J/ApJ/682/445 Spitzer observations of S254-S258 (Chavarria+, 2008)
Spitzer observations of the massive star-forming complex S254-S258: structure
and evolution.
Chavarria L.A., Allen L.E., Hora J.L., Brunt C.M., Fazio G.G.
<Astrophys. J., 682, 445-462 (2008)>
=2008ApJ...682..445C 2008ApJ...682..445C
ADC_Keywords: H II regions ; Photometry, infrared ; YSOs
Mission_Name: Spitzer
Keywords: H II regions - infrared: stars - stars: early-type -
stars: formation - stars: pre-main sequence
Abstract:
We present Spitzer IRAC, NOAO 2.1m Flamingos, Keck NIRC, and FCRAO
SEQUOIA observations of the massive star-forming complex S254-S258,
covering an area of 25'x20'. Using a combination of the IRAC and NIR
data, we identify and classify the young stellar objects (YSOs) in the
complex. We detect 510 sources with near- or mid-IR excess, and we
classify 87 Class I and 165 Class II sources. The YSOs are found in
clusters surrounded by isolated YSOs in a low-density distributed
population. The ratio of clustered to total YSOs is 0.8. We identify
six new clusters in the complex. One of them, G192.63-00, is located
around the ionizing star of the HII region S255. We hypothesize that
the ionizing star of S255 was formed in this cluster. We also detect a
southern component of the cluster in HII region S256. The cluster
G192.54-0.15, located inside HII region S254 has a VLSR of 17km/s
with respect to the main cloud, and we conclude that it is located in
the background of the complex. The structure of the molecular cloud is
examined using 12CO, and 13CO, as well as a near-IR extinction
map. The main body of the molecular cloud has VLSR between 5 and
9km/s. The arc-shaped structure of the molecular cloud following the
border of the HII regions and the high column density in the border of
the HII regions support the idea that the material has been swept up
by the expansion of the HII regions.
Description:
We observed the complex S254-S258 in mid-IR with the Spitzer Space
Telescope in 2004 December and 2007 October;
in NIR with Flamingos at the 2.1m telescope located at Kitt Peak
National Observatory in 2004 December and 2006 January. NIRC
observations of S255-2 were generously supplied by L. Hillenbrand. The
data includes observations in H and K bands, which were taken using
the Keck telescope in 1999.
Observations of the J=1-0 spectral lines of 12CO, and 13CO, were
conducted at the Five College Radio Astronomy Observatory (FCRAO) 14m
telescope in New Salem, Massachusetts.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 140 26821 JHK and Spitzer photometry of sources
table4.dat 90 10 *Parameters of clusters
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Note on table4.dat: We assumed a distance of 2.4kpc from the Sun in the
estimation of physical parameters.
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See also:
J/ApJ/643/965 : Spitzer photometry of the Trifid nebula (M20) (Rho+, 2006)
J/ApJ/642/972 : IR photometry of a star-forming core in NGC 2264 (Young+,
2006)
J/ApJS/177/551 : Spitzer c2d survey of Lupus dark clouds (Merin+, 2008)
J/ApJ/675/1375 : IRAC/MIPS photometry in Cha I (Luhman+, 2008)
J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)
J/A+A/503/107 : Spitzer/IRAC view of Sh2-284 (Puga+, 2009)
J/BaltA/19/1 : YSOs in Camelopardalis (Straizys+, 2010)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 F8.5 deg RAdeg Right Ascension in decimal degrees (J2000)
10- 17 F8.5 deg DEdeg Declination in decimal degrees (J2000)
19- 25 F7.3 mag Jmag ?=-99.99 KPNO/FLAMINGOS J band magnitude (1.24um)
27- 33 F7.3 mag e_Jmag ?=-99.99 Error in Jmag
35- 41 F7.3 mag Hmag ?=-99.99 KPNO/FLAMINGOS H band magnitude (1.65um)
43- 49 F7.3 mag e_Hmag ?=-99.99 Error in Hmag
51- 57 F7.3 mag Kmag ?=-99.99 KPNO/FLAMINGOS K band magnitude (2.21um)
59- 65 F7.3 mag e_Kmag ?=-99.99 Error in Kmag
67- 73 F7.3 mag 3.6um ?=-99.99 Spitzer/IRAC 3.6 micron band magnitude
75- 81 F7.3 mag e_3.6um ?=-99.99 Error in 3.6um
83- 89 F7.3 mag 4.5um ?=-99.99 Spitzer/IRAC 4.5 micron band magnitude
91- 97 F7.3 mag e_4.5um ?=-99.99 Error in 4.5um
99-105 F7.3 mag 5.8um ?=-99.99 Spitzer/IRAC 5.8 micron band magnitude
107-113 F7.3 mag e_5.8um ?=-99.99 Error in 5.8um
115-121 F7.3 mag 8.0um ?=-99.99 Spitzer/IRAC 8.0 micron band magnitude
123-129 F7.3 mag e_8.0um ?=-99.99 Error in 8.0um
131-140 F10.6 --- alpha ?=-99.99 Observed IRAC SED slope (αIRAC)
(1)
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Note (1): Spectral energy distribution (SED) slope is defined as
α=(dlog(λFλ))/(dlog(λ)) (equation 1).
Relations between classes and αIRAC are
(see section 3.2 for further details):
Class I = 0<αIRAC; star plus infalling envelope.
There could be some Class 0 sources in our Class I category,
but we are not able to separate them.
Class II = -2≤αIRAC≤0; star plus a disk;
Class III = αIRAC←2; post T-Tauri star.
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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- 14 A14 --- Name Cluster name(s)
16 I1 h RAh Hour of right ascension (J2000)
18- 19 I2 min RAm Minute of right ascension (J2000)
21- 22 I2 s RAs Second of right ascension (J2000)
24 A1 --- DE- Declination sign (J2000)
25- 26 I2 deg DEd Degree of declination (J2000)
28- 29 I2 arcmin DEm Arcminute of declination (J2000)
31- 32 I2 arcsec DEs Arcsecond of declination (J2000)
34- 36 I3 --- IR Number of stars with IR-excess, including Class
I and Class II.
38- 40 I3 --- N Corrected number of cluster members, see
section 4.2
42- 43 I2 --- I Number of Class I sources
45- 46 I2 --- II Number of Class II sources
48- 51 F4.2 --- I/II ? Ratio of Class II to Class I sources
52 A1 --- f_I/II [g] missed sources (1)
54- 57 F4.2 --- I/IR Ratio of Class I to IR-excess sources
59- 60 I2 pc-2 sigs Mean surface density of stars
62- 64 I3 pc-2 sigsM Peak surface density of stars
66- 72 E7.2 cm-2 sigg Mean 13CO surface density
74- 80 E7.2 cm-2 siggM Peak 13CO surface density
82- 85 I4 solMass Mgas Mass of gas in the cluster
87- 90 F4.2 --- eps Star formation efficiency (2)
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Note (1):
g = Likely to have missed some Class II objects (see end of section 3.2.2).
Note (2): Star formation efficiency of clusters is defined in equation 6 as:
ε=Mstars/(Mstars+Mgas) See section 4.2 for further details.
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Nomenclature notes:
In table 2, sources are <[CAH2008] DD.dddddd+DD.ddddd> in Simbad.
In table 4, new clusters are <[CAH2008] GLLL.ll+B.bb> in Simbad.
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 18-Nov-2010