TOWARD PRECISION PHOTOMETRY FOR THE ELT ERA: THE DOUBLE SUBGIANT BRANCH OF NGC 1851 OBSERVED WITH THE GEMINI/GeMS MCAO SYSTEM

The Extremely Large Telescopes currently under construction have a collecting area that is an order of magnitude larger than the present largest optical telescopes. For seeing-limited observations the performance will scale as the collecting area, but with the successful use of adaptive optics (AO), for many applications it will scale as D4 (where D is the diameter of the primary mirror). Central to the success of the ELTs, therefore, is the successful use of multi-conjugate adaptive optics (MCAO) which applies a high degree of correction over a field of view larger than the few arcseconds that limits classical AO systems. In this Letter, we report on the analysis of crowded field images taken on the central region of the galactic globular cluster NGC 1851 in the Ks band using the Gemini Multi-conjugate Adaptive Optics System (GeMS) at the Gemini South Telescope, the only science-grade MCAO system in operation. We use this cluster as a benchmark to verify the ability to achieve precise near-infrared photometry by presenting the deepest Ks photometry in crowded fields ever obtained from the ground. We construct a color–magnitude diagram in combination with the F606W band from the Hubble Space Telescope/Advanced Camera for Surveys. As well as detecting the "knee" in the lower main sequence at Ks 20.5, we also detect the double subgiant branch of NGC 1851, which demonstrates the high photometric accuracy of GeMS in crowded fields.

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

[2]  G. Carraro,et al.  UNCOVERING MULTIPLE POPULATIONS WITH WASHINGTON PHOTOMETRY. I. THE GLOBULAR CLUSTER NGC 1851 , 2014, 1406.0550.

[3]  S. Saracino,et al.  GEMINI/GeMS OBSERVATIONS UNVEIL THE STRUCTURE OF THE HEAVILY OBSCURED GLOBULAR CLUSTER LILLER 1. , 2015, 1505.00568.

[4]  S. Cassisi,et al.  THE INFRARED EYE OF THE WIDE-FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE REVEALS MULTIPLE MAIN SEQUENCES OF VERY LOW MASS STARS IN NGC 2808 , 2012, 1206.5529.

[5]  P. Stetson.  DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY , 1987 .

[6]  Angela Bragaglia,et al.  Multiple populations in globular clusters , 2012, 1201.6526.

[7]  Jean-Pierre Véran,et al.  Analytical modeling of adaptive optics: foundations of the phase spatial power spectrum approach. , 2006, Journal of the Optical Society of America. A, Optics, image science, and vision.

[8]  Bernard Delabre,et al.  On-sky Testing of the Multi-Conjugate Adaptive Optics Demonstrator , 2007 .

[9]  Charles P. Cavedoni,et al.  Gemini multiconjugate adaptive optics system review - I. Design, trade-offs and integration , 2013, 1310.6199.

[10]  E. Marchetti,et al.  ON A NEW NEAR-INFRARED METHOD TO ESTIMATE THE ABSOLUTE AGES OF STAR CLUSTERS: NGC 3201 AS A FIRST TEST CASE , 2009, 0912.0824.

[11]  E. Diolaiti,et al.  MAD about the Large Magellanic Cloud - Preparing for the era of Extremely Large Telescopes , 2011, 1109.0161.

[12]  T. J. Davidge.  GeMS in the Outer Galaxy: Near-infrared Imaging of Three Young Clusters at Large Galactic Radii , 2014 .

[13]  J. Anderson,et al.  The radial distribution of the two stellar populations in NGC 1851 , 2009, 0906.1779.

[14]  S. Cassisi,et al.  The Double Subgiant Branch of NGC 1851: The Role of the CNO Abundance , 2007, 0711.3823.

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

[16]  Stsci,et al.  Ground-based astrometry with wide field imagers - V. Application to near-infrared detectors: HAWK-I@VLT/ESO , 2014, 1401.3344.

[17]  G. Piotto,et al.  The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851 , 2007, 0709.3762.

[18]  Peter B. Stetson,et al.  THE CENTER OF THE CORE-CUSP GLOBULAR CLUSTER M15: CFHT AND HST OBSERVATIONS, ALLFRAME REDUCTIONS , 1994 .

[19]  Roberto Ragazzoni,et al.  Preparing for the phase B of the E-ELT MCAO module project , 2014, Astronomical Telescopes and Instrumentation.

[20]  Jean-Pierre Véran,et al.  Focus errors from tracking sodium layer altitude variations with laser guide star adaptive optics for the Thirty Meter Telescope , 2006, SPIE Astronomical Telescopes + Instrumentation.

[21]  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.

[22]  Peter B. Stetson,et al.  CCD photometry of the globular cluster M92 , 1988 .

[23]  Sarah J. Diggs,et al.  Gemini multiconjugate adaptive optics system review – II. Commissioning, operation and overall performance , 2014, 1402.6906.

[24]  M. Kasper,et al.  Adaptive Optics for Astronomy , 2012, 1201.5741.

[25]  Malcolm Smith,et al.  Adaptive optics program at TMT , 2014, Astronomical Telescopes and Instrumentation.

[26]  Gabe Bloxham,et al.  Gemini South Adaptive Optics Imager (GSAOI) , 2004, SPIE Astronomical Telescopes + Instrumentation.

[27]  Young-Wook Lee,et al.  THE PRESENCE OF TWO DISTINCT RED GIANT BRANCHES IN THE GLOBULAR CLUSTER NGC 1851 , 2009, 0911.5356.

[28]  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.

[29]  Eleazar R. Carrasco,et al.  Results from the commissioning of the Gemini South Adaptive Optics Imager (GSAOI) at Gemini South Observatory , 2012, Other Conferences.