Robin Leadbeater

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Viewing 20 posts - 501 through 520 (of 1,188 total)
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  • in reply to: C/2020 F3 (NEOWISE) #582772
    Robin Leadbeater
    Participant

    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

    in reply to: C/2020 F3 (NEOWISE) #582765
    Robin Leadbeater
    Participant

    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

    in reply to: C/2020 F3 (NEOWISE) #582752
    Robin Leadbeater
    Participant

    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

    in reply to: C/2020 F3 (NEOWISE) #582725
    Robin Leadbeater
    Participant

    Wow. the animated sequence linked from there showing it rising out of the clouds is pretty stunning

    in reply to: Another bright possible supernova (NGC4457) #582718
    Robin Leadbeater
    Participant

    Now also confirmed as a Ia and so could reach mag 12 or perhaps even a bit brighter at this distance depending on extinction

    in reply to: At 2020nlb – a possible Supernova in M85 #582691
    Robin Leadbeater
    Participant

    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

    https://www.flickr.com/photos/snimages/50047440476/

    in reply to: Instrument response with Lhires #582697
    Robin Leadbeater
    Participant

    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

    in reply to: Zeeman effect in sunspots? #582694
    Robin Leadbeater
    Participant

    Another (marginal) observation of the Zeeman effect by Buil at R~30000.  Also of doppler broadening/profile distortion due the to Evershed effect

    http://www.astrosurf.com/buil/lhires2_sun/sun250904/obs.htm

    in reply to: Zeeman effect in sunspots? #582693
    Robin Leadbeater
    Participant

    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

    in reply to: At 2020nlb – a possible Supernova in M85 #582686
    Robin Leadbeater
    Participant

    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 !)

    in reply to: How to validate observations #582677
    Robin Leadbeater
    Participant

    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

    in reply to: How to validate observations #582676
    Robin Leadbeater
    Participant

    – 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

    in reply to: A ring around a red star #582665
    Robin Leadbeater
    Participant

    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

    in reply to: A ring around a red star #582652
    Robin Leadbeater
    Participant

    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

    in reply to: A ring around a red star #582651
    Robin Leadbeater
    Participant

    Hi David,

    That was my first thought but this is reported to be a narrow band image in [OIII].  Though perhaps it is  possible that the filter leaks in the IR? 

    Cheers

    Robin

    in reply to: How to validate observations #582646
    Robin Leadbeater
    Participant

    Hi Keith,

    David mentioned MILES stars. I find a good way of checking the quality of  ones observations is to measure a few of these stars and compare the results directly with the spectra as measured professionally. Any differences can then be investigated and once they are close to the professional version  one can confidently submit spectra of other targets to the BAA database for example.  You can see an example of this sort of test here using the ALPY 600.

    https://britastro.org/node/8153

    and there are more examples and further information here on my website

    http://www.threehillsobservatory.co.uk/astro/spectroscopy_21.htm

    Cheers

    Robin

    in reply to: Request for monitoring of X Per #582640
    Robin Leadbeater
    Participant

    Hi Hugh,

    Time to place our bets on which way it will go next season !

    A comment from Paul Roche in January:- 

    It’s not obvious what’s going on here, as the declining EWs for H alpha and HeI suggest a diminishing disc, but the AAVSO photometry seems to suggest the opposite. We’ll have to keep an eye on things for the rest of the “X Per season” and see if it makes sense when we have a bit more data. It will be interesting to see how the (B-V) and (V-R) colour of the system is behaving, that might reveal a little more about the state of the disc”

    There is very little data in other bands in the AAVSO photometry data. Does your continuum data show any colour trends ?

    Cheers

    Robin

    in reply to: Request for monitoring of X Per #582636
    Robin Leadbeater
    Participant

    There are now over 230 spectra in the BAA spectroscopic database. Thanks to all contributors ! Continuing monitoring on a nominal 2 week basis during the next season is requested.  The following is a quick analysis of a selection of the available spectra.

    The fall in EW of both the H alpha and He 6680 lines plateaued during January 2020 and remained constant up to the last recorded spectra on 2020-04-06 so there was no complete loss of the disc, though the He line in particular became very weak at just -0.4A EW

    A snapshot of 5 heliocentric corrected line profiles during the monitoring period (marked A-E on the EW plots) shows the complex evolution of the lines and although the EW was approximately constant from Jan to April 2020, the line shape continued to evolve.

    Although noisy due to the weakness of the line, there are significant differences in the He 6680 line profile compared with the H alpha line with higher radial velocity features particularly on the red edge.

    Here is the AAVSO V mag light curve for the same period. There is no obvious correlation

    Cheers

    Robin

    in reply to: Photometric filters #582622
    Robin Leadbeater
    Participant

    The same would apply if using the G channel from a DSLR to estimate the V mag of the nova as the G channel response at H alpha is different again eg

    http://www.astrosurf.com/buil/50d/test.htm

    Robin

    in reply to: Photometric filters #582621
    Robin Leadbeater
    Participant

    I remember Gordon Myers talking about transformations (and extinction)  at the 2018 BAA/AAVSO joint meeting.

    https://britastro.org/video/13862/14771

    He put some numbers to the size of the effect for different systems he tested (6:39)

    At the end of the day though these are still approximations dependent on the actual spectrum and can be way out in some circumstances. As an extreme (though real) example, a Nova spectrum dominated by H alpha. eg

    https://britastro.org/specdb/data_graph.php?obs_id=650

    A significant fraction of the H alpha flux would appear in the standard Johnson-Cousins V passband but would be completely missed by the Chroma version. Spectroscopy is much more straightforward 😉

    Robin

Viewing 20 posts - 501 through 520 (of 1,188 total)