[Dr Andrew Smith]

Good spot Robin,  there was a warm pixel that was moving out of the photometry aperture.  

Thanks Andrew

[Dr Andrew Smith]

Nice work Robin, Regards Andrew 

[Dr Andrew Smith]

I decided that it was too much hassel to share it so I am just using it myself.

Regards Andrew 

[Dr Andrew Smith]

How about a montage starting with visual drawn observation through photography/ ccd or cmos to spectra and photometry.

This would illustrate the progression over the period.

Regards Andrew 

[Dr Andrew Smith]

Thanks Woody, I will give that a go.  Regards Andrew

[Dr Andrew Smith]

Thanks Robin, that might be just what I need. Just got to work out how to easily rename the files in a way ISIS expects. I have a rename program that should work!

[Dr Andrew Smith]

Yes you can but you have to establish what coordinates on the inage corresponds to the star being on the slit as unlike the reflective slit spectrographs you can’t see the slit in the guide camera.

Regards Andrew 

[Dr Andrew Smith]

I think Robin is right that they need to get some established spectroscopists to use it and publish results.

However, I would have to say i think all commercial spectroscopes (and my home made ones) have issues of one kind or another.

I had a Lhres III which had light leaks, was mechanically unstable, required focusing if you shifted wavelength via a crude mechanism etc.Then I had Lisa, it had fishtails and a flat lamp that produced flats with strong gradients etc. I will pass over the issues with mine!

I like the idea of air slits and all reflective oprics on the sx spectroscope but don’t like the beam splitter and not being able to see the star on the slit etc.

Regards Andrew

[Dr Andrew Smith]

When building up a carbon fibre bike I had to be very careful not to over compress the tubes. Most cf components had strict torque limits. 

Regards Andrew 

[Dr Andrew Smith]

The resolution is way too low. I would estimate you nee R ~ 27000 (assuming I did the sums right).

Regards Andrew 

[Dr Andrew Smith]

I don’t see any good reason not to use it. Photometrists often employ defocused stars to improve S/N. 

Regards Andrew

[Dr Andrew Smith]

A different take on the dimming: https://arxiv.org/abs/2006.09409

“Betelgeuse is the nearest Red Supergiant star and it underwent an unusually deep minimum at optical wavelengths during its most recent pulsation cycle. We present submillimetre observations taken by the James Clerk Maxwell Telescope and Atacama Pathfinder Experiment over a time span of 13 years including the optical dimming. We find that Betelgeuse has also dimmed by sim20% at these longer wavelengths during this optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity) of the star as opposed to the surrounding dust as was previously suggested in the literature.”

Regards Andrew

[Dr Andrew Smith]

It’s difficult to imagine what could be dark against the sky. To be a shadow or a silhouette requires a brighter background.

Regards Andrew 

[Dr Andrew Smith]

Thanks William, not that fussed about brand but wanted high transmission and only the three listed.

Thanks for the info.

Regards Andrew 

[Dr Andrew Smith]

I think it’s less of an issue with differential photometry as the camera response impact the target and comparison star equally. However, the filter and camera response will make some difference if the comparison star are of very different spectral classes.

Regards Andrew 

[Dr Andrew Smith]

Robin, they are different standards. Baader are Johnson-Cousins and Chroma are Bessell.

Regards Andrew 

[Dr Andrew Smith]

Grant, yes it’s been like that for ages and they are out of stock at dealers except of the odd filter. Regards Andrew 

[Dr Andrew Smith]

This camera has low amp glow by CMOS standard so it looks like your ok. I have had discussions on Stargazers Lounge with other users of this camera where we got differing results so there may be camera to camera variations. Always best to check the performance of your camera as it is not difficult. 

Regards Andrew 

[Dr Andrew Smith]

David, I would propose with CMOS the best strategy is to pick a range of exposures and stick to them. Then given the low read noise just add more exposures as needed. 3 or 4 should be than enough say 1, 10, 100, …. They also tend to be USB 3 with fast download so you don’t  lose much time between frames.

Regards Andrew 

[Dr Andrew Smith]

Here is a comment from ZWO https://astronomy-imaging-camera.com/tutorials/what-is-amp-glow.html

“Glows may not “grow” with time the same way dark current itself does, and may accelerate over time becoming brighter faster than dark current itself as exposures become longer.”

Although I could not find my initial source I found this analysis which is similar https://jonrista.com/the-astrophotographers-guide/the-zwo-asi1600-guide/the-zwo-asi1600/preliminary-analysis/

Just to be clear I am not saying the ASI1600MM is not linear. Like Simon Dawes I find mine is very linear but I use darks with the same exposure as the lights and I don’t use bias frames.

Regards Andrew

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