Abstract
Early in their lives, planets endure extreme amounts of ionizing radiation from their host stars. For planets with primordial hydrogen and helium-rich envelopes, this can lead to substantial ...mass loss. Direct observations of atmospheric escape in young planetary systems can help elucidate this critical stage of planetary evolution. In this work, we search for metastable helium absorption—a tracer of tenuous gas in escaping atmospheres—during transits of three planets orbiting the young solar analog V1298 Tau. We characterize the stellar helium line using HET/HPF, and find that it evolves substantially on timescales of days to months. The line is stable on hour-long timescales except for one set of spectra taken during the decay phase of a stellar flare, where absoprtion increased with time. Utilizing a beam-shaping diffuser and a narrowband filter centered on the helium feature, we observe four transits with Palomar/WIRC: two partial transits of planet d (
P
= 12.4 days), one partial transit of planet b (
P
= 24.1 days), and one full transit of planet c (
P
= 8.2 days). We do not detect the transit of planet c, and we find no evidence of excess absorption for planet b, with Δ
R
b
/
R
⋆
< 0.019 in our bandpass. We find a tentative absorption signal for planet d with Δ
R
d
/
R
⋆
= 0.0205 ± 0.054, but the best-fit model requires a substantial (−100 ± 14 minutes) transit-timing offset on a two-month timescale. Nevertheless, our data suggest that V1298 Tau d may have a high present-day mass-loss rate, making it a priority target for follow-up observations.
Abstract
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.
Strong absorption signatures in the helium line at 1083 nm have recently been detected in transmission spectra of several close-in exoplanets. This absorption line originates from neutral helium ...atoms in an excited, metastable 23S state. The population of helium atoms in this excited state is governed by the spectral shape and intensity of the incident stellar radiation field. We investigate what kind of stellar environments are most favorable for populating the metastable helium state in extended planetary atmospheres. Our results suggest that planets orbiting at close separations from late-type stars-particularly K-stars-are the most promising candidates for transit absorption signals at 1083 nm. This result is supported by observations, as all four exoplanets with currently reported helium detections orbit K-type stars. In general, conditions for exciting helium atoms become more favorable at closer orbital separations, and around stars with higher levels of extreme-ultraviolet (EUV) flux, which ionizes the helium ground state, and lower levels of mid-ultraviolet (mid-UV) flux, which ionizes the helium metastable state.
The morphology of massive star-forming galaxies at high redshift is often dominated by giant clumps of mass ~10 super( 8)-10 super( 9) M... and size ~100-1000 pc. Previous studies have proposed that ...giant clumps might have an important role in the evolution of their host galaxy, particularly in building the central bulge. However, this depends on whether clumps live long enough to migrate from their original location in the disc or whether they get disrupted by their own stellar feedback before reaching the centre of the galaxy. We use cosmological hydrodynamical simulations from the FIRE (Feedback in Realistic Environments) project which implement explicit treatments of stellar feedback and interstellar medium physics to study the properties of these clumps. We follow the evolution of giant clumps in a massive (M* ~ 10 super( 10.8) M... at z = 1), discy, gas-rich galaxy from redshift z ... 2 to z = 1. Even though the clumpy phase of this galaxy lasts over a gigayear, individual gas clumps are short-lived, with mean lifetime of massive clumps of ~20 Myr. During that time, they turn between 0.1 per cent and 20...per...cent of their gas into stars before being disrupted, similar to local giant molecular clouds. Clumps with M ... 10 super( 7) M... account for ~20 per cent of the total star formation in the galaxy during the clumpy phase, producing ~10 super( 10) M... of stars. We do not find evidence for net inward migration of clumps within the galaxy. The number of giant clumps and their mass decrease at lower redshifts, following the decrease in the overall gas fraction and star formation rate. (ProQuest: ... denotes formulae/symbols omitted.)
The Multiplanet System TOI-421 Gandolfi, Davide; Barragan, Oscar; Livingston, John H. ...
