Cdrom/AJ/V108/P0555 M68 (Walker 1994) bvi ccd photometry of Galactic Globular Clusters. II. M68 Alistair R. Walker =1994aj




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CDROM/AJ/V108/P0555 M68 (Walker 1994) ================================================================================ BVI CCD Photometry of Galactic Globular Clusters. II. M68 Alistair R. Walker <1994, AJ, 108, 555> =1994AJ....108..555W ================================================================================ Abstract: A total of 363 CCD frames in the B, V, and I passbands have been used to study the color-magnitude diagram (CMD) and the variable-star population of the metal-poor galactic globular cluster M68 (=NGC 4590,=C1236-264). Light curves have been prepared for 40 RR Lyrae variables, five of which are new discoveries, and for two probable SX Phe stars. The RR Lyraes have =15.64 +/- 0.01, and via several methods E(B-V)=0.07 +/- 0.01. [Fe/H]=-2.1 is adopted. From a comparison with Sandage's data for M3 (=NGC 5272,=C1339+286), a period shift of Delta(log P)/Delta([Fe/H])=-0.11 +/- 0.02 is derived, and the mass-to-light parameter is found to be =1.90. RR Lyrae masses are derived from Fourier fits to the light curves, from the RRd variables, and by comparison with HB (horizontal branch) evolutionary models calculated by Dorman. The light-curve structure agrees qualitatively with recent theoretical models. From short exposures, CMDs have been prepared that are complete from the tip of the red giant branch (RGB) to below the level of the HB, while from the long exposures a CMD to V ~ 23 is provided for 7298 stars more than 158 arcsec distant from the cluster center. The HB is skewed to the blue with the eight bluest stars clearly separated from the remainder of the HB stars. This HB gap is at the identical color to that in M15 (=NGC 7078,C2127+119), but M68 lacks the extensive population of the very blue HB stars present in M15. The total number of HB stars is deficient with respect to the RGB population, with the ratio of RGB to HB stars R=0.99. There are several likely blue stragglers identified on CMDs of inner annuli, but near to the cluster center photometric errors scatter stars off the main sequence (MS) into this region. The deep CMDs are in excellent agreement with existing CCD CMDs for M68, with the MS turnoff Delta(V)=3.42 +/- 0.10 mag below the HB. Matching the M68 CMD to that for M15 in the subgiant-MS turnoff region shows that the age of M68 is identical to that for M15 to within +/-0.4 Gyr. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table4.txt 120 969 Photometry of the RR Lyrae variables v01.dat 30 117 Table 4 photometry for star V1 v02.dat 30 117 Table 4 photometry for star V2 v03.dat 30 117 Table 4 photometry for star V3 v04.dat 30 117 Table 4 photometry for star V4 v05.dat 30 117 Table 4 photometry for star V5 v06.dat 30 117 Table 4 photometry for star V6 v07.dat 30 117 Table 4 photometry for star V7 v08.dat 30 117 Table 4 photometry for star V8 v09.dat 30 117 Table 4 photometry for star V9 v10.dat 30 117 Table 4 photometry for star V10 v11.dat 30 117 Table 4 photometry for star V11 v12.dat 30 117 Table 4 photometry for star V12 v13.dat 30 117 Table 4 photometry for star V13 v14.dat 30 117 Table 4 photometry for star V14 v15.dat 30 117 Table 4 photometry for star V15 v16.dat 30 117 Table 4 photometry for star V16 v17.dat 30 117 Table 4 photometry for star V17 v18.dat 30 117 Table 4 photometry for star V18 v19.dat 30 117 Table 4 photometry for star V19 v20.dat 30 117 Table 4 photometry for star V20 v21.dat 30 117 Table 4 photometry for star V21 v22.dat 30 117 Table 4 photometry for star V22 v23.dat 30 117 Table 4 photometry for star V23 v24.dat 30 117 Table 4 photometry for star V24 v25.dat 30 117 Table 4 photometry for star V25 v26.dat 30 117 Table 4 photometry for star V26 v29.dat 30 117 Table 4 photometry for star V29 v30.dat 30 117 Table 4 photometry for star V30 v31.dat 30 117 Table 4 photometry for star V31 v33.dat 30 117 Table 4 photometry for star V33 v34.dat 30 117 Table 4 photometry for star V34 v35.dat 30 117 Table 4 photometry for star V35 v36.dat 30 117 Table 4 photometry for star V36 v37.dat 30 117 Table 4 photometry for star V37 v38.dat 30 117 Table 4 photometry for star V38 v43.dat 30 117 Table 4 photometry for star V43 v44.dat 30 117 Table 4 photometry for star V44 v45.dat 30 117 Table 4 photometry for star V45 v46.dat 30 117 Table 4 photometry for star V46 v47.dat 30 117 Table 4 photometry for star V47 table12.dat 41 562 Photometry of the brighter M68 stars -------------------------------------------------------------------------------- Byte-by-byte Description of files: v01.dat v02.dat v03.dat v04.dat v05.dat v06.dat v07.dat v08.dat v09.dat v10.dat v11.dat v12.dat v13.dat v14.dat v15.dat v16.dat v17.dat v18.dat v19.dat v20.dat v21.dat v22.dat v23.dat v24.dat v25.dat v26.dat v29.dat v30.dat v31.dat v33.dat v34.dat v35.dat v36.dat v37.dat v38.dat v43.dat v44.dat v45.dat v46.dat v47.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 8 F8.3 day HJD *HJD - 2440000 9 1X --- --- Blank 10-16 F7.3 mag V V band magnitude 17-23 F7.3 mag B B band magnitude 24-30 F7.3 mag I I band magnitude -------------------------------------------------------------------------------- Notes for files: v01.dat v02.dat v03.dat v04.dat v05.dat v06.dat v07.dat v08.dat v09.dat v10.dat v11.dat v12.dat v13.dat v14.dat v15.dat v16.dat v17.dat v18.dat v19.dat v20.dat v21.dat v22.dat v23.dat v24.dat v25.dat v26.dat v29.dat v30.dat v31.dat v33.dat v34.dat v35.dat v36.dat v37.dat v38.dat v43.dat v44.dat v45.dat v46.dat v47.dat -------------------------------------------------------------------------------- HJD: Heliocentric Julian dates correspond to the start of the V-band exposures. The midpoints of the V, B, and I exposures are, respectively, 2.5, 11.0, and 18.5 min later than this HJD -------------------------------------------------------------------------------- Byte-by-byte Description of file: table12.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- Num Star number 4-10 F7.1 --- X X coordinate 11-17 F7.1 --- Y Y coordinate 18-25 F8.3 mag V V magnitude 26-33 F8.3 mag B-V B-V color 34-41 F8.3 mag V-I []? V-I color -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 10-Oct-1994


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