scholarly journals Mass and Luminosity Function of the Pleiades

1980 ◽  
Vol 85 ◽  
pp. 157-163 ◽  
Author(s):  
Floor van Leeuwen
Keyword(s):  
Proper Motion ◽  
Total Mass ◽  
Luminosity Function ◽  
Mass Range ◽  
Flare Star ◽  
Central Field ◽  
Photometric Measurement ◽  
Proper Motions ◽  
Total Field ◽  
Factor 20

From a proper motion survey by Pels and photometric measurement of selected stars it was found that the Pleiades cluster extends till at least 496 from the centre, corresponding to 10 pc at a distance of 125 pc. It turns out that the luminosity function of the Pleiades is a function of the distance to the centre, the proportion of faint stars increasing with this distance. Because of this, the luminosity function as it was determined before flattened towards fainter stars, whereas for the total field with a diameter of 20 pc one finds a luminosity function that is still increasing at the faint end. Flare star observations in the Pleiades field show that the increase amounts to at least a factor 20 in the mass range 2 to 0.4 M⊙. Accurate proper motions of stars in the projected central field show a dispersion of velocities in the cluster of 700 m/sec. This could indicate a total mass of the Pleiades cluster of the order of 2000 M⊙.

scholarly journals Proper Motion Survey in the Pleiades

1995 ◽  
Vol 148 ◽  
pp. 228-231
Author(s):  
J. Souchay ◽  
E. Schilbach
Keyword(s):  
Proper Motion ◽  
Open Cluster ◽  
Photometric Data ◽  
Proper Motions ◽  
Total Field

AbstractAs a first step of our open cluster programme a catalogue of proper motions and photographic U, B, V, R magnitudes for stars up to 18 mag within a region centered near Alcyone is presented. The catalogue is based on MAMA measurements of plates taken with Tautenburg and OCA (CERGA) Schmidt telescopes. The photometric survey includes ca. 65000 stars and covers a total field of about 25 square degrees. Proper motions have been obtained for ca. 40000 stars within a central 17 square degree region of this field. For the majority of stars in the survey an accuracy of 0.08 mag and 2 mas/year has been estimated for photometric data and proper motions, respectively. The results of the determination of the Pleiades membership up to 18th magnitude is presented.

scholarly journals Determining Motions and Birthplaces of Pulsars through VLBI Astrometry

1998 ◽  
Vol 164 ◽  
pp. 391-392
Author(s):  
T. J. Galama ◽  
J. Van Paradijs ◽  
E. P. J. van den Heuvel ◽  
A. G. de Bruyn ◽  
R. M. Campbell ◽  
...  
Keyword(s):  
Flux Density ◽  
Proper Motion ◽  
Mass Range ◽  
Solar Neighborhood ◽  
Proper Motions ◽  
First Results ◽  
Motion Measurements

AbstractWe present first results of global VLBI astrometric pulsar parallax and proper motion measurements (phase-reference). The aim is to obtain information on pulsar motions and pulsar birthplaces. Proper motions could provide answers to questions like: How large are pulsar velocities at birth? How are these velocities produced and what is the final galactic pulsar distribution? Identification of birthplaces (with, e.g., an OB-association) provides information on the pulsar progenitor population (the fraction of pulsars born in binaries; the mass range of the progenitors etc.). We have a first epoch on three pulsars, selected on the basis of age (young < 3 Myr), flux density (relatively strong) and presence in the solar neighborhood (d < 3 kpc). Gating increases the SNR by typically a factor of 5.

scholarly journals Statistical Analysis of Proper Motion Surveys

1986 ◽  
Vol 109 ◽  
pp. 43-45
Author(s):  
Robert B. Hanson
Keyword(s):  
Statistical Analysis ◽  
Proper Motion ◽  
Luminosity Function ◽  
Solar Neighborhood ◽  
Proper Motions ◽  
Stellar Kinematics ◽  
Kinematic Studies

Proper motion surveys offer a great deal of data bearing on important astronomical problems such as stellar kinematics and the luminosity function in the solar neighborhood. Major obstacles to the full use of proper motions have long been posed by: (1) incompleteness of proper motion surveys, (2) proper motion bias in kinematic studies, and (3) the indirect approaches and kinematical assumptions needed in traditional luminosity studies.

