J/A+A/573/A92 Horizontal branch stars in NGC 6723 (Gratton+, 2015) ================================================================================ The Na-O anticorrelation in horizontal branch stars. V. NGC 6723. Gratton R.G., Lucatello S., Sollima A., Carretta E., Bragaglia A., Momany Y., D'Orazi V., Salaris M., Cassisi S., Stetson P.B. =2015A&A...573A..92G ================================================================================ ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Stars, horizontal branch ; Abundances ; Photometry Keywords: stars: abundances - stars: Population II - globular clusters: general - globular clusters: individual: NGC 6723 - stars: evolution Abstract: We used FLAMES+GIRAFFE (Medusa mode) at the VLT to obtain moderately high resolution spectra for 30 red horizontal branch (RHB) stars, 4 RR Lyrae variables, and 17 blue horizontal branch (BHB) stars in the low-concentration, moderately metal-rich globular cluster NGC 6723 ([Fe/H]=-1.22+/-0.08 from our present sample). The spectra were optimized to derive O and Na abundances. In addition, we obtained abundances for other elements, including N, Fe, Mg, Ca, Ni, and Ba. We used these data to discuss the evidence of a connection between the distribution of stars along the horizontal branch (HB) and the multiple populations that are typically present in globular clusters. We found that all RHB and most (13 out of 17) BHB stars are O-rich, Na-poor, and N-poor; these stars probably belong to the first stellar generation in this cluster. Only the four warmest observed stars are (moderately) O-poor, Na-rich, and N-rich, and they probably belong to the second generation. While our sample is not fully representative of the whole HB population in NGC 6723, our data suggest that in this cluster only HB stars warmer than ~9000K, that is one fourth of the total, belong to the second generation, if at all. Since in many other clusters this fraction is about two thirds, we conclude that the fraction of first/second generation in globular clusters may be strongly variable. In addition, the wide range in colour of chemically homogeneous first-generation HB stars requires a considerable spread in mass loss (>0.10M_{sun}_). The reason for this spread is yet to be understood. Finally, we found a high Ba abundance, with a statistically significant radial abundance gradient. Description: We observed a total of 58 candidate HB stars of NGC 6723 with FLAMES + GIRAFFE at the VLT. The instrument was used in MEDUSA mode, with fibres pointing to each star and several (~20) fibres used for determining the local sky background. Observations were made between 2011-07-11 and 2011-08-27. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 78 51 Photometric data table3.dat 87 51 S/N of spectra, radial velocities, FWHM, and rotational velocities table5.dat 34 47 Atmospheric parameters table7.dat 56 17 Abundances for blue horizontal-branch stars table8.dat 68 30 Abundances for red horizontal-branch stars -------------------------------------------------------------------------------- See also: J/A+A/534/A123 : Horizontal branch stars in NGC 2808 (Gratton+, 2011) J/A+A/539/A19 : Horizontal branch stars in NGC 1851 (Gratton+, 2012) J/A+A/549/A41 : Horizontal branch stars in 47 Tuc and M5 (Gratton+, 2013) J/A+A/563/A13 : Horizontal branch stars in M22 (Gratton+, 2014) Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 A3 --- Type Star type (G1) 5- 9 I5 --- Star Star identification number 11- 19 F9.5 deg RAdeg Right ascension (J2000) 21- 29 F9.5 deg DEdeg Declination (J2000) 31- 36 F6.3 mag VmagL Lee et al. (2014ApJS..210....6L) V magnitude 38- 43 F6.3 mag BmagL Lee et al. (2014ApJS..210....6L) B magnitude 45- 50 F6.3 mag Vmag ? V magnitude (Stetson et al., in prep.) 52- 57 F6.3 mag Bmag ? B magnitude (Stetson et al., in prep.) 59- 64 F6.3 mag Jmag ? 2MASS J magnitude 66- 71 F6.3 mag Hmag ? 2MASS H magnitude 73- 78 F6.3 mag Kmag ? 