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BL Tel: General guidance for inferior images sought

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Ed Wiley_WEY
Ed Wiley_WEY's picture
BL Tel: General guidance for inferior images sought

I thought I might bring this to the forum as an example of what might be of interest to all; it concerns inferior images and what to do about them, The example below.

I have a satisfactory ensemble set for R and I and a decent check and comp for B and V for BL Tel from BSM-Berry as judged by the first set of images I received. However, the image set I received today was definitely inferior in quality to the first set I received, resulting in low SNR-values for comps and very high uncertainties for all transformed results after image stacking.

Options: (1) Reject this run, or (2) report the results with high uncertainties (range of 0.035-0.074). Switching to the two bright comps only (85, 88) would require repositioning the FOV as one is at the edge of the FOV.

I have not reported results and await advice. (My opinion, reject the set and await better quality images.)

Ed

hambsch
hambsch's picture
Submission

HI Ed,

I looked up the last observations for BL Tel and do not find much in the database for the past 500 days. Hence in this case I would submit even slightly worse data. You could see in the longer run how they fit to other measurements and if they would be really off you could still remove them, Otherwise during the last 5000 days of LC for BL Tel there are a few outliers which do not really harm the interpretattion of the LC.

my 2 cents,

Josch

HQA
HQA's picture
BL Tel

BL Tel is on the AAVSOnet "legacy" monitoring queue because of its unique characteristics.  it is a semiregular pulsator (period about 90 days) that is also in an eclipsing binary system (period 778 days).  The semiregular pulsation dies out during the eclipse, indicating that the SRD star is the one being eclipsed.  While there are many instances of a pulsating star in an eclipsing system, these are usually short-period pulsators (like white dwarfs) and small stars, not these giant SRD guys in a long-period system.  In the AAVSO chat room (https://www.aavso.org/chat), which seems deprecated these days, but where active discussion still continues, I threatened to write an article about the two dozen or so stars that I know of that seem weird - like BL Tel.  Maybe some day...

As for the data submission: I'm in agreement with Josch.  As long as there is a reasonable uncertainty attached to the submitted estimate, the researcher can decide whether to use the measure later, and in the meantime, it fills a gap.  That said, a significantly larger-than-normal uncertainty usually means there were clouds in the field.  With the large field of the BSM, you can have western stars in the clouds, and eastern stars in the clear.  The target photometry is then unknown - it could be obscured or not.  I usually include a "note" with the estimate that the count rate was lower than normal.  I'd also look at http://images.aavsonet.aavso.org/ for the night and see if images before/after look cloudy, and include that information with the estimate too.  The more information the researcher has, the better.

Arne

Ed Wiley_WEY
Ed Wiley_WEY's picture
BL Tel

Thanks for the comments, I have submitted all the data I have, the problem resides in B and V where there is no ensemble,only a check and comp, but I commented that the SNRs of these are very low.

Ed

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