HT Cas – Behaviour?

[Mr Ian David Sharp]

Hi all,

Since Gary recently sent out an alert for this star saying that it was in outburst I’ve started monitoring it. Last night I took a run of about 2.5 hours and got the attached V light curve. Is this to be expected?

I have every reason to believe the photometry is good as the images are fine and I have a S/N ratio of around 190 for the variable with a good ensemble of comparison stars well place near the centre of the field. The check star looks flat throughout.

Many Thanks
Ian.

Attachments:

1. 

   HT-Cas.png
   

[Jeremy Shears]

Very nice photometry, Ian.
Looks like a pre-eclipse hump (due to accretion hot spot).

[Mr Ian David Sharp]

Jeremy Shears wrote:

Very nice photometry, Ian.
Looks like a pre-eclipse hump (due to accretion hot spot).

Thanks Jeremy,

I’ll keep monitoring it and get longer and longer runs on it as we get our nights back!

Ian.

[Gary Poyner]

That’s exactly what it is Ian – orbital hump just prior to eclipse. I’ve seen these before visually, and it can take you by surprise!

Gary

[Mr Ian David Sharp]

Gary Poyner wrote:

That’s exactly what it is Ian – orbital hump just prior to eclipse. I’ve seen these before visually, and it can take you by surprise!

Thanks Gary,

Here are two more eclipses from last night. Getting slowly fainter overall.

Ian.

Attachments:

1. 

   20250730_HT-CAS_V_PixelSkies-C11_IDS_plot_lines_check.png
   

[Mr Ian David Sharp]

Hi all,

HT Cas now fading down to 16th/17th mag in V after being at 12-ish. Also, the big pre-eclipse humps seem to have gone, or reduced.

See last night’s run attached.

Ian.

Attachments:

1. 

   20250804_HT-CAS_IRB_PixelSkies-C11_IDS_plot_lines.png
   

[Jeremy Shears]

More nice data, Ian. The changes in eclipse width FWHM should reveal the disc shrinking as it cools.

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