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We present the results of 8 epochs of simultaneous UV and X-ray observationsof the highly variable ultraluminous X-ray source (ULX) Holmberg II X-1 withAstroSat -- Indian multiwavelength space satellite. During the entireobservation period from late 2016 to early 2020, Holmberg II X-1 showed amoderate X-ray luminosity of $8\times10^{39}$ erg/s and a hard power-lawspectrum with $\Gamma \lesssim 1.9$. Due to low variability of the object inX-rays (by a factor 1.5) and insignificant variability in the UV range (upperlimit $\approx25$%) we could not find reliable correlation between flux changesin these ranges. Inside each particular observation, the X-ray variabilityamplitude is higher, it reaches a factor of 2-3 respect to the mean level atthe time scales of $\sim10$ ks or even shorter. We discussed our results interms of three models of a heated donor star, a heated disk and a heated wind,and estimated the lower limit to the variability which would allow to reject atleast part of them.

Simultaneous X-ray/UV observations of ultraluminous X-ray source Holmberg II X-1 with Indian space mission AstroSat