The sanctuary of Apollo in Pompeii: new geophysical and archaeological investigations

The paper discusses recent and integrated investigations in the Sanctuary of Apollo in Pompeii, which contribute to the overall understanding of the diachronic evolution of this sacred place, from the archaic period to the eruption of AD 79. High-resolution geophysical surveys have been interpreted in comparison with a new reading of the publication of Maiuri’s excavations and the most recent excavations. The latest research offers significant additional information, not only on the constructive episodes of the architectural complex and the urban landscape in which it is inserted, but also on aspects related to the cult of Apollo and the associated rituality

Outflowing Helium from a Mature Mini-Neptune

We announce the detection of escaping helium from TOI 2134b, a mini-Neptune a few gigayears old. The average in-transit absorption spectrum shows a peak of 0.37% ± 0.05% and an equivalent width of Wavg = 3.3 ± 0.3 mÅ. Among all planets with helium detections, TOI 2134b is the only mature mini-Neptune, has the smallest helium signal, and experiences the lowest X-ray and ultraviolet (XUV) flux. Putting TOI 2134b in the context of all other helium detections, we report the detection of a strong (p = 3.0 × 10−5) and theoretically expected correlation between FXUV/ρXUV (proportional to the energy-limited mass-loss rate) and R*Wavg (roughly proportional to the observationally inferred mass-loss rate). Here Wavg is the equivalent width of the helium absorption, and ρXUV is the density of the planet within the XUV photosphere, but the correlation is similarly strong if we use the optical photosphere. Having the lowest value on both axes, TOI 2134b anchors the relation. We encourage further observations to fill in the missing regions of this parameter space and improve estimates of FXUV

Outflowing Helium from a Mature Mini-Neptune

We announce the detection of escaping helium from TOI 2134b, a mini-Neptune a few gigayears old. The average in-transit absorption spectrum shows a peak of 0.37% ± 0.05% and an equivalent width of Wavg = 3.3 ± 0.3 mÅ. Among all planets with helium detections, TOI 2134b is the only mature mini-Neptune, has the smallest helium signal, and experiences the lowest X-ray and ultraviolet (XUV) flux. Putting TOI 2134b in the context of all other helium detections, we report the detection of a strong (p = 3.0 × 10−5) and theoretically expected correlation between FXUV/ρXUV (proportional to the energy-limited mass-loss rate) and R*Wavg (roughly proportional to the observationally inferred mass-loss rate). Here Wavg is the equivalent width of the helium absorption, and ρXUV is the density of the planet within the XUV photosphere, but the correlation is similarly strong if we use the optical photosphere. Having the lowest value on both axes, TOI 2134b anchors the relation. We encourage further observations to fill in the missing regions of this parameter space and improve estimates of FXUV

Leveraging Space-based Data from the Nearest Solar-type Star to Better Understand Stellar Activity Signatures in Radial Velocity Data

Stellar variability is a key obstacle in reaching the sensitivity required to recover Earth-like exoplanetary signals using the radial velocity (RV) detection method. To explore activity signatures in Sun-like stars, we present SolAster, a publicly distributed analysis pipeline10 that allows for comparison of space-based measurements with ground-based disk-integrated RVs. Using high-spatial-resolution Dopplergrams, magnetograms, and continuum filtergrams from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory (SDO), we estimate "Sun-as-a-star" disk-integrated RVs due to rotationally modulated flux imbalances and convective blueshift suppression, as well as other observables such as unsigned magnetic flux. Comparing these measurements with ground-based RVs from the NEID instrument, which observes the Sun daily using an automated solar telescope, we find a strong relationship between magnetic activity indicators and RV variation, supporting efforts to examine unsigned magnetic flux as a proxy for stellar activity in slowly rotating stars. Detrending against measured unsigned magnetic flux allows us to improve the NEID RV measurements by ∼20% (∼50 cm s−1 in a quadrature sum), yielding an rms scatter of ∼60 cm s−1 over five months. We also explore correlations between individual and averaged spectral line shapes in the NEID spectra and SDO-derived magnetic activity indicators, motivating future studies of these observables. Finally, applying SolAster to archival planetary transits of Venus and Mercury, we demonstrate the ability to recover small amplitude (<50 cm s−1) RV variations in the SDO data by directly measuring the Rossiter–McLaughlin signals

