Hello everyone, my name is Kevin Alton
I was recently invited to join the Eclipsing Binary Forum leadership where I hope to provide technical and scientific support for anyone interested in studying eclipsing binary systems. Briefly my formal education includes a BS in Chemistry-Physics and an advanced degree in Analytical Chemistry. Both served me well for 40+ years ending as a Senior Director of a Drug Metabolism Group at a major pharmaceutical company. Since retiring in 2010, much of my leisure time involves studying an assortment of variable stars, exoplanets, and minor planets. My backyard observatory (UnderOak) in NJ remains fully operational for brighter objects (C11 SCT/ST8XME). However, starting in 2018 a new Meade ACF 16" remotely operated from Benson, AZ (Desert Blooms Observatory) serves as the main instrument for research. In toto since 2006 both sites have produced more than 50 papers published in peer reviewed journals. Most of these describe light curve modeling of overcontact binaries using the Wilson-Devinney code or deconvolution of light curves from HADS variables using discrete Fourier transform.
Notably the traffic on the EB forum is very light with just 22 postings over the past year. This is surprising given the mission of AAVSO and its large global membership. I would be interested in some feedback about attracting more discussion in the EB section. In the meantime, I have some questions to bounce off our readers:
- Considering the thousands of different mount, telescope and detector combinations, which EBs are best suited for your site and instrument?
- My personal goal in acquiring new lightcurve data from any variable target is to publish the results in some fashion. Aside from the satisfaction of obtaining your first high quality lightcurve, do you ever plan on publishing or uploading your results into a public archive?
- If you haven’t posted your data to a public archive or published your results, what factors keep you from doing so?
Hopefully these questions will familiarize me with the EB Forum readership and engender some further discussion.
Most of my work with EBs is done while mentoring local high school students. My focus is on the process of exposing them (as absolute beginners) to the world of variable stars and scientific data collection and analysis. I try to show them the value of physics-based modeling and the alignment of measurements with predictions using PHOEBE (or EXOTIC if we're doing exoplanets). However, to be perfectly honest, my own experience and skill with PHOEBE is poor (beginner level), and my students and I struggle with understanding how much of our poor model convergence is due to inexperience, misunderstanding of the physics of contact binaries, poor quality data, or the inherent ambiguities of what we're trying to model.
I would very much like to be able to give them the satisfaction of finding a ToM, adding it to an archive somewhere, and seeing it show up on an O-C curve, but I'm not really sure how to do that myself (because if there's a "central archive" of ToM data, I haven't found it). And I'm pretty sure that finding one ToM, while a real milestone for a high school student, isn't worthy of a published paper. (However, I would really like to impress on them the importance of sharing results.)
So, bottom line, I don't really post much on the EB forum because I just don't feel like I know what I'm doing.
Mark M (MMU)
I've been sampling the various EB software capabilities over the past two years. In my humble opinion, I have found Peranso to be a very intuitive software tool for modeling light curves and calculating times of minima for my EW work. For binary system modeling, I have used Binary Maker but my experience is still somewhat nascent in modeling versus performing O-C analyses. For me, it's all about the user interface as I am not well versed in python, and Windows based software tools are much more intuitive for me.
Like you, I have been an EB enthusiast for the past couple years. I have been performing surveys of unobserved EWs but have not yet published. I am an avid collector of observations for uploading to the AAVSO database, but could use some encouragement and mentoring to take the next step in analysis and publishing.
Might I suggest that this forum have a periodic virtual zoom to have those of you with collection, modelling and publishing experience mentor those of us that just haven't felt ready to take that plunge?
Though AAVSO sponsors webinars across the organization, could this section sponsor periodic mini webinars to gather like minded amateurs to interact?
Chuck, I think you have a great idea about virtual mentoring.
I like the direction this discussion is going. Over the new few days I will put together a response which covers all your replies
Good evening everyone! I enjoyed raising this topic.
First I would like to say that I am a beginner in the observations of EB's and that's why I don't usually report my data, because I'm unsure about the accuracy. I am a physics student and my course conclusion work (TCC as it is known here in Brazil) is a systematic observation of some stars with suspected variability.
I believe that in addition to mentoring, we in this area of EB's really need to understand the modeling and mini lectures or webinars would be of great help.
My equipment is very simple, but the location of my observations is splendid. I have views of both hemispheres, I live in the countryside of one of the driest regions of Brazil. Which favors 8 months a year of clear skies.
For new observers, I suggest that you start by observing stars on the AAVSO legacy program. We have a long history on these stars. If you send me a copy of your data, I will compare your time of minima to other recent data and let you know how it looks. This way you can build confidence in your process before you move on to unknown targets. I publish times of minima in each issue of the JAAVSO.
One thing that is often overlooked is the time of the observations. It is important to make sure that the computer clock is accurate to one second or better. Both WWV time signals and GPS are good time references. Also, make sure that the midpoint of each exposure is used. Some software uses the start time and will cause a systematic error in the lightcurve.
