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
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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 140 26821 JHK and Spitzer photometry of sources table4.dat 90 10 *Parameters of clusters
Note on table4.dat: We assumed a distance of 2.4kpc from the Sun in the estimation of physical parameters.
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
Bytes Format Units Label Explanations
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)
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.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
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)
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.
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
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