J/AJ/155/171 RR Lyrae stars in and around NGC 6441 (Kunder+, 2018)
Radial velocities of RR Lyrae stars in and around NGC 6441.
Kunder A., Mills A., Edgecomb J., Thomas M., Schilter L., Boyle C.,
Parker S., Bellevue G., Rich R.M., Koch A., Johnson C.I., Nataf D.M.
<Astron. J., 155, 171 (2018)>
=2018AJ....155..171K 2018AJ....155..171K (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Stars, variable ;
Radial velocities ; Photometry, VRI ; Stars, distances
Keywords: Galaxy: bulge - Galaxy: formation - Galaxy: kinematics and dynamics -
globular clusters: individual (NGC 6441) - stars: horizontal-branch -
stars: variables: RR Lyrae
Abstract:
Detailed elemental abundance patterns of metal-poor ([Fe/H]~-1 dex)
stars in the Galactic bulge indicate that a number of them are consistent
with globular cluster (GC) stars and may be former members of dissolved
GCs. This would indicate that a few per cent of the Galactic bulge was
built up from destruction and/or evaporation of GCs. Here, an attempt
is made to identify such presumptive stripped stars originating from
the massive, inner Galaxy GC NGC 6441 using its rich RR Lyrae variable
star (RRL) population. We present radial velocities of 40 RRLs centered
on the GC NGC 6441. All 13 of the RRLs observed within the cluster tidal
radius have velocities consistent with cluster membership, with an average
radial velocity of 24±5 km/s and a star-to-star scatter of 11 km/s.
This includes two new RRLs that were previously not associated with
the cluster. Eight RRLs with radial velocities consistent with cluster
membership but up to three time the distance from the tidal radius are
also reported. These potential extra-tidal RRLs also have exceptionally
long periods, which is a curious characteristic of the NGC 6441 RRL
population that hosts RRLs with periods longer than seen anywhere else
in the Milky Way. As expected of stripped cluster stars, most are inline
with the cluster's orbit. Therefore, either the tidal radius of NGC 6441
is underestimated and/or we are seeing dissolving cluster stars stemming
from NGC 6441 that are building up the old spheroidal bulge.
Description:
Observations were carried out using the AAOmega multi-fiber spectrograph
on the Anglo-Australian Telescope on three separate nights: 2016 August 09,
2016 August 10, and 2017 June 18 (OPTICON proposal code 17A/051, NOAO
PropID: 2017A-195 and NOAO PropID: 2016B-0058 PI: A. Kunder). The
spectrograph was centered on 8600 Å, with the 580V and 1700D gratings
to probe the Calcium Triplet, so the wavelength regime of ∼8300-8800 Å
was covered at a resolution of R∼10000. The exposure times ranged from
1800 to 7200 s, and one exposure per night was taken, meaning that we
had three epochs for each RRL.
Targets were selected using the Optical Gravitational Lensing Experiment
(OGLE) catalog of RRLs (Pietrukowicz et al. 2012ApJ...750..169P 2012ApJ...750..169P), and we
prioritized those stars with existing high-resolution spectroscopy from
Clementini et al. (2005ApJ...630L.145C 2005ApJ...630L.145C) to test the CaT metallicity
relation.
Objects:
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RA (ICRS) DE Designation(s)
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17 50 13.06 -37 03 05.2 NGC 6441 = GCl 78
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 115 40 RR Lyrae stars in and around NGC 6441
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See also:
II/213 : OGLE Galactic Bulge periodic variables (Udalski+ 1996)
V/150 : Updated catalog of variable stars in globular clusters (Clement+ 2017)
J/AJ/117/1313 : NGC 6441 VI photometry (Layden+, 1999)
J/ApJ/651/197 : OGLE fundamental-mode RR Lyrae in Galactic Bulge
(Collinge+, 2006)
J/A+A/464/953 : Abundances of red giants in NGC 6441 (Gratton+, 2007)
J/other/PZP/9.5 : I light curves of RR Lyrae from OGLE II (Bernhard+, 2009)
J/AcA/61/1 : VI light curves of Galactic Bulge RR Lyrae (Soszynski+, 2011)
J/AcA/64/177 : VI light curves of Galactic Bulge RR Lyrae (Soszynski+, 2014)
J/ApJ/821/L25 : Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR)
(Kunder+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- OGLE [3168/31080] OGLE identifier
(OGLE BLG-RRLYR-NNNNN in Simbad)
6 A1 --- n_OGLE [o] Note on OGLE (o=Star outside the cluster
tidal radius)
8- 14 F7.4 deg GLON [-6.6981/-6.2304] OGLE Galactic longitude
16- 22 F7.4 deg GLAT [-5.4911/-4.7158] OGLE Galactic latitude
24- 27 I4 km/s HRV [-207/360] Time averaged heliocentric radial
velocity HRVφ (1)
29- 30 I2 km/s e_HRV [5/15] Uncertainty in HRV
32 I1 --- o_HRV [1/3] Number of epochs to get HRV
34- 38 F5.3 mag IAmp [0.11/0.82] OGLE I band amplitude
40- 45 F6.3 mag Imagmean [14.552/16.663] OGLE mean I band magnitude
47- 52 F6.3 mag Vmagmean [15.781/17.752] OGLE mean V band magnitude
54- 63 F10.8 d Per [0.44560223/0.90449519] OGLE period
65- 69 F5.2 arcmin r [0.57/30.66] Distance from cluster center
71-115 A45 --- Note Additional note (2)
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Note (1): φ=0.38.
Note (2): In particular, the notes identify the RRLs observed here with known
NGC 6441 RRLs listed in Clement et al. (2001, Cat. V/150).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 19-Nov-2018