J/ApJ/420/612 Proper motions & radial velocities in M22 (Peterson+ 1994)
Proper motions and radial velocities in the globular cluster M22 and the
cluster distance
Peterson R.C., Cudworth K.M.
<Astrophys. J. 420, 612 (1994)>
=1994ApJ...420..612P 1994ApJ...420..612P
ADC_Keywords: Clusters, globular ; Radial velocities ; Stars, distances
Keywords: astrometry - globular clusters: individual (M22) - stars: distances -
techniques: radial velocities
Abstract:
The distance to the globular cluster M22 is reexamined from new
radial-velocity data and revised proper motions. Proper motions are
rederived for 672 stars in the field of M22 using plate constant
solutions from which stars of large proper motions have been removed,
to reduce systematic errors which depend on coordinates. Radial
velocities good to 1km/s have been obtained for 130 members of the
globular cluster M22. The mean radial velocity is -148.8±0.8km/s.
The radial velocity dispersion is 6.6±0.8km/s in the mean, and shows
little if any dependence on distance from the cluster center over a
3'-7' annulus. Ignoring the small effect of rotation, a mass-to-light
ratio M/L_V=0.85±0.15 in solar units is derived. The lack of stars
moving faster than the escape velocity suggests strongly that a value
M/L_V∼1 applies to the cluster as a whole. This value is among the
lowest observed for any globular cluster. Rotation is evident in both
proper motions and radial velocities, and its position angle is in
reasonable agreement with the major axis of the cluster's elongation.
Its amplitude diminishes with radius, from ∼6km/s for 1'≤r≤ 3', to
∼3km/s for 3'≤r≤7'. Rotation must be carefully modeled to determine
an accurate distance to the cluster. From the simple approximation
that the velocity dispersion is unaffected in the directions
perpendicular to the streaming motion, a comparison of the dispersions
in proper motion with those in radial velocity leads to a preliminary
estimate for the distance of 2.6±0.3kpc, and a horizontal-branch
magnitude M_V=0.71±0.27, using the reddening value E(B-V)=0.42 from
M22 BHB stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 86 130 Velocities for M22 members
table3.dat 82 1 *Velocities for M22 field stars
table4.dat 37 57 Stars with multiple velocity measurements
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Note on table3.dat: This table lists the same information as in Table 2 for the
nonmember star. The velocity of this star differs by nearly 100 km/s from that
of the cluster.
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Byte-by-byte Description of file: table2.dat table3.dat
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Bytes Format Units Label Explanations
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1- 7 F7.2 d HJD-2440000 *Julian date (-2440000) of each observation
10- 11 I2 h RAh Right ascension (equinox 1950.0)
13- 14 I2 min RAm Right ascension (equinox 1950.0)
16- 20 F5.2 s RAs Right ascension (equinox 1950.0)
22 A1 --- DE- Declination sign
23- 24 I2 deg DEd Declination (equinox 1950.0)
26- 27 I2 arcmin DEm Declination (equinox 1950.0)
29- 32 F4.1 arcsec DEs Declination (equinox 1950.0)
34- 37 F4.1 arcmin Dist *Radial distance from cluster center
39- 44 F6.1 deg PA *Position angle positive north through east
46- 53 F8.2 km/s RV *Measured radial velocity
55- 58 F4.2 km/s e_RV *Internal one-sigma uncertainty in RV
60- 65 F6.2 mag Vmag V magnitude
67- 69 I3 % Memb Percent probability of membership
72- 86 A15 --- ID *Identification
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Note on HJD-2440000:
Julian date of each observation, or that of the first observation
if the star was observed twice or more.
Note on Dist, PA:
Radius and position angle from the center of the cluster,
RA = 18h 33m 21.5s, DE = -23d 56m 44s, as measured by Shawl & White
(1986AJ.....91..312S 1986AJ.....91..312S)
Note on RV:
For all multiply observed stars, this is the weighted mean of the
set of observations in Table 4.
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 (1979AJ.....84.1511T 1979AJ.....84.1511T) 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:
First, when available, is the identification of Arp & Melbourne
(1959AJ.....64...28A 1959AJ.....64...28A) or its extension by Lloyd-Evans (1975MNRAS.171..647L 1975MNRAS.171..647L),
with Roman numerals I-IV for the quadrants and V for the center.
This is followed by identification from Alcaino (1977A&AS...29..383A 1977A&AS...29..383A) and the
extension by Alcaino & Liller (1983AJ.....88.1330A 1983AJ.....88.1330A), for which the annulus
number precedes the number of the star.
Last comes the variable number from Sawyer-Hogg (1973PDDO....3....6S 1973PDDO....3....6S), prefix
V, no hyphen.
If no other name is available, table2 list the Cudworth (1986AJ.....92..348C 1986AJ.....92..348C)
number, preceded by C.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 8 F8.3 d HJD-2440000 Julian date (-2440000) of each observation
10- 17 F8.2 km/s RV Measured radial velocity
19- 22 F4.2 km/s e_RV Internal uncertainty in RV
24- 29 F6.2 mag Vmag []? V magnitude
32- 37 A6 --- ID *Identification
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Note on ID:
Arp & Melbourne (1959AJ.....64...28A 1959AJ.....64...28A) or its extension by Lloyd-Evans
(1975MNRAS.171..647L 1975MNRAS.171..647L), with Roman numerals I-IV for the quadrants.
Sawyer-Hogg (1973PDDO....3....6S 1973PDDO....3....6S), prefix V, no hyphen.
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Origin: AAS CD-ROM series, Volume 4, 1995 Lee Brotzman [ADS] 06-May-1995
(End) [CDS] 11-Jul-1995