Observation by Steve Knight: T CrB Photometry

Uploaded by

Steve Knight

Observer

Steve Knight

Observed

2026 May 01 - 03:44

Uploaded

2026 May 04 - 17:35

Objects

T-CrB
Lightcurve
Variable star

Equipment

Seestar S50

Exposure

30 sec

Location

Skilgate, Somerset

Target name

T CrB

Title

T CrB Photometry

About this image

A first experiment with multi aperture photometry with AstroImageJ. Tried doing photometry from 21.05 UT to 03.44 UT. Signal to noise not great. Reference stars used were the magnitude 10.6 and 9.8 stars in the AAVSO finder chart. This is green channel only.

Files associated with this observation

T CrB green channel.JPG (127.9 kB)

Like this image

Dominic Ford, Alan Dowdell, Jeremy Shears, Paul Whitmarsh, Andy Wilson

Comments

Jeremy Shears, 2026 May 06 - 13:11 UTC

Good to see you trying this Steve. I assume each datapoint is a 30s exposure?

You could try stacking a few, say 5 or 6, before photometry. Or you could average the result of say 5 separate measurements.

But before doing that, have you looked at the most outlying frames to see if there is an obvious problem with the associated image? The bias seems to be to fainter mags. See if the photometry apertures are correctly centred on the stars and that the star profiles are not contaminating apertures they are not suppose to, especially the sky annulus.

Steve Knight, 2026 May 09 - 10:49 UTC

Thanks Jeremy, yes each exposure is 30 sec. Yes, there is an inconvenient star next to #106 on the AAVSO finder chart. Adjusted the annulus accordingly. Have a more fundamental problem though, this is all my nightly stacks using S50 from June 2024. You see the problem for recent stacks. Apparently a Seestar update in late July 2025 made the FITS non linear. Trying to get to the bottom of this. https://1drv.ms/f/c/9ca9ff6f92ba0730/IgCFTTw5stXgTaPo_7iyUTPCAZi4gWVBoyIN8hhStzzJ5Mg?e=LXh4O2

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