AAVSO Alert Notice 632 announces a new observing campaign on symbiotic star candidates. Please see the notice for details and observing instructions.
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
Hi! Project lead here (Adrian, a grad student at Columbia). Many thanks to all the observers---it is exciting to have such rapid data collection from my volunteer colleagues.
I will take a closer look at these this week---and soon I will post more candidates---, but here are some preliminary suggestions that hopefully illuminate how I'm thinking about this:
We probably have enough V band photometry from CD-28 10578 and NSVS J1444107-074451. The far-southern star ASAS J195948-8252.7 has not been observed, and it would be nice to have a light curve of at least a couple hours (continuous if possible) for ASASSN-V J081823.00-111138.9 if it is still visible (I haven't checked). And GSC 09276-00130 looks interesting enough to continue watching.
If anyone is comfortable taking B or U band photometry, go ahead and take a few hours for any target, since we only have V and CV observations so far. The further to the blue you get, the easier it is to see accretion disk flickering on top of the bright red giant---however, as you know, calibration also gets more difficult in these filters and SNR goes down (not to mention more expensive filters); B band should be fine, and very experienced volunteers could try U band.
Josch's data suggest GSC 09276-00130 might be interesting. Josch, it could be interesting to continue to monitor this object if you like (and verification by multiple observers is always good---especially if people at different locations can observe at very different airmass at the same time), but I think your data are already enough to flag it as a priority for observatory follow-up.
If anyone wants to be ambitious and take an optical spectrum of GSC 09276-00130, that would also be interesting! Useful wavelength coverage could include H-alpha at 6563 angstroms, [O III] at 5007 angstroms, the TiO bands around 5000--9000 angstroms (for M stars), and the Mg b triplet around 5050-5200 angstroms (for K stars).
thank you for the feedback. I will stop observations of CD ... and NSVS J14.... I will continue GSC.. I could also get B and U band images instead of V band if those are more interesting. For U band I would need to use a smaller telescope (40 cm instead of 50 cm). ASAS J19... still take a bit of time t get high enough to be able to follow it for a couple of hours as requested, but as soon as possible I will follow it.
I share the 50cm scope with a friend who is suing it during the new moon period (he is doing pretty pictures) so there will be a gap of about 2 weeks every month.
Hi Adrian, just to let you know that I've just started on the ASAS J195948-8252.7 and GSC 09276-00130 - fairly high in the sky using BV filters, I'll try and increase the cadence - plus as usual the weather here in Northern Tasmania is for want of a better word - "unsettled"!!
My colleague and I were debating whether the variability in GSC 09276-00130 is real or not, and decided that increasing the exposure time would help assess that, to reduce the fractional contribution of readnoise, etc. Would it be possible to take series of ~10 minute exposures instead of the ~2 minute cadence that it looks like is being used now? I am particularly interested in GSC 09276-00130, but longer-exposure monitoring of the other candidates (or even just some random ordinary red giants with similar V magnitudes, if you feel like it!) would be a useful control sample.
I do not understand this request The stars are bright so increasing exposure is not an issue. I guess you mean to do less exposures in a given time say one hour. So far I do imaging every few minutes as I cycle the stars. If you would have more stars in the same RA region I could observe all of them simultaneously by moving from one to the other. My mount is fast and this is my general observing philosophy (cycling up to 5 stars depending on their individual exposure). I could of course add the band images as well and maybe U band, but normally I do not have U band comp stars from AAVSO sequences. That would make the sequence much longer and you would get only once every maybe 15 min a new image in each band. Is this what you want?
I respond fully lower down in the forum. (No, a short exposure every 15 minutes is not what I want. We want to increase the signal to noise ratio by any means possible---but it's possible that you're already following the ideal strategy if you cannot increase exposure time.)
To ensure this doesn't get lost in the thread above: all observers, please note that "fast photometry" in the campaign announcement is a miscommunication on our part. Unless you have a professional observatory-class telescope, variability between short exposures will be dominated by noise, and we would rather cut down on the fractional contribution of readnoise with ~10 minute (maybe ~5 minute, depending on your equipment, object brightness, and sky conditions) exposures---ideally making such observations continually for at least 2-3 hours.
Many thanks! Don't hesitate to comment or ask questions. And thanks for the observations you have already obtained, which are still very useful after binning.
10 min exposure is much too long for my equipment (40cm f/6.8 scope with FLI ML16803 CCD). I guess you mean it is fine to get every 10 min or so a new image. Is this correct? Josch
Ah, interesting! No, I meant that we wanted longer exposure times on each individual image. We are not experts on small telescopes and this CCD, so we didn't know we might be asking for something impossible.
