An analysis of parallaxes determined in two coordinates

Lutz, T. E.; Upgren, A. R.

doi:10.1086/112812

Cited by 33 publications

(28 citation statements)

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“…Gott et al 2001). Throughout the kinematic analysis, when we mention a "mean", we are actually using the average of (1) the median, (2) the Chauvenet clipped mean (Bevington & Robinson 1992), and (3) the probit mean (Lutz & Upgren 1980), i.e. a "mean" that is remarkably immune to the effects of outliers.…”

Section: Kinematic Analysismentioning

confidence: 99%

“…When we mention a "standard error", we are actually using the average of (1) the error of the true median (Gott et al 2001), and (2) the standard error of the Chauvenet clipped mean (Bevington & Robinson 1992). When we mention "dispersion", we are quoting the average of (1) the 68 per cent confidence intervals, and (2) the probit standard deviation (Lutz & Upgren 1980). In the limit of a Gaussian distribution lacking outliers, these quantities are asymptotically identical to their normal counterparts: the mean, standard error of the mean, and standard deviation.…”

Section: Kinematic Analysismentioning

confidence: 99%

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On the age of the β Pictoris moving group

Mamajek

Bell

2014

Monthly Notices of the Royal Astronomical Society

289

254

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Jeffries & Binks (2014) and Malo et al. (2014) have recently reported Li depletion boundary (LDB) ages for the β Pictoris moving group (BPMG) which are twice as old as the oft-cited kinematic age of ∼ 12 Myr. In this study we present (1) a new evaluation of the internal kinematics of the BPMG using the revised Hipparcos astrometry and best available published radial velocities, and assess whether a useful kinematic age can be derived, and (2) derive an isochronal age based on the placement of the A-, F-and G-type stars in the colour-magnitude diagram (CMD). We explore the kinematics of the BPMG looking at velocity trends along Galactic axes, and conducting traceback analyses assuming linear trajectories, epicyclic orbit approximation, and orbit integration using a realistic gravitational potential. None of the methodologies yield a kinematic age with small uncertainties using modern velocity data. Expansion in the Galactic X and Y directions is significant only at the 1.7σ and 2.7σ levels, and together yields an overall kinematic age with a wide range (13 − 58 Myr; 95 per cent CL). The A-type members are all on the zero age-main-sequence, suggestive of an age of > 20 Myr, and the loci of the CMD positions for the late-F-and G-type pre-main-sequence BPMG members have a median isochronal age of 22 Myr (± 3 Myr stat., ± 1 Myr sys.) when considering four sets of modern theoretical isochrones. The results from recent LDB and isochronal age analyses are now in agreement with a median BPMG age of 23 ± 3 Myr (overall 1σ uncertainty, including ±2 Myr statistical and ±2 Myr systematic uncertainties).

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Section: Kinematic Analysismentioning

confidence: 99%

Section: Kinematic Analysismentioning

confidence: 99%

On the age of the β Pictoris moving group

Mamajek

Bell

2014

Monthly Notices of the Royal Astronomical Society

289

254

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“…3. In the bottom row of the same figure, we show probability plots (see, e.g., Lutz & Upgren 1980;Reid et al 2002b) to help assess how closely a single Gaussian distribution fits our data. As can be seen in the plots, a straight line, corresponding to a single Gaussian distribution, is only marginally consistent with our data.…”

Section: Potential Explanations Of the Old Agementioning

confidence: 99%

On the kinematic age of brown dwarfs: radial velocities and space motions of 43 nearby L dwarfs

Seifahrt

Reiners

Almaghrbi

et al. 2010

A&A

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We present radial velocity measurements of a sample of L0-L8 dwarfs observed with VLT/UVES and Keck/HIRES. We combine these measurements with distance and proper motion from the literature to determine space motions for 43 of our targets. We identify nine candidate members of young moving groups, which have ages of 50-600 Myr according to their space motion. From the total velocity dispersion of the 43 L dwarfs, we calculate a kinematic age of ∼5 Gyr for our sample. This age is significantly higher than the ∼3 Gyr age known for late M dwarfs in the solar neighbourhood. We find that the distributions of the U and V velocity components of our sample are clearly non-Gaussian, placing the age estimate inferred from the full space motion vector into question. The W-component exhibits a distribution more consistent with a normal distribution, and from W alone we derive an age of ∼3 Gyr, which is the same age found for late-M dwarf samples. Our brightness-limited sample is probably contaminated by a number of outliers that predominantly bias the U and V velocity components. The origin of the outliers remain unclear, but we suggest that these brown dwarfs may have gained their high velocities by means of ejection from multiple systems during their formation.

