Proper Motion Diagram Research Articles

A Systematic Search for Redback and Black Widow Candidates Based on the 4FGL-DR3 Unassociated Sources and the Zwicky Transient Facility Data

Spider pulsars represent a unique subclass of radio millisecond pulsars in binaries, and are further categorized into black widows and redbacks according to the mass of the low-mass companion. These pulsars, observable across multiple wavelengths, exhibit periodic variability in optical. The discovery and study of additional spider-type pulsars are crucial for a fuller understanding the evolution of binary stars in close orbits and the recycling theory of millisecond pulsars. In this work, we systematically searched for spider pulsar binary systems using time-domain variability data from the Zwicky Transient Facility and unassociated gamma-ray sources from the Fermi 4FGL-DR3 catalog. We developed a time-domain data processing pipeline that employs the Lomb–Scargle periodogram algorithm. As a result, we identified a total of 194 ellipsoidal variables and irradiation-type binary stars. Further refinement using the Gaia Hertzsprung–Russell diagram resulted in a selection of 24 spider pulsar candidates. Incorporating the 4FGL 95% confidence error ellipse reduced the sample to 19 candidates. An additional filter using the Gaia color-reduced proper motion diagram yielded nine “gold sample” candidates. These newly identified spider pulsar candidates will guide future observational campaigns in radio, X-ray, and optical spectroscopy, aiding in the comprehensive validation of their nature.

VVVX survey dusts off a new intermediate-age star cluster in the Milky Way disk

Context. In the last decade, many new star clusters have been discovered in heavily obscured regions of the Milky Way bulge and disk. Aims. Our primary long-term objective is to seek out additional star clusters in the poorly studied regions of the Milky Way, where detections pose significant challenges. The aim of this pursuit is to finalize the Milky Way’s globular and open cluster system census and to gain a comprehensive understanding of both the formation and evolution of these systems and our Galaxy as a whole. Methods. We report the discovery of a new star cluster, named Garro 03. We investigated this new target using a combination of near-infrared and optical databases. We employed the VISTA Variables in the Via Láctea Survey and Two Micron All Sky Survey data in the near-infrared, and the Gaia Data Release 3 and the DECam Plane Survey datasets in the optical passband. We constructed density maps and vector proper motion diagrams in order to highlight our target. We performed a photometrical analysis in order to derive its main physical parameters. Results. Garro 03 is located at equatorial coordinates RA = 14:01:29.3 and Dec = −65:30:57.0. From our photometric analysis we find that this cluster is not heavily affected by extinction with AKs = 0.25 ± 0.04 mag and AG = 1.54 ± 0.02 mag. It is located at heliocentric distance of 14.1 ± 0.5 kpc, which places Garro 03 at 10.6 kpc from the Galactic centre and Z = −0.89 kpc below the Galactic plane. We also calculated the mean cluster proper motion of (μα*,μδ)=(−4.57 ± 0.29, −1.36 ± 0.27) mas yr−1. We derived an age of 3 Gyr and metallicity [Fe/H] = −0.5 ± 0.2 by the isochrone-fitting method, employing the PARSEC models. The total luminosity was derived in the Ks and V bands, finding MKs = −6.32 ± 1.10 mag and MV = −4.06 mag. Finally, the core and tidal radii were measured constructing the Garro 03 radial density profile and fitting the King model. We obtained rc = 3.07 ± 0.98 pc and rt = 19.36 ± 15.96 pc, respectively. Conclusions. We photometrically confirm the cluster nature for Garro 03, located in the Galactic disk. It is a distant, low-luminosity, metal-rich star cluster of intermediate age. We also searched for possible signatures (streams or bridges) between Garro 03 and Garro 01, but we exclude a companionship with the present analysis. We need spectroscopic data to classify it as an old open cluster or a young globular cluster, and to understand its origin.