For my own edification, what prevents you from taking longer exposures? Is it just that the star would saturate? (I'm guessing this might be what you mean when you say "The stars are bright so increasing exposure is not an issue"? I did not quite understand that sentence.)
In any case, what is your current exposure time on each image? And is this roughly the longest exposure time you can use with your equipment on, say, a V~13.7 star?
Our goal is solely to improve the signal to noise ratio---as you can see from your data in the LCG, there is clearly some substantial scatter that is just due to noise and not due to real variability from the star. So if longer exposures are not possible, then don't change your observing strategy---it is good that there are many data points, because I can average them after you submit them.
(That said, dedicated sequences of just B band would be great, if you are comfortable observing in that band. As I said, the bluer you get, the less we have to worry about the red giant. Though these stars will probably be dimmer in B than V, so we will see what the noise is like. I see your point about the lack of U band comp stars---I will look into that, but for now only observe in U if you are very comfortable doing so and very comfortable doing the calibration.)
Many thanks for your help!
I read your request too late, I already had a series of 20 images of 1 min in V + 10 images in B of NSVS J1444107-074451. To compensate, I stacked the images 5 by 5 to give me 4 data points in V and 2 in B. Far from the 2-3 you requested, but better than nothing.
Thank you! That's good.
For future reference, I think it might in principle be better to report the individual image results to AAVSO, so that we don't lose information about how the data was obtained (i.e., your data points might be noisier than your usual for the reported slower cadence, since the readnoise from all those individual images got stacked into your composite data points). I can bin the processed data myself. But it is certainly not at all a problem for the data you just reported, since I know about it!
Perhaps a better way to accomplish what you are looking for is to set a goal for the SNR and maximum cadence for the campaign and let the observers monitor their resutls, and adjust for FWHM, sky transparancy, sky background, aperture, QE of their cameras, etc to get you what you need.
BTW: I have about 10 nights of data on NSVS J1444 which I have not been able to reduce because of a busy personal life at the moment. Hopefully I will get to it soon. In the meantime, my scope observes every clear night. I am using this object as one of the commissioning runs for a remote telescope.
Thanks, good advice! Ideally, when equipment permits, I would like SNR greater than or equal to 100, and as in the call for observations, cadence less than or equal to 20 minutes.
However, SNR < 100 (especially 30 < SNR < 100) is still great if that's all your equipment permits, and could easily find strongly variable symbiotics. And of course, on the other hand, if you can get millimag precision with a cadence of a couple minutes, go for it. Symbiotic stars have a great diversity of flickering amplitudes and timescales. If you see that you can get better SNR+cadence than some prior observer of an object, go for it.
Thanks in advance for the NSVS J1444 observations!
I took a test image of this star last night to se what exposures I need. I also too a spectrum with an R=1600. Interesting looking with Ha, Hb and some other emission lines.
!!! Thank you, Terry, far-southern circumpolar was going to be super annoying to get an observatory spectrum of. Could you send me the spectrum data (firstname.lastname@example.org), so that I can play around with this spectrum? (I can probably figure out any format...if you happen to have on hand both a fits file [w/ header] and an ascii file [w/ wavelength and flux axis as columns] I'd like both, but it doesn't matter.)
I can't tell from the low-resolution picture, but I wonder if there is emission at 6835 and 7088 angstroms. (That would be Raman O VI emission, which is only found in symbiotic stars.) But I'm about to go to sleep + I don't have the data, so I'm not to be trusted.
I took a look and I feel pretty confident that there is Raman O VI emission. So this appears to be the first confirmed symbiotic star discovered through this campaign / through the SkyMapper photometric cuts that I've been using to select candidates---and one of only ~300 known symbiotic stars. Many thanks and congrats!
This one was relatively quick to validate because of the Raman O VI emission---for non-burning, low-luminosity symbiotics, investigation will take longer.
Hi Adrian and All,
I've submitted V observation of ASAS J195948-8252.7 from three nights so far which indicate some low level variability (a few tens of millimags). Is it worth while continuing to monitor this star?
I can try B band photometry as well but Terry's observation on JD 2458255.06498 shows it to be 2 magnitudes fainter in B than in V. My V band images were 120 sec or 100 sec exposures. Much longer exposures will be required to achieve similar SNR in B images.
Yes, by all means, continue monitoring ASAS J195948-8252.7 in any band. These are interesting light curves, and become even more interesting if there really is Raman O VI emission as I speculate wildly above in Terry's subthread. I'll say more once I get the spectrum file from Terry...best not to speculate too far at this point. I don't see TiO bands that you might expect from an M giant, but dust can flatten the spectrum or it could be a K giant. RAVE thinks it's an M giant, and GAIA thinks it's like ~12 kpc away. So it's a great symbiotic star candidate.
