1,721,917 research outputs found
The Posttransit Tail of WASP-107b Observed at 10830 Å
Get PDFUnderstanding the effects of high-energy radiation and stellar winds on planetary atmospheres is vital for explaining the observed properties of close-in exoplanets. Observations of transiting exoplanets in the triplet of metastable helium lines at 10830 Å allow extended atmospheres and escape processes to be studied for individual planets. We observed one transit of WASP-107b with NIRSPEC on Keck at 10830 Å. Our observations, for the first time, had significant posttransit phase coverage, and we detected excess absorption for over an hour after fourth contact. The data can be explained by a comet-like tail extending out to ∼7 planet radii, which corresponds to roughly twice the Roche lobe radius of the planet. Planetary tails are expected based on three-dimensional simulations of escaping exoplanet atmospheres, particularly those including the interaction between the escaped material and strong stellar winds, and have been previously observed at 10830 Å in at least one other exoplanet. With both the largest midtransit absorption signal and the most extended tail observed at 10830 Å, WASP-107b remains a keystone exoplanet for atmospheric escape studies
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The Strength and Variability of the Helium 10830 Å Triplet in Young Stars, with Implications for Exosphere Detection
No full textYoung exoplanets trace planetary evolution, in particular the atmospheric mass loss that is most dynamic in youth. However, the high activity level of young stars can mask or mimic the spectroscopic signals of atmospheric mass loss. This includes the activity-sensitive He 10830 Å triplet, which is an increasingly important exospheric probe. To characterize the He-10830 triplet at young ages, we present time-series NIR spectra for young transiting planet hosts taken with the Habitable-zone Planet Finder. The He-10830 absorption strength is similar across our sample, except at the fastest and slowest rotations, indicating that young chromospheres are dense and populate metastable helium via collisions. Photoionization and recombination by coronal radiation only dominates metastable helium population at the active and inactive extremes. Volatile stellar activity, such as flares and changing surface features, drives variability in the He-10830 triplet. Variability is largest at the youngest ages before decreasing to ≲5-10 mÅ (or 3%) at ages above 300 Myr, with six of eight stars in this age range agreeing with there being no intrinsic variability. He-10830 triplet variability is smallest and age-independent at the shortest timescales. Intrinsic stellar variability should not preclude detection of young exospheres, except at the youngest ages. We recommend out-of-transit comparison observations taken directly surrounding transit and observation of multiple transits to minimize activity’s effect. Regardless, caution is necessary when interpreting transit observations in the context of stellar activity, as many scenarios can lead to enhanced stellar variability even on timescales of an hour. © 2024. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Observations de la raie de He I λ 10830 dans les spectres d'étoiles de type O
No full textAbstract. — The He I λ 10830 line has been observed in 44 O stars (mainly Of). Emission or P Cygni profiles are generally observed in the brightest objects (classes III and I) as well as in main sequence stars classified as Oe or Oef by P. S. Conti. In both cases we are dealing with objects with an extended atmosphere.Résumé. — Nous avons observé la raie de He I située à λ 10830 Å dans le spectre de 44 étoiles de type O (principalement de type Of). Elle a tendance à apparaître en émission dans les étoiles les plus lumineuses ainsi que dans les étoiles de la séquence principale classées Oe ou Oef par P.S. Conti. Dans chaque cas, il s'agit d'objets présentant une atmosphère étendue.Vreux Jean-Marie, Andrillat Yvette. Observations de la raie de He I λ 10830 dans les spectres d'étoiles de type O. In: Bulletin de la Classe des sciences, tome 61, 1975. pp. 577-581
Further observations of the lambda 10830 He line in stars and their significance as a measure of stellar activity
Get PDFMeasurements of the lambda 1030 He line in 198 stars are given along with data on other features in that spectral range. Nearly 80% of all G and K stars show some lambda 10830; of these, half are variable and 1/4 show emission. It was confirmed that lambda 10830 is not found in M stars, is weak in F stars, and is particularly strong in close binaries. The line is found in emission in extremely late M and S stars, along with P gamma, but P gamma is not in emission in G and K stars with lambda 10830 emissions. Variable He emission and Ti I emission are found in the RV Tauri variables R Scuti and U Mon. In R Aqr the Fe XIII coronal line lambda 10747 and a line at lambda 11012 which may be singlet He or La II are found, as well as lambda 10830 and P gamma. The nature of coronas or hot chromospheres in the various stars is discussed. It was concluded that the lambda 10830 intensity must be more or less proportional to the energy deposited in the chromosphere corona by non-thermal processes
Modeling H and He 10830 transmission spectrum of WASP-52b
Get PDFEscaping atmosphere has been detected by the excess absorption of Ly,
H and He triplet (10830) lines. Simultaneously modeling the
absorption of the H and He 10830 lines can provide useful constraints
about the exoplanetary atmosphere. In this paper, we use a hydrodynamic model
combined with a non-local thermodynamic model and a new Monte Carlo simulation
model to obtain the H(2) and He(2S) populations. The Monte Carlo
simulations of Ly radiative transfer are performed with assumptions of
a spherical stellar Ly radiation and a spherical planetary atmosphere,
for the first time, to calculate the Ly mean intensity distribution
inside the planetary atmosphere, necessary in estimating the H(2) population.
We model the transmission spectra of the H and He 10830 lines
simultaneously in hot Jupiter WASP-52b. We find that models with many different
H/He ratios can reproduce the H observations well if the host star has
(1) a high X-ray/extreme ultraviolet (XUV) flux () and a
relatively low X-ray fraction in XUV radiation (), or (2) a low
and a high . The simulations of He 10830
triplet suggest that a high H/He ratio ( 98/2) is required to fit the
observation. The models that fit both lines well confine to be
about 0.5 times the fiducial value and to have a value around 0.3.
The models also suggest that hydrogen and helium originate from the escaping
atmosphere, and the mass-loss rate is about 2.8 g s.Comment: Accepted for publication in ApJ, 48 page
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Quantile regression estimations for the different quantiles of the female (10517) and male (10830) children’s, dependent variable (HAZ) NFHS-1.
No full textQuantile regression estimations for the different quantiles of the female (10517) and male (10830) children’s, dependent variable (HAZ) NFHS-1.</p
Variation of the Solar He I 10830 A Line: 1977 - 1980
Get PDFDaily measurements of the equivalent width of the 10830 A He I line integrated over the visible disk show: (1) an increase from about 32 to about 74 mA in the monthly mean values from the minimum to the maximum of the current solar cycle; (2) the monthly mean values are more smoothly varying than most other indices of solar activity; (3) rotation modulates the daily values in a highly variable manner with amplitudes as large as plus or minus 20%; (4) the apparent synodic rotation period is 29 days rather than the expected 27 days associated with active regions; (5) despite great differences in the appearance of the sun in 3933 A Ca I and 10830 A He I, the central intensity of the former correlates with the equivalent width of the latter with a value r = 0.97
ULTRA-NARROW NEGATIVE FLARE FRONT OBSERVED in HELIUM-10830 USING the 1.6 m NEW SOLAR TELESCOPE
No full textSolar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles that have adverse effects on the near-Earth environment. By definition, flares are usually referred to as bright features resulting from excess emission. Using the newly commissioned 1.6 m New Solar Telescope at Big Bear Solar Observatory, we show a striking negative flare with a narrow but unambiguous dark moving front observed in He i 10830 , which is as narrow as 340 km and is associated with distinct spectral characteristics in Hα and Mg ii lines. Theoretically, such negative contrast in He i 10830 can be produced under special circumstances by nonthermal electron collisions or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in astronomical objects
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