scholarly journals Correcting the effect of stellar spots on ARIEL transmission spectra II. The limb darkening effect

2021 ◽  
Author(s):  
G Cracchiolo ◽  
G Micela ◽  
G Morello ◽  
G Peres
Keyword(s):  
Impact Parameter ◽  
Transmission Spectrum ◽  
Stellar Disk ◽  
Transmission Spectra ◽  
Potential Bias ◽  
Temperature Contrast ◽  
Planetary Transmission ◽  
Limb Darkening ◽  
The Impact

Abstract This paper is part of an effort to correct the transmission spectra of a transiting planet orbiting an active star. In Paper I (Cracchiolo et al. 2020) we have demonstrated a methodology to minimize the potential bias induced by unocculted star spots on the transmission spectrum, assuming a spot model parameterized by filling factor and temperature. In this work we introduce the limb darkening effect, therefore the position of the spot in the stellar disk and the impact parameter of the transiting planet now play a key role. The method is tested on simulations of planetary transits of three representative kinds of planetary systems, at ARIEL resolution. We find that a realistic treatment of the limb darkening is required to reliably estimate both the spots parameters and the transmission spectrum of the transiting planet. Furthermore, we show that the influence of the spots on the retrieval of the planetary transmission spectrum is significant for spots close to the center of the star, covering a fraction greater than 0.05 and with a temperature contrast greater than 500 K, and that for these cases our method can confidently extract the transmission spectrum and the impact parameter of the transiting planet for both cases of occulted and not occulted spots, provided that we have an accurate characterization of the stellar parameters and a reliable simulator of the instrument performances.

scholarly journals Role of the impact parameter in exoplanet transmission spectroscopy

2020 ◽  
Vol 640 ◽  
pp. A134
Author(s):  
X. Alexoudi ◽  
M. Mallonn ◽  
E. Keles ◽  
K. Poppenhäger ◽  
C. von Essen ◽  
...  
Keyword(s):  
Impact Parameter ◽  
Transmission Spectrum ◽  
Near Infrared ◽  
Transmission Spectra ◽  
Orbital Parameters ◽  
Transmission Spectroscopy ◽  
Limb Darkening ◽  
The Impact ◽  
Error Envelope

Context. Transmission spectroscopy is a promising tool for the atmospheric characterization of transiting exoplanets. Because the planetary signal is faint, discrepancies have been reported regarding individual targets. Aims. We investigate the dependence of the estimated transmission spectrum on deviations of the orbital parameters of the star-planet system that are due to the limb-darkening effects of the host star. We describe how the uncertainty on the orbital parameters translates into an uncertainty on the planetary spectral slope. Methods. We created synthetic transit light curves in seven different wavelength bands, from the near-ultraviolet to the near-infrared, and fit them with transit models parameterized by fixed deviating values of the impact parameter b. First, we performed a qualitative study to illustrate the effect by presenting the changes in the transmission spectrum slope with different deviations of b. Then, we quantified these variations by creating an error envelope (for centrally transiting, off-center, and grazing systems) based on a derived typical uncertainty on b from the literature. Finally, we compared the variations in the transmission spectra for different spectral types of host stars. Results. Our simulations show a wavelength-dependent offset that is more pronounced at the blue wavelengths where the limb-darkening effect is stronger. This offset introduces a slope in the planetary transmission spectrum that becomes steeper with increasing b values. Variations of b by positive or negative values within its uncertainty interval introduce positive or negative slopes, thus the formation of an error envelope. The amplitude from blue optical to near-infrared wavelength for a typical uncertainty on b corresponds to one atmospheric pressure scale height and more. This impact parameter degeneracy is confirmed for different host types; K stars present prominently steeper slopes, while M stars indicate features at the blue wavelengths. Conclusions. We demonstrate that transmission spectra can be hard to interpret, basically because of the limitations in defining a precise impact parameter value for a transiting exoplanet. This consequently limits a characterization of its atmosphere.

