CDROM/APJ/V448/P179 Stellar Mass Population in R136 (Hunter+ 1995) ================================================================================ The Intermediate Stellar Mass Population in R136 Determined from Hubble Space Telescope Planetary Camera 2 Images Deidre A. Hunter, Edward J. Shaya, Jon A. Holtzman, Robert M. Light, Earl J. O'Neil, Jr. & Roger Lynds <1995, ApJ, 448, 179> =1995ApJ...448..179H ================================================================================ Abstract: We have analyzed Hubble Space Telescope (HST) images of the compact, luminous star cluster R136 in the LMC that were taken with the refurbished HST and new Wide Field/Planetary Camera. These images allow us to examine the stellar population in a region of unusually intense star formation at a scale of 0.01 pc. We have detected stars to 23.5 in F555W and have quantified the stellar population to an M_555.0 of 0.9 or a mass of 2.8 Msun. Comparisons of HR diagrams with isochrones that were constructed for the HST flight filter system from theoretical stellar evolutionary tracks reveal massive stars, a main sequence to at least 2.8 Msun, and stars with M_555.0 >= 0.5 still on pre-main sequence tracks. The average stellar population is fit with a 3-4 Myr isochrone. Contrary to expectations from star formation models, however, the formation period for the massive stars and lower mass stars appear to largely overlap. We have measured the IMF for stars 2.8-15 Msun in three annuli from 0.5-4.7 pc from the center of the cluster. The slopes of the IMF in all three annuli are the same within the uncertainties, thus, showing no evidence for mass segregation beyond 0.5 pc. Furthermore, the combined IMF slope, -1.22 +/- 0.06, is close to a normal Salpeter IMF. The lower mass limit must be lower than the limits of our measurements: <= 2.8 Msun beyond 0.5 pc and <= 7 Msun within 0.1 pc. This is contrary to some predictions that the lower mass limit could be as high as 10 Msun in regions of intense massive star formation. Integrated properties of R136 are consistent with its being comparable to a rather small globular cluster when such clusters were the same age as R136. From the surface brightness profile, an upper limit for core radius of 0.02 pc is set. Within a radius of 0.4 pc we estimate that there have been roughly 20 crossing times and relaxation should be well along. Within 0.5 pc crowding prevents us from detecting the intermediate mass population, but there is a hint of an excess of stars brighter than M_555.0 = -5 and of a deficit in the highest mass stars between 0.6 pc and 1.2 pc. This would be consistent with dynamical segregation. Keywords: Hertzsprung-Russell diagram -- Magellanic Clouds -- open clusters and associations: individual (R136) -- stars: evolution -- stars: luminosity function, mass function File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table2.dat 98 3623 The photometry -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 6 I6 --- Star Star identification number 7-13 F7.1 pix X *X pixel coordinate 14-20 F7.1 pix Y *Y pixel coordinate 21-27 F7.2 mag F336W []?=100.00 F336W magnitude 28-34 F7.2 mag e_F336W []?=100.00 F336W magnitude uncertainty 35-41 F7.2 mag F555W []?=100.00 F555W magnitude 42-48 F7.2 mag e_F555W []?=100.00 F555W magnitude uncertainty 49-55 F7.2 mag F814W []?=100.00 F814W magnitude 56-62 F7.2 mag e_F814W []?=100.00 F814W magnitude uncertainty 63-71 F9.2 mag F336W-F555W []?=100.00 F336W-F555W color 72-80 F9.2 mag e_F336W-F555W []?=100.00 F336W-F555W color uncertainty 81-89 F9.2 mag F555W-F814W []?=100.00 F555W-F814W color 90-98 F9.2 mag e_F555W-F814W []?=100.00 F555W-F814W color uncertainty -------------------------------------------------------------------------------- Notes for file: table2.dat -------------------------------------------------------------------------------- X, Y: The X,Y coordinates are those in the short exposure F555W image, and the coordinate system is indicated in Figure 2 of the printed paper. -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 10-Oct-95