2100882

Target RA (J2000): 276.562744 and deg Target Dec (J2000): -14.84840 and deg Gaia GMag: 10.799 Programme ID: CH_PR230038 PI of observing programme: Wu Title of programme: Precise Mass Measurement for the Compact Object in LS 5039: The Heaviest Neutron Star or the Lightest Stellar-mass Black Hole? Abstract: LS 5039 is a gamma-ray binary containing a compact object within the mass gap (2-5 solar masses). It could potentially be the heaviest neutron star or the lightest stellar-mass black hole. However to precisely constrain its mass high-precision optical photometry at the level of 0.1 mmag (100 ppm) is required. Therefore we propose a CHEOPS monitoring campaign to obtain the needed light curve. [truncated! Please see actual data for full text]