J/MNRAS/442/3044 Photometry and abundances of NGC1851 stars (Marino+, 2014)
The halo+cluster system of the Galactic globular cluster NGC 1851.
Marino A.F., Milone A.P., Yong D., Dotter A., Da Costa G., Asplund M.,
Jerjen H., Mackey D., Norris J., Cassisi S., Sbordone L., Stetson P.B.,
Weiss A., Aparicio A., Bedin L.R., Lind K., Monelli M., Piotto G.,
Angeloni R., Buonanno R.
<Mon. Not. R. Astron. Soc., 442, 3044-3064 (2014)>
=2014MNRAS.442.3044M 2014MNRAS.442.3044M
ADC_Keywords: Clusters, globular ; Photometry ; Radial velocities ; Abundances
Keywords: techniques: imaging spectroscopy - globular clusters: general -
globular clusters: individual: NGC 1851
Abstract:
NGC 1851 is surrounded by a stellar component that extends more than
10 times beyond the tidal radius. Although the nature of this stellar
structure is not known, it has been suggested to be a sparse halo of
stars or associated with a stellar stream. We analyse the nature of
this intriguing stellar component surrounding NGC 1851 by
investigating its radial velocities and chemical composition, in
particular in comparison with those of the central cluster analysed in
a homogeneous manner. In total we observed 23 stars in the halo with
radial velocities consistent with NGC 1851, and for 15 of them we
infer [Fe/H] abundances. Our results show that (i) stars dynamically
linked to NGC 1851 are present at least up to ∼2.5 tidal radii,
supporting the presence of a halo of stars surrounding the cluster;
(ii) apart from the NGC 1851 radial velocity-like stars, our observed
velocity distribution agrees with that expected from Galactic models,
suggesting that no other substructure (such as a stream) at different
radial velocities is present in our field; (iii) the chemical
abundances for the s-process elements Sr and Ba are consistent
with the s-normal stars observed in NGC 1851; (iv) all halo
stars have metallicities, and abundances for the other studied
elements Ca, Mg and Cr, consistent with those exhibited by the
cluster. The complexity of the whole NGC 1851 cluster+halo system may
agree with the scenario of a tidally disrupted dwarf galaxy in which
NGC 1851 was originally embedded.
Description:
In this paper, we used four distinct photometric data sets. First, we
used Stetson (2000PASP..112..925S 2000PASP..112..925S) ground-based B, V, R and I
photometry. This photometric catalogue has been established from about
550 images taken at different telescopes, i.e. the Max Planck 2.2m,
the Cerro Tololo Inter-American Observatory (CTIO) 4, 1.5 and 0.9m
telescopes, and the Dutch 0.9m telescope in La Silla.
In the present work, we have complemented the Stetson catalogue with
images collected with the Wide Field Imager (WFI) of the Max Planck
2.2m telescope at La Silla (WFI@2.2m) through the U filter under the
SUrvey of Multiple pOpulations (SUMO) campaign.
Secondly, to study stars in the halo of NGC 1851, we collected BVI
images with WFI@2.2m of a field between ∼10 and 35 arcmin to the
south of the cluster centre. Photometry and astrometry for this data
set have been obtained by using the program img2xym_WFI and the
procedure described by Anderson et al. (2006A&A...454.1029A 2006A&A...454.1029A).
