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.
<Astron. Astrophys., 573, A92-92 (2015)>
=2015A&A...573A..92G 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☉). 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 2014ApJS..210....6L) V magnitude
38- 43 F6.3 mag BmagL Lee et al. (2014ApJS..210....6L 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 (mÅ)
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 2011A&A...534A.123G, Cat. J/A+A/534/A123
Gratton et al., Paper II 2012A&A...539A..19G 2012A&A...539A..19G, Cat. J/A+A/539/A19
Gratton et al., Paper III 2013A&A...549A..41G 2013A&A...549A..41G, Cat. J/A+A/549/A41
Gratton et al., Paper IV 2014A&A...563A..13G 2014A&A...563A..13G, Cat. J/A+A/563/A13
(End) Patricia Vannier [CDS] 23-Feb-2015