AAVSO Alert Notice 710 announces an observing campaign beginning now on the UXOR ASASSN-V J181654.06-202117.6. Please see the notice for details and observing instructions.
To stay informed about this campaign, subscribe to this forum thread (option 1 below under Subscribe) - see feedback from the PI, comments and questions from observers, and notes from AAVSO HQ. Add a post yourself - join in the discussion about this interesting target!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
Right now yes, anything we can get we can use, and it's now mostly about getting as much data as possible. Thanks for reacting so quickly to this alert.
I watched this target for 3 hours last night, taking CCD images in B, V, R, and I at about 9 minute intervals (see attached chart). The scatter in any of the bands was no more than about 0.02 mags, only slightly greater than the scatter for my check star (000-BNP-171). I would conclude, therefore, that any rapid variations (minutes to hours) for this target are no larger than a hundredth of a mag or so.
Thank you so much for taking part in this campaign and providing lots of photometry for J1816 (shorthand for the longer star name). Even though the star seems stable (very clear from your data), my prefence is for the shortest cadence possible. Of course I understand if you're observing other interesting targets that you would want to spread your focus. Could I ask you to observe the star at least once per hour?
I am glad these observations are useful. Unfortunately, observing from Southern California, there is only a 3-hour window when J1816 is above 30-deg elevation (airmass ~ 2). Are observations farther down in the "muck" still useful? Also, is it important to transform the observations, and if so, is there a preferred comparison star?
I think we should keep the observations above airmass 2, it's unfortunate that it's just a 3 hour window, but anything we can get is much appreciated. I don't have a preferred comparison star
Just wanted to let you know that I obtained data from ATLAS, which lines up with the deepest part of the eclipse (along with data from VMT). I also have data from ASAS, which seems to show a similar dip in the past (more analysis needed). I'm working on reducing the LCOGT data to see if we can get more data to fill out the eclipse, and I'll keep you posted! Thanks all for staying on board
Just wanted to thank you all for observing J1816 and provide a very basic plot. I just took all the AAVSO, ASAS-SN, ASAS, and ATLAS data (I've been on holiday so didn't have the time to reduce the LCOGT data yet), and just removed the median for each observer and filter to get a kind of first order plot. It looks like the object is still crossing in front of the star, so if you can keep observing this would be much appreciated.
For some reason I can't seem to upload the file here, so I made a GitHub repository with the plot in it (basic_plot.png found at https://github.com/dmvandam/j1816)
I´m observing this star from Namibia couple of days now. Today I will try to observ it as often I can. I do have V filter only... I did not send any of my observations yet.
Br, Grzegorz Duszanowicz - Sweden
Thank you for taking the time, let me know as soon as you've posted the data, I'm very interested in it. I'm posting basic plots and models to a github page (I'll repeat it in a public post instead of a reply).
Hello thanks to everyone for continuing to make observations of this interesting star. I'm "kind of" on holiday so won't be able to do any in depth analysis for now, but did want to share with all of you some new plots. So I've posted a plot of the possible ring system and the theoretical light curve obtained on the github page (https://github.com/dmvandam/j1816). I hope this keeps everyone motivated. This could be a very very interesting system. Let's keep our hopes up!
Hi Dirk, nice to be trying to help you with your project! - apart from the usual nightly cloud I've managed to obtain roughly 8 hours of observation for each night using BVR filters, with a cadence of approximately 20 minutes between each filter. I've noticed a rough sinusoidal movement in magnitude of approx. 0.1 magnitude peak to peak on my observing sessions and wondering about possible causes?
I'm sorry I missed your message. Yes I've been noticing the variations in other data, which is fantastic because this confirms (from data from Namibia) the fluctuations. I need to discuss this with my supervisor as the period of the oscillation (based on your data and done by eye is ~2.3 hours) is quite fast. I'll get back to you as soon as I know more!
Excellent Dirk and thanks for your reply - sounds great.
- will keep on with monitoring, weather is the only problem at present - I seem to get a couple of clear nights followed by many nights of cloud - not good when trying to see a trend!
Anyway, cheers and all the best, Merv
I talked with my supervisor and have been looking at the star in general, and we're thinking that these variations could be due to pulsations of the star (looking into it being an RR Lyrae or Delta Scuti Pulsator... the one thing we're wondering is why it's so fast [maybe multi mode?]). If you plot the light curve in the AAVSO environment you can see the variations very clearly by checking DGRA's data.
Hi, I observed last night with good sky conditions from Chile, tried to cover as much as I could with a cadence of roughly an hour, making a total of 7 blocks of observation with 3x20s exposures each (last images where taken with 2.49 airmass).
Should I average the 3 exposures of each block of observation?
I'll continue tonight,
Hi Juan Pablo,
Thanks for taking observations of J1816, great that you managed to take so many observations. It would be great if you can do block averages! Looking forward to seeing what your results!
Hola Juan Pablo,
Thanks a lot for processing and posting the data. Just a little confused by the title of the post... are you done as in with the processing or done / unable to do more observations?
(soy medio venezolano aunque no parece por el nombre)
Hola Dirk, I thought about it later and yes, the title is a little misleading. I meant to say that I had averaged and reported my observations. I couldn't do any observations on the night of aug 15 and last night I tried with tricolor filters to see if I improved my results but it wasn't the case, so two "wasted nights" but I'll continue my observations tonight and until this campaing is finished.
