Absolute Proper Motions Research Articles

KINEMATICS IN KAPTEYN'S SELECTED AREA 76: ORBITAL MOTIONS WITHIN THE HIGHLY SUBSTRUCTURED ANTICENTER STREAM

We have measured the mean three-dimensional kinematics of stars in Kapteyn's Selected Area (SA) 76 (l = 2093, b = 264) that were selected to be Anticenter Stream (ACS) members on the basis of their radial velocities (RVs), proper motions (PMs), and location in the color–magnitude diagram. From a total of 31 stars ascertained to be ACS members primarily from its main-sequence turnoff, a mean ACS RV (derived from spectra obtained with the Hydra multi-object spectrograph on the WIYN 3.5 m telescope) of Vhelio = 97.0 ± 2.8 km s−1 was determined, with an intrinsic velocity dispersion σo = 12.8 ± 2.1 km s−1. The mean absolute PMs of these 31 ACS members are μα cos δ = −1.20 ± 0.34 mas yr−1 and μδ = −0.78 ± 0.36 mas yr−1. At a distance to the ACS of 10 ± 3 kpc, these measured kinematical quantities produce an orbit that deviates by ∼30° from the well-defined swath of stellar overdensity constituting the ACS in the western portion of the Sloan Digital Sky Survey footprint. We explore possible explanations for this and suggest that our data in SA 76 are measuring the motion of a kinematically cold sub-stream among the ACS debris that was likely a fragment of the same infalling structure that created the larger ACS system. The ACS is clearly separated spatially from the majority of claimed Monoceros ring detections in this region of the sky; however, with the data in hand, we are unable to either confirm or rule out an association between the ACS and the poorly understood Monoceros structure.

PROPER-MOTION STUDY OF THE MAGELLANIC CLOUDS USING SPM MATERIAL

Absolute proper motions are determined for stars and galaxies to V=17.5 over a 450 square-degree area that encloses both Magellanic Clouds. The proper motions are based on photographic and CCD observations of the Yale/San Juan Southern Proper Motion program, which span over a baseline of 40 years. Multiple, local relative proper motion measures are combined in an overlap solution using photometrically selected Galactic Disk stars to define a global relative system that is then transformed to absolute using external galaxies and Hipparcos stars to tie into the ICRS. The resulting catalog of 1.4 million objects is used to derive the mean absolute proper motions of the Large Magellanic Cloud and the Small Magellanic Cloud; $(\mu_\alpha\cos\delta,\mu_\delta)_{LMC}=(1.89,+0.39)\pm (0.27,0.27)\;\;\{mas yr}^{-1}$ and $(\mu_\alpha\cos\delta,\mu_\delta)_{SMC}=(0.98,-1.01)\pm (0.30,0.29)\;\;\{mas yr}^{-1}$. These mean motions are based on best-measured samples of 3822 LMC stars and 964 SMC stars. A dominant portion (0.25 mas yr$^{-1}$) of the formal errors is due to the estimated uncertainty in the inertial system of the Hipparcos Catalog stars used to anchor the bright end of our proper motion measures. A more precise determination can be made for the proper motion of the SMC {\it relative} to the LMC; $(\mu_{\alpha\cos\delta},\mu_\delta)_{SMC-LMC} = (-0.91,-1.49) \pm (0.16,0.15)\;\;\{mas yr}^{-1}$. This differential value is combined with measurements of the proper motion of the LMC taken from the literature to produce new absolute proper-motion determinations for the SMC, as well as an estimate of the total velocity difference of the two clouds to within $\pm$54 kms$^{-1}$.

