May 24, 2017: T. Boyajian (Louisiana State University) et al. reported in ATel #10405 that an optical dip is underway in KIC 8462852 (Boyajian's Star, Tabby's Star) beginning on 2017 May 18 UT. Tentative signs of small dips had been seen beginning April 24, and enhanced monitoring had begun at once at Fairborn Observatory (Tennessee State University). Photometry and spectroscopy from there on May 18 and 19 UT showed a dip underway. Cousins V photometry showed a drop of 0.02 magnitude, the largest dip (and the first clear one) seen in more than a year of monitoring.
AAVSO observer Bruce Gary (GBL, Hereford, AZ) carried out V photometry which showed a fading from 11.906 V +/- 0.004 to 11.9244 V +/- 0.0033 between UT 2017 May 14 and May 19, a drop of 1.7%.
Swift/UVOT observations obtained May 18 15:19 did not show a statistically significant drop in v, but Gary's photometry is given more weight. r'-band observations from Las Cumbres Observatory obtained 2017 May 17 to May 19 showed a 2% dip.
I. Steele (Liverpool JMU) et al. report that spectra taken on 2017 May 20 with the 2.0 meter Liverpool Telescope, La Palma, showed no differences in the source compared to a reference spectrum taken 2016 July 4 when the system was not undergoing a dip (ATel #10406).
Dips typically last for a few days, and larger dips can last over a week. It is not clear that this dip is over.
Precision time-series V photometry is urgently requested from AAVSO observers, although all photometry is welcome. Dr. Boris Gaensicke (University of Warwick) has requested intense multi-color monitoring. Ongoing multiwavelength monitoring is being carried out at several sites. Swift observations will continue through June 9.
Dr. Dennis Conti, AAVSO Exoplanet Section chair, recommends the following procedure: "Start your observation when you can after twilight and continue taking images at an exposure that won't saturate your CCD camera (considering that it will brighten as it rises and dims as it falls from your local meridian). Use whatever filter [V is preferred] and exposure time you that gives the best SNR. If you can, do this for the next few days. After you have made a night's worth of observations (go for however long is convenient for you), create a light curve in AstroImageJ and forward it to firstname.lastname@example.org. Be sure to keep your original calibration and image files."
KIC 8462852 is 11.88 V at maximum (out of dip). It was the subject of AAVSO Alert Notices 532 and 542. Also, more information about it may be found in a 2016 paper by Boyajian et al. (2016MNRAS.457.3988B), available as a preprint at: http://arxiv.org/abs/1509.03622. General information about KIC 8462852 may be found at: http://www.wherestheflux.com/.
Coordinates (J2000): RA 20 06 15.46 , Dec +44 27 24.8
Finder charts with a comparison star sequence for KIC 8462852 may be created using the AAVSO Variable Star Plotter (VSP).
If observations are submitted to the AAVSO International Database, the name KIC 8462852 should be used.
For information on how to observe exoplanets and/or use AstroImageJ, please see the AAVSO Exoplanet Section page (https://www.aavso.org/exoplanet-section).
This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.
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