone could assist with possible explanations. Attached, is a jpeg pic of the 3 spectra together. 

If someone is able to assist, I can email the 1D fits files of the spectra if they would like to analyse themselves. Three files - 2016 spectra (1 file) and my current spectra (2 files - blue and red side).

Equipment for Dec 2016 Spectra - 6" Dob (F6), 200L Blazed Grating, Canon 650D

Equipment for Jan 2020 Spectra - 8" Maksutof (F12), 600L LOWSPEC slit Spectroscope, ZWO 178 Cam

Thanks & Regards

Percy (JPM)

Pretoria, South Africa

 

 

 

 

Robin Leadbeater
Evolution of low resolution spectrum

My relative flux calibrated low resolution spectra are now showing a consistent trend of increasing flux around 7500 A compared with the visible region. This is consistent with the AAVSO photometry which shows constant H,J brightness with the V magnitude dropping

spectra can be downloaded here

https://britastro.org/specdb

Cheers

Robin

stellakafka
stellakafka's picture
cool spots ... maybe?

Indeed, what you see in both data sets is a change in the spectral characeristics of the star in the red due to a cooler atmosphere. Makes it look liek it is of a later spectral type. This is consistent with the leading theories for this dimming - a large spot (coincidence of the two spot cycles) or perhaps dust. 

Very nice!

Best wishes - clear skies,

Stella.

Robin Leadbeater
change in spectral type

Yes indeed. The change to a later type (perhaps M2 to M3.5/4) was already apparent from the depth of the TiO bands in the visible region in the earlier spectra compared with pre dimming.

https://www.aavso.org/comment/67858#comment-67858

No further increase in the TiO depth in the visble region is evident in this set however, (though it may be too small to detect.) The change further into the IR though shown in these spectra suggests  that the trend is still continuing currently.

(I thought the brightness cycles were believed to be due to pulsations rather than spots

http://www.astronomerstelegram.org/?read=13410  )

Cheers

Robin 

stellakafka
stellakafka's picture
Verdict is still out!

Verdict is still out!

 

The star is not a pulsator, the cycles are due to convective cells in the star's atmosphere. Thing sunspots byt waaaaay more intense. Computer simulations showcase these convective motions that result to dark/bright spots - chech this out: https://www.astro.uu.se/~bf/publications/2015_10_24_Uppsala_Astronomdagarna/Talk/index.htm

 

Having said that ... competing theories claim that this is a dust event (Betelgeuse is known to have extensive features/plumes). So, until the event is being competed and the data are being analyzed, we truly don't know.

 

One thing is certain: there is no theory that connects this dimming with a SNe erruption. Although it would be spectacular, no?

 

Best wishes - clear skies,

Stella.

MFR
The Spectra of Betelgeuse

  On February 17, 2020 at 0:38 UT. I have obtained a low resolution of Betelgeuse's spectra by using a Rainbow Optics grating filter cell. It was taken through a ten-inch MEADE and the grating cell filter was attached to the DMK 21AU61.AS B&W camera. Also, I blurred a bit during imaging and I stretched the spectra vertically so the absorption bands can be seen easily. It was stacked in Registax 6. This is very close to raw image so not much processing was done. I do have the software where I can make a row intensity line with graph like but it is in my old computer. The wavelength is identify by Angstroms.This is my first shot of Betelgeuse's spectra so I can compare it with more images in the near future.

 There are many absorption bands. It is tough to identify each one them but I can name them few as I was using the references. The Red Supergiant like Betelgeuse which is a M2 spectral type star contains many molecules and some strong Titanium Oxide (Tio). According to the references, you will see a faint sharp band which is the H-Alpha line. It is very faint in many M-type stars. You will see other bands like 0 II (oxygen) and it absorbs by our atmosphere. Also, many Tio bands.

  Best,

     Frank J Melillo

    Holtsvile, NY

   

  

 

Bikeman
Bikeman's picture
Simulating dust with transmission curves?

Hi!

Ok, I'm still a beginner with this so this might be a dumb question:

Is there a way to simulate the influence of dust on a spectrum quantitatively ? My (very limited)  understanding is that the transmission of light thru dust depends mainly on two things: grain size and column density, where the grain size changes the spectral transmission curve and the density is influencing the extinction depth, so I guess grain size is actually the crucial thing here. So... if there were a set of transmission "spectra"/curves for different simulated types of dust, wouldn't that allow us (e.g. using the "math on series" feature of Rspec) to see if an observed spectrum can be explained by a combination of  a second spectrum (reference spectrum or previously observed spectrum) times the dust transmission curve?

