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Proper Motions (proper + motion)
Selected AbstractsDeep H, imagery of the Eridanus shellsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2001P. Boumis A deep H, image of interlocking filamentary arcs of nebulosity has been obtained with a wide-field (,30° diameter) narrow-band filter camera combined with a charge-coupled device as a detector. The resultant mosaic of images, extending to a galactic latitude of ,65°, has been corrected for field distortions and had galactic coordinates superimposed on it to permit accurate correlations with the most recent H i (21 cm), X-ray (0.75 keV) and FIR (IRAS 100 ,m) maps. Furthermore, an upper limit of 0.13 arcsec yr,1 to the expansion proper motion of the primary 25° long nebulous arc has been obtained by comparing a recent H, image obtained with the San Pedro Martir telescope of its filamentary edge with that on a Palomar Observatory Sky Survey E plate obtained in 1951. It is concluded that these filamentary arcs are the superimposed images of separate shells (driven by supernova explosions and/or stellar winds) rather than the edges of a single ,superbubble' stretching from Barnard's Arc (and the Orion Nebula) to these high galactic latitudes. The proper motion measurement argues against the primary H,-emitting arc being associated with the giant radio loop (Loop 2) except in extraordinary circumstances. [source] New photometry and astrometry of the isolated neutron star RX J0720.4,3125 using recent VLT/FORS observations,ASTRONOMISCHE NACHRICHTEN, Issue 3 2010T. Eisenbeiss Abstract Since the first optical detection of RX J0720.4,3125 various observations have been performed to determine astrometric and photometric data. We present the first detection of the isolated neutron star in the V Bessel filter to study the spectral energy distribution and derive a new astrometric position. At ESO Paranal we obtained very deep images with FORS 1 (three hours exposure time) of RX J0720.4,3125 in the V Bessel filter in January 2008. We derive the visual magnitude by standard star aperture photometry. Using sophisticated resampling software we correct the images for field distortions. Then we derive an updated position and proper motion value by comparing its position with FORS 1 observations of December 2000. We calculate a visual magnitude of V = 26.81 ± 0.09 mag, which is seven times in excess of what is expected from X-ray data, but consistent with the extant U, B, and R data. Over about a seven year epoch difference we measured a proper motion of , = 105.1 ± 7.4 mas yr,1 towards , = 296.951° ± 0.0063° (NW), consistent with previous data (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Flare stars in the TW Hydrae association: the HIP 57269 system,ASTRONOMISCHE NACHRICHTEN, Issue 6 2003B. König Abstract We discuss a new member candidate of the TW Hydrae association (TWA) among the stars of the Gershberg et al. (1999) flare star catalog. TWA is one of the closest known associations of young stars at about 60 pc. Three supposedly young flare stars are located in the same region of the sky as TWA. One of them (HIP 57269) shows strong lithium absorption with spectral type K1/K2V and a high level of chromospheric and coronal activity. It is located at a distance of 48.7 ± 6.3 pc in common with the five TWA members observed with Hipparcos (46.7 to 103.9 pc). HIP 57268 A has a wide companion C which also shows lithium absorption at 6707 Ĺ and which has common proper motion with HIP 57269, as well as a close companion resolved visually by Tycho. HIP 57269 A&C lie above the main sequence and are clearly pre-main-sequence stars. The UVW-space velocity is more consistent with the star system being a Pleiades super cluster member. The two other flare stars in the TWA sky region do not show lithium at all and are, hence, unrelated. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Discovery of new nearby L and late-M dwarfs at low Galactic latitude from the DENIS data baseMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008N. Phan-Bao ABSTRACT We report on new nearby L and late-M dwarfs (dphot, 30 pc) discovered in our search for nearby ultracool dwarfs (I,J, 3.0, later than M8.0) at low Galactic latitude (|b| < 15°) over 4800 deg2 in the Deep Near Infrared Survey of the Southern Sky (DENIS) data base. We used late-M (, M8.0), L and T dwarfs with accurate trigonometric parallaxes to calibrate the MJ versus I,J colour,luminosity relation. The resulting photometric distances have standard errors of ,15 per cent, which we used to select candidates dphot, 30 pc. We measured proper motions from multi-epoch images found in the public archives ALADIN, DSS, 2MASS and DENIS, with at least three distinct epochs and time baselines of 10,21 yr. We then used a maximum reduced proper motion cut-off to select 28 candidates as ultracool dwarfs (M8.0,L8.0) and to reject one as a distant red star. No T dwarf candidates were found in this search, which required an object to be detected in all three DENIS bands. Our low-resolution optical spectra confirmed that 26 were indeed ultracool dwarfs, with spectral types from M8.0 to L5.5. Two contaminants and one rejected by the maximum reduced proper motion cut-off were all reddened F,K main sequence stars. 