I think it would be great to try B band. How long exposures would you need? As long as they are shorter than 20 minutes, a multi-hour light curve should be interesting. Even if they need to be longer than 20 minutes, it still might be interesting.
After some additional thought, I think that (after any observations you're already conducting today) we could probably stop V band monitoring of ASAS J195948-8252.7. I'd still be interested in seeing a night or two of B (and/or U) band monitoring of this system from you, however---just in case! SkyMapper photometry indicates that the giant is certainly dominating in V, so it's worth checking in B to try to get a better look at the accreting hot component.
It is a symbiotic star, as Terry has verified spectroscopically, but because the spectrum indicates nuclear burning, the light curve should be flat in any given night (as opposed to non-burning symbiotics, where there can be strong flickering but only inconclusive spectroscopic signatures). Initially, I therefore thought these <0.04 mag variations were strange and intriguing; however, it is not actually uncommon to see apparent variability on a similar scale in such objects and then, even at professional observatories, have a lot of difficulty assessing whether the varibility is real or due to atmospheric effects, etc. See, e.g., chapter 6 of Jeno's thesis from 1999 (http://user.astro.columbia.edu/~jeno/thesis.html) and subsequent work. So unless we see more dramatic variability at shorter wavelengths, this is probably more trouble than it's worth.
Anyway, it's great to have high-quality fast photometry of this newly-discovered symbiotic star---it's important to check our scientific paradigms!---and your observations certainly won't go to waste.
thanks for the link to Jeno's thesis, I'll take a look when I get a chance.
I've submitted two nights of B band observations of ASAS J195948-8252.7 which don't show a lot of variability. Both nights were clear but seeing and transparency deteriorated over the course of the time series.
On both nights the B light curve shows a fading trend of about 0.03 to 0.04 mag over 7 hours as the target rose from air mass 2.2 to 1.6. I don't believe this is real because the Check star also shows similar trends. Probably due to differences in extinction between the Comp, Check and Target stars. On photometric nights I would be able to correct this but not with the data from these two nights.
Tonight will be my last chance to observe until July so I'll try for another B band run. Cheers,
At this point, I think we have a great set of V band observations, and going forward with these particular targets I am mainly interested in soliciting (1) B or U band observations, (2) higher SNR observations in any band including V, if you happen to notice that you can achieve higher SNR than prior observers of a given target, and (3) spectra. That said, all observations are useful, both scientifically and for fine-tuning my observational requirements for future iterations of this campaign---so if you are enjoying these observations, then don't let me stop you.
Many thanks for your excellent work. In this small set, we didn't seem to find any non-burning symbiotic stars with large, unambiguous flickering >=0.1 mag---however, we did find a traditional symbiotic star, validated spectroscopically! I'll study your results and post an alert notice with more targets soon.
I am returning from holidays and have started a session on CD.... and J14 with incresed exposures of 120 s and 180 s, respectvely using a V filter.
I will see how this improves SNR.
I finally got a chance to reduce my data on NSVS J1444........ I added about 13 days/nights with typically time series of several house per night. Using Vstar and all the data for the past 30 days, I was able to get the beginning of a phase plot with a period of 80 days. Enjoy.
Just updated some observations. I now have 18 days of several hour time series in the AID. It looks like it has brightened about 0.2 mag over the past 30 days and about 0.1 mag over the past 5 days.
NSVS J1444107-074451 had brightened on 0603 by 0.1 to 0.2 mags since this campaign started which was posted on 0603 by the author. Its brighened again and on 0610 its brighter than 13.3.
Is this normal?
Thanks, Gary! Yes, variability on this level over weeks/months is normal for the pulsating atmospheres of many (though not all---depends on the subtype) normal, isolated giants. The NSVS J1444107-074451 light curve looks normal to me (which is a useful constraint). I'll try to dig up a good paper showing some typical red giant light curves and share it with the forum later this week. Photometric evidence for binarity would typically come in the form of clearly outbursty/non-periodic long-term light curves, large/abrupt/non-periodic inter-day variability, and/or flickering/variability within a single night. Mainly I am looking for flickering on minutes-hours timescales.
(PS, I expect to be issuing a call for observations of new targets in about a week or so.)
A new version of AAVSO Alert Notice 650 has been issued. This notice continues and substantially expands the campaign first announced in AAVSO Alert Notice 632. I extend my sincere apologies to investigators Mx. Adrian Lucy and Dr. Jeno Sokoloski for the incorrect text in the earlier version of Alert Notice 650.