M-subdwarf Research. II. Atmospheric Parameters and Kinematics

Abstract We applied the revised M subdwarf classification criteria discussed in Zhang et al. to Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR7 and combined the result with the M subdwarf sample from Savcheva et al. to construct a new M subdwarf sample for further study. The atmospheric parameters for each object were derived from fitting to the PHOENIX grid, and the sources with available astrometry and photometry from Gaia DR2 were combined for further analysis. The relationship between the gravity and metallicity was explored according to the locus both in the color–absolute magnitude diagram and the reduced proper motion diagram. Objects that have both the largest gravity and the lowest metallicity are located away from the main-sequence cloud and may be considered as the intrinsic M subdwarfs, which can be classified as luminosity class VI. Another group of objects whose spectra show typical M subdwarf characteristics have lower gravity and relatively moderate metal deficiency and occupy part of the ordinary M dwarf region in both diagrams. The Galactic U, V, W space velocity components and their dispersion show that the local Galactic halo population sampled in the solar neighborhood is represented by objects of high gravity and an inconspicuous bimodal metallicity distribution, with a fraction of prograde orbits. The other M subdwarfs seem to belong in part to the thick disk component, with a significant fraction of thin disk, moderately metal-poor objects intricately mixed with them. However, selection effects, especially the favored anticenter direction of investigation in the LAMOST subsample, as well as contamination by multiplicity and parameter coupling, could play important roles and need to be investigated further.

The Canada–France Imaging Survey: Reconstructing the Milky Way Star Formation History from Its White Dwarf Population

Abstract As the remnants of stars with initial masses ≲8 M ⊙, white dwarfs contain valuable information on the formation histories of stellar populations. In this paper, we use deep, high-quality, u-band photometry from the Canada–France Imaging Survey, griz photometry from Pan-STARRS1, as well as proper motions from Gaia DR2, to select 25,156 white dwarf candidates over ∼4500 deg2 using a reduced proper motion diagram. We develop a new white dwarf population synthesis code that returns mock observations of the Galactic field white dwarf population for a given star formation history, while simultaneously taking into account the geometry of the Milky Way (MW), survey parameters, and selection effects. We use this model to derive the star formation histories of the thin disk, thick disk, and stellar halo. Our results show that the MW disk began forming stars (11.3 ± 0.5) Gyr ago, with a peak rate of (8.8 ± 1.4) M ⊙ yr −1 at (9.8 ± 0.4) Gyr, before a slow decline to a constant rate until the present day—consistent with recent results suggesting a merging event with a satellite galaxy. Studying the residuals between the data and best-fit model shows evidence for a slight increase in star formation over the past 3 Gyr. We fit the local fraction of helium-atmosphere white dwarfs to be (21 ± 3)%. Incorporating this methodology with data from future wide-field surveys such as the Large Synoptic Survey Telescope, Euclid, The Cosmological Advanced Survey Telescope for Optical and ultraviolet Research, and the Wide Field Infrared Survey Telescope should provide an unprecedented view into the formation of the MW at its earliest epoch through its white dwarfs.

Study of open cluster NGC 5617 in Gaia era

AbstractIdentification of member stars in open clusters is still an open question. Thanks to Gaia DR2 data base, which improves our statistics regarding true members in clusters to understand cluster properties much better way. In this paper, we identify the cluster members using proper motion and colour magnitude diagram for NGC 5617. In addition to this, we have determined more precise fundamental parameters as well.

Analysis of the physical nature of 22 New VVV Survey Globular Cluster candidates in the Milky Way bulge

In order to characterize 22 new globular cluster (GC) candidates in the Galactic bulge, we present their colour-magnitude diagrams (CMDs) and Ks-band luminosity functions (LFs) using the near-infrared VVV database as well as Gaia-DR2 proper motion dataset. CMDs were obtained, on one hand, after properly decontaminating the observed diagrams from background/foreground disc stars and other sources. On the other hand, CMDs were also obtained based upon star selection in proper motion diagrams. Taking into account our deep CMDs and LFs analyses, we find that 17 out of 22 new GC candidates may be real and should therefore be followed-up, while 5 candidates were discarded from the original sample. We also search for RR Lyrae and Mira variable stars in the fields of these new GC candidates. In particular, we confirm that Minni 40 may be a real cluster. If confirmed by further follow-up analysis, it would be the closest GC to the Galactic centre in projected angular distance, located only 0.5 deg away from it. We consider that it is very difficult to confirm the physical reality of these small, poorly-populated bulge GCs so in many cases alternative techniques are needed to corroborate our findings.

