In 2011 an observing campaign was launched to observe several bright giant variables in support of research being carried out by Drs. Steve Howell and Travis Rector. Part of the campaign was a request for long term monitoring - that request is still active. Please see AAVSO Alert Notice 441 for details and observing instructions. This forum thread is being created now to allow for discussion, etc. (the campaign predated the existence of our forums).
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
Dear AAVSO participants in the Bright Giant Campaign, your contributions over the years have been amazing and have led to numerous scientific and educational results. Travis Rector has been leading the educational work and I hope he will post here as well. I have been leading the science work, along with Travis and some others, and would like to highligh a few of the results. But please do have a look into the published papers listed below as they contain many more details including some of the oddest spectra you will ever see. We had been using the Kitt Peak Coude Feed telescope to obtain spectra of many of these stars with observers being out team and many high school teachers/students. Kitt Peak observatoyr, due to NSF budget cuts, has closed that telescope (and much of the mountain), so that aspect of the program is now over. However, your many contributions to light curves available through the AAVSO and our large collection of spectra are all available on-line. Travis will send out the link for the spectra.
I wanted to highlight my two favorite stellar targets, AS 325 and XX Oph - the Iron Stars! As these papers show (2005PASP..117..462C, 2009PASP..121...16H) they are odd binaries, with one massive wind producing evolved giant star and another hot smaller Be companion, Both eclipse.
AS 325 now, hanks to you, has a known orbital period of 513 days while for XX Oph, we are still waiting for the next eclipse. See attached files.
If you are interested, it'd be great to continue to monitor XX Oph in order to find the next eclipse and thus determine a pretty good orbital period. You can see we have a nice model for AS 325 (see attached figures) but are still in the dark when it comes to XX Oph.
Thank you for all your work and help in these projects!!
Cheers, Steve Howell
Dear AAVSO observers,
I am always so blown away by the commitment and great work you all do. The Bright Giant Observation Campaign is really something.
At this point, I'd suggest we try to gather the light curve data as well as the spectra I have from past years and think about a research note/paper - likely in the AAVSO journal, a very appropriate place for it. We can look at the total amassed data and see what gems of astrophysical wisdom we can learn from the observations.
With Gaia DR3 available, we know the distance (and thus absolute luminosity) for all the targets, so we can properly place them on a H-R diagram and glean their evolutionary status. The periods detected, or not, the spectral changes seen, or not, will give us a great idea of their ages and properties as well.
If you'd like to be involved in this work, as there is plenty to go around, please get in touch with me. Lets start to organize and see where it takes us.
In the meantime, collecting additional data is always useful, but for me, I'd like to see what we have to date and what we have learned from this decade long study.
Of the 22 stars in this long-running campaign on bright giant variables, 21 are well covered - thank you (and keep observing them)!
Only TZ Oph has zero observations - not a one. Oph is now in good position, and the sequence for TZ Oph has been augmented, so PLEASE add this mag 12.8-14.4 V semiregular to your observing program and observe it every 7-10 days.
Please post here to say if you are adding it to your program, or if you have other comments about it or other stars in this campaign.
Principal Investiagor Dr. Steve Howell posted fantastic feedback last month (thanks, Steve!) - be sure to read it further up in this thread.
Many thanks! and Good observing,
I'm adding TZ Oph to my observing program. The once every 7 to 10 days sample rate is about right for the current weather patterns here on the east coast of the USA as well!
Jim DeYoung (DEY)
One major disincentive for TZ Oph's coverage is the terrible comp stars available, with V uncertainties over 0.1 mag and I uncertainties of over 0.4 mags. This doesn't seem reasonable for 2020.
Have you looked at various non-AAVSO sources for photometry? An obvious check is to use VizieR to look at Pan-STARRS and SkyMapper, taking V = (g+r)/2 (it's remarkably close). Also the ASAS-SN database for candidate comp stars in V. Also GAIA2 (also in VizieR) works fairly well, taking V = BP - 0.2 for stars of intermediate color (say between B-V of 0.0 to 1.0), and GAIA2 'RP' = Cousins I within 0.1 mag or so. Compare I magnitudes further with DENIS for stars fainter than I mag 10 ro so. It is usually the case that you can cobble together a reasonable preliminary sequence for yourself by intercomparing all these sources for consistency.
I wonder to what extent the various wide-field surveys are covering all these targets, specifically ASAS-SN, ATLAS, ZTF, and Evryscope, probably others (MASTER etc). It is not clear to me whether the cadence, filters (or no), image-scale, saturation limits etc are suitable for these targets. Access to the data may not be straightforward either. Supposedly Evryscope is getting the entire accessible sky in Sloan g and r every two minutes(!) as weather permits down to mag 12 or so. The others are getting coverage every few days in various filters. Does anyone have a good idea of what the coverage is?
I observed TZ Oph with my Pentax Kp and Esprit 100 around 2459013.6. Magnitude records uploaded were/will be reported as transformed DSLR BVR and the non-transformed magnitudes placed in the comments field. Appears to be near maximum magnitude. My DSLR measures seem to be consistent with SDMs reported CCD-based magnitudes from the night before.
I observe several objects that are in/near the ecliptic. My experience with the survey data I have looked at for stars in/near the ecliptic shows that the automated systems do at best a marginal job when the Moon is close to the fields. Not sure why but I would suspect flat-fielding problems. Since I am not automated and I'm actually at the telescope I take pains to reduce Moon-light shinning down the OTA, etc. I think it makes a difference in my photometry.
I know the DSLR is not optimal for deep red variables that have molecular lines, etc. I have a CCD with clear, B,V, Rc and Ic filters and am currently getting it all configured for my portable observing requirement so my DSLR observing should be in its last days. The image scale will sample the psf sufficently well too.
Jim DeYoung (DEY)
Great to see the bonanza of new observations you all have contributed. As mentioned, sky surveys do indeed cover, well the sky, but especially in dense star fields, Oph for example, they are often not nearly as fine as the AAVSO results.
TZ Oph has just been updated with DR9 APASS Data.... a lot less uncertainity with this data.
I would urge all observers to DL this new data!
Tim Crawford, Sequence Team
Just uploaded a few more TZ Oph obs. Probably the last one for this obs. season as "it is in the trees" now for me.
Jim DeYoung (DEY)