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J/AJ/145/37      UBVI and Hα CCD photometry of NGC 6231      (Sung+, 2013)

The initial mass function and the surface density profile of NGC 6231. Sung H., Sana H., Bessell M.S. <Astron. J., 145, 37 (2013)> =2013AJ....145...37S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, pre-main sequence ; Photometry, H-alpha ; Photometry, UBVRI ; Photometry, CCD Keywords: open clusters and associations: individual: NGC 6231 - stars: formation - stars: pre-main sequence Abstract: We have performed new wide-field photometry of the young open cluster NGC6231 to study the shape of the initial mass function (IMF) and mass segregation. We also investigated the reddening law toward NGC6231 from optical to mid-infrared color excess ratios, and found that the total-to-selective extinction ratio is RV=3.2, which is very close to the normal value. But many early-type stars in the cluster center show large color excess ratios. We derived the surface density profiles of four member groups, and found that they reach the surface density of field stars at about 10', regardless of stellar mass. The IMF of NGC6231 is derived for the mass range 0.8-45M. The slope of the IMF of NGC6231 (Γ=-1.1±0.1) is slightly shallower than the canonical value, but the difference is marginal. In addition, the mass function varies systematically, and is a strong function of radius-it is very shallow at the center, and very steep at the outer ring suggesting the cluster is mass segregated. We confirm the mass segregation for the massive stars (m≳8 M) by a minimum spanning tree analysis. Using a Monte Carlo method, we estimate the total mass of NGC6231 to be about 2.6(±0.6)*103M. We constrain the age of NGC 6231 by comparison with evolutionary isochrones. The age of the low-mass stars ranges from 1 to 7Myr with a slight peak at 3Myr. However, the age of the high-mass stars depends on the adopted models and is 3.5±0.5Myr from the non-rotating or moderately rotating models of Brott et al. (2011, cat. J/A+A/530/A115) as well as the non-rotating models of Ekstrom et al. (2012, cat. J/A+A/537/A146). But the age is 4.0-7.0Myr if the rotating models of Ekstrom et al. (2012, cat. J/A+A/537/A146) are adopted. This latter age is in excellent agreement with the timescale of ejection of the high-mass runaway star HD153919 from NGC6231, albeit the younger age cannot be entirely excluded. Description: UBVI and Hα CCD photometry of NGC6231 was performed on 2000 June 22 (NW and SW regions) and 25 (NE and SE regions) at Siding Spring Observatory with the 40inch (1m) telescope (f/8) and a thinned SITe 2048*2048 CCD (24µm pixels). The filters used were the same as those used for the observation of NGC2244 (Park & Sung, 2002AJ....123..892P). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 236 27337 UBVIHα photometry of NGC 6231
See also: II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) J/A+A/530/A115 : Rotating massive MS stars evolutionary models (Brott+, 2011) J/AJ/135/441 : VRIHα photometry in NGC 2264 (Sung+, 2008) J/MNRAS/386/447 : RV catalogue of O-type stars in NGC 6231 (Sana+, 2008) J/A+A/454/1047 : XMM view of NGC 6231 open cluster (Sana+, 2006) J/AJ/128/1684 : NGC 2264: VRIHα photometry (Sung+, 2004) J/AJ/127/1014 : CCD UBVRIHa photometry in NGC 3603 (Sung+, 2004) J/AJ/120/333 : UBVRI and Hα in NGC 6530 (Sung+, 2000) J/MNRAS/310/982 : UBVI CCD Photometry of M11 - II. (Sung+ 1999) J/A+AS/137/233 : UBVI imaging photometry of NGC 6231 (Baume+, 1999) J/AJ/115/734 : NGC 6231 UBVRI and Hα photometry (Sung+ 