Planet-hosting Stars Research Articles

Chemical composition of planetary hosts: C, N, and α-element abundances

Accurate atmospheric parameters and chemical composition of planet hosts play a major role in characterising exoplanets and understanding their formation and evolution. Our objective is to uniformly determine atmospheric parameters and chemical abundances of carbon (C), nitrogen (N), oxygen(O), and the alpha -elements, magnesium (Mg) and silicon (Si), along with C/O, N/O and Mg/Si abundance ratios for planet-hosting stars. In this analysis, we aim to investigate the potential links between stellar chemistry and the presence of planets. e tai Observatory telescope. The determination of stellar parameters was based on a standard analysis using equivalent widths and one-dimensional, plane-parallel model atmospheres calculated under the assumption of local thermodynamical equilibrium. The differential synthetic spectrum method was used to uniformly determine the carbon C(C2), nitrogen N(CN), oxygen O I magnesium Mg I, and silicon Si I elemental abundances as well as the C/O, N/O, and Mg/Si ratios. We analysed elemental abundances and ratios in dwarf and giant stars, finding that C/Fe O/Fe and Mg/Fe are lower in metal-rich dwarf hosts; whereas N/Fe is close to the Solar ratio. Giants show smaller scatter in C/Fe and O/Fe and lower than the Solar average C/Fe and C/O ratios. The (C+N+O) abundances increase with Fe/H in giant stars, with a minimal scatter. We also noted an overabundance of Mg and Si in planet-hosting stars, particularly at lower metallicities, and a lower Mg/Si ratio in stars with planets. In giants hosting high-mass planets, nitrogen shows a moderate positive relationship with planet mass. C/O and N/O ratios show moderate negative and positive slopes in giant stars, respectively. The Mg/Si ratio shows a negative correlation with planet mass across the entire stellar sample.

SWEET-Cat: A view on the planetary mass-radius relation

SWEET-Cat (Stars With ExoplanETs Catalog) was originally introduced in 2013, and since then, the number of confirmed exoplanets has increased significantly. A crucial step for a comprehensive understanding of these new worlds is the precise and homogeneous characterization of their host stars. We used a large number of high-resolution spectra to continue the addition of new stellar parameters for planet-hosting stars in SWEET-Cat following the new detection of exoplanets listed both in the Extrasolar Planets Encyclopedia and in the NASA exoplanet archive. We obtained high-resolution spectra for a significant number of these planet-hosting stars, either observed by our team or collected through public archives. For FGK stars, the spectroscopic stellar parameters were derived for the spectra following the same homogeneous process using ARES+MOOG as for the previous SWEET-Cat releases. The stellar properties were combined with the planet properties to study possible correlations that could shed more light on the star-planet connection studies. We have increased the number of stars with homogeneous parameters by 232 (sim 25<!PCT!> -- from 959 to 1191). We focus on the exoplanets that have had both mass and radius determined to review the mass-radius relation, and we find results consistent with the ones previously reported in the literature. For the massive planets, we also revisit the radius anomaly, confirming a metallicity correlation for the radius anomaly already hinted at in previous results.

Detailed Abundances of the Planet-hosting TOI-1173 A/B System: Possible Evidence of Planet Engulfment in a Very Wide Binary

Over the last decade, studies of large samples of binary systems have identified chemical anomalies and shown that they might be attributed to planet formation or planet engulfment. However, both scenarios have primarily been tested in pairs without known exoplanets. In this work, we explore these scenarios in the newly detected planet-hosting wide binary TOI-1173 A/B (projected separation ∼11,400 au), using high-resolution MAROON-X and ARCES spectra. We determined photospheric stellar parameters both by fitting stellar models and via the spectroscopic equilibrium approach. Both analyses agree and suggest that they are cool main-sequence stars located in the thin disk. A line-by-line differential analysis between the components (B−A) displays an abundance pattern in the condensation temperature plane, where the planet-hosting star TOI-1173 A is enhanced in refractory elements such as iron by more than 0.05 dex. This suggests the engulfment of ∼18 M ⊕ of rocky material in star A. Our hypothesis is supported by the dynamics of the system (detailed in our companion paper), which suggest that the super-Neptune TOI-1173 A b might have been delivered to its current short period (∼7 days) through circularization and von Zeipel–Lidov–Kozai mechanisms, thereby triggering the engulfment of inner rocky exoplanets.

