Pan-STARRS comet spectrum

[Paolo Berardi]

Hi Martin, thank you very much for detailed geometric analysis and observations. I planned to go back to the observing site (finding similar conditions) and try to take a sequenced spectra of sky (fixed point at 5-7° above horizon with Sun related azimut) covering (I hope) a very similar geometry of 16 and 21 march observations but without comet. Bad weather is a real problem now because if a lot of time passes, Sun azimut move toward north where I have a high mountain obstruct the horizon.

I don't think there's any evidence of the Na emission, but maybe the Sun is to low at that time?

Lars, I don't understand if you refer to telluric sodium that, being an emission source over the entire field, is undetectable with slitless spectroscope like SA100.

Another topic we are discussing on Staranalyser Y group is the sodium tail image, well visible in Rob Kaufman SA100 spectrum (from Australia) but not appreciable in Lars spectra. For this I suppose is due to much larger comet image and a decreased sodium emission. Concerning the last aspect, Robin suggests to measure EW that I find a -50 value on my Lhires III spectrum of 16 march, normalizing on continuum around peak. I don't know if it's correct, should I normalize on the sky background?

Ciao
Paolo

[Robin Leadbeater]

Another topic we are discussing on Staranalyser Y group is the sodium tail image, well visible in Rob Kaufman SA100 spectrum (from Australia) but not appreciable in Lars spectra. For this I suppose is due to much larger comet image and a decreased sodium emission. Concerning the last aspect, Robin suggests to measure EW that I find a -50 value on my Lhires III spectrum of 16 march, normalizing on continuum around peak. I don't know if it's correct, should I normalize on the sky background?

Ciao
Paolo

Hi Paolo,

My idea was to measure the EW relative to the continuum (After removal of the sky background and division by the solar spectrum)
Lars, if you did the same for your spectrum we would get a comparison of the strength of the emission relative to the reflection continuum.
The continuum flux is of course also dropping with time but perhaps some photometric brightness estimates from elsewhere could be used to approximately correct for this to get a true measure of any change in Na emission strength.

Thinking about it more though, the slit spectrograph shows the relative values of reflectance and emission for a particular slice of the comet but the slitless spectrum integrates the reflection and emission components over the whole region so perhaps the comparison is not that meaningful after all



Cheers
Robin

[Paolo Berardi]

Yes Robin, mine is sky background removed and sun divided. Since remained a "bump" on the left side of continuum and a little lower level on the right I adjusted it dividing by extracted continuum:



Hope is a correct procedure.

Ciao
Paolo

[Lars Zielke]

Lars, I don't understand if you refer to telluric sodium that, being an emission source over the entire field, is undetectable with slitless spectroscope like SA100.

Of course, you're right, - I got lost in my idea on how to measure it.

When that's the case, isn't it correct to assume that the emission only can originate from a "point" source like the comet and not from a Na flash, since it is slitless spectroscope.

[Paolo Berardi]

Lars, when talking about slit and slitless spectra, like here, it's easy to get confused. The same also happened to me...

I think it would be interesting if you showed also here your processing with the isophotes, where you see clearly zero order comet tail. What CCD camera did you use? I notice on your bidimensional spectra there is a lot of energy in green spectral range while on mine the predominant part is in red. Perhaps the different airmass value (for 5 or 10° above horizon target) impacts a lot.

Ciao
Paolo

[Lars Zielke]

Hi Paolo

The data isn't good enough, I don't have a zero point on the tail. Even the comet "core" is to big for good wavelength calibration, so after a rough first zero order calibration with the dispersion from my ref. star, I identified the Na line and recalibrated with the Na 5893 line as the reference wavelength. That seems to fit very well.

I used an old Atik 320E mono (Sony ICX274) in 2x2 binding.

Cheers
Lars

[Lars Zielke]

Hi there

After a nice Easter dinner with family I got some data this evening. A very fast data reduction on some of the images shows the Na emission. More data will follow.

http://www.nightsky.dk/Astronomi/comets ... cal_na.jpg

[Paolo Berardi]

Very good Lars! Sodium emission is still considerable. Please show us the final profile and related 2d spectrum. Concerning tail in spectrum, there is another interesting observation performed by a japanese amateur with grating (or prism):

http://www.astroarts.jp/photo-gallery/photo/13209.html

Short focal was essential to "concentrate" (then capture) sodium tail. Consider also that spectrum is taken on 15 march when the comet was closest to the sun (and the Earth).

Ciao
Paolo

[Lars Zielke]

Thanks Paolo

I've been out every night for for some days now, so I have only just looked at the data. The recordings from yesterday, 2. April, was the first without any trace of the Na emission, but more processing must be done to verify that.

I'll try again this evening.

[Robin Leadbeater]

I pointed the LHIRES with a 600 l/mm grating at the comet this morning during a short 15 min gap between it clearing the trees and the bright dawn sky. no sign of the tail but I did capture a spectrum of the condensed part of the coma. The the NaD sky glow/light pollution is very strong though so I will need to do some careful background subtraction to see if there is still any emission. There is however a pair of clear emission lines about 90A to the red of the Na D lines. More later when I have reduced it.

Cheers
Robin