eclipsing binary 31cyg

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eclipsing binary 31cyg

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Dear colleagues,
Philip Bennett (my professional supervisor in researching the system VV Cep) asked me to share the following message in this forum:
Hi Ernst,
Would it be possible to include the eclipsing binary 31 Cygni (=V695 Cyg = HR 7735 = HD 192577) as a current ARAS campaign target? This system contains a red supergiant (K5 Ib) that eclipses its much hotter main-sequence companion (B3 V) every orbital period of 10.32 years.
The star is bright:
V=3.80, B= 5.08, U=5.50 (out of eclipse)
V=3.9, B=5.6, U-7.1 (during total eclipse)

The next eclipse is nearly here, with the following estimated timeline:
start of U-band partial eclipse: 2024 Feb 17: JD 2460357.7
start of U-band totality: 2024 Feb 21: JD 2460361.70
mid-eclipse on 2024 Mar 22: JD 2460391.72
end of U-band totality: 2024 Apr 18: JD 2460419.36
end of U-band partial eclipse: 2024 Apr 23: JD 2460423.70

The length of U-band total eclipse= 57.66 days.

The eclipse mostly affects the ultraviolet spectrum, as the red supergiant dominates the visible spectrum. But spectral regions at wavelengths shorter than 4500 A will be affected. Any spectroscopic observations of the 3200 – 4500 A region (and U,B,V photometry) during the eclipse time period (now – late June) would be greatly appreciated. Although the continuous spectrum will return to normal after 2024 Apr 23, many absorption lines due to circumstellar absorption by the red supergiant’s wind will remain visible for several weeks (and possible months) after eclipse.

This campaign will provide support for Hubble Space Telescope program GO-17416, on which I am Principal Investigator. This HST program which will observe the partial & total eclipse, and near-eclipse spectrum of 31 Cyg during 2024 in the near and far ultraviolet accessible from space (at wavelengths < 3100 A).

My apologies for the lateness of this request, but any help your observers can offer would be most appreciated!

Phil Bennett
Principal Investigator HST program GO-17416
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