Lithium Depletion Research Articles

The Li–age correlation: the Sun is unusually Li deficient for its age

The present work aims to examine in detail the depletion of lithium in solar twins to better constrain stellar evolution models and investigate its possible connection with exoplanets. We employ spectral synthesis in the region of the asymmetric 6707.75 \AA Li I line for a sample of 77 stars plus the Sun. As in previous works based on a smaller sample of solar twins, we find a strong correlation between Li depletion and stellar age. In addition, for the first time we show that the Sun has the lowest Li abundance in comparison with solar twins at similar age (4.6 $\pm$ 0.5 Gyr). We compare the lithium content with the condensation temperature slope for a sub-sample of the best solar twins and determine that the most lithium depleted stars also have fewer refractory elements. We speculate whether the low lithium content in the Sun might be related to the particular configuration of our Solar system.

Tailoring sandwich-like CNT@MnO@N-doped carbon hetero-nanotubes as advanced anodes for boosting lithium storage

Currently, constructing an advanced structure to address the weaknesses of MnO-based anode materials in regard to large volume variation upon cycling and inferior conductivity still needs to be further improved for endowing the MnO anode with a desirable lithium-storage performance. Herein, an ingenious sandwich-like CNT@MnO@N-doped carbon coating (NC) hetero-nanotube architecture with partial MnO being inlaid into CNT is synthesized through an elaborate route including template and coating strategy and utilized as a hopeful lithium-ion anode material exhibiting large specific capacity, long-term cyclability, and high rate capacity synchronously. The outer NC layer could not only enhance the electro-conductibility of MnO as well as efficiently confine the reaggregation and ameliorate the volume variation of MnO nanoparticles upon cycling, but also avert the direct contact between MnO and electrolyte which could lead to the unexpected depletion of lithium. The inner CNT could ensure the 1D hetero-nanotube structure benefiting to preserve the structural integrity during cycling, and also facilitate the electron transport. Additionally, the inlaying of MnO nanoparticles into CNT could boost the transfer and storage of lithium ion. Therefore, the CNT@MnO@NC electrode reveals a high Li+ storage capacity (665 mAh g−1 at 0.1 A g−1), outstanding cycling performance (617 mAh g−1 after 500 cycles at 1 A g−1) and superior rate capability (421 mAh g−1 at 2.0 A g−1), calculating based on the weight of CNT@MnO@NC composite. According to kinetic study, it is uncovered that the CNT@MnO@NC electrode presents an enhanced capacitive effect towards Li+ storage, featuring with the characteristic faradaic surface pseudocapacitive charge-storage mechanism. This work puts forward a promising strategy to prepare 1D heterostructured anode materials with improved conductivity and structure stability for boosting lithium-storage.

Incorporating Dendrite Growth into Continuum Models of Electrolytes: Insights from NMR Measurements and Inverse Modeling

In this work we develop a combined experimental and inverse continuum modeling approach to the problem of determining properties of a lithium electrolyte from NMR measurements of ion concentration in a test cell. The experimental set-up consists of an enclosed, lithium-electrolyte-filled tube with lithium electrodes at either end. A constant current is passed between these electrodes and the resulting evolution of the spatial distribution of the lithium ions is monitored using NMR imaging techniques. Using the recently developed tools of inverse modeling, in combination with the concentration measurements acquired with NMR imaging, it is shown that the standard Planck-Nernst electrolyte model results in predictions of negative transference numbers. The observation of growing lithium dendrites on the cathode suggests the cause for these unphysical predictions and motivates the formulation of a generalized Planck-Nernst model that explicitly accounts for the presence of these growing lithium-metal dendrites. In this approach, lithium depletion in a dendritic region adjacent to the cathode is modelled by adding a suitably-chosen spatially distributed sink term. It is demonstrated that a model in which lithium is lost from the electrolyte uniformly throughout the dendritic region provides predictions of electrolyte data consistent with the literature and thereby remedies the shortcoming of the standard Planck-Nernst model. In addition, a state-of-the-art Bayesian technique is used to quantify the uncertainty of the inferred material properties.