SPACE VELOCITIES OF SOUTHERN GLOBULAR CLUSTERS. VI. NINE CLUSTERS IN THE INNER MILKY WAY

We have measured the absolute proper motions of nine low-latitude, inner Galaxy globular clusters, namely, NGC 6273 (M 19), NGC 6284, NGC 6287, NGC 6293, NGC 6333 (M 9), NGC 6342, NGC 6356, NGC 6388, and NGC 6441. These are the first determinations ever made for these clusters. The proper motions are on the International Celestial Reference System via Hipparcos. The proper-motion errors range between 0.4 and 0.9 mas yr−1 and are dominated by the number of measurable cluster members in these regions which are very crowded by the bulge/bar and the thick disk. This sample contains five metal-poor ([Fe/H] < −1.0) and four metal-rich ([Fe/H] ⩾ −1.0) clusters; seven clusters are located within ∼4 kpc from the Galactic center, while the remaining two, namely NGC 6356 and NGC 6284, are in the background of the bulge at ∼7.5 kpc from the Galactic center. By combining proper motions with radial velocities and distances from the literature we derive three-dimensional velocities. In a number of cases, distance uncertainties make the kinematical classification ambiguous. For the metal-poor group of clusters, we find that three clusters, namely NGC 6273, NGC 6287, and NGC 6293 are members of a kinematically hot system, the inner halo. As for the remaining two metal-poor clusters, NGC 6284 is located at ∼7.5 kpc from the Galactic center and kinematically belongs to the thick disk, while NGC 6333, located in the inner ∼2 kpc, has an uncertain membership (between halo and thick disk) due to the distance uncertainty. Within the metal-rich group of clusters, NGC 6356 and NGC 6342 have velocities compatible with membership in the thick disk; however, velocity uncertainties do not allow us to rule out their belonging to a hotter system. NGC 6342 is within ∼2 kpc from the Galactic center, and thus it may belong to the bulge. NGC 6356 is at ∼7.5 kpc from the Galactic center and thus its metallicity, kinematics, and location argue together in favor of thick-disk membership. The remaining two metal-rich clusters, NGC 6388 and NGC 6441, have velocities incompatible with membership in the thick disk or the bar of the Milky Way. They can be thought of as members of a kinematically hot system in the inner Galaxy. Curiously, both clusters have similar velocity components. Together with their similar Galactic location and peculiar but similar stellar-population characteristics, these two clusters may share a common origin. Their velocities are also very low indicating that the two clusters are now at apocenter, i.e., they will not leave the inner ∼4 kpc of the Galaxy.

A GALACTIC ORIGIN FOR HE 0437–5439, THE HYPERVELOCITY STAR NEAR THE LARGE MAGELLANIC CLOUD

We use Hubble Space Telescope imaging to measure the absolute proper motion of the hypervelocity star (HVS) HE 0437-5439, a short-lived B star located in the direction of the Large Magellanic Cloud (LMC). We observe (\mu_\alpha, \mu_\delta)=(+0.53+-0.25(stat)+-0.33(sys), +0.09+-0.21(stat)+-0.48(sys)) mas/yr. The velocity vector points directly away from the center of the Milky Way; an origin from the center of the LMC is ruled out at the 3-sigma level. The flight time of the HVS from the Milky Way exceeds its main-sequence lifetime, thus its stellar nature requires it to be a blue straggler. The large space velocity rules out a Galactic-disk ejection. Combining the HVS's observed trajectory, stellar nature, and required initial velocity, we conclude that HE 0437-5439 was most likely a compact binary ejected by the Milky Way's central black hole.

Ground-based CCD astrometry with wide field imagers

High precision astrometry requires an accurate geometric distortion solution. In this work, we present an average correction for the Blue Camera of the Large Binocular Telescope which enables a relative astrometric precision of ~15 mas for the B_Bessel and V_Bessel broad-band filters. The result of this effort is used in two companion papers: the first to measure the absolute proper motion of the open cluster M67 with respect to the background galaxies; the second to decontaminate the color-magnitude diagram of M67 from field objects, enabling the study of the end of its white dwarf cooling sequence. Many other applications might find this distortion correction useful.

Proper Motions of Local Group Dwarf Spheroidal Galaxies I: First Ground-Based Results for Fornax11Based on observations made with ESO Telescopes at the La Silla Observatory under program ID 060.A-9701, 065.N-0472, 066.B.0276, 074.B-0456, 076.B-0528, 079.B-0379, 080.B-0144, 081.B-0534, and 082.B-0034.

ABSTRACTIn this article we present in detail the methodology and the first results of a ground-based program to determine the absolute proper motion of the Fornax dwarf spheroidal galaxy. The proper motion was determined using bona fide Fornax star members measured with respect to a fiducial at-rest background spectroscopically confirmed quasar, QSO J0240-3434B. Our homogeneous measurements, based on this one quasar gives a value of (μα cos δ,μδ) = (0.64 ± 0.08,-0.01 ± 0.11) mas yr-1. There are only two other (astrometric) determinations for the transverse motion of Fornax: one based on a combination of plates and HST data, and another (of higher internal precision) based on HST data. We show that our proper motion errors are similar to those derived from HST measurements on individual QSOs. We provide evidence that, as far as we can determine it, our motion is not affected by magnitude, color, or other potential systematic effects. Last epoch measurements and reductions are underway for other four quasar fields of this galaxy, which, when combined, should yield proper motions with a weighted mean error of ∼50 μas yr-1, allowing us to place important constraints on the orbit of Fornax.

