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AG Dra observing campaign

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weo
weo's picture
AG Dra observing campaign

AAVSO Alert Notice 572 announces an observing campaign on the symbiotic variable AG Dra. Please see the Alert Notice for details and observing instructions.

Many thanks, and good observing,

Elizabeth Waagen, AAVSO HQ

WGR
WGR's picture
New Format

Hi Elizabeth

 

I like the new format.

 

Gary

weo
weo's picture
Correct URL for AG Dra 2017 campaign

The correct thread for the April 2017 observing campaign on AG Dra is this one. The URL for it is https://www.aavso.org/ag-dra-observing-campaign

However, in Alert Notice 572, I accidentally gave the URL for a 2013 campaign on AG Dra: https://www.aavso.org/content/ag-dra-observing-campaign . Do not use this URL.

I have corrected the online text of Alert Notice 572 so it links to the right forum thread.

Please be sure to post all of your comments/questions about the current (April 2017) campaign to the correct thread (https://www.aavso.org/ag-dra-observing-campaign)! My apologies for the error and any confusion it may have caused.

Good observing,

Elizabeth Waagen, AAVSO HQ

 

 

lmk
lmk's picture
Visual estimate issue

I notice that the two closest comp stars are 99 and 105, but their true Vmag are 9.85 and 10.46, respectively. Now, this is resulting in my estimates being 0.05 mag fainter than they actually are, due to this coincidental "roundoff" error, more like a type of systematic error. Should I adjust my observations brighter by 0.05 mag, or leave them based on the roundoff?

Thanks!

Mike

lmk
lmk's picture
Bizarre estimates

I ahve submitted 4 visual observations of this star recently, and I notice a definite brightening trend of about half a magnitude. However, looking at the light curve https://www.aavso.org/lcg/plot?star=AG+DRA&height=450&visual=on&grid=on&...

The CCD measurements in B and V are pretty constant in the same interval. Also, the visual observers seem to be split, with half seeing the same brightening trend as I do, and the other half constant, similar to the CCD.

This is really baffling to me. If there was a marked color change occuring, that might explain it, but the B-V looks unchanged. There is no explanation of this divergence of estimates that comes to my mind !

Mike

Tonisee
Purkinje effect?

Mike, I suspect that noticed discrepancy could be caused by Purkinje effect in action... After all, AG Dra is pretty red star.

Tõnis 

lmk
lmk's picture
I suspect variations are real

Ok Toni, well Purkinje would explain offsets between visual and CCD estimates, but if CCD were constant, the star was in fact constant, the visual estimates by same observer would not be expected to change due to Purkinje alone.

However, another idea came to mind. I suspect my observed variations are real. I see other visual observers showing similar 0.5 mag differences over the same period, even though on average the CCD are "constant". My guess is that just by random chance, my 3 observations which were significantly fainter than my most recent one (v=9.75) were just made at the times when the star had short dips in brightness. Its possible none of the CCD measurements have caught any of these short dips.

But what are the time duration of these dips? Is this star a possible eclipser too? I think more dense coverage, esp. CCD time series may uncover these "dips".

Mike

TRE
TRE's picture
hint of EB

 

 

 

 

There is some suggestive data at 2454305.6 to 2454305.9.

It mimics your 0.5 mag observation.

245598.6 to 245598.9 suggests datataking during haze then clearing for the bottom of another possible eclipse.

Ray

jmerc
AG Dra observing campaign

Dear AAVSO observers,

first of all, thank you very much for your effort to obtain photometric data for our beloved :) symbiotic system AG Dra. We are monitoring the AAVSO database for new AG Dra observations daily and we are really delighted by the enthusiasm and passion of the AAVSO observers involved in our campaign. Thanks this huge effort, this symbiotic binary is monitored with around one-day resolution. The observational data of such amount (109 photometric measurements in B, V, R and I filters from the beginning of the campaign to this day) and quality will give us an unique opportunity to study the photometric activity of this interesting interacting binary in fine details.

As we mentioned in previous, according to our statistical analysis of photometric observations, we know that the the time interval between outbursts of AG Dra vary from 300–400 days, with median around 360 days. If we assume, that the last outburst occurred around JD 2 457 517, we can expect the next outburst in the interval from JD 2 457 877 (May 3, 2017) to JD 2 457 917 (June 12, 2017). Of course, please take this prediction without warranty, since it is based on typical photometric behaviour of this search-less system. There is also some probability that AG Dra will return to quiescence stage as we have already detected such behaviour during the weak activity stage 1963–66.

On the other hand, we have some hints that the symbiotic system AG Dra is still active. Even though the photometric behaviour of AG Dra indicates the typical quiescence low-amplitude variability, some spectroscopic characteristics clearly demonstrate that the system is awakened state. Indeed, the equivalent widths of strong emission lines are almost stable in this period. In contrast, their profiles are typical for the active stages of AG Dra, when the blue-wing absorption component observed only during the quiescence stages is almost completely smoothed away.

So, what can we expect from AG Dra? We will see in next days. In the case of this interesting object everything is possible and as we know this object, it will be certainly the less expected possibility:)

Once again thank you very much for your effort and we are look forward to new exciting photometric data for AG Dra!

On behalf of the scientific team,
Rudolf Gális and Jaroslav Merc

lmk
lmk's picture
Rapid short period variations

Last night I visually observed it at mag 10.35, quite faint for recent times. During the subsequent few minutes I saw it vary brighter 0.25 magnitude and fainter again. So, this object deserves some close scrutiny by time series observations.

The nature of the variations I am seeing seems to imply it is more likely an obscuration type events rather than simply an eclipse.

Mike

clkotnik
clkotnik's picture
CCD Observation Time Series

I collected  CCD observations for a couple of hours (2457887.765 to 2457887.857) in V and don't see any significant variability.

regards,

Cliff

lmk
lmk's picture
Strange

Yes, Thanks for looking! It is odd that only the visual observations seems to "catch" these fading and rapid changes. It may be just "bad luck", none of the CCD were done at the right moment? On May 13, I was surprised to see it as faint as 10.3, with fluctuations up to 10.1 in a matter of minutes. This rapid variation reminds me of EX Hya, a star which also exhibits these short term changes by CCD measures.

However, looking at a longer timescale via LCG, I see a few rare instances where a CCD measure is near the faint end of the visual measures. The most recent one is on Feb 01, 2015 V=10.27 by observer HBB. She also made other observations where it was more typically brighter.

So, I am more certain these visual fadings and rapid changes I have seen, are indeed real, possibly due to some obscuring material in the line of sight?

Mike

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