Measurement of Dysprosium Stark Width and the Electron Impact Width Parameter

2018 ◽  
Vol 73 (2) ◽  
pp. 203-213 ◽  
Author(s):  
Jhonatha R. dos Santos ◽  
Jonas Jakutis Neto ◽  
N. Rodrigues ◽  
M.G. Destro ◽  
José W. Neri ◽  
...  
Keyword(s):  
Electron Density ◽  
Impact Parameter ◽  
Plasma Temperature ◽  
Spectral Lines ◽  
Emission Lines ◽  
Spectroscopic Methods ◽  
Species Concentration ◽  
The Impact ◽  
Stark Width

In this work, we suggest a methodology to determine the impact parameter for neutral dysprosium emission lines from the characterization of the plasma generated by laser ablation in a sealed chamber filled with argon. The procedure is a combination of known consistent spectroscopic methods for plasma temperature determination, electron density, and species concentration. With an electron density of 3.1 × 1018 cm–3 and temperature close to 104 K, we estimated the impact electron parameter for nine spectral lines of the neutral dysprosium atom. The gaps in the impact parameter data in the literature, mainly for heavy elements, stress the importance of the proposed method.

scholarly journals PyTranSpot: A tool for multiband light curve modeling of planetary transits and stellar spots

2018 ◽  
Vol 610 ◽  
pp. A15 ◽  
Author(s):  
Ines G. Juvan ◽  
M. Lendl ◽  
P. E. Cubillos ◽  
L. Fossati ◽  
J. Tregloan-Reed ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Markov Chain ◽  
Light Curves ◽  
Transmission Spectra ◽  
Two Dimensional ◽  
Curve Modeling ◽  
Cartesian Coordinate ◽  
Limb Darkening ◽  
The Impact ◽  
Monte Carlo Framework

Several studies have shown that stellar activity features, such as occulted and non-occulted starspots, can affect the measurement of transit parameters biasing studies of transit timing variations and transmission spectra. We present PyTranSpot, which we designed to model multiband transit light curves showing starspot anomalies, inferring both transit and spot parameters. The code follows a pixellation approach to model the star with its corresponding limb darkening, spots, and transiting planet on a two dimensional Cartesian coordinate grid. We combine PyTranSpot with a Markov chain Monte Carlo framework to study and derive exoplanet transmission spectra, which provides statistically robust values for the physical properties and uncertainties of a transiting star-planet system. We validate PyTranSpot’s performance by analyzing eleven synthetic light curves of four different star-planet systems and 20 transit light curves of the well-studied WASP-41b system. We also investigate the impact of starspots on transit parameters and derive wavelength dependent transit depth values for WASP-41b covering a range of 6200−9200 Å, indicating a flat transmission spectrum.

scholarly journals ARES V: No Evidence For Molecular Absorption in the HST WFC3 Spectrum of GJ 1132 b

2021 ◽  
Author(s):  
Lorenzo V. Mugnai ◽  
Darius Modirrousta-Galia ◽  
Billy Edwards ◽  
Keyword(s):  
Transmission Spectrum ◽  
Hubble Space Telescope ◽  
Wide Field ◽  
Transmission Spectra ◽  
Molecular Signatures ◽  
Molecular Absorption ◽  
Space Telescope ◽  
James Webb Space Telescope ◽  
Planetary Transmission ◽  
Best Fit

<p>We present a study on the spatially scanned spectroscopic observations of the transit of GJ 1132 b, a warm (~500 K) Super-Earth (1.13 Re) that was obtained with the G141 grism (1.125 - 1.650 micron) of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope. We used the publicly available Iraclis pipeline to extract the planetary transmission spectra from the five visits and produce a precise transmission spectrum. We analysed the spectrum using the TauREx3 atmospheric retrieval code with which we show that the measurements do not contain molecular signatures in the investigated wavelength range and are best-fit with a flat-line model. Our results suggest that the planet does not have a clear primordial, hydrogen-dominated atmosphere. Instead, GJ 1132 b could have a cloudy hydrogen-dominated envelope, a very enriched secondary atmosphere, be airless, or have a tenuous atmosphere that has not been detected. Due to the narrow wavelength coverage of WFC3, these scenarios cannot be distinguished yet but the James Webb Space Telescope may be capable of detecting atmospheric features, although several observations may be required to provide useful constraints</p>

scholarly journals Gemini/GMOS Transmission Spectroscopy of the Grazing Planet Candidate WD 1856+534 b

