Accurate Proper Motions Research Articles

THE PROPER MOTIONS OF THE DOUBLE RADIO SOURCE n IN THE ORION BN/KL REGION

ABSTRACT We have extended the time baseline for observations of the proper motions of radio sources in the Orion BN/KL region from 14.7 to 22.5 years. We present improved determinations for the sources BN and I. In addition, we address the proper motions of the double radio source n, that have been questioned in the literature. We confirm that all three sources are moving away at transverse velocities of tens of kilometers per second from a region in-between them, where they were located about 500 years ago. Source n exhibits a new component that we interpret as due to a one-sided ejection of free–free emitting plasma that took place after 2006.36. We used the highly accurate relative proper motions between sources BN and I to determine that their closest separation took place in the year 1475 ± 6, when they were within ∼100 au or less from each other in the plane of the sky.

Proper motion survey and kinematic analysis of the ρ Ophiuchi embedded cluster

Context. The ρ Ophiuchi molecular complex and in particular the Lynds L1688 dark cloud is unique in its proximity (~130 pc), in its richness in young stars and protostars, and in its youth (0.5 Myr). It is certainly one of the best targets currently accessible from the ground to study the early phases of star-formation. Proper motion analysis is a very efficient tool for separating members of clusters from field stars, but very few proper motions are available in the ρ Ophiuchi region since most of the young sources are deeply embedded in dust and gas. Aims. We aim at performing a kinematic census of young stellar objects (YSOs) in the ρ Ophiuchi F core and partially in the E core of the L1688 dark cloud. Methods. We run a proper motion program at the ESO New Technology Telescope (NTT) with the Son of ISAAC (SOFI) instrument over nine years in the near-infrared. We complemented these observations with various public image databases to enlarge the time base of observations and the field of investigation to 0.5° × 0.5°. We derived positions and proper motions for 2213 objects. From these, 607 proper motions were derived from SOFI observations with a ~1.8 mas/yr accuracy while the remaining objects were measured only from auxiliary data with a mean precision of about ~3 mas/yr. Results. We performed a kinematic analysis of the most accurate proper motions derived in this work, which allowed us to separate cluster members from field stars and to derive the mean properties of the cluster. From the kinematic analysis we derived a list of 68 members and 14 candidate members, comprising 26 new objects with a high membership probability. These new members are generally fainter than the known ones. We measured a mean proper motion of (μαcosδ, μδ) = (−8.2,−24.3) ± 0.8 mas/yr for the L1688 dark cloud. A supervised classification was applied to photometric data of members to allocate a spectral energy distribution (SED) classification to the unclassified members. Conclusions. We kinematically confirmed that the 56 members that were known from previous studies of the ρ Ophiuchi F cluster and that were also part of our survey are members of the cluster, and we added 26 new members. We defined the evolutionary status of the unclassified members of the cluster. We showed that a large part (23) of these new members are probably brown dwarfs, which multiplies the number of known substellar objects in the cluster by a factor of 3.3.

GeMS/GSAOI PHOTOMETRIC AND ASTROMETRIC PERFORMANCE IN DENSE STELLAR FIELDS

ABSTRACT Ground-based imagers at 8 m class telescopes assisted by multi-conjugate adaptive optics are primary facilities with which to obtain accurate photometry and proper motions in dense stellar fields. We observed the central region of the globular clusters Liller 1 and NGC 6624 with the Gemini Multi-conjugate Adaptive Optics System (GeMS) feeding the Gemini South Adaptive Optics Imager (GSAOI) currently available at the Gemini South telescope, under different observing conditions. We characterized the stellar point-spread function (PSF) in terms of FWHM, Strehl ratio (SR), and encircled energy (EE), over the field of view (FOV). We found that, for sub-arcsecond seeing at the observed airmass, we can obtain the diffraction-limited PSF (FWHM mas), SR ∼ 40%, and EE ≥ 50% with a dispersion around 10% over the FOV of 85″ × 85″, in the K s band. In the J band the best images provide FWHMs between 60 and 80 mas, SR , and . For seeing at the observed airmass exceeding 1″, the performance worsens but it is still possible to perform PSF fitting photometry with 25% EE in J and 40% in K s . We also computed the geometric distortions of GeMS/GSAOI and we obtained corrected images with an astrometric accuracy of ∼1 mas in a stellar field with high crowding.

