spectro-aras.com

Hi all,

On 22 July I was able to take a spectrum of the comet c/2020 F3 (NEOWISE) in a narrow observation window (understandable in time) with the LHiRESIII and 2400 l/mm. The comet was followed on the core and the slit was positioned on the photocentric core. slit 32µm and C11 telescope on f/10. The aim was to observe the Na-doublet. An instrument response was performed on a nearby suitable star. Exposure time was 4 x 600 sec. I could not detect a doppler shift.

best regards
Erik.

Erik Bryssinck wrote: I could not detect a doppler shift.

Nice result Erik. That extends the time of Na D emission beyond my 2020-07-20 result
The comet was just about at its closest to earth so low RV (JPL Horizons gives just -0.7km/s RV geocentric)

***************************************************************************************************************
Date__(UT)__HR:MN R.A._____(ICRF)_____DEC T-mag N-mag delta deldot S-O-T /r S-T-O
****************************************************************************************************************
$$SOE
2020-Jul-22 21:30 10 24 58.63 +44 52 58.5 6.298 16.106 0.69189059531969 -0.7699724 37.3162 /T 100.6790
2020-Jul-22 21:35 10 25 02.78 +44 52 41.2 6.299 16.106 0.69188906883369 -0.7523755 37.3227 /T 100.6712
2020-Jul-22 21:40 10 25 06.92 +44 52 23.9 6.300 16.106 0.69188757763562 -0.7347802 37.3292 /T 100.6635
$$EOE
****************************************************************************************************************

Cheers
Robin

Robin Leadbeater wrote: The comet was just about at its closest to earth so low RV (JPL Horizons gives just -0.7km/s RV geocentric)

Can you see the NaD absorption lines in the scattered sunlight? These should have been shifted redward by a total of 38km/s according to JPL Horizons

Robin

NEOWISE spectrum taken by using an unusual setup : the UVEX prototype from Shelyak (I testing and evaluate) associated to a 50 microns fiber (15 m long) + a RC 10 inch telescope. The spectral resolution is very low (R=360 at 650 nm, R=590 at 400 nm because the large diameter of the fiber (equivalent to a 50 microns width slit). The spectrum (sky pollution is removed) :





The setup :





Change between high resolution (R=12000, eShel in the background) and very low resolution is nearly instantaneous.

Christian Buil

Thank Eric, for this spectra showing Na emission on July22.

We are the only one to look to that dynamic… Just discovered these 2 messages. The first is from Taiwan using Alpy and Lisa, the second is from Himalaya…

ATel 13886

Optical spectra on July 10 taken by the 20cm telescope, Aply 600 spectrograph and Atik 460ex CCD at KenTing observatory showed the strong sodium emission at 5890~5896A around the central nucleus. Follow-up observations on July 11 by the Lulin 15cm telescope, LISA spectrograph and QSI 660 CCD confirmed this identification. The sodium emission in cometary spectra is rare and only a few comets, like comet C/1996 B2 (Hyakutake), and C/1995 O1 (Hale-Bopp), showed this emission....

http://www.astronomerstelegram.org/?read=13886

ATel 13897

Optical spectra of comet C/2020 F3 (NEOWISE) were obtained on 22nd and 23rd July using the Hanle Faint Object Spectrograph (HFOSC) mounted on the Himalayan Chandra Telescope (HCT), India, with exposure times of a few minutes. HCT is located at 78:57:51E, 32:46:46N at an altitude of 4500 m… The sodium tail seen by other observers (see eg ATel #13886) is not seen in this photo. It is not very prominent in our spectra, which suggests that the Sodium feature may be short-lived and/or episodic in nature...

http://www.astronomerstelegram.org/?read=13897

Good to see such international attention.

Impressive Uvex setup from Christian..!

Thanks again for all these very interesting results.
Daniel

Attention à la date du spectre Christian car tu as mis 07 (Juillet) ça doit être Août plutôt, sinon il y aurait cette fameuse raie du Sodium (NaI) à cette date.
Merci pour tes reports.

Bonjour Etienne, effectivement cette date interpelle... Mais je profite de ton message pour souligner la qualité de ton spectre basse définition du 22/07/20 publié dans la base de donnée des observateurs de comètes :
https://lesia.obspm.fr/comets/lib/displ ... ?Num=22191
Il me semble montrer, qu'à cette date, l'émission Na était encore perceptible en basse définition. Merci de ta confirmation éventuelle.
Bon ciel,
Daniel

Oui, effectivement, il y a un problème de date, c'est bien aout et pas juillet. C'est corrigé dans les graphiques.

Christian

Erik, a very good Lhires III spectrum. I capture myself a eShel spectrum on the 21st with an equivalent resolution. I have adjusted the wavelength scale to your graph for easy comparison. Informative and excellent consistency :



I take 8 échelles spectra which clearly show the decrease of the sodium doublet. It became almost invisible on 28.8. July. The intensities in the spectrum for July 15, 8 must be taken with caution due to the presence of a bright sky background (?) :



The intensity inversion of the D1-D2 lines on July 19th is real (interesting to explain?), Which coincides with a very rapid variation of the overall intensity between July 16th and 19th. Note also the increase in the intensity of the NH2 lines in the same time.

The enlarged versions :

















(François, je vais t'envoyer ces spectres en zip, Etienne, pouvez-vous préciser comment publier dans la page du LESIA ?)

Christian

Hello,
This Na story is quite fascinating. The available measurements in low definition from July 09 to July 22. On my spectra of July24 and 26, if present, that emission is near the noise level . To better understand if this make sense, I did a quick evaluation of the relative intensity trend based on available data in low definition . Not sure I is the right thing to do but the results looks coherent…
For each spectra on the following table the measured intensity at 5160A (C2) and 5890A (Na) has been devided by the local continuum before to compute the ratio Na/C2 lines. Assuming the C2 5160 emission level is constant during that period, this ratio should give an estimation of the change in Na intensity. For easier reading the graph shows these ratio in decimal logarithm using an arbitrary formula 1.2 + log(ratio) for proper scaling.





That computed trend may explain why no evidence of the Na emission was found on low def observation of July24 and 26. Conclusion of that rough analysis may change for high resolution or better S/N measurements.

This is my first observation of a comet in spectroscopy. Hope I am not creating confusion by lack of experience. Any comment or criticism will be more than welcome.

Sources : Lesia data base (https://lesia.obspm.fr/comets/lib/all-o ... 1908&m1=01) and web screen.

Bon ciel,
Daniel