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J/AJ/122/1486 NGC 2451A proper motions and membership (Platais+, 2001)
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WIYN open cluster study. VII. NGC 2451A and the Hipparcos distance scale.
Platais I., Kozhurina-Platais V., Barnes S., Girard T.M., Demarque P.,
van Altena W.F., Deliyannis C.P., Horch E.
<Astron. J. 122, 1486 (2001)>
=2001AJ....122.1486P
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ADC_Keywords: Clusters, open ; Proper motions ; Radial velocities ;
Photometry, UBV
Keywords: astrometry - color-magnitude diagrams -
open clusters and associations: individual (NGC 2451A)
Abstract:
We provide new evidence that NGC 2451A is undoubtedly a young open
cluster, although sparsely populated. New cluster membership has been
derived from relative proper motions of 5868 stars. In total, 136
stars down to V~15 5 have membership probability P{mu}>=2%. New CCD BV
photometry indicates that about 70 stars are indeed main-sequence
stars of NGC 2451A. This is also supported by our measurements of
radial velocities. A total of 34 very likely cluster members yield a
mean heliocentric radial velocity for NGC 2451A equal to +22.9km/s.
The high quality of our BV photometry, a confirmation of cluster
membership from proper motions and radial velocities, and a recently
obtained metallicity estimate for several cluster stars allow us to
perform a precise isochrone fit. The Yale isochrones, updated by the
latest available input physics, have been fitted to the cluster's
color-magnitude diagram, yielding a distance modulus V_0_-M_V_ in the
range 6.35 to 6.38, which is in excellent agreement with the distance
modulus (m-M)_0_=6.38 derived from the Hipparcos data recently by van
Leeuwen and Robichon et al. (1998, Cat. <J/A+AS/130/157>).
We have used the high-resolution spectra acquired using the Hydra
multiobject spectrograph at the WIYN telescope (Kitt Peak, Arizona) in
1997 November and 1998 October.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 65 136 Astrometry and photometry for probable cluster
members in NGC 2451A
table3.dat 34 67 Radial velocities
spm.dat 129 5868 Catalog of positions, relative proper motions
and BV photographic photometry in the region of
open cluster NGC 2451
ccd.dat 71 14836 Catalog of CCD BV photometry in the region of
open cluster NGC 2451
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See also:
http://www.astro.yale.edu/astrom : SPM Home Page
I/252 : The USNO-A2.0 Catalogue (Monet+ 1998)
I/277 : SPM catalog 2.0 (Platais+, 1998)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- PKB Running identification number,
Cl* NGC 2451 PKB NNNNN in Simbad
6- 8 I3 --- Will ? The Williams (1967MNSSA..26...30W) number,
NGC 2451 NNN in Simbad
10 I1 h RAh Right Ascension (J2000, epoch J2000) (1)
12- 13 I2 min RAm Right Ascension (J2000, epoch J2000) (1)
15- 20 F6.3 s RAs Right Ascension (J2000, epoch J2000) (1)
22 A1 --- DE- Declination sign (J2000, epoch J2000) (1)
23- 24 I2 deg DEd Declination (J2000, epoch J2000) (1)
26- 27 I2 arcmin DEm Declination (J2000, epoch J2000) (1)
29- 33 F5.2 arcsec DEs Declination (J2000, epoch J2000) (1)
35- 39 F5.1 mas/yr pmX Relative proper motion along X (2)
41- 44 F4.1 mas/yr pmY Relative proper motion along Y (2)
46- 51 F6.3 mag Vmag The Johnson V band magnitude
53 A1 --- r_Vmag [aeu] Source of Vmag (3)
55- 60 F6.3 mag B-V The (B-V) color
62 I1 --- o_Vmag Number of observations for Vmag
64- 65 I2 % Prob Cluster membership probability
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Note (1): Epoch and equinox J2000.
Note (2): Relative proper motions to X, Y directions, specified in spm.dat file.
