Solar Analogs Research Articles

Near-infrared Spectroscopy of the Sun and Solar Analog Star HD 76151: Compiling an Extensive Line List in the Y, J, H, and K Bands

Determining the physical nature of a star requires precise knowledge of its stellar atmospheric parameters, including effective temperature, surface gravity, and metallicity. This study presents a new atomic line list covering a broad spectral range (1–2.5 μm; YJHK bands) for iron (Fe) and α-elements (Ca, Mg, Ti, Si) to improve stellar parameter determination using near-infrared (NIR) spectroscopy. We highlight the limitations of existing line lists, stemming primarily from inconsistencies in oscillator strengths for ionized iron lines within the Apache Point Observatory Galactic Evolution Experiment DR17. The line list was validated using the high-resolution and high-quality disk-center NIR spectra of the Sun and its solar analog HD 76151. As a result of the spectroscopic analyses, the effective temperature of HD 76151 was calculated as 5790 ± 170 K, surface gravity as 4.35 ± 0.18 cgs, metal abundance as 0.24 ± 0.09 dex, and microturbulence velocity of 0.30−0.3+0.5 km s−1 by combining the optical and NIR line lists. A comparison of the model atmospheric parameters calculated for HD 76151 with the PARSEC isochrones resulted in a stellar mass of 1.053−0.068+0.056M⊙ , radius 1.125−0.011+0.035R⊙ , and an age of 5.5−2.1+2.5 Gyr. For the first time, kinematic and dynamical orbital analyses of HD 76151 using a combination of Gaia astrometric and spectroscopic data showed that the star was born in a metal-rich region within the solar circle and is a member of the thin disk population. Thus, the slightly metal-rich nature of the star, as reflected in its spectroscopic analysis, was confirmed by dynamical orbital analysis.

A simple model for spectroscopic analyses of active stars

Abstract Spectroscopic analyses of young late-type stars suffer from systematic inaccuracies, typically under-estimating metallicities but over-estimating abundances of certain elements including oxygen and barium. Effects are stronger in younger and cooler stars, and recent evidence specifically indicates a connection to the level of chromospheric activity. We present here a two-component spectroscopic model representing a non-magnetic baseline plus a magnetic spot, and analyse the resulting synthetic spectra of young solar analogues using a standard spectroscopic technique. For a moderately active star with solar parameters and chromospheric activity index $\log R_\text{HK}^{\prime }= -4.3$ (∼100 Myr), we predict that [Fe/H] is underestimated by 0.06 dex while vmic is overestimated by 0.2 km s−1; for higher activity levels we predict effects as large as 0.2 dex and 0.7 km s−1. Predictions are in agreement with literature data on solar twins, and indicate that the model is a plausible explanation to the observed effects. The model is simple enough that it can be included in spectroscopic packages with only changes to the underlying spectrum synthesis modules, if a $\log R_\text{HK}^{\prime }$ value is provided.

Hamilton Echelle Spectrograph Observations of Solar Analog Field Stars: Lithium Abundance and Activity

We measured lithium (Li) abundance and instantaneous chromospheric Ca ii HK activity in Hamilton Echelle Spectrograph observations of 211 solar analog field stars, with one objective being potential identification of grand minimum candidates for ongoing multiyear observation. At the zero-age main sequence, Li abundance for a typical late-type dwarf begins at the local interstellar medium abundance and over the main sequence lifetime is steadily depleted by convection at a rate dependent on details of the star’s convection and mixing processes. Our Li abundance measurements show an overall decrease in Li abundance with age and effective temperature, consistent with earlier surveys. In our activity measurements, 41 stars show log R′HK ≤ −5.0, which can be considered very inactive. Of the very inactive stars closest to solar effective temperature, 24 show Li abundances within the range typically observed for midlife Sun-like stars. Another three show very low Li abundance, which, combined with the low activity, suggest an older main sequence star or a slightly evolved star. We suggest that the combination of relatively undepleted Li and instantaneous very low activity might make these stars promising candidates for long time-series observations to determine if they are in a grand minimum state. The Hamilton Echelle Spectrograph observations are publicly available for download and are potentially useful for a variety of survey tasks involving Sun-like stars.