A distant sample of halo wide binaries from SDSS

Samples of reliably identified halo wide binaries are scarce. If reasonably free from selection effects and with a small degree of contamination by chance alignments, these wide binaries become a powerful dynamical tool, having provided one of the very few experiments capable of constraining the nature of dark matter in the Milky Way halo. Currently, however, the best available sample of halo wide binaries is confined to the solar neighborhood, and is plagued by small number statistics at the widest separations. We present the results of a program aimed to probe the wide binary population of the Galactic halo at significantly larger distances, and which informs future searches that could improve the statistics by orders of magnitude. Halo stars were taken from the Sloan Digital Sky Survey after analysing the Galactic orbits of stars in the reduced proper motion diagram. We then select candidate binaries by searching for pairs with small differences in proper motion and small projected separation on the sky. Using medium-resolution spectroscopy, a subsample of candidates is validated via radial velocities, finding that about 68\% of candidate pairs up to 20$^{\prime\prime}$ separation can be considered genuine halo wide binaries, to the limits of the available data. Precise parallaxes from \textit{Gaia} confirm that most of our selected pairs have their components at the same distances, independently confirming the robustness of our selection method. These results should prove valuable to guide the optimal assembly of larger catalogs of halo wide binaries from upcoming large databases, e.g., \textit{Gaia} and LSST.

The Next Generation Virgo Cluster Survey. XXVIII. Characterization of the Galactic White Dwarf Population

Abstract We use three different techniques to identify hundreds of white dwarf (WD) candidates in the Next Generation Virgo Cluster Survey (NGVS) based on photometry from the NGVS and GUViCS, and proper motions derived from the NGVS and the Sloan Digital Sky Survey (SDSS). Photometric distances for these candidates are calculated using theoretical color–absolute magnitude relations, while effective temperatures are measured by fitting their spectral energy distributions. Disk and halo WD candidates are separated using a tangential velocity cut of 200 km s−1 in a reduced proper motion diagram, which leads to a sample of six halo WD candidates. Cooling ages, calculated for an assumed WD mass of 0.6M ⊙, range between 60 Myr and 6 Gyr, although these estimates depend sensitively on the adopted mass. Luminosity functions for the disk and halo subsamples are constructed and compared to previous results from the SDSS and SuperCOSMOS survey. We compute a number density of (2.81 ± 0.52) × 10−3 pc−3 for the disk WD population—consistent with previous measurements. We find (7.85 ± 4.55) × 10−6 pc−3 for the halo, or 0.3% of the disk. Observed stellar counts are also compared to predictions made by the TRILEGAL and Besançon stellar population synthesis models. The comparison suggests that the TRILEGAL model overpredicts the total number of WDs. The WD counts predicted by the Besançon model agree with the observations, although a discrepancy arises when comparing the predicted and observed halo WD populations; the difference is likely due to the WD masses in the adopted model halo.

PHYSICAL PROPERTIES OF THE CURRENT CENSUS OF NORTHERN WHITE DWARFS WITHIN 40 pc OF THE SUN

We present a detailed description of the physical properties of our current census of white dwarfs within 40 pc of the Sun, based on an exhaustive spectroscopic survey of northern hemisphere candidates from the SUPERBLINK proper motion database. Our method for selecting white dwarf candidates is based on a combination of theoretical color-magnitude relations and reduced proper motion diagrams. We reported in an earlier publication the discovery of nearly 200 new white dwarfs, and we present here the discovery of an additional 133 new white dwarfs, among which we identify 96 DA, 3 DB, 24 DC, 3 DQ, and 7 DZ stars. We further identify 178 white dwarfs that lie within 40 pc of the Sun, representing a 40% increase of the current census, which now includes 492 objects. We estimate the completeness of our survey at between 66 and 78%, allowing for uncertainties in the distance estimates. We also perform a homogeneous model atmosphere analysis of this 40 pc sample and find a large fraction of massive white dwarfs, indicating that we are successfully recovering the more massive, and less luminous objects often missed in other surveys. We also show that the 40 pc sample is dominated by cool and old white dwarfs, which populate the faint end of the luminosity function, although trigonometric parallaxes will be needed to shape this part of the luminosity function more accurately. Finally, we identify 4 probable members of the 20 pc sample, 4 suspected double degenerate binaries, and we also report the discovery of two new ZZ Ceti pulsators.

A TECHNIQUE TO DERIVE IMPROVED PROPER MOTIONS FORKEPLEROBJECTS OF INTEREST

We outline an approach yielding proper motions with higher precision than exists in present catalogs for a sample of stars in the Kepler field. To increase proper motion precision we combine first moment centroids of Kepler pixel data from a single Season with existing catalog positions and proper motions. We use this astrometry to produce improved reduced proper motion diagrams, analogous to a Hertzsprung-Russell diagram, for stars identified as Kepler Objects of Interest. The more precise the relative proper motions, the better the discrimination between stellar luminosity classes. With UCAC4 and PPMXL epoch 2000 positions (and proper motions from those catalogs as quasi-bayesian priors) astrometry for a single test Channel (21) and Season (0) spanning two years yields proper motions with an average per-coordinate proper motion error of 1.0 millisecond of arc per year, over a factor of three better than existing catalogs. We apply a mapping between a reduced proper motion diagram and an HR diagram, both constructed using HST parallaxes and proper motions, to estimate Kepler Object of Interest K-band absolute magnitudes. The techniques discussed apply to any future small-field astrometry as well as the rest of the Kepler field.

