J/AJ/151/126 Photometry of YSOs in eight bright-rimmed clouds (Sharma+, 2016)
Structural studies of eight bright rimmed clouds in the southern hemisphere.
Sharma S., Pandey A.K., Borissova J., Ojha D.K., Ivanov V.D., Ogura K.,
Kobayashi N., Kurtev R., Gopinathan M., Yadav R.K.
<Astron. J., 151, 126-126 (2016)>
=2016AJ....151..126S 2016AJ....151..126S (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; YSOs ; Photometry, infrared ; Morphology
Keywords: stars: formation - stars: pre-main sequence
Abstract:
We carried out deep- and wide-field near- and mid-infrared
observations for a sample of eight bright-rimmed clouds (BRCs).
Supplemented with the Spitzer archival data, we have identified and
classified 44 to 433 young stellar objects (YSOs) associated with
these BRCs. The Class I sources are generally located toward the
places with higher extinction and are relatively closer to each other
than the Class II sources, confirming that the young protostars are
usually found in regions with denser molecular material. On the other
hand the comparatively older population, Class II objects, are more
randomly found throughout the regions, which can be due to their
dynamical evolution. Using the minimal sampling tree analyses, we have
extracted 13 stellar cores of eight or more members, which contain 60%
of the total YSOs. The typical core is ∼0.6pc in radii and somewhat
elongated (aspect ratio of 1.45), of relatively low stellar density
(surface density 60pc-2), consisting of a small (35) number of YSOs
of relatively young sources (66% Class I), and partially embedded
(median AK=1.1mag). But the cores show a wide range in their mass
distribution (∼20 to 2400M☉), with a median value of around
130M☉. We found the star-formation efficiencies in the cores to
be between 3% and 30% with an average of ∼14%, which agrees with the
efficiencies needed to link the core mass function to the initial mass
function. We also found a linear relation between the density of the
clouds and the number of YSOs. The peaked nearest neighbor spacing
distributions of the YSOs and the ratio of Jeans lengths to the YSO
separations indicates a significant degree of non-thermally driven
fragmentation in these BRCs.
Description:
Near-infrared (J, H, K') data for eight selected Bright-Rimmed Clouds
(BRCs) along with two nearby field regions (see Table1) were collected
with the Infrared Side Port Imager (ISPI) camera
(FOV∼10.5*10.5arcmin2; scale 0.3arcsec/pixel) on the 4m Blanco
telescope at Cerro Tololo Inter-American Observatory (CTIO), Chile,
during the nights of 2010 March 03-04. The seeing was ∼1arcsec. The
individual exposure times were 60 s per frame for all filters. The
total exposure time for the target fields was 540s for each J, H, and
K' band.
We also used the infrared archived data taken from the Infrared Array
Camera (IRAC) of the space-based Spitzer telescope at the 3.6, 4.5,
5.8, and 8.0µm bands. We obtained Basic Calibrated Data (BCD) from
the Spitzer data archive for all BRCs (except SFO 76, which has no
Spitzer data). The exposure time of each BCD was 10.4s
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 71 10 Regions observed in the present study
table3.dat 130 1347 YSOs identified on the basis of their excess
IR-emission using CTIO/Spitzer data
table4.dat 52 21 Center coordinates of the identified cores and
active regions
table5.dat 86 21 Properties of the identified cores and active
regions
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See also:
J/MNRAS/443/1614 : YSOs in BRC 5, 7 and 39 (Panwar+, 2014)
J/MNRAS/396/964 : T Tauri in and around bright-rimmed clouds (Chauhan+, 2009)
J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)
J/AJ/135/2323 : Hα stars and HH objects near BRCs (Ikeda+, 2008)
J/PASJ/51/791 : Molecular clouds in southern HII regions (Yamaguchi+ 1999)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Name of the region observed (1)
9- 10 I2 h RAh Hour of Right Ascension (J2000)
12- 13 I2 min RAm Minute of Right Ascension (J2000)
15- 18 F4.1 s RAs Second of Right Ascension (J2000)
20 A1 --- DE- Sign of the Declination (J2000)
21- 22 I2 deg DEd Degree of Declination (J2000)
24- 25 I2 arcmin DEm Arcminute of Declination (J2000)
27- 28 I2 arcsec DEs Arcsecond of Declination (J2000)
30- 39 F10.6 deg GLON Galactic longitude (l)
41- 49 F9.6 deg GLAT Galactic latitude (b)
51- 54 F4.2 kpc Dist [0.95/2.8]? Heliocentric distance (2)
56- 61 F6.4 pc pix [0.0014/0.0041]? Pixel size
63- 66 F4.2 Msun Mass1 [0.03/0.8]? Stellar mass at the 90% completeness
limit of Young Stellar Object (YSO) detection (3)
68- 71 F4.2 Msun Mass2 [0.1/3]? Stellar mass at the 90% completeness
limit of YSO detection (4)
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Note (1): We selected eight triggered Bright-Rimmed Clouds (BRCs) from the SFO
catalog of 89 BRCs (Sugitani, Fukui, and Ogura, 1991ApJS...77...59S 1991ApJS...77...59S;
Sugitani & Ogura, 1994ApJS...92..163S 1994ApJS...92..163S).