An investigation of the absolute proper motions of the XPM catalogue

The XPM-1.0 is the regular version of the XPM catalogue. In comparison with XPM the astrometric catalogue of about 280 millions stars covering entire sky from -90 to +90 degrees in declination and in the magnitude range 10^m<B<22^m is something improved. The general procedure steps were followed as for XPM, but some of them are now performed on a more sophisticated level. The XPM-1.0 catalogue contains star positions, proper motions, 2MASS and USNO photometry of about 280 millions of the sources. We present some investigations of the absolute proper motions of XPM-1.0 catalogue and also the important information for the users of the catalogue. Unlike previous version, the XPM-1.0 contains the proper motions over the whole sky without gaps. In the fields, which cover the zone of avoidance or which contain less than of 25 galaxies a quasi absolute calibration was performed. The proper motion errors are varying from 3 to 10 mas/yr, depending on a specific field. The zero-point of the absolute proper motion frame (the absolute calibration) was specified with more than 1 million galaxies from 2MASS and USNO-A2.0. The mean formal error of absolute calibration is less than 1 mas/yr.

THE PPMXL CATALOG OF POSITIONS AND PROPER MOTIONS ON THE ICRS. COMBINING USNO-B1.0 AND THE TWO MICRON ALL SKY SURVEY (2MASS)

USNO-B1.0 and 2MASS are the most widely used full-sky surveys. However, 2MASS has no proper motions at all, and USNO-B1.0 published only relative, not absolute (i.e. on ICRS) proper motions. We performed a new determination of mean positions and proper motions on the ICRS system by combining USNO-B1.0 and 2MASS astrometry. This catalog is called PPMXL {VO-access to the catalog is possible via http://vo.uni-hd.de/ppmxl}, and it aims to be complete from the brightest stars down to about $V \approx 20$ full-sky. PPMXL contains about 900 million objects, some 410 million with 2MASS photometry, and is the largest collection of ICRS proper motions at present. As representative for the ICRS we chose PPMX. The recently released UCAC3 could not be used because we found plate-dependent distortions in its proper motion system north of -20$^\circ$ declination. UCAC3 served as an intermediate system for $\delta \leq -20^\circ$. The resulting typical individual mean errors of the proper motions range from 4 mas/y to more than 10 mas/y depending on observational history. The mean errors of positions at epoch 2000.0 are 80 to 120 mas, if 2MASS astrometry could be used, 150 to 300 mas else. We also give correction tables to convert USNO-B1.0 observations of e.g. minor planets to the ICRS system.

DETECTION OF A STELLAR STREAM BEHIND OPEN CLUSTER NGC 188: ANOTHER PART OF THE MONOCEROS STREAM

We present results from a WIYN/OPTIC photometric and astrometric survey of the field of the open cluster NGC 188 ((l,b) = (122.8\arcdeg, 22.5\arcdeg)). We combine these results with the proper-motion and photometry catalog of Platais et al. and demonstrate the existence of a stellar overdensity in the background of NGC 188. The theoretical isochrone fits to the color-magnitude diagram of the overdensity are consistent with an age between 6 and 10 Gyr and an intermediately metal poor population ([Fe/H] = -0.5 to -1.0). The distance to the overdensity is estimated to be between 10.0 and 12.6 kpc. The proper-motions indicate that the stellar population of the overdensity is kinematically cold. The distance estimate and the absolute proper motion of the overdensity agree reasonably well with the predictions of the Pe\~{n}arrubia et al. model of the formation of the Monoceros stream. Orbits for this material constructed with plausible radial-velocity values, indicate that dynamically, this material is unlikely to belong to the thick disk. Taken together, this evidence suggests that the newly-found overdensity is part of the Monoceros stream.

Absolute proper motion of the Galactic open cluster M 67

We derived the absolute proper motion (PM) of the old, solar-metallicity Galactic open cluster M67 using observations collected with CFHT (1997) and with LBT (2007). About 50 galaxies with relatively sharp nuclei allow us to determine the absolute PM of the cluster. We find (mu_alpha cos(delta),mu_delta)_J2000.0 = (-9.6+/-1.1,-3.7+/-0.8) mas/yr. By adopting a line-of-sight velocity of 33.8+/-0.2 km/s, and assuming a distance of 815+/-50 pc, we explore the influence of the Galactic potential, with and without the bar and/or spiral arms, on the galactic orbit of the cluster.