The inflated, eccentric warm Jupiter TOI-4914 b orbiting a metal-poor star, and the hot Jupiters TOI-2714 b and TOI-2981 b

Recent observations of giant planets have revealed unexpected bulk densities. Hot Jupiters, in particular, appear larger than expected for their masses compared to planetary evolution models, while warm Jupiters seem denser than expected. These differences are often attributed to the influence of the stellar incident flux, but it has been unclear if they also result from different planet formation processes, and if there is a trend linking the planetary density to the chemical composition of the host star. In this work, we present the confirmation of three giant planets in orbit around solar analogue stars. TOI-2714 b (P ≃ 2.5 d, Rp ≃ 1.22 RJ, Mp = 0.72 MJ) and TOI-2981 b (P ≃ 3.6 d, RP ≃ 1.2 RJ, MP = 2 MJ) are hot Jupiters on nearly circular orbits, while TOI-4914 b (P ≃ 10.6 d, RP ≃ 1.15 RJ, Mp = 0.72 MJ) is a warm Jupiter with a significant eccentricity (e = 0.41 ± 0.02) that orbits a star more metal-poor ([Fe/H] = −0.13) than most of the stars known to host giant planets. Similarly, TOI-2981 b orbits a metal-poor star ([Fe/H] = −0.11), while TOI-2714 b orbits a metal-rich star ([Fe/H] = 0.30). Our radial velocity follow-up with the HARPS spectrograph allows us to detect their Keplerian signals at high significance (7, 30, and 23σ, respectively) and to place a strong constraint on the eccentricity of TOI-4914 b (18σ). TOI-4914 b, with its large radius (Rp ≃ 1.15 RJ) and low insolation flux (F⋆ < 2 × 108 erg s−1 cm−2), appears to be more inflated than what is supported by current theoretical models for giant planets. Moreover, it does not conform to the previously noted trend that warm giant planets orbiting metal-poor stars have low eccentricities. This study thus provides insights into the diverse orbital characteristics and formation processes of giant exoplanets, in particular the role of stellar metallicity in the evolution of planetary systems.

Exploring the Small-scale Magnetic Fields of the Solar Analog KIC 8006161 Using Asteroseismology

The magnetic field is a significant and universal physical phenomenon in modern astrophysics. Small-scale magnetic fields are very important in the stellar atmosphere. They are ubiquitous and strongly couple with acoustic waves. Therefore, their presence affects the properties of acoustic waves in the stellar outer layer. In the present work, under the assumption that small-scale magnetic features are the cause of the asteroseismic surface term (the frequency-dependent frequency offset between stars and their models), we explore the strength of such fields in the solar analog KIC 8006161. By considering the effect of small-scale magnetic fields in the stellar photosphere, we use the observed oscillation frequencies to constrain the inner structures and surface small-scale magnetic fields of solar-like star KIC 8006161. To agree with the existing observations, such as oscillation frequencies, and their frequency separation ratios, the theoretical model requires a small-scale magnetic field to form a magnetic-arch splicing layer in the stellar outer atmosphere. The small-scale magnetic field strengths for KIC 8006161 obtained from best-fit model with Y init = 0.249 + 1.33 Z init and Y init as a free parameter are approximately 96 and 89 G, respectively. The corresponding locations of the magnetic-arch splicing layer are about 522 and 510 km, respectively.

