J/ApJ/754/91 Abundances and velocities of NGC 6397 stars (Lovisi+, 2012)
Chemical and kinematical properties of blue straggler stars and horizontal
branch stars in NGC 6397.
Lovisi L., Mucciarelli A., Lanzoni B., Ferraro F.R., Gratton R.,
Dalessandro E., Contreras Ramos R.
<Astrophys. J., 754, 91 (2012)>
=2012ApJ...754...91L 2012ApJ...754...91L
ADC_Keywords: Clusters, globular ; Abundances ; Radial velocities ;
Rotational velocities ; Stars, masses ; Photometry, VRI
Keywords: blue stragglers; globular clusters: individual: NGC 6397;
stars: abundances; stars: evolution; techniques: spectroscopic
Abstract:
We used three sets of high-resolution spectra acquired with the
multifiber facility FLAMES at the Very Large Telescope of the European
Southern Observatory to investigate the chemical and kinematical
properties of a sample of 42 horizontal branch (HB) stars, 18 blue
straggler stars (BSSs), and 86 main-sequence (MS) turnoff (TO) and
sub-giant branch stars in the nearby globular cluster NGC 6397. We
measured rotational velocities and Fe, O, and Mg abundances. All of
the unevolved stars in our sample have low rotational velocites (vsin
i<10km/s), while the HB stars and BSSs show a broad distribution, with
values ranging from 0 to ∼70km/s. For HB stars with T<10500K there is
a clear temperature-oxygen anticorrelation that can be understood if
the star position along the HB is mainly determined by the He content.
The hottest BSSs and HB stars (with temperatures T>8200K and T>10500K,
respectively) also show significant deviations in their iron abundance
with respect to the cluster metallicity (as traced by the unevolved
stars, [Fe/H]=-2.12). While similar chemical patterns have already
been observed in other hot HB stars, this is the first evidence ever
collected for BSSs. We interpret these abundance anomalies as due to
the metal radiative levitation, occurring in stars with shallow or no
convective envelopes.
Description:
This work is based on the analysis of spectra of individual stars in
NGC 6397, obtained with the multi-object facility FLAMES mounted at
the ESO VLT. Observations were performed during two different runs
(073.D-0058(A) and 081.D-0356(A), hereafter P73 and P81, respectively)
with the UVES+GIRAFFE combined mode, during three nights between 2004
April and July for P73 and three nights in 2008 June for P81. Spectra
have been acquired for 33 blue straggler stars (BSSs) and 42
horizontal branch (HB) stars, most of them being observed in both P73
and P81. In order to compare the results obtained for BSSs and HB
stars with a sample of unevolved cluster stars, we also analyzed
archive GIRAFFE data obtained within program 075.D-0125(A) (hereafter
P75), including spectra for 86 main-sequence turnoff (TO) and
sub-giant branch stars (hereafter both called TO stars), already
discussed by Lind et al. (2008, Cat. J/A+A/490/777).
The spectroscopic target selection has been performed from a
photometric catalog obtained by combining Advanced Camera for Surveys
(ACS) at the Hubble Space Telescope data for the central region
(within r<140" from the cluster center) and WFI at ESO observations
for the outer region (R. Contreras Ramos et al. 2012, in preparation).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 116 18 Coordinates, magnitudes, atmospherical parameters,
masses, radial and rotational velocities, Fe,
Mg, and O abundances of the BSS (blue straggler
star) sample
table3.dat 105 42 Coordinates, magnitudes, atmospherical parameters,
masses, radial and rotational velocities, Fe,
Mg, and O abundances of the HB (horizontal
branch) sample
table4.dat 94 86 Coordinates, magnitudes, atmospherical parameters,
masses, radial and rotational velocities, Fe
and Mg abundances of the TO (main-sequence
turnoff) sample
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/A+A/540/A27 : Spectroscopy in Galactic globular clusters (Saviane+, 2012)
J/A+A/503/545 : Equivalent widths of Li, Na, Fe, Ca in NGC 6397 (Lind+, 2009)
J/A+A/490/777 : Abundances of Population II stars in NGC 6397 (Lind+, 2008)
J/A+A/483/183 : Catalogue of Blue Stragglers (Moretti+, 2008)
J/AJ/135/2141 : F814W+F606W photometry of NGC 6397 faint stars (Richer+, 2008)
J/A+A/425/509 : VI photometry of NGC 6397 (Andreuzzi+, 2004)
J/A+A/287/769 : UV photometry of NGC 6397 (Burgarella+ 1994)
Byte-by-byte Description of file: table[234].dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- ID Identifier from the FLAMES 081.D-0356(A) run
9- 19 F11.7 deg RAdeg [264.8/265.5] Right Ascension (J2000)
21- 31 F11.7 deg DEdeg [-53.81/-53.44] Declination (J2000)
33- 37 F5.2 mag Vmag [13/16.4] The V band magnitude
39- 43 F5.2 mag Imag [12.6/15.8] The I band magnitude
45- 49 I5 K Teff [5433/13183] Effective temperature
51- 53 F3.1 [cm/s2] log(g) [3.2/4.7] Log of the surface gravity
55- 57 F3.1 Msun M [0.6/2] Star mass
59- 62 F4.1 km/s RV [11.8/32] Radial velocity
64- 67 F4.2 km/s e_RV Uncertainty in RV
69- 70 I2 km/s vsini [1/70]? Projected rotational velocity
72 I1 km/s e_vsini ? Uncertainty in vsini
74- 78 F5.2 [Sun] [Fe/H] [-2.5/0.1]? Metallicity
80- 83 F4.2 [Sun] e_[Fe/H] ? Uncertainty in [Fe/H]
85- 89 F5.2 [Sun] [Mg/H] ? Log of the magnesium abundance
91- 94 F4.2 [Sun] e_[Mg/H] ? Uncertainty in [Mg/H]
96-100 F5.2 [Sun] [O/H] ? Log of the oxygen abundance
102-105 F4.2 [Sun] e_[O/H] ? Uncertainty in [O/H]
107-116 A10 --- Notes Notes
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 04-Mar-2014