Project Leader: Peter Williams
Visual observers are invited to participate in monitoring of BL Tel for which ongoing observations are required. BL Tel was the subject of a long-term visual study between 1983 and 2000 with 8 eclipses recorded during that time. Results of those eclipses are summarised in Publications 25 (C99) of the VSS RASNZ (2000). BL Tel is an Algol type system well suited to visual observation and need only be followed during the 3 months centred on the predicted date of mid eclipse.
BL Tel was the subject of a long-term visual study between 1983 and 2000 with the recording of 8 eclipses during that time. Results of those eclipses are summarised in Publications 25 (C99) of the VSS RASNZ (2000). BL Tel is an Algol type system of mean period near 778 days and a visual range between magnitudes 7 and 10. Eclipses are of duration up to 2 months and ongoing observations of these eclipses are looking for any changes in the behaviour of this massive binary system. Observations are generally required for the 3 months centred on the predicted date of mid eclipse to ensure both the onset and completion of the eclipse are recorded.
The objective is to produce a complete visual light curve based on daily mean magnitudes and from this to determine the basic parameters of each eclipse – the date of mid eclipse, daily rate of brightness change, overall duration of each eclipse and the amplitude. These results can then be compared with those from the earlier eclipses and to look for any unexpected changes in behaviour.
Visual observers should obtain magnitude measurements on a daily basis, commencing a week or two prior to the expected onset of eclipse and continue a through to a week or two after the perceived end of the eclipse. BL Tel is suitable for observation with binoculars when at maximum and during the early and late stages of eclipse. Large binoculars or small telescopes will follow it through minimum.
A chart showing suitable comparison stars is included below.
All observations should be included in usual reporting to the AAVSO. Electronic measurements with DSLR cameras and multi-colour photometry is also most welcome and indeed encouraged. These observations can be ongoing between eclipses to monitor the small amplitude semi regular variations and secondary eclipse that are generally beyond the scope of visual observation.
|Epoch||Start Date||Mid Eclipse||End Date|
|2458037.0||01 Sep 2017||10 Oct 2017||18 Nov 2017|
|2458815.0||19 Oct 2019||27 Nov 2019||05 Jan 2020|
|2459593.0||05 Dec 2021||13 Jan 2022||21 Feb 2022|
|2460371.0||22 Jan 2024||01 Mar 2024||09 Apr 2024|
|2461149.0||10 Mar 2026||18 Apr 2026||27 May 2026|
|2461927.0||26 Apr 2028||04 Jun 2028||13 Jul 2028|
|2462705.0||13 Jun 2030||22 Jul 2030||30 Aug 2030|
|2463483.0||30 Jul 2032||07 Sep 2032||16 Oct 2032|
|2464261.0||16 Sep 2034||25 Oct 2034||03 Dec 2034|
|2465039.0||02 Nov 2036||11 Dec 2036||19 Jan 2037|
Eclipse ephemeris courtesy of the AAVSO Variable Star Index (VSX). https://www.aavso.org/vsx/index.php?view=detail.ephemeris&nolayout=1&oid=36332
Results for the 2011 eclipse appear in the VSS Newsletter – August 2011.