Leveraging Space-based Data from the Nearest Solar-type Star to Better Understand Stellar Activity Signatures in Radial Velocity Data

Stellar variability is a key obstacle in reaching the sensitivity required to recover Earth-like exoplanetary signals using the radial velocity (RV) detection method. To explore activity signatures in Sun-like stars, we present SolAster, a publicly distributed analysis pipeline10 that allows for comparison of space-based measurements with ground-based disk-integrated RVs. Using high-spatial-resolution Dopplergrams, magnetograms, and continuum filtergrams from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory (SDO), we estimate "Sun-as-a-star" disk-integrated RVs due to rotationally modulated flux imbalances and convective blueshift suppression, as well as other observables such as unsigned magnetic flux. Comparing these measurements with ground-based RVs from the NEID instrument, which observes the Sun daily using an automated solar telescope, we find a strong relationship between magnetic activity indicators and RV variation, supporting efforts to examine unsigned magnetic flux as a proxy for stellar activity in slowly rotating stars. Detrending against measured unsigned magnetic flux allows us to improve the NEID RV measurements by ∼20% (∼50 cm s−1 in a quadrature sum), yielding an rms scatter of ∼60 cm s−1 over five months. We also explore correlations between individual and averaged spectral line shapes in the NEID spectra and SDO-derived magnetic activity indicators, motivating future studies of these observables. Finally, applying SolAster to archival planetary transits of Venus and Mercury, we demonstrate the ability to recover small amplitude (<50 cm s−1) RV variations in the SDO data by directly measuring the Rossiter–McLaughlin signals

Investigating stellar activity through eight years of Sun-as-a-star observations

Stellar magnetic activity induces both distortions and Doppler-shiftsin the absorption line profiles of Sun-like stars. Those effects produce apparent radial velocity (RV) signals which greatly hamper the search for potentially habitable, Earth-like planets. In this work, we investigate these distortions in the Sun using cross-correlation functions (CCFs), derived from intensive monitoring with the high-precision spectrograph HARPS-N. We show that the RV signal arising from line-shape variations on time-scales associated with the Sun’s rotation and activity cycle can be robustly extracted from the data, reducing the RV dispersion by half. Once these have been corrected, activity-induced Doppler-shifts remain, that are modulated at the solar rotation period, and that are most effectively modelled in the time domain, using Gaussian processes (GPs). Planet signatures are still best retrieved with multidimensonal GPs, when activity is jointly modelled from the raw RVs and indicators of the line width or of the Ca II H & K emission. After GP modelling, the residual RVs exhibit a dispersion of 0.6–0.8 m s−1, likely to be dominated by signals induced by supergranulation. Finally, we find that the statistical properties of the RVs evolve significantly over time, and that this evolution is primarily driven by sunspots, which control the smoothness of the signal. Such evolution, which reduces the sensitivity to long-period planet signatures, is no longer seen in the activity-induced Doppler-shifts, which is promising for long term RV monitoring surveys such as the Terra Hunting Experiment or the PLATO follow-up campaign

