J/ApJ/809/143 K-band spectra of stars within central 1pc of the MW (Do+, 2015)
Discovery of low-metallicity stars in the central parsec of the Milky Way.
Do T., Kerzendorf W., Winsor N., Stostad M., Morris M.R., Lu J.R.,
Ghez A.M.
<Astrophys. J., 809, 143 (2015)>
=2015ApJ...809..143D 2015ApJ...809..143D (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Radial velocities ; Stars, giant ; Milky Way
Keywords: Galaxy: center; stars: abundances; stars: late-type;
techniques: high angular resolution; techniques: spectroscopic
Abstract:
We present a metallicity analysis of 83 late-type giants within the
central 1pc of the Milky Way. K-band spectroscopy of these stars was
obtained with the medium spectral resolution integral-field
spectrograph NIFS on Gemini North using laser-guided star adaptive
optics. Using spectral template fitting with the MARCS synthetic
spectral grid, we find that there is a large variation in the
metallicity, with stars ranging from [M/H]←1.0 to above solar
metallicity. About 6% of the stars have [M/H]←0.5. This result is in
contrast to previous observations with smaller samples that show stars
at the Galactic center having approximately solar metallicity with
only small variations. Our current measurement uncertainties are
dominated by systematics in the model, especially at [M/H]>0, where
there are stellar lines not represented in the model. However, the
conclusion that there are low-metallicity stars, as well as large
variations in metallicity, is robust. The metallicity may be an
indicator of the origin of these stars. The low-metallicity population
is consistent with that of globular clusters in the Milky Way, but
their small fraction likely means that globular cluster infall is not
the dominant mechanism for forming the Milky Way nuclear star cluster.
The majority of stars are at or above solar metallicity, which
suggests they were formed closer to the Galactic center or from the
disk. In addition, our results indicate that it will be important for
star formation history analyses using red giants at the Galactic
center to consider the effect of varying metallicity.
Description:
The spectra in this paper were obtained using the Gemini North
Near-infrared Facility Spectrograph (NIFS) with the natural and
laser-guided star AO system ALTAIR. The spectra were obtained using
the K broadband filter (1.99-2.40um; GN-2012A-Q-41 and GN-2014A-Q-71;
PI: Do). The observations span a projected radius of 8-22 arcsec
(0.3-0.9pc) from Sgr A*. More details about the observations and data
reduction were presented by Stostad et al. (2015ApJ...808..106S 2015ApJ...808..106S). We
restrict our analysis here to stars with signal-to-noise ratios (S/Ns)
greater than 35.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 65 83 Measured physical parameters of stars at
the Galactic Center
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See also:
J/ApJ/808/106 : NIR spectroscopic obs. in the Galactic Center (Stostad+, 2015)
J/A+A/564/A125 : AGN Torus model comparison of AGN in the CDFS (Buchner+, 2014)
J/ApJ/779/L6 : 3D kinematic obs. of stars in Galactic Centre (Do+, 2013)
J/ApJ/764/154 : Stellar populations in the central 0.5pc. I. (Do+, 2013)
J/A+A/549/A147 : Abundances of microlensed Bulge dwarf stars V. (Bensby+, 2013)
J/A+A/549/A129 : Equivalent widths of cool stars (Cesetti+, 2013)
J/ApJ/751/132 : Keck observations of the Arches cluster (Clarkson+, 2012)
J/A+A/535/A42 : Metal rich stars in solar neighbourhood (Trevisan+, 2011)
J/A+A/502/91 : Proper motions of stars near SgrA* (Schoedel+, 2009)
J/ApJ/681/1254 : Radial velocities of stars in the Galactic Center (Zhu+, 2008)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star name
11- 14 F4.1 --- Kmag [10.4/16.7] K magnitude
16- 18 I3 --- S/N [35/133] Signal to noise ratio
20- 24 F5.2 arcsec oRA [1.4/22.73] R.A. offset from SgrA* (1)
26- 30 F5.2 arcsec oDE [-4.55/11.57] Dec. offset from SgrA* (1)
32- 35 I4 K Teff [3447/4613] Effective temperature
37- 39 I3 K e_Teff [413/425] Teff uncertainty
41- 44 F4.2 --- logg [2.7/4] Log of Surface gravity
46- 49 F4.2 --- e_logg [0.91] logg uncertainty
51- 55 F5.2 --- [M/H] [-1.3/1] Metallicity
57- 60 F4.2 --- e_[M/H] [0.3/0.4] [M/H] uncertainty
62- 65 I4 km/s RV [-225/228] Radial velocity νz
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Note (1): From Stostad et al. (2015ApJ...808..106S 2015ApJ...808..106S)
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 10-Dec-2015