J/MNRAS/446/3797 Westerlund 2 UBVIc photometry (Hur+, 2015)
Reddening, distance, and stellar content of the young open cluster Westerlund 2.
Hur H., Park B.-G., Sung H., Bessell M.S., Lim B., Chun M.-Y., Sohn S.T.
<Mon. Not. R. Astron. Soc., 446, 3797-3819 (2015)>
=2015MNRAS.446.3797H 2015MNRAS.446.3797H (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Photometry, UBVRI ; Photometry, infrared
Keywords: stars: luminosity function, mass function - stars: pre-main-sequence -
open clusters and associations: individual: Westerlund 2
Abstract:
We present deep UBVIc photometric data of the young open cluster
Westerlund 2. An abnormal reddening law of RV,cl=4.14±0.08 was
found for the highly reddened early-type members (E(B-V)≥1.45),
whereas a fairly normal reddening law of RV,fg=3.33±0.03 was
confirmed for the foreground early-type stars (E(B-V)fg<1.05). The
distance modulus was determined from zero-age main-sequence fitting to
the reddening-corrected colour-magnitude diagram of the early-type
members to be V0-MV=13.9±0.14 (random error) -0.1+0.4 (the
upper limit of systematic error) mag (d=6.0±0.4-0.3+1.2kpc). To
obtain te initial mass function, pre-main-sequence (PMS) stars were
selected by identifying the optical counterparts of Chandra X-ray
sources and mid-infrared emission stars from the Spitzer GLIMPSE
(Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) source
catalogue. The initial mass function shows a shallow slope of
Γ=-1.1±0.1 down to log(m)=0.7. The total mass of Westerlund 2
is estimated to be at least 7400M☉. The age of Westerlund 2 from
the main-sequence turn-on and PMS stars is estimated to be ≲1.5Myr.
We confirmed the existence of a clump of PMS stars located ∼1-arcmin
north of the core of Westerlund 2, but we could not find any clear
evidence for an age difference between the core and the northern
clump.
Description:
Deep UBVIC observations were obtained on 2009 March 28 and 29 with
the 8kx8k Mosaic II CCD camera (0.268arcsec/pix) of the 4m
Blanco telescope at Cerro Tololo Inter-American Observatory (CTIO). We
used the SDSS u filter for U-band photometry and the Harris BVI filter
set for BVIC photometry. The exposure times were 7 and 150s in I, 10
and 300s in V, 20 and 300s in B, and 100 and 1200 s in u. The
average seeing was ∼0.9-arcsec.
For the photometry of bright stars and for the standardization of U-B,
we performed additional observations with the Y4KCam CCD camera and
UBVIC filter set of the 1m telescope at CTIO on 2011 March 5. The
exposure times were 5 and 180s in I, 5 and 180s in V, 10 and 300s
in B, and 30 and 600s in U.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 158 17679 The combined photometric data obtained with the
CTIO 4m and 1m telescopes
table6.dat 96 144 *V-NIR colours and the reddening-corrected
magnitude and colours of the early-type stars
--------------------------------------------------------------------------------
Note on table6.dat: derived using equation (5).
--------------------------------------------------------------------------------
See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/293 : GLIMPSE Source Catalog (I + II + 3D) (IPAC 2008)
J/A+A/466/137 : Westerlund 2 JHKs photometry (Ascenso+, 2007)
J/AJ/102/642 : UBV photometry in Westerlund 2 (Moffat+, 1991)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- Seq Sequential number
7- 8 I2 h RAh Right ascension (J2000)
10- 11 I2 min RAm Right ascension (J2000)
13- 17 F5.2 s RAs Right ascension (J2000)
19 A1 --- DE- Declination sign (J2000)
20- 21 I2 deg DEd Declination (J2000)
23- 24 I2 arcmin DEm Declination (J2000)
26- 29 F4.1 arcsec DEs Declination (J2000)
31- 36 F6.3 mag Vmag ? Johnson V magnitude
38- 43 F6.3 mag Imag ? Cousins I magnitude
45- 50 F6.3 mag U-B ? Johnson U-B colour index
52- 57 F6.3 mag B-V ? Johnson B-V colour index
59- 64 F6.3 mag V-I ? Johnson-Cousins V-I colour index
66- 70 F5.3 mag e_Vmag ? rms uncertainty on Vmag
72- 76 F5.3 mag e_Imag ? rms uncertainty on Imag
78- 82 F5.3 mag e_U-B ? rms uncertainty on U-B
85- 89 F5.3 mag e_B-V ? rms uncertainty on B-V
92- 96 F5.3 mag e_V-I ? rms uncertainty on V-I
99 I1 --- o_Vmag Number of observations for Vmag
101 I1 --- o_Imag Number of observations for Imag
103 I1 --- o_U-B Number of observations for U-B
105 I1 --- o_B-V Number of observations for B-V
107 I1 --- o_V-I Number of observations for V-I
109-113 A5 --- Rem [123DEUXe ] Remarks (1)
116-118 I3 --- MSP ? ID in Moffat et al. (1991,
Cat. J/AJ/102/642),
Cl* Westerlund 2 MSP NNN in Simbad
120-123 I4 --- A07 ? ID in Ascenso et al. (2007,
Cat. J/A+A/466/137),
Cl* Westerlund 2 AAB NNNN in Simbad
125-140 A16 --- 2MASS 2MASS designation (HHMMSSss+DDMMSSs)
142-158 A17 --- GLIMPSE GLIMPSE designation (GLLL.llll+BB.bbbb)
--------------------------------------------------------------------------------
Note (1): Remarks as follows:
D = photometric doubles
X = X-ray emission stars
U = red leak affected by a close neighbour
E = the early-type members with E(B-V)≥1.45
e = the foreground early-type stars with E(B-V)<1.45
1 = class 0/I
2 - class II
3 = class III
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- Seq Sequential number
7- 11 F5.3 mag V-J ? V-J colour index
13- 17 F5.3 mag V-H ? V-H colour index
19- 23 F5.3 mag V-Ks ? V-Ks colour index
25- 29 F5.3 mag e_V-J ? rms uncertainty on V-J
32- 36 F5.3 mag e_V-H ? rms uncertainty on V-H
39- 43 F5.3 mag e_V-Ks ? rms uncertainty on V-Ks
46- 51 F6.3 mag V0mag Reddening-corrected V magnitude (1)
53- 58 F6.3 mag (U-B)0 Reddening-corrected U-B colour index
60- 65 F6.3 mag (B-V)0 Reddening-corrected B-V colour index
67- 72 F6.3 mag (V-I)0 ? Reddening-corrected V-I colour index
74- 79 F6.3 mag (V-J)0 ? Reddening-corrected V-J colour index
81- 86 F6.3 mag (V-H)0 ? Reddening-corrected V-H colour index
88- 93 F6.3 mag (V-Ks)0 ? Reddening-corrected V-Ks colour index
95- 96 A2 --- Rem [BDUb ] Remarks (2)
--------------------------------------------------------------------------------
Note (1): MV=V0-13.9mag (the distance modulus).
Note (2): Remarks as follows:
D = photometric doubles
U = red leak affected by a close neighbour
B = known binaries
b = binary candidates from table 1 of Rauw et al. (2011A&A...535A..40R 2011A&A...535A..40R)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 30-Jun-2015