J/MNRAS/454/2621 M4 Core Project with HST. Radial velocities (Malavolta+, 2015)
The M 4 Core Project with HST.
IV. Internal kinematics from accurate radial velocities of 2771 cluster members.
Malavolta L., Piotto G., Bedin L.R., Sneden C., Nascimbeni V., Sommariva V.
<Mon. Not. R. Astron. Soc., 454, 2621-2635 (2015)>
=2015MNRAS.454.2621M 2015MNRAS.454.2621M (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Radial velocities
Keywords: techniques: radial velocities - techniques: spectroscopic -
stars: kinematics and dynamics -
globular clusters: individual: NGC 6121
Abstract:
We present a detailed study of the internal kinematics of the Galactic
globular cluster M 4 (NGC 6121), by deriving the radial velocities
from 7250 spectra for 2771 stars distributed from the upper part of
the red giant branch down to the main sequence. We describe new
approaches to determine the wavelength solution from day-time
calibrations and to determine the radial velocity drifts that can
occur between calibration and science observations when observing with
the GIRAFFE spectrograph at Very Large Telescope. Two techniques to
determine the radial velocity are compared, after a qualitative
description of their advantages with respect to other commonly used
algorithm, and a new approach to remove the sky contribution from the
spectra obtained with fibre-fed spectrograph and further improve the
radial velocity precision is presented. The average radial velocity of
the cluster is =71.08±0.08km/s with an average
dispersion of µvc=3.97km/s. Using the same data set and the same
statistical approach of previous analyses, 20 additional binary
candidates are found, for a total of 87 candidates. A new
determination of the internal radial velocity dispersion as a function
of cluster distance is presented, resulting in a dispersion of 4.5km/s
within 2-arcmin from the centre of cluster and steadily decreasing
outward. We statistically confirm the small amplitude of the cluster
rotation, as suggested in the past by several authors. This new
analysis represents a significant improvement with respect to previous
results in literature and provides a fundamental observational input
for the modelling of the cluster dynamics.
Description:
The spectra for our project were originally used by Sommariva et al.
(2009A&A...493..947S 2009A&A...493..947S) to study the internal velocity dispersion of M4
and to search for spectroscopic binaries.
A total of 2771 stars covering colour-magnitude diagram (CMD)
positions from the upper RGB to about 1mag fainter than the
main-sequence turnoff (TO) luminosity were observed between 2003 and
2009, including 306 new spectra obtained in 2009 and targeting MS
stars already observed in the previous epochs. Determination of the M
4 velocity dispersion and binary star fraction were the prime
motivators for obtaining these data. Therefore nearly all stars were
observed at least twice, and three or more spectra were obtained for
nearly 40 per cent of the sample.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 90 2719 Average RVs of 2719 stars of the sample
table4.dat 107 7075 Individual RVs of 2730 stars of the sample
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See also:
J/ApJS/120/265 : HST photometry of M4 (Ibata+, 1999)
J/MNRAS/442/2381 : Variable stars in M4 primary field (Nascimbeni+, 2014)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 F10.6 deg RAdeg Rigth ascension (J2000)
12- 21 F10.6 deg DEdeg Declination (J2000)
23- 27 I5 --- ID Identification number
29- 34 F6.3 mag Vmag V magnitude
36- 41 F6.3 mag B-V B-V colour index
43- 48 F6.3 mag V0mag Dereddened V magnitude
50- 55 F6.3 mag (B-V)0 Dereddened B-V colour index
57- 58 I2 --- o_Vmag Number of observations
60- 67 F8.3 km/s RV Mean radial velocity
69- 75 F7.3 km/s sigma ?=-9.990 Radial velocity dispersion
77- 81 F5.3 km/s Average radial velocity dispersion
83- 90 F8.3 --- stdratio sigma/ ratio
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID Identification number
7- 18 F12.6 d MJD Modified Julian date
20- 21 I2 --- j j index referring to individual exposure
23- 51 A29 --- GIRFile GIRAFFE file name
53- 55 I3 --- Fib Fiber number
57- 63 F7.3 km/s BERV Barycentric earth radial velocity
65- 72 F8.3 km/s vobsrj Observed velocity, vobsr,j (1)
74- 81 F8.3 km/s vrj Velocity, vr,j(1)
83- 89 F7.3 km/s FWHM Full width at half maximum
91- 96 F6.2 --- SNR Signql-to-noise ratio
98-107 F10.5 --- 1/chi2 Inverse of χ2
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Note (1): The weighted mean velocity of a star vr is determined using
Equation 5 , where r is the index of the star, j is the index referring to
individual exposures and n is the total number of observations available for
the given star. The weight wr,j is the inverse of the minimum of the
LSQ function after normalizing it for the number of pixels used.
<vr≥({Sum}{j=1,n}wr,j*v-r,j)/{Sum}{j=1,n}wr,j_)
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History:
From electronic version of the journal
References:
Bedin et al., Paper I 2013AN....334.1062B 2013AN....334.1062B
Milone et al., Paper II 2014MNRAS.439.1588M 2014MNRAS.439.1588M
Nascimbeni et al., Paper III 2014MNRAS.442.2381N 2014MNRAS.442.2381N, Cat. J/MNRAS/442/2381
(End) Patricia Vannier [CDS] 15-Jul-2016