Gaia16aye microlensing event monitoring urgently requested

PTS

AAVSO Alert Notice 552
September 20, 2016

Gaia16aye microlensing event monitoring urgently requested

Dr. Kirill Sokolovsky (National Observatory of Athens and Sternberg
Astronomical Institute, Moscow State University), has requested
AAVSO assistance in monitoring the ongoing microlensing event
Gaia16aye beginning immediately to catch transient behavior
occurring now and continuing through the end of October (or until
further notice).

Dr. Sokolovsky writes: "Gaia16aye was first identified as an
unusual variable object by Gaia on 2016 August 5 (V. Bakis et al.,
ATel #9376, http://www.astronomerstelegram.org/?read=9376) and it
was later realized that its achromatic light variations are
consistent with being caused by microlensing of a distant M-type
giant star by a binary star system (possibly consisting of main
sequence dwarfs) crossing the line of sight. The complex geometry
of the lens causes multiple brightness peaks corresponding to
caustic crossings. According to preliminary modeling, the object's
variability was noticed during decline after the first caustic
crossing. The second brightness peak was observed on August 13 and
the third peak on September 19. The source is expected to decline
quickly in next days from its current magnitude V~14 to reach the
plateau around V~16 between the caustics, in order to start rising
again to cross the caustic in one or couple of weeks (L. Wyrzykowski
et al., ATel #9507, http://www.astronomerstelegram.org/?read=9507).
A well-sampled lightcurve of the microlensing event, especially
during the caustic crossing, is needed to constrain geometry and
some physical parameters of the lens and the lensed star.

"CCD observations of Gaia16aye using any subset of B, V, Rc, Ic, g,
r, i filters are requested starting immediately and continuing for
about four weeks (until the decline from the expected next caustic
crossing). If the object is at its bright state around V~14, time
series observations are needed. If the object is found at the
plateau level around V~16, one-two observations per night are
sufficient. Unfiltered CCD observations are also useful if
photometric measurements are collected during multiple nights
(otherwise it would be difficult to match the unfiltered
measurements to the data collected by other observers).

"Observers are asked to... [reduce their data in their usual way
using] UCAC4 601-089811 as the comparison star and submit
observations to the AAVSO International Database using the standard
procedure." UCAC4 601-089811 is the 145 comparison star in the
AAVSO sequence for Gaia16aye.

Observers are also requested to upload their calibrated
(dark and flat-field corrected) images to the anonymous FTP server
ftp://scan.sai.msu.ru/uploads/ for semi-automated processing with
the Cambridge Photometry Calibration Server pipeline."

Coordinates (2000.0): R.A. 19 40 01.13  Dec. +30 07 53.4

Charts with a comparison star sequence for Gaia16aye may be created
using the AAVSO Variable Star Plotter (VSP,https://www.aavso.org/vsp).
Creating an 'e' or 'f' scale chart is recommended.

Please submit observations to the AAVSO International Database
using the name Gaia16aye (there are no spaces within the name).

This campaign is being followed on the AAVSO Observing Campaigns
webpage (https://www.aavso.org/observing-campaigns). A thread has
been created on the Campaigns and Observation Reports forum at
(https://www.aavso.org/content/gaia16aye-microlensing-campaign).


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

----------------------------------
SUBMIT OBSERVATIONS TO THE AAVSO

Information on submitting observations to the AAVSO may be found at:
https://www.aavso.org/webobs

ALERT NOTICE ARCHIVE AND SUBSCRIPTION INFORMATION

An Alert Notice archive is available at the following URL:
https://www.aavso.org/alert-notice-archive

Subscribing and Unsubscribing may be done at the following URL:
https://www.aavso.org/observation-notification#alertnotices

-------------------------------------------------