The Star–Planet Composition Connection

The mantra “know thy star, know thy planet” has proven to be very important for many aspects of exoplanet science. Here I review how stellar abundances inform our understanding of planet composition and, thus, formation and evolution. In particular, I discuss how: ▪The strongest star–planet connection is still the giant planet–metallicity correlation, the strength of which may indicate a break point between the formation of planets versus brown dwarfs.▪We do not have very good constraints on the lower metallicity limit for planet formation, although new statistics from TESS are helping, and it appears that, at low [Fe/H], α elements can substitute for iron as seeds for planet formation.▪The depletion of refractory versus volatile elements in stellar photospheres (particularly the Sun) was initially suggested as a sign of small planet formation but is challenging to interpret, and small differences in binary star compositions can be attributed mostly to processes other than planet formation.▪We can and should go beyond comparisons of the carbon-to-oxygen ratio in giant planets and their host stars, incorporating other volatile and refractory species to better constrain planet formation pathways.▪There appears to be a positive correlation between small planet bulk density and host star metallicity, but exactly how closely small planet refractory compositions match those of their host stars—and their true diversity—is still uncertain.

Do anomalously dense hot Jupiters orbit stealth binary stars?

ABSTRACT The Wide Angle Search for Planets (WASP) survey used transit photometry to discover nearly 200 gas-giant exoplanets and derive their planetary and stellar parameters. Reliable determination of the planetary density depends on accurate measurement of the planet’s radius, obtained from the transit depth and photodynamical determination of the stellar radius. The stellar density and hence the stellar radius are typically determined in a model-independent way from the star’s reflex orbital acceleration and the transit profile. Additional flux coming from the system due to a bright, undetected stellar binary companion can, however, potentially dilute the transit curve and radial velocity signal, leading to underestimation of the planet’s mass and radius, and to overestimation of the planet’s density. In this study, we cross-check the published radii of all the WASP planet-host stars, determined from their transit profiles and radial velocity curves, against radiometric measurements of stellar radii derived from their angular diameters (via the infrared flux method) and trigonometric parallaxes. We identify eight systems showing radiometric stellar radii significantly greater than their published photodynamical values: WASPs 20, 85, 86, 103, 105, 129, 144, and 171. We investigate these systems in more detail to establish plausible ranges of angular and radial velocity separations within which such ‘stealth binaries’ could evade detection, and deduce their likely orbital periods, mass ratios, and flux ratios. After accounting for the dilution of transit depth and radial velocity amplitude, we find that, on average, the planetary densities for the identified stealth binary systems should be reduced by a factor of 1.3.

Statistics and Habitability of F-type Star–Planet Systems

F-type star–planet systems represent an intriguing case for habitability studies. Although F-type stars spend considerably less time on the main sequence (MS) than G-, K-, and M-type stars, they still offer a unique set of features, allowing for the principal possibility of exolife. Examples of these features include the increased widths of stellar habitable zones as well as the presence of enhanced UV flux, which in moderation may have added to the origin of life in the Universe. In this study, we pursue a detailed statistical analysis of the currently known planet-hosting F-type stars by making use of the NASA Exoplanet Archive. After disregarding systems with little or no information on the planet(s), we identify 206 systems of interest. We also evaluate whether the stars are on the MS based on various criteria. In one approach, we use the stellar evolution code MESA. Depending on the adopted criterion, about 60–80 stars have been identified as MS stars. In 18 systems, the planet spends at least part of its orbit within the stellar habitable zone. In one case, i.e., HD 111998, known as 38 Vir, the planet is situated in the habitable zone at all times. Our work may serve as a basis for future studies, including studies on the existence of Earth-mass planets in F-type systems, as well as investigations of possibly habitable exomoons hosted by exo-Jupiters, as the lowest-mass habitable zone planet currently identified has a mass estimate of 143 Earth masses.

