robin_astro

From North Cumbria. Not in colour but directly overhead and very dynamic around 23:00 UT (West is up north over the Solway to the right) http://threehillsobservatory.co.uk/allsky_camera/allsky_20241010_aurora.mp4 Here is a single frame

I remember as a young lad reading Fred Hoyle's "Black Cloud" https://en.wikipedia.org/wiki/The_Black_Cloud

I see the "Journal of Modern Physics" (As opposed to the "International Journal of Modern Physics") is on the list of predatory journals designed to make money from people who are unable to get their work published in reputable peer review journals https://predatoryjournals.org/journals-list-4

Dr Noel Richardson has announced a Pro-Am campaign covering the upcoming periastron period when the winds of WR140 and its companion O star collide. Details of the latest campaign are on the AAVSO website https://apps.aavso.org/v2/campaigns/865 Amateur spectroscopists were also involved in the previous two periastrons in 2008 and 2016, making radial velocity measurements to improve the orbital parameters, resulting in these papers https://ui.adsabs.harvard.edu/abs/2011MNRAS.418....2F/abstract https://ui.adsabs.harvard.edu/abs/2021MNRAS.504.5221T/abstract Cheers Robin

The atmosphere (Ozone) ultimately limits measurements from the ground to ~3200A Robin

No, it is the spectrum in the visible from the fainter star to the right of the bright one which happens to fall in line. If you rotate the camera plus grating you can separate them. Cheers Robin

It is not just the camera though. The grating response (and the lack of IR in the target star) is equally significant. The grating is blazed to give maximum efficiency at ~500nm and tails off either side of this. Gratings designed for use in the IR have a higher blaze angle

Leaking of filters in the IR though is an interesting problem. There are examples of claimed discoveries of Planetary Nebulae in images which turn out to be cool bright stars imaged using narrow band [OIII] filters, surrounded by out of focus leaked IR. Similarly with photometric filters affected by the same problem giving wrong values on cool stars. Cheers Robin

Yes it is weak but it is there though and the signal in the IR is so low that it becomes a significant proportion of the signal (perhaps ~20% or so roughly from the plot?) when dividing the with filter by the without filter spectra to produce the filter passband curve

You will need to be a bit careful when measuring the response of the 850nm IR pass filter as there will be some contamination from the 2nd order spectrum in the unfiltered spectrum. (It is quite low with the blazed SA200 but with a blue light source like Delta Cas some of the light at 425nm will also appear at 850nm) To avoid this when measuring spectra in the IR, an order filter can be used (for example a filter only passing wavelengths above 500nm will allow measurements from 500-1000nm) Cheers Robin

Here they are in the database that comes with ISIS

Here are a couple of good references to help with identification of lines in WR stars https://ui.adsabs.harvard.edu/abs/1987ApJS...65..459T/abstract for WC/WO stars (which includes WR140) https://ui.adsabs.harvard.edu/abs/1995A%26AS..113..459H/abstract for WN stars Cheers Robin

Note also that using Pickles spectra for comparison with measured stars is only applicable provided the measured star has low interstellar extinction. This is true for Vega but interstellar dust can significantly redden the spectrum. The attached note "A tale of two stars" describes an example of this. Cheers Robin A Tale of Two Stars.pdf

? The curve you want to compare with Vega is A0V. A3V is slightly cooler

Time to review this document then 😉 http://www.threehillsobservatory.co.uk/astro/Relative_flux_calibration_20221222.pdf Note that the correction needed is not just the response of the instrument. The effect of the atmosphere is equally significant (but included provided the air mass of the reference and target stars are similar) Cheers Robin