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Hello Giovanni, I borrowed a D3000 and was able to make some checks. It’s not a camera I’m very familiar with, but I used settings – manual, monochrome,ISO 100, NEF raw, auto white balance, standard picture,colour space sRGB,active D-lighting off, noise reduction off and shot a sequence of different exposures. You mentioned using AIP4Win so I did the same and set preferences for DSLR to debayer with camera white balance. Just plotted a few green channel points, but they look as I’d expect for raw image. Hopefully yours just a settings and not camera problem. As Nick suggests maybe a few of your raw NEF images plus settings summary would help resolve problems.
Attachments:
Alan,
Thanks for posting this. I don’t feel the usual ‘outlier’ that I normally do when the ‘How was it for you’ posts appear. My observing opportunities have been about average, I guess my ‘average’ = rest of UK ‘dire’. Since the start of the year I’ve had 14 sessions long enough to collect polarimetry data for 7 targets including T CrB plus another 9 short ‘image for fun’ opportunities. Hope conditions improve for you (and don’t get any worse for me!).john s
Hello Les,
I use AIJ without problems for polarimetry mostly, but have also used for photometry also without problems with an earlier version of the BAA spreadsheet. Can’t claim to be an expert though, but can try to help. Just wondering why your measurement file has ALT_OBJ as NaN but AIRMASS OK, presume your use of DP Coordinate Converter and call to SIMBAD was OK. You can specify that ALT_OBJ should be decimal in aperture settings keyword tab in AIJ – perhaps check it’s there in the header (apologies if you’ve tried all of these already). I don’t know if the presence of NaN anywhere in the data would be enough to cause a problem in BAA spreadsheet even if that piece of data unused. Anyway, my email john-dot-jean-dot-simpson-at-gmail-dot-com.
john s
Hello Kevin,
I’ve attached a screenshot – this builds master-flat for me in AstroImageJ using bias and flat-darks. When you process lights, change the file reference to relevant master-dark for lights and change “build” to “enable” for master-flat.
john sAttachments:
I wondered if there might be evidence of any asymmetry in the nova due to shocks or clumping of fast/slow ejecta and if it might show up in linear polarisation and wavelength dependence. Measurements from 21-22/07/2021 [file attached] don’t seem to show much other than interstellar polarisation characteristic.
I realise the interest is in photometry & spectroscopy, but noticed in P.Roche paper [1] that some polarisation measurements were referenced, so thought I’d try a few measurements. The table gives the calculated normalised intrinsic polarisations [%].
Band
18/11/2018
14/11/2019
19/11/2019
U
–
–
0.44 +/-0.12
B
–
0.54 +/-0.10
0.51 +/-0.08
V
0.63 +/-0.07
0.59 +/-0.09
0.60 +/-0.07
Rc
–
0.62 +/-0.08
0.58 +/-0.08
The attached figure shows these in relation to results referred to in ref.[1] as Extended Low and Fading stages. The calculated average circumstellar disc polarisation angle is 173.2 +/-4 deg compared to ref. [1] value 171 +/-0.7 deg.
[1] Observations of the recent disc loss in X Persei Astronomy & Astrophysics 322, 139-146 [1997]
#EDIT corrected uploaded image & table !!
When the Event Horizon Telescope project started in 2009 the UK was still part funding and involved in operation of the James Clerk Maxwell telescope which has been part of the project – then we pulled the plug on funding and walked away in 2015 [ironically the UNESCO International Year of Light which celebrated the achievements of all those who had contributed to our understanding of light – foremost amongst them Maxwell]. I think there may still be a bit of involvement somewhere via UCL, but I’m not sure. But, you are right, sadly we don’t have a place at this particular top table.
john s
For info, I was able to download and open all these files using my mobile phone – without logging into the BAA – despite the notice saying otherwise.
john s
Hi Tony,
I bought a Wollaston prism and some lenses from Thorlabs just before Xmas – they arrived in similar box with similar goodies. Same thing happened to mine, even the box was taken away and used for something else!
