J/ApJ/899/121 127 early type and pre-main-sequence stars in W4 (Lim+, 2020)
The Origin of a Distributed Stellar Population in the Star-forming Region W4.
Lim B., Hong J., Yun H.-S., Hwang N., Kim J.S., Lee J.-E., Park B.-G.,
Park S.
<Astrophys. J., 899, 121 (2020)>
=2020ApJ...899..121L 2020ApJ...899..121L
ADC_Keywords: Clusters, open; Stars, early-type; Stars, pre-main sequence;
Star Forming Region; Spectra, optical; Radial velocities;
Proper motions
Keywords: Star formation ; Stellar kinematics ; Stellar associations ;
Stellar dynamics ; Open star clusters
Abstract:
Stellar kinematics provides the key to understanding the formation
process and dynamical evolution of stellar systems. Here, we present a
kinematic study of the massive star-forming region (SFR) W4 in the
Cassiopeia OB6 association using the Gaia Data Release 2 and
high-resolution optical spectra. This SFR is composed of a core
cluster (IC1805) and a stellar population distributed over 20pc, which
is a typical structural feature found in many OB associations.
According to a classical model, this structural feature can be
understood in the context of the dynamical evolution of a star
cluster. The core-extended structure exhibits internally different
kinematic properties. Stars in the core have an almost isotropic
motion, and they appear to reach virial equilibrium given their
velocity dispersion (0.9±0.3km/s) comparable to that in a virial
state (∼0.8km/s). On the other hand, the distributed population shows
a clear pattern of radial expansion. From the N-body simulation for
the dynamical evolution of a model cluster in subvirial state, we
reproduce the observed structure and kinematics of stars. This model
cluster experiences collapse for the first 2Myr. Some members begin to
radially escape from the cluster after the initial collapse,
eventually forming a distributed population. The internal structure
and kinematics of the model cluster appear similar to those of W4. Our
results support the idea that the stellar population distributed over
20pc in W4 originate from the dynamical evolution of IC1805.
Description:
We observed 198 low-mass pre-main-sequence (PMS) star candidates on
2018 November 29 using the high-resolution multi-object spectrograph
Hectochelle on the 6.5m telescope of the Multi-Mirror Telescope (MMT)
observatory. The spectra of these stars were taken with the RV31
filter in 2x2 binning mode to achieve good signal-to-noise ratios.
Stars with proper motions within three times the standard deviations
from the weighted mean values were selected as genuine members; a
total of 127 members (55 early-type and 72 PMS stars) were selected.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 132 127 Catalogue of kinematic members
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/AJ/105/499 : OB Associations and Spiral Structure in M33 (Regan+ 1993)
J/ApJ/454/151 : OB Associations of the Northern Milky Way (Massey+ 1995)
J/AJ/120/333 : UBVRI and Hα in NGC 6530 (Sung+, 2000)
J/A+A/371/497 : OB associations in spiral galaxy NGC 300 (Pietrzynski+, 2001)
J/AJ/128/805 : Low-mass stars in Cepheus OB2 region (Sicilia-Aguilar+, 2004)
J/AJ/134/1368 : Proper motions in NGC 2244 and NGC 6530 (Chen+, 2007)
J/ApJ/688/1142 : Star formation in W5: Spitzer observations (Koenig+, 2008)
J/A+A/502/1015 : OB associations in IC 1613 (Garcia+, 2009)
J/ApJ/726/19 : Intermediate-mass stars in IC 1805 (Wolff+, 2011)
J/ApJ/746/15 : Runaway massive stars from R136 (Banerjee+, 2012)
J/A+A/537/A146 : Stellar models rotation. 0.8<M<120, Z=0.014 (Ekstrom+, 2012)
J/AJ/145/37 : UBVI and Hα CCD photometry of NGC 6231 (Sung+, 2013)
J/MNRAS/443/454 : UBVIHα photometry in NGC 1893 (Lim+, 2014)
J/A+A/594/A82 : XMM sources in IC 1805 (Rauw+, 2016)
J/ApJS/230/3 : Optical & Spitzer photometry in IC 1805 (Sung+, 2017)
J/A+A/618/A93 : Gaia DR2 open clusters in the Milky Way (Cantat-Gaudin+, 2018)
J/MNRAS/477/1993 : NGC 1893 stars LSR velocities (Lim+, 2018)
J/AJ/157/109 : Stellar proper motions in the Orion Nebula Cluster (Kim+, 2019)
J/ApJ/870/32 : Kinematics in young star clusters & associations (Kuhn+, 2019)
J/ApJ/884/6 : Known members of Orion A with Gaia DR2 data (McBride+, 2019)
J/AJ/157/112 : IR photometry of YSOs in the W4 cloud complex (Panwar+, 2019)
J/ApJ/873/66 : Massive stars SDSS/APOGEE-2. II. W3-W4-W5 (Roman-Lopes+, 2019)
J/AJ/159/272 : Orion Nebula Cluster PMs HST Treasury Program (Platais+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/127] Sequential number
5- 6 I2 h RAh [2] Hour of Right Ascension (J2000)
8- 9 I2 min RAm [29/35] Minute of Right Ascension (J2000)
11- 15 F5.2 s RAs Second of Right Ascension (J2000)
17- 17 A1 --- DE- [+] Sign of the Declination (J2000)
18- 19 I2 deg DEd [61] Degree of Declination (J2000)
21- 22 I2 arcmin DEm [9/48] Arcminute of Declination (J2000)
24- 27 F4.1 arcsec DEs Arcsecond of Declination (J2000)
29- 34 F6.4 mas Plx [0.31/0.64] Absolute parallax from Gaia DR2
36- 41 F6.4 mas e_Plx [0.01/0.2] Uncertainty in Plx
43- 48 F6.3 mas/yr pmRA [-1.1/-0.32] Gaia DR2 Proper motion, in
right-ascension
50- 54 F5.3 mas/yr e_pmRA [0.02/0.2] Uncertainty in pmRA
56- 61 F6.3 mas/yr pmDE [-1.4/-0.22] Gaia DR2 proper motion, in
declination
63- 67 F5.3 mas/yr e_pmDE [0.03/0.229] Uncertainty in pmDE
69- 75 F7.4 mag Gmag [8.28/17.95] Gaia DR2 G band magnitude
77- 82 F6.4 mag e_Gmag [0.0002/0.02] Uncertainty in Gmag
84- 90 F7.4 mag BPmag [8.55/19.01] Gaia DR2 BP band magnitude
92- 97 F6.4 mag e_BPmag [0.0007/0.1017] Uncertainty in BBmag
99-105 F7.4 mag RPmag [7.88/16.86] Gaia DR2 RB band magnitude
107-112 F6.4 mag e_RPmag [0.0005/0.09] Uncertainty in RPmag
114-121 F8.3 km/s RVel [-117.1/-10.09]? Radial Velocity
123-128 F6.3 km/s e_RVel [0.4/15]? Uncertainty in RVel
130-132 A3 --- Bin Binarity flag; SB2 = double-lined spectroscopic
binary candidate (2 occurrences)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 18-Oct-2021