J/MNRAS/438/3507 NGC 5824 calcium triplet equivalent widths (Da Costa+, 2014)
NGC 5824: a luminous outer halo globular cluster with an intrinsic
abundance spread.
Da Costa G.S., Held E.V., Saviane I.
<Mon. Not. R. Astron. Soc., 438, 3507-3520 (2014)>
=2014MNRAS.438.3507D 2014MNRAS.438.3507D (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Radial velocities ; Equivalent widths
Keywords: stars: abundances - stars: Population II -
globular clusters: general - globular clusters: individual: NGC 5824
Abstract:
We present a detailed study of the strengths of the calcium triplet
absorption lines in the spectra of a large sample of red giant members
of the luminous outer Galactic halo globular cluster NGC 5824. The
spectra were obtained with the FORS2 and GMOS-S multi-object
spectrographs at the VLT and the Gemini-S telescope, respectively. By
comparing the line strengths of the NGC 5824 stars with those for red
giants in clusters with well-established abundances, we conclude that
there is an intrinsic abundance dispersion in NGC 5824 characterized
by an inter-quartile range in [Fe/H] of 0.10dex and a total range of
∼0.3dex. As for ω Cen and M22, the abundance distribution shows
a steep rise on the metal-poor side and a shallower decline on the
metal-rich side. There is also some indication that the distribution
is not unimodal with perhaps three distinct abundance groupings
present. NGC 5824 has a further unusual characteristic: the outer
surface density profile shows no signs of a tidal cutoff. Instead, the
profile has a power-law distribution with cluster stars detected to a
radius exceeding 400pc. We postulate that NGC 5824 may be the remnant
nuclear star cluster of a now disrupted dwarf galaxy accreted during
the formation of the Galaxy's halo. We further speculate that the
presence of an intrinsic [Fe/H] spread is the characteristic that
distinguishes former nuclear star clusters from other globular
clusters.
Description:
Observing time to follow up the possibility of an intrinsic [Fe/H]
spread in NGC 5824 was allocated for intermediate-resolution
spectroscopy of candidate red giant members on both the VLT with the
FORS2 multi-object spectrograph, and on the Gemini-S telescope with
the GMOS-S multi-object spectrograph.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 73 190 NGC 5824 stars observed
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- ID Star identification number
10- 18 F9.5 deg RAdeg Right ascension (J2000)
20- 28 F9.5 deg DEdeg Declinaiton (J2000)
30- 35 F6.3 mag Vmag V magnitude
37- 41 F5.3 mag V-I V-I colour index
43- 46 I4 km/s RV Radial velocity
48- 51 F4.2 0.1nm Sum(W) Ca 8542Å and 8862Å lines equivalent
widths sum (W8542+W8862)
53- 56 F4.2 0.1nm e_Sum(W) rms uncertainty on Sum(W)
58- 61 F4.2 0.1nm W8807 ? Ca 8807Å line equivalent width
63- 66 F4.2 0.1nm e_W8807 ? rms uncertainty on W8807
68 I1 --- NF Number of observations with FORS2 at the VLT
70 I1 --- NG Number of observations with GMOS-S at
Gemini South
72- 73 A2 --- Class Class code (1)
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Note (1): Class code as follows:
MR = star is member of the final RGB sample
MA = stars in the final AGB member sample
NM = probable non-member of the cluster.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 13-Jun-2016