Investigating stellar activity through eight years of Sun-as-a-star observations

Funding: BK, SA, OB, HY, and NKOS acknowledge funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no 865624, GPRV). MC acknowledges the SNSF support under grant P500PT_211024. FR is funded by the University of Exeter’s College of Engineering, Maths and Physical Sciences, UK. ACC acknowledges support from STFC consolidated grant number ST/V000861/1, and EPSRC grant number EP/Z000181/1 towards the ERC Synergy project REVEAL.Stellar magnetic activity induces both distortions and Doppler-shifts in the absorption line profiles of Sun-like stars. Those effects produce apparent radial velocity (RV) signals which greatly hamper the search for potentially habitable, Earth-like planets. In this work, we investigate these distortions in the Sun using cross-correlation functions (CCFs), derived from intensive monitoring with the high-precision spectrograph HARPS-N. We show that the RV signal arising from line-shape variations on time-scales associated with the Sun’s rotation and activity cycle can be robustly extracted from the data, reducing the RV dispersion by half. Once these have been corrected, activity-induced Doppler-shifts remain, that are modulated at the solar rotation period, and that are most effectively modelled in the time domain, using Gaussian processes (GPs). Planet signatures are still best retrieved with multidimensonal GPs, when activity is jointly modelled from the raw RVs and indicators of the line width or of the Ca ii H & K emission. After GP modelling, the residual RVs exhibit a dispersion of 0.6–0.8 m s−1, likely to be dominated by signals induced by supergranulation. Finally, we find that the statistical properties of the RVs evolve significantly over time, and that this evolution is primarily driven by sunspots, which control the smoothness of the signal. Such evolution, which reduces the sensitivity to long-period planet signatures, is no longer seen in the activity-induced Doppler-shifts, which is promising for long term RV monitoring surveys such as the Terra Hunting Experiment or the PLATO follow-up campaign.Peer reviewe

Investigating stellar activity through eight years of Sun-as-a-star observations

Stellar magnetic activity induces both distortions and Doppler-shiftsin the absorption line profiles of Sun-like stars. Those effects produce apparent radial velocity (RV) signals which greatly hamper the search for potentially habitable, Earth-like planets. In this work, we investigate these distortions in the Sun using cross-correlation functions (CCFs), derived from intensive monitoring with the high-precision spectrograph HARPS-N. We show that the RV signal arising from line-shape variations on time-scales associated with the Sun’s rotation and activity cycle can be robustly extracted from the data, reducing the RV dispersion by half. Once these have been corrected, activity-induced Doppler-shifts remain, that are modulated at the solar rotation period, and that are most effectively modelled in the time domain, using Gaussian processes (GPs). Planet signatures are still best retrieved with multidimensonal GPs, when activity is jointly modelled from the raw RVs and indicators of the line width or of the Ca II H & K emission. After GP modelling, the residual RVs exhibit a dispersion of 0.6–0.8 m s−1, likely to be dominated by signals induced by supergranulation. Finally, we find that the statistical properties of the RVs evolve significantly over time, and that this evolution is primarily driven by sunspots, which control the smoothness of the signal. Such evolution, which reduces the sensitivity to long-period planet signatures, is no longer seen in the activity-induced Doppler-shifts, which is promising for long term RV monitoring surveys such as the Terra Hunting Experiment or the PLATO follow-up campaign

The magnetically quiet solar surface dominates HARPS-N solar RVs during low activity

Using images from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory (SDO/HMI), we extract the radial-velocity (RV) signal arising from the suppression of convective blue-shift and from bright faculae and dark sunspots transiting the rotating solar disc. We remove these rotationally modulated magnetic-activity contributions from simultaneous radial velocities observed by the HARPS-N solar feed to produce a radial-velocity time series arising from the magnetically quiet solar surface (the ‘inactive-region radial velocities’). We find that the level of variability in the inactive-region radial velocities remains constant over the almost 7 year baseline and shows no correlation with well-known activity indicators. With an RMS of roughly 1 m s−1, the inactive-region radial-velocity time series dominates the total RV variability budget during the decline of solar cycle 24. Finally, we compare the variability amplitude and timescale of the inactive-region radial velocities with simulations of supergranulation. We find consistency between the inactive-region radial-velocity and simulated time series, indicating that supergranulation is a significant contribution to the overall solar radial velocity variability, and may be the main source of variability towards solar minimum. This work highlights supergranulation as a key barrier to detecting Earth twins