J/MNRAS/480/3739 Extended main sequence turnoff in open cluster (Bastian+, 2018)
Extended main sequence turnoffs in open clusters as seen by Gaia.
I. NGC 2818 and the role of stellar rotation.
Bastian N., Kamann S., Cabrera-Ziri I., Georgy C., Ekstrom S.,
Charbonnel C., de Juan Ovelar M., Usher C.
<Mon. Not. R. Astron. Soc., 480, 3739-3746 (2018)>
=2018MNRAS.480.3739B 2018MNRAS.480.3739B (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Clusters, galaxy ; Rotational velocities ;
Optical
Keywords: stars: rotation -
open clusters and associations: individual: NGC 2818 -
galaxies: star clusters: general
Abstract:
We present an analysis of the relatively low mass (∼2400M☉),
∼800Myr, Galactic open cluster, NGC 2818, using Gaia DR2 results
combined with VLT/FLAMES spectroscopy. Using Gaia DR2 proper motions
and parallax measurements, we are able to select a clean sample of
cluster members. This cluster displays a clear extended main sequence
turn-off (eMSTO), a phenomenon previously studied mainly in young and
intermediate age massive clusters in the Magellanic clouds. The main
sequence of NGC 2818 is extremely narrow, with a width of ∼0.01
magnitudes (GBP-GRP), suggesting very low levels of differential
extinction. Using VLT/FLAMES spectroscopy of 60 cluster members to
measure the rotational velocity of the stars (Vsini), we find that
stars on the red side of the eMSTO have high Vsini(>160km/s) while
stars on the blue side have low Vsini(<160km/s), in agreement with
model predictions. The cluster also follows the previously discovered
trend between the age of the cluster and the extent of the eMSTO. We
conclude that stellar rotation is the likely cause of the eMSTO
phenomenon.
Description:
We searched the Gaia DR database for all sources within 12' of the
centre of NGC 2818 (Gaia Collaboration et al. 2016A&A...595A...1G 2016A&A...595A...1G,
Cat. I/337, 2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/354). We then looked at the
resulting proper motion map of these stars and a clear overdensity
could be seen at pmRA=-4.425 and pmDec=4.532. We used all stars with
proper motion values of 0.3milli-arcseconds of this centre for our
first selection. These stars showed a clear peak in the parallax
distribution at 0.281milli-arcseconds, corresponding to a distance of
3.56kpc which we will adopt throughout this work. We then made a
further selection in parallax, 0.1885=<parallax=<0.365 and applied a
radial cut of 10' to obtain our final member sample.
Spectroscopic observations of main-sequence(MS) and turn-off(TO) stars
in NGC 2818 are publicly available in the ESO archive. Observations
were conducted in 2014 March using the GIRAFFE multi-object
spectrograph in its MEDUSA mode under the programme 093.D-0868(A) (PI:
Simunovic). The employed setups are HR05 and HR09 that offer a nominal
resolution of R∼20250 and 18000 at the central wavelengths of 4471 and
5258Å, respectively. Stars were observed for 2x45min in each
grating, leading to a signal-to-noise (S/N) of ∼100 and ∼20 (per
single exposure) for the brightest and the faintest star in the
sample, respectively. A total of 60 stars from 093.D-0868(A) are
included in the Gaia DR2 photometric catalogue.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 100 239 Properties of the selected cluster candidate
using the position, Plx and proper motions
table2.dat 92 60 Properties of the stars with Vsini measurements
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 F13.9 deg RAdeg Right ascension (J2000)
15- 27 F13.9 deg DEdeg Declination (J2000)
29- 34 F6.4 mas plx Parallax
36- 41 F6.4 mas e_plx Error on plx
43- 49 F7.4 mas/yr pmRA Proper motion in Right Ascension
(pmRA*cosDE)
51- 56 F6.4 mas/yr e_pmRA Error on pmRA
58- 63 F6.4 mas/yr pmDE Proper motion in Declination
65- 70 F6.4 mas/yr e_pmDE Erron on pmDE
72- 78 F7.4 mag BPmag Gaia Integrated BP mean magnitude
80- 85 F6.4 mag e_BPmag Error on BPmag
87- 93 F7.4 mag RPmag Gaia Integrated RP mean magnitude
95-100 F6.4 mag e_RPmag Error on RPmag
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR2 Gaia DR2 Id
21- 33 F13.9 deg RAdeg Right ascension (J2000)
35- 47 F13.9 deg DEdeg Declination (J2000)
49- 53 F5.2 mag BPmag Gaia BP magnitude (1)
55- 59 F5.2 mag RPmag Gaia RP magnitude (1)
61- 65 F5.1 km/s vsini09 ?=0 Rotational velocity from the
HR09 grating (2)
67- 70 F4.1 km/s e_vsini09 ?=0 Error on vsini09
72- 76 F5.1 km/s vsini05 ?=0 Rotational velocity from the
HR05 grating (2)
78- 81 F4.1 km/s e_vsini05 ?=0 Error on vsini05
83- 87 F5.1 km/s vsiniad ?=0 Rotational velocity adopted value
89- 92 F4.1 km/s e_vsiniad ?=0 Error on vsiniad
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Note (1): Errors on the photometry are not given, as they are generally <0.01mag
Note (2): The employed setups are HR05 and HR09 that offer a nominal resolution
of R∼20250 and 18000 at the central wavelengths of 4471 and 5258Å,
respectively. 0.0 values denote stars where a measurement was not
possible in that grating.
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 25-May-2022