Spatially resolved spectroscopy across stellar surfaces

Dravins, Dainis; Ludwig, H.‐G.; Dahlén, Erik; Pazira, Hiva

doi:10.1051/0004-6361/201730901

Cited by 26 publications

(26 citation statements)

References 52 publications

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“…Note that unlike the RM curve in Figure 2 (which had CB variation, but no stellar rotation), these residuals are not symmetric about mid-transit (in agreement with that found in Dravins et al 2015); this is particularly evident in the ingress/ egress regions. From a purely mathematical point-of-view, these residuals should be symmetric as they are the result of an odd function (stellar rotation RVs) being subtracted from a function that is the sum of an odd and even function (stellar rotation RVs + radial CB variations).…”

Section: The Impact Of V Sin I and Intrinsic Profile Fwhmsupporting

confidence: 74%

Modeling the Rossiter–mclaughlin Effect: Impact of the Convective Center-to-Limb Variations in the Stellar Photosphere

Cegla¹,

Oshagh²,

Watson³

et al. 2016

ApJ

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Observations of the Rossiter-McLaughlin (RM) effect provide information on star-planet alignments, which can inform planetary migration and evolution theories. Here, we go beyond the classical RM modeling and explore the impact of a convective blueshift that varies across the stellar disk and non-Gaussian stellar photospheric profiles. We simulated an aligned hot Jupiter with a four-day orbit about a Sun-like star and injected center-to-limb velocity (and profile shape) variations based on radiative 3D magnetohydrodynamic simulations of solar surface convection. The residuals between our modeling and classical RM modeling were dependent on the intrinsic profile width and v sin i; the amplitude of the residuals increased with increasing v sin i and with decreasing intrinsic profile width. For slowly rotating stars the center-to-limb convective variation dominated the residuals (with amplitudes of 10 s of cm s −1 to ∼1 m s −1 ); however, for faster rotating stars the dominant residual signature was due a non-Gaussian intrinsic profile (with amplitudes from 0.5 to 9 m s −1 ). When the impact factor was 0, neglecting to account for the convective center-to-limb variation led to an uncertainty in the obliquity of ∼10°-20°, even though the true v sin i was known. Additionally, neglecting to properly model an asymmetric intrinsic profile had a greater impact for more rapidly rotating stars (e.g., v sin i = 6 km s −1 ) and caused systematic errors on the order of ∼20°in the measured obliquities. Hence, neglecting the impact of stellar surface convection may bias starplanet alignment measurements and consequently theories on planetary migration and evolution.

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Section: The Impact Of V Sin I and Intrinsic Profile Fwhmsupporting

confidence: 74%

Modeling the Rossiter–mclaughlin Effect: Impact of the Convective Center-to-Limb Variations in the Stellar Photosphere

Cegla¹,

Oshagh²,

Watson³

et al. 2016

ApJ

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“…On the other hand, the RossiterMcLaughlin effect can mimic an exoplanetary atmospheric absorption and imprint features at similar level in a transmission spectrum. This should average out during a whole transit, however, if the exposures are equally distributed over the transit (Dravins et al 2014). This is the case for our three analyzed transit events.…”

Section: Summary Of the Na I D Detectionmentioning

confidence: 97%

Spectrally resolved detection of sodium in the atmosphere of HD 189733b with the HARPS spectrograph