20 of these 26 ultracool dwarfs are new nearby ultracool dwarf members, three L dwarfs within 15 pc with one L3.5 at only ,10 pc. We determine a stellar density of dwarfs pc,3 mag,1 over 11.1 ,MJ, 13.1 based on this sample of M8,L3.5 ultracool dwarfs. Our ultracool dwarf density value is in good agreement with the measurement by Cruz et al. of the ultracool dwarf density at high Galactic latitude. [source] Kinematic structure in the Galactic halo at the North Galactic Pole: RR Lyrae and blue horizontal branch stars show different kinematicsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007T. D. Kinman ABSTRACT Radial velocities and proper motions (derived from the GSC-II data base) are given for 38 RR Lyrae (RRL) stars and 79 blue horizontal branch (BHB) stars in a ,200 deg2 area around the North Galactic Pole (NGP). Both heliocentric (UVW) and galactocentric (VR, V,, Vz) space motions are derived for these stars using a homogeneous distance scale consistent with (m,M)0= 18.52 for the Large Magellanic Cloud (LMC). An analysis of the 26 RRL and 52 BHB stars whose height (Z) above the plane is less than 8 kpc shows that this halo sample is not homogeneous. Our BHB sample (like that of Sirko et al.) has a zero galactic rotation (V,) and roughly isotropic velocity dispersions. The RRL sample shows a definite retrograde rotation (V,=,95 ± 29 km s,1) and non-isotropic velocity dispersions. The combined BHB and RRL sample has a retrograde galactic rotation (V) that is similar to that found by Majewski for his sample of subdwarfs in Selected Area (SA) 57. The velocity dispersion of the RRL stars that have a positive W motion is significantly smaller than the dispersion of those ,streaming down' with a negative W. Also, the ratio of RRL to BHB stars is smaller for the sample that has positive W. Our halo sample occupies 10.4 kpc3 at a mean height of 5 kpc above the Galactic plane. In this volume, one component (rich in RRL stars) shows retrograde rotation and the streaming motion that we associate with the accretion process. The other component (traced by the BHB stars) shows essentially no rotation and less evidence of streaming. These two components have horizontal branch (HB) morphologies that suggest that they may be the field star equivalents of the young and old halo globular clusters, respectively. Clearly, it is quite desirable to use more than one tracer in any kinematic analysis of the halo. [source] A fast hybrid algorithm for exoplanetary transit searchesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006A. Collier Cameron ABSTRACT We present a fast and efficient hybrid algorithm for selecting exoplanetary candidates from wide-field transit surveys. Our method is based on the widely used SysRem and Box Least-Squares (BLS) algorithms. Patterns of systematic error that are common to all stars on the frame are mapped and eliminated using the SysRem algorithm. The remaining systematic errors caused by spatially localized flat-fielding and other errors are quantified using a boxcar-smoothing method. We show that the dimensions of the search-parameter space can be reduced greatly by carrying out an initial BLS search on a coarse grid of reduced dimensions, followed by Newton,Raphson refinement of the transit parameters in the vicinity of the most significant solutions. We illustrate the method's operation by applying it to data from one field of the SuperWASP survey, comprising 2300 observations of 7840 stars brighter than V= 13.0. We identify 11 likely transit candidates. We reject stars that exhibit significant ellipsoidal variations caused indicative of a stellar-mass companion. We use colours and proper motions from the Two Micron All Sky Survey and USNO-B1.0 surveys to estimate the stellar parameters and the companion radius. We find that two stars showing unambiguous transit signals pass all these tests, and so qualify for detailed high-resolution