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Full author list: A Pieres, L Girardi, E Balbinot, B Santiago, L N da Costa, A Carnero Rosell, A B Pace, K Bechtol, M A T Groenewegen, A Drlica-Wagner, T S Li, M A G Maia, R L C Ogando, M dal Ponte, H T Diehl, A Amara, S Avila, E Bertin, D Brooks, D L Burke, M Carrasco Kind, J Carretero, J De Vicente, S Desai, T F Eifler, B Flaugher, P Fosalba, J Frieman, J García-Bellido, E Gaztanaga, D W Gerdes, D Gruen, R A Gruendl, J Gschwend, G Gutierrez, D L Hollowood, K Honscheid, D J James, K Kuehn, N Kuropatkin, J L Marshall, R Miquel, A A Plazas, E Sanchez, S Serrano, I Sevilla-Noarbe, E Sheldon, M Smith, M Soares-Santos, F Sobreira, E Suchyta, M E C Swanson, G Tarle, D Thomas, V Vikram, A R Walker, We present a technique to fit the stellar components of the Galaxy by comparing Hess Diagrams (HDs) generated from TRILEGAL models to real data. We apply this technique, which we call MWFITTING, to photometric data from the first 3 yr of the Dark Energy Survey (DES). After removing regions containing known resolved stellar systems such as globular clusters, dwarf galaxies, nearby galaxies, the Large Magellanic Cloud, and the Sagittarius Stream, our main sample spans a total area of ~2300 deg2. We further explore a smaller subset (~1300 deg2) that excludes all regions with known stellar streams and stellar overdensities. Validation tests on synthetic data possessing similar properties to the DES data show that the method is able to recover input parameters with a precision better than 3 per cent. We fit the DES data with an exponential thick disc model and an oblate double power-law halo model. We find that the best-fitting thick disc model has radial and vertical scale heights of 2.67 ± 0.09 kpc and 925 ± 40 pc, respectively. The stellar halo is fit with a broken power-law density profile with an oblateness of 0.75 ± 0.01, an inner index of 1.82 ± 0.08, an outer index of 4.14 ± 0.05, and a break at 18.52 ± 0.27 kpc from the Galactic centre. Several previously discovered stellar overdensities are recovered in the residual stellar density map, showing the reliability of MWFITTING in determining the Galactic components. Simulations made with the best-fitting parameters are a promising way to predict Milky Way star counts for surveys such as the LSST and Euclid., The DESDM is supported by the National Science Foundation under grants AST-1138766 and AST-1536171. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2015-71825, ESP2015-66861, FPA2015-68048, SEV-2016-0588, SEV-2016-0597, and MDM-2015-0509, some of which include ERDF funds from the European Union. IFAE is partially funded by the CERCA program of the Generalitat de Catalunya. Research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013) including ERC grant agreements 240672, 291329, and 306478. We acknowledge support from the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020, and the Brazilian Instituto Nacional de Ci?ncia e Tecnologia (INCT) do e-Universe (CNPq grant 465376/2014-2). This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Centre for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Centre for Cosmology and AstroParticle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundac¸ão Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência, Tecnologia e Inovac¸ão, the Deutsche Forschungsgemeinschaft, and the Collaborating Institutions in the DES.

The abundance and narrow magnitude dispersion of Red Clump (RC) stars make them a popular candidate for mapping the morphology of the bulge region of the Milky Way. Using an estimate of the RC's intrinsic luminosity function, we extracted the three-dimensional density distribution of the RC from deep photometric catalogues of the VISTA Variables in the Via Lactea (VVV) survey. We used maximum entropy based deconvolution to extract the spatial distribution of the bulge from Ks-band star counts. We obtained our extrapolated non-parametric model of the bulge over the inner 40 by 40 degrees squared region of the Galactic centre. Our reconstruction also naturally matches onto a parametric fit to the bulge outside the VVV region and inpaints overcrowded and high extinction regions. We found a range of bulge properties consistent with other recent investigations based on the VVV data. In particular, we estimated the bulge mass to be in the range 13 to 17 billion solar masses, the X-component to be between 18% and 25% of the bulge mass, and the bulge angle with respect to the Sun-Galactic centre line to be between 18 and 32 degrees. Studies of the Fermi Large Area Telescope (LAT) gamma-ray Galactic centre excess suggests that the excess may be traced by Galactic bulge distributed sources. We applied our deconvolved density in a template fitting analysis of this Fermi-LAT GeV excess and found an improvement in the fit compared to previous parametric based templates., 25 pages, 27 figures, minor typo corrected

Careful analyses of photometric and star count data available for the nine putative young clusters identified by Camargo et al. (2015, 2016) at high Galactic latitudes reveal that none of the groups contain early-type stars, and most are not significant density enhancements above field level. 2MASS colours for stars in the groups match those of unreddened late-type dwarfs and giants, as expected for contamination by (mostly) thin disk objects. A simulation of one such field using only typical high latitude foreground stars yields a colour-magnitude diagram that is very similar to those constructed by Camargo et al. (2015, 2016) as evidence for their young groups as well as the means of deriving their reddenings and distances. Although some of the fields are coincident with clusters of galaxies, one must conclude that there is no evidence that the putative clusters are extremely young stellar groups., Accepted for publication (MNRAS)

We use Monte Carlo simulations to explore the statistical challenges of constraining the characteristic mass ($m_c$) and width ($\sigma$) of a lognormal sub-solar initial mass function (IMF) in Local Group dwarf galaxies using direct star counts. For a typical Milky Way (MW) satellite ($M_{V} = -8$), jointly constraining $m_c$ and $\sigma$ to a precision of $\lesssim 20\%$ requires that observations be complete to $\lesssim 0.2 M_{\odot}$, if the IMF is similar to the MW IMF. A similar statistical precision can be obtained if observations are only complete down to $0.4M_{\odot}$, but this requires measurement of nearly 100$\times$ more stars, and thus, a significantly more massive satellite ($M_{V} \sim -12$). In the absence of sufficiently deep data to constrain the low-mass turnover, it is common practice to fit a single-sloped power law to the low-mass IMF, or to fit $m_c$ for a lognormal while holding $\sigma$ fixed. We show that the former approximation leads to best-fit power law slopes that vary with the mass range observed and can largely explain existing claims of low-mass IMF variations in MW satellites, even if satellite galaxies have the same IMF as the MW. In addition, fixing $\sigma$ during fitting leads to substantially underestimated uncertainties in the recovered value of $m_c$ (by a factor of $\sim 4$ for typical observations). If the IMFs of nearby dwarf galaxies are lognormal and do vary, observations must reach down to $\sim m_c$ in order to robustly detect these variations. The high-sensitivity, near-infrared capabilities of JWST and WFIRST have the potential to dramatically improve constraints on the low-mass IMF. We present an efficient observational strategy for using these facilities to measure the IMFs of Local Group dwarf galaxies., Comment: Accepted to MNRAS with minor revisions since v1. 12 pages, 9 figures, plus appendices

