The center-to-limb variation across the Fraunhofer lines of HD 189733

Czesla, S.; Klocová, T.; Khalafinejad, S.; Wolter, Uwe; Schmitt, J. H. M. M.

doi:10.1051/0004-6361/201526386

Cited by 97 publications

(126 citation statements)

References 70 publications

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“…But A sp is more important for determining The strongest absorption signal, or in this case contrast signal, is when the planet is near the edge of the stellar disk but still almost completely covers the limb. This is very similar behavior to the Na I D calculations presented by Czesla et al (2015).…”

Section: A Note On Parameter Importancesupporting

confidence: 89%

“…They demonstrated that the Na I lines show limb-brightening in the wings of the line compared with the line core or neighboring continuum. This is important since a transiting planet with no atmosphere can produce a transmission signal, even if there are no active regions present on the stellar surface, due to the fact that the ratio of the line core to the continuum changes as a function of the transit (see Figures 1-5 of Czesla et al 2015). This effect was recently included in Na I transit modeling by Khalafinejad et al (2016).…”

Section: Contrast and Limb-darkening/brighteningmentioning

confidence: 99%

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A Decade of Hα Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere

Cauley

Redfield

Jensen

2017

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HD 189733 b is one of the most well-studied exoplanets due to its large transit depth and host star brightness. The focus on this object has produced a number of high-cadence transit observations using high-resolution optical spectrographs. Here we present an analysis of seven full Hα transits of HD 189733 b using HARPS on the 3.6 meter La Silla telescope and HIRES on Keck I, taken over the course of nine years from 2006 to 2015. Hα transmission signals are analyzed as a function of the stellar activity level, as measured using the normalized core flux of the Ca II H and K lines. We find strong variations in the strength of the Hα transmission spectrum from epoch to epoch. However, there is no clear trend between the Ca II core emission and the strength of the in-transit Hα signal, although the transit showing the largest absorption value also occurs when the star is the most active. We present simulations of the in-transit contrast effect and find that the planet must consistently transit active latitudes with very strong facular and plage emission regions in order to reproduce the observed line strengths. We also investigate the measured velocity centroids with models of planetary rotation and show that the small line profile velocities could be due to large velocities in the upper atmosphere of the planet. Overall, we find it more likely that the measured Hα signals arise in the extended planetary atmosphere, although a better understanding of active region emission for active stars such as HD 189733 are needed.

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Section: A Note On Parameter Importancesupporting

confidence: 89%

Section: Contrast and Limb-darkening/brighteningmentioning

confidence: 99%

A Decade of Hα Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere

Cauley

Redfield

Jensen

2017

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“…1 and Czesla et al 2015). Czesla et al (2015) compare the integrated flux from the individual chips with model spectra (Castelli & Kurucz 2004;Kurucz 1970) and a blackbody spectrum and find that they generally agree well (see their Table 4); they further attribute the remaining variations in the observed flux of about 20% (also shown in Fig. 1) to slit losses and the residual influence of airmass and atmospheric conditions.…”

Section: Observations and Data Reductionmentioning

confidence: 73%

“…This dip can probably be attributed to the center-to-limb variation, which is described in more detail in Czesla et al (2015).…”

Section: Temporal Evolution Of the Chromospheric Activity Indexmentioning

confidence: 89%

“…0.806 ± 0.048 T R s [R ] 0.756 ± 0.018 T Age [Gyr] 0.6 M Distance [pc] 19.5 ± 0.3 H P orb [days] 2.21857567 ± 1. data reduction can be found in Czesla et al (2015). The spectroscopic echelle observations of HD 189733 were obtained during the night of July 1/2, 2012, with the UVES spectrograph mounted at the VLT-UT2 telescope in Chile.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

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Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit

Klocová

Czesla

Khalafinejad

et al. 2017

A&A

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Context. HD 189733 is an exoplanetary system consisting of a transiting hot Jupiter and an active K2V-type main sequence star. Rich manifestations of a stellar activity, like photometric spots or chromospheric flares were repeatedly observed in this system in optical, UV and X-rays. Aims. We aim to use VLT/UVES high resolution (R = 60 000) echelle spectra to study a stellar flare. Methods. We have performed simultaneous analyses of the temporal evolution in several chromospheric stellar lines, namely, the, H (3970 Å), the Ca ii infrared triplet line (8498, 8542 and 8662 Å), and He i D3 (5875.6 Å). Observations were carried out with a time resolution of approximately 1 min for a duration of four hours, including a complete planetary transit. Results. We determine the energy released during the flare in all studied chromospheric lines combined to be about 8.7 × 10 31 erg, which puts this event at the upper end of flare energies observed on the Sun. Our analysis does not reveal any significant delay of the flare peak observed in the Balmer and Ca ii H & K lines, although we find a clear difference in the temporal evolution of these lines. The He i D3 shows additional absorption possibly related to the flare event. Based on the flux released in Ca ii H & K lines during the flare, we estimate the soft X-ray flux emission to be 7 × 10 30 erg. Conclusions. The observed flare can be ranked as a moderate flare on a K-type star and confirms a rather high activity level of HD 189733 host star. The cores of the studied chromospheric lines demonstrate the same behavior and let us study the flare evolution. We demonstrate that the activity of an exoplanet host star can play an important role in the detection of exoplanet atmospheres, since these are frequently discovered as an additional absorption in the line cores. A possible star-planet interaction responsible for a flare occurrence during a transit can neither be confirmed nor ruled out.

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Detection of radial velocity variability of HD 16673 with TIGRE

Mittag¹,

Hempelmann²,

Fuhrmeister³

et al. 2017

Astron Nachr

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During our TIGRE activity monitoring of late-type stars, large radial velocity (RV) variations in the F-type star HD 16673 were noticed. An automatic pipeline procedure using data in the wavelength range from 6000 to 7900 Å was developed and telluric lines are used as reference to determine accurate radial velocities. The RV curve demonstrates the binary nature of the HD 16673 system and allows the determination of the orbital parameters of the system. Based on the derived mass function, we obtain inclination-dependent mass estimates for the secondary component, which orbits with a period of 37.09 days in a slightly eccentric orbit and is probably a late-type star.

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The center-to-limb variation across the Fraunhofer lines of HD 189733

Cited by 97 publications

References 70 publications

A Decade of Hα Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere

A Decade of Hα Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere

Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit

Detection of radial velocity variability of HD 16673 with TIGRE

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