Optical follow-up of MAXI J0709-159
ATel #15194; Roberto Nesci (INAF/IAPS-Roma)
on 1 Feb 2022; 08:42 UT
Credential Certification: Roberto Nesci (roberto.nesci@inaf.it)
Subjects: Optical, Binary, Neutron Star, Star, Transient
In the announcement of two X-ray flares detected by MAXI (ATel #15181, #15188) of the source MAXI J0709-159, the star HD 54786 was indicated as a possible optical counterpart. I made therefore V,R,I (Cousins filters) imaging of the star on 2022-01-28, as well as a slitless spectrum at very low resolution (R=50) with the 30cm telescope of the Foligno Observatory (K56).
Aperture photometry was made with IRAF apphot, using four nearby stars as comparisons, taken from the UCAC4 catalog. The star was at V=8.92+/-0.06; R=8.96+/-0.03; I=8.79+/-0.02. Noticeably,
the star was about 0.5 mag brighter that the catalog values in all three bands.
Optical V-band observations by Gerard Samolyk (AAVSO public lightcurve) performed one year ago (2021-01-15) showed a possible periodic variation with mean value V=9.05, peak to peak amplitude of 0.3 mag and 3 hours time scale. His mean value is in very good agreement with my finding.
My (very poor) spectrum shows clearly an H-alpha emission line, as expected from its B1/2 Ie spectral type, with 23 A equivalent width.
The identification of the optical counterpart of the X-ray source was confirmed by a NuSTAR observation in ATel 15193. Intranight optical follow-up to check a possible source periodicity is encouraged.