Addressing the acoustic tachocline anomaly and the lithium depletion problem at the same time

Current standard solar models neither account properly for the photospheric lithium abundance nor reproduce the inferred solar sound speed profile. Diffusive overshooting at the base of the solar convective envelope has previously been shown to solve either of these model inadequacies. In this paper, we present an analysis of solar models with four different parametrizations of diffusive overshooting. We find that these models are able to recover the correct lithium depletion, regardless of the parametrization, if overshooting is suppressed, during the early evolutionary stages. Further, parametrizations of diffusive overshooting have been shown to improve the inferred sound speed profile. However, none of the presented models are able to simultaneously solve both model inadequacies, showing that diffusive overshooting on its own is deficient to account for observations.

Improved Main-sequence Turnoff Ages of Young Open Clusters: Multicolor UBV Techniques and the Challenges of Rotation

Abstract Main-sequence turnoff ages in young open clusters are complicated by turnoffs that are sparse, have high binarity fractions, can be affected by differential reddening, and typically include a number of peculiar stars. Furthermore, stellar rotation can have a significant effect on a star’s photometry and evolutionary timescale. In this paper we analyze in 12 nearby open clusters, ranging in age from 50 to 350 Myr, how broadband UBV color–color relations can be used to identify turnoff stars that are Be stars, blue stragglers, certain types of binaries, or those affected by differential reddening. This UBV color–color analysis also directly measures a cluster’s E(B − V) and estimates its [Fe/H]. The turnoff stars unaffected by these peculiarities create a narrower and more clearly defined cluster turnoff. Using four common isochronal models, two of which consider rotation, we fit cluster parameters using these selected turnoff stars and the main sequence. Comparisons of the photometrically fit cluster distances to those based on parallaxes from Gaia data release 2 find that they are consistent for all clusters. For older (>100 Myr) clusters, such as the Pleiades and the Hyades, comparisons to ages based on the lithium depletion boundary method find that these cleaned turnoff ages agree to within ∼10% for all four isochronal models. For younger clusters, however, only the Geneva models that consider rotation fit turnoff ages consistent with lithium-based ages, while the ages based on non-rotating isochrones quickly diverge to become 30%–80% younger. This illustrates the importance of rotation in deriving ages in the youngest (<100 Myr) clusters.

(Invited) Influences of Interfaces on Performance of Solid-State Batteries

Lithium-ion batteries have been used in portable equipment as a key component in an information society. In addition, much larger batteries are now required for energy storage in vehicles and smart grids. We have to tackle the inherent issues, which originate from non-aqueous electrolytes, in lithium-ion batteries again for developing the large batteries. The increasing size makes the safety issues more serious due to the increasing amounts of flammable electrolytes and the lowering heat radiation. Moreover, much longer durability is required for large batteries; however, the current liquid electrolytes are not stable enough to meet this requirement. Solid electrolytes are expected to provide fundamental solutions to these issues. Solid-state batteries had been suffering from the low power density due to low ionic conductivities of solid electrolytes. On the other hand, the highest ionic conductivities have reached 10−2 S cm−1 among sulfides, which is comparable to, or even higher than that of the liquid electrolytes, when the transport number of unity is taken into account. Since ionic conductivities of solid electrolytes have become high enough, interfaces between the battery materials are now playing critical roles in battery performance, which can be recognized in a recent paper that reports higher power density in a solid-state battery than in liquid systems [1]. The high-power solid-state battery indeed employ a solid electrolyte with high ionic conductivity of 2.5 × 10−2 S cm−1; however, it also uses some materials that are not highly-conductive curiously [2]. Surface of the cathode material, LiCoO2, is covered with LiNbO3, although the ionic conductivity of LiNbO3 is only of the order of 10−6 S cm−1. In addition, Li4Ti5O12 is used as the anode in the batteries, although it is poor in ionic conduction and electronically insulating. The reasons for their use can be understood by anomalous transport properties at the interfaces. Although some sulfide electrolytes exhibit high ionic conductivity, they show so high resistance at the interface to high-voltage cathodes that LiNbO3 interposed at the interface lowers the interfacial resistance in spite of its low ionic conductivity. The LiNbO3 eliminates the origin of the huge resistance, which is lithium depletion at the interface, because it is an oxide-based solid electrolyte. On the other hand, electrode reactions promote mass transfer. The lithium insertion does not generate interstitials that contribute to ionic conduction, because it proceeds under a two-phase reaction between Li4Ti5O12 and Li7Ti5O12. Moreover, the Li7Ti5O12 is also a bad conductor; however, the electrode reaction is promoted due to the enhanced transport at the Li4Ti5O12/Li7Ti5O12 interface [3]. [1] Y. Kato, S. Hori, T. Saito, K. Suzuki, M. Hirayama, A. Mitsui, M. Yonemura, H. Iba. R. Kanno, Nat. Energy 1, 16030 (2016). [2] K. Takada, T. Ohno, N. Ohta, T. Ohnishi, and Y. Tanaka, ACS Energy Lett., 3, 98 (2018). [3] Y. Tanaka, M. Ikeda, M. Sumita, T. Ohno, and K. Takada, Phys. Chem. Chem. Phys., 18, 23383 (2016).