Gaiareference frame amid quasar variability and proper motion patterns in the data

Gaia's very accurate astrometric measurements will allow the International Celestial Reference Frame (ICRF) to be improved by a few orders of magnitude in the optical. Several sets of quasars are used to define a kinematically stable non-rotating reference frame with the barycentre of the Solar System as its origin. Gaia will also observe a large number of galaxies which could obtain accurate positions and proper motions although they are not point-like. The optical stability of the quasars is critical and we investigate how accurately the reference frame can be recovered. Various proper motion patterns are also present in the data, the best known is caused by the acceleration of the Solar System Barycentre, presumably, towards the Galactic centre. We review some other less-well-known effects that are not part of standard astrometric models. We model quasars and galaxies using realistic sky distributions, magnitudes and redshifts. Position variability is introduced using a Markov chain model. The reference frame is determined using the algorithm developed for the Gaia mission which also determines the acceleration of the Solar System. We also test a method to measure the velocity of the Solar System barycentre in a cosmological frame. We simulate the recovery of the reference frame and the acceleration of the Solar System and conclude that they are not significantly disturbed in the presence of quasar variability which is statistically averaged. However, the effect of a non-uniform sky distribution of the quasars can result in a correlation between the reference frame and acceleration which degrades the solution. Our results suggest that an attempt should be made to astrometrically determine the redshift dependent apparent drift of galaxies due to our velocity relative to the CMB, which in principle could allow the determination of the Hubble parameter.

THE REFINED SHOCK VELOCITY OF THE X-RAY FILAMENTS IN THE RCW 86 NORTHEAST RIM

ABSTRACT A precise measurement of shock velocities is crucial for constraining the mechanism and efficiency of cosmic-ray (CR) acceleration at supernova remnant (SNR) shock fronts. The northeastern rim of the SNR RCW 86 is thought to be a particularly efficient CR acceleration site, owing to the recent result in which an extremely high shock velocity of ∼6000 km s−1 was claimed. Here, we revisit the same SNR rim with the Chandra X-ray Observatory, 11 years after the first observation. This longer baseline than previously available allows us to determine a more accurate proper motion of the nonthermal X-ray filament, revealing a much lower velocity of 3000 ± 340 km s−1 (and even slower at a brighter region). Although the value has dropped to one-half of that from the previous X-ray measurement, it is still higher than the mean velocity of the Hα filaments in this region (∼1200 km s−1). This discrepancy implies that the filaments bright in nonthermal X-rays and Hα emission trace different velocity components, and thus a CR pressure constrained by combining the X-ray kinematics and the Hα spectroscopy can easily be overestimated. We also measure the proper motion of the thermal X-ray filament immediately to the south of the nonthermal one. The inferred velocity (720 ± 360 km s−1) is significantly lower than that of the nonthermal filament, suggesting the presence of denser ambient material, possibly a wall formed by a wind from the progenitor, which has drastically slowed down the shock.

A Pan-STARRS 1 study of the relationship between wide binarity and planet occurrence in theKeplerfield

The NASA Kepler mission has revolutionised time-domain astronomy and has massively expanded the number of known extrasolar planets. However, the effect of wide multiplicity on exoplanet occurrence has not been tested with this dataset. We present a sample of 401 wide multiple systems containing at least one Kepler target star. Our method uses Pan-STARRS1 and archival data to produce an accurate proper motion catalogue of the Kepler field. Combined with Pan-STARRS1 SED fits and archival proper motions for bright stars, we use a newly developed probabilistic algorithm to identify likely wide binary pairs which are not chance associations. As by-products of this we present stellar SED templates in the Pan-STARRS1 photometric system and conversions from this system to Kepler magnitudes. We find that Kepler target stars in our binary sample with separations above 6 arcseconds are no more or less likely to be identified as confirmed or candidate planet hosts than a weighted comparison sample of Kepler targets of similar brightness and spectral type. Therefore we find no evidence that binaries with projected separations greater than 3,000AU affect the occurrence rate of planets with P<300days around FGK stars.