Destruction of interstellar methyl cyanide (CH3CN) via collisions with He+⋅ ions

Context. CH3CN (methyl cyanide) is one of the simplest and most abundant interstellar complex organic molecules (iCOMs), and has been detected in young solar analogues, shocked regions, protoplanetary discs, and comets. CH3CN can therefore be considered a key species to explore the chemical connections between the planet-forming disk phase and comets. However, for such comparison to be meaningful, kinetics data for the reactions leading to CH3CN formation and destruction must be updated. Aims. Here we focus on the destruction of methyl cyanide through collisions with He+. . We employed a combined experimental and theoretical methodology to obtain cross sections (CSs) and branching ratios (BRs) as a function of collision energy, from which we calculated reaction rate coefficients k(T) in the temperature range from 10 to 300 K. Methods. We measured CSs and BRs using a guided ion beam setup, and developed a theoretical treatment based on an analytical formulation of the potential energy surfaces (PESs) for the charge exchange process. The method employs a Landau Zener model to obtain reaction probabilities at crossings between the entrance and exit PESs, and an adiabatic centrifugal sudden approximation to calculate CSs and k(T), from subthermal to hyper-thermal regimes. Results. k(T) and experimental BRs differ from those predicted from widely used capture models. In particular, the rate coefficient at 10 K is estimated to be almost one order of magnitude smaller than what is reported in the KIDA database. In addition, the charge exchange is completely dissociative and the most abundant fragments are HCCN+/CCNH+ , HCNH+ and CH2+. Conclusions. Our results, combined with a revised chemical network for the formation of CH3CN, support the hypothesis that methyl cyanide in protoplanetary discs could be mostly the product of gas-phase processes rather than grain chemistry, as currently proposed. These findings are expected to have implications in the comparison of the abundance ratios of N-bearing molecules observed in discs with cometary abundance ratios.

The [Y/Mg] chemical clock in the Galactic disk

Context. Stellar ages are an important parameter in studies of the chemical evolution of the Galaxy. To better estimate these ages, various methods complementary to the conventional isochrone fitting method have been implemented in the past decade. Several recent studies have established the existence of a relationship between chemical clocks and stellar ages. The [Y/Mg] clock is a promising technique, but there are still several open questions, such as its validity for metal-poor stars and differences between the thin and thick disk populations. Aims. Our aim is to study the relationship between the [Y/Mg] chemical clock and stellar ages for a sample of solar-type disk stars and to provide the empirical dating relation(s) for the stellar age determination from their precise chemical abundances. We also studied the effect of metallicity and populations on this chemical clock. Methods. We derived precise stellar atmospheric parameters as well as the elemental abundances of Mg and Y through line-by-line differential spectroscopic analysis for a sample of 48 metal-poor solar-type stars based on high-quality, high-resolution ESO/HARPS spectra. From high-precision Gaia astrometric data, stellar masses and ages were estimated through isochrone fitting using Yonsei-Yale isochrones. A joint analysis of our sample, together with a sample of 185 solar twins and analogues from our previous works, was performed to calibrate the [Y/Mg] chemical clock in the Galactic disk for −0.71 < [Fe/H] < +0.34. Open clusters and stars with asteroseismic ages were used to validate our relations. Results. Two different populations are clearly seen in the [Mg/Fe]−[Fe/H] plane: the thick and thin disks. Thick disk stars show an age-metallicity relation, whereas the thin disk shows a flatter age–metallicity distribution. We find a strong, metallicity–dependent anti-correlation between the [Y/Mg] ratio and the stellar ages of our sample. For the first time in the literature, we report similar correlations for thin and thick disk stars. Conclusions. We find that the [Y/Mg] relation(s) found here for solar-type stars in a wide metallicity range are compatible with those found for solar twins in the literature. Our relation provides high accuracy and precision (0.45 and 0.99 Gyr, respectively) comparable with the best accuracy achieved for solar twins to date.