1998) J/ApJS/116/263 : VI photometry of open clusters (Piatti+ 1998) J/AJ/114/2644 : UBVRIHa photometry of NGC 2264 (Sung+, 1997) J/A+A/325/167 : Geneva photometry in NGC 6231 (Raboud+ 1997) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 5 I5 --- Star [-15/30123] Running star number (1) 7 A1 --- n_Star [*] Star missed in the new photometry (2) 9- 10 I2 h RAh Hour of Right Ascension (J2000) 12- 13 I2 min RAm Minute of Right Ascension (J2000) 15- 19 F5.2 s RAs Second of Right Ascension (J2000) 21 A1 --- DE- Sign of the Declination (J2000) 22- 23 I2 deg DEd Degree of Declination (J2000) 25- 26 I2 arcmin DEm Arcminute of Declination (J2000) 28- 31 F4.1 arcsec DEs Arcsecond of Declination (J2000) 33- 38 F6.3 mag Vmag The V band magnitude 40- 44 F5.3 mag V-I ? The (V-I) color index 46- 51 F6.3 mag B-V ? The (B-V) color index 53- 58 F6.3 mag U-B ? The (U-B) color index 60- 65 F6.3 mag Ha ? Hα index (R-Hα) 67- 71 F5.3 mag e_Vmag Uncertainty in Vmag 73- 77 F5.3 mag e_V-I ? Uncertainty in V-I 79- 83 F5.3 mag e_B-V ? Uncertainty in B-V 85- 89 F5.3 mag e_U-B ? Uncertainty in U-B 91- 95 F5.3 mag e_Ha ? Uncertainty in Ha 97 I1 --- o_Vmag Number of Vmag observations 99 I1 --- o_V-I Number of V-I observations 101 I1 --- o_B-V Number of B-V observations 103 I1 --- o_U-B Number of U-B observations 105 I1 --- o_Ha Number of Ha observations 107-122 A16 --- 2MASS The 2MASS identifier (from cat. II/246) 124 A1 --- Mm [VXHh±] Membership code (3) 126 A1 --- f_Star [DV] Duplicity or Variability flag (4) 128-131 I4 --- SBL98 [-8/9999]? Identifier in Sung et al. (1998, cat. J/AJ/115/734) 133-136 F4.2 --- SpTn ? Numerical spectral type (5) 138-140 F3.1 --- Lum ? Numerical luminosity class (6) 142-153 A12 --- OName Other name 155-165 A11 --- OName2 Other name 167-177 A11 --- OName3 Other name 179-191 A13 --- SpT MK spectral type and luminosity class 193-236 A44 --- Com Comment (variable type, or origin of Hα emission star)
Note (1): <[SSB2013] NNNNN> in Simbad. The 12 stars with a negative star were saturated in our image, and we have substituted data from SIMBAD (, WEBDA (Open cluster database;, or Sung et al. (1998, cat. J/AJ/115/734). Note (2): Data for these stars were taken from Sung et al. (1998, cat. J/AJ/115/734). Note (3): Membership related code, defined as follows: X = X-ray emission star (Sana et al., 2006, cat. J/A+A/454/1047); H = Strong Hα emission star; h = Weak Hα emission candidate; + = X-ray emission star with Hα emission; - = X-ray emission star with weak Hα emission. V = (not explained) exists for 9 stars. Note (4): Duplicity or Variability flag as follows: D = star whose PSF shows a double, but measures as a single star; V = variable from the literature, variable types if available noted in the last column (dSct: δ Scuti type variable, bCep: β Cephei type variable). Note (5): We use numerical spectral type for analysis: 0 for O; 1 for B; 2 for A; 3 for F; 4 for G; 5 for K; 6 for M. For example, 1.05 stands for B0.5, 0.97 stands for O9.7, 6.5 stands for M5, etc. There are exceptions for WR stars (we use -0.# for WC#, and -1.# for WN#). Note (6): We use numerical luminosity class for analysis: 0 for V, 1 for IV, 2 for III, 3 for II, 4 for Ib, 5 for Iab, 6 for Ia, 7 for Ia-0. For exemple, 1.5 means III-IV, 3.5 means Ib-II, etc.
History: * 10-Mar-2014: From electronic version of the journal * 23-May-2014: the last column of table2 was truncated in the paper; the first author mailed the truncated comments to CDS
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 10-Mar-2014
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