We present a self-consistent, absolute isochronal age scale for young ( 200 Myr), nearby ( 100 pc) moving groups in the solar neighbourhood based on homogeneous fitting of semi-empirical pre-main-sequence model isochrones using the τ 2 maximumlikelihood fitting statistic of Naylor & Jeffries in the M V , V − J colour-magnitude diagram. The final adopted ages for the groups are: 149 +51 −19 Myr for the AB Dor moving group, 24 ± 3 Myr for the β Pic moving group (BPMG), 45 +11 −7 Myr for the Carina association, 42 +6 −4 Myr for the Columba association, 11 ± 3 Myr for the η Cha cluster, 45±4 Myr for the Tucana-Horologium moving group (Tuc-Hor), 10±3 Myr for the TW Hya association, and 22 +4 −3 Myr for the 32 Ori group. At this stage we are uncomfortable assigning a final, unambiguous age to the Argus association as our membership listfor the association appears to suffer from a high level of contamination, and therefore it remains unclear whether these stars represent a single population of coeval stars.Our isochronal ages for both the BPMG and Tuc-Hor are consistent with recent lithium depletion boundary (LDB) ages, which unlike isochronal ages, are relatively insensitive to the choice of low-mass evolutionary models. This consistency between the isochronal and LDB ages instills confidence that our self-consistent, absolute age scale for young, nearby moving groups is robust, and hence we suggest that these ages be adopted for future studies of these groups. Software implementing the methods described in this study is available from http: //www.astro.ex.ac.uk/people/timn/tau-squared/.

Jeffries & Binks (2014) and Malo et al. (2014) have recently reported Li depletion boundary (LDB) ages for the β Pictoris moving group (BPMG) which are twice as old as the oft-cited kinematic age of ∼ 12 Myr. In this study we present (1) a new evaluation of the internal kinematics of the BPMG using the revised Hipparcos astrometry and best available published radial velocities, and assess whether a useful kinematic age can be derived, and (2) derive an isochronal age based on the placement of the A-, F-and G-type stars in the colour-magnitude diagram (CMD). We explore the kinematics of the BPMG looking at velocity trends along Galactic axes, and conducting traceback analyses assuming linear trajectories, epicyclic orbit approximation, and orbit integration using a realistic gravitational potential. None of the methodologies yield a kinematic age with small uncertainties using modern velocity data. Expansion in the Galactic X and Y directions is significant only at the 1.7σ and 2.7σ levels, and together yields an overall kinematic age with a wide range (13 − 58 Myr; 95 per cent CL). The A-type members are all on the zero age-main-sequence, suggestive of an age of > 20 Myr, and the loci of the CMD positions for the late-F-and G-type pre-main-sequence BPMG members have a median isochronal age of 22 Myr (± 3 Myr stat., ± 1 Myr sys.) when considering four sets of modern theoretical isochrones. The results from recent LDB and isochronal age analyses are now in agreement with a median BPMG age of 23 ± 3 Myr (overall 1σ uncertainty, including ±2 Myr statistical and ±2 Myr systematic uncertainties).

We have derived ages for 13 young (< 30 Myr) star-forming regions and find they are up to a factor two older than the ages typically adopted in the literature. This result has wide-ranging implications, including that circumstellar discs survive longer ( 10 − 12 Myr) and that the average Class I lifetime is greater ( 1 Myr) than currently believed.For each star-forming region we derived two ages from colour-magnitude diagrams. First we fitted models of the evolution between the zero-age main-sequence and terminal-age main-sequence to derive a homogeneous set of main-sequence ages, distances and reddenings with statistically meaningful uncertainties. Our second age for each star-forming region was derived by fitting pre-main-sequence stars to new semi-empirical model isochrones. For the first time (for a set of clusters younger than 50 Myr) we find broad agreement between these two ages, and since these are derived from two distinct mass regimes that rely on different aspects of stellar physics, it gives us confidence in the new age scale. This agreement is largely due to our adoption of empirical colour-T eff relations and bolometric corrections for pre-main-sequence stars cooler than 4000 K.The revised ages for the star-forming regions in our sample are -∼ 2 Myr for NGC 6611 (Eagle Nebula; M 16), IC 5146 (Cocoon Nebula), NGC 6530 (Lagoon Nebula; M 8), and NGC 2244 (Rosette Nebula); ∼ 6 Myr for σ Ori, Cep OB3b, and IC 348; 10 Myr for λ Ori (Collinder 69); 11 Myr for NGC 2169; 12 Myr for NGC 2362; 13 Myr for NGC 7160; 14 Myr for χ Per (NGC 884); and 20 Myr for NGC 1960 (M 36).

The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg 2 (distributed over ∼2400 square degrees at ∼20% filling factor) to ∼24thmag in ugriz. The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ∼15 mas and the accuracy is ∼2 mas with respect to the Gaia reference frame. The photometric precision is ∼0.5%-0.7% in griz and ∼1% in u with a calibration accuracy of ∼1.3% in all bands. The median 5σ point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R∼18.4 kpc. SMASH DR1 contains measurements of ∼100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.

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 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 β Pictoris moving group, with an age of 24 ± 4 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 W 4-band at 22 µm. Based on the limited number of W 4 detections we estimate a debris disc fraction of 32 +12 −8 per cent for the 32 Ori group.

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We present a critical assessment of commonly used pre-main-sequence isochrones by comparing their predictions to a set of well-calibrated colour-magnitude diagrams of the Pleiades in the wavelength range 0.4-2.5 μm. Our analysis shows that for temperatures less than 4000 K, the models systematically overestimate the flux by a factor of 2 at 0.5 μm, though this decreases with wavelength, becoming negligible at 2.2 μm. In optical colours this will result in the ages for stars younger than 10 Myr being underestimated by factors of between 2 and 3.We show that using observations of standard stars to transform the data into a standard system can introduce significant errors in the positioning of pre-main sequences in colour-magnitude diagrams. Therefore, we have compared the models to the data in the natural photometric system in which the observations were taken. Thus we have constructed and tested a model of the system responses for the Wide-Field Camera on the Isaac Newton Telescope.As a benchmark test for the development of pre-main-sequence models, we provide both our system responses and the Pleiades sequence.

WISE J080822.18-644357.3 (WISE J0808-6443) was recently identified as a new M dwarf debris disc system and a candidate member of the 45 Myr-old Carina association. Given that the strength of its infrared excess (L IR /L 0.1) appears to be more consistent with a young protoplanetary disc, we present the first optical spectra of the star and reassess its evolutionary and membership status. We find WISE J0808−6443 to be a Li-rich M5 star with strong Hα emission (−125 < EW < −65 Å over 4 epochs) whose strength and broad width are consistent with accretion at a low level (∼10 −10 M yr −1 ) from its disc. The spectral energy distribution of the star is consistent with a primordial disc and is well-fit using a two-temperature blackbody model with T inner 1100 K and T outer 240 K. AllWISE multi-epoch photometry shows the system exhibits significant variability in the 3.4 µm and 4.6 µm bands. We calculate an improved proper motion based on archival astrometry, and combined with a new radial velocity, the kinematics of the star are consistent with membership in Carina at a kinematic distance of 90 ± 9 pc. The spectroscopic and photometric data are consistent with WISE J0808−6443 being a ∼0.1 M Classical T-Tauri star and one of the oldest known accreting M-type stars. These results provide further evidence that the upper limit on the lifetimes of gas-rich discsand hence the timescales to form and evolve protoplanetary systems -around the lowest mass stars may be longer than previously recognised, or some mechanism may be responsible for regenerating short-lived discs at later stages of pre-main sequence evolution.