Galactic bulge microlensing surveys provide a probe of Galactic structure. We present the first field-by-field comparison between microlensing observations and the Besan\c{c}on population synthesis Galactic model. Using an updated version of the model we provide maps of optical depth, average event duration and event rate for resolved source populations and for difference imaging (DIA) events. We also compare the predicted event timescale distribution to that observed. The simulation follows the selection criteria of the MOA-II survey (Sumi et al. 2013). We modify the Besan\c{c}on model to include M dwarfs and brown dwarfs. Our best fit model requires a brown dwarf mass function slope of $-0.4$. The model provides good agreement with the observed average duration, and respectable consistency with the shape of the timescale distribution (reduced $\chi^2 \simeq 2.2$). The DIA and resolved source limiting yields bracket the observed number of events by MOA-II ($2.17\times$ and $0.83\times$ the number observed, respectively). We perform a 2-dimensional fit to the event spatial distribution to predict the optical depth and event rate across the Galactic bulge. The most serious difficulty for the model is that it provides only $\sim 50\%$ of the measured optical depth and event rate per star at low Galactic latitude around the inner bulge ($|b, Comment: 17 pages, 12 figures, 6 tables, Submitted to MNRAS. This work uses the Manchester-Besancon Microlensing Simulator - MaBulS, which is publicly available online at http://www.mabuls.net/

A new sample of stars, representative of the solar neighbourhood luminosity function, is constructed from the Hipparcos catalogue and the Fifth Catalogue of Nearby Stars. We have cross-matched to sources in the 2MASS catalogue so that for all stars individually determined Near Infrared photometry (NIR) is available on a homogeneous system (typically Ks). The spatial completeness of the sample has been carefully determined by statistical methods, and the NIR luminosity function of the stars has been derived by direct star counts. We nd a local volume luminosity of 0:121 0:004LK pc 3 , corresponding to a volumetric mass-to-light ratio of M=LK = 0:31 0:02M =LK , where giants contribute 80 per cent to the light but less than 2 per cent to the stellar mass. We derive the surface brightness of the solar cylinder with the help of a vertical disc model. We nd a surface brightness of 99LK pc 2 with an uncertainty of approximately 10 per cent. This corresponds to a mass-to-light ratio for the solar cylinder of M=LK = 0:34M =LK . The mass-tolight ratio for the solar cylinder is only 10 per cent larger than the local value despite the fact that the local population has a much larger contribution of young stars. It turns out that the eective scale heights of the lower main sequence carrying most of the mass is similar to that of the giants, which are dominating the NIR light. The corresponding colour for the solar cylinder is V K = 2:89 mag compared to the local value of V K = 2:46 mag. An extrapolation of the local surface brightness to the whole Milky Way yields a total luminosity of MK = 24:2 mag. The Milky Way falls in the range of K band Tully-Fisher (TF) relations from the literature.

We have compiled a significantly updated and comprehensive census of massive stars in the nearby Cygnus OB2 association by gathering and homogenising data from across the literature. The census contains 169 primary OB stars, including 52 O-type stars and 3 Wolf-Rayet stars. Spectral types and photometry are used to place the stars in a Hertzprung-Russell diagram, which is compared to both non-rotating and rotating stellar evolution models, from which stellar masses and ages are calculated. The star formation history and mass function of the association are assessed, and both are found to be heavily influenced by the evolution of the most massive stars to their end states. We find that the mass function of the most massive stars is consistent with a `universal' power-law slope of Gamma = 1.3. The age distribution inferred from stellar evolutionary models with rotation and the mass function suggest the majority of star formation occurred more or less continuously between 1 and 7 Myr ago, in agreement with studies of low- and intermediate mass stars in the association. We identify a nearby young pulsar and runaway O-type star that may have originated in Cyg OB2 and suggest that the association has already seen its first supernova. Finally we use the census and mass function to calculate the total mass of the association of 16500^+3800_-2800 Msun, at the low end, but consistent with, previous estimates of the total mass of Cyg OB2. Despite this Cyg OB2 is still one of the most massive groups of young stars known in our Galaxy making it a prime target for studies of star formation on the largest scales., Comment: 22 pages, 9 figures, 4 tables. Accepted for publication in Monthly Notices of the Royal Astronomical Society

We analyse the kinematics of ˜400 000 stars that lie within ˜2 kpc of the Sun and have spectra measured in the Radial Velocity Experiment. We decompose the sample into hot and cold dwarfs, red-clump and non-clump giants. The kinematics of the clump giants are consistent with being identical with those of the giants as a whole. Without binning the data we fit Gaussian velocity ellipsoids to the meridional-plane components of velocity of each star class and give formulae from which the shape and orientation of the velocity ellipsoid can be determined at any location. The data are consistent with the giants and the cool dwarfs sharing the same velocity ellipsoids, which have vertical velocity dispersion rising from 21 km s-1 in the plane to ˜55 km s-1 at |z| = 2 kpc and radial velocity dispersion rising from 37 km s-1 to 82 km s-1 in the same interval. At (R, z), the longest axis of one of these velocity ellipsoids is inclined to the Galactic plane by an angle ˜0.8 arctan(z/R). We use a novel formula to obtain precise fits to the highly non-Gaussian distributions of vφ components in eight bins in the (R, z) plane. We compare the observed velocity distributions with the predictions of a published dynamical model fitted to the velocities of stars that lie within ˜150 pc of the Sun and star counts towards the Galactic pole. The predictions for the vz distributions are exceptionally successful. The model's predictions for vφ are successful except for the hot dwarfs, and its predictions for vr fail significantly only for giants that lie far from the plane. If distances to the model's stars are overestimated by 20 per cent, the predicted distributions of vr and vz components become skew, and far from the plane broader. The broadening significantly improves the fits to the data. The ability of the dynamical model to give such a good account of a large body of data to which it was not fitted inspires confidence in the fundamental correctness of the assumed, disc-dominated, gravitational potential.

