Context : It is of broad interest for galaxy formation theory to carry out a full inventory of the numbers and properties of dwarf galaxies in the Local Volume , both satellites and isolated ones .

Aims : Ultra-deep imaging in wide areas of the sky with small amateur telescopes can help to complete the census of these hitherto unknown low surface brightness galaxies , which can not be detected by the current resolved stellar population and HI surveys .
We report the discovery of Donatiello I , a dwarf spheroidal galaxy located one degree from the star Mirach ( \beta And ) in a deep image taken with an amateur telescope .

Methods : The color–magnitude diagram obtained from follow-up observations obtained with the Gran Telescopio Canarias ( La Palma , Spain ) reveals that this system is beyond the Local Group and is mainly composed of old stars .
The absence of young stars and HI emission in the ALFALFA survey are typical of quenched dwarf galaxies .
Our photometry suggests a distance modulus for this galaxy of ( m - M ) = 27.6 \pm 0.2 ( 3.3 Mpc ) , although this distance can not yet be established securely owing to the crowding effects in our color–magnitude diagram .
At this distance , Donatiello I ’ s absolute magnitude ( M _ { V } = -8.3 ) , surface brightness ( \mu _ { V } = 26.5 mag arcsec ^ { -2 } ) and stellar content are similar to the “ classical ” Milky Way companions Draco or Ursa Minor .

Results : The projected position and distance of Donatiello I are consistent with being a dwarf satellite of the closest S0-type galaxy NGC 404 ( “ Mirach ’ s Ghost ” ) .
Alternatively , it could be one of the most isolated quenched dwarf galaxies reported so far behind the Andromeda galaxy .

Conclusions :