J/AJ/158/201 Young star cluster Westerlund 2 observed with MUSE (Zeidler+, 2019)
The young massive star cluster Westerlund 2 observed with MUSE.
II. MUSEpack - a Python package to analyze the kinematics of young star
clusters.
Zeidler P., Nota A., Sabbi E., Luljak P., McLeod A.F., Grebel E.K.,
Pasquali A., Tosi M.
<Astron. J., 158, 201-201 (2019)>
=2019AJ....158..201Z 2019AJ....158..201Z (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, open ; Spectroscopy
Keywords: Radial velocity - Young star clusters - Spectroscopy -
Pre-main sequence stars
Abstract:
We mapped the Galactic young massive star cluster Westerlund 2 with
the integral field spectrograph MUSE (spatial resolution: 0.2 arcsec/px,
spectral resolution: Δλ=1.25 Å, wavelength range:
4600-9350 Å) mounted on the Very Large Telescope. We present the fully
reduced data set and introduce our new Python package "MUSEpack", which
we developed to measure stellar radial velocities (RVs) with an absolute
precision of 1-2 km/s without the necessity of a spectral template library.
This novel method uses the two-dimensional spectra and an atomic transition
line library to create templates around strong absorption lines for each
individual star. Automatic, multi-core processing makes it possible to
efficiently determine stellar RVs of a large number of stars with the
necessary precision to measure the velocity dispersion of young star
clusters. MUSEpack also provides an enhanced method for removing telluric
lines in crowded fields without sky exposures, and a Python wrapper for
ESO's data reduction pipeline. We observed Westerlund 2 with a total
of 11 short and 5 long exposures (survey area: ∼11 arcmin2 or 15.8 pc2)
to cover the bright nebular emission and OB stars, as well as the fainter
pre-main-sequence stars (≥1 M☉). We extracted 1725 stellar spectra
with a mean signal-to-noise ratio of S/N>5 per pixel. Typical RV
uncertainties of 4.78 km/s, 2.92 km/s, and 1.1 km/s are reached for stars
with a mean S/N>10, S/N>20, and S/N>50 per pixel, respectively. It is
possible to reach RV accuracies of 0.9 km/s, 1.3 km/s, and 2.2 km/s with
≥5, 3-4, and 1-2 spectral lines used to measure the RVs, respectively.
The combined statistical uncertainty on the RV measurements is 1.10 km/s.
Description:
Westerlund 2 was observed with MUSE in extended mode, both with and
without adaptive optics (AO) during the ESO periods 97 and 99 (Program
ID: 097.C-0044(A), 099.C-0248(A), PI: P. Zeidler). In total, we
acquired 16 pointings with three dither positions each, with a total
telescope time (exposure time + overheads) of almost 21 hr. The dither
pattern follows a 90° and 180° rotation strategy to minimize
detector defects and impurities. Eleven out of the 16 pointings are
obtained with a total exposure time of 660 s (hereafter: short
exposures), while the remaining five pointings have a total exposure
time of 10800 s (hereafter: long exposures). An overview of all
pointings is given in Table 1.
Objects:
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RA (ICRS) DE Designation(s)
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10 23 58.1 -57 45 49 Westerlund 2 = Cl Westerlund 2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 87 48 Overview of the observations
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See also:
J/AJ/102/642 : UBV photometry in Westerlund 2 (Moffat+, 1991)
J/A+AS/127/423 : VI photometry of Westerlund 1 and 2 (Piatti+ 1998)
J/A+A/463/981 : BV CCD photometry in Westerlund 2 (Rauw+, 2007)
J/A+A/466/137 : Westerlund 2 JHKs photometry (Ascenso+, 2007)
J/A+A/555/A50 : UBVIc photometry of stars in Westerlund 2 (Carraro+, 2013)
J/AJ/145/125 : Spectroscopy and HST photometry in Westerlund 2
(Vargas+, 2013)
J/MNRAS/446/3797 : Westerlund 2 UBVIc photometry (Hur+, 2015)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Hour of Right Ascension (J2000)
4- 5 I2 min RAm Minute of Right Ascension (J2000)
7- 11 F5.2 s RAs Second of Right Ascension (J2000)
13 A1 --- DE- Sign of the Declination (J2000)
14- 15 I2 deg DEd Degree of Declination (J2000)
17- 18 I2 arcmin DEm Arcminute of Declination (J2000)
20- 24 F5.2 arcsec DEs Arcsecond of Declination (J2000)
26- 36 A11 "date" Date Date of observation
38- 48 A11 --- Name Name of exposure
50- 56 I7 --- ID [1323877/1987401] Observing block (OB) ID (1)
58- 61 I4 s Texp [220/3600] Exposure time
63- 66 F4.2 arcsec Seeing1 [0.41/1.5] First value of seeing
68- 71 F4.2 arcsec Seeing2 [0.42/1.5] Second value of seeing
73- 77 F5.3 --- AirM1 [1.195/1.468] First value of airmass
79- 83 F5.3 --- AirM2 [1.196/1.593] Second value of airmass
85- 87 A3 --- AO [yes/no] Whether this pointing was obtained using
wide-field mode with adaptive optics (WFM-AO)
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Note (1): OBs that had to be repeated do not appear in this table. We grouped
the three exposures that are combined into one pointing.
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History:
From electronic version of the journal
References:
Zeidler et al. Paper I. 2018AJ....156..211Z 2018AJ....156..211Z
(End) Tiphaine Pouvreau [CDS] 17-Jan-2020