We present a deep, wide-field optical study of the M81 group dwarf galaxy Holmberg II (HoII) based on Subaru/Suprime-Cam imaging. Individual stars are resolved down to I~25.2, i.e. about 1.5 mag below the tip of the red giant branch (RGB). We use resolved star counts in the outskirts of the galaxy to measure the radial surface brightness profile down to \mu_V~32 mag arcsec^-2, from which we determine a projected exponential scalelength of 0.70'+-0.01' (i.e. 0.69+-0.01 kpc). The composite profile, ranging from the cored centre out to R=7', is best fit by an EFF profile which gives a half-light radius of 1.41'+-0.04' (i.e. 1.39+-0.04 kpc), and an absolute magnitude M_V=-16.3. The low surface-brightness stellar component of HoII is regular and symmetric and has an extent much smaller than the vast HI cloud in which it is embedded. We compare the spatial distribution of the young, intermediate age, and old stellar populations, and find that the old RGB stars are significantly more centrally concentrated than the young stellar populations, contrary to what is observed in most dwarf galaxies of the Local Universe. We discuss these properties in the context of the comet-like distribution of HI gas around HoII, and argue for the presence of a hot intragroup medium in the vicinity of HoII to explain the contrasting morphologies of the gas and stars.

Jets and outflows accompany the mass accretion process in protostars and young stellar objects. Using a large and unbiased sample, they can be used to study statistically the local feedback they provide and the typical mass accretion history. Here we analyse such a sample of Molecular Hydrogen emission line Objects in the Serpens and Aquila part of the Galactic Plane. Distances are measured by foreground star counts with an accuracy of 25%. The resulting spacial distribution and outflow luminosities indicate that our objects sample the formation of intermediate mass objects. The outflows are unable to provide a sizeable fraction of energy and momentum to support, even locally, the turbulence levels in their surrounding molecular clouds. The fraction of parsec scale flows is one quarter and the typical dynamical jet age of the order of 1E4yrs. Groups of emission knots are ejected every 1E3yrs. This might indicate that low level accretion rate fluctuations and not FU-Ori type events are responsible for the episodic ejection of material. Better observational estimates of the FU-Ori duty cycle are needed.

The stars in the Chinese star catalogue, Yixiangkaocheng, which were edited by the Jesuit astronomer Kogler in ad 1744 and published in ad 1756, are identified with their counterparts in the Hipparcos catalogue. The equinox of the catalogue is confirmed to be J1744.0. By considering the precession of equinox, proper motions and nutation, the star closest to the location of each star in Yixiangkaocheng, having a proper magnitude, is selected as the corresponding identified star. I identified 2848 stars and 13 nebulosities out of 3083 objects in Yixiangkaocheng, and so the identification rate reached 92.80 per cent. I find that the magnitude classification system in Yixiangkaocheng agrees with the modern magnitude system. The catalogue includes dim stars, whose visual magnitudes are larger than 7, but most of these stars have Flamsteed designations. I find that the stars whose declination is lower than −30° have relatively larger offsets and different systematic behaviour from other stars. This indicates that there might be two different sources of stars in Yixiangkaocheng. In particular, I find that μ1 Sco and γ1 Sgr approximately mark the boundary between two different source catalogues. The observer’s location, as estimated from these facts, agrees with the latitude of Greenwich where Flamsteed made his observations. The positional offsets between the Yixiangkaocheng stars and the Hipparcos stars are 0.6 arcmin, which implies that the source catalogue of stars with δ > −30° must have come from telescopic observations. Nebulosities in Yixiangkaocheng are identified with a few double stars, o Cet (the variable star, Mira), the Andromeda galaxy, ω Cen and NGC6231. These entities are associated with listings in Halley’s Catalogue of the Southern Stars of ad 1679 as well as Flamsteed’s catalogue of ad 1690.

We have used a combination of high-resolution Hubble Space Telescope Wide Field Planetary Camera 2 and wide-field ground-based observations in ultraviolet and optical bands to study the blue straggler star (BSS) population of the outer halo globular cluster NGC 6229 over its entire radial extent. A total of 64 bright BSS (with m255≤ 21.30, corresponding to m555≤ 20.75) has been identified. The BSS-projected radial distribution is found to be bimodal, with a high central peak, a well-defined minimum at intermediate radii (r∼ 40 arcsec) and an upturn in the outskirts. From detailed star counts even in the very inner region, we compute the centre of gravity of the cluster and the most accurate and extended radial density profile ever published for this system. The profile is reasonably well reproduced by a standard King model with an extended core (rc≃ 9.5 arcsec) and a modest value of the concentration parameter (c≃ 1.49). However, a deviation from the model is noted in the most external region of the cluster (at r > 250 arcsec from the centre). This feature needs to be further investigated in order to assess the possible presence of a tidal tail in this cluster.