Exploring the production and depletion of lithium in the Milky Way stellar disk

Despite the recent availability of large samples of stars with high-precision Li abundances, there are many unanswered questions about the evolution of this unique element in the Galaxy and in the stars themselves. It is unclear which parameters and physical mechanisms govern Li depletion in late-type stars and if Galactic enrichment has proceeded differently in different stellar populations. With this study we aim to explore these questions further by mapping the evolution of Li with stellar mass, age, and effective temperature for Milky Way disk stars, linking the metal-poor and metal-rich regimes, and how Li differs in the thin and thick disks. We determine Li abundances for a well-studied sample of 714 F and G dwarf, turn-off, and subgiant stars in the solar neighbourhood. The analysis is based on line synthesis of the 7Li line at 6707 Å in high-resolution and high-signal-to-noise ratio echelle spectra, obtained with the MIKE, FEROS, SOFIN, UVES, and FIES spectrographs. The presented Li abundances are corrected for non-LTE effects. Out of the sample of 714 stars, we are able to determine Li abundances for 394 stars and upper limits on the Li abundance for another 121 stars. Out of 36 stars that are listed as exoplanet host stars, 18 have well-determined Li abundances and 6 have Li upper limits. Our main finding is that there are no signatures of Li production in stars associated with the thick disk. Instead the Li abundance trend is decreasing with metallicity for these thick disk stars. Significant Li production is however seen in the thin disk, with a steady increase towards super-solar metallicities. At the highest metallicities, however, around [Fe/H] ≈ +0.3, we tentatively confirm the recent discovery that the Li abundances level out. Our finding contradicts the other recent studies that found that Li is also produced in the thick disk. We find that this is likely due to the α-enhancement criteria which those studies used to define their thick disk samples. By using the more robust age criteria, we are able to define a thick disk stellar sample that is much less contaminated by thin disk stars. Furthermore, we also tentatively confirm the age-Li correlation for solar twin stars, and we find that there is no correlation between Li abundance and whether the stars have detected exoplanets or not. The major conclusion that can be drawn from this study is that no significant Li production relative to the primordial abundance took place during the first few billion years of the Milky Way, an era coinciding with the formation and evolution of the thick disk. Significant Li enrichment then took place once long-lived low-mass stars (acting on a timescale longer than SNIa) had had time to contribute to the chemical enrichment of the interstellar medium.

Lithium in the Hyades L5 brown dwarf 2MASS J04183483+2131275

Aims. From the luminosity, effective temperature and age of the Hyades brown dwarf 2MASS J04183483+2131275 (2M0418), substellar evolutionary models predict a mass in the range 39−55 Jupiter masses (MJup) which is insufficient to produce any substantial lithium burning except for the very upper range >53 MJup. Our goal is to measure the abundance of lithium in this object, test the consistency between models and observations and refine constraints on the mass and age of the object. Methods. We used the 10.4-m Gran Telescopio Canarias (GTC) with its low-dispersion optical spectrograph to obtain ten spectra of 2277 s each covering the range 6300–10 300 Å with a resolving power of R ~ 500. Results. In the individual spectra, which span several months, we detect persistent unresolved Hα in emission with pseudo equivalent widths (pEW) in the range 45–150 Å and absorption lines of various alkalis with the typical strengths found in objects of L5 spectral type. The lithium resonance line at 6707.8 Å is detected with pEW of 18 ± 4 Å in 2M0418 (L5). Conclusions. We determine a lithium abundance of log N(Li) = 3.0 ± 0.4 dex consistent with a minimum preservation of 90% of this element which confirms 2M0418 as a brown dwarf with a maximum mass of 52 MJup. We infer a maximum age for the Hyades of 775 Myr from a comparison with the BHAC15 models. Combining recent results from the literature with our study, we constrain the mass of 2M0418 to 45–52 MJup and the age of the cluster to 580–775 Myr (1σ) based on the lithium depletion boundary method.

