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Alert Notice 562: Photometry of V725 Tau needed immediately

November 15, 2016: Dr. Franco Giovannelli (Istituto di Astrofisica e Planetologia Spaziali di Roma) has requested AAVSO assistance in monitoring V725 Tau, the Be star in the high-mass X-ray transient A0535+26/HDE245770, in order to plan for the X-ray outburst that follows 8 days after the optical brightening that occurs at periastron passage.

Periastron passage will occur on 16 November 2016, so coverage is needed beginning immediately and continuing for at least 15 days after periastron, until December 2.

BVRI photometry - V is most important - is requested. V725 Tau has a range of V=8.88-9.47; visual and V observations in the AAVSO International Database show it between about 8.6 and 9.2 since late 2011, about 8.6-8.9 as of May 2016.

Dr. Giovannelli writes: "The cadence [needed] is at least one photometric point each night, maybe averaged with several images. However, if it is possible to get more points (2-3 in the same night) it is of course better. We are searching for variations of order 0.02-0.05 magnitudes. Sometimes these variations can reach about 0.2 mag depending on the state of the O9.7 IIIe star."

Coordinates (2000.0):  R.A. 05 38 54.57   Dec. +26 18 56.8

Charts with a comparison star sequence for V725 Tau may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the name V725 TAU.

This campaign is being followed on the AAVSO Observing Campaigns webpage. A thread has been created on the Campaigns and Observation Reports forum at (https://www.aavso.org/content/v725-tau-photometry-needed-urgently).

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.

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