Modeling proper motions beyond the Galactic bulge

We analyse the radial and tangential velocity fields in the Galaxy as seen from the Sun by using as a first approximation a simple axisymmetric model, which we then compare with the corresponding fields in a barred N-body model of the Milky Way. This provides a global description of these quantities missing in the literature, showing where they take large values susceptible to be used in future observations even for sources well beyond the Galactic center. Absolute largest proper motions occur at a distance slightly behind the Galactic Center, which are there 1.5 times larger than the highest local proper motions due to the Galactic differential rotation. Large proper motions well beyond the Galactic center are well within the current astrometric accuracy.

Astrometry withCarte du Cielplates, San Fernando zone

The historic plates of the "Carte du Ciel", an international cooperative project launched in 1887, offer valuable first-epoch material for the determination of absolute proper motions. We present the CdC-SF, an astrometric catalogue of positions and proper motions derived from the "Carte du Ciel" plates of the San Fernando zone, photographic material with a mean epoch of 1901.4 and a limiting magnitude of V~16, covering the declination range of -10deg < declination < -2deg. Digitization has been made using a conventional flatbed scanner. Special techniques have been developed to handle the combination of plate material and the large distortion introduced by the scanner. The equatorial coordinates are on the ICRS defined by Tycho-2, and proper motions are derived using UCAC2 as second-epoch positions. The result is a catalogue with positions and proper motions for 560000 stars, covering 1080 degrees squared. The mean positional uncertainty is 0.20" (0.12" for well-measured stars) and the proper-motion uncertainty is 2.0 mas/yr (1.2 mas/yr for well-measured stars). The proper motion catalogue CdC-SF is effectively a deeper extension of Hipparcos, in terms of proper motions, to a magnitude of 15.

ASTROMETRY WITH THEHUBBLE SPACE TELESCOPE: TRIGONOMETRIC PARALLAXES OF PLANETARY NEBULA NUCLEI NGC 6853, NGC 7293, ABELL 31, AND DeHt 5

We present absolute parallaxes and relative proper motions for the central stars of the planetary nebulae NGC 6853 (The Dumbbell), NGC 7293 (The Helix), Abell 31, and DeHt 5. This paper details our reduction and analysis using DeHt 5 as an example. We obtain these planetary nebula nuclei (PNNi) parallaxes with astrometric data from Fine Guidance Sensors FGS 1R and FGS 3, white-light interferometers on the Hubble Space Telescope (HST). Proper motions, spectral classifications and VJHKT_2M and DDO51 photometry of the stars comprising the astrometric reference frames provide spectrophotometric estimates of reference star absolute parallaxes. Introducing these into our model as observations with error, we determine absolute parallaxes for each PNN. Weighted averaging with previous independent parallax measurements yields an average parallax precision, \sigma_{\pi}/\pi = 5 %. Derived distances are: d_{NGC 6853}=405^{+28}_{-25}pc, d_{NGC 7293}=216^{+14}_{-12} pc, d_{Abell 31} = 621^{+91}_{-70} pc, and d_{DeHt 5} = 345^{+19}_{-17} pc. These PNNi distances are all smaller than previously derived from spectroscopic analyses of the central stars. Derived absolute magnitudes and previously measured effective temperatures permit estimates of PNNi radii, through both the Stefan-Boltzmann relation and Eddington fluxes. Comparing absolute magnitudes with post-AGB models provides mass estimates. Masses cluster around 0.57 M(sun), close to the peak of the white dwarf mass distribution. Adding a few more PNNi with well-determined distances and masses, we compare all the PNNi with cooler white dwarfs of similar mass, and confirm, as expected, that PNNi have larger radii than white dwarfs that have reached their final cooling tracks. (Abridged)

PROPER MOTIONS IN KAPTEYN SELECTED AREA 103: A PRELIMINARY ORBIT FOR THE VIRGO STELLAR STREAM

We present absolute proper motions in Kapteyn Selected Area (SA) 103. This field is located 7 degrees west of the center of the Virgo Stellar Stream (VSS, Duffau et al. 2006), and has a well-defined main sequence representing the stream. In SA 103 we identify one RR Lyrae star as a member of the VSS according to its metallicity, radial velocity and distance. VSS candidate turnoff stars and subgiant stars have proper motions consistent with that of the RR Lyrae star. The 3D velocity data imply an orbit with a pericenter of 11 kpc and an apocenter of ~90 kpc. Thus, the VSS comprises tidal debris found near the pericenter of a highly destructive orbit. Examining the six globular clusters at distances larger than 50 kpc from the Galactic center, and the proposed orbit of the VSS, we find one tentative association, NGC 2419. We speculate that NGC 2419 is possibly the nucleus of a disrupted system of which the VSS is a part.