Ground-based surveys have mapped the stellar outskirts of Local Group galaxies in unprecedented detail, but extending this work to other galaxies is necessary to overcome stochastic variations in evolutionary history and provide more stringent constraints on cosmological galaxy formation models. As part of our continuing program of ultra-deep imagery of galaxies beyond the Local Group, we present a wide-field analysis of the isolated late-type spiral NGC2403 using data obtained with Suprime-Cam on Subaru. The survey reaches a maximum projected radius of 30 kpc or deprojected radius of R_dp~60 kpc. The colour-magnitude diagram reaches 1.5 mag below the tip of the metal-poor red giant branch (RGB) at a completeness rate > 50% for R_dp >12 kpc. Using the combination of diffuse light photometry and resolved star counts, we are able to trace the radial surface brightness (SB) profile over a much larger range of radii and surface brightness than is possible with either technique alone. The exponential disc as traced by RGB stars dominates the SB profile out to >8 disc scale-lengths, or R_dp~18 kpc, and reaches a V-band SB of 29 mag per sq. arcsec. Beyond this radius, we find evidence for an extended structural component with a significantly flatter SB profile than the inner disc and which we trace to R_dp~40 kpc and ~32 mag per sq. arcsec. This component can be fit with a power-law index of ~3, has an axial ratio consistent with that of the inner disc and has a V-band luminosity of 1-7% that of the whole galaxy. At R_dp~20 - 30 kpc, we estimate a peak metallicity [M/H]= -1.0+/-0.3. Although the extant data are unable to discriminate between stellar halo or thick disc interpretations of this component, our results support the notion that faint, extended stellar structures are a common feature of all disc galaxies, even isolated, low-mass systems.

We present and discuss new CCD-based photometric material in the UBVI pass-bands for nine Galactic star clusters located inside the solar ring, for which no CCD data are currently available. They are: IC 2714, NGC 4052, ESO131SC09, NGC 5284, NGC 5316, NGC 5715, VdB-Hagen ~164, NGC 6268, and Czernik 38. We first perform star counts by combining our optical photometry wi th 2MASS, and derive cluster sizes and radial density profiles. The fundamental parameters - age, reddening and distance- are then inferred from the analysis of the star distribution in color-color and color-magnitude diagrams of only the spatially selected likely members. Our analysis shows that ESO131SC09, NGC 5284, and VdB-Hagen 164 are most probably not clusters, but random enhancements of a few bright stars along the line of sight, with prop erties much similar to open cluster remnants. The remaining clusters are physical groups, and are all younger than about 1 Gyr . We use the newly derived set of parameters, in particular distance and reddening, to investigate their position in the Galaxy in the context of the spiral structure of the Milky Way. We find that the youngest clusters (IC 2714, NGC 5316, and NGC 6268) are located close to or inside the Carina-Sagittarius arm, and are therefore {\i t bona fide} spiral structure tracers. On the other hand, the oldest (Czernik 38, NGC 4052, and NGC 5715) are floating in the inter-arm space between the Carina-Sagittarius and the more distant Scutum-Crux arm. Interestingly enough, the oldest clusters of this sample - Czernik 38 and NGC 5715- are among the few known open clusters to be older or as old as the Hyades in the inner Galactic disk, where star clusters are not expected to survive for a long time, because of the strong tidal field and the higher probability of close encounters .

We have used the self-consistent vertical disc models of the solar neighbourhood presented in Just & Jahreiss (2010), which are based on different star formation histories (SFR) and fit the local kinematics of main sequence stars equally well, to predict star counts towards the North Galactic Pole (NGP). We combined these four different models with the local main sequence in the filter system of the SDSS and predicted the star counts in the NGP field with b>80deg. All models fit the Hess diagrams in the F-K dwarf regime better than 20 percent and the star number densities in the solar neighbourhood are consistent with the observed values. The chi^2 analysis shows that model A is clearly preferred with systematic deviations of a few percent only. The SFR of model A is characterised by a maximum at an age of 10Gyr and a decline by a factor of four to the present day value of 1.4Msun/pc^2/Gyr. The thick disc can be modelled very well by an old isothermal simple stellar population. The density profile can be approximated by a sech^(alpha_t) function. We found a power law index alpha_t=1.16 and a scale height of 800pc corresponding to a vertical velocity dispersion of 45.3km/s. About 6 percent of the stars in the solar neighbourhood are thick disc stars.

We investigate whether the subhalos of Lambda-CDM galaxy halos have potentials consistent with the observed properties of Milky Way satellites, particularly those with high-quality photometric and kinematic data: Fornax, Leo I, Sculptor, Sextans, and Carina. We compare spherical models with isotropic velocity dispersion tensors to the observed, circularly averaged star counts, line-of-sight velocity dispersion profiles and line-of-sight velocity distributions. We identify subhalos within the six high-resolution dark matter halos of the Aquarius Project for which the spherically averaged potentials result in excellent fits to each of the five galaxies. In particular, our simple one-integral models reproduce the observations in the inner regions, proving that these data are fully consistent with Lambda-CDM expectations and do not require cored dark matter distributions. For four of the five satellites the fits require moderately cusped {\it stellar} density profiles. The star count data for Leo I, however, do require a cored distribution of star counts. Current data suggest that these five satellites may be hosted by Lambda-CDM subhalos with maximum circular velocities in the range 10 to 30 km/s.

We present CCD photometry in the Johnson UBV and Kron-Cousins I systems down to V~ 22.0 for the open clusters NGC 2311, Trumpler 6, NGC 2432 and BH 54 and their surrounding fields. Trumpler 6 and BH 54 have never been studied before and so we provide, for the first time, estimates of their fundamental parameters. We obtained colour-magnitude diagrams (CMDs) and colour-colour diagrams cleaned from field star contamination by statistically subtracting stars in terms of spatial density, magnitude and colour distributions. Cluster angular radii were estimated from star counts in appropriate-sized boxes distributed throughout the entire observed fields. Using the cleaned CMDs and colour-colour diagrams, we applied sound photometric membership criteria to discriminate cluster members from interloper field stars. The interstellar extinction across the cluster fields derived from the 100-μm dust emission full-sky maps can be considered uniform within the quoted uncertainties. The E(B-V) and E(V-I) colour excesses and the apparent distance moduli of the clusters were estimated from the fit of the zero-age main-sequence to the colour-colour diagrams and CMDs, respectively. Cluster ages were determined from the comparison of the four clusters' CMDs with solar metallicity theoretical isochrones of the Geneva group. All the clusters were found to be moderately young objects, their ages ranging between 60 and 250 Myr. © 2010 The Authors. Journal compilation © 2010 RAS.