Thank you for your continued support on J1816, it looks like we're approaching pre-eclipse levels. I'd like to ask you to keep monitoring J1816, because 1) I don't believe we're quite at quiescent levels, 2) I hope that this is half of the eclipse and that we'll see two similar dips as we continue to observe the star.
Please print a new chart.
Grzegorz Duszanowicz discovered that the 131 comp is variable (possibly a DSCT). I have replaced this with a 129 comp.
Ad Astra & Good Observing
Tim Crawford, Sequence Team
I'm a little new to this game, so I had some questions for you. Are you requesting me to change the chart, or are you (as part of the sequence team) changing the chart for everyone? Do I have to request everyone to rereduce their data and post the new data on AAVSO? (that is everyone who used 131 in calculating their magnitudes).
Dirk van Dam
Thanks to Grzegorz Duszanowicz for discovering that Comparison Star 131 is a variable star (perhaps a DSCT). I don't know how many of you used this star to determine the magnitude of J1816. I would very much appreciate if you could check and potentially re-reduce/upload new data and let me know when you have done so. Tim (from the sequence team) has suggested to replace this with Comparison Star 129.
Hi, first congrats to Grzegorz Duszanowicz for the discovery and thanks to Tim Crawford for updating the sequence.
I was wondering the same so I did a time series including 131 and other without it and including the new 129 comp. It didn't make a significant difference, maybe because I'm using an ensemble of eight comps. It would be good to hear the opinion of those who have more observations than me for this tartet, to see how this affected their measurement.
Re-uploading the data with the new comp wouldn't be a problem to me except that I will have to manually add the air mass to each observation again (is the air mass data being used?), but if necesary I will get into it.
Hi Juan Pablo,
For now I'm just shifting the observations by eye, but I plan on doing transformations that include airmass in the measurements, so if you could add those that would be great!
Hi Juan, I.m using VPhot and removed 131 and could see no real different - as you suggest the ensemble is probably the reason - I'm also using an ensemble of eight comps.
Hi Merv, thanks for your confirmation, that's why it's good to use as many comps as possible. Just to be sure I deleted all my observations and uploaded again with the new ensemble of comps.
I just wanted to thank you all for supporting us throughout this campaign. It looks like the star is approaching its quiescent level. I'm still hoping for another dip - reflection symmetry - that could show rings! Asking you all to monitor intensively seems unfair, so instead I would like to ask all of you to monitor the star twice per night (at least an hour apart). If you see a large drop in brightness, please report this to me or on this forum, so we can start up the intensive monitoring again. I'll keep everyone informed on the progress on the modelling as this goes on.
This is what I was hoping for! It looks like J1816 is dropping again. If everyone could resume their original cadences that would be excellent, maybe we can fully capture the eclipse this time (if that is what we are looking at now - fingers crossed).
Aldrin B.Gabuya here from Al Sadeem Observatory, Abu Dhabi, UAE (OAAA).
As it was reported here that the previous comp star 131 is variable; mistakenly used for the photometry, I deleted my previous measurements and just uploaded the re-calibrated measurements to the AAVSO WebObs.
My last observation was from Sept. 10, 2020. I'll try to do quick observations of J1816 for few nights this month in just a short period since it is now situated just < 40 deg altitude after dusk in our location.
I'm looking forward to the outcome of this research. Thank you very much. Clear skies.
J1816 is brightening again, but this is giving me more confidence than ever. It looks like this most recent dip is done, but this is actually perfect! I'll highlight here. If you look at the AAVSO light curve and select for example HMB data you'll see two "shallow" dips, the most recent one and one at ~2459060. These are of similar length (~8 days) and similar depth (~0.2 mag). This is really exciting because it makes me believe that we are past the half way point of an eclipsing ring system and that we will see another major dip in the light curve in about ~35 days. Please continue observing this star, because we are missing tons of detail on this deep eclipse and I feel like we are onto something really exciting!
Good stargazing all,
Just wanted to let you all know that J1816 is dimming again (see DFS), and this is fantastic, I'm growing more and more confident that we will see the original 0.8 mag dip in the next 20-30 days. Good luck with observations. I'll post some more analysis to the GitHub, interesting plots, potential models and then let all of you know when I've done that so you can follow what I've been doing up until now.
If you're interested in the evidence for the ring system please checkout https://github.com/dmvandam/j1816 and particularly the two plots j1816_full.png and j1816_2nd_eclipse.png.
j1816_full.png shows the data from ASAS-SN, DFS (all filters) and HMB (all filters), aligned simply. I chose a mid point and took all the data before this mid point and reflected it across the midpoint (the black data). Plotted on top of that is the real data.
In j1816_2nd_eclipse.png you can see a zoom of the 2nd eclipse, which shows that the real data overlays the reflected data very well.
Because of this I can make the prediction that the light curve will drop by ~0.8 mag (~50%) on the 9th of November 2020. Please keep observing this star, as I am quite certain this will happen on approximately this day.
Good observing and clear skies,
Perfect, thanks TG,
I'm thinking that the intra-night variability is pulsations of the star and not related to the occulting object. (They're very stable and I'm working on some plots to show the model I've developed and how it applies across multiple bands and observers)