Connections between Planetary Populations and Chemical Characteristics of Their Host Stars

Chemical anomalies in planet-hosting stars (PHSs) are studied in order to assess how the planetary nature and multiplicity affect the atmospheric chemical abundances of their host stars. We employ APOGEE DR17 to select thin-disk stars of the Milky Way, and crossmatch them with the Kepler Input Catalog to identify confirmed PHSs, which results in 227 PHSs with available chemical abundance ratios for six refractory elements. We also examine an ensemble of stars without planet signals, which are equivalent to the selected PHSs in terms of evolutionary stage and stellar parameters, to correct for Galactic chemical evolution effects, and derive the abundance gradient of refractory elements over the condensation temperature for the PHSs. Using the Galactic chemical evolution corrected abundances, we find that our PHSs do not show a significant difference in abundance slope from the stars without planets. However, when we examine the trends of the refractory elements of PHSs, based on the total number of their planets and their planet types, we find that the PHSs with giant planets are more depleted in refractory elements than those with rocky planets. Among the PHSs with rocky planets, the refractory depletion trends are potentially correlated with the terrestrial planets’ radii and multiplicity. In the cases of PHSs with giant planets, sub-Jovian PHSs demonstrate more depleted refractory trends than stars hosting Jovian-mass planets, raising questions on different planetary formation processes for Neptune-like and Jupiter-like planets.

Unveiling MOA-2007-BLG-192: An M Dwarf Hosting a Likely Super-Earth

We present an analysis of high-angular-resolution images of the microlensing target MOA-2007-BLG-192 using Keck adaptive optics and the Hubble Space Telescope. The planetary host star is robustly detected as it separates from the background source star in nearly all of the Keck and Hubble data. The amplitude and direction of the lens–source separation allows us to break a degeneracy related to the microlensing parallax and source radius crossing time. Thus, we are able to reduce the number of possible binary-lens solutions by a factor of ∼2, demonstrating the power of high-angular-resolution follow-up imaging for events with sparse light-curve coverage. Following Bennett et al., we apply constraints from the high-resolution imaging on the light-curve modeling to find host star and planet masses of M host = 0.28 ± 0.04 M ☉ and mp=12.49−8.03+65.47M⊕ at a distance from Earth of D L = 2.16 ± 0.30 kpc. This work illustrates the necessity for the Nancy Grace Roman Galactic Exoplanet Survey to use its own high-resolution imaging to inform light-curve modeling for microlensing planets that the mission discovers.

Evolution of Flare Activity in GKM Stars Younger Than 300 Myr over Five Years of TESS Observations

Stellar flares are short-duration (< hours) bursts of radiation associated with surface magnetic reconnection events. Stellar magnetic activity generally decreases as a function of both the age and Rossby number, R 0, a measure of the relative importance of the convective and rotational dynamos. Young stars (<300 Myr) have typically been overlooked in population-level flare studies due to challenges with flare-detection methods. Here, we select a sample of stars that are members of 26 nearby moving groups, clusters, or associations with ages <300 Myr that have been observed by the Transiting Exoplanet Survey Satellite at 2 minute cadence. We identified 26,355 flares originating from 3160 stars and robustly measured the rotation periods of 1847 stars. We measure and find the flare frequency distribution slope, α, saturates for all spectral types at α ∼ −0.5 and is constant over 300 Myr. Additionally, we find that flare rates for stars t age = 50–250 Myr are saturated below R 0 < 0.14, which is consistent with other indicators of magnetic activity. We find evidence of annual flare rate variability in eleven stars, potentially correlated with long-term stellar activity cycles. Additionally, we crossmatch our entire sample with the Galaxy Evolution Explorer and find no correlation between flare rate and far- and near-ultraviolet flux. Finally, we find the flare rates of planet-hosting stars are relatively lower than comparable, larger samples of stars, which may have ramifications for the atmospheric evolution of short-period exoplanets.