A study of an X-ray flare on the solar analogue V895 Tau

Using observations with XMM-Newton, we study the characteristics of a flare emanating from a solar analogous V895 Tau. At the peak of the flare, its luminosity reached 3.3×1030ergs−1, which is ∼ 600 times more energetic than the X10 class flare on the Sun. The quiescent state corona of V895 Tau is depicted by a two-temperature plasma model with temperatures of 3.9 and 11 MK. The flare’s evolution was carefully scrutinized through time-resolved X-ray spectroscopy, unveiling the variations in temperature, emission measure, abundance and luminosity during the flare. The temperature peaked at 36.1 MK, which is approximately four times higher than the pre-flare temperature. Employing a hydrodynamic loop model, we have estimated the half length of the flaring loop to be 5.9×1010 cm. Using the loop scaling laws, other loop parameters like density, pressure, volume, and minimum magnetic field are also estimated, and are found to be similar to those of other flares from similar type of stars.

Correction to: TOI-2447 b / NGTS-29 b: a 69-day Saturn around a Solar analogue

Correction to: TOI-2447 b / NGTS-29 b: a 69-day Saturn around a Solar analogue

Simulated Coronal Mass Ejections on a Young Solar-type Star and the Associated Instantaneous Angular Momentum Loss

Coronal mass ejections (CMEs) on stars can change the stars’ magnetic field configurations and mass-loss rates during the eruption and propagation and therefore, may affect the stars’ rotation properties on long timescales. The dynamics of stellar CMEs and their influence on the stellar angular momentum loss rate are not yet well understood. In order to start investigating these CME-related aspects on other stars, we conducted a series of magnetohydrodynamic simulations of CMEs on a solar-type star of moderate activity levels. The propagation and evolution of the CMEs were traced in the three-dimensional outputs and the temporal evolution of their dynamic properties (such as masses, velocities, and kinetic energies) were determined. The simulated stellar CMEs are more massive and energetic than their solar analog, which is a result of the stronger magnetic field on the surface of the simulated star than that of the Sun. The simulated CMEs display masses ranging from ∼1016 to ∼1018 g and kinetic energies from ∼1031 to ∼1033 erg. We also investigated the instantaneous influence of the CMEs on the star’s angular momentum loss rate. Our results suggest that angular momentum can either be added to or removed from the star during the evolution of CME events. We found a positive correlation between the amplitude of the angular momentum loss rate variation and the CME’s kinetic energy as well as mass, suggesting that more energetic/massive CMEs have a higher possibility to add angular momentum to the star.

The Ice Chemistry in Comets and Planet-forming Disks: Statistical Comparison of CH3OH, H2CO, and NH3 Abundance Ratios

Comets are frozen remnants of our solar system’s formation, and comparing their chemical composition to that of planet-forming systems can reveal crucial insights about our origins, potentially answering one of the most challenging questions in planetary science, i.e., whether cometary material was mainly inherited from the protosolar nebula or reprocessed during the solar system formation. Here we provide the first statistical analysis of methanol, formaldehyde, and ammonia abundances in 35 comets and 11 protostellar solar analogs and planet-forming disks. We show that comets from different dynamical families have comparable compositions on average, implying that their chemistry is preserved even after formation. While abundances retrieved from infrared and (sub)millimeter ground-based observations are in agreement, there are significant differences with those obtained via mass spectroscopy for 67P/Churyumov–Gerasimenko, target of the ESA-Rosetta mission; we discuss the implication of relying solely on the latter data for comparisons with disk abundance ratios. Finally, we find a significant difference in the [CH3OH]/[H2CO] ratio in comets observed within or farther than 1 au from the Sun, suggesting that temperature-activated mechanisms can enhance the H2CO production in the coma; this bias can strongly influence our understanding of comet chemistry in the context of planet formation. When compared to planet-forming systems, the [CH3OH]/[H2CO] and [NH3]/[CH3OH] molecular abundance ratios in comets are consistent with those measured in Class 0 hot corinos and in the inner regions of Class II disks, hence suggesting an inheritance scenario.