Challenges regarding thin film deposition of garnet electrolytes for all-solid-state lithium batteries with high energy density

In this work, we studied the deposition of garnet electrolyte thin films in order to realize an all-solid-state battery with high energy density. Therefore, in a first step we investigated the stability of the garnet Li5La3Ta2O12 with the spinel LiCoMnO4 in order to determine the temperature window for a successful thin film deposition on high-voltage spinels. A mixture of both materials showed a thermal stability up to 600 °C, so that all-solid-state batteries could be realized when the electrolyte is applied at a low deposition temperature. The second part of the work was the thin film deposition of Li5La3Ta2O12 by a sputter deposition process. When a stoichiometric Li5La3Ta2O12 sputter target was used, the surface of the target showed a depletion of lithium after several depositions, which leads to decreasing Li content in the thin films. In order to compensate the lithium loss we enriched the target with LiOH∙H2O. Depositions carried out with the lithium rich target showed the garnet structure on glass substrates after deposition at 500 °C. The garnet structure was observed on Au-coated EN 1.4767 substrates already at a substrate temperature of 400 °C, which is 300 K lower than comparable depositions of Li7La3Zr2O12. These results show that the combination of thin garnet-structured electrolytes and high-voltage spinels is possible.

Operando analysis of lithium profiles in Li-ion batteries using nuclear microanalysis

A wide variety of analytical methods are used for studying the behavior of lithium-ion batteries and particularly the lithium ion distribution in the electrodes. However, the development of in situ/operando techniques proved powerful to understand the mechanisms responsible for the lithium trapping and then the aging phenomenon. Herein, we report the design of an electrochemical cell to profile operando lithium concentration in LiFePO4 electrodes using Ion Beam Analysis techniques. The specificity of the cell resides in its ability to not only provide qualitative information about the elements present but above all to measure quantitatively their content in the electrode at different states of charge of the battery. The nuclear methods give direct information about the degradation of the electrolyte and particularly reveal inhomogeneous distributions of lithium and fluorine along the entire thickness of the electrode. Higher concentrations of fluorine is detected near the electrode/electrolyte interface while a depletion of lithium is observed near the current collector at high states of charge.

TheGaia-ESO Survey: open clusters inGaia-DR1

Context.Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas.Aims.We describe the methodologies that, taking advantage ofGaia-DR1 and theGaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators.Methods.We perform a homogeneous analysis of eight open clusters using theGaia-DR1 TGAS catalogue for bright members and information from theGaia-ESO Survey for fainter stars. Cluster membership probabilities for theGaia-ESO Survey targets are derived based on several spectroscopic tracers. TheGaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis.Results.For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017, A&A, 601, A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values.Conclusions.The systematic parallax errors inherent in theGaiaDR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combiningGaiaand ground-based spectroscopic datasets.

The Lithium Depletion Boundary and the Age of the Hyades Cluster∗

Abstract Determination of the lithium depletion boundary (LDB), i.e., the observational limit below which the cores of very low-mass objects do not reach high enough temperatures for Li destruction, has been used to obtain ages for several open clusters and stellar associations younger than 200 Myr—which until now has been considered the practical upper limit on the range of applicability of this method. In this work, we show that the LDB method can be extended to significant older ages than previously thought. Intermediate resolution optical spectra of six L-type candidate members in the Hyades cluster obtained using Optical System for Imaging and Low Resolution Integrated Spectroscopy at the 10.4 m Gran Telescopio Canarias are presented. The 670.8 nm resonance doublet is clearly detected only in the two faintest and coolest of these objects, which are classified as L3.5 to L4 brown dwarf (BD) cluster members with luminosities around 10−4 solar. Lithium depletion factors are estimated for our targets with the aid of synthetic spectra and they are compared with predictions from evolutionary models. An LDB age of 650 ± 70 Myr for the Hyades provides a consistent description of our data using a set of state-of-the-art evolutionary models for BDs calculated by Baraffe et al.