Lorentzian’ analysis of the accuracy of modern catalogues of stellar positions

There is a new approach for the estimation of the position accuracy and proper motions of the stars in astrometric catalogues by comparison of the stars' positions in the researched and Hipparcos catalogues in different periods, but under a standard equinox. To verify this method was carried out the analysis of the star positions and proper motions UCAC2, PPM, ACRS, Tycho-2, ACT, TRC, FON and Tycho catalogues. As a result of this study was obtained that the accuracy of positions and proper motions of the stars in Tycho-2 and UCAC2 catalogues are approximately equal. The results of the comparison are represented graphically.

UrHip PROPER MOTION CATALOG

Proper motions are computed and collected in a catalog using the Hipparcos positions (epoch 1991.25) and URAT1 positions (epoch 2012.3 to 2014.6). The goal is to obtain a significant improvement on the proper motion accuracy of single stars in the northern hemisphere, and to identify new astrometric binaries perturbed by orbital motion. For binaries and multiple systems, the longer baseline of Tycho2 (~ 100 yr) makes it more reliable despite its larger formal uncertainties. The resulting proper motions obtained for 67,340 stars have a consequent gain in accuracy by a factor of ~ 3 compared to Hipparcos. Comparison between UrHip and Hipparcos shows that they are reasonably close, but also reveals stars with large discrepant proper motions, a fraction of which are potential binary candidates.

HSTASTROMETRY IN THE 30 DORADUS REGION: MEASURING PROPER MOTIONS OF INDIVIDUAL STARS IN THE LARGE MAGELLANIC CLOUD

We present measurements of positions and relative proper motions in the 30 Doradus region of the Large Magellanic Cloud (LMC). We detail the construction of a single-epoch astrometric reference frame, based on specially-designed observations obtained with the two main imaging instruments ACS/WFC and WFC3/UVIS onboard the Hubble Space Telescope (HST). Internal comparisons indicate a sub milli-arc-second (mas) precision in the positions and the presence of semi-periodic systematics with a mean amplitude of ~0.8 mas. We combined these observations with numerous archival images taken with WFPC2 and spanning 17 years. The precision of the resulting proper motions for well-measured stars around the massive cluster R 136 can be as good as ~20 microarcsec/yr, although the true accuracy of proper motions is generally lower due to the residual systematic errors. The observed proper-motion dispersion for our highest-quality measurements is ~0.1 mas/yr. Our catalog of positions and proper motions contains 86,590 stars down to V~25 and over a total area of ~70 square arcmin. We examined the proper motions of 105 relatively bright stars and identified a total of 6 candidate runaway stars. We are able to tentatively confirm the runaway status of star VFTS 285, consistent with the findings from line-of-sight velocities, and to show that this star has likely been ejected from R 136. This study demonstrates that with HST it is now possible to reliably measure proper motions of individual stars in the nearest dwarf galaxies such as the LMC.

NEW INSIGHTS ON THE GALACTIC BULGE INITIAL MASS FUNCTION

We have derived the Galactic bulge initial mass function of the SWEEPS field in the mass range 0.15 $< M/M_{\odot}<$ 1.0, using deep photometry collected with the Advanced Camera for Surveys on the Hubble Space Telescope. Observations at several epochs, spread over 9 years, allowed us to separate the disk and bulge stars down to very faint magnitudes, F814W $\sim$ 26 mag, with a proper-motion accuracy better than 0.5 mas/yr. This allowed us to determine the initial mass function of the pure bulge component uncontaminated by disk stars for this low-reddening field in the Sagittarius window. In deriving the mass function, we took into account the presence of unresolved binaries, errors in photometry, distance modulus and reddening, as well as the metallicity dispersion and the uncertainties caused by adopting different theoretical color-temperature relations. We found that the Galactic bulge initial mass function can be fitted with two power laws with a break at M $\sim$ 0.56 $M_{\odot}$, the slope being steeper ($\alpha$ = -2.41$\pm$0.50) for the higher masses, and shallower ($\alpha$ = -1.25$\pm$0.20) for the lower masses. In the high-mass range, our derived mass function agrees well with the mass function derived for other regions of the bulge. In the low-mass range however, our mass function is slightly shallower, which suggests that separating the disk and bulge components is particularly important in the low-mass range. The slope of the bulge mass function is also similar to the slope of the mass function derived for the disk in the high-mass regime, but the bulge mass function is slightly steeper in the low-mass regime. We used our new mass function to derive stellar M/L values for the Galactic bulge and we obtained 2.1 $<M/L_{F814W}<$ 2.4 and 3.1 $< M/L_{F606W}<$ 3.6 according to different assumptions on the slope of the IMF for masses larger than 1 $M_{\odot}$.

