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comète 46p/wirtanen Alpy600 T400

PostPosted: Fri Dec 07, 2018 6:55 pm
by Dubreuil Pierre
bonsoir à tous

Hier soir, imagerie et spectres pour la comète du mois, 46P/wirtanen à l'observatoire Amateur de Calern (06 Fr).

Telescopt T400, Alpy600 caméra Atik 314L+

Comete 46P_20181206_pierre dubreuil.png
46P/wirtanen au T400 O.C.A. Calern

A suivre


Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Sat Dec 08, 2018 8:38 pm
by Robin Leadbeater
Hello Pierre,

I was also thinking of trying this comet but you got it, congratulations!
It must be a difficult target because it is so diffuse. How did it look in the guider ? How did you guide ? How did you subtract the background ?


Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Sun Dec 09, 2018 12:08 am
by Hubert Boussier
Bonsoir Pierre,

Je vois que tu prends goût aux comètes ;) .
46P Wirtanen est pratiquement au plus proche de la terre, il fallait en profiter, nous en avons fait un spectre au même moment : ... ?Num=20132

Cette fin d'années est riche en comètes, il y en a eu trois ou quatre faisables avec des "petits" télescopes : 46P, 64P, 38P et C/2018 V1 (Machholz-Fujikawa-Iwamoto).

Robin ==> It was not so difficult to guide with a Atik 314L, 8s of exposure time, the comet core is quite condensed. I did subtract the background like I do for a star, but staying away (30pixel) from the comet.
After reduction data reduction, I divided the 46P spectrum by a spectrum of the moon light taken a few days before, this did not change drastically the shape of the spectrum.

Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Sun Dec 09, 2018 8:25 am
by Dubreuil Pierre
hello Robin, Hubert

I join Hubert for the guiding , not easy but feasible with times of poses for the guiding camera of several seconds (8s in our case).
In my spectrum we can see Halpha! but I did not subtract the solar spectrum.

Je vais envoyer le FIT du spectre à François Teyssier pour le déposer dans la rubrique qui va bien.



Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Sun Dec 09, 2018 1:52 pm
by Robin Leadbeater
Excellent ! Thank you both

I will try it tonight if it stays clear


Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Mon Dec 10, 2018 12:45 am
by Robin Leadbeater
A raw spectrum image (9x300s) from this evening taken using the Celestron C11 and ALPY 600

Comet 46P-Wirtanen_20181209_ALPY600_9x300s_raw_crop.jpg
Comet 46P-Wirtanen_20181209_ALPY600_9x300s_raw_crop.jpg (148.45 KiB) Viewed 5196 times

It shows the very condensed (almost stellar in appearance) dusty? central region, which appears to be dominated by the spectrum of reflected sunlight. (A solar analogue reference star was also recorded to attempt to extract the comet spectral signature in this region)

The diffuse outer region of the coma which extends well beyond the length of the slit (6 arcmin) shows clear Swan and other molecular bands, along with many sky lines from air glow and artificial light pollution. (which hopefully can be subtracted using separate sky measurements a couple of degrees away from the comet)



Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Mon Dec 10, 2018 3:36 pm
by David Boyd
Here is a spectrum of comet 46P taken last night Dec 9.908 with a LISA on a C11. Total exposure time was 3000 sec.The spectrum was integrated in the Y direction over 27 arcsec on the sky which is approximately 3x the FWHM of the bright central region of the spectrum. Sky subtraction regions were approx 3 arcmin away for the comet so although they will contain some light from the coma this is relatively faint at that distance and so should not significantly reduce the intensity of the central spectrum. Response profile was obtained from HD28978 which was at the same altitude as the comet.
Comet_46PWirtanen_20181209.908_D.Boyd.png (36.65 KiB) Viewed 5148 times

I have tentatively identified the most prominent lines using the table in Brown et al., Astronomical Journal, 112, 1197-1202 (1996). Although there is also an emission line from NH2 at 6300A, most references appear to attribute the very bright line at that wavelength to [O I].


Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Mon Dec 10, 2018 10:12 pm
by Robin Leadbeater
Here are my reduced spectra.

C46P_20181209_876_Leadbeater.png (54.28 KiB) Viewed 5112 times

The diffuse coma integrated along the slit above and below the bright condensed region between 15 and 105 arcsec from the centre. Since the coma extended beyond the length of the slit the sky background was measured separately and subtracted. All the usual molecular components are there. Additionally CN, is particularly intense in the UV beyond the range of David's spectrum but no obvious Sodium.

The bright central region (6 arcsec diameter), again with the separately measured sky background subtracted showing the same emission components seen in the outer coma superimposed on a continuum spectrum with absorption lines.

C46P_20181209_876_solar_analogue.png (51.68 KiB) Viewed 5112 times

The overall shape of the continuum and the absorption features match that of the solar spectrum (here compared with a solar analogue star taken the same night), though there appears to be a lack of flux from the comet around 4000-5000A ie the reflected light from the comet is deficient in the blue part of the spectrum


Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Mon Dec 10, 2018 11:12 pm
by James Foster
Here is my spectra of the comet taken from Mt. Pinos, CA (elevation 2500meters) at very low altitude on 12Nov18:
All identified spectral lines are speculative. I may try to shot it from the city when its elevation is higher, but my
site at Mt. Pinos has over a foot of snow so no "dark sky" spectra possible. So far the December spectra of Comet Wirtanen
taken by Robin and others looks great!


Re: comète 46p/wirtanen Alpy600 T400

PostPosted: Tue Dec 11, 2018 11:52 am
by Terry Bohlsen
I also had a try t obtaining a spectra.
This was from the zenith but with some hazy cloud around.
I could not remove the sky background as this was too contaminated with the coma of the comet.
_46p-wirtanen_20181204_457_TBohlsen.png (9 KiB) Viewed 5056 times