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Hi guys,
I’ve been following the thread with interest so when the first clear (dark!) night, for what seems like several decades, occurred on Wednesday I couldn’t resist a shot at VV Cep. Fascinating object.
Too low resolution to be of any scientific interest but this was ‘first light’ after a summer of faffing about – and I’d fitted a photometric slit to my Aply which I was fine tuning. (n.b. 23 um narrow slit used for this obs).
Regards
Tony
Yes Andrew. I realised that after a few attempts at ‘tinkering’ with PHD2!
At first, on guiding on the target star, I noticed a few zig-zags in the PHD trace as it hunted for the star in the slit. I tried to train that out with an increased hysteresis value but that just caused decreased ‘reactiveness’ either side of the slit and led to worse guiding (it would).
So I went back to my original values when I realised that it was, as you say, sampling the whole disc by default and thereby negating (to some extent) the chromatic aberration.
I wouldn’t say ‘bad guiding is good’ but “iffy” guiding certainly has it’s benefits!
I still guide on a nearby star given the opportunity.
Regards
T
I might consider a wider slit or indeed the Shelyak photometric combo slit.
Regards (and thanks once more for your time).
T
Hi Steve,
I found these useful…
http://uncle-rods.blogspot.co.uk/2017/03/issue-534-getting-your-phd.html
(Check the ‘Algorithms’ paragraph. Makes sense of the whole thing!).
http://openphdguiding.org/phd2-best-practices/
Regards
T
Robin,
I’ll check but I think it was HD87737 (another A class). It was a fair distance away if memory serves but roughly the same airmass. I used it for HD112413 and then (having got a good result) used that as a standard for the other two.
I have also been tinkering with a Relco bulb for better blue end calibration, mount backlash settings and PHD hysteresis to improve tracking. Most of the time it’s one step forward, two back, but I’m slowly making progress.
Not enough nights to observe and tinker at the same time.
Regards
T
Hi David, thanks (once again) for your responses.
I was making life difficult for myself in the belief that I needed a reference star close in proximity AND in spectrum to the intended target. (Indeed I’d noticed a better fit when I did that).
I’ll relax that spectrum requirement (and the time it takes to find a suitable ref star!).
(That does indeed solve the issue of ‘what ref star do I choose for a binary of differing spectral components?’. Doh!).
It looks like being fine up here tonight so I’ll chase a few more Be and ARAS symbiotics. I received a good response and a few ‘pointers’ from Francios T on submission of my first spectrum to him and I’m keen to try a few more.
Regards
T
David (et al),
The apparent ‘lack’ of a photospheric spectrum and a dual component means ‘what’ in terms of how we measure a symbiotic star?
Using another M3 standard star got the correct result for AG Dra. Is that assumption correct? That is, use the spectral response for the more luminous component?
Regards
T
I’d played around with AOD having gained an idea of what it might be from here…
https://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MODAL2_M_AER_OD
Experimenting with varying target altitudes obviously give quite serious differences but using differing AOD values between 01 – 0.2 (the UK apparent variances) produced huge differences in the Aerosol component. It seems to vary considerably from week to week (?).
I’m not sure how ISIS applies this (?) or indeed whether UK values are accounted for. (They certainly appear different from the guides given in ISIS).
Or am I reading this wrong?
Regards
T
Very good point. If I set the ISIS “Settings” >> “Spectral Domain for profile scaling” boxes to zeroes the output is in counts per second (or ADUs, I’m not sure). I only know this because I’ve been playing around with Flux Calibrated spectra.
I think that that means I can follow your method (?).
Regards
Tony
Thanks Robin, I’ll check those out.
I’ve already downloaded BeSS spectra in an attempt to check my own obs of several BeSS stars but I wasn’t sure as to whether BeSS altered the format on submission. I’ve since read the BeSS published papers to check fits format etc. and I’m much happier.
I suppose I just wanted the comfort of confirmation from people I know who’ve done it.
I posted my first four Be spectra on this forum earlier & to the BAA database. Thanks for confirming cross compatibility Andy. That had escaped me. I think I’ll bite the bullet and use one to submit to BeSS and see what happens.
I’m keen to get the BAA its money’s worth! But hasn’t the weather been appalling!!!!
Regards
T
Hi Paul,
First stop is the BAA Variable Star Section, here…
Check out the left hand menus on the home page. Lots of info on the ‘how’ and the ‘what’ to observe.
Very rewarding.
You don’t say what your mount is? Can it guide?
Regards
Tony
That makes sense, I think I understand now. To paraphrase – process both target and ‘sky’ in the usual (separate) ways, with ‘sky not removed’ ticked in ISIS to produce two spectra using a nearby reference star, then mathematically subtract sky profile from target profile (in ISIS tab 5 “Profile”).
Regards
T