Stellar Characterization and a Chromospheric Activity Analysis of a K2 Sample of Planet-hosting Stars

Effective temperatures, surface gravities, and iron abundances were derived for 109 stars observed by the K2 mission using equivalent width measurements of Fe i and Fe ii lines. Calculations were carried out in local thermodynamic equilibrium using Kurucz model atmospheres. Stellar masses and radii were derived by combining the stellar parameters with Gaia Data Release 3 parallaxes, V magnitudes, and isochrones. The derived stellar and planetary radii have a median internal precision of 1.8% and 2.3%, respectively. The radius gap near R planet ∼ 1.9 R ⊕ was detected in this K2 sample. Chromospheric activity was measured from the Ca ii H and K lines using the values of logRHK′ , which were investigated as a function of stellar rotational period (P rot), and we found that chromospheric activity decreases with increasing P rot, although there is a large scatter in logRHK′ (∼0.5) for a given P rot. The activity levels in this sample reveal a paucity of F and G dwarfs with intermediate activity levels (the Vaughan–Preston gap). The effect that stellar activity might have on the derivation of stellar parameters was investigated by including magnetically sensitive Fe i lines in the analysis and we find no significant differences between parameters with and without magnetically sensitive lines, although the more active stars ( logRHK′>−5.0 ) exhibit a larger scatter in the differences in T eff and [Fe/H].

A Larger Sample Confirms Small Planets around Hot Stars Are Misaligned ∗ ∗ The data presented herein were obtained at the W. M. Keck Observatory, operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M.

The distribution of stellar obliquities provides critical insight into the formation and evolution pathways of exoplanets. In the past decade, it was found that hot stars hosting hot Jupiters are more likely to have high obliquities than cool stars, but it is not clear whether this trend exists only for hot Jupiters or holds for other types of planets. In this work, we extend the study of the obliquities of hot (6250–7000 K) stars with transiting super-Earth-sized and sub-Neptune-sized planets. We constrain the obliquity distribution based on measurements of the stars’ projected rotation velocities. Our sample consists of 170 TESS and Kepler planet-hosting stars and 180 control stars chosen to have indistinguishable spectroscopic characteristics. In our analysis, we find evidence suggesting that the planet hosts have a systematically higher 〈sini〉 compared to the control sample. This result implies that the planet hosts tend to have lower obliquities. However, the observed difference in 〈sini〉 is not significant enough to confirm spin–orbit alignment as it is 3.8σ away from perfect alignment. We also find evidence that within the planet-hosting stars there is a trend of higher obliquity (lower 〈sini〉 ) for the hotter stars (T eff > 6250 K) than for the cooler stars in the sample. This suggests that hot stars hosting smaller planets exhibit a broader obliquity distribution ( 〈sini〉=0.79±0.053 ) than cooler planet-hosting stars, indicating that high obliquities are not exclusive to hot Jupiters and instead are more broadly tied to hot stars.

No Signature of the Birth Environment of Exoplanets from Their Host Stars’ Mahalanobis Phase Space

The architectures of extrasolar planetary systems often deviate considerably from the “standard” model for planet formation, which is largely based on our own solar system. In particular, gas giants on close orbits are not predicted by planet formation theory and so some processes are thought to move the planets closer to their host stars. Recent research has suggested that hot-Jupiter host stars display a different phase space compared to stars that do not host hot Jupiters. This has been attributed to these stars forming in star-forming regions of high stellar density, where dynamical interactions with passing stars have perturbed the planets. We test this hypothesis by quantifying the phase space of planet-hosting stars in dynamical N-body simulations of star-forming regions. We find that stars that retain their planets have a higher phase space than nonhosts, regardless of their initial physical density. This is because an imprint of the kinematic substructure from the regions birth is retained, as these stars have experienced fewer and less disruptive encounters than stars whose planets have been liberated and become free-floating. However, host stars whose planets remain bound but have had their orbits significantly altered by dynamical encounters are also primarily found in high phase space regimes. We therefore corroborate other research in this area that has suggested the high phase space of hot-Jupiter host stars is not caused by dynamical encounters or stellar clustering, but rather reflects an age bias in that these stars are (kinematically) younger than other exoplanet host stars.

