Proposal for Analysis of Legacy Data for the Variable BL Tel
Member Name and Observer Code: Edward Wiley/WEY
Summary of why the observations of each Target is important scientifically or educationally useful to the member.
BL Tel is a long period eclipsing binary (P ~ 778.0 d; Cousins and Feast, 1954) with an SRD F41b giant primary and an M-class secondary. A considerable literature exists for this system, some of what is cited below.
AAVSO data base observations to date include BSM transformed BVRI data for three previous eclipses (2013, 2015, 2017 one previous eclipse in transformed BV and several additional eclipses in vis (by Woodward). So, there are a lot of existing data that can be used for the project. All these data have been downloaded and placed in an Excel file.
In terms of SRD variation, Zsoldos (1994) found two periods outside the eclipse, concluding that the primary was a double mode pulsator (P0 = 92.5 d, P1 = 64.8 d) and that the system is a UU Her system. Alternatively, the GCVS remarks in VSX suggest a single period of 65.1 d based on van Genderen, 1977. Earlier work on this system is summarized in van Genderen (1983). This that paper, van Genderen attempts to model the color and light variations observed in different eclipses caused by the pulsations of the primary.
Several science goals will be investigated with the existing data.
(1) Refine the eclipse period. Most of the minimum estimates reported in the O-C gateway are visual estimates made by Peter Williams (N=8) and indicate a period of P= 778.2 d and a flat O-C with understandable scatter. Two methods will be employed: Bob Nelson’s Minima and Peranso. These will be analyzed and compared to existing period estimates. O-C analysis will be performed.
(2) Analyze the variation between eclipses to test the one period versus two period competing hypotheses (van Genderen v. Zsoldos). Peranso will be used for this part of the analysis. Interpretation of the results may require more professional assistance.
(3) Investigate light and color changes during eclipses possible due to variability of the primary. This will be approached by plotting color indices. I have never done this kind of analysis, so some help may be needed in interpreting the results.
User’s plan for the data, i.e. AAVSO data base, journal article, education or outreach.
The eventual goal will be to publish a paper on the results. I would like to collaborate with a professional, I suspect such collaboration would be needed to accomplish all research goals.
Request images be sent to VPHOT (free to members): I note that data from BSM for all four filters are appearing, transformed, in the AAVSO data base. Given continuing input of new data in transformed form, I would not have to have any images placed in my VPhot file, I can simply download the data, as I have for all existing 4000+ observations now available. If new, untransformed data appear, I would like the images to be placed in my VPhot account to perform the transformations needed before placing the data into the AAVSO data base.
Check Variable Star Index (https://www.aavso.org/vsx/):
Target(s) name verification to ensure name is listed: BL Tel
Target Sky Coordinates (J2000): RA: 19 06 38.11, Dec: -51 25 03.2 (286.65879 -51.41756)
Target V magnitude range: 7.08 – 9.08 V
Appropriate comparison stars with standard photometry.
A number of suitable comparison stars are in the 120’ chart. I also note a large number of ASA and other variables, some of which are probably AAVSO comp stars, so selection will have to be made with care.
Observation Parameters: Note that this is a Legacy proposal, thus cadence, filters, number of images and other observational parameters are already determined. Start and finish dates are determined by the Legacy data as those data appear.
Preliminary analysis of period.
One analysis of a BSM eclipse (JD 2457235.19 - 2457286.933) in Minima23a/Kwee and van Woorden was plotted using O-C Gateway. The ToM (JD 2457262.22930 +/- 0.07904) indicated that no major change has occurred in the period (M0 = JD 2434692.6).
van Genderen, A. M. AsAp 119, 265, 1983.
Zsoldos, E., 1994, A&A, 286, 870