The M 4 Core Project with HST – III. Search for variable stars in the primary field

We present the results of a photometric search for variable stars in the core of the Galactic globular cluster Messier 4 (M 4). The input data are a large and unprecedented set of deep Hubble Space Telescope WFC3 images (large programme GO-12911; 120 orbits allocated), primarily aimed at probing binaries with massive companions by detecting their astrometric wobbles. Though these data were not optimized to carry out a time-resolved photometric survey, their exquisite precision, spatial resolution and dynamic range enabled us to firmly detect 38 variable stars, of which 20 were previously unpublished. They include 19 cluster-member eclipsing binaries (confirming the large binary fraction of M 4), RR Lyrae and objects with known X-ray counterparts. We improved and revised the parameters of some among published variables.

[1]  J. Anderson,et al.  The ACS survey of Galactic globular clusters. XII. Photometric binaries along the main sequence , 2011, 1111.0552.

[2]  G. Piotto,et al.  THE END OF THE WHITE DWARF COOLING SEQUENCE IN M4: AN EFFICIENT APPROACH , 2009, 0903.2839.

[3]  B. A. McLeod,et al.  Deep MMT Transit Survey of the Open Cluster M37. II. Variable Stars , 2007, 0709.3484.

[4]  M. Zechmeister,et al.  The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms , 2009, 0901.2573.

[5]  Jay Anderson,et al.  Toward High‐Precision Astrometry with WFPC2. I. Deriving an Accurate Point‐Spread Function , 2000, astro-ph/0006325.

[6]  松永 典之.  Stellar Pulsation : Challenges for Theory and Observation , 2009 .

[7]  J. Koppenhofer,et al.  Four ultra-short-period eclipsing M-dwarf binaries in the WFCAM Transit Survey , 2012, 1206.1200.

[8]  J. Rowe,et al.  Variable Stars in Galactic Globular Clusters , 2001, astro-ph/0108024.

[9]  S. Cassisi,et al.  The M 4 Core Project with HST - II. Multiple stellar populations at the bottom of the main sequence , 2014, 1401.1091.

[10]  A. Collier Cameron,et al.  Short period eclipsing binary candidates identified using SuperWASP , 2011 .

[11]  F. Grundahl,et al.  Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members , 2010, Astronomy & Astrophysics.

[12]  B. Scott Gaudi,et al.  Achieving Better Than 1 Minute Accuracy in the Heliocentric and Barycentric Julian Dates , 2010, 1005.4415.

[13]  R. Rich,et al.  An HST search for planets in the lower main sequence of the globular cluster NGC 6397 , 2012, 1202.5112.

[14]  W. Krzemiński,et al.  A SECOND NEUTRON STAR IN M4? , 2012, 1203.5971.

[15]  W. Krzemiński,et al.  CCD Photometry of Faint Variable Stars in the Field of the Globular Cluster M4 , 1997 .

[16]  Tsevi Mazeh,et al.  Correcting systematic effects in a large set of photometric light curves , 2005, astro-ph/0502056.

[17]  S. Sóderhjelm,et al.  Eclipsing binary statistics – Theory and observation , 2005, astro-ph/0509426.

[18]  A. Marín-Franch,et al.  The ACS survey of Galactic globular clusters , 2012 .

[19]  Frederic Pont,et al.  The effect of red noise on planetary transit detection , 2006, astro-ph/0608597.

[20]  William E. Harris,et al.  A Catalog of Parameters for Globular Clusters in the Milky Way , 1996 .

[21]  B. Gibson,et al.  Searching for Variability in the Globular Cluster Messier 4 , 2003, astro-ph/0304470.

[22]  Amsterdam,et al.  X-Ray Sources and Their Optical Counterparts in the Globular Cluster M4 , 2004, astro-ph/0402197.

[23]  H. Richer,et al.  A Young White Dwarf Companion to Pulsar B1620-26: Evidence for Early Planet Formation , 2003, Science.

[24]  N. Lomb.  Least-squares frequency analysis of unequally spaced data , 1976 .

[25]  Giampaolo Piotto,et al.  THE ACS SURVEY OF GLOBULAR CLUSTERS. V. GENERATING A COMPREHENSIVE STAR CATALOG FOR EACH CLUSTER , 2008 .

[26]  Piet Hut,et al.  BOOK REVIEW: The Gravitational Million-Body Problem: A Multidisciplinary Approach to Star Cluster Dynamics , 2003 .

[27]  A. Schwarzenberg-Czerny.  On the advantage of using analysis of variance for period search. , 1989 .

[28]  Ata Sarajedini,et al.  The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters without Previous Hubble Space Telescope Photometry , 2006, astro-ph/0612598.

[29]  F. Rasio.  The Gravitational Million-Body Problem: A Multidisciplinary Approach to Star Cluster Dynamics , 2003 .

[30]  G. S. Burley,et al.  THE CLUSTER AGES EXPERIMENT (CASE). V. ANALYSIS OF THREE ECLIPSING BINARIES IN THE GLOBULAR CLUSTER M4 , 2013, 1301.2946.

[31]  S. Ortolani,et al.  The M 4 Core Project with HST: I. Overview and first epoch , 2013, 1312.1096.

[32]  Scott Trager,et al.  Catalogue of Galactic globular-cluster surface-brightness profiles , 1995 .

[33]  S. Roweis,et al.  ASTROMETRY.NET: BLIND ASTROMETRIC CALIBRATION OF ARBITRARY ASTRONOMICAL IMAGES , 2009, 0910.2233.

[34]  J. Scargle.  Studies in astronomical time series analysis. II - Statistical aspects of spectral analysis of unevenly spaced data , 1982 .

[35]  G. Kov'acs,et al.  A box-fitting algorithm in the search for periodic transits , 2002, astro-ph/0206099.