J/ApJ/443/124 Radial Velocities of Stars in M4 (Peterson+ 1995)
Radial Velocities of Stars in the Globular Cluster M4 and the Cluster Distance
Peterson R.C., Rees R.F., Cudworth K.M.
<Astrophys. J. 443, 124 (1995)>
=1995ApJ...443..124P 1995ApJ...443..124P
ADC_Keywords: Clusters, globular; Radial velocities; Positional data; Photometry
Keywords: globular clusters: individual (M4) - stars: kinematics -
techniques: radial velocities
Abstract:
The internal stellar velocity distribution of the globular cluster M4
is evaluated from nearly 200 new radial velocity measurements good to
1 km/s and a rederivation of existing proper motions. The mean radial
velocity of the cluster is 70.9 ± 0.6 km/s. The velocity dispersion
is 3.5 ± 0.3 km/s at the core, dropping marginally towards the
outskirts. Such a low internal dispersion is somewhat at odds with the
cluster's orbit, for which the perigalacticon is sufficiently close to
the galactic center that the probability of cluster disruption is
high; a tidal radius two-thirds the currently accepted value would
eliminate the discrepancy. The cluster mass-to-light ratio is also
small, M/L_V = 1.0 ± 0.4 in solar units. M4 thus joins M22 as a
cluster of moderate mass and concentration with a mass-to-light ratio
among the lowest known.
The astrometric distance to the cluster is also smaller than expected,
1.72 ± 0.14 kpc. This is only consistent with conventional estimates
of the luminosity of horizontal branch stars provided an extinction
law R = A_V/E(B-V) ∼ 4 is adopted, as has been suggested recently by
several authors.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 88 182 Velocities for M4 members
table2.dat 85 11 *Velocities for M4 nonmembers
table3.dat 28 93 Duplicate velocities
table5.dat 68 531 Proper-motion data superseding Table 3 of
Cudworth & Rees =1990AJ.....99.1491C 1990AJ.....99.1491C
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Note on table2.dat:
Table 2 lists the same information as in Table 1 for the nonmembers of
M4. The velocities of these stars average -12.8 km/s with a dispersion
of 34.5 km/s. Thus the radial velocity of M4 is quite distinct from
that of the field, differing by more than 80 km/s.
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (equinox 1950.0)
4- 5 I2 min RAm R.A.
7-11 F5.2 s RAs R.A.
13 A1 --- DE- Declination sign
14-15 I2 deg DEd Declination (equinox 1950.0)
17-18 I2 arcmin DEm Dec.
20-23 F4.1 arcsec DEs Dec.
25-29 F5.2 arcmin Dist Radial distance from cluster center
31-35 F5.1 deg PA Position angle positive north through east
38-42 F5.2 mag Vmag V magnitude
43-47 F5.2 mag B-V B-V color
50-59 F10.2 d Date *Julian date of each observation
62-66 F5.2 km/s RV *Measured radial velocity
67-71 F5.2 km/s e_RV *Internal uncertainty in RV
72-74 I3 % Memb []?=-1 Percent probability of membership
77-88 A12 --- ID *Identification
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Note on Date:
Julian date of each observation, or that of the first observation
if the star was observed twice or more.
Note on RV:
For all multiply observed stars, this is the weighted mean of the
set of observations in Table 3.
Note on e_RV:
The uncertainty is derived from the ratio R of the height of the
cross-correlation peak relative to a typical noise fluctuation,
according to the Tonry & Davis [1979, AJ, 84, 1511] formula
sigma_R = K/(1+R) (in km/s), with K=8.3 for sharp-lined spectra
obtained with the Mount Hopkins echelle spectrographs.
Note on ID:
Star Name: Lee (1977, A&AS, 27, 367) number, no prefix;
Sawyer-Hogg (1973, Pub. DDO, 3, No. 6) variable, prefix V;
Alcaino (1975, A&AS, 21, 5) single letter or prefix A;
Greenstein (1939, ApJ, 90, 387) prefix G
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (equinox 1950.0)
4- 5 I2 min RAm R.A.
7-11 F5.2 s RAs R.A.
13 A1 --- DE- Declination sign
14-15 I2 deg DEd Declination (equinox 1950.0)
17-18 I2 arcmin DEm Dec.
20-23 F4.1 arcsec DEs Dec.
24-29 F6.2 arcmin Dist Radial distance from cluster center
31-35 F5.1 deg PA Position angle positive north through east
38-42 F5.2 mag Vmag V magnitude
43-47 F5.2 mag B-V B-V color
50-59 F10.2 d Date Julian date of each observation
61-66 F6.2 km/s RV Measured radial velocity
68-71 F4.2 km/s e_RV Internal uncertainty in RV
72-74 I3 % Memb []? Percent probability of membership
77-85 A9 --- ID Identification
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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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1-10 F10.2 d Date Julian date of each observation
12-17 F6.2 km/s RV Measured radial velocity
19-22 F4.2 km/s e_RV Internal uncertainty in RV
25-28 A4 --- ID Number from Lee 1977, A&AS, 27, 367
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1-16 A16 --- Names *Star names
18-24 F7.1 arcsec X *X coordinate relative to cluster center
25-31 F7.1 arcsec Y *Y coordinate relative to cluster center
32-37 I6 0.01mas/yr mu_x Relative proper motion in X coordinate
38-41 I4 0.01mas/yr emux Standard error in mu_x
42-47 I6 0.01mas/yr mu_y Relative proper motion in Y coordinate
48-51 I4 0.01mas/yr emuy Standard error in mu_y
52-58 F7.2 mag Vmag V magnitude
59-64 F6.2 mag B-V B-V color
65-68 I4 % Pr Probability of membership based on
relative proper motion
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Note on Names:
Lee (1977, A&AS, 27, 367) number, no prefix; Sawyer-Hogg (1973, Pub.
DDO, 3, No. 6) variable, prefix V; Alcaino (1975, A&AS, 21 5), single
letter or prefix A; Alcaino and Liller (1984), AL -- second number is
ring number; Zinn et al. (1972) UV-bright star, Z; Greenstein (1939,
ApJ, 90, 387), prefix G
Note on X, Y:
X and Y coordinates (arcsec) relative to the cluster center of Shawl
and White (1986, AJ, 91, 312) and oriented along right ascension and
declination for equator and equinox 1950
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Origin: AAS CD-ROM series, Volume 4, 1995 Lee Brotzman [ADS] 06-May-1995
Historical Notes: the Julian Dates were converted to absolute scale
(initially with offset 2440000)
(End) [CDS] 11-Jul-1995