Note (3): Reference for photometry:
a = B and V photometry adopted from Hipparcos, Cat. <I/239>
e = B and V photometry from SPM photometry (see Sec.2.2)
u = B and V photometry from Williams (1967MNSSA..26...30W)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- PKB Running identification number,
Cl* NGC 2451 PKB NNNNN in Simbad
6- 16 F11.3 d HJD Heliocentric Julian date
18- 23 F6.2 km/s HRV Heliocentric radial velocity
24 A1 --- n_HRV [a] indicates a broad cross-correlation peak
27- 30 A4 --- Memb Membership status based on membership
probability (2)
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Note (2): Membership status:
ms: star located on the main sequence of NGC 2451A or up to 0.75mag above
B-cl: probable NGC 2451B members
fld: star located below or well above the main sequence of NGC 2451A,
considered as field star
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Byte-by-byte Description of file: spm.dat
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Bytes Format Units Label Explanations
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2- 5 I4 --- PKB Running identification number,
Cl* NGC 2451 PKB NNNNN in Simbad
7- 12 F6.2 mm Xpos X position (1)
14- 19 F6.2 mm Ypos Y position (1)
21- 30 F10.7 rad RArad Right ascension for the epoch 1991.25
and in the ICRS reference system
(i.e. equinox 2000.0)
32- 41 F10.7 rad DErad Declination for the epoch 1991.25 and
equinox 2000.0
43- 45 I3 mas e_RArad Estimated standard error in right ascension
multiplied by cos(DE)
47- 49 I3 mas e_DErad Estimated standard error in declination
51- 56 F6.1 mas/yr pmRA Relative proper motion in right ascension
multiplied by cos(DE)
58- 63 F6.1 mas/yr pmDE Relative proper motion in declination
65- 66 I2 --- o_Bmag The number of grating images per star detected
on blue plates (grating image pairs are
counted as one image)
68- 69 I2 --- o_Vmag The number of grating images per star on
visual plates
71- 74 F4.1 mas/yr e_pmRA Estimated standard error in right ascension's
proper motion
76- 79 F4.1 mas/yr e_pmDE Estimated standard error in declination's
proper motion
81- 85 F5.2 mag Bmag ?=0.00 Photographic B-magnitude
(if missing then set to 0.00)
87- 90 F4.2 mag e_Bmag Estimated standard error of B-magnitude
92- 96 F5.2 mag Vmag ?=0.00 Photographic V-magnitude
(if missing then set to 0.00)
98-101 F4.2 mag e_Vmag Estimated standard error of V-magnitude
103-108 F6.3 mag Vmagc ?=-1.000 CCD V-magnitude
(if missing then set to -1.000)
110-115 F6.3 mag B-Vc ?=-1.000 CCD B-V color
(if missing then set to -1.000)
117-121 F5.3 mag e_Vmagc IRAF generated error in CCD V-magnitude
123-127 F5.3 mag e_B-Vc IRAF generated error in CCD B-V color
129 I1 --- Nframe [0/4]? Number of frames per star (G1)
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Note (1): Approximate rectangular coordinates on the SPM plate #18.
The scale of SPM plates is 55.1"/mm. East is in the direction of
increasing X, North is in the direction of Y.
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Byte-by-byte Description of file: ccd.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- Seq Object identifier (1)
11- 19 F9.5 deg RAdeg Right ascension
(mean epoch=1996.6, equinox 2000.0)
21- 29 F9.5 deg DEdeg Declination (mean epoch=1996.6, equinox 2000.0)
31- 36 F6.3 mag Vmag CCD V magnitude
38- 43 F6.3 mag B-V CCD B-V magnitude
45- 49 F5.3 mag e_Vmag IRAF generated error in CCD V-magnitude
51- 55 F5.3 mag e_B-V IRAF generated error in CCD B-V color
57- 62 F6.3 arcsec DRA "CCD-USNOA2.0" (<I/252>) coordinate difference
in right ascension multiplied by cos(DE)
64- 69 F6.3 arcsec DDE "CCD-USNOA2.0" (<I/252>) coordinate difference
in declination
71 I1 --- Nframe [1/4] Number of frames per star (G1)
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Note (1): Normally, first four digits indicate the probable NGC 2451A member
which usually was placed at the center of CCD chip
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Global notes:
Note (G1): Number of frames per star:
If it is 2, 3, or 4 then mean CCD BV magnitudes have been averaged
from 2, 3, or 4 frames. (Note that for spm.dat, many entries entirely
miss this item!)
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History:
From electronic version of the journal
References:
Von Hippel & Sarajedini, Paper I 1998AJ....116.1789V
Sarajedini et al., Paper II 1999AJ....118.2894S
Sarajedini, Paper III 1999AJ....118.2321S
Barrado y Navascues et al., Paper V 2001ApJ...549..452B
Sills & Sarajedini, Paper VI 2000ApJ...544..944S
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(End) Greg Schwarz [AAS], Patricia Bauer [CDS] 14-Jan-2002