A NEW SAMPLE OF COOL SUBDWARFS FROM SDSS: PROPERTIES AND KINEMATICS

We present a new sample of M subdwarfs compiled from the 7th data release of the Sloan Digital Sky Survey. With 3517 new subdwarfs, this new sample significantly increases the number of spectroscopically confirmed low-mass subdwarfs. This catalog also includes 905 extreme and 534 ultra sudwarfs. We present the entire catalog including observed and derived quantities, and template spectra created from co-added subdwarf spectra. We show color-color and reduced proper motion diagrams of the three metallicity classes, which are shown to separate from the disk dwarf population. The extreme and ultra subdwarfs are seen at larger values of reduced proper motion as expected for more dynamically heated populations. We determine 3D kinematics for all of the stars with proper motions. The color-magnitude diagrams show a clear separation of the three metallicity classes with the ultra and extreme subdwarfs being significantly closer to the main sequence than the ordinary subdwarfs. All subdwarfs lie below (fainter) and to the left (bluer) of the main sequence. Based on the average $(U,V,W)$ velocities and their dispersions, the extreme and ultra subdwarfs likely belong to the Galactic halo, while the ordinary subdwarfs are likely part of the old Galactic (or thick) disk. An extensive activity analysis of subdwarfs is performed using H$\alpha$ emission and 208 active subdwarfs are found. We show that while the activity fraction of subdwarfs rises with spectral class and levels off at the latest spectral classes, consistent with the behavior of M dwarfs, the extreme and ultra subdwarfs are basically flat.

OPTICALBVRIPHOTOMETRY OF COMMON PROPER MOTION F/G/K+M WIDE SEPARATION BINARIES

We present optical (BVRI) photometric measurements of a sample of 76 common proper motion wide separation main sequence binary pairs. The pairs are composed of a F-, G-, or K-type primary star and an M-type secondary. The sample is selected from the revised NLTT catalog and the LSPM catalog. The photometry is generally precise to 0.03 mag in all bands. We separate our sample into two groups, dwarf candidates and subdwarf candidates, using the reduced proper motion (RPM) diagram constructed with our improved photometry. The M subdwarf candidates in general have larger $V-R$ colors than the M dwarf candidates at a given $V-I$ color. This is consistent with an average metallicity difference between the two groups, as predicted by the PHOENIX/BT-Settl models. The improved photometry will be used as input into a technique to determine the metallicities of the M-type stars.

AN IMPROVED CATALOG OF HALO WIDE BINARY CANDIDATES

We present an improved catalog of halo wide binaries, compiled from an extensive literature search. Most of our binaries stem from the common proper motion binary catalogs by Allen et al. (2004), and Chanam\'e \& Gould. (2004) but we have also included binaries from the lists of Ryan (1992) and Zapatero-Osorio \& Martin (2004). All binaries were carefully checked and their distances and systemic radial velocities are included, when available. Probable membership to the halo population was tested by means of reduced proper motion diagrams for 251 candidate halo binaries. After eliminating obvious disk binaries we ended up with 211 probable halo binaries, for 150 of which radial velocities are available. We compute galactic orbits for these 150 binaries and calculate the time they spend within the galactic disk. Considering the full sample of 251 candidate halo binaries as well as several subsamples, we find that the distribution of angular separations (or expected major semiaxes) follows a power law $f(a) \sim a^{-1}$ (Oepik's relation) up to different limits. For the 50 most disk-like binaries, those that spend their entire lives within $z = \pm 500$~pc, this limit is found to be 19,000 AU (0.09 pc), while for the 50 most halo-like binaries, those that spend on average only 18\% of their lives within $z = \pm 500$~pc, the limit is 63,000 AU (0.31 pc). In a companion paper we employ this catalog to establish limits on the masses of the halo massive perturbers (MACHOs).

