J/MNRAS/419/1887 Young stellar objects in NGC 6823 (Riaz+, 2012)
Young stellar objects in NGC 6823.
Riaz B., Martin E.L., Tata R., Monin J.-L., Phan-bao N., Bouy H.
<Mon. Not. R. Astron. Soc., 419, 1887-1912 (2012)>
=2012MNRAS.419.1887R 2012MNRAS.419.1887R (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, pre-main sequence ; Photometry, infrared ;
Photometry, VRI ; Photometry, millimetric/submm
Keywords: circumstellar matter - stars: low-mass - stars: pre-main-sequence -
open clusters and associations: individual: NGC 6823
Abstract:
NGC 6823 is a young open cluster that lies at a distance of ∼2kpc in
the Vulpecula OB1 association. Previous studies using CCD photometry
and spectroscopy have identified a Trapezium system of bright O- and
B-type stars at its centre, along with several massive O-, B- and
A-type stars in the cluster. We present optical VRI and near-infrared
JHK photometric observations, complemented with Spitzer/Infrared Array
Camera archival data, with an aim to identify the young low-mass
population and the disc candidates in this region. Our survey reaches
down to I∼22mag and Ks∼18mag. There is significant differential
reddening within the cluster. We find a bimodal distribution for AV,
with a peak at ∼3mag and a broader peak at ∼10mag. We have classified
the sources based on the [4.5]-[8] colour, which is least affected by
extinction. We find a ∼20 per cent fraction of Class I/Class II young
stellar objects (YSOs) in the cluster, while a large 80 per cent
fraction of the sources have a Class III classification. We have made
use of the INT Photometric Hα Survey (IPHAS) in order to probe
the strength in Hα emission for this large population of Class
III sources. Nearly all of the Class III objects have photospheric
(r'-Hα) colours, implying an absence of Hα in emission.
This large population of Class III sources is thus likely the extinct
field star population rather than the discless YSOs in the cluster.
There is a higher concentration of the Class I/II systems in the
eastern region of the cluster and close to the central Trapezium. The
western part of the cluster mostly contains Class III/field stars and
seems devoid of disc sources. We find evidence of a pre-main-sequence
population in NGC 6823, in addition to an upper main-sequence
population. The pre-main-sequence population mainly consists of young
disc sources with ages between ∼1 and 5Myr, and at lower masses of
∼0.1-0.4M☉. There may be a possible mass-dependent age spread in
the cluster, with the older stars being more massive than the younger
ones. The presence of young disc sources in NGC 6823 indicates similar
star formation properties in the outer regions of the Galaxy as
observed for young clusters in the solar neighbourhood.
Description:
The optical V-, R- and I-band images were obtained using the Prime
Focus camera [William Herschel Telescope (WHT)/Wide Field Camera (WFC)
detector] mounted on 4-m WHT in La Palma, Canary Islands, Spain.
Observations were performed in 2005 May,
The NIR J-, H-, Ks-band images were obtained using the Infrared Side
Port Imager (ISPI) mounted on Cerro Tololo Inter-American Observatory
(CTIO) 4-m Blanco Telescope in Cerro Tololo, Chile.
Observations were performed in 2007 March.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 138 490 Optical, NIR and MIR photometry
table2.dat 34 16 MIPS photometry
table3.dat 65 213 IPHAS photometry
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See also:
II/293 : GLIMPSE Source Catalog (I + II + 3D) (IPAC 2008)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 24 F5.2 arcsec DEs Declination (J2000)
26- 30 F5.2 mag Vmag ?=- WHT/WFC V magnitude
32- 35 F4.2 mag e_Vmag ? rms uncertainty on Vmag
37- 41 F5.2 mag Rmag ?=- WHT/WFC R magnitude
43- 46 F4.2 mag e_Rmag ? rms uncertainty on Rmag
48- 52 F5.2 mag Imag WHT/WFC I magnitude
54- 57 F4.2 mag e_Imag rms uncertainty on Imag
59- 63 F5.2 mag Jmag ?=- CTIO/ISPI J magnitude on 2MASS system
65- 68 F4.2 mag e_Jmag ? rms uncertainty on Jmag
70- 74 F5.2 mag Hmag ?=- CTIO/ISPI H magnitude on 2MASS system
76- 79 F4.2 mag e_Hmag ? rms uncertainty on Hmag
81- 85 F5.2 mag Ksmag ?=- CTIO/ISPI Ks magnitude on 2MASS system
87- 90 F4.2 mag e_Ksmag ? rms uncertainty on Ksmag
92- 96 F5.2 mag [3.6] IRAC 3.6um magnitude
98-101 F4.2 mag e_[3.6] rms uncertainty on [3.6]
103-107 F5.2 mag [4.5] IRAC 4.5um magnitude
109-112 F4.2 mag e_[4.5] rms uncertainty on [4.5]
114-118 F5.2 mag [5.8] IRAC 5.8um magnitude
120-123 F4.2 mag e_[5.8] rms uncertainty on [5.8]
125-129 F5.2 mag [8.0] IRAC 8.0um magnitude
131-134 F4.2 mag e_[8.0] rms uncertainty on [8.0]
136-138 A3 --- Class SED Class
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 24 F5.2 arcsec DEs Declination (J2000)
26- 30 F5.2 mag [24] ?=- MIPS 24um magnitude (1)
32- 34 A3 --- Class SED Class
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Note (1): The uncertainty on the 24-um photometry is estimated to be
<0.2mag (Billot et al., 2010, Cat. J/ApJ/712/797).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 24 F5.2 arcsec DEs Declination (J2000)
26- 30 F5.2 mag r'mag ?=- IPHAS r' magnitude
32- 36 F5.3 mag e_r'mag ? rms uncertainty on r'mag
38- 42 F5.2 mag i'mag ?=- IPHAS i' magnitude
44- 48 F5.3 mag e_i'mag ? rms uncertainty on i'mag
50- 54 F5.2 mag Hamag IPHAS Hα magnitude
56- 60 F5.3 mag e_Hamag rms uncertainty on Hamag
62- 64 A3 --- Class SED Class
65 A1 --- n_Class [*] Note on EW Ha (1)
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Note (1): * indicates sources that lie above the Hα EW=10Å track.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 17-Oct-2016