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Discussing a paper via the letters page in a bi-monthy journal all seems rather 19th century to me. Given that we are here using this forum, does anyone else find it rather ironic and a little odd that we are discussing the “meta-subject” rather than the subject itself?
Robin
Hi Tony,
I can’t see the attachment for some reason (was it below the maximum 640×48 size?) but my field has significant off axis coma, something I plan discussing with Francois at the workshop. I believe it is a feature of the guider optics and it is ok close to the axis where the slit is but I would be interested to explore if it could be improved as sometimes I would like to be able to use guide stars well off axis. I have attached an example guider frame from my setup
The shadowing might be because the mirror slit in the ALPY module is not quite aligned at the optimum angle relative to the guider. You can rotate the ALPY module to optimise the illumination and then rotate the guide camera to align the slit in the field. My slit is slightly offset. I am not sure where this arises, possibly in the camera coupling. These will be good subjects for the workshop however when we have Francois to demonstrate how to set the spectrograph up optimally.
Cheers
Robin
Hi Nick,
Doesn’t it just screw onto the male C thread ?
(This photo in the manual shows a T threaded camera with a C to T adapter)
If you switch a calibration lamp on (or in twilight if you don’t have the calibration module) you can see the slit in the guider image. I use PHD2 for guiding and note the XY position in pixels of the point on the slit where I want to place the star. If everything is screwed down tight the spectrograph is sufficiently stable that I can then set that location in PHD (or an offset from that location if guiding on a field star, the offset having been measured on a stack of longer exposure guider images)
Robin
Hi Tony,
Yes I will be there. I have some techniques which we can discuss there which should help get your fainter targets on the slit. (Most targets with my modified ALPY 200 are so faint that they are not visible in the guider image at all.)
Robin
Hi Gary,
ATel 9418 makes the suggestion that the H alpha emission at least may be present at times weakly even in the normal quiescent state and stays at the same absolute strength but becomes more obvious as the continuum drops (ie constant flux but increasing Equivalent Width relative to the continuum) My spectrum is not really good enough to confirm this though.
I did also have a try with the ALPY at normal resolution (Thanks to the support from the Harold Rildley grant I now have the capability to switch resolution more easily) but the SNR at this magnitude is too poor to show any more than the general continuum shape. I wonder if the Asiago team are still keeping an eye on it with the 1.2m telescope?
Robin
This time it is the confirming spectrum.
at2016gfr was discovered by Tim Puckett’s amateur team 6 days ago but was embedded in the host galaxy and too faint at mag 17.6 for a spectrum.
When I checked on Saturday there was still no confirming spectrum but it had brightened to around mag 16 so I was able to extract a spectrum (confirming it as a type Ia) using the modified ALPY 200 despite a full moon. Guider image and spectrum (compared with best fit from GELATO) attachedCheersRobin
I have a second hand 2 inch flip mirror sitting in a box, bought on impulse after I saw Bernard Heathcote’s combined spectroscopy/imaging setup a few years ago. I still have vague ideas of mounting the LHIRES and the ALPY together on the C11. The Alpy would need a focal reducer though so there may be issues bringing them to focus, let alone ideally making them parfocal.
Robin
Hi Alun,
That is an interesting setup. I have wondered myself if the guide unit (which can be the tricky part of a DIY spectrograph design) could be incorporated into other spectrograph designs. How did you couple the two together? Did you use the reflective slit from the ALPY?
Cheers
Robin
EDIT: Ah sorry, rereading I see you have two separate spectrographs/telescopes. How are you guiding the DIY higher resolution setup?
It really just covers simple applications of the Star Analyser and RSpec so if you have done any spectroscopy already or have been to any of my general spectroscopy talks (Chasing Rainbows, Science from Starlight, BAAVSS workshops etc) then it is probably not worth it. (Tom is a good software writer and speaker but he has mostly picked up his knowledge of spectroscopy from others rather than from personal experience)
Cheers
Robin
Hi Roger,
I am not that familiar with AIP4WIN but it works this way in IRIS. In IRIS, if you want the dynamic range of the combined channel (greyscale) image to be the same as for a single channel, either the multipliers for the three channels have to add up to 1 or the resulting image has to be normalised (The multipliers allow the white balance to be set correctly)
Cheers
Robin
Hi Nick,
The corresponding figures for a 150mm f5 scope under the same circumstances would be ~ 14.2/15.6
Cheers
Robin
Nick said: “I wonder what people would have thought back in 2003 when we had the last transit of Mercury if you had told them that in 2016 we’d be taking pictures like this with a mobile phone!”
Ha! Us webcammers of 2003 would have scoffed at your technology 😉
http://www.threehillsobservatory.co.uk/astro/astro_image_40.htm
This time I was on holiday in Malta and despite various attempts, failed to make contact with any astronomers there so missed it. Thanks to everyone who posted images here !
Robin
Hi Andy,
It looks like your optimisation is paying dividends. My limit at H alpha for verifying faint Be stars was around Vmag 10 with the LHIRES 2400 and C11, though these were much bluer stars of course.
Steve,
I think mag13 should be doable with your setup too. I’ve not tested the limit of my ALPY in 600 form but for example doing the same back of envelope calculation from the other end with my modified ALPY 200, I can get to mag 17, where sky background becomes an issue. The resolution of the ALPY 600 is ~4x higher and your aperture area is ~1/3 of mine giving a 12x factor overall or ~2-3 mags
Cheers
Robin
Hi David,
I modified my ALPY using a 200l/mm grism in place of the standard 600l/mm. This gives a lower resolution but still sufficient for SN classification for example. (I estimate this gives perhaps a 1.5 mag increase in sensitivity over the standard ALPY. I have been down to mag 17.5 supernovae in favourable conditions with this setup on a 280mm aperture C11 so mag 15-16 supernovae should be reachable with an unmodified ALPY)
The modification is fairly straightforward and reversible but requires a bespoke grism which Paton Hawksley (manufacturers of the Star Analyser and the supplier of the grism used in the ALPY) made for me. There are more details of my modified “ALPY 200” on my website here.
http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm
Cheers
Robin
Hi Tony,
I have a LHIRES III and an ALPY 600. I would not say the LHIRES is more advanced as such, they just complement each other and fulfill different roles. The ALPY 600 is more “fit and forget” and although the LHIRES is an excellent high resolution instrument, the ALPY is easier to use and performs much better than the LHIRES when used at low resolution. In many ways I find that producing good quality spectra can be more challenging at low resolution than at high resolution. (eg the targets are fainter, the sky background higher and atmospheric extinction correction more important)
Regarding rough guides from acquisition to final spectrum, I gave some very general walk thoughs for Star Analyser, ALPY600 and LHIRES using Vspec and ISIS at the recent BAA workshop at NLO Sidmouth, which can be downloaded here
http://www.shelyak.com/dossier.php?id_dossier=36&lang=2
They may not be totally self explanatory though so I am in the process of writing some words to accompany the slides which hopefully should make them more useful
For ISIS, Christain Buil has some tutorials which take you through the steps, though because ISIS is continuously evolving, the current version of the program does not always match the tutorials
http://www.astrosurf.com/buil/isis/isis_en.htm
Cheers
Robin