We have used the recently reduced Hipparcos data and the Washington Double Star catalogue to derive two volume- and magnitude-limited samples of single stars in the Galactic plane. The star count method has been used to compare synthetic to empirical samples of stars within both the main sequence and the evolved regions of the Hertzsprung–Russell diagram. Corrections have been made for unrecognized binaries and the residual incompleteness of the Hipparcos catalogue. Two methods of binary reduction have been compared, a flat 71 per cent binary fraction (including multiples) and a mass-dependent binary fraction, which decreases with primary mass from 71 to 57 per cent. A semi-empirical relation between the vertical scaleheight and stellar age has been derived from kinematic data provided by the OSACA data base. This relation is used to prescribe the loss of stellar content vertically from the plane due to heating. When employing the fixed binary ratio, we find that the best fit is provided by a Scalo initial mass function (IMF) with an exponent of 1.85 ± 0.15, together with an average Galactic thin-disc star formation rate (SFR) of 618(±15) stars Myr −1 kpc −3 with –

We present a fully consistent evolutionary disc model of the solar cylinder. The model is based on a sequence of stellar subpopulations described by the star formation history (SFR) and the dynamical heating law [given by the age-velocity dispersion relation (AVR)]. The stellar subpopulations are in dynamical equilibrium and the gravitational potential is calculated self-consistently including the influence of the dark matter halo and the gas component. The combination of kinematic data from Hipparcos and the finite lifetimes of main-sequence (MS) stars enables us to determine the detailed vertical disc structure independent of individual stellar ages and only weakly dependent on the initial mass function (IMF). The disc parameters are determined by applying a sophisticated best-fitting algorithm to the MS star velocity distribution functions in magnitude bins. We find that the AVR is well constrained by the local kinematics, whereas for the SFR the allowed range is larger. The model is consistent with the local kinematics of MS stars and fulfils the known constraints on scaleheights, surface densities and mass ratios. A simple chemical enrichment model is included in order to fit the local metallicity distribution of G dwarfs. In our favoured Model A, the power-law index of the AVR is 0.375 with a minimum and maximum velocity dispersion of 5.1 and 25.0 km s -1 , respectively. The SFR shows a maximum 10 Gyr ago and declines by a factor of four to the present-day value of 1.5 M ⊙ pc -2 Gyr -1 . A best fit of the IMF leads to power-law indices of -1.46 below and -4.16 above 1.72M ⊙ avoiding a kink at 1 M ⊙ . An isothermal thick-disc component with local density of ~6 per cent of the stellar density is included. A thick disc containing more than 10 per cent of local stellar mass is inconsistent with the local kinematics of K and M dwarfs. Neglecting the thick-disc component results in slight variations of the thin-disc properties, but has a negligible influence on the AVR and the normalized SFR. The model allows detailed predictions of the density, age, metallicity and velocity distribution functions of MS stars as a function of height above the mid-plane. The complexity of the model does not allow to rule out other star formation scenarios using the local data alone. The incorporation of multiband star count and kinematic data of larger samples in the near future will improve the determination of the disc structure and evolution significantly.

Photoelectric UBV photometry and star counts are presented for the previously unstudied open cluster Collinder 236, supplemented by observations for stars near the Cepheid WZ Car. Collinder 236 is typical of groups associated with Cepheids, with an evolutionary age of (3.4+-1.1)x10^7 years, but it is 1944+-71 pc distant, only half the predicted distance to WZ Car. The cluster is reddened by E(B-V)~0.26, and has nuclear and coronal radii of rn~2 arcmin (1.1 pc) and Rc~8 arcmin (4.5 pc), respectively. The Cepheid is not a member of Collinder 236 on the basis of location beyond the cluster tidal radius and implied distance, but its space reddening can be established as E(B-V)=0.268+-0.006 s.e. from 5 adjacent stars. Period changes in WZ Car studied with the aid of archival data are revised. The period of WZ Car is increasing, its rate of +8.27+-0.19 s yr^(-1) being consistent with a third crossing of the instability strip., Accepted for publication (MNRAS)

Photoelectric, photographic, and CCD UBV photometry, spectroscopic observations, and star counts are presented for the open cluster Berkeley 58 to examine a possible association with the 4.37d Cepheid CG Cas. The cluster is difficult to separate from the early-type stars belonging to the Perseus spiral arm, in which it is located, but has reasonably well-defined parameters: an evolutionary age of ~10^8 years, a mean reddening of E(B-V)_(B0)=0.70+-0.03 s.e., and a distance of 3.03+-0.17 kpc (V_0-M_V=12.40+-0.12 s.d.). CG Cas is a likely cluster coronal member on the basis of radial velocity, and its period increase of +0.170+-0.014 s yr^(-1) and large light amplitude describe a Cepheid in the third crossing of the instability strip lying slightly blueward of strip centre. Its inferred reddening and luminosity are E(B-V)=0.64+-0.02 s.e. and =-3.06+-0.12. A possible K supergiant may also be a cluster member., Comment: Accepted for Publication (MNRAS)

We present CCD BVI photometry for the southern open cluster NGC 2489 and its surrounding field. The sample consists of 2182 stars measured in an area of 13.6 × 13.6 arcmin2, extending down to V ∼ 21.5. These data are supplemented with CORAVEL radial-velocity observations for seven red giant candidates. A cluster angular radius of 6.7 ± 0.6 arcmin, equivalent to 3.5 ± 0.3 pc, is estimated from star counts carried out inside and outside the cluster region. The comparison of the cluster colour–magnitude diagrams with isochrones of the Padova group yields E(B − V) = 0.30 ± 0.05, E(V − I) = 0.40 ± 0.05 and V − MV = 12.20 ± 0.25 for log t = 8.70 (t = 500+130 −100 Myr) and Z = 0.019. NGC 2489 is then located at 1.8 ± 0.3 kpc from the Sun and 25 pc below the Galactic plane. The analysis of the kinematical data allowed us to confirm cluster membership for six red giants, one of them being a spectroscopic binary. A mean radial velocity of 38.13 ± 0.33 km s−1 was derived for the cluster red giants. The properties of a sample of open clusters aligned along the line of sight of NGC 2489 are examined. Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Mermilliod, Jean Claude. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina Fil: Parisi, Maria Celeste. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

