John Coffin

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Viewing 20 posts - 1 through 20 (of 63 total)
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  • in reply to: Alpy 200, what minimum size scope for supernova ID? #622887
    John Coffin
    Participant

    Hi Robin, thanks for the reply. Yes, I did see your presentation on Shelyak’s YouTube webinar. That’s what inspired me to look into the possibility of using an Alpy 200. Now to save up some pennies!
    John

    in reply to: Finding good reference stars #622410
    John Coffin
    Participant

    Thank you Robin for your detailed explanation which is very helpful, John

    in reply to: Finding good reference stars #622387
    John Coffin
    Participant

    Hi Robin, you mentioned in your post that ideally a reference star should have a low interstellar extinction. In terms of E(B-V) what upper limit would you recommend? Thanks, John

    in reply to: Where is the ARAS spectroscopy forum now? #620456
    John Coffin
    Participant

    Thanks Robin, that’s very helpful. John

    in reply to: Nova Cas 2021 #583997
    John Coffin
    Participant

    This is Monday night’s spectrum with bright helium emission lines.

    There are P Cygni profiles in the hydrogen Balmer series and the helium lines With a velocity of about 1400 km/ sec.

    in reply to: Lodestar Pro, has anyone used one? #583650
    John Coffin
    Participant

    Thanks Callum, I’ll try that. John

    in reply to: Pier on artificial grass #583202
    John Coffin
    Participant

    I’ve just installed a permanent pier in my garden. I keep the mount on it with a Telegizmos 365 scope cover. It makes it so much easier to set up. I no longer have to carry my heavy mount and counterweights outside and polar align it. If it’s possible to have a permanent pier rather than a tripod I think it is worthwhile. My pier was from Altair Astro.

    in reply to: Nova in Cas #583179
    John Coffin
    Participant

    It looks as if there are P Cygni profiles in sodium. Is the sodium interstellar, and if so, what causes the P Cygni profile? Is the emission component due to photoexcitation by UV from the white dwarf or some other mechanism? Thanks. 

    in reply to: Nova in Cas #583102
    John Coffin
    Participant

    Last nights spectrum shows P Cygni profiles in He I, Fe II, Na I and [O I] which have deepened or appeared since 5th September.

    1920p

    in reply to: Nova in Cas #583095
    John Coffin
    Participant

    Thanks very much for that. Maybe next year you will be able to teach us how to do this, perhaps in another spectroscopy workshop.

    in reply to: Nova in Cas #583072
    John Coffin
    Participant

    H alpha is still prominent, possibly even brighter. It needs someone cleverer than me to do a flux calibrated spectrum. I’ve attached a plot of three spectra taken over the last three weeks to show the changes. This object continues to fascinate me. Any interpretation of what we are seeing would be welcome.

     

    in reply to: Paper includes supernova classified using the ALPY200 #583064
    John Coffin
    Participant

    Congratulations! 

    in reply to: Nova in Cas #583022
    John Coffin
    Participant

    The H alpha line has become very prominent again and the P Cygni profile has disappeared. There appear to be emission lines for Fe II, He I and [O I]. The spectrum was recorded around midnight on 18th/19th August with an Alpy 600 and the resolution is ~ 550.

    in reply to: Nova in Cas #583019
    John Coffin
    Participant

    Thanks Robin, very useful.

    John

    in reply to: Nova in Cas #582999
    John Coffin
    Participant

    This is a spectrum from the early hours of 12th August. It looks very different from those of the 30th and 31st July in this thread. The H alpha line is much reduced and there appears to be a P Cygni profile, presumably due to expansion of the nova. I haven’t tried to identify the other broad absorption features. I would be interested in other people’s comments on what this spectrum tells us about the evolution of the nova. I see from the database that others have also noticed the changing profile.

    in reply to: C/2020 F3 (NEOWISE) #582891
    John Coffin
    Participant

    This is a photo taken with an astro-modified Canon 350D on a tripod on 13th July at 0100. Exposure 3 secs, F4, ISO 6400, focal length 55mm.

    in reply to: C/2020 F3 (NEOWISE) #582889
    John Coffin
    Participant

    Hi Robin, What exposure time did you need to capture the spectrum of the tail and what scope and camera did you use?

    Thanks

    John 

    in reply to: C/2020 F3 (NEOWISE) #582887
    John Coffin
    Participant

    Hi, I live on the Essex marshes with views almost to the horizon, so managed to get a spectrum of the coma of this comet on Tuesday am. Didn’t try for the tail. The Swan Bands are stunningly beautiful (to a spectroscopist). The image is the raw unprocessed spectrum.

    This is an annotated plot of the spectrum, the relative intensity of the emission lines is not reliable because the instrument response was calibrated using Merak which was at an altitude of 20 deg but the comet was at only 10 deg. Neither the sky background or the solar spectrum was subtracted when processing the spectrum. The emission lines were labelled according to data in Richard Walker’s Spectral Atlas and on the following website http://web.gps.caltech.edu/~mbrown/comet/all.txt

    The full size images are attached.

    Robin can advise on whether the annotations are reasonable. John.

    in reply to: Spectrum of M87 Nucleus #580969
    John Coffin
    Participant

    Thanks for sharing that. Can you add any links to the radio image?

    in reply to: Scintillation and ALPY spectra #580930
    John Coffin
    Participant

    Dear Hugh, I read that you work in alt-az mode to avoid the effects of atmospheric dispersion.  I’d be interested to know how you do this. I have an AZ-EQ6 Mount but haven’t tried the AZ mode. I normally guide on a different star to the target. Does field rotation interfere with your guiding? Do you have more difficulty synchronising your telescope to your planetarium software? I’ve been put off trying AZ mode because I had heard that it’s “go to“ function was not so accurate. 

Viewing 20 posts - 1 through 20 (of 63 total)