29 research outputs found
Assessing telluric correction methods for Na detections with high-resolution exoplanet transmission spectroscopy.
Using high-resolution ground-based transmission spectroscopy to probe
exoplanetary atmospheres is difficult due to the inherent telluric
contamination from absorption in Earth's atmosphere. A variety of methods have
previously been used to remove telluric features in the optical regime and
calculate the planetary transmission spectrum. In this paper we present and
compare two such methods, specifically focusing on Na detections using
high-resolution optical transmission spectra: (a) calculating the telluric
absorption empirically based on the airmass, and (b) using a model of the
Earth's transmission spectrum. We test these methods on the transmission
spectrum of the hot Jupiter HD 189733 b using archival data obtained with the
HARPS spectrograph during three transits. Using models for Centre-to-Limb
Variation and the Rossiter-McLaughlin effect, spurious signals which are
imprinted within the transmission spectrum are reduced. We find that correcting
tellurics with an atmospheric model of the Earth is more robust and produces
consistent results when applied to data from different nights with changing
atmospheric conditions. We confirm the detection of sodium in the atmosphere of
HD 189733 b, with doublet line contrasts of -0.64 0.07 % (D2) and -0.53
0.07 % (D1). The average line contrast corresponds to an effective
photosphere in the Na line located around 1.13 . We also confirm an
overall blueshift of the line centroids corresponding to net atmospheric
eastward winds with a speed of 1.8 1.2 km/s. Our study highlights the
importance of accurate telluric removal for consistent and reliable
characterisation of exoplanetary atmospheres using high-resolution transmission
spectroscopy
A survey of sodium absorption in ten giant exoplanets with high-resolution transmission spectroscopy
The alkali metal sodium (Na) is one of the most commonly detected chemical
species in the upper atmospheres of giant exoplanets. In this work we conducted
a homogeneous survey of Na in a diverse sample of ten highly irradiated giant
exoplanets using high-resolution transmission spectroscopy. Our sample includes
nine planets with previous Na detections and one new detection. We confirm
previous detections and assess multiple approaches for deriving Na line
properties from high-resolution transmission spectra. The homogeneously
measured sodium line depths were used to constrain the atmospheric heights
() with respect to the planetary radii (). We
assess an empirical trend describing the relative atmospheric height
() as a function of planetary equilibrium
temperature () and surface gravity (), in which
decreases exponentially with , approaching a constant at large . We also report the
sodium D2/D1 line ratios across our sample and find that seven targets have
line ratios that are consistent with unity. Finally, we measured net
blueshifted offsets of the sodium absorption lines from their rest frame
wavelengths for all ten planets, corresponding to day-night wind velocities of
a few km s. This suggests that the broad sample of exoplanets share
common underlying processes that govern atmospheric dynamics. Our study
highlights a promising avenue for using high-resolution transmission
spectroscopy to further our understanding of how atmospheric characteristics
vary over a diverse sample of exoplanets.Comment: Accepted in MNRAS. 22 pages, 10 figure
Measurement of CP-Violating Asymmetries in B0 Decays to CP Eigenstates
We present measurements of time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurement uses a data sample of 23×10^6 ϒ(4S)→BB̅ decays collected by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we find events in which one neutral B meson is fully reconstructed in a CP eigenstate containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the standard model is proportional to sin2β, is derived from the decay time distributions in such events. The result is sin2β = 0.34±0.20(stat)±0.05(syst)
Observation of CP violation in the B0 meson system
We present an updated measurement of time-dependent CP-violating asymmetries
in neutral B decays with the BABAR detector at the PEP-II asymmetric B Factory
at SLAC. This result uses an additional sample of Upsilon(4S) decays collected
in 2001, bringing the data available to 32 million B-anti-B pairs. We select
events in which one neutral B meson is fully reconstructed in a final state
containing charmonium and the flavor of the other neutral B meson is determined
from its decay products. The amplitude of the CP-violating asymmetry, which in
the Standard Model is proportional to sin2beta, is derived from the decay time
distributions in such events. The result sin2beta = 0.59 +/- 0.14 (stat) +/-
0.05 (syst) establishes CP violation in the B^0 meson system. We also determine
|lambda| = 0.93 +/- 0.09 {stat} +/- 0.03 {syst}, consistent with no direct CP
violation.Comment: 8 pages, 2 figures, submitted to Physical Review Letter