We present an analysis of the photometric parallaxes of stars in 21 BATC fields carried out with the National Astronomical Observatories (NAOC) 60/90 cm Schmidt Telescope in 15 intermediate-band filters from 3000 to 10000 {\AA}. In this study, we have adopted a three-component (thin disk, thick disk and halo) model to analyze star counts information. By calculating the stellar space density as a function of distance from the Galactic plane, we determine that the range of scale height for the thin disk varies from 220 to 320 pc. Although 220 pc seems an extreme value, it is close to the lower limit in the literature. The range of scale height for the thick disk is from 600 to 1100 pc, and the corresponding space number density normalization is 7.0-1.0% of the thin disk. We find that the scale height of the disk may be variable with observed direction, which cannot simply be attributed to statistical errors. Possibly the main reasons can be attributed to the disk (mainly the thick disk) is flared, with a scale height increasing with radius. The structure is consistent with merger origin for the thick disk formation. Adopting a de Vaucouleurs $r^{1/4}$ law halo, we also find that the axis ratio towards the Galactic center is somewhat flatter ($\sim 0.4$), while the shape of the halo in the anticentre and antirotation direction is rounder with $c/a> 0.4$. Our results show that star counts in different lines of sight can be used directly to obtain a rough estimate of the shape of the stellar halo. Our solutions support the Galactic models with a flattened inner halo, possibly it is formed by a merger early in the Galaxy's history.

The near infrared extinction powerlaw index ($\beta$) and its uncertainty is derived from three different techniques based on star counts, colour excess and a combination of them. We have applied these methods to 2MASS data to determine maps of $\beta$ and near infrared extinction of the small cloud IC 1396 W. The combination of star counts and colour excess results in the most reliable method to determine $\beta$. It is found that the use of the correct $\beta$-map to transform colour excess values into extinction is fundamental for column density profile analysis of clouds. We describe how artificial photometric data, based on the model of stellar population synthesis of the Galaxy (Robin et al. 2003), can be used to estimate uncertainties and derive systematic effects of the extinction methods presented here. We find that all colour excess based extinction determination methods are subject to small but systematic offsets, which do not affect the star counting technique. These offsets occur since stars seen through a cloud do not represent the same population as stars in an extinction free control field.

CCD observations in the Johnson V, Kron–Cousins I and the Washington system C and T1 passbands have been used to generate colour–magnitude diagrams (CMDs) reaching down to V ∼ 21.0 mag and T1 ∼ 19.0 for Trumpler 5, an old open cluster located towards the Galactic anticentre. Our data analysis confirms the existence of non-uniform extinction over the face of the cluster, the mean E(V − I) and E(C − T1) values being 0.80 ± 0.05 and 1.17 ± 0.15, respectively. Through comparison of the cluster CMDs with theoretical isochrones of the Geneva group, Washington Standard Giant Branches and measures of δV and δT1 indices, we derive the following values for the cluster apparent distance modulus, age, and metallicity: V − MV = 13.80 ± 0.30 (corresponding to a distance from the Sun of 2.4 ± 0.5 kpc and 0.04 kpc above the Galactic plane), t = 5.0 ± 0.5 Gyr and [Fe/H] = −0.30 ± 0.15. We estimate the cluster angular radius to be about 7.7 arcmin (= 5.4 pc) from star counts carried out within and outside the cluster field. Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Claria Olmedo, Juan Jose. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina Fil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina

We determine the initial mass function (IMF) of the ``thin disk'' by means of a direct comparison between synthetic stellar samples (for different matching choices of IMF, star formation rate SFR and depletion) and a complete (volume-limited) sample of single stars near the galactic plane (|z| < 25pc), selected from the Hipparcos catalogue (d < 100pc, M_v < +4.0). Our synthetic samples are computed from first principles: stars are created with a random distribution of mass M_* and age t_* which follow a given (genuine) IMF and SFR(t_*). They are then placed in the HR diagram by means of a grid of empirically well-tested evolution tracks. The quality of the match (synthetic versus observed sample) is assessed by means of star counts in specific regions in the HR diagram. 7 regions are located along the MS (main sequence, mass sensitive), while 4 regions represent different evolved (age-sensitive) stages of the stars. The counts of evolved stars, in particular, give valuable evidence of the history of the ``thin disk'' (apparent) star formation and lift the ambiguities in models restricted to MS star counts.

We interpret published CCD UBVI data to deduce the stellar density distribution and metallicity distribution function in the region from 2 8 kpc from the Galactic Plane, and compare our results to several star count models. A feature of extant star count models is degeneracy between the adopted scale heights of the thin and thick disks, and their local normalisation. We illustrate the utility of this small data set, and future l arger sets (e.g. SDSS), by explicitly considering consistency between the derived density laws, and the implied solar neighbourhood luminosity function. Our data set, from Hall et al. (1996) (l = 52 o ,b = 39 o ) contains 566 stars, selected to be consistent with stellar loci in col our-colour diagrams. The effective apparent V-magnitude interval is 15.5 � Vo � 20.5. Our analysis supports the parameterisation of the recent (SDSS) galaxy model of Chen et al. (2001), except in preferring the stellar halo axis ratio to be � = 0.84. Photometric metal-abundances have been derived for 329 stars with (B V )o � 1.0 using a new calibration. This show a multimodal distribution with peaks at [Fe/H]=-0.10, -0.70, and -1.50 and a tail down to -2.75 dex. The vertical distance-dependent metallicity distribution function, if parameterised by a single mean value, can be described by a metallicity gradient d[Fe/H]/dz � 0.2 dex/kpc for the thin disk and thick disk, and d[Fe/H]/dz � 0.1 dex/kpc for the inner halo, to z=8 kpc. The data are however better described as the sum of three discrete distribution functions, each of which has a small or zero internal gradient. The changing mix of thin disk, thick disk and halo populations with distance from the plane generates an illusion of a smooth gradient.

