Colorado Ultraviolet Transit Experiment data simulator

Sreejith, A. G.; Fossati, L.; Fleming, Brian; Koskinen, Tommi; Egan, Arika; Rüdisser, Hannah T.; Steller, M.

doi:10.1117/1.jatis.5.1.018004

Cited by 8 publications

(12 citation statements)

References 48 publications

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“…3). To this end, we first converted the log R HK values into disk-integrated chromospheric emission flux in erg cm −2 s −1 following Fossati et al (2017b) and Sreejith et al (2019). In short, the disk-integrated Ca II H&K chromospheric line emission at a distance of 1 AU (F HK (1 AU)) is (see Sect.…”

Section: Discussionmentioning

confidence: 99%

Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

Sreejith

Fossati

Youngblood

et al. 2020

A&A

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Atmospheric escape is an important factor shaping the exoplanet population and hence drives our understanding of planet formation. Atmospheric escape from giant planets is driven primarily by the stellar X-ray and extreme ultraviolet (EUV) radiation. Furthermore, EUV and longer wavelength UV radiation power disequilibrium chemistry in the middle and upper atmospheres. Our understanding of atmospheric escape and chemistry, therefore, depends on our knowledge of the stellar UV fluxes. While the far-ultraviolet (FUV) fluxes can be observed for some stars, most of the EUV range is unobservable due to the lack of a space telescope with EUV capabilities and, for the more distant stars, due to interstellar medium absorption. Therefore, it becomes essential to have an indirect means for inferring EUV fluxes from features observable at other wavelengths. We present here analytic functions for predicting the EUV emission of F-, G-, K-, and M-type stars from the log R′HK activity parameter that is commonly obtained from ground-based optical observations of the Ca II H&K lines. The scaling relations are based on a collection of about 100 nearby stars with published log R′HK and EUV flux values, the latter of which are either direct measurements or inferences from high-quality FUV spectra. The scaling relations presented here return EUV flux values with an accuracy of about a factor of three, which is slightly lower than that of other similar methods based on FUV or X-ray measurements.

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Section: Discussionmentioning

confidence: 99%

Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

Sreejith

Fossati

Youngblood

et al. 2020

A&A

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show abstract

“…Considering this exposure time, two transit observations, and the E140M and E230M gratings, we obtained average S/N values per pixel of about 85 and 310, respectively. For CUTE, instead, the S/N calculator, based on the CUTE data simulator (Sreejith et al 2019), indicates that the average S/N value per pixel obtained for KELT-9b following a 5 minutes exposure (the baseline for CUTE observations; Fleming et al 2018) is about 40. Assuming an observing efficiency of 65% (i.e.…”

Section: Comparison With Observationsmentioning

confidence: 99%

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Fossati

Young²,

Shulyak³

et al. 2021

A&A

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Context. Several observational and theoretical results indicate that the atmospheric temperature of the ultra-hot Jupiter KELT-9b in the main line formation region is a few thousand degrees higher than predicted by self-consistent models. Aims. Our aim was to test whether non-local thermodynamic equilibrium (NLTE) effects are responsible for the presumably higher temperature. Methods. We employed the Cloudy NLTE radiative transfer code to self-consistently compute the upper atmospheric temperature-pressure (TP) profile of KELT-9b, assuming solar metallicity and accounting for Roche potential. In the lower atmosphere, we used an updated version of the HELIOS radiative-convective equilibrium code to constrain the Cloudy model. Results. The Cloudy NLTE TP profile is ≈2000 K hotter than that obtained with previous models assuming LTE. In particular, in the 1–10−7 bar range the temperature increases from ≈4000 to ≈8500 K, remaining roughly constant at lower pressures. We find that the high temperature in the upper atmosphere of KELT-9b is driven principally by NLTE effects modifying the Fe and Mg level populations, which strongly influence the atmospheric thermal balance. We employed Cloudy to compute LTE and NLTE synthetic transmission spectra on the basis of the TP profiles computed in LTE and NLTE, respectively, finding that the NLTE model generally produces stronger absorption lines, particularly in the ultraviolet, than the LTE model (up to 30%). We compared the NLTE synthetic transmission spectrum with the observed Hα and Hβ line profiles obtaining an excellent match, thus supporting our results. Conclusions. The NLTE synthetic transmission spectrum can be used to guide future observations aiming at detecting features in the KELT-9b transmission spectrum. Metals, such as Mg and Fe, and NLTE effects shape the upper atmospheric temperature structure of KELT-9b, and thus affect the mass-loss rates derived from it. Finally, our results call for checking whether this is the case also for cooler planets.

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“…Therefore we compared the log R ′ HK vs EUV fluxes obtained following that approach as well as this work's method presented in Section 3. To this end, we first converted the log R ′ HK values into diskintegrated chromospheric emission flux in erg cm −2 s −1 following Fossati et al (2017b) and Sreejith et al (2019). In short, the disk-integrated Ca ii H&K chromospheric line emission at a distance of 1 AU ( F HK (1 AU)) is (see Sect.…”

Section: Discussionmentioning

confidence: 99%

Ca II H&K stellar activity parameter: a proxy for stellar Extreme Ultraviolet Fluxes

Sreejith,

Fossati,

Youngblood

et al. 2020

Preprint

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Atmospheric escape is an important factor shaping the exoplanet population and hence drives our understanding of planet formation. Atmospheric escape from giant planets is driven primarily by the stellar X-ray and extreme-ultraviolet (EUV) radiation. Furthermore, EUV and longer wavelength UV radiation power disequilibrium chemistry in the middle and upper atmosphere. Our understanding of atmospheric escape and chemistry, therefore, depends on our knowledge of the stellar UV fluxes. While the far-ultraviolet fluxes can be observed for some stars, most of the EUV range is unobservable due to the lack of a space telescope with EUV capabilities and, for the more distant stars, to interstellar medium absorption. Thus, it becomes essential to have indirect means for inferring EUV fluxes from features observable at other wavelengths. We present here analytic functions for predicting the EUV emission of F-, G-, K-, and M-type stars from the log R ′ HK activity parameter that is commonly obtained from ground-based optical observations of the Ca ii H&K lines. The scaling relations are based on a collection of about 100 nearby stars with published log R ′ HK and EUV flux values, where the latter are either direct measurements or inferences from high-quality far-ultraviolet (FUV) spectra. The scaling relations presented here return EUV flux values with an accuracy of about three, which is slightly lower than that of other similar methods based on FUV or X-ray measurements.

show abstract

Colorado Ultraviolet Transit Experiment data simulator

Cited by 8 publications

References 48 publications

Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Ca II H&K stellar activity parameter: a proxy for stellar Extreme Ultraviolet Fluxes

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Colorado Ultraviolet Transit Experiment data simulator

Cited by 8 publications

References 48 publications

Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Ca II H&K stellar activity parameter: a proxy for stellar Extreme Ultraviolet Fluxes

Contact Info

Product

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Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes