N 2024 Oph (V4370)

[Stewart John Bean]

Hi all,
I have taken an image with the Slooh Chile 2 V to follow this nova. The images look fine ( although a crowded field) but the magnitudes produced using the Vphot, using the Variable star plotter sequence for V4370, produce a magnitude of 12.0. Others are giving a magnitude of 13.5 for the same date. This is the first time that I found a big discrepancy between Vphot and the results reported to the AAVSO.

Saturation of the detector looks fine. I am using COMP stars 113, 128, 133 from the V4370 sequence.

If anyone is also following this nova what are your COMP star details?

Regards

Stewart

[Jeremy Shears]

Hello Stewart,

I was looking at Mazin Younis’s fine image of the nova (https://britastro.org/observations/observation.php?id=20240316_060436_8e8e3dc829f92b9d) and noticed it was a busy field, yet the VSP chart shows no bright stars that might contaminate the photometry aperture. The nearest is 113, but that’s still a fair distance. What does a visual sense check of the image suggest relative to the comps: 12 or 13.5?

The most recent obs at 13.2V on March 16.792, though that observer seems to report almost a mag brighter than others. What is the time of your observation compare? And just to confirm you deployed a V filter (the nova is much brighter in R).

JS

[Stewart John Bean]

Jeremy,
The image has a JD of …384.896.
Gary Poyner has, I think, taken the ultra wide field ( Y Slooh in his nomenclature) scope image from the same run and obtained Mag 11.6 (V) so that is reassuring. He has done the same the following night and obtained 12.3 .

Mazin has marked star 113 as the nova and given different coordinates to VSX. VSX gives 17 39 57.08 -26 27 41.9.
The nova is close by and very red towards 10 o clock.

Direct measure of the brightest pixels in my image gives

V4370 113 128
11,000 21,000 4000

So I think around Mag 12 is about right for Mar 15.9 but means that there is a two mag difference in V between these results and those from some experienced observers. This is a situation that is unsettling and probably has to do with the redness of the nova. I have not reported my results to AAVSO.
Stewart

[Gary Poyner]

I too am a little mystified by the photometry in the AAVSO database. I went back to the image after I saw it, and double checked I had ID’d the correct star – which I had.

I used the normal wide field image from the Slooh Chile 2 scope for both measures. The ‘Y’ is the AAVSO code for active. The image was measured with AIP4WIN.

Gary

[Stewart John Bean]

I have emailed Andrew Pearce to ask for the sequence he is using.

[Robin Leadbeater]

A spectrum from 2024-03-12 by the 2SPOT team (amateur remote echelle spectrograph in Chile)
http://www.spectro-aras.com/forum/viewtopic.php?t=3122

Very red continuum with very intense, very broad H alpha

[Stewart John Bean]

thanks Robin. Redness is probably at the centre of this topic.

[Stewart John Bean]

Andrew Pearce has kindly provided me with the three sequences used on each of the telescopes he uses.

I have applied each sequence to the Mar 15 Slooh V image in question and found that all sequences, plus AAVSO, give a Magnitude of 12 or there about. Min is 11.86; max is 11.99.

I will now reply to Andrew with fuller details and share the Mar 15 image with him via Vphot.

Stewart

[Stewart John Bean]

~I checked that saturation effects are not relevant by using a short exposure of 10 s instead of 45s. The V magnitude is in line with the trend.
So no further to understand why Slooh Chile 2 V produces much lower magnitude values.
Stewart

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