Biases in the determination of dynamical parameters of star clusters: today and in the Gaia era

The structural and dynamical properties of star clusters are generally derived by means of the comparison between steady-state analytic models and the available observables. With the aim of studying the biases of this approach, we fitted different analytic models to simulated observations obtained from a suite of direct N-body simulations of star clusters in different stages of their evolution and under different levels of tidal stress to derive mass, mass function and degree of anisotropy. We find that masses can be under/over-estimated up to 50% depending on the degree of relaxation reached by the cluster, the available range of observed masses and distances of radial velocity measures from the cluster center and the strength of the tidal field. The mass function slope appears to be better constrainable and less sensitive to model inadequacies unless strongly dynamically evolved clusters and a non-optimal location of the measured luminosity function are considered. The degree and the characteristics of the anisotropy developed in the N-body simulations are not adequately reproduced by popular analytic models and can be detected only if accurate proper motions are available. We show how to reduce the uncertainties in the mass, mass-function and anisotropy estimation and provide predictions for the improvements expected when Gaia proper motions will be available in the near future.

TOWARD AN EMPIRICAL THEORY OF PULSAR EMISSION. XI. UNDERSTANDING THE ORIENTATIONS OF PULSAR RADIATION AND SUPERNOVA “KICKS”

Two entwined problems have remained unresolved since pulsars were discovered nearly 50 years ago: the orientation of their polarized emission relative to the emitting magnetic field and the direction of putative supernova ``kicks' relative to their rotation axes. The rotational orientation of most pulsars can be inferred only from the (``fiducial') polarization angle of their radiation, when their beam points directly at the Earth and the emitting polar fluxtube field is $\parallel$ to the rotation axis. Earlier studies have been unrevealing owing to the admixture of different types of radiation (core and conal, two polarization modes), producing both $\parallel$ or $\perp$ alignments. In this paper we analyze the some 50 pulsars having three characteristics: core radiation beams, reliable absolute polarimetry, and accurate proper motions. The ``fiducial' polarization angle of the core emission, we then find, is usually oriented $\perp$ to the proper-motion direction on the sky. As the primary core emission is polarized $\perp$ to the projected magnetic field in Vela and other pulsars where X-ray imaging reveals the orientation, this shows that the proper motions usually lie $\parallel$ to the rotation axes on the sky. Two key physical consequences then follow: first, to the extent that supernova ``kicks' are responsible for pulsar proper motions, they are mostly $\parallel$ to the rotation axis; and second that most pulsar radiation is heavily processed by the magnetospheric plasma such that the lowest altitude ``parent' core emission is polarized $\perp$ to the emitting field, propagating as the extraordinary (X) mode.

Messier 35 (NGC 2168) DANCe

We aim at identifying the cluster's members by deriving membership probabilities for the sources within 1 degree of the cluster's center, going further away than equivalent previous studies. We measure accurate proper motions and multi-wavelength (optical and near-infrared) photometry using ground based archival images of the cluster. We use these measurements to compute membership probabilities. The list of candidate members from Barrado+2001 is used as training set to identify the cluster's locus in a multi-dimensional space made of proper motions, luminosities and colors. The final catalog includes 338892 sources with multi-wavelength photometry. Approximately half (194452) were detected at more than two epochs and we measured their proper motion and used it to derive membership probability. A total of 4349 candidate members with membership probabilities greater than 50% are found in this sample in the luminosity range between 10 and 22mag. The slow proper motion of the cluster and the overlap of its sequence with the field and background sequences in almost all color-magnitude and color-color diagrams complicate the analysis and the contamination level is expected to be significant. Our study nevertheless provides a coherent and quantitative membership analysis of Messier 35 based on a large fraction of the best ground-based data sets obtained over the past 18 years. As such, it represents a valuable input for follow-up studies using in particular the Kepler K2 photometric time series.

