[Robin Leadbeater]

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/

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

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 !)

[Robin Leadbeater]

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

[Robin Leadbeater]

– 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

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

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

[Robin Leadbeater]

Hi Andrew,

I thought Bessell was pretty much the same as Johnson-Cousins eg here half way down the page

http://spiff.rit.edu/classes/phys440/lectures/filters/filters.html

Of course the elephant in the room is the response of the sensor which is very different today compared with detectors of previous eras

Robin

[Robin Leadbeater]

The response curve of those Chroma filters

https://www.chroma.com/products/sets/27103-bessell-ubvri

looks very different from the Baader (and other) versions I’ve seen

http://astrograph.net/Baader-Planetarium-Johnson-/-Bessel-V-Filter-125-and-50mm-x-50mm

Robin

[Robin Leadbeater]

Christian Buil has an interesting  CCD/CMOS comparison. Though specifically concentrating on spectroscopy,he covers camera noise, amp glow  and linearity 

http://www.astrosurf.com/buil/CMOSvsCCD/index.html

With high resolution spectroscopy of faint objects at the limit of detectability the sky signal is insignificant so camera noise becomes the most significant source of noise. To minimise read noise contribution, exposure lengths used with CCD are typically  >1200sec and it takes many hours to get a sufficiently noise free stack of darks, though  cloudy nights can be used of course!

Although low, the read noise in CMOS is not insignificant and once the typical slit width relative to pixel size is considered, is not that different from that of good CCD because of the ability to bin pixels with CCD  so there is not much latitude for combining shorter exposures with CMOS (though an spectrograph optimised specifically for the small pixels found in common CMOS sensors could perhaps avoid this).  The thermal noise is also typically higher for CMOS cameras which need much lower temperatures to match that of a CCD so although the performance gap is not large these days, CCD still appears to have the edge in performance (Though not in cost per area) when used with currently available commercial spectrographs.

Cheers

Robin

[Robin Leadbeater]

With the help of Thomas Bayes perhaps I can now claim to have previously detected both the Balmer H beta absorption with emission core and H alpha emission 😉

My rectified spectrum from 2020-05-30 (red) overlaid on the spectrum published in the Atel

(I also see the problem of not being able to insert images. I had to press “preview” before I got the “insert”  option)

Robin

[Robin Leadbeater]

OK  here are the spectra for 2020-05-29 and 30.   

Apart from the hot continuum there is nothing common between them so unfortunately  the details are probably just noise. They were taken at 5 deg altitude (air mass 10) in a bright sky though so to be honest it was a surprise to get anything

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