Photometry and Spectroscopy of WR 140 (V1687 Cyg) through its upcoming periastron
Abstract:
Dr. Noel Richardson (Embry-RIddle Aeronautical University) writes: WR 140 (V1687 Cyg) is a long-period binary with a carbon-rich Wolf-Rayet star and a hot O supergiant. The orbital period is 7.93 yr with an eccentricity of 0.9. When the two stars come together, the shocks in the wind collision produce dust as the gas cools and our campaign will address how the optical variations work to provide the material that forms this dust. Our team has approved programs with the CHARA Array interferometer along with X-ray monitoring with NICER on the ISS. The observations here will help provide the comparisons needed to understand this Rosetta Stone of colliding winds system. A multiwavelength campaign is underway over the next several months on this bright (6.78 - 6.95 V) binary; AAVSO observers are requested to obtain UBVRIJHK photometry and spectroscopy as detailed below.
Justification:
WR 140 was one of the first released images from JWST, immediately revealing over a century of past dust being formed in the wind shocks. While geometric models provided immediate clues as to the general locations of the dust formation, the exact conditions of where the dust condenses have not yet been identified. To that end, we have already proposed for and been awarded observing time with various instruments including: -NICER will be providing a detailed X-ray light curve to diagnose the conditions of the hot gas as the winds collide. The X-ray brightness should increase until close to the periastron passage (Nov 22, 2024) and then go into a brief eclipse-like event, later falling off in a symmetric way to the increasing luminosity in the following months. -The CHARA Array will be observing WR 140 ten times around periastron. These observations will be taken with 6 telescopes spread across Mt. Wilson (CA) with the light coming into a lab allowing us to image the region with milli-arcsecond resolution and a field-of-view of ~200 milliarcseconds. These times are centered around the periastron passage when the dust will begin to form, thus allowing us to pinpoint where the dust condenses in the shocks. HOW CAN THE AAVSO HELP OUR EFFORTS? -Optical Photometry is useful, especially just after periastron. The dust can form clumps in our line of sight, and these clumps act different every periastron (Peatt & Richardson 2022, RNAAS, 6, 20). Through sampling several periastron passages and dust episodes, we can start to understand how the system's dust may form. We are asking for data in UBVR filters for this. The U band, while difficult, helps provide constraints on the dust grain size better than the other filters, but all filters are welcome. -NIR JHK photometry. During the periastron, the dust condenses, and the system brightens by 0.2-0.3 mag in J and 1.5 mag in K. The exact timing and shape of the onset of dust formation (late October - early November 2024) is still not constrained by more than a few photometric points in orbital phase. -Optical spectroscopy is very useful. Pollock et al. (2021, ApJ, 923, 131) showed that when the X-ray cooling of the gas starts to turn off, the cooling seems to switch into the C III 5696 emission. During the previous periastron in 2016, our team noticed in a few spectra that there seems to be additional excess around the H-alpha line. The H-alpha excess is not characterized well at all, and the switching from X-rays to C III is likely critical to dust condensation. Please try to observe these lines with reasonable S/N and throughout the campaign. **While the campaign says nightly observing, this is most important in the October-December time frame for spectroscopy, and in the November-February time frame for optical photometry. We understand that the target is difficult for much of this time period as it is situated in the heart of Cygnus, but we hope the AAVSO can also help us understand the system.**
Requested Data Types:
Spectroscopy, Photometry
Targets
| Name | Magnitude | Variability Type | Photometry Notes | Spectroscopy Notes |
|---|---|---|---|---|
| V1687 Cyg | 6.86 | WR |
Cadence: Custom Precision: 50 |
Cadence: Custom Resolution: 5000 Desired SNR: 100 |
Spectroscopy Lines:
C III (5696.0 Å), H-alpha (6563.0 Å)
Photometry Filters:
U (Johnson), B (Johnson), V (Johnson), R (Cousins), Other (Please Specify)
Comparison Stars:
Finder charts with comparison stars are available via the AAVSO Variable Star Plotter (VSP, https://apps.aavso.org/vsp/).
Co-Authorship
Observers are eligible for co-authorship.
Additional Observer Input:
The V range for V1687 Cyg is 6.78 - 6.95. Be careful not to saturate the detectors on your camera when observing this very bright target, and stack images to reduce scintillation. Optical photometry UBVR cadence: 2-3 times/week until November, then nightly November through February. Near-infrared photometry filters and cadence: JHK filters, 2-3 times/week, then nightly November through February. Spectroscopy resolution and cadence: 5,000 or better for RV precision; 2-3 times/week until November, then nightly November through February. Finder charts with comparison stars for V187 Cyg maybe created using the AAVSO Variable Star Plotter (https://apps.aavso.org/vsp/).
Additional Submission Location:
None requested.
Notes:
In addition to the optical photometry, photometry in the NIR (JHK) will show a brightness increase as the dust begins to condense. This would be extremely helpful in the October-December time frame as the CHARA observations happen (see instructions above).