A DOUBLE MAIN SEQUENCE IN THE GLOBULAR CLUSTER NGC 6397

Journal Article · Fri Jan 20 04:00:00 EST 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/745/1/27· OSTI ID:22011990

Milone, A P; Aparicio, A ^[1]; Marino, A F ^[2]; Piotto, G ^[3]; Bedin, L R; Anderson, J ^[4]; Cassisi, S ^[5]

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1. Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife, Canary Islands (Spain)
2. Max Planck Institute for Astrophysics, Postfach 1317, D-85741 Garching (Germany)
3. Dipartimento di Astronomia, Universita di Padova, Vicolo dell'Osservatorio 3, Padova I-35122 (Italy)
4. Space Telescope Science Institute, 3800 San Martin Drive, Baltimore, MD 21218 (United States)
5. INAF-Osservatorio Astronomico di Collurania, via Mentore Maggini, I-64100 Teramo (Italy)

High-precision multi-band Hubble Space Telescope (HST) photometry reveals that the main sequence of the globular cluster NGC 6397 splits into two components, containing {approx}30% and {approx}70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (1) a primordial population that has a composition similar to field stars, containing {approx}30% of the stars, and (2) a second generation with enhanced sodium and nitrogen, depleted carbon and oxygen, and a slightly enhanced helium abundance ({Delta}Y {approx} 0.01). We examine the color difference between the two sequences across a variety of color baselines and find that the second sequence is anomalously faint in m{sub F336W}. Theoretical isochrones indicate that this could be due to NH depletion.

• OSTI ID: 22011990
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 745; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
CARBON
COLOR
HELIUM
NITROGEN
OXYGEN
PHOTOMETRY
SODIUM
STARS
TELESCOPES