J/ApJ/703/1323 Spectroscopy of stars in the Galaxy's nuclear cluster (Do+ 2009)
High angular resolution integral-field spectroscopy of the Galaxy's nuclear
cluster: a missing stellar cusp?
Do T., Ghez A.M., Morris M.R., Lu J.R., Matthews K., Yelda S., Larkin J.
<Astrophys. J., 703, 1323-1337 (2009)>
=2009ApJ...703.1323D 2009ApJ...703.1323D
ADC_Keywords: Equivalent widths ; Spectra, infrared ; Stars, early-type ;
Stars, late-type ; Milky Way
Keywords: Galaxy: center - infrared: stars - stars: late-type -
techniques: high angular resolution - techniques: spectroscopic
Abstract:
We report on the structure of the nuclear star cluster in the
innermost 0.16pc of the Galaxy as measured by the number density
profile of late-type giants. Using laser guide star adaptive optics in
conjunction with the integral field spectrograph, OSIRIS, at the Keck
II telescope, we are able to differentiate between the older,
late-type (∼1Gyr) stars, which are presumed to be dynamically relaxed,
and the unrelaxed young (∼6Myr) population. This distinction is
crucial for testing models of stellar cusp formation in the vicinity
of a black hole, as the models assume that the cusp stars are in
dynamical equilibrium in the black hole potential. In the survey
region, we classified 60 stars as early-type (O and early B; 22 newly
identified) and 74 stars as late-type (K and M; 61 newly identified).
We find that contamination from young stars is significant, with more
than twice as many young stars as old stars in our sensitivity range
(K'<15.5) within the central arcsecond.
Description:
Near-IR spectra of the central 4" of the Galaxy were obtained between
2007 and 2008 using the OSIRIS integral field spectrograph in
conjunction with the LGS AO system on the Keck II telescope. All
observations were taken with the narrowband filter Kn3 (2.121-2.229um)
centered on the Brγ hydrogen line at 2.1661um, with a pixel
scale of 35mas and a spectral resolution of ∼3000. With the goal of
covering an ∼8"x6" area centered on Sgr A*, we divided this region
into seven fields (figure 1).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 62 74 OSIRIS observations of late-type stars
table3.dat 62 60 OSIRIS observations of early-type stars
table4.dat 39 54 OSIRIS spectra with unknown spectral type
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See also:
J/A+A/534/A117 : NIR polarimetry of sources near SgrA* (Buchholz+, 2011)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/A+A/499/483 : NIR observations of sources in galactic center (Buchholz+,
2009)
J/A+A/502/91 : Proper motions of stars near SgrA* (Schoedel+, 2009)
J/ApJ/697/1741 : Warped disks of YSOs in Galactic center (Bartko+, 2009)
J/ApJ/659/1241 : Stellar variability in Galactic Center (Rafelski+, 2007)
J/ApJ/643/1011 : Early-type stars in the center of the Galaxy (Paumard+, 2006)
J/A+A/373/608 : Early-type stars towards the Galactic Center. II. (Dufton+,
2001)
J/A+AS/128/35 : New Sample of OH/IR stars (Sjouwerman+ 1998)
J/ApJ/470/864 : JHKL photometry of the Galactic Center (Blum+, 1996)
Byte-by-byte Description of file: table[23].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star identification (SN-NNN or IRS16WW-W)
11- 14 F4.1 mag K'mag KeckII/OSIRIS K'-band magnitude (∼2.2um)
16- 20 F5.2 arcsec RAoff Offset in right ascension from Sgr A*
22- 26 F5.2 arcsec DEoff Offset in declination from Sgr A*
28- 31 F4.2 arcsec Rad Projected distance from Sgr A* in the plane of
the sky
33- 39 F7.2 yr Epoch Epoch in decimal years
41 I1 --- Ref [1,5] Reference for spectral identification (1)
43- 47 F5.2 0.1nm EW ? Equivalent width (NaI line for late-type stars
or Brγ for early-type stars) (2)
49- 52 F4.2 0.1nm e_EW ? 1σ error in EW
54- 55 I2 --- Nobs ? Number of observation(s) (3)
57- 59 I3 --- S/N ? Signal to noise per pixel calculated between
2.212 and 2.218um.
61- 62 A2 --- Field [CEWSN] Field short name (4)
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Note (1): Note on spectral identification as follows:
1 = Spectral type first reported in this work.
2 = Paumard et al. 2006, Cat. J/ApJ/643/1011;
3 = Genzel et al. 2000MNRAS.317..348G 2000MNRAS.317..348G;
4 = Gillessen et al. 2009ApJ...692.1075G 2009ApJ...692.1075G;
5 = Bartko et al. 2009, Cat. J/ApJ/697/1741.
Note (2): Equivalent widths for the NaI lines in the spectra of the
late-type stars (table 2) were measured by normalizing the spectra
and integrating between 2.2053um and 2.2101um as in Forster Schreiber
(2000AJ....120.2089F 2000AJ....120.2089F), after shifting the spectra to rest wavelengths.
The equivalent widths of the Brγ lines are measured by fitting a
Gaussian to the line and integrating the model Gaussian parameters. In
table 3, stars with no reported equivalent widths have no detectable
Brγ lines, with the exception of the IRS 16 sources, which all
have strong Brγ emission lines from strong winds. See section 4
for further details.
Note (3): Each observation has an integration time of 900s.
Note (4): Summary of OSIRIS observations:
----------------------------------------------------------------------
Field Name Field Center (") Date (UT) Nframes FWHM (mas)
RA, DE offset
from Sgr A*
----------------------------------------------------------------------
GC Central (C) 0 , 0 2008 May 16 11 84x85
GC East (E) 2.88, -0.67 2007 Jul 18 10 85x70
GC South (S) -0.69, -2.00 2007 Jul 19 10 73x63
GC West (W) -2.70, 0.74 2007 Jul 20 11 110x86
GC Southeast (SE) 1.67, -2.23 2008 Jun 3 11 68x63
GC North (N) 0.33, 2.01 2008 Jun 7 7 102x85
2008 Jun 10 5 75x70
GC Northeast (NE) 2.55, 1.27 2008 Jun 10 5 74x68
----------------------------------------------------------------------
See section 2 for further details and figure 1.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name Star identification (SN-NNN)
8- 11 F4.1 mag K'mag KeckII/OSIRIS K'-band magnitude (∼2.2um)
13- 17 F5.2 arcsec RAoff Offset in right ascension from Sgr A*
19- 23 F5.2 arcsec DEoff Offset in declination from Sgr A*
25- 28 F4.2 arcsec Rad Projected distance from Sgr A* in the plane
of the sky
30- 36 F7.2 yr Epoch Epoch in decimal years
38- 39 I2 --- S/N Signal to noise per pixel calculated between
2.212 and 2.218um.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 26-Oct-2011