A preliminary search for stars that may have formed coevally with the apparently young halo B-type star PHL 346 has been performed with the 2dF multifibre spectrograph on the Anglo-Australian Telescope (AAT). Candidates were selected for spectroscopy from APM scans of B and R Schmidt plates centred on PHL 346. A total of 476 stars of spectral type A or F were found; radial velocity estimates and more accurate spectral type assignments narrowed the number of possible coeval candidates to 6 A-type and 14 F-type stars. A statistical analysis of these results using a comparison with a control field suggests that the number of A-type or F-type candidate stars around PHL 346 is not unexpected, and that they need not be associated with PHL 346. A number of ways to improve the project are suggested.

This paper presents a global analysis of the 2MASS (Two Micron All Sky Survey) data as observed in seven fields at different galactic latitudes in our Galaxy. The data allow the preliminary determination of the scale parameters, which lead to strong constraints on the radial and vertical structure of the galactic thin and thick disc. The interpretation of star counts and colour distributions of stars in the near-infrared with the synthetic stellar population model gives strong evidence that the galactic thin disc density scalelength (h R ) is rather short (2.8 ± 0.3 kpc). The galactic thick disc population is revisited in the light of new data. We find the thick disc to have a local density of 3.5 ± 2.0 per cent of the thin disc, exponential scaleheight (h z ) of 860±200 pc and exponential scalelength (h R ) of 3.7 ± 0.8 0.5 kpc.

We present near-IR colour--magnitude diagrams and star counts for a number of regions along the Galactic plane. It is shown that along the l=27 b=0 line of sight there is a feature at 5.7 +-0.7kpc with a density of stars at least a factor two and probably more than a factor five times that of the disc at the same position. This feature forms a distinct clump on an H vs. J-H diagram and is seen at all longitudes from the bulge to about l=28, but at no longitude greater than this. The distance to the feature at l=20 is about 0.5kpc further than at l=27 and by l=10 it has merged with, or has become, the bulge. Given that at l=27 and l=21 there is also a clustering of very young stars, the only component that can reasonably explain what is seen is a bar with half length of around 4kpc and a position angle of about 43+-7., 5 pages, 5 figures accepted as a letter in MNRAS

This article reports optical photometric and spectroscopic observations of the M33 star B416, establishing it as the fifth identified luminous blue variable (LBV) in that galaxy.

ABSTRA C T The Hipparcos mission discovered a few dozen M giant stars with periods P shorter than 10 d. Similar stars may be found in other large data bases of new variables (e.g., OGLE). The three possible sources of the magnitude variations ‐ pulsation, starspots and ellipsoidal deformation ‐ are discussed in general terms. The parallaxes and V 2 I colour indices are used to calculate radii and temperatures for all M giant variables with P , 100 d. Masses are estimated from the positions of the stars in a Hertzsprung‐Russell (HR) diagram, using evolutionary tracks. Using these data, it is shown that starspots can be ruled out as a variability mechanism in almost all cases, and ellipsoidal variations in about half of the stars. Pulsation in very high-overtone modes appears to be the only viable explanation for the stars with P , 10 d. Many of the stars may be multiperiodic. IRAS data are used to deduce information about reddening and circumstellar dust. The apparently low level of mass-loss, as well as the kinematics and the spatial distribution of the stars, indicates that they are from a relatively young (i.e., thin disc) giant star population.

We present the results of a study that uses numerical simulations to interpret observations of tidally disturbed satellites around the Milky Way. When analysing the simulations from the viewpoint of an observer, we find a break in the slope of the star count and velocity dispersion profiles in our models at the location where unbound stars dominate. We conclude that `extra-tidal' stars and enhanced velocity dispersions observed in the outskirts of Galactic satellites are due to contamination by stellar debris from the tidal interaction with the Milky Way. However, a significant bound population can exist beyond the break radius and we argue that it should not be identified with the tidal radius of the satellite. We also develop and test a method for determining the mass loss rate from a Galactic satellite using its extra-tidal population. We apply this method to observations of globular clusters and dwarf spheroidal satellites of the Milky Way, and conclude that a significant fraction of both satellite systems are likely be destroyed within the next Hubble time. Finally, we demonstrate that this mass loss estimate allows us to place some limits on the initial mass function (IMF) of stars in a cluster from the radial dependence of its present day mass function (PDMF)., 18 pages including 22 figures. Submitted to MNRAS

We present first results of Hipparcos observations of nearby low-mass pre-main-sequence (PMS) stars (T Tauri and Herbig Ae/Be stars). The data obtained by Hipparcos allow us to derive weighted mean parallaxes for three major nearby star-forming regions (SFRs), Lupus, Chamaeleon I and Taurus–Auriga. Furthermore, results on the isolated objects AB Dor and TW Hya are presented. Finally, we discuss the evolutionary status of Herbig Ae/Be (HAEBE) stars on the basis of Hipparcos results.

A comparison is made between the age-metallicity relation obtained from four different types of studies: F and G stars in the Solar Neighbourhood, analysis of open clusters, galactic structure studies with the stellar population synthesis technique, and chemical evolution models. Metallicities of open clusters are corrected for the effects of the radial gradient, which we find to be -0.09 dex/kpc and to be most likely constant in time. We do not correct for the vertical gradient, since its existence and value are not firmly established. Stars and clusters trace a similar age-metallicity relation, showing an excess of rather metal-rich objects in the age range 5-9 Gyr. Galactic structure studies tend to give a more metal-poor relation than chemical evolution models. Both relations do not explain the presence of old, relatively metal-rich stars and clusters. This might be due to uncertainties in the ages of the local stars, or to pre-enrichment of the disc with material from the bulge, possibly as a result of a merger event in the early phases of the formation of our Galaxy., 12 pages LaTeX, 8 figures, to appear in MNRAS; replaced figures 6 and 8, added Table 3, and extended the discussion

We present survey data in the narrow-band L filter (nbL), taken at UKIRT, for a total area of 277 square arcmin, roughly equally divided between four regions at zero Galactic latitude and longitudes +-4.3 deg and +-2.3 deg. The 80% completeness level for these observations is at roughly magnitude 11.0. This magnitude limit, owing to the low coefficient for interstellar extinction at this wavelength (A(nbL)=0.047 A(V)), allows us to observe bulge giants. We match the nbL-magnitudes with DENIS survey K magnitudes, and find 95 per cent of nbL sources are matched to K sources. Constructing colour-magnitude diagrams, we deredden the magnitudes and find evidence for a longitude dependent asymmetry in the source counts. We find that there are ~15% and ~5% more sources at the negative longitude than at the corresponding positive longitude, for the fields at +-4.3 deg and +-2.3 deg respectively. This is compared with the predictions of some Galactic bar models. We find an asymmetry in the expected sense, which favours gas dynamical models and the recent deconvolution of surface photometry data (Binney et al. 1991; Binney, Gerhard & Spergel 1997), over earlier treatments of photometric data (e.g. Dwek et al. 1995)., 10 pages, Latex, MNRAS accepted

