KK 242, a faint companion to the isolated Scd galaxy NGC 6503
  Using Hubble Space Telescope imaging of the resolved stellar population of
KK~242 = NGC6503-d1 = PGC~4689184, we measure the distance to the galaxy to be
$6.46\pm0.32$ Mpc and find that KK~242 is a satellite of the low-mass spiral
galaxy NGC~6503 located on the edge of the Local Void. Observations with the
Karl G. Jansky Very Large Array show signs of a very faint HI-signal at the
position of KK~242 within a velocity range of $V_{hel} = -80\pm10$
km\,s$^{-1}$. This velocity range is severely contaminated by HI emission from
the Milky Way and from NGC6503. The dwarf galaxy is classified as the
transition type, dIrr/dSph, with a total HI-mass of $< 10^6 M_{\odot}$ and a
star formation rate SFR(H$\alpha$) = --4.82 dex ($M{\odot}$/yr). Being at a
projected separation of 31 kpc with a radial velocity difference of -- 105
km\,s$^{-1}$ relative to NGC~6503, KK~242 gives an estimate of the halo mass of
the spiral galaxy to be $\log(M/M_{\odot}$) = 11.6. Besides NGC~6503, there are
8 more detached low-luminosity spiral galaxies in the Local Volume: M~33,
NGC~2403, NGC~7793, NGC~1313, NGC~4236, NGC~5068, NGC~4656 and NGC~7640, from
whose small satellites we have estimated the average total mass of the host
galaxies and their average total mass-to-K-band-luminosity $\langle
M_T/M_{\odot}\rangle = (3.46\pm0.84)\times 10^{11}$ and $(58\pm19)
M_{\odot}/L_{\odot}$, respectively.
