38 research outputs found
Alkaline Exospheres of Exoplanet Systems: Evaporative Transmission Spectra
Hydrostatic equilibrium is an excellent approximation for the dense layers of
planetary atmospheres where it has been canonically used to interpret
transmission spectra of exoplanets. Here we exploit the ability of
high-resolution spectrographs to probe tenuous layers of sodium and potassium
gas due to their formidable absorption cross-sections. We present an
atmosphere-exosphere degeneracy between optically thick and optically thin
mediums, raising the question of whether hydrostatic equilibrium is appropriate
for Na I lines observed at exoplanets. To this end we simulate three
non-hydrostatic, evaporative, density profiles: (i) escaping, (ii) exomoon, and
(iii) torus to examine their imprint on an alkaline exosphere in transmission.
By analyzing an evaporative curve of growth we find that equivalent widths of
mA are naturally driven by evaporation rates
kg/s of pure atomic Na. To break the degeneracy between
atmospheric and exospheric absorption, we suggest that if the line ratio is
the gas is optically thin on average and roughly
indicating a non-hydrostatic structure of the atmosphere/exosphere. We show
this is the case for Na I observations at hot Jupiters WASP-49b and HD189733b
and also simulate their K I spectra. Lastly, motivated by the slew of metal
detections at ultra-hot Jupiters, we suggest a toroidal atmosphere at WASP-76b
and WASP-121b is consistent with the Na I data at present.Comment: 23 pages, 21 figures, accepted by MNRA
Linking the evolution of terrestrial interiors and an early outgassed atmosphere to astrophysical observations
A terrestrial planet is molten during formation and may remain so if subject
to intense insolation or tidal forces. Observations continue to favour the
detection and characterisation of hot planets, potentially with large outgassed
atmospheres. We aim to determine the radius of hot Earth-like planets with
large outgassed atmospheres and explore differences between molten and solid
silicate planets and their influence on the mass-radius relationship and
transmission and emission spectra. An interior-atmosphere model, combined with
static structure calculations, tracks the evolving radius of a rocky mantle
that is outgassing CO and HO. Synthetic emission and transmission
spectra are generated for CO and HO dominated atmospheres. Atmospheres
dominated by CO suppress the outgassing of HO to a greater extent than
previously realised, as previous studies have applied an erroneous relationship
between volatile mass and partial pressure. We therefore predict more HO
can be retained by the interior during the later stages of magma ocean
crystallisation. Furthermore, formation of a lid at the surface can tie
outgassing of HO to the efficiency of heat transport through the lid,
rather than the atmosphere's radiative timescale. Contraction of the mantle as
it solidifies gives radius decrease, which can partly be offset by
addition of a relatively light species to the atmosphere. We conclude that a
molten silicate mantle can increase the radius of a terrestrial planet by
around compared to its solid counterpart, or equivalently account for a
decrease in bulk density. An outgassing atmosphere can perturb the total
radius according to its speciation. Atmospheres of terrestrial planets around
M-stars that are dominated by CO or HO can be distinguished by
observing facilities with extended wavelength coverage (e.g., JWST).Comment: 19 pages, published in A&A, abstract shortene
Planetary evolution with atmospheric photoevaporation II: Fitting the slope of the radius valley by combining boil-off and XUV-driven escape
The Kepler satellite has revealed a gap between sub-Neptunes and super-Earths
that atmospheric escape models had predicted as an evaporation valley. We seek
to contrast results from a simple XUV-driven energy-limited (ELIM) escape model
against those from a direct hydrodynamic (HYDRO) model. Besides XUV-driven
escape, the latter also includes the boil-off regime. We couple the two models
to an internal structure model and follow the planets' temporal evolution over
Gyr. To see the population-wide imprint of the two models, we first employ a
rectangular grid in initial conditions. We then study the slope of the valley
also for initial conditions derived from the Kepler planets. For the
rectangular grid, we find that the power-law slope of the valley with respect
to orbital period is -0.18 and -0.11 in the ELIM and HYDRO model, respectively.
