X-Ray and Ultraviolet Emission of the Young Planet-hosting Star V1298 Tau from Coordinated Observations with XMM-Newton and Hubble Space Telescope

Abstract

Atmospheric mass loss plays a major role in the evolution of exoplanets. This process is driven by the stellar high-energy irradiation, especially in the first hundreds of millions of years after dissipation of the proto-planetary disk. A major source of uncertainty in modeling atmospheric photoevaporation and photochemistry is due to the lack of direct measurements of the stellar flux at extreme-UV (EUV) wavelengths. Several empirical relationships have been proposed in the past to link EUV fluxes to emission levels in X-rays, but the stellar samples employed for this aim are heterogeneous, and the available scaling laws provide significantly different predictions, especially for very active stars. We present new far-UV and X-ray observations of V1298 Tau with Hubble Space Telescope/Cosmic Origins Spectrograph and XMM-Newton, aimed to determine more accurately the high-energy emission of this solar-mass pre-main-sequence star, which hosts four exoplanets. Spectroscopic data were employed to derive the plasma emission measure distribution versus temperature, from the chromosphere to the corona, and the possible variability of this irradiation on short and year-long timescales, due to magnetic activity. As a side result, we have also measured the chemical abundances of several elements in the outer atmosphere of V1298 Tau. We employ our results as a new benchmark point for the calibration of the X-ray to EUV scaling laws, and hence to predict the time evolution of the irradiation in the EUV band, and its effect on the evaporation of exo-atmospheres.

The metal-poor atmosphere of a Neptune/Sub-Neptune planet’s progenitor

“…Alternatively, photolytic destruction of methane could also potentially produce a methane poor atmosphere [55], which may be feasible given the youth and high activity levels of V1298 Tau. We test this hypothesis by running self-consistent forward model using published UV spectrum of V1298 Tau [56]. However, for V1298 Tau b photochemistry does not impact the methane abundance for pressures higher than 10 −4 bar even for extreme case (1000×solar XUV flux, Supplementary Figure 4).…”

X-Ray, Near-ultraviolet, and Optical Flares Produced by Colliding Magnetospheres in the Young High-eccentricity Binary DQ Tau

“…Furthermore, Marino et al (2006) reported no substantial evidence of long-term X-ray variability in the stellar members of the approximately 100-million-yearold open cluster NGC 2516. Similarly, Maggio et al (2023) reported only a small long-term X-ray variability with an amplitude of approximately ∼2 for the 12-million-year-old young star V1298 Tau.…”

The High-energy Spectrum of the Young Planet Host V1298 Tau

“…The integrated XUV (X-ray + EUV, <912 Å) flux from V1298 Tau using our combination of the XSPEC model and the DEM-generated EUV spectra is 3.2 ± 0.3 × 10 −12 erg s −1 cm −2 with additional uncertainty scaling factors of 15% and 20% introduced to the SED for the FUV flux calibration and n(H I) column density uncertainties, respectively. Poppenhaeger et al (2021) and more recently Maggio et al (2023) have also estimated the total EUV flux of V1298 Tau using different sets of observations and methods than this work. Between all three sets of observations, it is clear in the data that V1298 Tau exhibits significant long-term X-ray variability, but assessing the EUV variability is more difficult given the modeldependence of the EUV estimation.…”

“…dependence of the EUV estimation. The X-ray fluxes reported by Poppenhaeger et al (2021), Maggio et al (2023), and this work are listed in Table 5. Maggio et al (2023) fits emission measure distributions to two sets of observations with different X-ray fluxes labeled "quiescent" and "elevated," finding that the bulk of the difference in X-ray flux can be attributed to the enhancement of a hotter 10 7 K plasma component in the elevated state.…”

“…The panchromatic SED is presented in Figure 1. Section 2 lists the X-ray and ultraviolet observations contributing to the spectrum, Section 3 describes our analysis of the star's far-ultraviolet (FUV, 1140-1710 A ̊) emission lines and coronal properties, and Section 4 explains the method used to predict the unobserved extreme ultraviolet (EUV; 100-912 Å) flux and compares this work's inferred EUV flux to similar work by Poppenhaeger et al (2021) and Maggio et al (2023). Section 5 concludes by using the V1298 Tau spectrum to characterize the lifetime high-energy irradiation of planets orbiting solar-mass stars.…”