[Andy Wilson]

Hi Steve,

Purely by coincidence I observed AG Peg the night after you. I include my uncorrected spectrum, along with a spectrum corrected for atmospheric and instrument response using HD209459. I’m not sure the correction is perfect, but I was having some computer issues that mucked up my guiding.

Best wishes,

Andy

[Andy Wilson]

Hi Steve,

Nice spectrum!

Interesting to see how Chi Cyg looked in July. It is a difficult to be sure with our different setups, but I wonder if there is a hint of the hydrogen emission lines weakening from July to August. Though this is obvious when comparing the spectra on the screen, I wonder if this might be an effect of different resolutions. We’d probably need to get an accurate measure of equivalent widths to be sure.

I’m looking forward to the October meeting.

Best wishes,

Andy

[Andy Wilson]

Hi Bill,

Yes, it is wonderful that Christian makes his software available for free. Spectroscopy is particularly well catered for in having a number of free good software packages out there. I’m also just learning to use PHD2 for guiding. Another free software package, really easy to use and even allows you to place a rectangle on the screen for spectroscopy so you know where the slit is.

I hope you enjoy the International Meteor Conference.

Andy

[Andy Wilson]

Hi Bill,

I might give meteor spectroscopy a go sometime, but probably not just yet. I’m in the final stages of getting a new telescope and observatory setup for spectroscopy, so that is taking up all my astronomy time at the moment. I’m guessing you use a grating in front of the camera lens? Apologies if you posted above in the thread. I’d be interested to see a picture of your meteor setup.

I’ve been using a mix of BASS and ISIS. I’m gradually moving more to ISIS now as it is highly automated but a steeper learning curve.

If I’m trying to get an accurate corrected spectrum then I’ll crop off the areas I can’t properly correct. However, if I’m just looking and measuring the lines which are in the spectrum then I’ll usually keep the whole spectrum.

Cheers,

Andy

[Andy Wilson]

Hi Paul,

Thanks for the advice. Your setup sounds not too disimilar to mine so it is good to hear that a powered USB hub and active cables worked for you.

I got things working with a powered hub for an observing run last weekend, and I am now waiting for another clear night to see if this really has fixed the problem. I’ve found everything just works fine in the daytime, it is only when I start proper night time observing that I get drop outs! From the sound of it powered USB cables will be the way to go if I still have problems.

Thanks,

Andy

[Andy Wilson]

Hi Bill,

Reading your post I notice that you say:

“when you divide a meteor spectrum through by a stellar spectrum”

I’m not sure if this is what you really meant, as this is not how corrections are applied.

When creating a response correction you divide a stellar spectrum by a professional corrected spectrum for the same star, or at least by a standard spectrum for the spectral class of the star. This gives you your instrument and atmospheric correction. This is an imperfect process since the resolutions will be different resulting different line widths, the alignment may not be perfect, and you have atmospheric telluric lines in your spectrum. However, a smooth curve can usually be obtained by tweaking parameters and applying some smoothing to get rid of sharp bumps due to anomalies near absorption lines.

This is then your response correction. Robin’s links show this process with illustrations of actual spectra. You can the apply this response correction curve to a meteor spectrum.

The problem is this is best done with the star at the same altitude as the target. Otherwise the effect of increasing airmass has a big impact on the spectrum with decreasing altitude and the response correction will be wrong. So ideally you’d have an image with the same setup, but perhaps a longer exposure, that would include an A type star at the same altitude as the meteor. Of course the meteor is not at a single altitude so even this is not straight forward. A star at around the mid-altitude of the meteor might suffice as an approximation.

I also find it difficult to get a good correction at the extreme blue or red. When producing a corrected spectrum I just accept that I may have to crop off the extreme wavelengths.

Apologies if this is just going over what you already know.

Best wishes,

Andy

[Andy Wilson]

John,

That is a really nice spectrum you have captured with the SA200. The 2 spectra match really well and I’m particularly interested to see you have the 4 first hydrogen Balmer emission lines. I’d be interested to see if this changes over the coming days and weeks.

I intend to switch to high resolution mode with my LHIRES III soon, so I may not be monitoring it at low resolution.

Best wishes,

Andy

[Andy Wilson]

Here is a low resolution spectrum I took of Chi Cygni last night, 15th August 2015.

I used Richard Walker’s spectroscopic atlas to identify the Titanium Oxide and Zirconium Oxide absorption bands, though TiO is most definitely dominant. I also picked out what I believe to be the first 4 emission lines in the hydrogen Balmer series. I understand the hydrogen emission lines are caused by a radiative and hypersonic shock wave propagating through the stellar atmosphere (http://arxiv.org/pdf/1109.6500v1.pdf). I was a little hesitant in the identification of H-alpha as I have not seen it in other online spectra, but I think this is correct.

Best wishes,

Andy

[Andy Wilson]

Hi Bill,

That makes sense, in as much as something odd at the blue end in the reference spectra gives you trouble correcting the continuum. Do you know what the rough continuum shape should be for meteors? Any speculation on my part would more than likely be wrong.

I’m not sure if this will help, but sometimes I use BASS to process my spectra. This creates the response correction in a slightly different way. You still use your spectrum and a reference spectrum, but once you’ve done the division you use your mouse to select specific points on the divided spectrum. BASS then joins the dots to create a smooth response curve. I’m not sure if that would give you a way to create a response curve avoiding the dips or peaks.

Instrument and atmospheric correction is a tricky area. I’ve been struggling with it myself for the better part of this year, but I think I’m about there with my latest spectra.

Fascinating work you are doing. Like you say you can get lots of useful information even without the continuum correction.

