CDROM/APJ/V443/P124 Radial Velocities of Stars in M4 (Peterson+ 1995) ================================================================================ Radial Velocities of Stars in the Globular Cluster M4 and the Cluster Distance Ruth C. Peterson, Richard F. Rees, & Kyle M. Cudworth <1995, ApJ, 443, 124> =1995ApJ...443..124P ================================================================================ 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. Keywords: globular clusters: individual (M4) -- stars: kinematics -- techniques: radial velocities File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table1.dat 85 182 Velocities for M4 members table2.dat 82 11 Velocities for M4 nonmembers table3.dat 26 93 Duplicate velocities table5.dat 68 531 Proper-motion data superseding Table 3 of Cudworth & Rees 1990, AJ, 99, 1491 -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 2 I2 h RAh Right ascension (equinox 1950.0) 3 1X --- --- ':' separator 4- 5 I2 min RAm R.A. 6 1X --- --- ':' separator 7-11 F5.2 s RAs R.A. 12 1X --- --- Blank 13 A1 --- DE- Declination sign 14-15 I2 deg DEd Declination (equinox 1950.0) 16 1X --- --- ':' separator 17-18 I2 arcmin DEm Dec. 19 1X --- --- ':' separator 20-23 F4.1 arcsec DEs Dec. 24-29 F6.2 arcmin Dist Radial distance from cluster center 30-35 F6.1 deg PA Position angle positive north through east 36-42 F7.2 mag V V magnitude 43-47 F5.2 mag B-V B-V color 48-56 F9.2 d Date *Julian date (- 2440000) of each observation 57-63 F7.2 km/s RV *Measured radial velocity 64-68 F5.2 km/s e_RV *Internal uncertainty in RV 69-71 I3 % Memb []?=-1 Percent probability of membership 72-73 2X --- --- Blank 74-85 A12 --- ID *Identification -------------------------------------------------------------------------------- Notes for file: table1.dat -------------------------------------------------------------------------------- Date: Julian date of each observation, or that of the first observation if the star was observed twice or more. RV: For all multiply observed stars, this is the weighted mean of the set of observations in Table 3. 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. 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 -------------------------------------------------------------------------------- Comments for file: 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: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 2 I2 h RAh Right ascension (equinox 1950.0) 3 1X --- --- ':' separator 4- 5 I2 min RAm R.A. 6 1X --- --- ':' separator 7-11 F5.2 s RAs R.A. 12 1X --- --- Blank 13 A1 --- DE- Declination sign 14-15 I2 deg DEd Declination (equinox 1950.0) 16 1X --- --- ':' separator 17-18 I2 arcmin DEm Dec. 19 1X --- --- ':' separator 20-23 F4.1 arcsec DEs Dec. 24-29 F6.2 arcmin Dist Radial distance from cluster center 30-35 F6.1 deg PA Position angle positive north through east 36-42 F7.2 mag V V magnitude 43-47 F5.2 mag B-V B-V color 48-56 F9.2 d Date Julian date (- 2440000) of each observation 57-63 F7.2 km/s RV Measured radial velocity 64-68 F5.2 km/s e_RV Internal uncertainty in RV 69-71 I3 % Memb []? Percent probability of membership 72-73 2X --- --- Blank 74-82 A9 --- ID Identification -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 8 F8.3 d Date Julian date (- 2440000) of each observation 9-15 F7.2 km/s RV Measured radial velocity 16-20 F5.2 km/s e_RV Internal uncertainty in RV 21-22 2X --- --- Blank 23-26 A4 --- ID Number from Lee 1977, A&AS, 27, 367 -------------------------------------------------------------------------------- Byte-by-byte Description of file: table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1-16 A16 --- Names *Star names 17 1X --- --- Blank 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 e_mu_x 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 e_mu_y Standard error in mu_y 52-58 F7.2 mag V V magnitude 59-64 F6.2 mag B-V B-V color 65-68 I4 % P Probability of membership based on relative proper motion -------------------------------------------------------------------------------- Notes for file: table5.dat -------------------------------------------------------------------------------- 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 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 -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 06-May-1995