I am the PI of Mega-MUSCLES Treasury program, a HST Cycle 25 follow-on
to the successful MUSCLES project. Mega-MUSCLES has obtained
panchromatic (X-ray, UV, optical) light curves and spectra of twelve
M stars that probe a range of stellar and exoplanet properties, with a
particular focus on stars <0.3 Msolar and with a range of rotation
periods than can be used as proxies for M dwarf planet hosts after
HST's lifetime. Our targets also include current rocky exoplanet host
systems GJ1132 and Trappist-1. To date, six papers have been published by the Mega-MUSCLES team with two
additional papers making use of the data. The main survey paper will be published in late 2021.



The MUSCLES Project

The
MUSCLES Treasury Program is a large program
using COS and STIS on the Hubble Space Telescope, Chandra and XMM X-ray
observatories, and ground-based optical spectrographs and imagers at
Apache Point Observatory and LCOGT to determine the high energy
radiation environment experienced by planets in the Habitable Zones
(HZ) of low mass (K and M) stars. The first Earth-mass planet in the HZ
around its star is likely to be found around a cool star, yet the X-ray
and UV radiation from these stars and their levels of flaring activity
differ dramatically from those from solar-like stars. This irradiation
environment will have strong effects on the heating and photochemistry
of the planet's atmosphere and the potential habitability of the
planet. Until this survey, the high energy spectrum and activity
behavior of "normal" cool stars was poorly understood. We have now
generated broadband stellar spectral energy distributions for eleven K
and M stars hosting exoplanets which are being used as inputs for
models of exoplanet atmospheres.
The MUSCLES data products are now available on the
MAST archive.
Compact binaries and accretion disk physics
Compact binares are interacting binary systems in which a normal type
star loses mass to a compact object (a white dwarf, neutron star, or
black hole) via an accretion disk. The figures below illustrate two
black hole X-ray binary systems (illustrations courtesy of Robert
Hynes'
BinSym
program). The appeal of these systems is that they allow probes of
accretion processes, physics in extreme environments, and the formation and evolution of black holes in objects
that are relatively nearby and unobscured. The "Fundamental Plane of
Black Hole Accretion" (
Merloni et al. 2003,
Falcke et al. 2004)
has demonstrated that the physics that governs accretion onto black
holes is directly scalable over eight orders of magnitude, from stellar
mass black holes to the central engines of AGN. Because the time scale
of variability is significantly faster for the stellar mass objects and
confusion from the host galaxy is eliminated, we are able to probe a wide
range of accretion phenomenologies in X-ray binaries that is
challenging or precluded entirely in AGN. My interests center on the
physics of disk accretion and the link between accretion and outflows
in the forms of winds and jets. I am currently undertaking
multiwavelength studies of X-ray binaries centered around the first
far-ultraviolet spectra of several systems (e.g.,
Froning et al. 2010,
Froning et al. 2014).
I have also been pursuing a long-term program to obtain precise masses
for black holes and neutron stars in X-ray binary systems to constrain
models of the formation and evolution of collapsed objects and provide
accurate inputs for measurements of black hole spins (e.g.,
Khargharia et al. 2010).

The atmospheres of transiting exoplanets
With the beginning of science operations for the Cosmic Origins
Spectrograph, I have become involved in several programs centered on
ultraviolet observations of transiting hot Jupiters and a survey to
characterize the UV radiation environment in M star systems hosting
exoplanets. The transit observations (
Haswell et al. 2012,
Linsky et al. 2010,
Fossati et al. 2010,
France et al. 2010)
gave the first velocity-resolved UV transit data for HD209458b,
confirming the presence of high velocity ions escaping from the
planet's Roche lobe. In WASP-12b, we detected enhanced transit
signatures in ten different elements and evidence for an absorbing
cloud around the star, likely procuded by material stripped from the
planet. The UV radiation environment study (
France et al. 2012;
France et al. 2012, submitted) has shown strong and variable UV
radiation, particularly from Lya, even in optically quiet systems. The
UV radiation will affect the photochemistry of planets in the habitable
zones of these stars and may even lead to the presence of detectable O2
and O3 in the planetary atmospheres
even in the absence of biological life.