Elizabeth O. Waagen, AAVSO HQ
I am working my way through a few of these stars, after following a previous star of yours I have really come to enjoy the ZAND stars for there dynamic nature.
Anyway please check the star ASASSN-V J173832.43-492840.2 in the VSP, I have several hours of data on this taken last night and was expecting a star about mag 14 but the star indicated is sitting at a V mag of about 15.3. I note the near neighbour is about mag 14 so am just confirming their is no mix up with the neighbour.
Thanks for calling our attention to ASASSN-V J173832.43-492840.2. The identification is right and it is a mira with a large range. It gets fainter than 17.5 but ASAS-SN measures it blended with the 14.7 Vmag. star 9" to its west, that's why the published range was small and brighter than the actual magnitudes.
The VSX entry has been updated and a note about the companion has been included in VSP:
If it is visible for anyone, a quick V band magnitude for EN Sgr 19 22 42.08 -13 59 56.5 (and potentially continued monitoring) would be very useful. Thanks! ---Adrian
(Forrest Sims got a couple interesting spectra showing the appearance of TiO bands between Sep 18 and Oct 10, and it would be nice to know the corresponding photometric evolution. It may just be normal mira pulsation, but the presence of Balmer lines with a normal decrement on top of an apparently O-rich giant spectrum is intriguing.)
AAVSO Alert Notice 681 announces more symbiotic variable candidates requiring photometry - the next installment in the campaign underway since April 2018. Please see the notice for targets, details, and observing instructions.
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
I tried to image GSC 05140-03255 in V band last night but patchy clouds interferred. Also SNR of the target was only ~25 in 2 minute exposures which is the limit of my unguided mount. I'll be concentrating on the brigter candidates in future. I'll try for 3 hours on ASAS J185604-2327.2 tonight. Cheers,
Hi all! Thank you again, from both me and Jeno, for all your work on this. Your observations have helped guide our observing proposal decisions, and some of these targets are being observed at the SAAO 1-meter. We also have a proposal out to the Las Cumbres Observatory (LCO) network. There weren't any very clear detections of flickering in the AAVSO data, although for a time I thought GSC 05140-03255 was a clear flickering detection (we are now still working on figuring out whether the B band variability is real vs. artifacts of the instrument...jury's still out).
In anticipation of the possible LCO observations, and because LCO as a robotic telescope network would require us to pick exposure times in advance, we expect to post a new and shorter campaign sometime soon requesting B, V, and U magnitudes for 17 targets (no need to search for flickering, just test exposures so that we don't saturate/underexposure in LCO). If you are still interested in symbiotic stars, please keep an eye out for that upcoming posting in the next week or two.
In the meantime, there are 2 of these targets for which we now have X-ray detections, and one more for which we have another upcoming X-ray observation, and we would like to know their current V band magnitudes (and IR magnitudes if you have the capability) in order to assess the any risk of optical loading in Swift XRT or Chandra, in which optical photons can masquerade as X-ray photons for bright red sources. No need for long-term right now monitoring, just enough to get the current brightness. They are in VSX as:
ASAS J152058-4519.7, 15:20:58.3 -45:19:44.4, V~12.8?, Requested magnitudes: V, I, J
ASASSN-V J132541.71-585505.9, 13:25:41.7 -58:55:05.9,V~13.4, Requested magnitudes: V
Gaia DR2 6043925532812301184, 16:27:49.8 -29:16:45.5, V~14.7?, Requested magnitudes: V, I, J
Regardless, thanks again to all!
ASASSN-V J132541.71-585505.9 now has a small sequence
Both ASAS J152058-4519.7 & Gaia DR2 6043925532812301184 now each have one comp & check star that will show JHK data
Tim, Crawford, Sequence Team
I have now taken spectra and V mags for each of these targets.
Gaia DR2 6043925532812301184, JD 2458996.92998, V=15.39
ASAS J152058-4519.7,JD 2459000.02715,V=12.60
ASASSN-V J132541.71-585505.9,JD 2458999.96549, V=13.77
It's great to see these spectra. For IRAS 13224-5839 there is a (semi-)published spectral classification of M7 by Jack MacConnell from objective-prism plates in the far-red. This late type seems to be confirmed in Terry's spectrum by the big drop in the TiO bandhead near 7100A, which also shows weak H-alpha emission.
It is perhps worth noting that multiple photometric data-points across the visible and near-IR are available for all these stars using the VizieR catalogue-query service, including APASS, SkyMapper, DENIS, etc.