spectroscopic follow-up. [source] On the kinematic deconvolution of the local neighbourhood luminosity functionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002C. Pichon A method for inverting the statistical star counts equation, including proper motions, is presented; in order to break the degeneracy in that equation, it uses the supplementary constraints required by dynamical consistency. The inversion gives access to both the kinematics and the luminosity function of each population in three régimes: the singular ellipsoid, the constant ratio Schwarzschild ellipsoid plane-parallel models and the epicyclic model. This more realistic model is tailored to account for the local neighbourhood density and velocity distribution. The first model is fully investigated, both analytically and by means of a non-parametric inversion technique, while the second model is shown to be formally its equivalent. The effect of noise and incompleteness in apparent magnitude is investigated. The third model is investigated by a non-parametric inversion technique where positivity of the underlying luminosity function is explicitly accounted for. It is argued that its future application to data such as the Tycho catalogue (and in the upcoming satellite GAIA) could lead , provided that the vertical potential and or the asymmetric drift or w, are known , to a non-parametric determination of the local neighbourhood luminosity function without any reference to stellar evolution tracks. It should also yield the proportion of stars for each kinematic component and a kinematic diagnostic to split the thin disc from the thick disc or the halo. [source] Spatial and velocity clumping in a Sloan Digital Sky Survey blue horizontal branch star catalogueMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006L. Clewley ABSTRACT We present evidence for eight new clumps of blue horizontal branch stars discovered in a catalogue of these stars compiled from the Sloan Digital Sky Survey by Sirko et al. and published in 2004. Clumps are identified by selecting pairs of stars separated by distances ,2 kpc and with differences in galactocentric radial velocities <25 km s,1. Each clump contains four or more stars. Four of the clumps have supporting evidence: two of them also contain overdensities of RR Lyrae stars which makes their reality very likely. At least one of the clumps is likely to be associated with the tidal debris of the Sagittarius dwarf spheroidal galaxy. We emphasize that more accurate observations of the radial velocities or proper motions of the stars in the clumps, as well as the identification of other halo stars in these regions, are required to establish the reality of the remaining clumps. [source] Error analysis of proper motions in decination obtained for 807 Hipparcos stars from PZT observations over many decadesASTRONOMISCHE NACHRICHTEN, Issue 8 2010G. Damljanovi Abstract After publication of the Hipparcos catalogue (in 1997), a few new astrometric catalogues have appeared (TYCHO-2, ARIHIP, etc.), as a good combination of the Hipparcos satellite and ground-based data, to get more accurate coordinates and proper motions of stars than the Hipparcos catalogue ones. There are also investigations on improving the Hipparcos coordinates and proper motions by using the astrometric observations of latitude and universal time variations (via observed stars referred to Hipparcos catalogue), together with Hipparcos data, carried out during the last few years. These kind of ground-based data were collected at the end of the last century by J. Vondrák. There are about 4.4 million optical observations made worldwide at 33 observatories and with 47 instruments during 1899.7,1992.0; our Belgrade visual zenith telescope data (for the period 1949.0-1986.0) were included. First of all, these data were used to determine the Earth Orientation Parameters , EOP, but they are also useful for the opposite task , to check the accuracy of coordinates and proper motions of Hipparcos stars which were observed from the ground over many decades. Here, we use the latitude part of ten Photographic Zenith Tubes , PZT data (more than 0.9 million observations made at 6 observatories during the time interval 1915.8,1992.0), and combine them with the Hipparcos catalogue ones, with suitable weights, in order to check the proper motions in declination for 807 common PZT/Hipparcos stars (and to construct the PZT catalogue of ,, for 807 stars). Our standard errors in proper motions in declination of these stars are less than or equal to the Hipparcos ones for 423 stars. The mean value of standard