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I’ve finally got round to analysing the high resolution spectrum from 10th July. The velocities relative to sun and earth are satisfyingly close to those published by JPL Horizons
https://britastro.org/node/23284
Robin
I have indeed. (Taken with the ALPY)
I just need to get round to reducing them (I am currently just finishing off the Doppler shift calculations on the high resolution spectrum)
I have checked with the SPI team who have confirmed that their published image was mirrored so their observation now agrees with Torsten’s ie the sodium tail is anticlockwise relative to the dust tail
Robin
There’s now a NEOWISE image showing the sodium tail embedded within the dust tail.
https://psi.edu/news/neowisesodiumtail
This image is close in though so perhaps the sodium tail emerges from the dust tail further out to produce the narrow reddish tail. Not sure why it is at a larger angle than the ion tail rather than between them like Hale Bopp but perhaps that is a geometry effect ?
There has been some discussions about this reddish tail on Cloudy Nights.
https://www.cloudynights.com/topic/716780-comet-neowise-high-resolution-spectrum/?p=10332533
I wondered about sodium but the neutral sodium tail seen with Hale Bopp fell between the dust and ion tails rather than at a larger angle as here. I am wondering if it could be from NH2, the emission bands of which fall in the red region of the spectrum. Perhaps some mechanism separating ions by molecular weight, CN, C2 being heavier ?
Robin
Hi Mike,
Yep definitely a little orange image of the comet complete with tail in the spectrum there.
Hi Nick,
The sodium emission is so intense in the spectrum that I wonder if there is any sign of a sodium tail like in Hale Bopp? I hope to take a spectrum of a cross section through the tails if the weather cooperates but a narrow band image though an Na D pass filter could be interesting. Not a common filter among amateurs though I guess. The inverse filter response is more common !
Robin
This is what the spectrum in the region near the Na D lines looked like tonight at ~1A resolution. (The inset is the guider image showing the position of the slit). Note the Doppler blue-shift in the comet Na D lines relative to the sky lines
Robin
Not visible for a few days yet from the observatory so I rigged up a portable setup last night using a Star Analyser in front of a 50mm lens on an AS120mm camera, normally used as a guide camera on the ALPY spectrograph.
There is not much contrast between the spectrum and the bright sky but the sodium emission is clear.
Cheers
Robin
Now also confirmed as a Ia and so could reach mag 12 or perhaps even a bit brighter at this distance depending on extinction
I see there is a non detection by Koichi Itagaki at >mag 18.5 20200624.570 just 16 hours before the ATLAS discovery so definitely young
https://www.flickr.com/photos/snimages/50048748781/
his latest estimate 20200626.514 is 16.1 C
Hi Kevin,
Glad to hear you have cracked it
Yes the light tightness of the LHIRES leaves much to be desired ! I know several owners (me and Jack on here for example) supplement the tape with a lightproof hood over the whole thing (keeping the cameras outside for air flow)
Cheers
Robin
Another (marginal) observation of the Zeeman effect by Buil at R~30000. Also of doppler broadening/profile distortion due the to Evershed effect
Indeed. The splitting in the solar spectrum needs much higher resolution than the ALPY. It seems it is possible though with a LHIRES stopped down and using a very narrow slit giving ~R=43,000 (Christian Buil, near the bottom of the page)
http://www.astrosurf.com/buil/polar3/index.html
Cheers
Robin
Now classified as a Ia but the classifiers suggest it could be a subluminous supernova around/post maximum light rather than caught early.
https://wis-tns.weizmann.ac.il/object/2020nlb
It seems odd in that case though that it was not visible to ATLAS 2 days previously
https://wis-tns.weizmann.ac.il/astronotes/astronote/2020-126
(hopefully link not mangled this time !)
Hi Keith,
I don’t know what version of Demetra you have but I see Shelyak have just (19th June) brought out a version specifically including support for the LISA
https://www.shelyak.com/logiciel-demetra/?lang=en
https://www.shelyak.com/wp-content/uploads/20200619-ChangeLog.pdf
Robin
– Calibration – still having problems in getting Demetra to ‘automatically’ recognize the calibration image and to properly assign the right spectral line. When I use ‘automatic’ I cannot get better than 2.4 RMS, where if I go in an manually set the lines to the image (5852, 6562, 6965, 7067, 7383) my calibration gets a very good .2-.8 RMS.
Yes these automatic systems tend to either work or fail catastrophically. (I often tell the tale from my other life in paper technology where we had developed a sensor which used a neural network to measure a property using the NIR spectrum. It was trained on a range of products and worked flawlessly….. until one day it started producing compete nonsense. It turned out the manufacturer of one of the materials used in the paper had made a subtle change in the formulation which he had not told us about !)
I can’t help with Demetra, though at Francois Cochard’s zoom workshop meeting on calibration, I did promise to try it!
https://www.youtube.com/watch?v=vijEMrow0hQ
(ISIS has an automatic function which works flawlessly for me with my ALPY and LHIRES, though unlke Demetra it does need some manual input to tune it initially and you need to point it to the approximate position of one line, then it can find them all)
Cheers
Robin
Well the sensor would not have much sensitivity that far into the IR but the star in question is the bright (V mag 6.6) star V419 Cep / HD203380. It is spectral class M2i which will be about 3x brighter at 1000nm compared with in the visual so pretty bright where the filter is transparent.
Robin
As here for example
http://www.astrosurf.com/buil/filters/curves.htm#Astronomik%20Visual%20OIII
OK for visual use but most of these would need an IR block with a CCD camera
Robin
