J/AJ/129/393 UBV photometry in W3 (Oey+, 2005)
Hierarchical triggering of star formation by superbubbles in W3/W4.
Oey M.S., Watson A.M., Kern K., Walth G.L.
<Astron. J., 129, 393-401 (2005)>
=2005AJ....129..393O 2005AJ....129..393O
ADC_Keywords: Interstellar medium ; Photometry, UBV
Keywords: ISM: bubbles - ISM: clouds - ISM: individual (W3, W4) -
ISM: structure -
open clusters and associations: individual (IC 1795, IC 1805) -
stars: formation
Abstract:
It is generally believed that expanding superbubbles and mechanical
feedback from massive stars trigger star formation, because there are
numerous examples of superbubbles showing secondary star formation at
their edges. However, although these systems show an age sequence,
they do not provide strong evidence of a causal relationship. The
W3/W4 Galactic star-forming complex suggests a three-generation
hierarchy: the supergiant shell structures correspond to the oldest
generation; these triggered the formation of IC 1795 in W3, the
progenitor of a molecular superbubble that in turn triggered the
current star-forming episodes in the embedded regions W3-North,
W3-Main, and W3-OH. We present UBV photometry and spectroscopic
classifications for IC 1795, which show an age of 3-5 Myr. This age is
intermediate between the reported 6-20 Myr age of the supergiant shell
system and the extremely young ages (104-105yr) for the embedded
knots of the ultracompact HII regions, W3-North, W3-Main, and W3-OH.
Thus, an age sequence is indeed confirmed for the entire W3/W4
hierarchical system. This therefore provides some of the first
convincing evidence that superbubble action and mechanical feedback
are indeed a triggering mechanism for star formation.
Description:
Our UBV imaging was obtained on 1999 October 6-9 at the 84cm telescope
of the Observatorio Astronomico Nacional at San Pedro Martir (SPM),
Baja California Norte, Mexico. Spectroscopic observations of
candidates for the earliest-type stars were obtained with the 2.1m
telescope at SPM during the nights of 1999 October 15-17.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 89 399 Photometry and spectral types for the W3 region
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- [OWK2005] Identification number from this work
7- 8 A2 --- f_[OWK2005] Flag on [OWK2005] (1)
10- 12 I3 --- OI ? Ogura & Ishida (1976PASJ...28..651O 1976PASJ...28..651O)
identification number
14 I1 h RAh Hour of Right Ascension (J2000)
16- 17 I2 min RAm Minute of Right Ascension (J2000)
19- 23 F5.2 s RAs Second of Right Ascension (J2000)
25- 26 I2 deg DEd Degree of Declination (J2000)
28- 29 I2 arcmin DEm Arcminute of Declination (J2000)
31- 34 F4.1 arcsec DEs Arcsecond of Declination (J2000)
36- 41 F6.3 mag Vmag The V band magnitude
43- 47 F5.3 mag e_Vmag Formal uncertainty in Vmag
49- 54 F6.3 mag Bmag The B band magnitude
56- 60 F5.3 mag e_Bmag Formal uncertainty in Bmag
62- 67 F6.3 mag Umag The U band magnitude
69- 73 F5.3 mag e_Umag Formal uncertainty in Umag
75 I1 --- Nobs Number of measurements averaged
77- 88 A12 --- SpType Spectroscopic classification
89 A1 --- n_SpType [*] *: from Mathys, 1989A&AS...81..237M 1989A&AS...81..237M
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Note (1): Flag on [OWK2005], defined as follows:
* = Star in IC 1795
a = Photometry suspect, yielding unphysical parameters; star omitted
from analysis.
b = Foreground star.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Marianne Brouty [CDS] 06-Jul-2005