Context.
The determination of stellar age is a crucial task in astrophysics research. At present, the various methods employed in such studies are either model-dependent or based on calibrated ...empirical relations. The most reliable results are generally obtained when different methods are applied in a complementary manner.
Aims.
We propose a new method for the age determination of young stellar associations and open clusters (ages ≲ 125 Myr), which may allow for the placement of further constraints on the age when used in tandem with other methods.
Methods.
We explore the amplitude of the photometric variability in bins of color and rotation period of five young associations and clusters spanning an interval of ages from ∼1−3 Myr to ∼ 625 Myr (Taurus,
ρ
Ophiuchi, Upper Scorpius, Pleiades, and Praesepe), which all have high-quality time-series photometry from
Kepler
K2 campaigns.
Results.
In the low-mass regime, we find that stars with similar color and rotation periods but different ages exhibit a range of amplitudes for their photometric variability, with younger stars showing a larger photometric variability than older stars.
Conclusions.
The decline of photometric variability amplitude versus age in stars with similar color and rotation period may, in principle, be calibrated and adopted as an additional empirical relation for constraining the age of young associations and open clusters, provided that time-series photometry is available for their low-mass members.
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Biomolecule-polymer conjugates are constructs that take advantage of the functional or otherwise beneficial traits inherent to biomolecules and combine them with synthetic polymers ...possessing specially tailored properties. The rapid development of novel biomolecule-polymer conjugates based on proteins, peptides, or nucleic acids has ushered in a variety of unique materials, which exhibit functional attributes including thermo-responsiveness, exceptional stability, and specialized specificity. Key to the synthesis of new biomolecule-polymer hybrids is the use of controlled polymerization techniques coupled with either grafting-from, grafting-to, or grafting- through methodology, each of which exhibit distinct advantages and/or disadvantages. In this review, we present recent progress in the development of biomolecule-polymer conjugates with a focus on works that have detailed the use of grafting-from methods employing ATRP, RAFT, or ROMP.
Reactive oxygen species (ROS) like hydrogen peroxide (H
O
) are transient species that have broad actions in signaling and stress, but spatioanatomical understanding of their biology remains ...insufficient. Here, we report a tandem activity-based sensing and labeling strategy for H
O
imaging that enables capture and permanent recording of localized H
O
fluxes. Peroxy Green-1 Fluoromethyl (PG1-FM) is a diffusible small-molecule probe that senses H
O
by a boronate oxidation reaction to trigger dual release and covalent labeling of a fluorescent product, thus preserving spatial information on local H
O
changes. This unique reagent enables visualization of transcellular redox signaling in a microglia-neuron coculture cell model, where selective activation of microglia for ROS production increases H
O
in nearby neurons. In addition to identifying ROS-mediated cell-to-cell communication, this work provides a starting point for the design of chemical probes that can achieve high spatial fidelity by combining activity-based sensing and labeling strategies.
An efficient method for chemoselective cysteine arylation of unprotected peptides and proteins using Au(III) organometallic complexes is reported. The bioconjugation reactions proceed rapidly (<5 ...min) at ambient temperature in various buffers and within a wide pH range (0.5–14). This approach provides access to a diverse array of S-aryl bioconjugates including fluorescent dye, complex drug molecule, affinity label, poly(ethylene glycol) tags, and a stapled peptide. A library of Au(III) arylation reagents can be prepared as air-stable, crystalline solids in one step from commercial reagents. The selective and efficient arylation procedures presented in this work broaden the synthetic scope of cysteine bioconjugation and serve as promising routes for the modification of complex biomolecules.
The satellite Planetary Transits and Oscillations of stars (PLATO), due to be launched late 2026, will provide us with an unprecedented sample of light curves of solar-type stars that will exhibit ...both solar-type oscillations and signatures of activity-induced brightness modulations. Solar-type pulsators only have moderate levels of activity because high levels of activity inhibit oscillations. This means that these targets represent a specific challenge for starspot modelling. In order to assess the possibilities that PLATO will soon open, we wish to characterise the morphology of active regions at the surface of stars for which we also have a detection of solar-like acoustic oscillations. In this context, we report the results of an ensemble starspot modelling analysis of the Sun and ten solar-type pulsators observed by the
Kepler
satellite. We implement a Bayesian starspot modelling approach based on a continuous-grid model, accounting for the combined starspot and facular contribution to activity-induced brightness modulations. From our analysis, we find that several stars of our sample exhibit clear signatures of stable longitudinal active nests while sharing activity levels and convection versus rotation regimes similar to the solar regime. By searching for modulations in the reconstructed starspot coverage, we found significant periodicities that we identify as possible signatures of cyclic modulations similar to the quasi-biennal oscillation or the Rieger cycle. We can infer the corresponding intensity of the magnetic field at the bottom of the convective envelope based on the hypothesis that internal magneto-Rossby waves acting on the tachocline cause these modulations.
Context. The origin of the observed diversity of planetary system architectures is one of the main topics of exoplanetary research. The detection of a statistically significant sample of planets ...around young stars allows us to study the early stages of planet formation and evolution, but only a handful are known so far. In this regard a considerable contribution is expected from the NASA TESS satellite, which is now performing a survey of ~85% of the sky to search for short-period transiting planets. Aims. In its first month of operation TESS found a planet candidate with an orbital period of 8.14 days around a member of the Tuc-Hor young association (~40 Myr), the G6V main component of the binary system DS Tuc. If confirmed, it would be the first transiting planet around a young star suitable for radial velocity and/or atmospheric characterisation. Our aim is to validate the planetary nature of this companion and to measure its orbital and physical parameters. Methods. We obtained accurate planet parameters by coupling an independent reprocessing of the TESS light curve with improved stellar parameters and the dilution caused by the binary companion; we analysed high-precision archival radial velocities to impose an upper limit of about 0.1 MJup on the planet mass; we finally ruled out the presence of external companions beyond 40 au with adaptive optics images. Results. We confirm the presence of a young giant (R = 0.50 RJup) planet having a non-negligible possibility to be inflated (theoretical mass ≲ 20 M⊕) around DS Tuc A. We discuss the feasibility of mass determination, Rossiter-McLaughlin analysis, and atmosphere characterisation allowed by the brightness of the star.