Third and finally, to investigate the most crowded central regions, we
use Hubble Space Telescope (HST) F606W and F814W photometry obtained
with the Wide Field Channel of the Advanced Camera for Survey
(WFC/ACS) and F275W photometry collected with the Ultraviolet and
Visual Channel of the Wide Field Camera 3 (UVIS/WFC3).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 106 191 Coordinates, basic photometric data and radial
velocities for the NGC 1851-halo and
cluster (inner field) stars
table3.dat 96 104 Adopted atmospheric parameters and chemical
abundances for the NGC 1851-halo and
cluster (central field) stars
--------------------------------------------------------------------------------
See also:
J/PASP/104/1063 : BV Color-Magnitude Diagram for NGC 1851 (Walker 1992)
J/A+A/333/479 : NGC 1851 dynamical & evolutionary properties (Saviane+ 1998)
J/AJ/122/2569 : VI photometry of NGC 288, 362 and 1851 (Bellazzini+, 2001)
J/A+A/525/A148 : Radial velocities in two globular clusters (Scarpa+, 2011)
J/A+A/533/A69 : Spectroscopy of 124 RGB stars in NGC 1851 (Carretta+, 2011)
J/A+A/539/A19 : Horizontal branch stars in NGC 1851 (Gratton+, 2012)
J/MNRAS/426/1137 : Radial velocities in NGC 1851 (Sollima+, 2012)
J/AJ/148/27 : Photometry in globular clusters. NGC1851 (Cummings+, 2014)
J/ApJS/216/19 : Spectroscopic HK' index for 3 globular clusters (Lim+, 2015)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Field Field (halo or cluster)
9- 19 A11 --- Name Star name
21- 22 I2 h RAh Right ascension (J2000)
24- 25 I2 min RAm Right ascension (J2000)
27- 32 F6.3 s RAs Right ascension (J2000)
34 A1 --- DE- Declination sing (J2000)
35- 36 I2 deg DEd Declination (J2000)
38- 39 I2 arcmin DEm Declination (J2000)
41- 46 F6.3 arcsec DEs Declination (J2000)
48- 53 F6.3 mag Bmag ?=- SUMO B magnitude
55- 60 F6.3 mag Vmag ?=- SUMO V magnitude
62- 67 F6.3 mag Rmag ?=- SUMO R magnitude
69- 74 F6.3 mag Imag ?=- SUMO I magnitude
76- 81 F6.3 mag F606W ?=- HST F606W magnitude
83- 88 F6.3 mag F814W ?=- HST F814W magnitude
90- 96 F7.3 km/s RV [-83/382] Radial velocity
98-106 A9 --- SGB Location of star in HR diagram: bSGB, fSGB,
field or uncertain (1)
--------------------------------------------------------------------------------
Note (1): the meaning is:
bSGB = bright sub-giant branch
fSGB = faint sub-giant branch
field = field star (not member of the cluster)
uncertain = ambiguous
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Field Field (halo or cluster)
9- 19 A11 --- Name Star name
22- 25 I4 K Teff Effective temperature
27- 30 I4 K e_Teff rms uncertainty on Teff
32- 35 F4.2 [cm/s2] logg [3.1/4.5] Surface gravity
37- 40 F4.2 km/s vt [1/1.4] Micro-turbulent velocity
42- 46 F5.2 [Sun] [Fe/H] [-1.7/-1.0]?=- Metallicity
47 A1 --- u_[Fe/H] [*] *: less than 5 Fe lines
49- 52 F4.2 [Sun] e_[Fe/H] [0.02/0.32]?=- rms uncertainty on [Fe/H]
54- 58 F5.2 [Sun] [C/Fe] ?=- [C/Fe] abundance
60- 63 F4.2 [Sun] [Mg/Fe] ?=- [Mg/Fe] abundance
65- 68 F4.2 [Sun] s_[Mg/Fe] ?=- Scatter of measurements derived from
individual measurements on [Mg/Fe]
70- 74 F5.2 [Sun] [Ca/Fe] ?=- [Ca/Fe] abundance
76- 80 F5.2 [Sun] [Cr/Fe] ?=- [Cr/Fe] abundance
82- 86 F5.2 [Sun] [Sr/Fe] ?=- [Sr/Fe] abundance
88- 91 F4.2 [Sun] s_[Sr/Fe] ?=- Scatter of measurements derived from
individual measurements on [Sr/Fe]
93- 96 F4.2 [Sun] [Ba/Fe] ?=- [Ba/Fe] abundance
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 04-Mar-2015