For the initial conditions derived from the Kepler planets, the results are
similar (-0.16 and -0.10). While the slope found with the ELIM model is steeper
than observed, the one of the HYDRO model is in excellent agreement with
observations. The reason for the shallower slope is caused by the two regimes
in which the ELIM model fails: First, puffy planets at low stellar irradiation.
For them, boil-off dominates mass loss. However, boil-off is absent in the ELIM
model, thus it underestimates escape relative to HYDRO. Second, massive compact
planets at high XUV irradiation. For them, the ELIM approximation overestimates
escape relative to the HYDRO case because of cooling by thermal conduction,
neglected in the ELIM model. The two effects act together in concert to yield
in the HYDRO model a shallower slope of the valley that agrees very well with
observations. We conclude that an escape model that includes boil-off and a
more realistic treatment of cooling mechanisms can reproduce one of the most
important constraints, the valley slope.Comment: 20 pages, 11 figures, accepted to A&
Radio-Loud Exoplanet-Exomoon Survey (RLEES): GMRT Search for Electron Cyclotron Maser Emission
We conducted the first dedicated search for signatures of exoplanet-exomoon
interactions using the Giant Metrewave Radio Telescope (GMRT) as part of the
radio-loud exoplanet-exomoon survey (RLEES). Due to stellar tidal heating,
irradiation, and subsequent atmospheric escape, candidate `exo-Io' systems are
expected to emit up to times more plasma flux than the Jupiter-Io DC
circuit. This can induce detectable radio emission from the exoplanet-exomoon
system. We analyze three `exo-Io' candidate stars: WASP-49, HAT-P 12, and HD
189733. We perform 12-hour phase-curve observations of WASP-49b at 400 MHz
during primary secondary transit, as well as first third quadratures
achieving a 3 upper-limit of 0.18 mJy/beam averaged over four days.
HAT-P~12 was observed with GMRT at 150 and 325 MHz. We further analyzed the
archival data of HD 189733 at 325 MHz. No emission was detected from the three
systems. However, we place strong upper limits on radio flux density. Given
that most exo-Io candidates orbit hot Saturns, we encourage more
multiwavelength searches (in particular low frequencies) to span the lower
range of exoplanet B-field strengths constrained here.Comment: 7 pages, 3 figures, accepted for publication in The Astronomical
Journa
uGMRT observations of the hot-Saturn WASP 69b: Radio-Loud Exoplanet-Exomoon Survey II (RLEES II)
Exomoons have so far eluded ongoing searches. Several studies have exploited
transit and transit timing variations and high-resolution spectroscopy to
identify potential exomoon candidates. One method of detecting and confirming
these exomoons is to search for signals of planet-moon interactions. In this
work, we present the first radio observations of the exomoon candidate system
WASP 69b. Based on the detection of alkali metals in the transmission spectra
of WASP-69b, it was deduced that the system might be hosting an exomoon. WASP
69b is also one of the exoplanet systems that will be observed as part of JWST
cycle-1 GTO. This makes the system an excellent target to observe and follow
up. We observed the system for 32 hrs at 150 MHz and 218 MHz using the upgraded
Giant Metrewave Radio Telescope (uGMRT). Though we do not detect radio emission
from the systems, we place strong upper limits of 3.3 mJy at 150 MHz
and 0.9 mJy at 218 MHz. We then use these upper limits to estimate the maximum
mass loss from the exomoon candidate.Comment: Accepted in MNRAS, 8 pages, 4 Figure
The First ALLWISE Proper Motion Discovery: WISEA J070720.50+170532.7
While quality checking a new motion-aware co-addition of all 12.5 months of Wide-field Infrared Survey Explorer (WISE) data, we found that the source WISE J070720.48+170533.0 moved 0".9 in six months. Backtracking this motion allowed us to identify this source as 2MASS J07071961+1705464, with several entries in the USNO B catalog. An astrometric fit to these archival data gives a proper motion of μ = 1793 ± 2 mas yr^(–1) and a parallax of ω = 35 ± 42 mas. Photometry from WISE, 2MASS, and the POSS can be fit reasonably well by a blackbody with T = 3658 K and an angular radius of 4.36 × 10^(–11) radians. No clear evidence of H_2 collision-induced absorption is seen in the near-infrared. An optical spectrum shows broad deep CaH bands at 638 and 690 nm, broad deep Na D at 598.2 nm, and weak or absent TiO, indicating that this source is an ultra-subdwarf M star with a radial velocity v_(rad) ≈ –21 ± 18 km s^(–1) relative to the Sun. Given its apparent magnitude, the distance is about 39 ± 9 pc and the tangential velocity is probably ≈330 km s^(–1), but a more precise parallax is needed to be certain
High contrast imaging at the LBT: the LEECH exoplanet imaging survey
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began
its 130-night campaign from the Large Binocular Telescope (LBT) atop Mt
Graham, Arizona. This survey benefits from the many technological achievements
of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual
adaptive secondary mirrors for high Strehl performance, and a cold beam
combiner to dramatically reduce the telescope's overall background emissivity.