The kinematics and zero-point of the log P-〈MK〉 relation for Galactic RR Lyrae variables via statistical parallax

We use accurate absolute proper motions and Two-Micron All-Sky Survey K s -band apparent magnitudes for 364 Galactic RR Lyrae variables to determine the kinematical parameters of the Galactic RR Lyrae population and constrain the zero-point of the K s -band period-luminosity relation for these stars via statistical parallax. We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be [U o (Halo), V 0 (Halo), W 0 (Halo)] = (―12 ± 10, ―217 ± 9, ―6 ± 6) km s ―1 and [U 0 (Disc), V 0 (Disc), W 0 (Disc)] = (―15 ± 7, ―44 ± 7, ―25 ± 5) km s ―1 , respectively, and the corresponding components of the velocity-dispersion ellipsoids, [σ V R (Halo), σ V θ (Halo), σ W(Halo)] = (167 ± 9, 86 ± 6, 78 ± 5) km s ―1 and [σ V R (Disc), σ V θ (Disc), σ W(Disc)] = (55 ± 7, 44 ± 6, 30 ± 4) km s ―1 , respectively. The fraction of thick-disc stars is estimated at 0.25 ± 0.03. The corrected infrared period-luminosity relation is = ― 2.33 log P F ― 0.818 ± 0.081, implying a Large Magellanic Cloud (LMC) distance modulus of 18.27 ± 0.08 and a solar Galactocentric distance of 7.58 ± 0.40 kpc. Our results suggest no or slightly prograde rotation for the population of halo RR Lyraes in the Milky Way.

The UKIDSS-2MASS proper motion survey - I. Ultracool dwarfs from UKIDSS DR4

The UK Infrared Telescope Infrared Deep Sky Survey (UKIDSS) is the first of a new generation of infrared surveys. Here, we combine the data from two UKIDSS components, the Large Area Survey (LAS) and the Galactic Cluster Survey (GCS), with Two-Micron All-Sky Survey (2MASS) data to produce an infrared proper motion survey for low-mass stars and brown dwarfs. In total, we detect 267 low-mass stars and brown dwarfs with significant proper motions. We recover all 10 known single L dwarfs and the one known T dwarf above the 2MASS detection limit in our LAS survey area and identify eight additional new candidate L dwarfs. We also find one new candidate L dwarf in our GCS sample. Our sample also contains objects from 11 potential common proper motion binaries. Finally, we test our proper motions and find that while the LAS objects have proper motions consistent with absolute proper motions, the GCS stars may have proper motions which are significantly underestimated. This is possibly due to the bulk motion of some of the local astrometric reference stars used in the proper motion determination.

THE KINEMATICS OF LATE-TYPE STARS IN THE SOLAR CYLINDER STUDIED WITH SDSS DATA

We study the velocity distribution of Milky Way disk stars in a kiloparsec-sized region around the Sun, based on {approx}2 million M-type stars from DR7 of SDSS, which have newly re-calibrated absolute proper motions from combining SDSS positions with the USNO-B catalogue. We estimate photometric distances to all stars, accurate to {approx}20%, and combine them with the proper motions to derive tangential velocities for this kinematically unbiased sample of stars. Based on a statistical deprojection method we then derive the vertical profiles (to heights of Z = 800 pc above the disk plane) for the first and second moments of the three-dimensional stellar velocity distribution. We find that (W) = -7 {+-} 1 km s{sup -1} and (U) = -9 {+-} 1 km s{sup -1}, independent of height above the mid-plane, reflecting the Sun's motion with respect to the local standard of rest. In contrast, (V) changes distinctly from -20 {+-} 2 km s{sup -1} in the mid-plane to (V) = -32 km s{sup -1} at Z = 800 pc, reflecting an asymmetric drift of the stellar mean velocity that increases with height. All three components of the M-star velocity dispersion show a strong linear rise away from the mid-plane,more » most notably {sigma} {sub ZZ}, which grows from 18 km s{sup -1} (Z = 0) to 40 km s{sup -1} (at Z = 800 pc). We determine the orientation of the velocity ellipsoid, and find a significant vertex deviation of 20{sup 0}-25{sup 0}, which decreases only slightly to heights of Z = 800 pc. Away from the mid-plane, our sample exhibits a remarkably large tilt of the velocity ellipsoid toward the Galactic plane, which reaches 20{sup 0} at Z = 800 pc and which is not easily explained. Finally, we determine the ratio {sigma}{sup 2} {sub {phi}}{sub {phi}}/{sigma}{sup 2} {sub RR} near the mid-plane, which in the epicyclic approximation implies an almost perfectly flat rotation curve at the solar radius.« less

