V1687 CYGNI (WR 140)

[lindhardDeltager Super Nova]

Nyt observationsprojekt

Dr. Noel Richardson (University of Toledo) and colleagues have requested

assistance in optical monitoring of the bright, colliding-winds binary V1687

Cyg 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 2016 Dec 18. 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.

“We were hoping for assistance 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 [now] 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, “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.

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 and also report to Gary Poyner monthly.

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mvh
Lars

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