We address the question of the occurrence of star formation bursts in the solar neighbourhood by using the metallicity distribution of the G dwarfs. We present a method to recover the star formation history using simultaneously the metallicity distribution and the age-metallicity relation. The method associates the number of stars in a given metallicity interval with the corresponding time interval predicted by the age-metallicity relation. We take into account corrections relative to observational errors, cosmic scatter and scale height effects. The method is tested by simulations of the chemical evolution of a galaxy with irregular star formation rate, and our results show that it is possible to recover the star formation history fairly well. The application of the method to the solar neighbourhood shows evidences for at least two strong events of star formation: a burst 8 Gyr ago, and a lull 2-3 Gyr ago. These features confirm some previous studies on the star formation history in the local disk.

The red and infrared intrinsic colours of B stars are derived from photometric observations through the UBV(R1)cJHK and H,8 filters of 257 early-type stars. Those stars for which the UBV and H,8 measurements match the published spectral class, and which show no other signs of peculiarity, are used to determine the intrinsic photometric colours of B stars in the red and infrared. From these intrinsic colours the interstellar reddening relationships for the red and infrared colours are evaluated, and the results are compared with previous estimates of these quantities. The values of R, E(B - V) and the distance are then determined for the individual stars. R is confirmed to be close to 3.1 in most cases, but was found to be much larger in some directions. The relationship between R and the location of a star in the Galaxy is investigated. Usually the abnormally reddened stars seemed to be associated with known regions of star formation. The paper also identifies seven likely variable stars and a number of stars with possible dust shells.

We use star counts from 13 deep HST fields imaged with the {\it Wide Field Camera - 2} in order to constrain the amount of dark matter in the Galaxy that can be in the form of low-mass main sequence stars or white-dwarfs. Based on the number of red stars found in our fields, we exclude the possibility that more than 25\% of the massive dark halo is made up of M dwarfs or subdwarfs; fairly massive ($M \sim 0.2 M_\odot$) and yet extremely faint ($M_I$ \gtsima $14.5$) stellar candidates would have to be invoked in order to make the observed number of stars compatible with that predicted by a stellar dark halo. White dwarfs must also be intrinsically very faint ($M_I$ \gtsima $14$) in order to be consistent with the observed number of faint stars in the HST fields. We also rule out an increasing or flat stellar luminosity function beyond $M_V \sim 13$. The inferred slope of the disk luminosity function is intermediary between local, volume-limited surveys and ground-based photometric ones. Finally, the magnitude counts are well fitted by existing models for the structure of the Galaxy, with only small changes in the fiducial values of the model parameters. The colour distribution, however, is not well reproduced by the models. It is unclear at present if this reflects inadequacies of the available models or uncertainties in the colour-magnitude diagrams for low metallicity stars and in the photometric calibration., 18 pages plus 6 figures

The stellar haloes of galaxies can currently be studied either through observations of resolved halo stars or through surface photometry. Curiously, the two methods appear to give conflicting results, as a number of surface photometry measurements have revealed integrated colours that are too red to be reconciled with the halo properties inferred from the study of resolved stars. Several explanations for this anomaly have been proposed - including dust photoluminescence, extinction of extragalactic background light and a bottom-heavy stellar initial mass function. A decisive test is, however, still lacking. Here, we explain how observations of the halo of a nearby galaxy, involving a combination of both surface photometry and bright star counts, can be used to distinguish between the proposed explanations. We derive the observational requirements for this endeavour and find that star counts in filters VI and surface photometry in filters VIJ appears to be the optimal strategy. Since the required halo star counts are already available for many nearby galaxies, the most challenging part of this test is likely to be the optical surface photometry, which requires several nights of exposure time on a 4-8 m telescope, and the near-IR surface photometry, which is most readily carried out using the upcoming James Webb Space Telescope.

We develop a new method to account for the finite lifetimes of stars and trace individual abundances within a semi-analytic model of galaxy formation. At variance with previous methods, based on the storage of the (binned) past star formation history of model galaxies, our method projects the information about the metals produced by each simple stellar population (SSP) in the future. Using this approach, an accurate accounting of the timings and properties of the individual SSPs composing model galaxies is possible. We analyse the dependence of our chemical model on various ingredients, and apply it to six simulated haloes of roughly Milky Way mass and with no massive close neighbour at z = 0. For all models considered, the [Fe/H] distributions of the stars in the disc component are in good agreement with Milky Way data, while for the spheroid component (whose formation we model only through mergers) these are offset low with respect to observational measurements for the Milky Way bulge. This is a consequence of narrow star formation histories, with relatively low rates of star formation. The slow recycling of gas and energy from supernovae in our chemical model has important consequences on the predicted star formation rates, which are systematically lower than the corresponding rates in the same physical model but with an instantaneous recycling approximation. The halo that resembles most our Galaxy in terms of its global properties also reproduces the observed relation between the average metallicity and luminosity of the Milky Way satellites, albeit with a slightly steeper slope.

We have discovered three very faint carbon stars (m V >19) in the course of a multicolour survey for high-redshift quasars. Proper motion measurements have been made of these stars to determine their luminosity class. On this basis, the star 0045-259 is confirmed as a halo dwarf, joining the four dwarf carbon stars already known. These five dwarfs appear to have similar absolute magnitudes and tangential velocities. A second star, 0041 - 295, is also a dwarf, yet either its absolute magnitude or its tangential velocity differs from those of the five other dwarfs; it may be the first disc dwarf carbon star found. The time baseline for the proper motion measurement for the third star, 2048-48, is too small to allow the luminosity class to be determined