Observations and detectability of young Suns’ flaring and CME activity in optical spectra

ABSTRACT The Sun’s history is still a subject of interest to modern astrophysics. Observationally constrained rates of Coronal Mass Ejections (CMEs) of young solar analogues are still lacking, as those require dedicated monitoring. We present medium-resolution optical spectroscopic monitoring of a small sample of bright and prominent solar analogues over a period of 3 yr using the 0.5-m telescope at observatory Lustbühel Graz (OLG) of the University of Graz, Austria. The aim is the detection of flares and CMEs from those spectra. In more than 1700 h of spectroscopic monitoring, we found signatures of four flares and one filament eruption on EK Dra which has been reported in previous literature, but we complementarily extended the data to cover the latter phase. The other stars did not reveal detectable signatures of activity. For these non-detections, we derive upper limits of occurrence rates of very massive CMEs, which are detectable with our observational setup, ranging from 0.1 to 2.2 d−1, but these may be even smaller than the given rates considering observational biases. Furthermore, we investigate the detectability of flares/CMEs in OLG spectra by utilizing solar 2D Hα spectra from Mees Solar Observatory. We find that solar-sized events are not detectable within our observations. By scaling up the size of the solar event, we show that with a fractional active region area of 18 per cent in residual spectra and 24 per cent in equivalent width time series derived from the same residuals that solar events are detectable if they had hypothetically occurred on HN Peg.

Asteroid reflectance spectra from Gaia DR3: Near-UV in primitive asteroids

Context. In the context of charge-coupled devices (CCDs), the ultraviolet (UV) region has mostly remained unexplored after the 1990s. Gaia DR3 offers the community a unique opportunity to explore tens of thousands of asteroids in the near-UV as a proxy of the UV absorption. This absorption has been proposed in previous works as a diagnostic of hydration, organics, and space weathering. Aims. In this work, we aim to explore the potential of the NUV as a diagnostic region for primitive asteroids using Gaia DR3. Methods. We used a corrective factor over the blue part of Gaia spectra to erase the solar analog selection effect. We identified an artificial relation between the band noise and slope and applied a signal-to-noise ratio (S/N) threshold for Gaia bands. Meeting the quality standards, we employed a Markov chain Monte Carlo (MCMC) algorithm to compute the albedo threshold, maximizing primitive asteroid inclusion. Utilizing one- and two-dimensional (1D and 2D) projections, along with dimensionality-reduction methods (such as PCA and UMAP), we identified primitive asteroid populations. Results. We uncovered: (a) the first observational evidence linking UV absorption to the 0.7 µm band, tied to hydrated iron-rich phyllosilicates; and (b) a 2D space revealing a split in C-type asteroids based on spectral features, including UV absorption. The computed average depth (3.5 ± 1.0 %) and center (0.70 ± 0.03 µm) of the 0.7 µm absorption band for primitive asteroids observed with Gaia is in agreement with the literature values. Conclusions. In this paper, we shed light on the importance of the UV absorption feature to discriminate among different mineralogies (i.e., iron-rich phyllosilicates vs. iron-poor) or to identify taxonomies that are conflated in the visible (i.e., F-types vs. B-types). We have shown that this is a promising region for diagnostic studies of the composition of primitive asteroids.

A graphene-CuNWs@PAMPS mixed aerogel for composite phase change materials with high thermal conductivity and excellent solar-thermal to electrical conversion