Positive and Negative Aspects of Interfaces in Solid-State Batteries

Solid-state lithium batteries are regarded as promising energy storage devices that meet the requirements for realizing a low-carbon society. Although solid-state batteries have been suffering from low power density, the power density has become comparable to or greater than that of liquid systems in a recently developed battery, which has been achieved not only by the high ionic conductivity of the used sulfide solid electrolyte. This Perspective presents anomalous transport properties appearing at the interfaces in solid-state batteries to highlight the importance of controlling the interface phenomena in achieving the high performance. The battery employs not only the highly conductive sulfide but also some oxides in spite of their low conductivity. LiNbO3 interposed to the cathode interface effectively reduces the cathode impedance by suppressing lithium depletion at the interface. Li4Ti5O12 used as the anode becomes a good conductor in its two-phase region because of enhanced transport properties at ...

Iota Horologii Is Unlikely to Be an Evaporated Hyades Star

Abstract We present a high-precision chemical analysis of ι Hor (iota Horologii), a planet-host field star thought to have formed in the Hyades. Elements with atomic number have abundances that are in excellent agreement with those of the cluster within the ±0.01 dex (or ) precision errors. Heavier elements show a range of abundances such that about half of the species analyzed are consistent with those of the Hyades, while the other half are marginally enhanced by 0.03 ± 0.01 dex ( ). The lithium abundance, A(Li), is very low compared to the well-defined A(Li)– relation of the cluster. For its , ι Hor’s lithium content is about half the Hyades’. Attributing the enhanced lithium depletion to the planet would require a peculiar rotation rate, which we are unable to confirm. Our analysis of ι Hor’s chromospheric activity suggests days, which is significantly shorter than previously reported. Models of Galactic orbits place ι Hor hundreds of parsecs away from the cluster at formation. Thus, we find the claim of a shared birthplace very difficult to justify.

Wide σ Orionis binaries resolved by UKIDSS

In spite of its importance for the study of star formation at all mass domains, the nearby young σ Orionis cluster still lacks a comprehensive survey for multiplicity. We try to fill that observational gap by looking for wide resolved binaries with angular separations between 0.4 and 4.0 arcsec. We search for companions to 331 cataloged cluster stellar members and candidates in public K‐band UKIDSS images outside the innermost 1 arcmin, which is affected by the glare of the bright, eponymous σ Ori multiple system, and investigate their cluster membership with color–magnitude diagrams and previous knowledge of youth features. Of the 18 identified pairs, 10 have very low individual probabilities of chance alignment (< 1%) and are considered here as physical pairs. Four of them are new, while the other six had been discovered previously but never investigated homogeneously and in detail. Projected physical separations and magnitude differences of the 10 probably bound pairs range from 180 to 1220 au, and from 0.0 to 3.4 mag in K, respectively. Besides, we identify two cluster stars with elongated point spread functions. We determine the minimum frequency of wide multiplicity in the interval of projected physical separations s = 160–1600 au in σ Orionis at 3.0%. We discover a new Lindroos system, find that massive and X‐ray stars tend to be in pairs or trios, conclude that multiplicity truncates circumstellar disks and enhances X‐ray emission, and ascribe a reported lithium depletion in a young star to unresolved binarity in spectra of moderate resolution. When accounting for all known multiples, including spectroscopic binaries, the minimum frequency of multiplicity increases to about 10%, which implies that of the order of 80–100 unknown multiple systems still await discovery in σ Orionis.

Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

Abstract We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ∼50 Myr to ∼4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

Signatures of rocky planet engulfment in HAT-P-4

Aims. To explore the possible chemical signature of planet formation in the binary system HAT-P-4, by studying abundance vs condensation temperature Tc trends. The star HAT-P-4 hosts a planet detected by transits while its stellar companion does not have any detected planet. We also study the Lithium content, which could shed light on the problem of Li depletion in exoplanet host stars. Conclusions. The exoplanet host star HAT-P-4 is found to be ~0.1 dex more metal rich than its companion, which is one of the highest differences in metallicity observed in similar systems. This could have important implications for chemical tagging studies, disentangling groups of stars with a common origin. We rule out a possible peculiar composition for each star as lambda Boo, delta Scuti or a Blue Straggler. The star HAT-P-4 is enhanced in refractory elements relative to volatile when compared to its stellar companion. Notably, the Lithium abundance in HAT-P-4 is greater than in its companion by ~0.3 dex, which is contrary to the model that explains the Lithium depletion by the presence of planets. We propose a scenario where, at the time of planet formation, the star HAT-P-4 locked the inner refractory material in planetesimals and rocky planets, and formed the outer gas giant planet at a greater distance. The refractories were then accreted onto the star, possibly due to the migration of the giant planet. This explains the higher metallicity, the higher Lithium content, and the negative Tc trend detected. A similar scenario was recently proposed for the solar twin star HIP 68468, which is in some aspects similar to HAT-P-4. We estimate a mass of at least Mrock ~ 10 Mearth locked in refractory material in order to reproduce the observed Tc trends and metallicity.