2021 ◽  
Vol 162 (6) ◽  
pp. 296
Author(s):  
Siyi Xu ◽  
Hannah Diamond-Lowe ◽  
Ryan J. MacDonald ◽  
Andrew Vanderburg ◽  
Simon Blouin ◽  
...  
Keyword(s):  
Transmission Spectrum ◽  
Main Sequence ◽  
Giant Planet ◽  
Stellar Disk ◽  
Atmospheric Models ◽  
Content Type ◽  
Substellar Objects ◽  
Type Object ◽  
Limb Darkening ◽  
Absorption Features

Abstract WD 1856+534 b is a Jupiter-sized, cool giant planet candidate transiting the white dwarf WD 1856+534. Here, we report an optical transmission spectrum of WD 1856+534 b obtained from ten transits using the Gemini Multi-Object Spectrograph. This system is challenging to observe due to the faintness of the host star and the short transit duration. Nevertheless, our phase-folded white light curve reached a precision of 0.12%. WD 1856+534 b provides a unique transit configuration compared to other known exoplanets: the planet is 8× larger than its star and occults over half of the stellar disk during mid-transit. Consequently, many standard modeling assumptions do not hold. We introduce the concept of a “limb darkening corrected, time-averaged transmission spectrum” and propose that this is more suitable than ( R p , λ / R s ) 2 for comparisons to atmospheric models for planets with grazing transits. We also present a modified radiative transfer prescription. Though the transmission spectrum shows no prominent absorption features, it is sufficiently precise to constrain the mass of WD 1856+534 b to be >0.84 M J (to 2σ confidence), assuming a clear atmosphere and a Jovian composition. High-altitude cloud decks can allow lower masses. WD 1856+534 b could have formed either as a result of common envelope evolution or migration under the Kozai–Lidov mechanism. Further studies of WD 1856+534 b, alongside new dedicated searches for substellar objects around white dwarfs, will shed further light on the mysteries of post-main-sequence planetary systems.

scholarly journals Assessing telluric correction methods for Na detections with high-resolution exoplanet transmission spectroscopy

2021 ◽  
Vol 502 (3) ◽  
pp. 4392-4404
Author(s):  
Adam B Langeveld ◽  
Nikku Madhusudhan ◽  
Samuel H C Cabot ◽  
Simon T Hodgkin
Keyword(s):  
High Resolution ◽  
Transmission Spectrum ◽  
Atmospheric Model ◽  
Atmospheric Conditions ◽  
Transmission Spectroscopy ◽  
Doublet Line ◽  
Exoplanetary Atmospheres ◽  
Planetary Transmission ◽  
Spurious Signals

ABSTRACT 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: (1) calculating the telluric absorption empirically based on the airmass and (2) 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 $-0.64 \pm 0.07~{{\ \rm per\ cent}}$ (D2) and $-0.53 \pm 0.07~{{\ \rm per\ cent}}$ (D1). The average line contrast corresponds to an effective photosphere in the Na line located around 1.13 Rp. 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−1. Our study highlights the importance of accurate telluric removal for consistent and reliable characterization of exoplanetary atmospheres using high-resolution transmission spectroscopy.

scholarly journals The stellar variability noise floor for transiting exoplanet photometry with PLATO

2020 ◽  
Vol 493 (4) ◽  
pp. 5489-5498 ◽  
Author(s):  
Brett M Morris ◽  
Monica G Bobra ◽  
Eric Agol ◽  
Yu Jin Lee ◽  
Suzanne L Hawley
Keyword(s):  
Impact Parameter ◽  
Solar Dynamics Observatory ◽  
Depth Measurement ◽  
Stellar Oscillations ◽  
Mission Duration ◽  
Intensity Images ◽  
Solar Dynamics ◽  
In Transit ◽  
Limb Darkening ◽  
The Impact