Age Analysis of Extrasolar Planets: Insight from Stellar Isochrone Models

There is growing evidence from stellar kinematics and galactic chemical evolution suggesting that giant planets (M P ≥ 0.3M J ) are relatively young compared to the most commonly occurring population of small planets (M P < 0.3M J ). To further test the validity of these results, we analyzed the ages for a large number of 2336 exoplanet hosting stars determined using three different but well-established isochrone fitting models, namely, PARSEC, MIST, and Yonsei Yale. As input parameters, we used Gaia DR3 parallaxes, magnitudes, and photometric temperature, as well as spectroscopically determined more accurate temperatures and metallicities from the Sweet Catalog. Our analysis suggests that ∼50%–70% of stars with planets are younger than the Sun. We also find that, among the confirmed exoplanetary systems, stars hosting giant planets are even younger compared to small planet hosts. The median age of ∼2.61–3.48 Gyr estimated for the giant planet-hosting stars (depending on the model input parameters) suggests that the later chemical enrichment of the galaxy by the iron-peak elements, largely produced from Type Ia supernovae, may have paved the way for the formation of gas giants. Furthermore, within the giant planet population itself, stars hosting hot Jupiters (orbital period ≤10 days) are found to be younger compared to the stellar hosts of cool and warm Jupiters (orbital period >10 days), implying that hot Jupiters could be the youngest systems to emerge in the progression of planet formation.

The Kinematic and Chemical Properties of the Close-in Planet Host Star 8 UMi

A recent study by Hon et al. reported that a close-in planet around the red clump star, 8 UMi, should have been engulfed during the expansion phase of its parent star’s evolution. They explained the survival of this exoplanet through a binary-merger channel for 8 UMi. The key to testing this formation scenario is to derive the true age of this star: is it an old “imposter” resulting from a binary merger, or a genuinely young red clump giant? To accomplish this, we derive kinematic and chemical properties for 8 UMi using astrometric data from Gaia DR3 and the element-abundance pattern measured from a high-resolution (R ∼ 75,000) spectrum taken by SOPHIE. Our analysis shows that 8 UMi is a normal thin-disk star with orbital rotation speed of V ϕ = 244.96 km s−1, and possesses a solar metallicity ([Fe/H] = −0.05 ± 0.07) and α-element-abundance ratio ([α/Fe] = +0.01 ± 0.03). By adopting well-established relationships between age and space velocities/elemental abundances, we estimate a kinematic age of 3.50−2.00+3.00 Gyr, and a chemical age of 3.25−1.50+2.50 Gyr from [C/N] and 3.47 ± 1.96 Gyr from [Y/Mg] for 8 UMi, respectively. These estimates are consistent with the isochrone-fitting age ( 1.90−0.30+1.15 Gyr) of 8 UMi, but are all much younger than the timescale required in a binary-merger scenario. This result challenges the binary-merger model; the existence of such a closely orbiting exoplanet around a giant star remains a mystery yet to be resolved.

Metallicities and Refined Stellar Parameters for 52 Cool Dwarfs with Transiting Planets and Planet Candidates

We collected near-infrared spectra of 65 cool stars with the NASA Infrared Telescope Facility and analyzed them to calculate accurate metallicities and stellar parameters. The sample of 55 M dwarfs and 10 K dwarfs includes 25 systems with confirmed planets and 27 systems with planet candidates identified by the K2 and TESS missions. Three of the 25 confirmed planetary systems host multiple confirmed planets and two of the 27 planet candidate systems host multiple planet candidates. Using the new stellar parameters, we refit the K2 and TESS light curves to calculate updated planet properties. In general, our updated stellar properties are more precise than those previously reported and our updated planet properties agree well with those in the literature. Lastly, we briefly examine the relationship between stellar mass, stellar metallicity, and planetary system properties for targets in our sample and for previously characterized planet-hosting low-mass stars. We provide our spectra, stellar parameters, and new planetary fits to the community, expanding the sample available with which to investigate correlations between stellar and planetary properties for low-mass stars.

