Three spectra

[Ags]

Vega (the green lines are Balmer/hydrogen lines). As a hot A type star, Vega's spectrum is simple, showing a few prominent Balmer absorption lines.

Navi. Navi rotates very fast and has thrown off a ring of gas that glows brightly on the Ha line (middle of the red area).

WR140. This super-hot Wolf-Rayet star shows prominent emission lines that aren't hydrogen (I will try and identify them next).

As raw spectra (no denoising, not yet calibrated for the response curve of my sensor):

These were shot with an ASI120MM Mini, FMA135 telescope (30 mm aperture) and a Star Analyser 200 grating (about 17 mm distance to the sensor).

Vega - 0.5 second exposure

Navi - 0.5 second exposure

WR 140 - 10 x 10-second exposures, stacked in DSS

Edited September 6 by Ags

[Ags]

Based on the above, I have made a rough chart of exposure time for various visual magnitudes using either the FMA135+ASI120MM or RC6+ASI485MC (using a mono bin and assuming 1/3 the effective QE vs the mono camera). This is for a relatively clean spectrum like Vega above. It looks like I could get away with a quarter of the below times (in seconds) assuming I can tolerate more noise (something more like the Navi spectrum).

Fun fact: Navi is the first star named by a space traveller, in space.

Edited September 6 by Ags

[Ags]

WR140 was made famous by JWST:

[robin_astro]

On 06/09/2024 at 12:00, Ags said:

Based on the above, I have made a rough chart of exposure time for various visual magnitudes

Don't forget that if you want to get an accurate continuum shape, you need a minimum total of 20 sec exposure (in a number of stacked shorter exposures) to beat variations due to seeing (scintillation)

Cheers

Robin

[robin_astro]

On 06/09/2024 at 07:45, Ags said:

WR140. This super-hot Wolf-Rayet star shows prominent emission lines that aren't hydrogen (I will try and identify them next).

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

[Ags]

@robin_astro here is my effort at assigning the emission lines:

[Ags]

Looking at the spectrum, I wonder if this star would appear visually as green? It's a truism that no stars are green, but what about this one?

[Zermelo]

1 hour ago, Ags said:

Looking at the spectrum, I wonder if this star would appear visually as green? It's a truism that no stars are green, but what about this one?

That's an interesting thought.

I think the "no green stars" idea is based on how a black-body spectrum changes with temperature as a typical star moves through its lifestyle. Its "path" through the human eye's colour space doesn't pass through the green part. But stars are not exactly black bodies, and the metal-rich ones with multiple emission lines are presumably furthest from the vanilla black-body spectrum, so perhaps they can exhibit colours that a simple analysis wouldn't predict?

[robin_astro]

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

[Ags]

Here is Scheat with TiO, Telluric and VO lines mapped.  The user interface to add the lines is a bit basic (a text box) but that can be improved in due course.

[Ags]

The tourist brochure promised dazzling emission lines, but when I got to Sadr it was just another featureless hot star.

[Ags]

My notes say this is Beta Cygni, but I believe it is Beta Lyrae aka Sheliak. It is showing a little Be spike. (the spike in blue is a little photobombing star). I learned about the Chara array today, which took the following picture of the Beta Lyrae and its partially connected companion star. 

CHARA array - Wikipedia

And here is my more humble spectroscopic observation of the primary. I had to smooth the spectrum a lot as the data shows a sawtooth pattern and I don't know how to avoid that yet.

 

Edited September 18 by Ags