All-sky Co-moving Recovery Of Nearby Young Members (ACRONYM). II. The β Pictoris Moving Group∗

Abstract We confirm 66 low-mass stellar and brown dwarf systems (K7–M9) plus 19 visual or spectroscopic companions of the β Pictoris moving group (BPMG). Of these, 41 are new discoveries, increasing the known low-mass members by 45%. We also add four objects to the 14 known with masses predicted to be less than . Our efficient photometric + kinematic selection process identified 104 low-mass candidates, which we observed with ground-based spectroscopy. We collected infrared observations of the latest spectral types (>M5) to search for low-gravity objects. These and all <M5 candidates were observed with high-resolution optical spectrographs to measure the radial velocities and youth indicators, such as lithium absorption and Hα emission, needed to confirm BPMG membership, achieving a 63% confirmation rate. We also compiled the most complete census of BPMG membership, with which we tested the efficiency and false-membership assignments using our selection and confirmation criteria. Using the new census, we assess a group age of 22 ± 6 Myr, consistent with past estimates. With the now–densely sampled lithium depletion boundary, we resolve the broadening of the boundary by either an age spread or astrophysical influences on lithium-burning rates. We find that 69% of the now-known members with AFGKM primaries are M stars, nearing the expected value of 75%. However, the new initial mass function for the BPMG shows a deficit of 0.2–0.3 stars by a factor of ∼2. We expect that the AFGK census of the BPMG is also incomplete, probably due to biases of searches toward the nearest stars.

The Curious Case of PDS 11: A Nearby, >10 Myr Old, Classical T Tauri Binary System

Abstract We present results of our study of the PDS 11 binary system, which belongs to a rare class of isolated, high Galactic latitude T Tauri stars. Our spectroscopic analysis reveals that PDS 11 is an M2–M2 binary system with both components showing similar Hα emission strengths. Both the components appear to be accreting and are classical T Tauri stars. The lithium doublet Li i λ6708, a signature of youth, is present in the spectrum of PDS 11A, but not in PDS 11B. From the application of lithium depletion boundary age-dating method and a comparison with the Li i λ6708 equivalent width distribution of moving groups, we estimated an age of 10–15 Myr for PDS 11A. Comparison with pre-main sequence evolutionary models indicates that PDS 11A is a 0.4 M ⊙ T Tauri star at a distance of 114–131 pc. PDS 11 system does not appear to be associated with any known star-forming regions or moving groups. PDS 11 is a new addition, after TWA 30 and LDS 5606, to the interesting class of old, dusty, wide binary classical T Tauri systems in which both components are actively accreting.

A stellar census of the nearby, young 32 Orionis group

The 32 Orionis group was discovered almost a decade ago and despite the fact that it represents the first northern, young (age ~ 25 Myr) stellar aggregate within 100 pc of the Sun ($d \simeq 93$ pc), a comprehensive survey for members and detailed characterisation of the group has yet to be performed. We present the first large-scale spectroscopic survey for new (predominantly M-type) members of the group after combining kinematic and photometric data to select candidates with Galactic space motion and positions in colour-magnitude space consistent with membership. We identify 30 new members, increasing the number of known 32 Ori group members by a factor of three and bringing the total number of identified members to 46, spanning spectral types B5 to L1. We also identify the lithium depletion boundary (LDB) of the group, i.e. the luminosity at which lithium remains unburnt in a coeval population. We estimate the age of the 32 Ori group independently using both isochronal fitting and LDB analyses and find it is essentially coeval with the {\beta} Pictoris moving group, with an age of $24\pm4$ Myr. Finally, we have also searched for circumstellar disc hosts utilising the AllWISE catalogue. Although we find no evidence for warm, dusty discs, we identify several stars with excess emission in the WISE W4-band at 22 {\mu}m. Based on the limited number of W4 detections we estimate a debris disc fraction of $32^{+12}_{-8}$ per cent for the 32 Ori group.