Phase change materials could store and release heat energy through phase change. However, the shortcomings of low thermal conductivity in the photothermal conversion process and easy leakage in the solid-liquid conversion seriously hinder the application of heat energy utilization. Graphene had high thermal conductivity, and it was an ideal material for improving the solar absorption, solar energy conversion and thermal conductivity of phase change materials. In this paper, a graphene aerogel composed of copper nanowires (CuNWs)/2-acrylamide-2-methylpropanesulfonic acid (AMPS) was designed. The thermal conductivity and shape stability of phase change materials for solar-thermal-electrical conversion applications were enhanced by composite CuNWs. Furthermore, PAMPS was coated on the surface of copper nanowires to avoid the oxidation of copper nanowires, and the sulfonic acid group of PAMPS was used to induce CuNWs to disperse uniformLy on the graphene sheets, which further constructed a good conductive network. After vacuum impregnation of PW, the best thermal conductivity phase change composite (PW-CuNWs@PAMPS-GA(1:1)) was obtained. The PCC loaded with CuNWs with the same graphene content achieved a thermal conductivity of 1.46 W/(m·K) and a high latent heat of 206.8 J/g. The latent heat retention rate was as high as 99.57 %. The photothermal conversion efficiency of PW-CuNWs@PAMPS-GA(1:1) was remarkable at 96.4 %. Due to its excellent solar-thermal-electrical conversion efficiency, the output voltage and output current were 800.8 mV and 85.8 mA, respectively, at a solar analog intensity of 5 kW/m2. Even after the sunlight was stopped, the voltage output could be maintained for a while by releasing the heat energy stored in the phase change composite.

The Sun Remains Relatively Refractory Depleted: Elemental Abundances for 17,412 Gaia RVS Solar Analogs and 50 Planet Hosts

The element abundances of stars, particularly the refractory elements (e.g., Fe, Si, and Mg), play an important role in connecting stars to their planets. Most Sun-like stars do not have refractory abundance measurements since obtaining a large sample of high-resolution spectra is difficult with oversubscribed observing resources. In this work we infer abundances for C, N, O, Na, Mn, Cr, Si, Fe, Ni, Mg, V, Ca, Ti, Al, and Y for solar analogs with Gaia Radial Velocity Spectrometer (RVS) spectra (R = 11,200) using TheCannon, a data-driven method. We train a linear model on a reference set of 34 stars observed by Gaia RVS with precise abundances measured from previous high-resolution spectroscopic efforts (R > 30,000–110,000). We then apply this model to several thousand Gaia RVS solar analogs. This yields abundances with average upper limit precisions of 0.04–0.1 dex for 17,412 stars, 50 of which are identified planet (candidate) hosts. We subsequently test the relative refractory depletion of these stars with increasing element condensation temperature compared to the Sun. The Sun remains refractory depleted compared to other Sun-like stars regardless of our current knowledge of the planets they host. This is inconsistent with theories of various types of planets locking up or sequestering refractories. Furthermore, we find no significant abundance differences between identified close-in giant planet hosts, giant planet hosts, and terrestrial/small planet hosts with the rest of the sample within our precision limits. This work demonstrates the utility of data-driven learning for future exoplanet composition and demographics studies.

FAUST

Context. The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. Aims. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. Methods. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH3OH, H2CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Results. Methanol emission reveals an arc-like structure at ∼1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H2CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H2 column density of ∼7 × 1021 cm−2, a mass of ∼9 × 10−3 M⊙, and a lower limit on the dust spectral index of 1.4. Conclusions. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues.

