Campaign on V1687 Cyg (WR 140)
AAVSO Alert Notice 546August 3, 2016
Campaign on V1687 Cyg (WR 140)
Dr. Noel Richardson (University of Toledo) and colleagues have
requested AAVSO assistance in optical monitoring of the bright,
colliding-winds binary V1687 Cyg (WR 140, HD 193793) as part of
their multi-wavelength campaign on this system.
Dr. Richardson writes: "WR 140 (HD 193793)...is a long-period
(P~8yr), highly eccentric (e=0.8964) system with a carbon-rich
Wolf-Rayet star and an O star in the orbit. Both stars lose mass,
which collides, and the density at the collision point is much
higher around the periastron passage, which should occur on the
18th of December . In the months just after periastron, the
system creates a large amount of dust. Our team will be monitoring
the system in the X-rays with XMM, NuSTAR, and Swift, in the optical
with spectroscopy and spectropolarimetry, and in the infrared with
Gemini-N, along with other telescopes still being proposed for,
including Keck and the CHARA Array to image the dust production
locations.
"We were hoping that the AAVSO could assist us with optical
photometry. Some other dust-producing WR+O binaries show dramatic
increases in the infrared, while getting much fainter in the
optical. In particular, if observers are set-up with U and/or B band
filters, the decrease could be drastic. Unfortunately, the star is
well-situated in Cygnus, and the possible drop-off in optical flux
(particularly in the blue) would occur in the January-April 2017
time frame. We hope that the observers could start monitoring the
star in order to best gauge the variations and flux level now,
and monitor it until next summer, trying to get the observations
even in the months that are most difficult (January-March) so that
we can better determine the properties of the dust production. This
is the only dust-producing Wolf-Rayet binary with a fully resolved
orbit (both spectroscopically and with interferometry), so all
constraints we can place on the dust will allow us to better
constrain the process of dust production in these systems."
Observers are requested to obtain one set of UBVRI (or as many of
these filters as you have) photometry each night, starting now and
continuing until at least August 2017. Exposures should be long
enough to obtain a good S/N, but the target is bright so be careful
not to saturate. The most recent data in the AAVSO International
Database are visual observations from May 2014, at which time V1687
Cyg was visual magnitude 6.7.
Dr. Richardson continues, "Marchenko et al.
(2003, http://adsabs.harvard.edu/abs/2003ApJ...596.1295M)
WR 140] optical photometry...There are observed dips in the light
curve after the periastron passage that get to be ~20% deep in U,
and a bit less at longer wavelengths (peaks in the infrared). The
dips are caused by occultations of dust, and we do not know if the
optical dips are repeatable.
"Currently, we have Swift measurements being made through October,
and plan to request more. Along with the Swift X-ray measurements
that come from the colliding winds, we will be analyzing the data
from the UVOT onboard for UV photometry, where the dip will likely
be much deeper than the optical dips. The color changes give us
information about the dust properties (such as grain size), and we
don’t know how they grow in such an environment yet, so this is a
very exciting project...I’m happy to have the AAVSO on-board for an
exciting time for an interesting binary."
Coordinates (2000.0):R.A. 20 20 27.98 Dec. +43 51 16.3
Charts: Charts with a comparison star sequence for V1687 Cyg
may be created using the AAVSO Variable Star Plotter (VSP) at
https://www.aavso.org/vsp.
Please submit observations to the AAVSO International Database
using the name V1687 CYG.
This campaign is being monitored on the AAVSO Observing Campaigns
webpage at https://www.aavso.org/observing-campaigns.
This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.
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