LEECH neatly complements other high-contrast planet imaging efforts by
observing stars at L' (3.8 m), as opposed to the shorter wavelength
near-infrared bands (1-2.4 m) of other surveys. This portion of the
spectrum offers deep mass sensitivity, especially around nearby adolescent
(0.1-1 Gyr) stars. LEECH's contrast is competitive with other extreme
adaptive optics systems, while providing an alternative survey strategy.
Additionally, LEECH is characterizing known exoplanetary systems with
observations from 3-5m in preparation for JWST.Comment: 12 pages, 5 figures. Proceedings of the SPIE, 9148-2
The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions
We present the results of the largest (m) direct
imaging survey for exoplanets to date, the Large Binocular Telescope
Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98
stars with spectral types from B to M. Cool planets emit a larger share of
their flux in compared to shorter wavelengths, affording LEECH an
advantage in detecting low-mass, old, and cold-start giant planets. We
emphasize proximity over youth in our target selection, probing physical
separations smaller than other direct imaging surveys. For FGK stars, LEECH
outperforms many previous studies, placing tighter constraints on the hot-start
planet occurrence frequency interior to au. For less luminous,
cold-start planets, LEECH provides the best constraints on giant-planet
frequency interior to au around FGK stars. Direct imaging survey
results depend sensitively on both the choice of evolutionary model (e.g., hot-
or cold-start) and assumptions (explicit or implicit) about the shape of the
underlying planet distribution, in particular its radial extent. Artificially
low limits on the planet occurrence frequency can be derived when the shape of
the planet distribution is assumed to extend to very large separations, well
beyond typical protoplanetary dust-disk radii ( au), and when
hot-start models are used exclusively. We place a conservative upper limit on
the planet occurrence frequency using cold-start models and planetary
population distributions that do not extend beyond typical protoplanetary
dust-disk radii. We find that of FGK systems can host a 7 to 10
planet from 5 to 50 au. This limit leaves open the
possibility that planets in this range are common.Comment: 31 pages, 13 figures, accepted to A
LEECH: A 100 Night Exoplanet Imaging Survey at the LBT
In February 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began
its 100-night campaign from the Large Binocular Telescope atop Mount Graham in
Arizona. LEECH nearly complements other high-contrast planet imaging efforts by
observing stars in L' band (3.8 microns) as opposed to the shorter wavelength
near-infrared bands (1-2.3 microns). This part of the spectrum offers deeper
mass sensitivity for intermediate age (several hundred Myr-old) systems, since
their Jovian-mass planets radiate predominantly in the mid-infrared. In this
proceedings, we present the science goals for LEECH and a preliminary contrast
curve from some early data.Comment: IAUS 299 Proceeding
LEECH: A 100 Night Exoplanet Imaging Survey at the LBT
In February 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its 100-night campaign from the Large Binocular Telescope atop Mount Graham in Arizona. LEECH neatly complements other high-contrast planet imaging efforts by observing stars in L' band (3.8 microns) as opposed to the shorter wavelength near-infrared bands (1-2.3 microns). This part of the spectrum offers deeper mass sensitivity for intermediate age (several hundred Myr-old) systems, since their Jovian-mass planets radiate predominantly in the mid-infrared. In this proceedings, we present the science goals for LEECH and a preliminary contrast curve from some early dat