scholarly journals Berkeley Studies of Faint Stars at High Latitudes

1977 ◽  
Vol 4 (2) ◽  
pp. 67-67
Author(s):  
Richard G. Kron ◽  
Liang-Tai George Chiu ◽  
Kate O. Brooks
Keyword(s):  
Standard Error ◽  
Proper Motion ◽  
Luminosity Function ◽  
Density Gradients ◽  
High Latitudes ◽  
Proper Motions ◽  
Frequency Distributions ◽  
Density Distributions ◽  
Halo Stars

Several Lick 3-m prime-focus plates of Selected Areas 57, 68, and 51 (taken by I. King) in B, V, and R have been measured for stellar magnitudes down to the plate limit by L. Hinrichs and King, and are currently being measured by Chiu for proper motions (several hundred stars per plate) with the Berkeley PDS microdensitometer. Prime-focus plates are also available from the Hale 5-m and Mayall 4-m telescopes, giving an overall baseline of 20 years. Work so far indicates that on the Lick plates stars brighter then V = 19 can be measured to within one micron standard error; the error becomes unacceptably large for stars fainter than V = 20. A large number of stars bluer than B-V =0.4 show proper motion and are therefore excellent candidates for white dwarfs. For 0.4 ≤ B-V ≤ 0.8, the proper motion stars are expected to be predominantly subdwarfs.The frequency distributions of the stars in V and B-V for the three fields are being analysed by Brooks; the fields are advantageously placed for study of the density distributions in both the disk and the halo. These data should allow the halo stars to be studied out to a distance of 10 to 15 kpc, as well as a determination of the degree of flattening of the halo. Also, a study will be made of the z and ῶ density gradients in the disk, and the luminosity function of disk stars.

scholarly journals Gaia DR2 reveals a very massive runaway star ejected from R136

2018 ◽  
Vol 619 ◽  
pp. A78 ◽  
Author(s):  
D. J. Lennon ◽  
C. J. Evans ◽  
R. P. van der Marel ◽  
J. Anderson ◽  
I. Platais ◽  
...  
Keyword(s):  
Lower Limit ◽  
Proper Motion ◽  
Evolutionary History ◽  
Massive Star ◽  
Position Angle ◽  
Proper Motions ◽  
Central Cluster ◽  
Dynamical Constraints ◽  
Runaway Stars ◽  
Gaia Dr2

A previous spectroscopic study identified the very massive O2 III star VFTS 16 in the Tarantula Nebula as a runaway star based on its peculiar line-of-sight velocity. We use the Gaia DR2 catalog to measure the relative proper motion of VFTS 16 and nearby bright stars to test if this star might have been ejected from the central cluster, R136, via dynamical ejection. We find that the position angle and magnitude of the relative proper motion (0.338±0.046 mas yr−1, or approximately 80±11 km s−1) of VFTS 16 are consistent with ejection from R136 approximately 1.5±0.2 Myr ago, very soon after the cluster was formed. There is some tension with the presumed age of VFTS 16 that, from published stellar parameters, cannot be greater than 0.9+0.3−0.2 Myr. Older ages for this star would appear to be prohibited due to the absence of He I lines in its optical spectrum, since this sets a firm lower limit on its effective temperature. The dynamical constraints may imply an unusual evolutionary history for this object, perhaps indicating it is a merger product. Gaia DR2 also confirms that another very massive star in the Tarantula Nebula, VFTS 72 (alias BI 253; O2 III-V(n)((f*)), is also a runaway on the basis of its proper motion as measured by Gaia. While its tangential proper motion (0.392±0.062 mas yr−1 or 93±15 km s−1) would be consistent with dynamical ejection from R136 approximately 1 Myr ago, its position angle is discrepant with this direction at the 2σ level. From their Gaia DR2 proper motions we conclude that the two ∼100 M⊙ O2 stars, VFTS 16 and VFTS 72, are fast runaway stars, with space velocities of around 100 km s−1 relative to R136 and the local massive star population. The dynamics of VFTS 16 are consistent with it having been ejected from R136, and this star therefore sets a robust lower limit on the age of the central cluster of ∼1.3 Myr.

