10 research outputs found
An Earth-like stellar wind environment for Proxima Centauri c
A new planet has been recently discovered around Proxima Centauri. With an
orbital separation of au and a minimum mass of about
, Proxima c is a prime direct imaging target for atmospheric
characterization. The latter can only be performed with a good understanding of
the space environment of the planet, as multiple processes can have profound
effects on the atmospheric structure and evolution. Here, we take one step in
this direction by generating physically-realistic numerical simulations of
Proxima's stellar wind, coupled to a magnetosphere and ionosphere model around
Proxima c. We evaluate their expected variation due to the magnetic cycle of
the host star, as well as for plausible inclination angles for the exoplanet
orbit. Our results indicate stellar wind dynamic pressures comparable to
present-day Earth, with a slight increase (by a factor of 2) during high
activity periods of the star. A relatively weak interplanetary magnetic field
at the distance of Proxima c leads to negligible stellar wind Joule heating of
the upper atmosphere (about of the solar wind contribution on Earth) for
an Earth-like planetary magnetic field ( G). Finally, we provide an
assessment of the likely extreme conditions experienced by the exoplanet
candidate Proxima d, tentatively located at au with a minimum mass of
.Comment: 9 Pages, 4 Figures, 1 Table. Accepted for publication in The
Astrophysical Journal Letters (ApJL
Tuning the Exo-Space Weather Radio for Stellar Coronal Mass Ejections
Coronal mass ejections (CMEs) on stars other than the Sun have proven very
difficult to detect. One promising pathway lies in the detection of type II
radio bursts. Their appearance and distinctive properties are associated with
the development of an outward propagating CME-driven shock. However, dedicated
radio searches have not been able to identify these transient features in other
stars. Large Alfv\'en speeds and the magnetic suppression of CMEs in active
stars have been proposed to render stellar eruptions "radio-quiet". Employing
3D magnetohydrodynamic simulations, we study here the distribution of the
coronal Alfv\'en speed, focusing on two cases representative of a young
Sun-like star and a mid-activity M-dwarf (Proxima Centauri). These results are
compared with a standard solar simulation and used to characterize the
shock-prone regions in the stellar corona and wind. Furthermore, using a
flux-rope eruption model, we drive realistic CME events within our M-dwarf
simulation. We consider eruptions with different energies to probe the regimes
of weak and partial CME magnetic confinement. While these CMEs are able to
generate shocks in the corona, those are pushed much farther out compared to
their solar counterparts. This drastically reduces the resulting type II radio
burst frequencies down to the ionospheric cutoff, which impedes their detection
with ground-based instrumentation.Comment: 13 Pages, 6 Figures, 2 Tables. Accepted for publication in The
Astrophysical Journa
The discovery space of ELT-ANDES. Stars and stellar populations
The ArmazoNes high Dispersion Echelle Spectrograph (ANDES) is the optical and
near-infrared high-resolution echelle spectrograph envisioned for the European
Extremely Large Telescope (ELT). We present a selection of science cases,
supported by new calculations and simulations, where ANDES could enable major
advances in the fields of stars and stellar populations. We focus on three key
areas, including the physics of stellar atmospheres, structure, and evolution;
stars of the Milky Way, Local Group, and beyond; and the star-planet
connection. The key features of ANDES are its wide wavelength coverage at high
spectral resolution and its access to the large collecting area of the ELT.
These features position ANDES to address the most compelling and potentially
transformative science questions in stellar astrophysics of the decades ahead,
including questions which cannot be anticipated today.Comment: 46 pages, 8 figures; submitted to Experimental Astronomy on behalf of
the ANDES Science Tea
An x-ray interferometry concept for ESA's Voyage 2050 programme
© 2020 SPIE We have proposed the development of X-ray interferometry as part of ESA's Voyage 2050 programme, to reveal the universe at high energies with ultra-high spatial resolution. With only a 1 m baseline, which could be accommodated on a single spacecraft, X-ray interferometry can reach 100 µas resolution at 10 Å (1.24 keV) and exceed that of the Event Horizon Telescope at 2 Å (6.2 keV). A multi-spacecraft 'constellation' interferometer would resolve well below 1 µas. Here we focus on the single-spacecraft interferometer design and discuss the process of fringe detection and image reconstruction from multiple baselines, showing simulated images of test cases from our Voyage 2050 White Paper. We also discuss the challenges and feasibility of reaching the technical requirements needed for a single-spacecraft interferometer. Most key requirements are already feasible or within easy reach. Besides a ground-based testbed, covered elsewhere in these proceedings, the most important areas for development include large format, small-pixel X-ray detectors and pointing which is stable or can be reconstructed to tens of µas precision
The high energy universe at ultra-high resolution: the power and promise of X-ray interferometry
We propose the development of X-ray interferometry (XRI), to reveal the universe at high energies with ultra-high spatial resolution. With baselines which can be accommodated on a single spacecraft, XRI can reach 100 as resolution at 10 \AA (1.2 keV) and 20 as at 2 \AA (6 keV), enabling imaging and imaging-spectroscopy of (for example) X-ray coronae of nearby accreting supermassive black holes (SMBH) and the SMBH `shadow'; SMBH accretion flows and outflows; X-ray binary winds and orbits; stellar coronae within ~100 pc and many exoplanets which transit across them. For sufficiently luminous sources XRI will resolve sub-pc scales across the entire observable universe, revealing accreting binary SMBHs and enabling trigonometric measurements of the Hubble constant with X-ray light echoes from quasars or explosive transients. A multi-spacecraft `constellation' interferometer would resolve well below 1 as, enabling SMBH event horizons to be resolved in many active galaxies and the detailed study of the effects of strong field gravity on the dynamics and emission from accreting gas close to the black hole