[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

[Robin Leadbeater]

https://groups.yahoo.com/neo/groups/spectro-l/conversations/topics/14084

Robin

[Robin Leadbeater]

Hi Tony

Yep they are Relco 480 starters, though I believe Shelyak sort them, probably based on trigger voltage. Their power supply is also designed to prolong their life (constant current ?)

I have some notes on this that Francois Cochard published somewhere. I will dig them out

Cheers

Robin

[Robin Leadbeater]

Francois Teyssier on the ARAS forum is a good amateur contact for information on spectroscopy of symbiotics. He produces a regular Eruptive Stars Spectroscopy Newletter which includes regular comentaries by Prof Steve Shore and is now listed on ADS, unusual for an independent amateur publication

http://www.spectro-aras.com/forum/viewtopic.php?f=33&t=2254

Back issues are also available here

http://www.astrosurf.com/aras/novae/InformationLetter/InformationLetter.html

Cheers

Robin

[Robin Leadbeater]

Hi Kevin,

With the manual dispersion function in ISIS you double click either side of each line in the uncalibrated (combo) spectrum and ISIS calculates the exact pixel position of the centroid of the line and enters the value in the table. You have to tell it to look for either an emission or absorption line within the two clicked positions though (buttons at the top of the window) so you would need to click “absorption” before measuring the water line positions and “emission” before measuring a lamp line.

Yes, if you set the reference line to 0,0 it just uses the predefined dispersion equation but if your dispersion was measured on a reference star with the telescope pointing in a different direction to the target, this can be out by a constant shift due to flexure so adding a reference point using a lamp spectrum corresponding to the target will correct for this. (correcting the constant in the polynomial)

Robin

[Robin Leadbeater]

Hi Kevin, 

It should work ok provided you don’t see any fixed offset between water and lamp lines. (You would see this for example at H alpha if you always need to make a consistent correction using the water lines.). Don’t forget to switch between absorption and emission for the specific line you are measuring in the dispersion calculation tab.  I would suggest calculating the dispersion just on the reference star where the SNR in the water lines is likely to be higher and then using this calculated dispersion on the target with one of the neon lines as a reference point to correct for any flexure offsets.

Alternatively have you tried a long exposure with the Ne lamp to see if you can see any weak Ar lines to use instead of the Ne lines?  (I could see some with my Ne lamp  but they are more obvious now I have upgraded to the NeAr lamp)

Cheers

Robin

[Robin Leadbeater]

Note that the dedicated 1:1 duplicators designed for use with full frame SLR will crop slides when used with DSLR with smaller sensors so you might need to modify them eg with an extension tube.   I think you can get versions with 0.6 reduction for DSLR though

[Robin Leadbeater]

If you have a digital camera with a macro lens you could rig up something like this.

https://www.scantips.com/g4/p1230510.jpg

from this page

https://www.scantips.com/es-1.html

I have used this sort of setup in the past using the sky as a light source and a cardboard tube to keep the light out but the results depend on the quality of the lens (Star fields tend to show up any deficiencies, like pincushion etc)

Cheers

Robin

[Robin Leadbeater]

I see today that S&T prefers Godzillas

https://www.skyandtelescope.com/astronomy-news/pluto-charon-missing-small-craters

Robin

[Robin Leadbeater]

Note that although an early spectrum of sn2019np was taken by the Li-Jiang telescope, the official confirming spectrum was actually taken several hours earlier using Faulkes Telescope North and uploaded to the Transient Name Server (As it happens 4 minutes before the Atel #12374 was issued, though since 2016 the TNS has been the official IAU system for recording supernova discoveries and confirmation) 

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

There are also three amateur spectra of this SN in the BAA Spectroscopic database

 https://britastro.org/specdb/data_graph.php?obs_id=3641%2C3594%2C3640&multi=yes&mix_flux=no&plot=Plot+up+to+20+Spectra

and more spectra on the ARAS forum here covering the evolution up to currently 17th Feb

http://www.spectro-aras.com/forum/viewtopic.php?f=38&t=2205

Cheers

Robin

[Robin Leadbeater]

Another spectrum last night. It has cooled significantly (to ~15000K) and the Balmer absorption lines are more pronounced

Robin

[Robin Leadbeater]

Hi David,

I’m afraid I am not enough of an expert to interpret spectra of CVs, beyond being able to tell the difference between the spectrum of a classical nova and one of a dwarf nova. This is a typical spectrum of a dwarf nova in outburst. In this case a large amplitude outburst of a star with no previous history of outbursts so a likely WZ Sge (UGWZ)  type (I am reliant on Patrick Schmeer for this classification)

The source of the additional flux is impressively hot. The continuum fits to a ~35000K Planck curve, like an O star

Robin

[Robin Leadbeater]

I thought this was a BAA meeting

[Robin Leadbeater]

I’ve just seen there is now a revision to the path noted at the bottom of the page.  (The original track was calculated based on the position of the centre of mass of the A-B system rather than Sirius A !

I hope you have not already made your travel plans !

Robin

[Robin Leadbeater]

Just spotted this on the S&T website

https://www.skyandtelescope.com/observing/will-sirius-disappear

“Monday night, February 18th. That evening around 10:30 p.m. MST (5:30 UT February 19th), there’s a good probability that the 17th-magnitude 4388 Jürgenstock will occult the sky’s brightest star for up to 1.8 seconds.”

The event is not visible from the UK but anyone on the narrow path though North America could get (very a brief) view of Sirius B free from the glare of its bright companion. (Sirius is predicted to be totally eclipsed for just 0.2sec !)

Robin

[Robin Leadbeater]

I’ve not done any scientific measurements but when I made mine I read that most dew shields are too made short and they should be 3x the aperture. This does look rather long though and gives  problems with the mount in a breeze.  

I first saw the newspaper trick on a small refractor at a sky party in Denmark. Most people who did not have heaters were struggling with dew but not this guy. (I think perhaps he changed it once during the night when it got too soggy)

Robin

[Robin Leadbeater]

As an aside,  dew is less of a problem in breezy conditions as the airflow is constantly removing the cooling boundary layer of air over the surface where dew is forming. (Which is just as well as my dew shield acts as a sail !)

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