TheCannon for abundances in solar analogues

TheCannon for abundances in solar analogues

Contamination of spectroscopic observations by satellite constellations

Context. With the onset of large telecommunication constellations, the number of satellites on low orbits has dramatically increased over the past years, raising concerns among the astronomical community about their impact on observations. Aims. Since spectroscopic observations represent a large fraction of professional astronomical observations and given that spectro-graphs lack spatial information that can reveal the presence of a satellite, this paper is focused on how satellites affect spectroscopic optical observations. Methods. We simulated how often satellites contaminate spectrograph observations by using realistic constellations with over 400 000 objects. We counted the satellites that crossed a representative 10 × 1" slit during a 1000 s exposure, for different solar elevations and observation directions. We also measured how a satellite affects a spectrum by using real data from different scientific targets and a scaled solar analog as the satellite. We then used standard tools to measure astrophysical parameters and compare them with the clean spectrum. Results. As expected, the fraction of affected spectra varies dramatically with the direction of the observation and the elevation of the sun, with a maximum of 10% at twilight down to no contamination when the sun reaches −30°, with a nightly average of ~2%. The probability of a satellite crossing over the astronomical target will be further reduced depending on the target’s apparent size. Because of the fast motion of the satellites and the limiting magnitude of the spectrographs, high-resolution instruments are essentially blind to most satellites. For lower resolution spectrographs, the effect on the measured astrophysical parameters depends strongly on the signal-to-noise ratio of the exposure, longer exposures on brighter targets being the least affected at ≲1%. Satellites that are brighter and/or higher than the constellation satellites, while less numerous, can also contaminate the spectra. Conclusions. Satellites (either coming from a large constellation or not) have the potential to contaminate spectra. While the fraction of affected spectra is likely to remain low even with a number of satellites about 100× larger than today, some of these contaminated spectra will be difficult to identify, as is already the case with existing satellites and asteroids. The best mitigation is to ensure that their brightness is fainter than V = 7 and that the satellites’ absolute magnitude V1000 km is also fainter than 7, and whenever possible to shoot multiple exposures.

Devolatilization of extrasolar planetesimals by 60Fe and 26Al heating

ABSTRACT Whilst the formation of Solar system planets is constrained by meteoritic evidence, the geophysical history of low-mass exoplanets is much less clear. The bulk composition and climate states of rocky exoplanets may vary significantly based on the composition and properties of the planetesimals they form. An important factor influenced by planetesimal composition is water content, where the desiccation of accreting planetesimals impacts the final water content of the resultant planets. While the inner planets of the Solar system are comparatively water-poor, recent observational evidence from exoplanet bulk densities and planetary formation models suggests that rocky exoplanets engulfed by substantial layers of high-pressure ices or massive steam atmospheres could be widespread. Here, we quantify variations in planetesimal desiccation due to potential fractionation of the two short-lived radioisotopes 26Al and 60Fe relevant for internal heating on planetary formation time-scales. We focus on how order of magnitude variations in 60Fe can affect the water content of planetesimals, and how this may alter the formation of extrasolar ocean worlds. We find that heating by 26Al is the dominant cause of planetesimal heating in any Solar system analogue scenario, thus validating previous works focussing only on this radioisotope. However, 60Fe can become the primary heating source in the case of high levels of supernova enrichment in massive star-forming regions. These diverging scenarios can affect the formation pathways, bulk volatile budget, and climate diversity of low-mass exoplanets.

The variable magnetic field of V889 Her and the challenge of detecting exoplanets around young Suns using Gaussian process regression

ABSTRACT Discovering exoplanets orbiting young Suns can provide insight into the formation and early evolution of our own solar system, but the extreme magnetic activity of young stars obfuscates exoplanet detection. Here we monitor the long-term magnetic field and chromospheric activity variability of the young solar analogue V889 Her, model the activity-induced radial velocity variations, and evaluate the impacts of extreme magnetism on exoplanet detection thresholds. We map the magnetic field and surface brightness for 14 epochs between 2004 and 2019. Our results show potential 3–4 yr variations of the magnetic field that evolves from weak and simple during chromospheric activity minima to strong and complex during activity maxima but without any polarity reversals. A persistent, temporally varying polar spot coexists with weaker, short-lived lower-latitude spots. Due to their different decay time-scales, significant differential rotation, and the limited temporal coverage of our legacy data, we were unable to reliably model the activity-induced radial velocity using Gaussian Process regression. Doppler Imaging can be a useful method for modelling the magnetic activity jitter of extremely active stars using data with large phase gaps. Given our data and using Doppler Imaging to filter activity jitter, we estimate that we could detect Jupiter-mass planets with orbital periods of $\sim$3 d. A longer baseline of continuous observations is the best observing strategy for the detection of exoplanets orbiting highly active stars.