A Drop in Optical Flux from Boyajian's Star
ATel #10405; Tabetha Boyajian (Louisiana State), Steve Croft (UC Berkeley), Jason Wright (Penn State), Andrew Siemion (UC Berkeley), Matthew Muterspaugh (Tennessee State), Michael Siegel (Penn State), Bruce Gary (amateur), Shelley Wright (UCSD), Jerome Maire (UCSD), Andres Duenas (UCSD), Clayton Hultgren (UCSD), JonJohn Ramos (UCSD)
on 20 May 2017; 00:29 UT
Credential Certification: Steve Croft (firstname.lastname@example.org)
Subjects: Optical, Request for Observations, Star
Referred to by ATel #: 10406
Boyajian's Star (KIC 8462852) is an F3 dwarf that exhibits irregular and unexplained dips in optical brightness of up to tens of percent, as seen in Kepler observations (Boyajian et al. 2016).
As part of an ongoing monitoring campaign, we obtained observations with a robotic 14-inch Celestron Telescope at Tennessee State University / Fairborn Observatory in Southern Arizona. Tentative evidence of small dips was seen beginning 2017 April 24, and enhanced monitoring at TSU/Fairborn (nightly photometry and spectra) commenced at that time. Cousins V-band images taken on UT 2017 May 18 and 19 showed that Boyajian's Star has entered into a new dip. Photometry differential to many comparison stars in the field showed a drop from an offset of Delta-V = 0.65144 +/- 0.00125 mag (UT 2017 May 16 09:16) to Delta-V = 0.67415 +/- 0.00261 (UT 2017 May 19 06:08) - a drop of 0.02 mag. This is the largest and first clear dip seen in over a year of monitoring, and shows no sign of having yet reached a minimum.
V-band observations by amateur astronomer Bruce Gary using a Meade LX200 GPS 14" with an SBIG ST-10XME CCD confirmed that Boyajian's Star had dimmed from V = 11.906 +/- 0.004 to V = 11.9244 +/- 0.0033 between UT 2017 May 14 and UT 2017 May 19 (an abrupt drop of 1.7%).
Swift/UVOT observations taken UT 2017 May 18 15:19 show a slight but not statistically significant drop in flux (from v = 11.93 +/- .012 to v = 11.94 +/- .030) since UT 2017 May 10. The ground-based absolute photometry is to be preferred over that from UVOT.
r'-band observations with the 1-m telescope at the Las Cumbres Observatory (LCO) in Maui show a 2% dip over two days from UT 2017 May 17 to 2017 May 19.
A number of explanations have been proposed for dimming events seen in Boyajian's Star observations (both slow fades of <1% per year, and abrupt and irregular short-term fades). Some explanations postulate the presence of large amounts of gas and dust in the system (which would be expected to have an IR signature, not seen in Spitzer observations of the star by Marengo et al. 2015). However, the Spitzer observations were not taken at the time of a dip; to constrain the models, optical and infrared spectroscopy and photometry are urgently needed. Dips typically last for a few days. Larger dips can last over a week.
We will continue our monitoring observations using Swift, LCO, and Fairborn, as well as our spectroscopic observations as part of the Breakthrough Listen program using the APF-Levy spectrometer at Lick Observatory (27 epochs obtained since Nov 21, 2015). Near-InfraRed Optical SETI (NIROSETI) on the Nickel 1-m telescope at Lick Observatory has been monitoring Boyajian's Star, conducting 65 minutes of observations of the star UT 2017 May 20, and will continue to monitor the star UT 2017 May 21, 22, and 23.
We encourage additional multi-wavelength follow-up. Especially interesting would be lines in the region between H-alpha and the sodium doublet, inclusive, and thermal infrared measurements.