J/ApJ/816/70 High resolution spectra of 3 NGC104 member stars (Ferraro+, 2016)
Weighing stars: the identification of an evolved blue straggler star in the
globular cluster 47 Tucanae.
Ferraro F.R., Lapenna E., Mucciarelli A., Lanzoni B., Dalessandro E.,
Pallanca C., Massari D.
<Astrophys. J., 816, 70 (2016)>
=2016ApJ...816...70F 2016ApJ...816...70F (SIMBAD/NED BibCode)
ADC_Keywords: Equivalent widths ; Clusters, globular ; Radial velocities ;
Photometry, VRI
Keywords: blue stragglers; globular clusters: individual: 47 Tucanae;
stars: abundances; techniques: spectroscopic
Abstract:
Globular clusters are known to host peculiar objects named blue
straggler stars (BSSs), significantly heavier than the normal stellar
population. While these stars can be easily identified during their
core hydrogen-burning phase, they are photometrically
indistinguishable from their low-mass sisters in advanced stages of
the subsequent evolution. A clear-cut identification of these objects
would require the direct measurement of the stellar mass. We used the
detailed comparison between chemical abundances derived from neutral
and from ionized spectral lines as a powerful stellar "weighing
device" to measure stellar mass and to identify an evolved BSS in
47Tucanae. In particular, high-resolution spectra of three bright
stars, located slightly above the level of the "canonical" horizontal
branch (HB) sequence in the color-magnitude diagram of 47 Tucanae,
have been obtained with the UVES spectrograph. The measurements of
iron and titanium abundances performed separately from neutral and
ionized lines reveal that two targets have stellar parameters fully
consistent with those expected for low-mass post-HB objects, while for
the other target the elemental ionization balance is obtained only by
assuming a mass of ∼1.4M☉, which is significantly larger than
the main sequence turn-off mass of the cluster (∼0.85M☉). The
comparison with theoretical stellar tracks suggests that this is a BSS
descendant possibly experiencing its core helium-burning phase. The
large applicability of the proposed method to most of the globular
clusters in our Galaxy opens the possibility to initiate systematic
searches for evolved BSSs, thus giving access to still unexplored
phases of their evolution.
Description:
In the context of the ESO Large Programme 193.D-0232 (PI: Ferraro)
aimed at studying the internal kinematics of Galactic globular
clusters, we have secured UVES-FLAMES high-resolution spectra of three
stars in 47 Tuc (NGC 104). The (V,V-I) CMD is obtained from the Hubble
Space Telescope (HST)-Advanced Camera for Surveys (ACS) photometric
catalog of Sarajedini et al. (2007AJ....133.1658S 2007AJ....133.1658S). The target spectra
have been acquired with the grating 580 Red Arm CD#3, which provides a
spectral resolution R∼40000 between 4800 and 6800Å. The three stars
are all cluster members.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 71 3 Observational parameters of the three targets
table2.dat 46 220 Adopted line list
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See also:
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/MNRAS/443/2492 : Δa observations of 3 GCs (Paunzen+, 2014)
J/A+A/572/A108 : 47 Tuc red giants chemical composition (Thygesen+, 2014)
J/ApJ/780/94 : Abundances of red giants in 47 Tuc (Cordero+, 2014)
J/A+A/550/A34 : Abundances of red giants in M4 and 47 Tuc (Carretta+, 2013)
J/A+A/549/A41 : Horizontal branch stars in 47 Tuc and M5 (Gratton+, 2013)
J/A+A/537/A2 : 8.6um imaging of 47 Tuc (Momany+, 2012)
J/A+A/524/A44 : CN and CH line strengths in 12 globulars (Pancino+, 2010)
J/A+A/517/A81 : 2nd & 3d param. of HB of globular clusters (Gratton+, 2010)
J/MNRAS/405/839 : Spectroscopic obs. of globular clusters (Sharina+, 2010)
J/A+A/505/139 : Abundances of red giants in 17 GCs (Carretta+, 2009)
J/A+A/505/117 : Abundances of red giants in 15 GCs (Carretta+, 2009)
J/MNRAS/383/183 : CaII triplet of RGB from VLT/FLAMES obs. (Battaglia+, 2008)
J/AJ/135/1551 : Abundances of stars in 47 Tuc (Koch+, 2008)
J/AJ/134/1298 : CaII equivalent widths in 29 GCs (Carrera+, 2007)
J/ApJS/166/249 : Stellar dynamics & proper motions in 47Tuc (McLaughlin+, 2006)
J/A+A/435/657 : Equivalent widths of 5 giants in 47 Tuc (Alves-Brito+, 2005)
J/ApJ/625/796 : X-ray sources in the globular cluster 47 Tuc (Heinke+, 2005)
J/AJ/130/2140 : Abundances and velocities in globular clusters (Pritzl+, 2005)
J/AJ/130/1693 : HST-ACS observations of 5 globular clusters (Brown+, 2005)
J/AJ/127/1588 : 47 Tuc main-sequence star abundances (Briley+, 2004)
J/A+A/391/945 : HST photometry of 74 galactic GCs (Piotto+, 2002)
J/A+AS/128/19 : Variable stars in 47 Tuc fields 104A-E (Kaluzny+ 1998)
J/A+AS/113/299 : Abundances and velocities for cluster giants (Minniti 1995)
J/ApJS/93/161 : CCD photometry of 6 globular clusters (Sarajedini+ 1994)
J/PASP/99/739 : BV photometry in 4 fields of 47 Tuc (Hesser+, 1987)
http://www.cosmic-lab.eu/Cosmic-Lab : Cosmic-Lab project home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Name Star name
8- 14 I7 --- ID [1090214/2625792] ID number
16- 24 F9.7 deg RAdeg [5.93/6.1] Righ ascension (J2000)
26- 36 F11.7 deg DEdeg [-72.11/-72] Declination (J2000)
38- 43 F6.3 mag Vmag [13.5/13.8] V-band magnitude
45- 49 F5.3 mag V-I [0.92/0.98] V-I color index
51- 55 F5.1 arcsec r [42.1/132.2] Distance from the center (1)
57- 60 I4 K Teff [4896/5013] Effective temperature
62- 66 F5.1 km/s RVel [-24.3/-7.8] Radial velocity
68- 71 F4.2 km/s e_RVel [0.05/0.06] RVel uncertainty
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Note (1): The cluster center used to compute the distance from the center is
from Miocchi et al. (2013ApJ...774..151M 2013ApJ...774..151M).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 F8.3 0.1nm lambda [4834.5/6750.2] Wavelength; in Angstroms
10- 13 A4 --- El Elemental species identification (FeI, FeII,
TiI or TiII)
15- 18 F4.2 eV ExPot [0/5] Excitation potential
20- 25 F6.3 [-] log(gf) [-5.6/0.7] Log of the oscillator strength
27- 32 F6.2 10-13m E-BSS1 [0/162.2] Equivalent width of E-BSS1 (1)
34- 39 F6.2 10-13m bHB1 [0/150.2] Equivalent width of bHB1 (1)
41- 46 F6.2 10-13m bHB2 [0/169.5] Equivalent width of bHB2 (1)
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Note (1): In units of milli-Angstroms.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 23-Mar-2016