Proposal #575

The name of the source is LS I +61°302. This stellar binary object is
detected across the electromagnetic spectrum into the TeV regime. It is
also included in the search for neutrinos. Periodic signals have been
detected in its emission with at least three period values: 26.5 d, 26.9
d, 1667 d. These three periods are related via a beating. In particular
the long history of radio observations has shown that this beating
phenomenon has remained stable for the past 45 years [1].

In order for any timing analysis to be able to resolve the two close
periods 25.5 and 25.9 days, it is absolutely necessary to have a light
curve with a sufficiently high sampling rate and - most importantly - a
long enough time series. The length of the light curve has to be more
than ~5 years.

It would be great to have continued monitoring at optical wavelengths.
In particular, it is known that the long-term modulation, resulting from
the beating of 25.5 d and 25.9 d, has systematic phase-shifts across the
electromagnetic spectrum [2]. Unfortunately, when I did this
investigation, the situation in the optical regime did not allow me to
determine the long-term phase, leaving this data point vacant in my Fig.
2. It would be an immediate science case to fill this gap in order to
better understand the physical processes behind this phenomenon.

[1] https://ui.adsabs.harvard.edu/abs/2024A%26A...683A.228J/abstract
[2] https://ui.adsabs.harvard.edu/abs/2021Univ....7..245J/abstract

Daily observations would of course be fantastic. However, given the
shortest periods in question (~26.5 d), such a high cadence is not a
strict requirement. The most important is a continuous monitoring
without larger gaps.

Simultaneous monitoring in multiple filters in order to investigate the
SED in the time domain would be of great interest.
Based on this e-mail of the PI F. Jaron, I request observation of the target in BVI filters if possible on a daily basis.
Regards,
F.-J. (Josch) Hambsch