The Astronomical journal,
09/2020, Volume:
160, Issue:
3
Journal Article
Peer reviewed
Open access
We report the discovery of a warm Neptune and a hot sub-Neptune transiting TOI-421 (BD-14 1137, TIC 94986319), a bright (V = 9.9) G9 dwarf star in a visual binary system observed by the Transiting ...Exoplanet Survey Satellite (TESS) space mission in Sectors 5 and 6. We performed ground-based follow-up observations-comprised of Las Cumbres Observatory Global Telescope transit photometry, NIRC2 adaptive optics imaging, and FIbre-fed Echelle Spectrograph, CORALIE, High Accuracy Radial velocity Planet Searcher, High Resolution echelle Spectrometer, and Planet Finder Spectrograph high-precision Doppler measurements-and confirmed the planetary nature of the 16 day transiting candidate announced by the TESS team. We discovered an additional radial velocity signal with a period of five days induced by the presence of a second planet in the system, which we also found to transit its host star. We found that the inner mini-Neptune, TOI-421 b, has an orbital period of P-b = 5.19672 +/- 0.00049 days, a mass of M-b = 7.17 +/- 0.66 M-circle plus, and a radius of R-b = R-circle plus, whereas the outer warm Neptune, TOI-421 c, has a period of P-c = 16.06819 +/- 0.00035 days, a mass of M-c = 16.42(-1.04)(+1.06)M(circle plus), a radius of R-c = 5.09(-0.15)(+0.16)R(circle plus), and a density of rho(c) = 0.685(-0.072)(+0.080) cm(-3). With its characteristics, the outer planet (rho(c) = 0.685(-0.0072)(+0.080) cm(-3)) is placed in the intriguing class of the super-puffy mini-Neptunes. TOI-421 b and TOI-421 c are found to be well-suited for atmospheric characterization. Our atmospheric simulations predict significant Ly alpha transit absorption, due to strong hydrogen escape in both planets, as well as the presence of detectable CH4 in the atmosphere of TOI-421 c if equilibrium chemistry is assumed.
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 hr after egress until the target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1. 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.
Abstract
The metastable helium line at 1083 nm can be used to probe the extended upper atmospheres of close-in exoplanets and thus provide insight into their atmospheric mass loss, which is likely to ...be significant in sculpting their population. We used an ultra-narrow band filter centered on this line to observe two transits of the low-density gas giant HAT-P-18b, using the 200″ Hale Telescope at Palomar Observatory, and report the detection of its extended upper atmosphere. We constrain the excess absorption to be 0.46% ± 0.12% in our 0.635 nm bandpass, exceeding the transit depth from the Transiting Exoplanet Survey Satellite (TESS) by 3.9
σ
. If we fit this signal with a 1D Parker wind model, we find that it corresponds to an atmospheric mass loss rate between
8.3
−
1.9
+
2.8
×
10
−
5
M
J
Gyr
−1
and
2.63
−
0.64
+
0.46
×
10
−
3
M
J
Gyr
−1
for thermosphere temperatures ranging from 4000 K to 13,000 K, respectively. With a
J
magnitude of 10.8, this is the faintest system for which such a measurement has been made to date, demonstrating the effectiveness of this approach for surveying mass loss on a diverse sample of close-in gas giant planets.
The helium absorption triplet at a wavelength of 10833 has been proposed as a way to probe the escaping atmospheres of exoplanets. Recently this feature was detected for the first time using Hubble ...Space Telescope (HST) WFC3 observations of the hot Jupiter WASP-107b. We use similar HST/WFC3 observations to detect helium in the atmosphere of the hot Neptune HAT-P-11b at the 4 confidence level. We compare our observations to a grid of 1D models of hydrodynamic escape to constrain the thermospheric temperatures and mass loss rate. We find that our data are best fit by models with high mass loss rates of g s−1. Although we do not detect the planetary wind directly, our data are consistent with the prediction that HAT-P-11b is experiencing hydrodynamic atmospheric escape. Nevertheless, the mass loss rate is low enough that the planet has only lost up to a few percent of its mass over its history, leaving its bulk composition largely unaffected. This matches the expectation from population statistics, which indicate that close-in planets with radii greater than 2 R⊕ form and retain H/He-dominated atmospheres. We also confirm the independent detection of helium in HAT-P-11b obtained with the CARMENES instrument, making this the first exoplanet with the detection of the same signature of photoevaporation from both ground- and space-based facilities.
Abstract
Hot Jupiters orbiting extremely close to their host star may experience atmospheric escape due to the large amounts of high-energy radiation they receive. Understanding the conditions under ...which this occurs is critical, as atmospheric escape is believed to be a driving factor in sculpting planetary populations. In recent years, the near-infrared 10833 Å helium feature has been found to be a promising spectral signature of atmospheric escape. We use transmission spectroscopy to search for excess helium absorption in the extended atmosphere of WASP-48b, a hot Jupiter orbiting a slightly evolved, rapidly rotating F star. The data were collected using the Habitable-zone Planet Finder spectrograph on the Hobby–Eberly Telescope. Observations were taken over the course of seven nights, from which we obtain three transits. No detectable helium absorption is seen, as absorption depth is measured to −0.0025 ± 0.0021, or 1.2
σ
from a null detection. This nondetection follows our current understanding of decreasing stellar activity (and thus high-energy radiation) with age. We use a 1D isothermal Parker wind model to compare with our observations and find that our nondetection can best be explained with a low planetary mass-loss rate and high thermosphere temperature. We explore our results within the context of the full sample of helium detections and nondetections to date. Surprisingly, comparing helium absorption with the stellar activity index
log
R
HK
′
reveals a large spread in the correlation between these two factors, suggesting that there are additional parameters influencing the helium absorption strength.
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