Thank you for chiming in with your sage advise about making sure the the computer clock is updated before any imaging run and that the midpoint of each exposure is used to determine each ToM. For those who do not know Gerard he is the other EB Forum Leader who is also the gate master for nearly all the ToMs that are published in JAAVSO. If you have time-of-minimum data from an eclipsing binary he can publish them.
I've now had a few days to digest some of the comments from my introductory posting and get the sense that some of you are:
1) Interested in acquiring new LC data from a known eclipsing binary star, determine the ToM and then get these values published or
2) learn how to model lightcurves from EBs using Binary Maker 3 and/or Phoebe.
3) For some, the ultimate goal is to publish your results in JAAVSO or another peer-reviewed journal.
Over a decade ago I self-published four volumes of a magazine entitled "The UnderOak Observer". These are available on the website (http://www.underoakobservatory.com/Publications.html). Included is a photometry primer (Parts I-III) as well as a detailed discussion about the challenges faced with trying to model LCs from RT LMi, an eclipsing overcontact binary (OCB). Some of the links may be dated but these articles should give everyone some basic background on how times-of-minima are used to perform secular analyses of the orbital period (Yes, many binary systems undergo orbital period changes over a long time). In addition, the effects of changing the effective temperature, mass ratio, Roche potential and orbital inclination are discussed at some length for RT LMi
Baby steps first, so let's begin with acquiring LC data from an EB which contains some minima, usually designated as Min I (the deepest) and Min II. I am assuming for the moment that you already have some LC data which contain at least one minimum or that you know how to mine some precise time-series LCs from AAVSO. I archived a complete set of BVIc LCs for BV Sex at AAVSO which contain 6-7 minima for each bandpass. This is an OCB that does not undergo a total eclipse (more on the significance of this later). If you have Peranso 3, you should be able to directly download each bandpass from these AAVSO lightcurves and determine each ToM using the method from Kwee van Woerden or a polynomial fit. Just remember to apply the Heliocentric Julian Date correction for each different star since the data downloaded from AAVSO is in Julian Date (JD). For those of you who are serious about acquiring ToM data, I would strongly recommend purchasing ($60 US) Peranso 3 or at least trying it out for a 10-day trial period. BTW, there is a sale going on at half price ($31). At some point you will absolutely need Excel or one of its open source clones to prepare your data for analysis with most applications. Bob Nelson offers a free program ("Minima") which can be found at https://www.variablestarssouth.org/software-by-bob-nelson/. This program finds the precise ToMs for EBs using 6 different methods. Lastly, I have recently started using an open source program named MAVKA (https://arxiv.org/ftp/arxiv/papers/1812/1812.06949.pdf) which has some very interesting algorithms for handling symmetrical and asymmetrical extrema. My challenge to those interested is to prepare a list of all evaluable minima using one or even all programs. The value added is that no ToMs have been published for these LCs so that we can collectively provide Gerard with these new results. If you have any questions, post them or send them privately to firstname.lastname@example.org.
The next time we can discuss how to predict when a minimum will occur so that you are prepared to acquire just that portion of the curve needed to determine a ToM value.
Three software sources have been mentioned for determining ToM.
We should remember that VStar, found on the AAVSO website under Tools and Observer Resources, can also do this.
I'm in the process of setting up a remote observatory in Benson, AZ as well. I have my scope and a CCD camera that'll have to work for the moment. I have a mount and wedge en route to be delivered this week and once I get my pier situation straightened out there'll be an install of equipment and commissioning the setup. I'm an avid visual deep sky observer and experienced astrophotographer and returning to the CCD side of the equation to pursue some science objectives - to make a contribution and learn along the way.
As I have no experience gathering data for a light curve and I don't yet have the requisite filters, a friend and mentor who does photometry suggested that eclipsing binaries would be a good place to start, so here I am.
I've thought about diving into photometry for awhile....three or four years now, and just now getting around to doing it, but I'm quite looking forward to the adventure.
Good luck with getting your remote system set up soon while you can take advantage of clear winter skies. You will greatly appreciate the fork mount which obviates the need for a meridian flip in the middle of a run. If you don't have a temperature compensating focuser, you should consider getting one since there can be as much as a 60° F change in temperature throughout the night.
Eclipsing binary stars such as W UMa-like variables (aka EW, overcontact binaries; OCB) are attractive targets for the inexperienced photometrist. There are many fairly bright (V-mag 10-12) OCBs well within the light grasp of your equipment with orbital periods less than 0.4 days. Use the VSX (https://www.aavso.org/vsx/index.php?view=search.top) to search through each constellation that is viewable in the eastern skies to find an EW variable with an amplitude change of at least 0.5 V-mag. Keep us up to date with your progress.
In addition to EW type eclipsers, there are some Algol type stars that have deep eclipses that can be observed in two or three hours. XZ And, X Tri, RT Per, Y Leo, and SZ Her come to mind. And ephemeris for these stars as well as the entire AAVSO legacy program can be found on the section web site at:
This ephemeris is for North American observers.
I also invite new observers to send me a copy of your data. I can compare your time of minima with other recent observations and let you know how your data fits.