72 research outputs found
Using near infra-red spectroscopy for characterization of transiting exoplanets
We propose a method for observing transiting exoplanets with near-infrared
high-resolution spectrometers. We aim to create a robust data analysis method
for recovering atmospheric transmission spectra from transiting exoplanets over
a wide wavelength range in the near infrared. By using an inverse method
approach, combined with stellar models and telluric transmission spectra, the
method recovers the transiting exoplanet's atmospheric transmittance at high
precision over a wide wavelength range. We describe our method and have tested
it by simulating observations. This method is capable of recovering
transmission spectra of high enough accuracy to identify absorption features
from molecules such as O2, CH4, CO2, and H2O. This accuracy is achievable for
Jupiter-size exoplanetsat S/N that can be reached for 8m class telescopes using
high-resolution spectrometers (R>20 000) during a single transit, and for
Earth-size planets and super-Earths transiting late K or M dwarf stars at S/N
reachable during observations of less than 10 transits. We also analyse
potential error sources to show the robustness of the method. Detection and
characterization of atmospheres of both Jupiter-size planets and smaller rocky
planets looks promising using this set-up.Comment: 14 pages, 14 figures, accepted to A&
PySME -- Spectroscopy Made Easier
The characterization of exoplanet requires reliable determination of the
fundamental parameters of their host stars. Spectral fitting plays an important
role in this process. For the majority of stellar parameters matching synthetic
spectra to the observations provides a robust and unique solution for
fundamental parameters, such as effective temperature, surface gravity,
abundances, radial and rotational velocities and others. Here we present a new
software package for fitting high resolution stellar spectra that is easy to
use, available for common platforms and free from commercial licenses. We call
it PySME. It is based on the proven Spectroscopy Made Easy (later referred to
as IDL SME or "original SME") package. The IDL part of the original SME code
has been rewritten in Python, but we kept the efficient C++ and FORTRAN code
responsible for molecular-ionization equilibrium, opacities and spectral
synthesis. In the process we have updated some components of the optimization
procedure offering more flexibility and better analysis of the convergence. The
result is a more modern package with the same functionality of the original
SME. We apply PySME to a few stars of different spectral types and compared the
derived fundamental parameters with the results from IDL SME and other
techniques. We show that PySME works at least as well as the original SME.Comment: 23 pages, 13 figures, code is available on
https://github.com/AWehrhahn/SM
Pinning Down Gravitational Settling
We analyse high-resolution archival UVES data of turnoff and subgiant stars
in the nearby globular cluster NGC 6397 ([Fe/H] = -2). Balmer-profile analyses
are performed to derive reddening-free effective temperatures. Due to the
limited S/N and uncertainties related to blaze removal, we find the data
quality insufficient to exclude the existence of gravitational settling. If the
newly derived effective temperatures are taken as a basis for an abundance
analysis, the photospheric iron (Fe II) abundance in the turnoff stars is 0.11
dex lower than in the (well-mixed) subgiants.Comment: 4 pages, 3 figures. Summary of a talk given at the ESO-Arcetri
workshop in September of 2004. See also astro-ph/060820
The HARPS polarimeter
We recently commissioned the polarimetric upgrade of the HARPS spectrograph
at ESO's 3.6-m telescope at La Silla, Chile. The HARPS polarimeter is capable
of full Stokes spectropolarimetry with large sensitivity and accuracy, taking
advantage of the large spectral resolution and stability of HARPS. In this
paper we present the instrument design and its polarimetric performance. The
first HARPSpol observations show that it can attain a polarimetric sensitivity
of ~10^-5 (after addition of many lines) and that no significant instrumental
polarization effects are present.Comment: To be published in ASP Conf Series, Solar Polarization Workshop
Weather in stellar atmosphere: the dynamics of mercury clouds in alpha Andromedae
The formation of long-lasting structures at the surfaces of stars is commonly
ascribed to the action of strong magnetic fields. This paradigm is supported by
observations of evolving cool spots in the Sun and active late-type stars, and
stationary chemical spots in the early-type magnetic stars. However, results of
our seven-year monitoring of mercury spots in non-magnetic early-type star
alpha Andromedae show that the picture of magnetically-driven structure
formation is fundamentally incomplete. Using an indirect stellar surface
mapping technique, we construct a series of 2-D images of starspots and
discover a secular evolution of the mercury cloud cover in this star. This
remarkable structure formation process, observed for the first time in any
star, is plausibly attributed to a non-equilibrium, dynamical evolution of the
heavy-element clouds created by atomic diffusion and may have the same
underlying physics as the weather patterns on terrestrial and giant planets.Comment: 10 pages, 2 figures; to be published in Nature Physic
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