In This Day and Age: An Empirical Gyrochronology Relation for Partially and Fully Convective Single Field Stars

Gyrochronology, the field of age dating stars using mainly their rotation periods and masses, is ideal for inferring the ages of individual main-sequence stars. However, due to the lack of physical understanding of the complex magnetic fields in stars, gyrochronology relies heavily on empirical calibrations that require consistent and reliable stellar age measurements across a wide range of periods and masses. In this paper, we obtain a sample of consistent ages using the gyro-kinematic age-dating method, a technique to calculate the kinematics ages of stars. Using a Gaussian process model conditioned on ages from this sample (∼1–14 Gyr) and known clusters (0.67–3.8 Gyr), we calibrate the first empirical gyrochronology relation that is capable of inferring ages for single, main-sequence stars between 0.67 and 14 Gyr. Cross-validating and testing results suggest our model can infer cluster and asteroseismic ages with an average uncertainty of just over 1 Gyr, and the inferred ages for wide binaries agree within 0.83 Gyr. With this model, we obtain gyrochronology ages for ∼100,000 stars within 1.5 kpc of the Sun with period measurements from Kepler and Zwicky Transient Facility and 384 unique planet host stars. A simple code is provided to infer gyrochronology ages of stars with temperature and period measurements.

The GAPS programme at TNG

Context. The intrinsic variability due to the magnetic activity of young active stars is one of the main challenges in detecting and characterising exoplanets. The stellar activity is responsible for jitter effects observed both in photometric and spectroscopic observations that can impact our planetary detection sensitivity. Aims. We present a method able to model the stellar photosphere and its surface inhomogeneities (starspots) in young, active, and fast-rotating stars based on the cross-correlation function (CCF) technique, and we extract information about the spot configuration of the star. Methods. We developed Spot CCF, a tool able to model the deformation of the CCF profile due to the presence of multiple spots on the stellar surface. Within the Global Architecture of Planetary Systems (GAPS) Project at the Telescopio Nazionale Galileo, we analysed more than 300 spectra of the young planet-hosting star V1298 Tau provided by the HARPS-N high-resolution spectrograph. By applying the SpotCCF model to the CCFs, we extracted the spot configuration (latitude, longitude, and projected filling factor) of this star, and provide a new radial velocity (RV) time series for this target. Results. We find that the features identified in the CCF profiles of V1298 Tau are modulated by the stellar rotation, supporting our assumption that they are caused by starspots. The analysis suggests a differential rotation velocity of the star with lower rotation at higher latitudes. Also, we find that SpotCCF provides an improvement in RV extraction, with a significantly lower dispersion with respect to the commonly used pipelines. This allows mitigation of the stellar activity contribution modulated with stellar rotation. A detection sensitivity test, involving the direct injection of a planetary signal into the data, confirms that the SpotCCF model improves the sensitivity and ability to recover planetary signals. Conclusions. Our method enables us to model the stellar photosphere and extract the spot configuration of young, active, and rapidly rotating stars. It also allows the extraction of optimised RV time series, thereby enhancing our detection capabilities for new exoplanets and advancing our understanding of stellar activity.

Constraining planetary formation models using conditional occurrences of various planet types

ABSTRACT We report the conditional occurrences between three planetary types: super-Earths (m sin i &amp;lt; 10 M⊕, P &amp;lt; 100 d), warm Jupiters (m sin i &amp;gt; 95 M⊕, 10 &amp;lt; P &amp;lt; 100 d), and cold Jupiters (m sin i &amp;gt; 95 M⊕, P &amp;gt; 400 d) for sun-like stars. We find that while the occurrence of cold Jupiters in systems with super-Earths is $22.2\substack{+8.3 \\ -5.4}$ per cent, compared to 10 per cent for the absolute occurrence rate of cold Jupiters, the occurrence of super-Earths in systems with cold Jupiters is $66.0\substack{+18.0 \\ -16.0}$ per cent, compared to 30 per cent for the absolute occurrence rate of super-Earths for Sun-like stars. We find that the enhancement of super-Earths in systems with cold Jupiters is evident for Sun-like stars, in agreement with several previous studies. We also conduct occurrence studies between warm Jupiters and super-Earths, and between warm Jupiters and cold Jupiters, to consolidate our methods. We conduct an independent observational test to study the effects of cold Jupiters against the inner multiplicity using the well-established giant planet host star metallicity correlation for all transiting planets found to date. The conditional occurrences we find here can be used to constrain the validity of various planetary formation models. The extremely interesting correlations between the super-Earths, cold Jupiters, and warm Jupiters can also be used to understand the formation histories of these planetary types.