Note (2): Taken from the available literature (Yamaguchi et al. 1999,
cat. J/PASJ/51/791; Urquhart et al. 2009A&A...497..789U 2009A&A...497..789U, and references
therein) and were derived mostly from the photometric data of the O-type
stars that are being assigned as the exciting star(s) of the HII regions in
which these bright-rimmed clouds are located.
Note (3): After correcting foreground extinction value (see Section 3.2).
Note (4): After correcting peak extinction value (see Section 3.2).
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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- 5 A5 --- Name Name of the Bright-Rimmed Cloud (BRC)
7- 9 I3 --- YSO [1/433] Identifier of the Young Stellar Object
11- 12 I2 h RAh Hour of Right Ascension (J2000)
14- 15 I2 min RAm Minute of Right Ascension (J2000)
17- 21 F5.2 s RAs Second of Right Ascension (J2000)
23 A1 --- DE- Sign of the Declination
24- 25 I2 deg DEd Degree of Declination (J2000)
27- 28 I2 arcmin DEm Arcminute of Declination (J2000)
30- 33 F4.1 arcsec DEs Arcsecond of Declination (J2000)
35- 40 F6.3 mag Jmag [5.417/19.505]? CTIO Blanco/ISPI J band magnitude
42- 46 F5.3 mag e_Jmag [0.002/0.198]? Uncertainty in Jmag
48- 53 F6.3 mag Hmag [4.601/19.398]? CTIO Blanco/ISPI H band magnitude
55- 59 F5.3 mag e_Hmag [0.002/0.237]? Uncertainty in Hmag
61- 66 F6.3 mag Kmag [4.16/17.819]? CTIO Blanco/ISPI K band magnitude
68- 72 F5.3 mag e_Kmag [0.002/0.29]? Uncertainty in Kmag
74- 79 F6.3 mag [3.6] [6.4/15.6]? Spitzer/IRAC 3.6µm band magnitude
81- 85 F5.3 mag e_[3.6] [0.02/0.2]? Uncertainty in [3.6]
87- 92 F6.3 mag [4.5] [5.4/14.9]? Spitzer/IRAC 4.5µm band magnitude
94- 98 F5.3 mag e_[4.5] [0.01/0.2]? Uncertainty in [4.5]
100-105 F6.3 mag [5.8] [4.5/13.2]? Spitzer/IRAC 5.8µm band magnitude
107-111 F5.3 mag e_[5.8] [0.01/0.2]? Uncertainty in [5.8]
113-118 F6.3 mag [8.0] [3.3/13.2]? Spitzer/IRAC 8.0µm band magnitude
120-124 F5.3 mag e_[8.0] [0.006/0.2]? Uncertainty in [8.0]
126 I1 --- Cl [1/4]? First classification flag (1-4) (1)
128 I1 --- II [5]? Flag "5"=class II through CTIO data) (1)
130 I1 --- I [6]? Flag "6"=class I through CTIO data) (1)
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Note (1): Scheme used to classify the YSOs is defined as below:
1 = Class I (through Spitzer data);
2 = Class II (through Spitzer data);
3 = Class I (through CTIO/Spitzer data);
4 = Class II (through CTIO/Spitzer data);
5 = Class II (through Cerro Tololo Inter-American Observatory (CTIO) data);
6 = Class I (through CTIO data).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Name Name of the Bright-Rimmed Cloud (BRC)
7- 8 A2 --- Reg C#=core, A=active region
10- 11 I2 h RAh Hour of Right Ascension (J2000)
13- 14 I2 min RAm Minute of Right Ascension (J2000)
16- 19 F4.1 s RAs Second of Right Ascension (J2000)
21 A1 --- DE- Sign of the Declination (J2000)
22- 23 I2 deg DEd Degree of Declination (J2000)
25- 26 I2 arcmin DEm Arcminute of Declination (J2000)
28- 29 I2 arcsec DEs Arcsecond of Declination (J2000)
31- 33 I3 --- NYSO [8/269] Number of Young Stellar Objects (YSOs)
35- 37 I3 --- NI1 [0/181] Number of class I YSOs
39- 40 I2 --- NI2 [0/12] Number of class I YSOs (classified by
using the Spitzer/IRAC data)
42- 43 I2 --- NII1 [1/88] Number of class II YSOs
45- 46 I2 --- NII2 [0/45] Number of class II YSOs (classified by
using the Spitzer/IRAC data)
48- 49 I2 % FI1 [38/91]? Class I YSOs fraction (NI1/NYSO*100) (1)
51- 52 I2 % FI2 [0/50]? Class I YSOs fraction by using the
Spitzer/IRAC data (NI2/(NI2+NII2))
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Note (1): We calculated the fraction of the Class I objects among all the YSOs
as an indicator of the "star-formation age" of a region.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Name Name of the Bright-Rimmed Cloud (BRC)
7- 8 A2 --- Reg C#=core, A=active region
10- 13 F4.2 pc Rhull [0.18/2.63] The hull radius (2)
15- 18 F4.2 pc Rcir [0.24/3.22] The circle radius (3)
20- 23 F4.2 --- Ratio [0.89/2.36] Aspect ratio (4)
25- 30 F6.2 pc-2 [4.2/331.9] Mean stellar surface density
(ρmean) (5)
32- 37 F6.1 pc-2 rpk [17/1330.4] Peak stellar surface density
(ρpeak) (5)
39- 42 F4.2 pc [0.04/0.32] Mean Minimal Sampling Tree (MST)
branch length (6)
44- 47 F4.2 pc [0.03/0.15] Mean Nearest Neighbor (NN) distance
