[David Boyd]

I am curious about the wavelengths which both John (implicitly in the ISIS listings) and Robin give for their calibration lamps. These are different from the standard Ar and Ne wavelengths given by NIST, for example here https://physics.nist.gov/PhysRefData/ASD/lines_form.html

If you look at the discrepancies which ISIS lists in John’s calibration fit, these appear to be almost exactly what is needed to bring the lines into agreement with the NIST values.

I have the Shelyak Ar-Ne lamp in my LISA and use a .lst file in ISIS which contains the NIST wavelength values. This routinely gives me a 4th order polynomial fit with rms residual less than 0.1.

David

[David Boyd]

To mitigate this problem, if I am recording the spectrum of a target at low altitude (close to 30 deg) I will look for a reference star as close as possible in altitude to my target and then record spectra of the reference star both before and after the set of spectra of the target. I compute response profiles from both sets of reference star spectra and take the mean of these to use in correcting the target spectrum. Although not perfect, this is better than choosing just one of the response profiles. It is instructive to see how much the response profile can change over an hour for a star at low altitude.

David

[David Boyd]

I confirm Kevin’s recipe for getting gnuplot to work with ISIS. I run v4.6.6 on Win10. There is indeed a pgnuplot.exe in that release. My only difference is that I don’t have ‘full control’ ticked in the folder permissions and it still seems to work OK.

David

[David Boyd]

The spectrum has changed a lot from June 30 to July 2 and then relatively little from July 2 to July 3. H-alpha emission is growing.

David

[David Boyd]

In my view there are two aspects to this we should be considering:

a) does the proposed activity have a clearly defined observing programme and what are its goals and timescales?

b) where are the skills and experience most likely to be found to pursue that programme and achieve these goals?

At the moment, the answer to the second question is probably within the Variable Star Section. These observers are used to measuring the faint, low amplitude signals required, using a range of filters and processing the data. It would therefore seem logical to consider launching the new activity within that body of observers and attempting to build a sufficient level of interest and activity that the goals can be seen to be achievable and the timescales realistic. Once a firm base of activity has been established, useful results are being achieved and a long term programme looks viable, then is the time to consider forming a new section or group within the BAA.

Regards,

David

[David Boyd]

Thanks Andy. Good call Robin.

David

[David Boyd]

The full programme of talks at the BAA/AAVSO joint meeting on variable stars at Warwick University in July is now available at https://britastro.org/summer2018.

There is still an opportunity to present a poster at the meeting by contacting Roger Pickard at roger.pickard@sky.com.

David

[David Boyd]

2017 was my worst year for clear nights since 2006. I managed to record useful photometry and/or spectroscopy on 102 out of the 273 nights when I was available to observe. Assuming this is representative of the whole year, observing should have been possible on 37.4% of nights. In 2016, the equivalent figure was 45.3%. The best months in 2017 were March, August and November and the worst February and September.

During 2017 I measured 25427 photometry images and recorded 2333 spectra.

Best wishes for clearer skies in 2018!

David

[David Boyd]

A quick calculation using the spec of the QHY5L II camera from their website with a 225mm FL scope indicates a field of view of around one degree. This is probably larger than the field you see in the Alpy guider camera but still quite small if your mount’s pointing is not very accurate. A shorter FL camera lens would give a wider field in proportion to the ratio of their FLs. You could attach a camera lens to the QHY camera with an appropriate adaptor taking account of the distance of the CCD chip behind the front plate of the camera so the lens focuses on the CCD. I don’t know about webcams these days. I imagine the problem would be finding camera driver software compatible with the other software you are using.

Best wishes,

David

[David Boyd]

Hi John,

This is a common problem unless you happen to have a mount capable of very accurate pointing. You can either use your finder scope visually, or more conveniently, attach a small CCD or CMOS camera fitted with a normal camera lens on top of your scope so you can see the wide angle field to which the telescope is pointing on the computer screen. Within this you should be able to see your intended target. By working out where the small field you see in the Alpy guide camera is within the wider field from the piggy-back camera, you can work out how to adjust your mount’s pointing to bring the target into the Alpy guider field.

David

[David Boyd]

Following on from Robin’s comments above, the plots below show how the EW, continuum level and flux of the H-alpha emission line of AG Peg have varied over the past couple of years. Clearly what the continuum is doing has a big influence on how you interpret changes in the EW as an indication of how the line flux is varying.

David

[David Boyd]

Hi Robin,

Rotating the camera was one of the many things I tried but the results were inconclusive.

SX cameras have three sets of push-pull screws round the front of the camera which enable the front face of the camera body to be made exactly parallel to the CCD surface. When Terry reassembles the camera, one of the checks he makes is to adjust this using a collimating system which reflects light off the chip surface.

David

[David Boyd]

Hi Paul,

Terry showed me the chip and I could not detect the presence of the oil visually. He said one effect it had was to change the colour of the surrounding chip package slightly. I think you would need the experience of what that subtle difference between clean and contaminated chips looked like to pick it up.

David

[David Boyd]

Hi Hugh,

There is a more recent paper on EG And by Kenyon & Garcia at http://iopscience.iop.org/article/10.3847/0004-6256/152/1/1/pdf.

Regards,

David

[David Boyd]

It is also worth keeping an eye on the H-alpha emission line in AX Per which shows strong orbital modulation, as do all the Balmer lines. The following plot shows my flux measurements over the last two orbital cycles. Coverage of the first cycle was patchy. The phase is currently about 0.4 and the flux is now rising. It will be interesting to see if the peak is as high as last cycle.

Regards,

David

[David Boyd]

Robin,

Thanks for the reference to Huggins’ publication. His description of his equipment and his early visual spectroscopic observations is fascinating. His efforts to reliably calibrate his spectra are positively heroic. You get a real sense of his excitement in discovering the nature of the objects he was observing spectroscopically for the first time. He was one of the first to attempt to classify spectra in a systematic way. You can also sense his competitiveness in promoting his discoveries. It’s a great read.

David

[David Boyd]

Hi Paul,

Have you tried measuring some RV standard stars to calibrate your capability? The Soubiran et al catalogue prepared for Gaia gives a good list – https://www.aanda.org/articles/aa/abs/2013/04/aa20927-12/aa20927-12.html.

These are 6th to 10th mag stars and there are several dozen with RVs greater than 50km/s, both +ve and -ve. They are F, G and K type stars so good for using in cross-correlation. About 20% of them have southern Decs down to -10deg. This would let you see what consistency you can expect.

David

[David Boyd]

I sent the spectrum to Elena Kazarovets and just got the following reply. David

Dear Dr. Boyd,
Thank you very much. I have revised the type of variability for NSV 11988 (LB instead RCB:) in the new (82-nd) Name-list we are preparing.

Best wishes,
Elena Kazarovets

[David Boyd]

Hi Marc,

Welcome to the BAA spectroscopy forum. It is great to see someone with your experience joining us.

As you will have seen from some of the earlier posts to the forum, several of our members have recently acquired low resolution spectrographs such as the Alpy and LISA. It would be helpful if you could explain whether, and how, such low resolution devices can make a useful contribution to the VV Cep campaign. The analysis Ernst has been describing clearly requires high resolution H-alpha observations. If low resolution observations are useful, I am sure some of us would contribute.

Regards,

David

[David Boyd]

Hi Tony,

Did you see the recent posts on the ARAS Forum about professional interest in the symbiotics SU Lyn and AG Dra? Consider adding these to your target list.

Cheers, David

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