2MASS Ks magnitude -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 A3 --- Type Star type (G1) 5- 9 I5 --- Star [32170/77469] Star identification number 11- 12 I2 --- S/N(12A) [14/31] Signal-to-noise ratio of HR12A set up (2011-07-11T07:14:23.5) 14- 15 I2 --- S/N(12B) [23/48]?=- Signal-to-noise ratio of HR12B set up (2011-08-27T00:10:09.5) 17- 18 I2 --- S/N(19A) [33/75] Signal-to-noise ratio of HR19A set up (2011-07-18T06:03:41.7) 20- 21 I2 --- S/N(19B) [35/69] Signal-to-noise ratio of HR19B set up (2011-07-18T06:52:18.1) 23- 29 F7.2 km/s RV(12A) [-110/-66]?=- Radial velocity from HR12A set up 31- 37 F7.2 km/s RV(12B) [-110/-66]?=- Radial velocity from HR12B set up 39- 45 F7.2 km/s RV(19A) [-110/-66]?=- Radial velocity from HR19A set up 47- 53 F7.2 km/s RV(19B) [-110/-66]?=- Radial velocity from HR19B set up 55- 61 F7.2 km/s [-105/-66]Mean radial velocity 63- 67 F5.2 km/s e_ [0.1/11] rms uncertainty on 69- 72 F4.2 0.1nm [0.6/0.9]? Mean FWHM of the OI triplet (777nm) 74- 77 F4.2 0.1nm e_ [0.01/0.06]? rms uncertainty on 79 A1 --- l_vsini Limit flag on vsini 80- 83 F4.1 km/s vsini [5/15]? Rotational velocity 85- 87 F3.1 km/s e_vsini [0/4]? rms uncertainty on vsini -------------------------------------------------------------------------------- Byte-by-byte Description of file: table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 A3 --- Type Star type (G1) 5- 9 I5 --- Star [32170/77469] Ster number 11- 14 I4 K Teff Effective temperature 16- 18 I3 K e_Teff rms uncertainty on Teff 20- 23 F4.2 [cm/s2] logg Surface gravity 25- 28 F4.2 km/s vt Microturbulent velocity 30- 34 F5.2 [Sun] [M/H] [-1.25] Model metal abundance (fixed) -------------------------------------------------------------------------------- Byte-by-byte Description of file: table7.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 I5 --- Star [32170/77469] Star identification number 7- 10 F4.1 0.1pm EW(Y) ?=- Helium equivalent width (m{AA}) 12- 15 F4.2 --- Y [0.36/0.38]?=- Helium abundance (NLTE) 17- 20 F4.2 [Sun] [N/Fe] Abundance [N/Fe] 22- 25 F4.2 [Sun] e_[N/Fe] rms uncertainty on [N/Fe] 27- 30 F4.2 [Sun] [O/Fe] Abundance [O/Fe] 32- 35 F4.2 [Sun] e_[O/Fe] rms uncertainty on [O/Fe] 37- 41 F5.2 [Sun] [Na/Fe] Abundance [Na/Fe] 43- 46 F4.2 [Sun] e_[Na/Fe] rms uncertainty on [Na/Fe] 48- 51 F4.2 [Sun] [Mg/Fe] Abundance [Mg/Fe] 53- 56 F4.2 [Sun] e_[Mg/Fe] ? rms uncertainty on [Mg/Fe] -------------------------------------------------------------------------------- Byte-by-byte Description of file: table8.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 I5 --- Star [32170/77469] Star identification number 7- 11 F5.2 [Sun] [Fe/H] Abundance [Fe/H] 13- 16 F4.2 [Sun] e_[Fe/H] rms uncertainty on [Fe/H] 18- 21 F4.2 [Sun] [O/Fe] Abundance [O/Fe] 23- 26 F4.2 [Sun] e_[O/Fe] rms uncertainty on [O/Fe] 28- 32 F5.2 [Sun] [Na/Fe] Abundance [Na/Fe] 34- 37 F4.2 [Sun] e_[Na/Fe] rms uncertainty on [Na/Fe] 39- 42 F4.2 [Sun] [Mg/Fe] ?=- Abundance [Mg/Fe] 44- 47 F4.2 [Sun] [Si/Fe] ? Abundance [Si/Fe] 49- 52 F4.2 [Sun] e_[Si/Fe] ? rms uncertainty on [Si/Fe] 54- 57 F4.2 [Sun] [Ca/Fe] ? Abundance [Ca/Fe] 59- 63 F5.2 [Sun] [Ni/Fe] ? Abundance [Ni/Fe] 65- 68 F4.2 [Sun] [Ba/Fe] ? Abundance [Ba/Fe] -------------------------------------------------------------------------------- Global notes: Note (G1): Star type as follows: BHB = Blue horizontal branch RHB = Red horizontal branch RRL = RR Lyrae -------------------------------------------------------------------------------- History: From electronic version of the journal References: Gratton et al., Paper I 2011A&A...534A.123G, Cat. J/A+A/534/A123 Gratton et al., Paper II 2012A&A...539A..19G, Cat. J/A+A/539/A19 Gratton et al., Paper III 2013A&A...549A..41G, Cat. J/A+A/549/A41 Gratton et al., Paper IV 2014A&A...563A..13G, Cat. J/A+A/563/A13 ================================================================================ (End) Patricia Vannier [CDS] 23-Feb-2015