SEARCH FOR BRIGHT NEARBY M DWARFS WITH VIRTUAL OBSERVATORY TOOLS

Using Virtual Observatory tools, we cross-matched the Carlsberg Meridian 14 and the 2MASS Point Source catalogs to select candidate nearby bright M dwarfs distributed over ~ 25,000 deg^2. Here, we present reconnaissance low-resolution optical spectra for 27 candidates that were observed with the Intermediate Dispersion Spectrograph at the 2.5m Isaac Newton Telescope (R ~ 1600). We derived spectral types from a new spectral index, R, which measures the ratio of fluxes at 7485-7015 A and 7120-7150 A. We also used VOSA, a Virtual Observatory tool for spectral energy distribution fitting, to derive effective temperatures and surface gravities for each candidate. The resulting 27 targets were M dwarfs brighter than J = 10.5 mag, 16 of which were completely new in the Northern hemisphere and 7 of which were located at less than 15 pc. For all of them, we also measured H{\alpha} and Na I pseudo-equivalent widths, determined photometric distances, and identified the most active stars. The targets with the weakest sodium absorption, namely J0422+2439 (with X-ray and strong H{\alpha} emissions, J0435+2523, and J0439+2333, are new members in the young Taurus-Auriga star-forming region based on proper motion, spatial distribution, and location in the color-magnitude diagram, which reopens the discussion on the deficit of M2-4 Taurus stars. Finally, based on proper motion diagrams, we report on a new wide M-dwarf binary system in the field, LSPM J0326+3929EW.

Apex determination and detection of stellar clumps in the open cluster M 67

We determined the cluster’s apex coordinates, studied the substructures and performed membership analysis in the central part (34′×33′) of the open cluster M 67. We used the individual stellar apexes method developed earlier and classical technique of proper motion diagrams in coordinate system connected with apex. The neighbour-to-neighbour distance technique was applied to detect space details. The membership list was corrected and some stars were excluded from the most probable members list. The apex coordinates have been determined as: A0=132.97°±0.81° and D0=11.85°±0.90°. The 2D-space star density field was analysed and high degree of inhomogeneity was found.

A deep WISE search for very late type objects and the discovery of two halo/thick-disc T dwarfs: WISE 0013+0634 and WISE 0833+0052

A method is defined for identifying late T and Y dwarfs in WISE down to low values of signal-to-noise. This requires a WISE detection only in the W2-band and uses the statistical properties of the WISE multi-frame measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources. To trace our desired parameter space we use a control sample of isolated non-moving non-variable point sources from the SDSS, and identify a sample of 158 WISE W2-only candidates down to a signal-to-noise limit of 8. For signal-to-noise ranges >10 and 8-10 respectively, ~45% and ~90% of our sample fall outside the selection criteria published by the WISE team (Kirkpatrick et al. 2012), due mainly to the type of constraints placed on the number of individual W2 detections. We present follow-up of eight candidates and identify WISE 0013+0634 and WISE 0833+0052, T8 and T9 dwarfs with high proper motion (~1.3 and ~1.8 arcsec/yr). Both objects show a mid-infrared/near-infrared excess of ~1-1.5 magnitudes, and are K-band suppressed. Distance estimates lead to space motion constraints that suggest halo (or at least thick disk) kinematics. We then assess the reduced proper motion diagram of WISE ultracool dwarfs, which suggests that late T and Y dwarfs may have a higher thick-disk/halo population fraction than earlier objects.

New companions in the stellar systems of DI Cha, Sz 22, CHXR 32, and Cha Hα5 in the Chamaeleon I star-forming region

The star-forming regions in Chamaeleon (Cha) are among the nearest (distance ~165 pc) and youngest (age ~2 Myrs) conglomerates of recently formed stars and among the ideal targets for studies of star formation. We search for new, hitherto unknown binary or multiple-star components and investigate their membership in Cha and their gravitationally bound nature. We used the NACO instrument at the VLT UT 4/YEPUN of the Paranal Observatory, at 2 or 3 different epochs, in order to obtain relative and absolute astrometric measurements, as well as differential photometry in the J, H, and Ks band. On the basis of known proper motions and these observations, we analysed the astrometric results in proper motion diagrams to eliminate possible (non-moving) background stars and establish co-moving binaries and multiples. DI Cha turns out to be a quadruple system with a hierachical structure, consisting of two binaries: a G2/M6 pair and a co-moving pair of two M5.5 dwarfs. For both pairs we detected orbital motion (P~130 and ~65 years), although in opposite directions. Sz 22 is a binary whose main component is embedded in a circumstellar disc or reflection nebula, accompanied by a co-moving M4.5 dwarf. CHXR 32 is a triple system, consisting of a single G5 star, weakened by an edge-on disc and a co-moving pair of M1/M3.5 dwarfs whose components show significant variations in their angular separation. Finally, Cha Halpha 5 is a binary consisting of two unresolved M6.5 dwarfs whose strong variations in position angle at its projected separation of only 8 AU imply an orbital period of ~46 years. DI Cha D and Cha Halpha 5 A&B are right at the stellar mass limit and could possibly be brown dwarfs. In spite of various previously published studies of the star-forming regions in Cha we found four hitherto unknown components in young low-mass binaries and multiple systems. (abridged)

