CDROM/AJ/V105/P0938 Dynamics of NGC 1850 (Fischer+ 1993) ================================================================================ Dynamics of the Young Binary LMC Cluster NGC 1850 Philippe Fischer, Douglas L. Welch & Mario Mateo <1993, AJ, 105, 938> =1993AJ....105..938F ================================================================================ Abstract: In this paper we have examined the age and internal dynamics of the young binary LMC cluster NGC 1850 using BV CCD images and echelle spectra of 52 supergiants. Isochrone fits to a BV color-magnitude diagram revealed that the primary cluster has an age of Tau = 90 +/- 30 Myr while the secondary member has Tau = 6 +/- 5 Myr. The reddening was found to be E(B-V) = 0.17 mag. BV surface brightness profiles were constructed out to R > 40 pc, and single-component King-Michie (KM) models were applied. The total cluster luminosity varied from L(B) = 2.60-2.65 x 10^6 L(Bsun) and L(V) = 1.25-1.35 x 10^6 as the anisotropy radius varied from infinity to three times the scale radius with the isotropic models providing the best agreement with the data. Simple tests were made to check for tidal truncation in the profiles and we concluded that there was slight evidence favoring truncation. The bright background and binary nature of NGC 1850 render this conclusion somewhat uncertain. Of the 52 stars with echelle spectra, a subset of 36 was used to study the cluster dynamics. The KM radial velocity distributions were fitted to these velocities yielding total cluster masses of 5.4-5.9 +/- 2.4 x 10^4 Msun corresponding to M/L(B) = 0.02 +/- 0.01 Msun/L(Bsun) or M/L(V) = 0.05 +/- 0.02 Msun/L(Vsun). A rotational signal in the radial velocities has been detected at the 93% confidence level implying a rotation axis at a position angle of 100 deg. A variety of rotating models were fit to the velocity data assuming cluster ellipticities of Epsilon = 0.1-0.3. These models provided slightly better agreement with the radial velocity data than the KM models and had masses that were systematically lower by a few percent. Values for the slope of the mass function were determined using the derived M/L, theoretical mass-luminosity relationships, and several forms for the IMF. The preferred value for the slope of the power-law IMF is a relatively shallow, x = 0.29 [+0.3,-0.8] assuming the B band M/L or x = 0.71 [+0.2,-0.4] for the V band. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table1.dat 27 643 BV Photometry for the inner region of NGC 1850 -------------------------------------------------------------------------------- Comments for file: table1.dat -------------------------------------------------------------------------------- Table 1 contains CCD positions and apparent BV magnitudes for stars in the region within 1 arcmin of the center of the main cluster of NGC 1850. It includes all the stars in a companion cluster directly to the west of NGC 1850 with a center-to-center separation of 30 arcsec. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- Id Stellar identification 4- 9 F6.1 --- X X pos on the CCD, increases toward the south 10-15 F6.1 --- Y Y pos on the CCD, increases toward the east 16-21 F6.2 mag V Apparent V magnitude 22-27 F6.2 mag B-V Apparent B-V magnitude -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 27-Feb-1995