errors of 313 stars observed over more than 20 years by PZT is 0.40 mas/yr. This is 53% of 0.75 mas/yr (the suitable value from the Hipparcos catalogue). We used the Least Squares Method , LSM with the linear model. Our results are in good agreement with the Earth Orientation Catalogue , EOC-2 and the new Hipparcos ones. The main steps of the method and the investigations of systematic errors in determined proper motions (the proper motion differences with respect to the Hipparcos values, the EOC-2 ones and the new Hipparcos ones, as a function of ,, ,, and magnitude) are presented here. A comparison of the four catalogues by pairs shows that there is no significant relationship between the differences of their ,, values and magnitudes and color indices of the common 807 stars. All catalogues have relatively small random and systematic errors which are close to each other. However, the comparison shows that our formal errors are too small. They are underestimated by a factor of nearly 1.7 (for EOC-2, it is 2.0) if we take the new Hipparcos (or Hipparcos) data as reference (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Finding the most variable stars in the Orion Belt with the All Sky Automated SurveyASTRONOMISCHE NACHRICHTEN, Issue 3 2010J.A. Caballero Abstract We look for high-amplitude variable young stars in the open clusters and associations of the Orion Belt. We use public data from the ASAS-3 Photometric V -band Catalogue of the All Sky Automated Survey, infrared photometry from the 2MASS and IRAS catalogues, proper motions, and the Aladin sky atlas to obtain a list of the most variable stars in a survey area of side 5° centred on the bright star Alnilam (, Ori) in the centre of the Orion Belt. We identify 32 highly variable stars, of which 16 had not been reported to vary before. They are mostly variable young stars and candidates (16) and background giants (8), but there are also field cataclysmic variables, contact binaries, and eclipsing binary candidates. Of the young stars, which typically are active Herbig Ae/Be and T Tauri stars with H, emission and infrared flux excess, we discover four new variables and confirm the variability status of another two. Some of them belong to the well known , Orionis cluster. Besides, six of the eight giants are new variables, and three are new periodic variables (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transverse motions in CSOs?ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009C. Stanghellini Abstract The measurement of proper motions in CSOs is a powerful tool to determine the dynamical evolution of the newly born extragalactic radio sources. We observed 3 CSOs with the VLBA in 2004 and in 2006 to monitor changes in their structure and measure the separation velocity of the hot spots. It is important to increase the size of the samples of CSOs with measured expansion velocity to test the existence of frustrated objects, and put stringent constraints on the current models. We found for all the three objects observed a transverse motion of the hot-spots, and we suggest as the more likely explanation a precession in the jet axis. This behaviour likely inhibits or at least slows down the radio source growth because the head of the hot-spot continuously hits new regions of the ISM. Therefore these radio sources may represent an old population of GPS/CSOs (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Star cluster kinematics in the GAIA eraASTRONOMISCHE NACHRICHTEN, Issue 9-10 2008H. Baumgardt Abstract The GAIA astrometric satellite will measure positions, proper motions and parallaxes of millions of stars with microarcsecond accuracy. This will greatly increase our understanding of the stellar populations of the Milky Way and their dynamics. In particular, it will be possible to determine internal and space motions of a large number of open or globular clusters with an accuracy of a few km/s or better, which will bring new insights into the way star clusters evolve and how they and the Milky Way as a whole have formed. It will also be possible to look for clusters which have a common space motion and follow tidal streams from dissolving globular clusters over many orbits by kinematically selecting their members, which will constrain the form of the galactic potential. I illustrate how GAIA will improve our knowledge on the kinematics and dynamics of star clusters and what can be learned by comparing the GAIA data with realistic N -body simulations of star clusters, possible with e.g. future GPU or GRAPE computers. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||