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Campaign on V1687 Cyg (WR 140)

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發表於 2016-8-4 06:26:55 | 顯示全部樓層 |閱讀模式
[size=13.3333px]AAVSO Alert Notice 546
[size=13.3333px]August 3, 2016

[size=13.3333px]Campaign on V1687 Cyg (WR 140)

[size=13.3333px]Dr. Noel Richardson (University of Toledo) and colleagues have
[size=13.3333px]requested AAVSO assistance in optical monitoring of the bright,  
[size=13.3333px]colliding-winds binary V1687 Cyg (WR 140, HD 193793) as part of
[size=13.3333px]their multi-wavelength campaign on this system.

[size=13.3333px]Dr. Richardson writes: "WR 140 (HD 193793)...is a long-period
[size=13.3333px](P~8yr), highly eccentric (e=0.8964) system with a carbon-rich
[size=13.3333px]Wolf-Rayet star and an O star in the orbit. Both stars lose mass,
[size=13.3333px]which collides, and the density at the collision point is much
[size=13.3333px]higher around the periastron passage, which should occur on the
[size=13.3333px]18th of December [2016]. In the months just after periastron, the
[size=13.3333px]system creates a large amount of dust. Our team will be monitoring
[size=13.3333px]the system in the X-rays with XMM, NuSTAR, and Swift, in the optical
[size=13.3333px]with spectroscopy and spectropolarimetry, and in the infrared with
[size=13.3333px]Gemini-N, along with other telescopes still being proposed for,
[size=13.3333px]including Keck and the CHARA Array to image the dust production
[size=13.3333px]locations.

[size=13.3333px]"We were hoping that the AAVSO could assist us with optical
[size=13.3333px]photometry. Some other dust-producing WR+O binaries show dramatic
[size=13.3333px]increases in the infrared, while getting much fainter in the
[size=13.3333px]optical. In particular, if observers are set-up with U and/or B band
[size=13.3333px]filters, the decrease could be drastic. Unfortunately, the star is
[size=13.3333px]well-situated in Cygnus, and the possible drop-off in optical flux
[size=13.3333px](particularly in the blue) would occur in the January-April 2017
[size=13.3333px]time frame. We hope that the observers could start monitoring the
[size=13.3333px]star [now] in order to best gauge the variations and flux level now,
[size=13.3333px]and monitor it until next summer, trying to get the observations
[size=13.3333px]even in the months that are most difficult (January-March) so that
[size=13.3333px]we can better determine the properties of the dust production. This
[size=13.3333px]is the only dust-producing Wolf-Rayet binary with a fully resolved
[size=13.3333px]orbit (both spectroscopically and with interferometry), so all
[size=13.3333px]constraints we can place on the dust will allow us to better
[size=13.3333px]constrain the process of dust production in these systems."  

[size=13.3333px]Observers are requested to obtain one set of UBVRI (or as many of
[size=13.3333px]these filters as you have) photometry each night, starting now and
[size=13.3333px]continuing until at least August 2017. Exposures should be long
[size=13.3333px]enough to obtain a good S/N, but the target is bright so be careful
[size=13.3333px]not to saturate. The most recent data in the AAVSO International
[size=13.3333px]Database are visual observations from May 2014, at which time V1687
[size=13.3333px]Cyg was visual magnitude 6.7.

[size=13.3333px]Dr. Richardson continues, "Marchenko et al.
[size=13.3333px](2003, [size=13.3333px]http://adsabs.harvard.edu/abs/2003ApJ...596.1295M[size=13.3333px]) [examine
[size=13.3333px]WR 140] optical photometry...There are observed dips in the light
[size=13.3333px]curve after the periastron passage that get to be ~20% deep in U,
[size=13.3333px]and a bit less at longer wavelengths (peaks in the infrared). The
[size=13.3333px]dips are caused by occultations of dust, and we do not know if the
[size=13.3333px]optical dips are repeatable.

[size=13.3333px]"Currently, we have Swift measurements being made through October,
[size=13.3333px]and plan to request more. Along with the Swift X-ray measurements
[size=13.3333px]that come from the colliding winds, we will be analyzing the data
[size=13.3333px]from the UVOT onboard for UV photometry, where the dip will likely
[size=13.3333px]be much deeper than the optical dips. The color changes give us
[size=13.3333px]information about the dust properties (such as grain size), and we
[size=13.3333px]don’t know how they grow in such an environment yet, so this is a
[size=13.3333px]very exciting project...I’m happy to have the AAVSO on-board for an
[size=13.3333px]exciting time for an interesting binary."

[size=13.3333px]Coordinates (2000.0):  R.A. 20 20 27.98   Dec. +43 51 16.3

[size=13.3333px]Charts: Charts with a comparison star sequence for V1687 Cyg
[size=13.3333px]may be created using the AAVSO Variable Star Plotter (VSP) at
[size=13.3333px]https://www.aavso.org/vsp[size=13.3333px].

[size=13.3333px]Please submit observations to the AAVSO International Database
[size=13.3333px]using the name V1687 CYG.

[size=13.3333px]This campaign is being monitored on the AAVSO Observing Campaigns
[size=13.3333px]webpage at [size=13.3333px]https://www.aavso.org/observing-campaigns[size=13.3333px].


[size=13.3333px]This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.

[size=13.3333px]----------------------------------
[size=13.3333px]SUBMIT OBSERVATIONS TO THE AAVSO

[size=13.3333px]Information on submitting observations to the AAVSO may be found at:
[size=13.3333px]https://www.aavso.org/webobs

[size=13.3333px]ALERT NOTICE ARCHIVE AND SUBSCRIPTION INFORMATION

[size=13.3333px]An Alert Notice archive is available at the following URL:
[size=13.3333px]https://www.aavso.org/alert-notice-archive

[size=13.3333px]Subscribing and Unsubscribing may be done at the following URL:
[size=13.3333px]https://www.aavso.org/observation-notification#alertnotices

[size=13.3333px]-------------------------------------------------
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