4 research outputs found
On the frequencies of circumbinary discs in protostellar systems
We report the analysis of circumbinary discs formed in a radiation
hydrodynamical simulation of star cluster formation. We consider both pure
binary stars and pairs within triple and quadruple systems. The protostellar
systems are all young (ages < yrs). We find that the systems that host a
circumbinary disc have a median separation of au, and the median
characteristic radius of the discs is au. We find that per
cent of pure binaries with semi-major axes au have a circumbinary disc,
and the occurrence rate of circumbinary discs is bimodal with log-separation in
pure binaries with a second peak at au. Systems with au
almost never have a circumbinary disc. The median size of a circumbinary disc
is between depending on the order of the system, with higher
order systems having larger discs relative to binary separation. We find the
underlying distribution of mutual inclinations between circumbinary discs and
binary orbit of both observed and simulated discs to not differ statistically.Comment: 12 pages, 11 figures, 1 table, accepted for publication in MNRA
The magnetically quiet solar surface dominates HARPS-N solar RVs during low activity
Using images from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory (SDO/HMI), we extract the radial-velocity (RV) signal arising from the suppression of convective blue-shift and from bright faculae and dark sunspots transiting the rotating solar disc. We remove these rotationally modulated magnetic-activity contributions from simultaneous radial velocities observed by the HARPS-N solar feed to produce a radial-velocity time series arising from the magnetically quiet solar surface (the ‘inactive-region radial velocities’). We find that the level of variability in the inactive-region radial velocities remains constant over the almost 7 year baseline and shows no correlation with well-known activity indicators. With an RMS of roughly 1 m s−1, the inactive-region radial-velocity time series dominates the total RV variability budget during the decline of solar cycle 24. Finally, we compare the variability amplitude and timescale of the inactive-region radial velocities with simulations of supergranulation. We find consistency between the inactive-region radial-velocity and simulated time series, indicating that supergranulation is a significant contribution to the overall solar radial velocity variability, and may be the main source of variability towards solar minimum. This work highlights supergranulation as a key barrier to detecting Earth twins
The magnetically quiet solar surface dominates HARPS-N solar RVs during low activity
Using images from the Helioseismic and Magnetic Imager aboard the
\textit{Solar Dynamics Observatory} (SDO/HMI), we extract the radial-velocity
(RV) signal arising from the suppression of convective blue-shift and from
bright faculae and dark sunspots transiting the rotating solar disc. We remove
these rotationally modulated magnetic-activity contributions from simultaneous
radial velocities observed by the HARPS-N solar feed to produce a
radial-velocity time series arising from the magnetically quiet solar surface
(the 'inactive-region radial velocities'). We find that the level of
variability in the inactive-region radial velocities remains constant over the
almost 7 year baseline and shows no correlation with well-known activity
indicators. With an RMS of roughly 1 m/s, the inactive-region radial-velocity
time series dominates the total RV variability budget during the decline of
solar cycle 24. Finally, we compare the variability amplitude and timescale of
the inactive-region radial velocities with simulations of supergranulation. We
find consistency between the inactive-region radial-velocity and simulated time
series, indicating that supergranulation is a significant contribution to the
overall solar radial velocity variability, and may be the main source of
variability towards solar minimum. This work highlights supergranulation as a
key barrier to detecting Earth twins.Comment: 12 pages, 11 figures, accepted to MNRA