Wyttenbach

Ehrenreich

Lovis

et al. 2015

A&A

305

487

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Context. Atmospheric properties of exoplanets can be constrained with transit spectroscopy. At low spectral resolution, this technique is limited by the presence of clouds. The signature of atomic sodium (Na ), known to be present above the clouds, is a powerful probe of the upper atmosphere, where it can be best detected and characterized at high spectral resolution. Aims. Our goal is to obtain a high-resolution transit spectrum of HD 189733b in the region around the resonance doublet of Na  at 589 nm, to characterize the absorption signature that was previously detected from space at low resolution.Methods. We analyzed archival transit data of HD 189733b obtained with the HARPS spectrograph (R = 115 000) at the ESO 3.6-m telescope. We performed differential spectroscopy to retrieve the transit spectrum and light curve of the planet, implementing corrections for telluric contamination and planetary orbital motion. We compared our results to synthetic transit spectra calculated from isothermal models of the planetary atmosphere.Results. We spectrally resolve the Na  D doublet and measure line contrasts of 0.64 ± 0.07% (D2) and 0.40 ± 0.07% (D1) and FWHMs of 0.52 ± 0.08 Å. This corresponds to a detection at the 10σ level of excess of absorption of 0.32 ± 0.03% in a passband of 2 × 0.75 Å centered on each line. We derive temperatures of 2600 ± 600 K and 3270 ± 330 K at altitudes of 9800 ± 2800 and 12 700 ± 2600 km in the Na  D1 and D2 line cores, respectively. We measure a temperature gradient of ∼0.2 K km −1 in the region where the sodium absorption dominates the haze absorption from a comparison with theoretical models. We also detect a blueshift of 0.16 ± 0.04 Å (4σ) in the line positions. This blueshift may be the result of winds blowing at 8 ± 2 km s −1 in the upper layers of the atmosphere. Conclusions. We demonstrate the relevance of studying exoplanet atmospheres with high-resolution spectrographs mounted on 4-m-class telescopes. Our results pave the way for an in-depth characterization of physical conditions in the atmospheres of many exoplanetary systems with future spectrographs such as ESPRESSO on the VLT or HiReS and METIS on the E-ELT.

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“…Normally a one-dimensional LTE stellar model can produce a reasonably realastic CLV feature, however, non-LTE and three-dimensional (3D) models can produce more precise results. Dravins et al (2016) used the transit spectrum of HD 209458b to study the CLV of Fe i lines with a 3D model.…”

Section: Stellar Atmosphere Modelmentioning

confidence: 99%

Effect of the stellar absorption line centre-to-limb variation on exoplanet transmission spectrum observations

Yan

Πάλλη

Fosbury

et al. 2017

A&A

101

109

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Transit spectroscopy is one of the most commonly used techniques for exoplanet atmosphere characterisation. This technique has been used to detect ionized and neutral species in exoplanet atmospheres by comparing the observed stellar lines in and out of transit. The centre-to-limb variation (CLV) of the stellar lines across the stellar disk is an important effect for transmission spectroscopy, since it results in a change of stellar line depth when the planet transits different parts of the stellar disk. We reanalyse the transit data of HD 189733b taken with the HARPS spectrograph to study the CLV effect during transit. The transmission light curve of the Na i D line so obtained shows a clear imprint of the CLV effect. We use a one-dimensional non-LTE stellar spectral model to simulate the CLV effect. After applying the correction, the measurement of the Na i absorption in the atmosphere of HD 189733b becomes better determined. We compare the CLV effect of HD 189733b to that of HD 209458b. The CLV effects are different for these two benchmark planetary systems and this is attributed to their different stellar effective temperatures and transit impact parameters. We then explore the general CLV effect that occurs during exoplanet transits. Normally, a star with a lower effective temperature exhibits a stronger CLV effect and its CLV feature extends over a relatively broad wavelength range. The transit impact parameter (b) describes the transit trajectory on the stellar disk and thus determines the actual manifestation of the CLV effect. We introduce a b-diagram which describes the behavior of the CLV effect as the function of different impact parameters. With improving observational precision, a careful modeling and correction of the CLV effect is necessary for exoplanet atmosphere characterisation using transit spectroscopy.

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Spatially resolved spectroscopy across stellar surfaces

Cited by 26 publications

References 52 publications

Modeling the Rossiter–mclaughlin Effect: Impact of the Convective Center-to-Limb Variations in the Stellar Photosphere

Modeling the Rossiter–mclaughlin Effect: Impact of the Convective Center-to-Limb Variations in the Stellar Photosphere

Spectrally resolved detection of sodium in the atmosphere of HD 189733b with the HARPS spectrograph

Effect of the stellar absorption line centre-to-limb variation on exoplanet transmission spectrum observations

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