Campaign continued through 2017. Also, updated in Special Notice #419 (20160809) to encourage spectroscopy.
August 3, 2016: 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 [2016]. 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 [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, "Marchenko et al. (2003, http://adsabs.harvard.edu/abs/2003ApJ...596.1295M) [examine 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).
Please submit observations to the AAVSO International Database using the name V1687 CYG.
This campaign is being monitored on the AAVSO Observing Campaigns webpage.
This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.
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