The extremely collimated bipolar H$_{\sf 2}$O jet from the NGC 1333–IRAS 4B protostar

We have performed observations of water maser emission towards a sample of low-mass protostars, in order to investigate the properties of jets associated with the earliest stages of star formation and their interaction with the surrounding medium. The main aim is to measure the absolute positions and proper motions of the H_2O spots in order to investigate the kinematics of the region from where the jet is launched. We imaged the protostars in the nearby region NGC 1333-IRAS 4 in the water maser line at 22.2 GHz by using the VLBA in phase-reference mode at the milliarcsecond scale over four epochs, spaced by one month to measure proper motions. Two protostars (A2 and B) were detected in a highly variable H_2O maser emission, with an active phase shorter than four weeks. The H_2O maps allow us to trace the fast jet driven by the B protostar: we observed both the red- and blue-shifted lobes very close to the protostar, =< 35 AU, moving away with projected velocities of ~10-50 km/s. The comparison with the molecular outflow observed at larger scale suggests a jet precession with a 18'/yr rate. By measuring the positional spread of the H_2O spots we estimate a jet width of ~2 AU at a distance of ~12 AU from the driving protostar.

The XPM Catalogue: absolute proper motions of 280 million stars

We combined data from the Two-Micron All Sky Survey (2MASS) and USNO-A2.0 catalogues in order to derive the absolute proper motions of about 280 million stars distributed all over the sky excluding a small region near the Galactic Centre, in the magnitude range 12 < B < 19 mag. The proper motions were derived from the 2MASS Point Sources and USNO-A2.0 catalogue positions with a mean epoch difference of about 45 years for the Northern hemisphere and about 17 years for the Southern one. The zero-point of the absolute proper motion frame (the ‘absolute calibration’) was specified with the use of about 1.45 million galaxies from 2MASS. Most of the systematic zonal errors inherent in the USNO-A2.0 catalogue were eliminated before the calculation of proper motions. The mean formal error of absolute calibration is less than 1 mas yr−1. The XPM Catalogue will be available via CDS in Strasbourg during 2010. The generated catalogue contains the International Celestial Reference System positions of stars for the J2000 epoch, original absolute proper motions, as well as B, R, J, H and K magnitudes. A comparison of the proper motions obtained in this work with the data of other recent catalogues of quasars was fulfilled.

Trigonometric parallaxes of ten ultracool subdwarfs

Aims. We measure absolute trigonometric parallaxes and proper motions with respect to many background galaxies for a sample of ten ultracool subdwarfs. Methods. Observations were taken in the H-band with the OMEGA2000 camera on the 3.5 m-telescope at Calar Alto, Spain during a time period of 3.5 years. For the first time, the reduction of the astrometric measurements was carried out directly with respect to background galaxies. We obtained absolute parallaxes with mean errors ranging between 1 and 3 mas. Results. With six completely new parallaxes we more than doubled the number of benchmark ultracool (>sdM7) subdwarfs. Six stars in the MKs vs. J −Ks diagram fit perfectly to model subdwarf sequences from M7 to L4 with [M/H] between −1.0 and −1.5, whereas 4 are consistent with a moderately low metallicity ([M/H] = −0.5) from M7 to T6. All but one of our objects have large tangential velocities between 200 and 320 km s −1 typical of the Galactic halo population. Our results are in good agreement with recent independent measurements for three of our targets and confirm the previously measured parallax and absolute magnitude MKs of the nearest and coolest (T-type) subdwarf 2MASS 0937+29 with higher accuracy. For all targets, we also obtained infrared J, H,Ks photometry at a level of a few milli-magnitudes relative to 2MASS standards.