49- 52 F4.2 mag [0.42/1.64] The mean extinction value (AKmean)
54- 57 F4.2 mag AK [0.86/2.84] The peak extinction value (AKpeak)
59- 64 F6.1 Msun Mhull [19.8/5286.7] The cloud mass in the convex hull
derived using the extinction maps
66- 71 F6.1 Msun M0.8 [2.2/4601.4] The mass of the dense cloud with AK
greater that 0.8mag (7)
73- 76 F4.2 --- Q [0.55/0.85] The structural Q parameter value (8)
78- 81 F4.2 pc J [0.23/1.21] The Jeans length (λJ) (9)
83- 86 F4.2 pc Dcrit [0.12/0.84] The critical branch length for Minimal
Sampling Tree (MST) (Dcrit.)
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Note (2):
See Gutermuth et al. 2009 (cat. J/ApJS/184/18):
* "The effective radial size, Rhull is the square root of the area
(divided by π) of the convex hull that contains each grouping,
adjusted to account for the fraction of sources that are vertices of the
convex hull (Aadjusted=Ahull/(1-nhull/ntotal); Schmeja & Klessen,
2006A&A...449..151S 2006A&A...449..151S). This is an effective radius that accounts for the
often elongated geometries..."
* "The convex hull of a set of points in two dimensions is the minimum area
polygon that contains those points such that all internal angles between
adjacent edges are less than 180°."
Note (3): See Gutermuth et al. 2009 (cat. J/ApJS/184/18):
"The circular radial size, Rcirc, is calculated as half of the largest
distance between any two members, the radius of the minimum area circle
that encloses the entire grouping."
Note (4): See Gutermuth et al. 2009 (cat. J/ApJS/184/18):
"The ratio R2circ/R2hull corresponds to the aspect ratio of
elongated distributions."
Note (5): Obtained using the isodensity contours. See Section 4.2.2 in the paper
for additional details.
Note (6): All the studied bright-rimmed clouds contain a number of subgroups or
cores of young stellar objects, presumably due to fragmentation of the
molecular cloud. The physical parameters of these cores, which might have
formed in a single star-forming event, play a very important role in the
study of star formation. Minimal Sampling Tree (MST) technique (see
Gutermuth et al. 2009, Cat. J/ApJS/184/18) is used to isolate star-forming
stellar cores from a diffuse, sparsely distributed, and potentially varying
density background. We extracted 13 stellar cores of eight or more members.
The active regions in all studied bright-rimmed clouds contain in total 997
young stellar objects, out of which 602 (60%) belong to the cores. The
median MST branch length in these cores is found to be 0.09pc. The members
of these cores are mostly younger young stellar objects.
Note (7): Lada et al. (2010ApJ...724..687L 2010ApJ...724..687L) found that the number of young
stellar objects in a cluster is directly proportional to the dense cloud
mass M0.8 (the mass above a column density equivalent to AK∼0.8mag)
with a slope equal to one.
Note (8): The spatial distribution of young stellar objects associated with the
bright-rimmed clouds is also investigated by their structural Q parameter
values. The Q parameter (Cartwright & Whitworth, 2004MNRAS.348..589C 2004MNRAS.348..589C;
Schmeja & Klessen, 2006A&A...449..151S 2006A&A...449..151S) is used to measure the level of
hierarchical versus radial distributions of a set of points, and is defined
by the ratio of the Minimal Sampling Tree (MST) normalized mean branch
length and the normalized mean separation between points (cf. Chavarria et
al. 2014MNRAS.439.3719C 2014MNRAS.439.3719C, for details). Please refer to Section 4.2.4 in
the paper for further details.
Note (9): Gutermuth et al. 2009 (cat. J/ApJS/184/18) analyzed the young stellar
object spacings of the young stellar objects in the stellar cores of 36
star-forming clusters and suggested that Jeans fragmentation is a starting
point for understanding the primordial structure in star-forming regions.
We also calculated the minimum radius required for the gravitational
collapse of a homogeneous isothermal sphere (Jeans length "λJ") in
order to investigate the fragmentation scale by using the formulae given in
Chavarria et al. (2014MNRAS.439.3719C 2014MNRAS.439.3719C). See Section 4.2.6 for more details.
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(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 11-Aug-2016