[Robin Leadbeater]

According to VSX, EF Cep is an eclipsing variable type W Uma with a period of 0.606072d which if Wikipedia is correct makes it a type A and should consist of two stars of type A-F  which from the look of the spectrum I would say is correct. (A quick overlay of Pickles spectra suggests a type F2iii is a pretty good match for example)

Robin

[Robin Leadbeater]

Hello Jack,

I think the HD43378 in the filename refers to the reference star used (a MILES star). The spectrum is of EF Cep which does not even appear in Brian Skiff’s huge database of published spectral types so yes this might well be the first published spectrum of this star.

Cheers

Robin

[Robin Leadbeater]

Thanks Andy,

I wonder how compact the emission line source is compared to the region shown in the radio image. (unfortunately the spectrum was not very well focused at H alpha so the extent is not clear in my spectrum)

Robin

EDIT this image and spectra from HST suggests the main emission region region extends around 1 arcsec or so across

http://www.rpi.edu/dept/phys/courses/79205/Pics/HST95/diskM87Data.gif

[Robin Leadbeater]

Hi John, 

I have added links to the AAS article on the radio image (just 50 micro arcsec across !) and the source of the 2008 comparison professional spectrum.

Cheers

Robin

[Robin Leadbeater]

Ah SPC, Western Electric Rules etc. I remember that became the thing at work after my  boss made a trip to Japan. I  then pointed out the various places in the paper mill where I had effectively already implemented it (though not by name) !

[Robin Leadbeater]

Hi Andrew,

If you are working in the first order there is no overlap at the UV end so no need to use an IR cut to get the UV part of the spectrum. The response of the Star Analyser rolls off quite rapidly at the UV end though.   Note that the zero order has a rather odd spectral content. (Effectively the inverse of the grating response, so predominantly contains the blue and red ends with the central wavelengths missing.) An IR cut filter before the grating might therefore be useful to enhance the sensitivity of the zero order to changes specifically in the blue without affecting the spectrum as the IR part of the 1st order spectrum would be invalid in any case without an order filter to cut the overlapping 2nd order blue end.  I’ll see if I can dig out the raw spectra for you to play with

Cheers

Robin

[Robin Leadbeater]

An interesting idea Andrew.

For anyone interested, there is a more in depth analysis of that event here (2:28-12:30)

https://britastro.org/video/13862/14769

I was indeed lucky and spent a  few more nights without catching anything. An auto system should determine how common they are.  What do you plan to trigger on? 

Increase in total (or wavelength specific eg blue) flux relative to other field stars ?  (Might still be triggered by cloud movement at high cadence)

Increased temperature – flux(blue)/flux(red)?  (Should be relatively insensitive to clouds which are ~grey and slow changes due to extinction)

Change in H alpha flux ?  (Does H alpha generally change during these events?  In this case the excess flux did appear to show some additional H alpha/beta emission). Andy Wilson’s speciality I think

Robin

[Robin Leadbeater]

Hi Ron,

I don’t have much experience in planetary imaging but in slit spectroscopy the sky background, measured above and below the target spectrum, is similarly subtracted from the spectrum image.  When this is done however it is important that the software preserves any negative pixel values that are generated (due to noise in the image). If the negative values are clipped to 0 you do not get the correct total flux values. I think the same will apply here.  Are the two images in your document before any sharpening ?  If so I would say there is clear signs of clipping. (You could perhaps check by taking a profile through the two images before sharpening . The brightness of the planet limb should merge smoothly into the background due to the finite resolution of the imaging system). It depends to what use the image is going to be put but if there is any clipping, I would expect any measurement of total flux or diameter for example not to be reliable.

Robin

[Robin Leadbeater]

Planetary imaging with an undriven mount is very hard work because of the rate of drift at the high focal length used to get good resolution. 

Robin 

[Robin Leadbeater]

There are now 2 pro spectra confirming it as a supernova, type 1c

[Robin Leadbeater]

Hi Martin,

Thanks for the update. That is bad luck. I think in Ron’s position I would have reported it on TNS as a possible SN noting there that it appears to be coincident with SN2010ct.  If it was SN2010ct, that would mean that it was not classified correctly originally so it could have been an SN this time. It is still only a possible though so far of course until a spectrum is taken. Only 18% of possible SN submitted to TNS were confirmed last year.