Context.
Gyrochronology is one of the methods currently used to estimate the age of stellar open clusters. Hundreds of new clusters, associations, and moving groups unveiled by
Gaia
and complemented ...by accurate rotation period measurements provided by recent space missions such as
Kepler
and TESS are allowing us to significantly improve the reliability of this method.
Aims.
We use gyrochronology, that is, the calibrated age-mass-rotation relation valid for low-mass stars, to measure the age of the recently discovered moving group Group X.
Methods.
We extracted the light curves of all candidate members from the TESS full frame images and measured their rotation periods using different period search methods.
Results.
We measured the rotation period of 168 of a total of 218 stars and compared their period-colour distribution with those of two age-benchmark clusters, the Pleiades (125 Myr) and Praesepe (625 Myr), as well as with the recently characterised open cluster NGC 3532 (300 Myr).
Conclusions.
As result of our analysis, we derived a gyro age of 300 ± 60 Myr. We also applied as independent methods the fitting of the entire isochrone and of the three brightest candidate members individually with the most precise stellar parameters, deriving comparable values of 250 Myr and 290 Myr, respectively. Our dating of Group X allows us to definitively rule out the previously proposed connection with the nearby but much older Coma Berenices cluster.
Context. Examining the angular momentum of stars and its interplay with their magnetic fields represent a promising way to probe the stellar internal structure and evolution of low-mass stars. Aims. ...We attempt to determine the rotational and magnetic-related activity properties of stars at different stages of evolution.We focused our attention primarily on members of clusters and young stellar associations of known ages. In this study, our targets are 6 young loose stellar associations within 100 pc and with ages in the range 8–70 Myr: TW Hydrae (~8 Myr), β Pictoris (~10 Myr), Tucana/Horologium, Columba, Carina (~30 Myr), and AB Doradus (~70 Myr). Additional rotational data for α Persei and the Pleiades from the literature are also considered. Methods. Rotational periods of stars exhibiting rotational modulation due to photospheric magnetic activity (i.e., starspots) were determined by applying the Lomb-Scargle periodogram technique to photometric time-series data obtained by the All Sky Automated Survey (ASAS). The magnetic activity level was derived from the amplitude of the V lightcurves. The statistical significance of the rotational evolution at different ages was inferred by applying a two-sided Kolmogorov-Smirnov test to subsequent age-bins. Results. We detected the rotational modulation and measured the rotation periods of 93 stars for the first time, and confirmed the periods of 41 stars already known from the literature. For an additional 10 stars, we revised the period determinations by other authors. The sample was augmented with periods of 21 additional stars retrieved from the literature. In this way, for the first time we were able to determine the largest set of rotation periods at ages of ~8, ~10 and ~30 Myr, as well as increase by 150% the number of known periodic members of AB Dor. Conclusions. The analysis of the rotation periods in young stellar associations, supplemented by Orion Nebula Cluster (ONC) and NGC 2264 data from the literature, has allowed us to find that in the 0.6–1.2 $M_{\odot}$ range the most significant variations in the rotation period distribution are the spin-up between 9 and 30 Myr and the spin-down between 70 and 110 Myr. Variations of between 30 and 70 Myr are rather doubtful, despite the median period indicating a significant spin-up. The photospheric activity level is found to be correlated with rotation at ages greater than ~70 Myr and to show some additional age dependence besides that related to rotation and mass.
Aims. This is the first of a series of papers in which we present the results of a long-term photometric monitoring project carried out at Catania Astrophysical Observatory aimed at studying magnetic ...activity in late-type components of close binary systems, its dependence on global stellar parameters, and its evolution on different time scales from days to years. In this first paper, we present the complete observation dataset and new results of an investigation into the origin of brightness and color variations observed in the well-known magnetically active close binary stars: AR Psc, VY Ari, UX Ari, V711 Tau, EI Eri, V1149 Ori, DH Leo, HU Vir, RS CVn, V775 Her, AR Lac, SZ Psc, II Peg and BY Dra Methods. About 38 000 high-precision photoelectric nightly observations in the U, B and V filters are analysed. Correlation and regression analyses of the V magnitude vs. U-B and B-V color variations are carried out and a comparison with model variations for a grid of active region temperature and filling factor values is also performed. Results. We find the existence of two different patterns of color variation. Eight stars in our sample: BY Dra, VY Ari, V775 Her, II Peg, V1149 Ori, HU Vir, EI Eri and DH Leo become redder when they become fainter, as is expected from the presence of active regions consisting of cool spots. The other six stars show the opposite behaviour, i.e. they become bluer when they become fainter. For V711 Tau this behaviour could be explained by the increased relative U-and B-flux contribution by the earlier-type component of the binary system when the cooler component becomes fainter. On the other hand, for AR Psc, UX Ari, RS CVn, SZ Psc and AR Lac the existence of hot photospheric faculae must be invoked. We also found that in single-lined and double-lined binary stars in which the fainter component is inactive or much less active the V magnitude is correlated to B-V and U-B color variations in more than 60% of observation seasons. The correlation is found in less than 40% of observation seasons when the fainter component has a non-negligible level of activity and/or hot faculae are present but they are either spatially or temporally uncorrelated to spots.
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