Joint astrometric solution of HIPPARCOS andGaia

The first release of astrometric data from Gaia is expected in 2016. It will contain the mean stellar positions and magnitudes from the first year of observations. For more than 100 000 stars in common with the Hipparcos Catalogue it will be possible to compute very accurate proper motions due to the time difference of about 24 years between the two missions. This Hundred Thousand Proper Motions (HTPM) project will be part of the first release. Our aim is to investigate how early Gaia data can be optimally combined with information from the Hipparcos Catalogue in order to provide the most accurate and reliable results for HTPM. The Astrometric Global Iterative Solution (AGIS) was developed to compute the astrometric core solution based on the Gaia observations and will be used for all releases of astrometric data from Gaia. We adapt AGIS to process Hipparcos data in addition to Gaia observations, and use simulations to verify and study the joint solution method. For the HTPM stars we predict proper motion accuracies between 14 and 134 muas/yr, depending on stellar magnitude and amount of Gaia data available. Perspective effects will be important for a significant number of HTPM stars, and in order to treat these effects accurately we introduce a scaled model of kinematics. We define a goodness-of-fit statistic which is sensitive to deviations from uniform space motion, caused for example by binaries with periods of 10-50 years. HTPM will significantly improve the proper motions of the Hipparcos Catalogue well before highly accurate Gaia- only results become available. Also, HTPM will allow us to detect long period binary and exoplanetary candidates which would be impossible to detect from Gaia data alone. The full sensitivity will not be reached with the first Gaia release but with subsequent data releases. Therefore HTPM should be repeated when more Gaia data become available.

From Flamsteed to Piazzi and Lalande: new standards in 18th century astrometry

Aims. The present high accuracy of stellar positions and proper motions allows us to determine the positional accuracy of old stellar catalogues. This has already been done for the most important catalogues from before the 18th century. Our aim is to extend this study to several 18th century catalogues.Methods. To do this, I studied ten catalogues: those of Flamsteed and Romer, four catalogues of La Caille, and catalogues of Tobias Mayer, Bradley, Piazzi, and Lalande. A comparison with modern data, mostly from Hipparcos, compiled in the Simbad database of the CDS allowed me to determine the position errors of these catalogues. I also compared the stellar visual magnitudes given in eight of these catalogues with photometric V magnitudes.Results. Thanks to novel instruments, the rms positional accuracy improved from thousands to hundreds of arcsec in older catalogues to less than one minute in that of Flamsteed, and to 2−6 arcsec in the other catalogues I examined. These improvements allowed for the first time relatively accurate proper motions to be determined by 19th century astronomers.

Determination of galactic rotation parameters and the solar galactocentric distance R 0 from 73 masers

We have determined the Galactic rotation parameters and the solar Galactocentric distance R 0 by simultaneously solving Bottlinger’s kinematic equations using data on masers with known line-of-sight velocities and highly accurate trigonometric parallaxes and proper motions measured by VLBI. Our sample includes 73 masers spanning the range of Galactocentric distances from 3 to 14 kpc. The solutions found are Ω0 = 28.86 ± 0.45 km s−1 kpc−1, Ω′0 = −3.96 ± 0.09 km s−1 kpc−2, Ω″0 = 0.790 ± 0.027 km s−1 kpc−3, and R 0 = 8.3 ± 0.2 kpc. In this case, the linear rotation velocity at the solar distance R 0 is V = 241 ± 7 km s−1. Note that we have obtained the R 0 estimate, which is of greatest interest, from masers for the first time; it is in good agreement with the most recent estimates and even surpasses them in accuracy.

HH 222: A GIANT HERBIG-HARO FLOW FROM THE QUADRUPLE SYSTEM V380 ORI

HH 222 is a giant shocked region in L1641 cloud, and is popularly known as Orion Streamers or the waterfall on account of its unusual structure. At center of these streamers are two infrared sources coincident with a nonthermal radio jet aligned along principal streamer. The unique morphology of HH 222 has long been associated with this radio jet. However, new infrared images show that two sources are distant elliptical galaxies, indicating that radio jet is merely an improbable line-of-sight coincidence. Accurate proper motion measurements of HH 222 reveal that shock structure is a giant bow shock moving directly away from well-known, very young, Herbig Be star V380 Ori. The already known Herbig-Haro object HH 35 forms part of this flow. A new Herbig-Haro object, HH 1041, is found precisely in opposite direction of HH 222 and is likely to form part of a counterflow. The total projected extent of this HH complex is 5.3 pc, making it among largest HH flows known. A second outflow episode from V380 Ori is identified as a pair of HH objects, HH 1031 to northwest and already known HH 130 to southeast, along an axis that deviates from that of HH 222/HH 1041 by only 37. V380 Ori is a hierarchical quadruple system, including a faint companion of spectral type M5 or M6, which at an age of ~1 Myr corresponds to an object straddling stellar-to-brown dwarf boundary. We suggest that HH 222 giant bow shock is a direct result of dynamical interactions that led to conversion from an initial non-hierarchical multiple system into a hierarchical configuration. This event occurred no more than 28,000 yr ago, as derived from proper motions of HH 222 giant bow shock.