ABSTRACT One of the main science motivations for the ESA PLAnetary Transit and Oscillations (PLATO) mission is to measure exoplanet transit radii with 3 per cent precision. In addition to flares and starspots, stellar oscillations and granulation will enforce fundamental noise floors for transiting exoplanet radius measurements. We simulate light curves of Earth-sized exoplanets transiting continuum intensity images of the Sun taken by the Helioseismic and Magnetic Imager (HMI) instrument aboard the Solar Dynamics Observatory (SDO) to investigate the uncertainties introduced on the exoplanet radius measurements by stellar granulation and oscillations. After modelling the solar variability with a Gaussian process, we find that the amplitude of solar oscillations and granulation is of order 100 ppm – similar to the depth of an Earth transit – and introduces a fractional uncertainty on the depth of transit of 0.73 per cent assuming four transits are observed over the mission duration. However, when we translate the depth measurement into a radius measurement of the planet, we find a much larger radius uncertainty of 3.6 per cent. This is due to a degeneracy between the transit radius ratio, the limb darkening, and the impact parameter caused by the inability to constrain the transit impact parameter in the presence of stellar variability. We find that surface brightness inhomogeneity due to photospheric granulation contributes a lower limit of only 2 ppm to the photometry in-transit. The radius uncertainty due to granulation and oscillations, combined with the degeneracy with the transit impact parameter, accounts for a significant fraction of the error budget of the PLATO mission, before detector or observational noise is introduced to the light curve. If it is possible to constrain the impact parameter or to obtain follow-up observations at longer wavelengths where limb darkening is less significant, this may enable higher precision radius measurements.

scholarly journals Broadband transmission spectroscopy of HD 209458b with ESPRESSO: evidence for Na, TiO, or both

2020 ◽  
Vol 644 ◽  
pp. A51
Author(s):  
N. C. Santos ◽  
E. Cristo ◽  
O. Demangeon ◽  
M. Oshagh ◽  
R. Allart ◽  
...  
Keyword(s):  
High Resolution ◽  
Transmission Spectrum ◽  
Optical Spectrum ◽  
High Resolution Spectroscopy ◽  
Transmission Spectra ◽  
Full Dataset ◽  
Synthetic Spectra ◽  
Observational Errors ◽  
The One

Context. The detection and characterization of exoplanet atmospheres is currently one of the main drivers pushing the development of new observing facilities. In this context, high-resolution spectrographs are proving their potential and showing that high-resolution spectroscopy will be paramount in this field. Aims. We aim to make use of ESPRESSO high-resolution spectra, which cover two transits of HD 209458b, to probe the broadband transmission optical spectrum of the planet. Methods. We applied the chromatic Rossiter–McLaughin method to derive the transmission spectrum of HD 209458b. We compared the results with previous HST observations and with synthetic spectra. Results. We recover a transmission spectrum of HD 209458b similar to the one obtained with HST data. The models suggest that the observed signal can be explained by only Na, only TiO, or both Na and TiO, even though none is fully capable of explaining our observed transmission spectrum. Extra absorbers may be needed to explain the full dataset, though modeling approximations and observational errors can also be responsible for the observed mismatch. Conclusions. Using the chromatic Rossiter–McLaughlin technique, ESPRESSO is able to provide broadband transmission spectra of exoplanets from the ground, in conjunction with space-based facilities, opening good perspectives for similar studies of other planets.

scholarly journals Correcting the effect of stellar spots on ARIEL transmission spectra

2020 ◽  
Vol 501 (2) ◽  
pp. 1733-1747
Author(s):  
G Cracchiolo ◽  
G Micela ◽  
G Peres
Keyword(s):  
Temporal Evolution ◽  
Transmission Spectra ◽  
Stellar Spectrum ◽  
Stellar Spectra ◽  
Chi Squared ◽  
Minimization Procedure ◽  
Systematic Biases ◽  
Planetary Transmission ◽  
The Impact ◽  
Average Uncertainty

ABSTRACT The goal of this study is to assess the impact of the stellar spots on the extraction of the planetary transmission spectra observed by ARIEL. We develop a method to model the stellar spectrum of a star in the presence of spots by using the out-of-transit observations. It is based on a chi squared minimization procedure of the out-of-transit spectrum on a grid of stellar spectra with different sizes and temperatures of the spots. The approach allows us also to study the temporal evolution of the spots when comparing stellar spectra observed at different epochs. We also present a method to correct the transit depth variations due to non-occulted stellar spots and estimate the error we introduce if we apply the same correction to crossings over the stellar spots. The method is tested on three types of stellar targets that ARIEL will observe in its 4-yr mission lifetime. In all the explored cases, the approach allows us to reliably recover the spot parameters (size and temperature) from out-of-transit observations and, for non-occulted spots, to confidently recover the planetary atmosphere transmission spectrum within the noise level (with average uncertainty of at most $3.3{{\ \rm per\ cent}}$ of the planetary signal). Conversely, we find systematic biases in the inferred planetary spectra due to the occulted spots, with measurable effects for the brightest targets especially for more contrasted spots.

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