J/MNRAS/432/3445 YSOs on HII complex Sh2-252 (Jose+, 2013)
Young stellar population and ongoing star formation in the HII complex Sh2-252.
Jose J., Pandey A.K., Samal M.R., Ojha D.K., Ogura K., Kim J.S.,
Kobayashi N., Goyal A., Chauhan N., Eswaraiah C.
<Mon. Not. R. Astron. Soc., 432, 3445-3461 (2013)>
=2013MNRAS.432.3445J 2013MNRAS.432.3445J (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; YSOs ; Infrared sources
Keywords: stars: formation - stars: pre-main-sequence - HII regions -
ISM: individual objects: Sh2-252 - infrared: ISM
Abstract: In this paper, an extensive survey of the star-forming
complex Sh2-252 has been undertaken with an aim to explore its hidden
young stellar population as well as to understand the structure and
star formation history for the first time. This complex is composed of
five prominent embedded clusters associated with the subregions A, C,
E, NGC 2175s and Teu 136. We used Two Micron All Sky
Survey-near-infrared and Spitzer-Infrared Array Camera,
Multiband Imaging Photometer for Spitzer photometry to identify
and classify the young stellar objects (YSOs) by their infrared (IR)
excess emission. Using the IR colour-colour criteria, we identified
577 YSOs, of which, 163 are Class I, 400 are Class II and 14 are
transition disc YSOs, suggesting a moderately rich number of YSOs in
this complex. Spatial distribution of the candidate YSOs shows that
they are mostly clustered around the subregions in the western half of
the complex, suggesting enhanced star formation activity towards its
west. Using the spectral energy distribution and optical
colour-magnitude diagram-based age analyses, we derived probable
evolutionary status of the subregions of Sh2-252. Our analysis shows
that the region A is the youngest (∼0.5Myr), the regions B, C and E
are of similar evolutionary stage (∼1-2Myr) and the clusters NGC
2175s and Teu 136 are slightly evolved (∼2-3Myr). Morphology of the
region in the 1.1 mm map shows a semicircular shaped molecular shell
composed of several clumps and YSOs bordering the western ionization
front of Sh2-252. Our analyses suggest that next generation star
formation is currently under way along this border and that possibly
fragmentation of the matter collected during the expansion of the Hii
region as one of the major processes is responsible for such stars. We
observed the densest concentration of YSOs (mostly Class I, ∼0.5Myr)
at the western outskirts of the complex, within a molecular clump
associated with water and methanol masers and we suggest that it is
indeed a site of cluster formation at a very early evolutionary stage,
sandwiched between the two relatively evolved CHII regions A and B.
Description:
The optically bright, extended HII region Sh2-252 is a part of the
Gemini OB1 association. This region is mainly composed of two small
clusters NGC 2175s and Teu 136 and four CHII regions namely A, B, C
and E. In this paper, an extensive survey of the star-forming complex
Sh2-252 has been undertaken with an aim to explore its hidden young
stellar population, its characteristics, spatial distribution,
morphology of the region and finally to understand the star formation
scenario of the complex for the first time. Spitzer-IRAC, MIPS
photometry (3.6-24um) are combined with 2MASS-NIR and optical data
sets to identify and classify the YSOs by their IR excess emission
from their circumstellar material.
From the well-fit models for each source derived from the SED fitting
tool, we calculated the χ2 weighted model parameters such as the
stellar mass (M*), temperature (T*), stellar age (t*), mass of the
disc (Mdisc), disc accretion rate (dMdisc/dt), envelope accretion
rate (dMenv/dt) presented in table1.dat.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 94 183 Physical parameters of YSOs from SED fits
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq Sequential number (1)
5- 13 F9.6 deg RAdeg Right ascension (J2000)
15- 23 F9.6 deg DEdeg Declination (J2000)
25- 27 F3.1 Msun M* Stellar mass
29- 31 F3.1 Msun e_M* rms uncertainty on M*
33- 36 F4.2 10+4K T* Stellar temperature
38- 41 F4.2 10+4K e_T* rms uncertainty on T*
43- 46 F4.2 10+6yr tau* Stellar age
48- 51 F4.2 10+6yr e_tau* rms uncertainty on tau*
53- 57 F5.3 Msun Mdisc Disc mass
59- 63 F5.3 Msun e_Mdisc rms uncertainty on Mdisc
65- 71 F7.3 Msun dMdisc/dt Disc accretion rate
73- 78 F6.3 Msun e_dMdisc/dt rms uncertainty on dMdisc/dt
80- 86 F7.3 Msun dMenv/dt Envelope accretion rate
88- 94 F7.3 Msun e_dMenv/dt rms uncertainty on dMenv/dt
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Note (1): The IDs 1-51 and 52-183 represent Class I and Class II sources,
respectively.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 16-Nov-2018