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“…The set of 12 plate constants fitting the Turner equations is unbiased if the residuals ∆ξ, ∆η of the final group of reference stars are of mean value zero, Gaussian and independent (Gauss-Markoff theorem, Babu & Feigelson 1996). A half-normal plot (Lutz & Upgren 1980) of these residuals was used to define the significant level σ µ of the total p.m. µ and we observed σ µ ≈ 3σ G , with a final percentage of stars fitting a normal distribution on the order of 75% of the total number of stars on a plate. As a result of this procedure, a set of 4.8 × 10 5 stars with significant p.m. µ ≥ (0.015 ± 0.005) yr −1 is extracted out of a survey of 1.9 × 10 6 stars and is considered as the set of foreground stars.…”

Section: Retrospective Of Early Astrographic Surveysmentioning

confidence: 99%

Sydney observatory Galactic survey

Fresneau¹,

Vaughan²,

Argyle³

2007

A&A

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Context. First Epoch astrometric and radiometric information of a survey in the optical along the Galactic fourth quadrant is archived for further analysis in the time-domain. Aims. A photographic survey of 1.9 × 10 6 stars down to B-magnitude 14 ± 0.5 along the galactic meridian l = (330 ± 5)• , −64• ≤ b ≤ −7• and along the galactic equator 272• , is provided from century old astrographic plates of Sydney Observatory. Stellar candidates to investigate the Galaxy disk kinematics up to a distance of 1 kpc from the Sun are tentatively selected. Methods. The early data are combined with late epoch observations into a set of 4.8 × 10 5 stars with significant proper motion µ ≥ 0.005 yr −1 and approximate color B − V. The selection effects and the kinematical bias on the stellar system are investigated. F-G stellar candidates with a mean transverse velocity dispersion of 45 km s −1 are suggested. Results. The spin rate of 1 2• pc −1 of the velocity ellipsoid along its long axis is observed over half a thickness of 25 pc of the galactic disk for stars at an estimated distance D ≤ 300 pc from the Sun. Conclusions. A catalogue of 4.8 × 10 5 stars is provided for further investigation of the galactic disk heating by transient spiral wave or by GMC encounter.Key words. surveys -stars: kinematics Retrospective of early astrographic surveysFirst epoch observations used in the proper motion (p.m.) determination of faint stars observed in the Tycho-2 catalogue are based on short exposure plates observed for the Astrographic Catalog (AC) at the beginning of the 20th century over a field of view of 2• × 2 • for each of the 4 × 10 4 AC plates at a scale of 1 mm −1 , proving that photographic observations from the past were indeed durable even at the time of space astrometry (Urban et al. 1998). In order to check the quality of the old plates with a fast measuring machine like APM, used for instance to scan large Schmidt plates (Evans 1992), a set of 104 short exposure plates dating from the late 19th century was selected from the plate vault of Sydney Observatory, archived at Macquarie University.The double exposure technique used in the astrophotographic survey is shown in Fig. 1: stars are identified in the image inventory of a plate scanned with APM by the combination of double images. Along with the x, y plate mean coordinates (in mm) and their errors ∆x, ∆y (in microns), an indication of short term magnitude variability ∆m, is also computed for each star: this information is not available from the AC measurements but is usable to search for flare stars (Fresneau et al. 2001). The (ξ, η) plate coordinates (in arcmin) for the Tycho-2 stars The quality of the best linear unbiased estimation of the set of 12 plate constants (A, B, C, D, E, F and A , B , C , D , E , F ) after the weighted least squares fit is measured by the rms error σ T between the computed and observed equatorial coordinates of the set of Tycho-2 stars (a couple of hundreds per 2 • × 2 • field of view). The same stars are also used to derive a calibrat...

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An analysis of parallaxes determined in two coordinates

Cited by 33 publications

References 0 publications

On the age of the β Pictoris moving group

On the age of the β Pictoris moving group

On the kinematic age of brown dwarfs: radial velocities and space motions of 43 nearby L dwarfs

Sydney observatory Galactic survey

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