X-ray and UV observations of the 56.35 min period star MGAB-V269

ATel #13444; L. Rivera Sandoval (TTU), G. Murawski (SOTES), C. Copperwheat (LJMU), T. Maccarone (TTU)
on 4 Feb 2020; 18:23 UT
Credential Certification: Liliana Rivera Sandoval (liliana.rivera@ttu.edu)

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We report on Swift observations of the recently discovered short period star MGAB-V269 (313.81658 +46.85181). The object was identified by Gabriel Murawski with a period of 56.35 min on 19th July 2019. We obtained a total of 3.7ks of Swift observations with XRT and UVOT divided in 2 epochs, the first one was taken on 24th Jan 2020 and the second one on 28th Jan 2020. No X-ray emission from the source in the 0.3-10 keV band was identified. This suggests that the source must have a X-ray flux < 1E-13 erg s-1 cm-2. The object matches to a Gaia source. Bailer-Jones+ 2018 places it at a distance of 2170 pc, which would lead to an X-ray luminosity of < 6E+31 ergs s-1.

Photometric results obtained with UVOT in the first and second epoch are given below:

V = 18.15 +/- 0.27 , 17.31 +/- 0.14
B = 17.72 +/- 0.09 , 18.07 +/- 0.12
U = 16.68 +/- 0.07 , 16.74 +/- 0.07
UVW1 = 16.91 +/- 0.08, 16.76 +/- 0.07
UVM2 = 17.71 +/- 0.12, 17.19 +/- 0.24
UVW2 = 17.10 +/- 0.06, 17.18 +/- 0.07

The light curves of the object in the g, r and i bands show a double humped profile with an amplitude of ~0.25 mags, which explains the large amplitude variability also observed in the UVOT data between both epochs.

Optical spectra obtained on 23rd July 2019 with the SPRAT spectrograph on the Liverpool Telescope show that the object has no emission lines, Balmer and He lines appear in absorption. This discards the possibility of MGAB-V269 to be an AM CVn star. A CV nature is also disfavored given the period, the X-ray and the spectral features.

MGAB-V269 seems to be a similar system to MGAB-V249, previously reported in ATel #12847, which is not either an X-ray source. The optical folded light curves and spectral features of both systems are alike. If MGAB-V249 is in fact a He-sdOB star as suggested by Ramsay+ 2019 (ATel #13048), MGAB-V269 could be a similar type of system. Further observations are encouraged.

We thank the Swift team for their prompt response and for approving our ToO requests.