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Hi David,
I don’t get to CAS very often these days, mainly when they need a speaker.
That is a curious design change. The big advantage with the ALPY is that provided everything is tightened up, it is a very stable instrument.
(The forum compresses large images to a smaller size but if you upload them as an attachment rather than an image, the original size and quality is maintained. It is also fussy about the file type. In any case 2MB is the maximum size allowed)
Cheers
Robin
This is how the sky spectrum looked when my ALPY arrived (one of the first batch in 2013) and how it looked after adjusting the Grism (full size in attachment)
Are you “local” then? I am in North Cumbria near Cockermouth
Interesting I was not aware they had changed the design Is the grism holder threaded now?. I have 4 grism holders (the one from my original beta model ALPY 600, the one I used to build the ALPY200, one I got through the BAA supported program and one I bought a few months back for another experiment.) All just have a plain barrel with stepped groove for the grub screw. This is the component I mean
Cheers
Robin
Hi David,
It is almost certainly the grism holder that that has come loose and is rotating relative to the slit. (It seems to be a quite common problem. Not sure why but I suspect Shelyak dont always tighten them up properly when the leave the factory as I have never had one move on its own after tightening. It is easy to fix though. The grim is held in the core module by an allen headed grub screw(s?). You view the sky spectrum for example visually through the core module, and rotate the grism until the spectrum is square and tighten. It is worthwhile getting it as precisely square as possible otherwise the ISIS software automatic wavelength calibration can fail. You can see a picture of the assembly here (page 4)
http://www.threehillsobservatory.co.uk/astro/ALPY200_VdS_BAAVSS_poster_2014.pdf
Take care if you slacken the grub screw off too far ,there is a spring underneath the grism assembly that holds the collimator lens in place which can launch everything if you are not careful!
Cheers
Robin
It turns out there is historic evidence from MASTER that AT2019lvs is a recurrent object with several historic outbursts
Update:
The optical transient AT2019lvs is now reported seen by PAN-STARRS 18 hours before the GW event. There is also a faint possible precursor visible on the SDSS image so most likely just a CV and not associated with the GW event see GCN 25204
https://gcn.gsfc.nasa.gov/gcn3/25204.gcn3
I also see that it is now reported outside the updated region of the sky
https://gcn.gsfc.nasa.gov/gcn3/25207.gcn3
and as I type, spectroscopic confirmation that it is indeed a CV
https://gcn.gsfc.nasa.gov/gcn3/25209.gcn3
so a false alarm this time I am afraid
Robin
Yes the “junk box” approach is a simple alternative to 3D printing these “linear” transmission spectrograph designs. eg
http://www.threehillsobservatory.co.uk/astro/spectroscopy_19.htm
http://www.threehillsobservatory.co.uk/astro/spectroscopy_18.htm
though I never got round to coupling them to the ALPY mirror slit guider
Claudio Balcon in Italy has recently classified a couple of faint supernovae using a similar home built collimated Star Analyser 100 setup
Ah OK, a bit high for really faint objects but I guess the SA200 could be swapped for an SA100? Are you using the PH wedge prism?
Looking forward to seeing how faint the TRAGOS might go. It could potentially be a nice alternative to the modded ALPY 200 for supernova work. (I have had some interest but copying it has been thwarted due the the unavailabity of the 200l/mm grism) What resolving power will your TRAGOS give ?
Robin
It is not down to social media though. Unfortunately this originates and is spread throughout the main stream media
From USA today
To the evening Chronicle
Now we have the date for maximum, we can compare the velocity in the Si II 6355 line with other type Ia supernovae. It does appear this one is indeed towards the high end, similar to sn2002bo for example.
Robin
It looks like maximum (g mag) was reached 2019-05-15 according to the ASAS-SN light curve
https://asas-sn.osu.edu/light_curves/078780dd-d80f-495e-95d6-d32d31ed2523
A very noisy low resolution ALPY 600 spectrum (It should be possible to do better) is similar to a low resolution 1981 spectrum from the literature.
It shows a blue continuum with no obvious emission lines, though there is a hint of some small features common to both spectra
Cheers
Robin
Assuming it does not get any brighter, the magnitude is about right for a Ia at the distance of NGC5353, perhaps a little faint but I think it is particularly tricky to measure redshift from Ia supernova spectra. Unlike type II where at least you have H alpha emission unshifted by the explosion velocity, you just have broad absorption lines blue shifted by the explosion, the velocity of which reduces with time. If I understand correctly how SNID for example estimates the age and redshift, it attempts to simultaneously fit these two parameters, comparing with other spectra in the library. It can be significantly out at times though. It is possible that the explosion velocity is higher than usual as suggested by the original classifiers, which could then throw out the redshift estimate. Also the published redshift of NGC5353 is probably for the nucleus and this SN is in the outer regions where the radial velocity might be different. The light curve should eventually give the age though which perhaps will pin things down better.
Cheers
Robin
At last some decent clear skies !
An ALPY 600 spectrum from 20190511 (black) overlaid on the best fit from SNID (red). A typical type Ia near maximum
Robin
Yes I noticed that too. I guess we don’t have our own mm wavelength capability (eMerlin works down to 1cm I think) though we must have a small share in ALMA through ESO I suppose.
Robin
