Variable Stars in the Globular Cluster NGC 6752
Kaluzny, J.; Thompson, I. B.
Abstract:
We report time-series photometry for 16 variable stars located in the central part of the globular cluster NGC 6752. The sample includes 13 newly identified objects. The precision of our differential photometry ranges from 1 mmag at V=14.0 mag to 10 mmag at V=18.0 mag. We detected four low amplitude variables located on the extended horizontal branch (EHB) of the cluster. They are candidate binary stars harboring sdB subdwarfs. A candidate degenerate binary was detected about 2 mag below the faint end of the EHB. The star is blue and its light curve is modulated with a period of 0.47 d. We argue that some of the identified variable red/blue stragglers are ellipsoidal binaries harboring degenerate stars. They have low amplitude sine-like light curves and periods from a few hours to a few days. Spectroscopic observations of such objects may lead to the detection of detached inactive binaries harboring stellar mass black holes or neutron stars. No binaries of this kind are known so far in globular clusters although their existence is expected based on the common occurrence of accreting LMXBs and millisecond pulsars. An eclipsing SB1 type binary was identified on the upper main sequence of the cluster. We detected variability of optical counterparts to two X-ray sources located in the core region of NGC 6752. The already known cataclysmic variable B1=CX4 experienced a dwarf nova type outburst. The light curve of an optical counterpart to the X-ray source CX19 exhibited modulation with a period of 0.113 d. The same periodicity was detected in the HST-ACS data. The variable is located on the upper main sequence of the cluster. It is an excellent candidate for a close degenerate binary observed in quiescence.

DOWNLOADS:
The paper (PDF) "Variable Stars in the Globular Cluster NGC 6752"
Kaluzny J. & Thompson I.B., 2009, Acta Astron., 59, 273
The reference
V-band image (FITS)
Photometric data for 27619 stars
ASCII table
N6752.BVRADEC
Description of the table columns readme.txt


Table 1:Basic properties of variable stars in NGC 6752
Star Xa Ya Period [days] Vmax Δ V B-V PMb Typec V light-curved B light-curved Remarks
V7 1007.20 1491.28 0.059051(2) 15.33 0.295 0.45 Y SX Phe v07.V v07.B
V8 550.60 1159.79 0.314938(36) 17.058 0.365 0.36 Y EW v08.V v08.B
V9 66.92 1712.85 0.363602(53) 15.018 0.613 0.06 N EW? v09.V v09.B
V12 1624.00 778.51 0.040901(2) 16.292 0.291 0.05 Y SX Phe v12.V v12.B
V15 517.77 1357.52 0.6895(12) 16.344 -0.146 0.02 Y EHB v15.V v15.B
V16 671.72 1147.20 > 8 16.53 -0.163 0.04 Y EHB v16.V v16.B
V17 735.57 1224.86 3.291(12) 15.27 0.111 0.02 Y EHB v17.V v17.B
V18 520.16 1949.17 0.4676(11) 20.74 -0.294 0.16 - EHB v18.V v18.B
V19 530.00 328.39 6.18: 16.321 1.072 0.12 N v19.V v19.B
V20 1146.63 902.78 > 8 16.090 0.742 0.02 N v20.V v20.B
V21 1263.78 1597.95 0.5514(15) 16.477 0.336 0.09 - v21.V v21.B
V22 1763.30 660.30 1.76(10) 18.437 0.769 0.13 N v22.V v22.B
V23 1604.51 1841.82 - 18.463 0.537 0.2 Y EA v23.V v23.B
V24 1710.17 1705.65 > 8 14.606 -0.054 0.01 Y EHB v24.V v24.B
V25 1099.87 1173.27 - - - - - CV - v25.B
a Pixel coordinate in the template image
b Proper motion membership status — Y - member, N - field star, U - uncertain
c Variable type

EW - contact binary; EB - close ecppsing binary; EA - detached ecppsing binary;

EHB - Extreme horizontal branch variable; SX Phe - SX-Phenicis type pulsator; CV - cataclismic variable.

d Data columns:
  1. HJD - 2 450 960.0
  2. V magnitude
  3. error of magnitude (dummy points are maked with the error=9.999)