Best wishes,

Andy

[Andy Wilson]

Hi Bill,

I’m glad you had a successful night with the weather cooperating! That is a nice spectrum you have captured.

I’m not sure if there is any reason why you could not apply this to meteor spectroscopy, but when I am correcting for the instrument and atmospheric response I use an A type star. Ideally one with an easily available professionally corrected spectrum. The temperature of the star is not the important thing, it does not need to match the target. The instrument response will be calculated from my spectrum compared to the professional spectrum across all wavelengths. What matters is that A stars have very simple spectra so it is easy to smooth the response as there will just be a few blips for the hydrogen lines.

Best wishes,

Andy

[Andy Wilson]

An interesting point Robin. I had thought that this would be better suited to a lower resolution setup than my own, and I should use my low resolution grating. However, since I know the spectral line I’m interested in, then high resolution should not be a problem and as you point out the increase in contrast will be a benefit.

Cheers,

Andy

[Andy Wilson]

Hi Robin,

Thanks, that is good to know. Taking a daylight spectrum sounds like a useful and interesting test anyway. It would be handy to see how well my flat correction works across the slit. With stellar spectroscopy I always aim to put the star in about the same position on the slit, but there will be times like this when I’ll want to use more of the slit height.

Best wishes,

Andy

[Andy Wilson]

Robin & Richard,

Thank you for your replies. It is good to hear it is not a crazy idea, though one that might only give negative results.

I had been thinking that one exposure might be sufficient with the slit appropriately aligned. Though it is a good point that 2 positions might be needed due to the contrast between day side and night side of Venus.

Robin, I have one of the newer LHIRES IIIs, do you think the flat field calibration lamp is sufficiently good?

If aurora were the cause, then I would hope there would be an “obvious” green line due to oxygen at 5577 Angstroms, or at least strong enough to be above the noise.

The other issue would be knowing when to look, as ideally this would be when CME has been ejected in the direction of Venus.

I’ll try it out with an early morning in September when Venus is better placed. See how feasible it is to get good data.

Thanks,

Andy

[Andy Wilson]

Dominic, Nick and Callum,

Some interesting ideas.

I’ve decided to opt for a middle of the road powered USB hub. If it doesn’t work then I’ve only spent £25. The computer is in the observatory at the moment, but I think 5m cables is just over the limit for stable usb camera connections. I’ll give some of the other suggestions a go if this doesn’t work.

I actually had 2 cat5 cables laid from the observatory to the house when I had the original observatory built. That gives me internet in the observatory, and also gives me the option to remotely control everything in future if I want to. However, they only go to the wall of the observatory, not to the pier.

Thanks,

Andy

[Andy Wilson]

Roy, Dominic and Martin,

Thank you for your responses. I hadn’t realised you get get powered cables, which gives me another option.

Martin, the Cat 5 to usb solution is also interesting. Like you say probably overkill for what I need, but worth looking at in more detail if I can’t solve the problem with simple extenders or hubs.

Thanks,

Andy

[Andy Wilson]

Hi Cameron,

Those are wonderful images. Great to be able to make the most of an opportunity to take images from a more Southerly location.

Best wishes,

Andy

[Andy Wilson]

Hi Mike,

It doesn’t look as though the spectroscopy meeting will be recorded. Hopefully the presentations will be made available after the event, as often happens.

Glad to hear you are already learning Visual Spec. Spectroscopy is a fascinating area that has really taken off in recent years. Variable stars make ideal targets for spectroscopy.

Best wishes,

Andy

[Andy Wilson]

Hi Mike,

Those are great looking spectra and an interesting comparison. Nice to see the BAA collection being put to good use.

If you fancy taking things to the next level then there is a wealth of free spectroscopy processing software now available. I’ve used BASS and ISIS, but there is also RSpec, Vspec and I think maybe a few others. These can produce a graph of a spectrum and help you to identify elements, along with various other functions.

I’m still a bit of a beginner in spectroscopy myself, starting out in September last year, but if you want pointers to any of the software then please let me know.

Do you know about the BAA spectroscopy workshop on 10th October at the Norman Lockyer observatory? It is being organised by the Variable Star Section noting it is more about an introduction to spectroscopy rather than variable stars.

Andy

[Andy Wilson]

Hi Donald,

May I also welcome you to the BAA. I became seriously interested in astronomy at around the same time as you, just over 30 years ago when I was 11. Jeremy has given you some excellent advice which I completely agree with. I find being involved with observing sections to be the most rewarding part of my BAA membership. You certainly don’t need to be an expert and there are plenty of people in the sections willing to offer help and advice.

As a variable star observer myself I concur with Jeremy that your equipment is ideally suited to making variable star observations. Although much useful work is done with CCDs and DSLRs, variable star observations made by eye are still of immense importance and value. Indeed the Variable Star Section has more active visual observers than CCD/DSLR observers.

Using binoculars or a small telescope to observe variable stars is a great way to use and improve your knowledge of the sky. I have a few variables that I follow with binoculars when I don’t have the time to do imaging or just want a relaxing observing session looking at the stars.

I’m sure any other section would welcome you too. The Comet and Deep Sky Section spring to mind with your equipment.

It is worth pointing out that next Saturday, 27th June, is the Exhibition meeting in Cardiff. If you are able to attend then it is a great place to see the work of the different observing sections and discuss how best to start contributing observations. That is how I started out in variable star observing, when I attend an exhibition meeting at Cambridge back in 2001, if my memory serves..

Best wishes,

Andy

[Andy Wilson]

I’d have to say that it looks a lot like an aeroplane vapour trail being illuminated by the setting Sun. A nice picture of one but in my opinion it is not a meteor or other astronomical phenomenom. Others have posted similar thoughts on the Bristol Post website.

Cheers,

Andy

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