76 T dwarfs from the UKIDSS LAS: benchmarks, kinematics and an updated space density

We report the discovery of 76 new T dwarfs from the UKIDSS Large Area Survey (LAS). Near-infrared broad and narrow-band photometry and spectroscopy are presented for the new objects, along with WISE and warm-Spitzer photometry. Proper motions for 128 UKIDSS T dwarfs are presented from a new two epoch LAS proper motion catalogue. We use these motions to identify two new benchmark systems: LHS 6176AB, a T8+M4 pair and HD118865AB, a T5.5+F8 pair. Using age constraints from the primaries and evolutionary models to constrain the radii we have estimated their physical properties from their bolometric luminosity. We compare the colours and properties of known benchmark T dwarfs to the latest model atmospheres and draw two principal conclusions. Firstly, it appears that the H - [4.5] and J - W2 colours are more sensitive to metallicity than has previously been recognised, such that differences in metallicity may dominate over differences in Teff when considering relative properties of cool objects using these colours. Secondly, the previously noted apparent dominance of young objects in the late-T dwarf sample is no longer apparent when using the new model grids and the expanded sample of late-T dwarfs and benchmarks. This is supported by the apparently similar distribution of late-T dwarfs and earlier-type T dwarfs on reduced proper motion diagrams that we present. Finally, we present updated space densities for the late-T dwarfs, and compare our values to simulation predictions and those from WISE.

TOWARD A SPECTROSCOPIC CENSUS OF WHITE DWARFS WITHIN 40 pc OF THE SUN

We present the preliminary results of a survey aimed at significantly increasing the range and completeness of the local census of spectroscopically confirmed white dwarfs. The current census of nearby white dwarfs is reasonably complete only to about 20 parsecs of the Sun, a volume that includes around 130 white dwarfs, a sample too small for detailed statistical analyses. This census is largely based on follow-up investigations of stars with very large proper motions. We describe here the basis of a method that will lead to a catalog of white dwarfs within 40 parsecs of the Sun and north of the celestial equator, thus increasing by a factor of 8 the extent of the northern sky census. White dwarf candidates are identified from the SUPERBLINK proper motion database, allowing us to investigate stars down to a proper motion limit mu>40 mas yr-1, while minimizing the kinematic bias for nearby objects. The selection criteria and distance estimates are based on a combination of color-magnitude and reduced proper motion diagrams. Our follow-up spectroscopic observation campaign has so far uncovered 193 new white dwarfs, among which we identify 127 DA (including 9 DA+dM and 4 magnetic), 1 DB, 56 DC, 3 DQ, and 6 DZ stars. We perform a spectroscopic analysis on a subsample of 84 DAs, and provide their atmospheric parameters. In particular, we identify 11 new white dwarfs with spectroscopic distances within 25 pc of the Sun, including 5 candidates to the D<20 pc subset.

Sub-stellar objects with habitable-zone temperatures: A new search for Y dwarfs in WISE

A method is defined for using the maximum sensitivity of WISE to find late T and Y dwarfs. This requires a WISE detection only in the W 2-band and uses the statistical properties of the WISE multi-frame measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources. To trace our desired parameter space we use a control sample of isolated non-moving non-variable point sources from the SDSS, and identify a sample of 158 WISE W 2-only candidates down to a signal-to-noise limit of 8. For signal-to-noise ranges >10 and 8-10 respectively, ∼45% and ∼90% of our sample fall outside the criteria published by the WISE team (Kirkpatrick et al. 2012), due mainly to the type of constraints placed on the number of individual W 2 detections. We present some early follow-up of our sample and identify two new very late objects with high proper motion (∼1.3 and ∼1.8 arcsec yr −1 ). Based on colour, brightness and proper motion, these object are either ∼T9 dwarfs with thick-disk/halo kinematics, or Y dwarfs with more disk-like kinematics. Reduced proper motion diagrams are also presented which suggest that late T and Y dwarfs may have a much higher thick-disk/halo population fraction than earlier objects.