WR140 (V1687 Cyg) periastron 2024 at low resolution

[HughAllen]

Whilst the uncertain eruption of TCrB has become a focus for observation this year, I think the forthcoming periastron of the binary Wolf Rayet star WR140 shouldn’t be neglected. A high-resolution pro-am campaign around the previous periastron in 2016 December resulted in improved orbital elements with an estimate of 2024 November 22 for the next. (‘The orbit and stellar masses of the archetype colliding-wind binary WR 140’ Joshua D Thomas et al, Monthly Notices of the Royal Astronomical Society, Volume 504, Issue 4, July 2021, Pages 5221–5230 https://arxiv.org/abs/2101.10563 ). Regular observations in low resolution during the weeks around periastron should make for a great project, allowing many of the broad emission lines to be monitored for changes:

WR140 2024 June 12.png (60.31 KiB) Viewed 1078 times

The flat-topped CIII emission was the focus for observation in 2016 and although I was at the beginning of my spectroscopic journey back then, I managed to observe changes in this line with my Alpy 600:

WR140 time series periastron 2016 - 2024 Jun.png (74.11 KiB) Viewed 1078 times

It would also be interesting to see how well the changes in radial velocity can be observed. And could a relative brightening in the infrared be detectable after periastron, due to dust formation? If I have properly understood the timings from the literature, then the first milestone is reached around now:

Conjunction of the O5 star in front of the Wolf Rayet WC7 star: 2024 July 14
Quadrature (RV of the WC7 star -130 km/sec, O5 star +50 km/sec): 2024 November 11
Periastron: 2024 November 22
Conjunction of the WC7 star in front of the O5 star: 2024 November 30
Quadrature (RV of the WC7 star +30 km/s, O5 star -20 km/sec (observe after 02:00UT)

WR140 will be well placed for evening observation during the crucial time period.
Cheers
Hugh

[Robin Leadbeater]

Thanks for the reminder Hugh !

The periastron previous to that one was also followed in 2008-9 by the same "Convento" pro-am team.
https://ui.adsabs.harvard.edu/abs/2011M ... F/abstract
Here is what happened to the flat topped CIII line as the winds collided

WR140_CIII_animation_fast.gif (50.07 KiB) Viewed 1061 times

http://www.threehillsobservatory.co.uk/ ... tra_41.htm

It is plotted in the WR star rest frame. You can see the excess emission from the wind collision and the tiny bump in the middle from the O star moving in velocity relative to that as they sweep past each other.

I've not heard if there is any planned organised campaign this time round though

Cheers
Robin

[James Foster]

Here is my recent Alpy600 and LhiresIII(2400 ln/mm grat) spectra as well as some photometry I'm submitting to AASVO.
Transformed Mag.'s:


Alpy600 Spectra:


LhiresIII Spectra:


I'll shot photometry on this semi-daily and shot spectra weekly.

James

[James Foster]

Here is a LhiresIII spectrum of WR140 centered near the CIV line, shot on 12Sep2024; R=10,729:


James

[HughAllen]

I think we could expect to see the first blue-shifted excess on the flat-topped CIII emission by October 16th or even earlier, based on what I observed during the last periastron. At the moment the CIII emission is still fairly constant:

WR140 time series 2024 Jan 05 - Sep 17 CIII zoom.png (60.83 KiB) Viewed 280 times

A heliocentric correction has been applied, and the calibration has then been adjusted based on the interstellar sodium absorption line in the spectra.
Here is the comparison at the full wavelength range:

WR140 time series 2024 Jan 05 - Sep 17.png (81.03 KiB) Viewed 280 times

Cheers
Hugh