The California-Kepler Survey. XI. A Survey of Chromospheric Activity through the Lens of Precise Stellar Properties

Surveys of exoplanet host stars are valuable tools for assessing population level trends in exoplanets, and their outputs can include stellar ages, activity, and rotation periods. We extracted chromospheric activity measurements from the California-Kepler Survey Gaia survey spectra in order to probe connections between stellar activity and fundamental stellar properties. Building on the California Kepler Survey's legacy of 1189 planet host star stellar properties including temperature, surface gravity metallicity, and isochronal age, we add measurements of the Ca ii H and K lines as a proxy for chromospheric activity for 879 planet hosting stars. We used these chromospheric activity measurements to derive stellar rotation periods. We find a discrepancy between photometrically derived and activity-derived rotation periods for stars on the Rossby Ridge. These results support the theory of weakened magnetic braking. We find no evidence for metallicity-dependent activity relations, within the metallicity range of −0.2 to +0.3 dex. With our single epoch spectra we identify stars that are potentially in Maunder minimum–like state using a combination of log( RHK′ ) and position below the main sequence. We do not yet have the multiyear time series needed to verify stars in Maunder minimum–like states. These results can help inform future theoretical studies that explore the relationship between stellar activity, stellar rotation, and magnetic dynamos.

Fractal Architecture of the Universe Based on Primary-Centric World-View - A Post Copernican Conjecture

This paper investigates the fractal architecture of our Universe based on Primary-Centric Theoretical Formulation. Through theoretical analysis of Earth-Moon System, I arrived at the planetary satellite dynamics which was found to apply equally well to Solar and Exo-solar systems. This gave the theoretical foundation of the New Perspective of the birth and evolution of Exo-solar Systems. This was further extended to the theoretical analysis of star pairs and Neutron-Star pairs. This laid down the Primarycentric World View which I postulate as the physical process which has been shaping the evolution of the Universe and the hot-spots of the Cosmic Microwave Background Radiation right from 380,000 yrs after the Big Bang to date in top-down model resulting into Super-clusters, Clusters, Galaxies and Solar Systems. Primary-centric analysis corresponds to keplerian Analysis for negligibly small mass ratio less than 0.001. In the Copernican Framework, Kepler’s Third Law places no restriction on the orbit of the secondary component in a celestial pair. In Primary Centric Framework there is a very definite constraint on the permitted stable orbit, introduced due to periodic tidal deformations . There are two Clarke’s Orbits which are fully circularized and synchronized and hence nondissipative and equilibrium orbits called inner and outer Clarke's orbits equivalent to two geosynchronous orbits in Earth-Moon scenario. Outer Clarke’s Orbit is permissible as a stable orbit if the mass ratio of secondary to primary is greater than 0.2, Inner Clarke’s Orbit is permissible if mass ratio is less than 10-4 . If the mass ratio is between 10-4 to 0.2 then secondary spirals-out from inner Clarke’s Orbit to outer Clarke’s Orbit if it tumbles into super-synchronous orbit and spirals-in if it tumbles into sub-synchronous orbit destined to be destroyed by the primary. My conjecture states that every cosmological sub-system has a Monarch (or dominant) Primary (M_primary) Component anchoring the given sub-system and this Primary decides the stable equilibrium orbits of the secondary/secondaries. Planet-Satellite has a Planet as the M_primary, Solar System and exo-Solar Systems have a planet hosting star (PHS) as the M_primary, Galaxy has a Super-Massive Black Hole(SMBH) as the M_primary, Cluster has a cD galaxy (central dominant Galaxy) which is also known as Brightest Cluster Galaxy(BCG) as the M_primary, Super-Cluster has a massive Cluster hosting a QUASER/Blazer as the M_primary. This goes adinfinitum until a Cosmic Web is woven with Cosmic filaments. This conjecture gains a definite credence after the recent discoveries of the over-massive Black Holes in M_Galaxies namely Messier 87 in Virgo Cluster, NGC 3842 in Leo Cluster, NGC 4889 in Coma Cluster[68] and NGC 1277 in Perseus Cluster[66] which had been proposed as M_Galaxies on general considerations even before the confirmation of over-massive black holes. In 2011, a group of floating planets have been discovered. This is a transitory event and is an exception to this conjecture.