62 research outputs found
Stellar Wind Confinement of Evaporating Exoplanet Atmospheres and Its Signatures in 1083 nm Observations
Atmospheric escape from close-in exoplanets is thought to be crucial in
shaping observed planetary populations. Recently, significant progress has been
made in observing this process in action through excess absorption in transit
spectra and narrowband light curves. We model the escape of
initially-homogeneous planetary winds interacting with a stellar wind. The ram
pressure balance of the two winds governs this interaction. When the
impingement of the stellar wind on the planetary outflow is mild or moderate,
the planetary outflow expands nearly spherically through its sonic surface
before forming a shocked boundary layer. When the confinement is strong, the
planetary outflow is redirected into a cometary tail before it expands to its
sonic radius. The resultant transmission spectra at the He 1083 nm line are
accurately represented by a 1D spherical wind solution in cases of mild to
moderate stellar wind interaction. In cases of strong stellar wind interaction,
the degree of absorption is enhanced and the cometary tail leads to an extended
egress from transit. The crucial features of the wind--wind interaction are,
therefore, encapsulated in the light curve of He 1083 nm equivalent width as a
function of time. The possibility of extended He 1083 nm absorption well beyond
the optical transit carries important implications for planning
"out-of-transit" observations that serve as a baseline for in-transit data.Comment: Accepted for publication in AAS Journals. Associated data and
software at: https://zenodo.org/record/5750747 and
https://zenodo.org/record/575077
WASP-69b's Escaping Envelope is Confined to a Tail Extending at Least Seven Planet Radii
Studying the escaping atmospheres of highly-irradiated exoplanets is critical
for understanding the physical mechanisms that shape the demographics of
close-in planets. A number of planetary outflows have been observed as excess
H/He absorption during/after transit. Such an outflow has been observed for
WASP-69b by multiple groups that disagree on the geometry and velocity
structure of the outflow. Here, we report the detection of this planet's
outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28
hours after egress until the target set, demonstrating the outflow extends at
least km or 7.5 planet radii. This detection is significantly
longer than previous observations which report an outflow extending 2.2
planet radii just one year prior. The outflow is blue-shifted by 23 km
s in the planetary rest frame. We estimate a current mass loss rate of 1
Gyr. Our observations are most consistent with an outflow
that is strongly sculpted by ram pressure from the stellar wind. However,
potential variability in the outflow could be due to time-varying interactions
with the stellar wind or differences in instrumental precision.Comment: 12 pages, 12 figures, Accepted for publication in The Astrophysical
Journal (ApJ
Constraints on Metastable Helium in the Atmospheres of WASP-69b and WASP-52b with Ultra-Narrowband Photometry
Infrared observations of metastable 2S helium absorption with ground- and
space-based spectroscopy are rapidly maturing, as this species is a unique
probe of exoplanet atmospheres. Specifically, the transit depth in the triplet
feature (with vacuum wavelengths near 1083.3 nm) can be used to constrain the
temperature and mass loss rate of an exoplanet's upper atmosphere. Here, we
present a new photometric technique to measure metastable 2S helium
absorption using an ultra-narrowband filter (full-width at half-maximum of
0.635 nm) coupled to a beam-shaping diffuser installed in the Wide-field
Infrared Camera (WIRC) on the 200-inch Hale Telescope at Palomar Observatory.
We use telluric OH lines and a helium arc lamp to characterize refractive
effects through the filter and to confirm our understanding of the filter
transmission profile. We benchmark our new technique by observing a transit of
WASP-69b and detect an excess absorption of % (11.1),
consistent with previous measurements after considering our bandpass. Then, we
use this method to study the inflated gas giant WASP-52b and place a
95th-percentile upper limit on excess absorption in our helium bandpass of
0.47%. Using an atmospheric escape model, we constrain the mass loss rate for
WASP-69b to be
() at 7,000 K
(12,000 K). Additionally, we set an upper limit on the mass loss rate of
WASP-52b at these temperatures of
(). These results show that
ultra-narrowband photometry can reliably quantify absorption in the metastable
helium feature.Comment: 17 pages, 8 figures (figures 1 and 2 are rasterized for arXiv file
size compliance), accepted to A
Star-forming Clumps in Local Luminous Infrared Galaxies
We present HST narrowband near-infrared imaging of Paα and Paβ emission of 48 local luminous infrared galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey. These data allow us to measure the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extranuclear clumps) and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs the star-forming clumps have radii ranging from ~90 to 900 pc and star formation rates (SFRs) of ~1 × 10⁻³ to 10 M⊙ yr⁻¹, with median values for extranuclear clumps of 170 pc and 0.03 M⊙ yr⁻¹. The detected star-forming clumps are young, with a median stellar age of 8.7 Myr, and have a median stellar mass of 5 × 10⁵ M ⊙. The SFRs span the range of those found in normal local star-forming galaxies to those found in high-redshift star-forming galaxies at z = 1–3. The luminosity function of the LIRG clumps has a flatter slope than found in lower-luminosity, star-forming galaxies, indicating a relative excess of luminous star-forming clumps. In order to predict the possible range of star-forming histories and gas fractions, we compare the star-forming clumps to those measured in the MassiveFIRE high-resolution cosmological simulation. The star-forming clumps in MassiveFIRE cover the same range of SFRs and sizes found in the local LIRGs and have total gas fractions that extend from 10% to 90%. If local LIRGs are similar to these simulated galaxies, we expect that future observations with ALMA will find a large range of gas fractions, and corresponding star formation efficiencies, among the star-forming clumps in LIRGs
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