scholarly journals Proper motions in the Galactic bulge: Plaut's window

2007 ◽  
Vol 3 (S245) ◽  
pp. 351-354
Author(s):  
Katherine Vieira ◽  
Dana Cassetti-Dinescu ◽  
René A. Méndez ◽  
R. Michael Rich ◽  
Terrence M. Girard ◽  
...  
Keyword(s):  
Proper Motion ◽  
Galactic Rotation ◽  
Red Giants ◽  
Proper Motions ◽  
Motion Study ◽  
Solar Motion ◽  
Two Samples ◽  
Red Clump ◽  
Good Agreement ◽  
Peak Value

AbstractA proper motion study of a field of 20′ × 20′ inside Plaut's low extinction window (l,b)=(0o, −8o), has been completed. Relative proper motions and photographicBVphotometry have been derived for ~ 21,000 stars reaching toV~ 20.5 mag, based on the astrometric reduction of 43 photographic plates, spanning over 21 years of epoch difference. Proper motion errors are typically 1 mas yr−1. Cross-referencing with the 2MASS catalog yielded a sample of ~ 8700 stars, from which predominantly disk and bulge subsamples were selected photometrically from theJHcolor-magnitude diagram. The two samples exhibited different proper-motion distributions, with the disk displaying the expected reflex solar motion. Galactic rotation was also detected for stars between ~2 and ~3 kpc from us. The bulge sample, represented by red giants, has an intrinsic proper motion dispersion of (σl, σb) = (3.39, 2.91)±(0.11, 0.09) mas yr−1, which is in good agreement with previous results. A mean distance of$6.37^{+0.87}_{-0.77}$kpc has been estimated for the bulge sample, based on the observedKmagnitude of the horizontal branch red clump. The metallicity [M/H] distribution was also obtained for a subsample of 60 bulge giants stars, based on calibrated photometric indices. The observed [M/H] shows a peak value at [M/H] ~ −0.1 with an extended metal poor tail and around 30% of the stars with supersolar metallicity. No change in proper motion dispersion was observed as a function of [M/H]. We are currently in the process of obtaining CCDUBV RIphotometry for the entire proper-motion sample of ~ 21,000 stars.

scholarly journals Wading Through the Quagmire of Schmidt-Plate Coordinate Systematics

1998 ◽  
Vol 179 ◽  
pp. 384-385 ◽  
Author(s):  
C.-L Lu ◽  
I. Platais ◽  
T.M. Girard ◽  
V. Kozhurina-Platais ◽  
W.F. Van Altena ◽  
...  
Keyword(s):  
Proper Motion ◽  
San Juan ◽  
Proper Motions ◽  
Positional Accuracy

We attempted to quantify the magnitude-dependent systematics in a sample of Schmidt plates by comparison to positions from the Yale/San Juan Southern Proper Motion program which offers star positions and absolute proper motions down to B = 18 with a mean density of about 50 stars per square degree and a positional accuracy of 0.1″ (Platais et al. 1995).

scholarly journals The Luyten – Control Data Stellar Proper Motion Measuring Machine

1970 ◽  
Vol 7 ◽  
pp. 5-25
Author(s):  
James Newcomb
Keyword(s):  
Proper Motion ◽  
Time Scale ◽  
Proper Motions ◽  
Control Data ◽  
Stellar Proper Motions ◽  
Measurement Function ◽  
Measuring Machine ◽  
Motion Measurements

The discovery and measurement of stellar proper motions has always been associated with machines: for proper motion measurements involve four activities: observation, recording, comparison and measurement. Participation by the astronomer in these activities has step by step been replaced partically or wholly by machines. First the observation and recording functions changed from visual to photographic – with the fine guiding done by the astronomer; then the comparison by the blink microscope and the measurement by visually operated measuring machines. On a comparative time scale, the next step – automation of the comparison and measurement function – has been much money, time, and effort away from the previous steps, but as this presentation and other presentations at this conference will show, machines of varying degrees of automation and astronomer participation are now in operation.

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