J/A+A/324/505 Core velocity dispersions of globular clusters (Dubath+ 1997)
Core velocity dispersions for 25 Galactic and 10 old Magellanic
globular clusters
Dubath P., Meylan G., Mayor M.
<Astron. Astrophys. 324, 505 (1997)>
=1997A&A...324..505D 1997A&A...324..505D (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Radial velocities ; Velocity dispersion
Keywords: (Galaxy:) globular clusters: general - stars: kinematics -
techniques: radial velocities - galaxies: star clusters -
Magellanic Clouds
Abstract:
We present, for 25 Galactic and 10 old Magellanic globular clusters,
projected velocity dispersion (σp) measurements obtained by
applying a cross-correlation technique to integrated-light spectra. In
order to understand and estimate the statistical errors of these
measurements due to small numbers of bright stars dominating the
integrated light, we provide an extensive discussion based on detailed
numerical simulations. These errors are smaller if the integration
area is larger and/or the cluster concentration higher. The
simulations show that measurements are reliable when the integrated
light within the integration area is brighter than a given magnitude.
The statistical errors on the σp measurements of Magellanic
globular clusters are small because of a physically large integration
area, whereas they can be important for measurements carried out
over small central areas in Galactic clusters. The present
observational results are used to outline a few characteristics of the
globular cluster fundamental plane. In this respect, the old
Magellanic globular clusters appear similar to the Galactic clusters.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table67 98 44 Radial velocities and core velocity dispersions
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table67
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Loc Localication (Gal, LMC or SMC)
5- 8 A4 --- Obs Observation number
10- 14 A5 --- NGC NGC number
16- 21 F6.1 km/s HRV Derived heliocentric radial velocity
23- 25 F3.1 km/s e_HRV rms uncertainty on HRV
27- 30 F4.1 km/s sigCCF Standard deviation of the cross-correlation
function (CCF)
32- 34 F3.1 km/s e_sigCCF rms uncertainty on sigCCF
36- 40 F5.3 % Depth Relative depth of the CCF
42- 45 F4.1 --- S/N Signal-to-noise ratio of the spectrum
47- 50 F4.2 km/s eps Uncertainty epsilon of HRV and sigCCF due to
the spectrum noise
52- 54 F3.1 km/s sigref Value used for the intrinsic standard
deviation from the standard CCFs
56- 59 F4.2 km/s e_sigref rms uncertainty on sigref
61- 64 F4.1 km/s sigpObs ? Observed cluster core projected
velocity dispersion
66- 68 F3.1 km/s E_sigpObs ? Error in sigpObs (upper limit) due to the
instrumental error and to the spectrum noise
70- 72 F3.1 km/s e_sigpObs ? Error in sigpObs (lower limit) due to the
instrumental error and to the spectrum noise
74- 76 F3.1 km/s StatErru ? Statistical error (upper limit) due to the
small sample of bright stars observed
through the slit
77 A1 --- u_StatErru Uncertainty flag on StatErru
79- 81 F3.1 km/s StatErrl ? Statistical error (lower limit) due to the
small sample of bright stars observed
through the slit
83- 86 F4.1 km/s sigp ? Calculated cluster core projected
velocity dispersion (1)
88- 90 F3.1 km/s E_sigp ? Error in sigp (upper limit) (2)
91 A1 --- uEsigp Uncertainty flag on E_sigp
93- 95 F3.1 km/s e_sigp ? Error in sigp (lower limit) (2)
--------------------------------------------------------------------------------
Note (1): sigp includes the contribution from the statistical error simulations
Note (2): Uncertainty, including the contribution from the statistical error
--------------------------------------------------------------------------------
Acknowledgements: Pierre Dubath
(End) Patricia Bauer [CDS] 20-Jan-1997