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Predicted and Observed Minima Differ

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CMJA
CMJA's picture
Predicted and Observed Minima Differ

While getting some observations of LPVs during March 19, their V-band magnitudes appear to be significantly different from their predicated minima for the month. It looks I am "running with the pack" in terms of where my observations are falling on the light curves. What am I missing? For example:

LPV
(1200-day
LCG link)

Observed
Vmag

Verr
Predicted
minima

Approximate
Predicted
Minima
mag

S LMi
9.988
+/-0.026
 2016-03-15
14

T Hya
9.108
+/-0.003
2016-03-13
13

X Gem
10.841
+/-0.005
2016-03-14
13

X Cam
9.301
+/-0.015
2016-03-12
13

RS UMA
8.887
+/-0.006
2016-03-12
14

Thanks for looking.

 

Michael

lmk
lmk's picture
Predicted time is off

[quote=CMJA]

While getting some observations of LPVs during March 19, their V-band magnitudes appear to be significantly different from their predicated minima for the month.

[/quote]

Well, looking at the light curve for the first one, S Lmi for example, the approx. min mag of 14 is correct, its just on its way down from max right now, the predicted time appears a bit early. Reason?

Mike

 

HQA
HQA's picture
predicted minima

Michael, I must be missing something.  Your data is falling close to everyone elses, but your table lists predicted minima that don't make sense.  For example, S LMI, according to bulletin 79, had a predicted maximum of February 6 and a predicted minimum of June 17.  Your other objects have similar date errors for the time of minimum.  Where were you getting your predicted minimum dates?  I think that is probably your problem.

I also note that your S LMi measure shows an error of 0.26mag - is your error estimate a typo?  This would normally mean an object very close to the limit of detection, and not a good point to submit on such a bright variable.  If you were expecting it to be 14th magnitude, then your frame may be overexposed.

Arne

CMJA
CMJA's picture
Predicted Minima - solved!

Thanks to Phil, I realized what I did wrong. OMG, I was using Bulletin 78 (2015)! I don't know why I didn't clue in (it says Bulletin 78 and/or 2015 everywhere), but the links on this page haven't been updated and I went right down that garden path :-(

https://www.aavso.org/observers#sections
(under Tools, Resources and Reference)

I ended up downloading a csv file of what I thought was the most recent bulletin. The downloaded file is even entitled "Bulletin2015.csv". That should have been my final obvious clue. Doh!

I'll drop a note to Elizabeth about gettign the links updated.

And yes that is a typo with S Lmi. I measured it at +/- 0.026, not +/-0.26. I corrected the original post, however moot!

Clear Skies!

Michael

weo
weo's picture
Link updated

My apologies for not replacing last year's AAVSO Bulletin with the current Bulletin on the 'For Observers' webpage! I have updated the page so that the 2016 Bulletin is referenced and linked.  I'm very sorry for leading you down the wrong path, Mike  :)    (Thank you for using the Bulletin !!)

Good observing,

Elizabeth

CMJA
CMJA's picture
Link Updated

No worries. I took the path without reading the "signs". Serves me right. Thanks for taking care of that so promptly.

Michael

spp
spp's picture
bulletin 78

Michael,

The dates of minima you're using are from bulletin 78 rather than the current bulletin 79.

Phil

CMJA
CMJA's picture
Oh yeah. See my reply to

Oh yeah. See my reply to Arne.blush

Thanks Phil

Michael

HQA
HQA's picture
miras at minimum

Good that things are cleared up, Michael!

I know that you are planning on covering a bunch of miras at minimum.  One thing that would be really useful is an extension of the "double-trouble" program.  Most miras have not had their near fields studied at minimum, and there may be faint companions.  Remember that a mira with V=14.5 at minimum will be measured 0.1mag too bright if there is a V=17.0 companion included in the measuring aperture.  I used to reserve good seeing nights for looking for faint companions of target objects.  You might also use B,V,Ic imaging, as companions may be very different in color from the target star, and you might see an elongation of the target, for example, for very close companions in one filter or another.

Arne

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