E.g. when I look at Robin's spectra at the BAA site (or my own first attempts with a Star Analyser), then they match quite well with reference spectra overlays except for an "IR excess" .. which could also mean it's really an extincted spectrum everywhere else *but* in IR. I guess you get the idea of trying to fold in the influence of dust quantitatively. Basically like a dust reference library...sort of. Does that make sense?

CS

HB   

Robin Leadbeater
IR excess ?

Note my spectra are in relative flux scaled at the V band so the increasing relative flux in the Red/IR is not neccesarily an indication of an IR excess as the V mag was dropping during this period. In fact the photometry shows the brightness in H,J has remained constant thoughout. There has therefore been a shift towards longer wavelengths but that would be consistent with cooling, which is also supported by an increase in the depth of the TiO bands.  From what I can see, the low resolution spectra in the visible range appear to be consistent with a cooling of the photosphere. The new image of the stellar disc from ESO taken in December does appear to show a partial obscuration of the stellar disc though so perhaps we are seeing a combination of the normal cycle plus a dust event which has deepened the normal cycle ?

Cheers

Robin

Robin Leadbeater
Dust extinction

Extinction is dependent on the characteristics of the dust and local heating can produce IR emission from the dust but  for a general description of techniques which can be used to correct amateur spectra for interstellar dust extinction  I can recommend David Boyd's SAS workshop  "scientific analysis of amateur spectra" the top item on the BAA website here

https://britastro.org/node/19378

Cheers

Robin

Bikeman
Bikeman's picture
Thanks

Thanks Robin, that workshop material is very interesting indeed. This refers to interstellar dust, but I guess it's applicable to circumstellar dust as well, with a few more complications perhaps.

To clarify, by "IR excess" I was referring to the naive observation that when you enable the reference spectrum overlay in the britastro.org/specdb/ plotting dialog, you get a pretty perfect match in visible wavelength but for > 700 nm, the measured low res spectra of alf Ori exceed the reference one, but of course, as I wrote, you could also scale up the reference spectra to match in IR instead and get an extinction below 700 nm, which might be part of what is really happening here.  

CS

HB

Robin Leadbeater
absolute flux calibration

Rescaling the spectra in absolute flux rather than relative flux would give the complete picture.  This would be possible since we have the V magnitudes from the AAVSO database (also covered in David's tutorial)

Cheers

Robin

JBD
JBD's picture
Of course, I do not yet

Of course, I do not yet master all the finesse of the treatment, but I tried to compare 3 spectras from December 2019, January 2020 and last night, February 17.​
By reading the causes and the verdict of the phenomenon "Betelgeuse" and knowing that its cycles is 423 days (cycles who should end around February 27, 2020), knowing also that it has always varied radially but also not-radial (personally, I can almost see it on the ESA comparison photos (https://www.universetoday.com/145011/betelgeuse-is-still-dimming-and-we-... prove-it /))

Knowing its environment of dust which it picks up and which can cause its spectacular variation ... As Stella wrote, Does Betelgeuse still deserve its Semi-regular late-type (SRC) classification?
https://aavso.org/vsx/index.php?view=detail.top&oid=24710

Best regards,

MFR
Re: The Spectra of Betelgeuse

I have attached the line intensity of Betelguse spectra on February 17, 2020 at0:38 UT.

Bikeman
Bikeman's picture
Hi res pro spectrum

This should be a great source to compare your own stectra to:

http://www.astronomerstelegram.org/?read=13525

I had a bit of a problem loading this into Rspec because this is just so hi-resolution/huge, but binning by 10 rows did the job.

Note tho that this doesn't extend into NIR, it goes up to 691nm only.

Cheers

HB

 

bskiff
alf Ori (Betelgeuse) - Dec 2016 spectra vs Jan 2020 spectra

Emily Levesque and Phil Massey have analyzed a recent spectrum in comparison to an earlier one in an astro-ph post, now accepted for the ApJ Letters:

https://arxiv.org/abs/2002.10463

Betelgeuse Just Isn't That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse

They suggest that large dust grains have formed to produce the strong dimming without changing the color or temperature of the star.

\Brian

Robin Leadbeater
not gray

Hi Brian,

The dimming was definitely not grey if the photmetry is extended into the H, J bands where there was effectively no dimming and there is even signs of a red excess in the optical spectroscopy. Would large grained dust be consistent with this ?

Cheers

Robin

Log in to post comments
AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484