WIYN OPEN CLUSTER STUDY. LV. ASTROMETRY AND MEMBERSHIP IN NGC 6819

We present proper motions and astrometric membership analysis for 15,750 stars around the intermediate-age open cluster NGC 6819. The accuracy of relative proper motions for well-measured stars ranges from ~0.2 mas yr–1 within 10' of the cluster center to 1.1 mas yr–1 outside this radius. In the proper motion vector-point diagram, the separation between the cluster members and field stars is convincing down to V ~ 18 and within 10' from the cluster center. The formal sum of membership probabilities indicates a total of ~2500 cluster members down to V ~ 22. We confirm the cluster membership of several variable stars, including some eclipsing binaries. The estimated absolute proper motion of NGC 6819 is and mas yr–1. A cross-identification between the proper motion catalog and a list of X-ray sources in the field of NGC 6819 resulted in a number of new likely optical counterparts, including a candidate CV. For the first time we show that there is significant differential reddening toward NGC 6819.

Dynamical analysis of nearby clusters

The kinematic properties of the different classes of objects in a given association hold important clues about its member's history, and offer a unique opportunity to test the predictions of the various models of stellar formation and evolution. DANCe (standing for Dynamical Analysis of Nearby ClustErs) is a survey program aimed at deriving a comprehensive and homogeneous census of the stellar and substellar content of a number of nearby (<1kpc) young (<500Myr) associations. Whenever possible, members will be identified based on their kinematics properties, ensuring little contamination from background and foreground sources. Otherwise, the dynamics of previously confirmed members will be studied using the proper motion measurements. We present here the method used to derive precise proper motion measurements, using the Pleiades cluster as a test bench. Combining deep wide field multi-epoch panchromatic images obtained at various obervatories over up to 14 years, we derive accurate proper motions for the sources present in the field of the survey. The datasets cover ~80 square degrees, centered around the Seven Sisters. Using new tools, we have computed a catalog of 6116907 unique sources, including proper motion measurements for 3577478 of them. The catalogue covers the magnitude range between i=12~24mag, achieving a proper motion accuracy <1mas/yr for sources as faint as i=22.5mag. We estimate that our final accuracy reaches 0.3mas/yr in the best cases, depending on magnitude, observing history, and the presence of reference extragalactic sources for the anchoring onto the ICRS.

The proper motion of PSR J0205+6449 in 3C 58

We report on sensitive phase-referenced and gated 1.4-GHz VLBI radio observations of the pulsar PSR J0205+6449 in the young pulsar-wind nebula 3C 58, made in 2007 and 2010. We employed a novel technique where the ~105-m Green Bank telescope is used simultaneously to obtain single-dish data used to determine the pulsar's period as well as to obtain the VLBI data, allowing the VLBI correlation to be gated synchronously with the pulse to increase the signal-to-noise. The high timing noise of this young pulsar precludes the determination of the proper motion from the pulsar timing. We derive the position of the pulsar accurate at the milliarcsecond level, which is consistent with a re-determined position from the Chandra X-ray observations. We reject the original tentative optical identification of the pulsar by Shearer and Neustroev (2008), but rather identify a different optical counterpart on their images, with R-band magnitude ~24. We also determine an accurate proper motion for PSR J0205+6449 of (2.3 +- 0.3) mas/yr, corresponding to a projected velocity of only (35 +- 6) km/s for a distance of 3.2 kpc, at p.a. -38 deg. This projected velocity is quite low compared to the velocity dispersion of known pulsars of ~200 km/s. Our measured proper motion does not suggest any particular kinematic age for the pulsar.