I have had a look at the original confirmation CBET for SN2010ct. I must say the description of the spectrum does sound convincingly like a type II SN and not an LBV outburst.

http://ned.ipac.caltech.edu/cgi-bin/ex_refcode?refcode=2010CBET.2323A…1S

Cheers

Robin

[Robin Leadbeater]

I see the Zwicky Transient Facility spotted it 9 days ago but only reported it on TNS today.

https://wis-tns.weizmann.ac.il/object/2019cda

There are not so many unique amateur discoveries these days with all the robotic surveys.  I am starting to see the same with my spectroscopic confirmations as more dedicated pro spectroscopic capability comes on line. Initially when I started in 2016, most of mine were stand alone confirmations but now most of them eventually get a second pro followup spectrum. 

[Robin Leadbeater]

Hi Paul,

I posted it here because it is time critical (The BAA meeting on Wednesday)

Cheers

Robin

[Robin Leadbeater]

Hi Dominic,

I would agree that follow up is likely to be more productive but you underestimate the determination of the amateur. It has already been done

https://arxiv.org/abs/1804.05551

The issue is not so much the precision of amateur photometry or lack of untouched sky to explore but the numbers game. You have to spend an awful lot of time looking at an awful lot of stars to find one transiting exoplanet candidate and even then you need luck.  You would need a survey on the scale of the one run by Stan Waterman for example who found a fascinating gamut of variabilty in  his “Kepler before Kepler”  survey but no planets as far as I recall

http://www.stanwaterman.co.uk/variablestars/

Cheers

Robin

[Robin Leadbeater]

There’s another returning supernova impostor (An LBV in NGC4559)  which might be in range currently (It was mag 17.5  a couple of weeks ago.)

http://www.rochesterastronomy.org/sn2012/lbvn4559.html

Robin

[Robin Leadbeater]

Hi Bill,

Well I had to guess as you have not revealed “where the experts went wrong”  😉

[Robin Leadbeater]

Hi Bill,

I remember reducing some photographic spectra for Ed Majden some years ago. Not sure what he did with the results though.

You can get variations in dispersion across the field in objective grating spectroscopy due to geometric distortions caused by the lens optics (eg pincushion/barrel etc) though I am guessing this was not the problem here. It is possible to characterise them (though not so easy retrospectively) by moving a check star spectrum around the frame (This technique also useful for characterising flat field effects which are very difficult to correct for otherwise in slitless spectra)

Cheers

Robin

[Robin Leadbeater]

Hi Andy,

I suppose it depends on exactly what happens at  the point of merger or perhaps just before. We do know that there are double degenerate systems with a total mass well beyond the Chandrasekhar limit eg

https://arxiv.org/abs/1609.00178

Although we do not have good independent distance measurements, the tight correlation between redshift and Ia maximum brightness (after correction for the light curve shape) does not suggest two obvious populations.

A mix of single and double degenerate progenitors giving different luminosity supernovae could be problematic for cosmological models though as the ratio of single and double degenerate systems might be dependent on the look back time. This has been even used in an argument supporting the double degenerate model as being the dominant mechanism.

https://academic.oup.com/mnras/article/417/2/916/983573

Cheers

Robin

[Robin Leadbeater]

Hi Paul

Since you have plenty of photons such that stochastic precision is not a problem it could be worth considering a choice of filter to minimise the systematic errors which are likely to dominate at the mmag level. Bruce Gary’s on line book has some suggestions 

http://brucegary.net/book_EOA/EOA.pdf    pp 28-29

Cheers

Robin

[Robin Leadbeater]

Yes the white dwarf merger scenario for Ia supernovae is still very much alive and I believe is suspected by many to the the primary mechanism. The empirical relationship between Ia supernova distances and other measurements of distance still seems to hold though regardless of the mechanism.  It is worrying though that we are relying on a standard candle without a clear understanding of the mechanism. 

A shameless plug here – studies of SN2018oh, which I classified, contributed to this Ia mechanism controversy  though without any clear conclusion.

https://www.skyandtelescope.com/astronomy-news/60-second-astro-news-helium-exoplanets-and-a-supernova-surprise

https://arxiv.org/abs/1811.09635

Robin

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