john s
Hello Kate,
I use this slit as a matter of course, primarily as a means of getting the best definition of the continuum that I can with my equipment & set-up. Although it means 4 measurements instead of 2 it’s a very useful piece of kit just for this function alone. I don’t use it for photometry though I have processed some of my measurements following the examples given in the Christian Buil references Robin has given, just to see what sort of results were produced – the instructions in the references are straightforward & clear.
john s
Hi Robin & Bill,
I had a cheap-n-cheerful Qumox intervalometer which I used with 1000D for transit of Venus because I could programme in delays, exposure etc. I thought it had such a facility. If I remember rightly I could programme the timer with delay, exposure time, interval between shots and number of shots up to 999 I think. With 1000D set to ‘bulb’ and then switched to liveview the mirror came up then timer went through the sequence – delay – exposure – mirror dropped down and lifted again immediately- interval – exposure – mirror drop & lift etc. I’ll try to find it to check.
john s
Hi Peter,
Think you use ISIS – to see which images are shifting the most you might try a run ticking “wavelength registration” under the tab [2.General], then when you click next to go to tab [3.Calibration] tell ISIS to use the zero order i.e. x-coord=0, whatever pixel that corresponds to in next box and tick emission. If you tell ISIS not to delete the intermediate files under the Settings tab, you’ll see how much drift there is in each image wrt the first and maybe be able to select the best to stack.
Hope that’s a help.
john s
Hello Andrew,
You posted this quite some time ago. Light nights & midges now arrived at my location so thought I’d take a look at IRAF. Thank-you for your instructions. It’s early days yet, but so far no major hiccups [see attached]. Are you still interested in any feedback? I’ll carry on and take it a bit further, up to prep. and use of instr, responses if I can.
Regards
john s
Tony,
I’ve been using the photometric slit for a few weeks now – plus the references [Robin quoted these in an earlier post]. It has been a great help in my case – just showing how bad my guiding has been [basically I need to replace my mount]. Example for HD205021 attached.
Regards
john s
Paul,
If we choose reference with same air mass doesn’t that ensure correction OK? Only if we try to use that instrument correction for target at different air mass then there will be a discrepancy. Since in practice it’s probable there will always be a difference, the question would be “how big a difference?” before it’s significant. [if it ever stops raining here I might try to explore that for myself].
john
Just to tidy up one point. Although the ALPY guide unit has just the single 23 micron slit, Shelyak offer a combined 23/200 micron photometric slit. In case anyone chooses to follow this route; I think I’ve solved my problems of inconsistency of continuum measurement by purchase of the latter – using the wide slit to determine the “instrument response”. It means taking 2 sets of measurements instead of 1 each time, but it seems worthwhile to overcome the variable effects of seeing, guiding errors, geometry & parallactic angle etc. I’ve not tested the new set-up extensively yet, but initial checks on some of Robin’s stars in Taurus get me to +/- 1.5 – 2% error w.r.t. references over range 4000A & 7000A. Also, had a quick look at HD35155 which is in the Miles library & used as ref. HD37507 [chose A5V in Pickles] – result in attached figure, still a bit of work to do, but seems promising.
Thanks David, Andrew, for your comments & also the Buil reference . No condensation trails at my location, but it is loch-side surrounded by hills & conditions sometime change quickly. Once I’ve sorted out my stray-light problem, I will set an evening aside to track a couple of targets to see the extent to which my observations change over the period of time.
Hi Robin,
Thanks for the suggestions & references. I’ve only been able to look at switching off optimised binning so far, but it makes no difference to the results. On the way I checked out switching everything out [no offset, dark or flat field correction, just raw images with no calibration]. I looked at the consistency in pixel location for several absorption lines across all the images and the standard deviations seem reasonable to me.
H.alpha=0.15px; H.beta=0.13px; H.gamma=0.11px; H.delta=0.16px; CaII=0.09px
I will look again at the data to see if the results show any obvious trends with time. However, more disturbing is that I have found what looks like a straylight problem with my set-up. If I turn up brightness & contrast to the maximum in the calculated image means, there is a streak of light running parallel to the spectrum [in all the images, to varying degrees]. It is approx 3% of the peak of the signal and about 50 pixels away. It wouldn’t have been summed in background removal, but not a good find. Am concentrating on this for the moment.
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