A Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz: Observational Data and Analyses

TL;DR: In this paper, the authors carried out observations toward the W3 complex and G34.3+0.15 using the TRAO 14 m radio telescope to examine in detail the chemical variations occurring while molecular clouds evolve from the prestellar to the H II region phase.

Abstract: We have carried out observations toward the W3 complex and G34.3+0.15 using the TRAO 14 m radio telescope to examine in detail the chemical variations occurring while molecular clouds evolve from the prestellar to the H II region phase. Observations include spectral surveys of these objects between 84.7 and 115.6 GHz; mapping observations toward W3(OH) with the emissions of CS (2-1), HCN (1-0), HNC (1-0), and HCO+ (1-0); and mapping of CS (2-1) emission toward W3 IRS 5. Chemical model calculations are used to estimate the age of W3(OH) by comparing with the fractional abundances of detected molecules. We found that G34.3+0.15 and W3(OH) are at a similar evolutionary stage, although large differences in the fractional abundances are found in CH3CN and HC3N. Overall, the properties of the detected species and abundances in three regions support the view that chemistry varies as molecular clouds evolve from a cold, collapsing phase to a high-temperature phase, such as the hot core and H II phase. Chemical model calculations for W3(OH) indicate that the evolutionary age of the cloud is 104-105 yr with temperature in the range 10-60 K.

Summary

1. INTRODUCTION

• It is known that chemical properties of molecular clouds vary during their evolution.
• Valuable information on interstellar chemistry and the evolution of molecular clouds has been obtained from the surveys.
• The authors surveyedW3 region to investigate the chemical evolution as predicted by recent chemical models.

2. W3 COMPLEX

• The W3 complex consists of several infrared sources (WynnWilliams & Becklin 1974; Jaffe et al. 1983; Colley 1980) at different evolutionary stages and core masses.
• W3 IRS 5 is younger than W3(OH) and appears to be at an earlier stage, evolving toward a hot corelike object (Helmich et al. 1994).

3. OBSERVATIONS

• The authors carried out molecular line surveys toward W3(OH) and W3 IRS 5 using the Taeduk Radio Astronomy Observatory (TRAO) 14 m telescope between 2001 November and 2002 February.
• For the observations of W3(OH), the back ends were two filter banks in serial mode, each of which has a 1MHz resolution and 256MHz bandwidth, providing a total bandwidth of 512 MHz at each local oscillator (LO) tuning.

4. DATA REDUCTION AND DISPLAY

• 1. Spectra and Images Spectra taken with the 1 MHz resolution of the 512 channels spectrometer in serial mode have been averaged and then baseline subtracted using the SPA data reduction package developed at the FCRAO observatory.
• The total bandwidth for every observation is 512MHz, but observations were carried out by stepping the central frequency by 500 MHz, resulting in an overlap of approximately 6 MHz between spectra.
• The number of detected lines in the catalog is sufficient for the use in the line identifications of their 3 mm observations.

5. INDIVIDUAL MOLECULES

• The authors present derived abundances of molecules.
• The chemical environment seems to be different in warm and giant molecular clouds in which the HNC/HCN ratios are observed to be between 0.015 and 0.40 (Goldsmith et al. 1981).
• Hence, aswill be described later in detail, the absorption/scattering by cold gas of the optically thick component (F ¼ 2 1) inG34.3+ 0.15 may be responsible for the observed hfs ratio.
• The rotational temperature and the column density appear to be in good agreement with those obtained from the lower energy transitions (Eu/k < 45 K) of CH3OH observed in G34.3+0.15.

6. CHEMICAL VARIATION OF W3(OH),

• The authors have so far investigated chemistry of several species of interest by categorizing them into four groups: ionized, sulfurbearing, HCN and HNC, and symmetric and asymmetric molecules.
• In comparison with W3(OH), high abundances of saturated molecules such as CH3CN and CH3CCH were derived in G34.3+0.15.
• On the other hand, the C34S line taken with 250 kHz resolution appears to be weaker than that taken with 1 MHz, suggesting observational errors in the 250 kHz data.

8. COMPARISONS WITH CHEMICAL MODELS

• Chemical model calculations have been performed by several authors to explain different chemical characteristics of Orion-KL and TMC-1 (Caselli et al. 1993;Millar & Freeman 1984).
• The plot of CH3OH, H2CS, and CH3CN shows that there are minor differences in the fractional abundances before 104 yr, but after 104 yr H2CS is most abundant, followed by CH3OH and CH3CN.
• As the maximum temperature of 35 K is derived from the CH3CN rotation diagram analyses, a boundary of two components with a warm core and cold envelope was assumed to exist around 35 K with a hydrogen volume density of 2 ; 105 cm 3 (Fig. 15).
• This 35 K model generates similar results to those from the 60 K model as expected, since there are only minor differences in temperature and density as well as a minor difference in Av. The authors model calculations and those MOLECULAR LINE SURVEY OF W3(OH) AND W3 IRS 5 201No.

9. SUMMARY

• A total of 45 transitions from 17 species in the 1 MHz resolution observations ofW3(OH) have been detected in the TRAO 3 mm surveys toward W3(OH).
• Most of the detected lines in W3 IRS 5 are from simple linear molecules, except for SO2, C3H2, and HNCO, suggesting thatW3 IRS 5 is in a state prior to the formation of the hot core or H ii phase.
• For molecules having only one detected transition without isotopic species, the authors derive a lower limit to the column densities by assuming that the rotation temperature of linear molecules is Trot ¼ Eu /k, and for symmetric or slightly asymmetric tops is Trot ¼ (2/3)Eu/k (see MacDonald et al. 1996).

Figures

Fig. 16.—Plot of fractional abundances derived from 10 K model calculations. A temperature of 10 K was derived from the rotation diagram analysis of methanol.

Fig. 11.—Overlaid images of HCO+ and CS in W3(OH). The solid and dashed lines are for CS and HCO+, respectively. This plot shows a slight deviation of the peak positions of the species, and HCO+ is more widely distributed than CS.

TABLE 5 Isotopic Ratios of W3(OH), W3 IRS 5, and G34.3+0.15

Fig. 4.—Spectra of lines in the ultracompact H ii region G34.3+0.15 observed with 250 kHz resolution.

TABLE 2—Continued

TABLE 2—Continued

TABLE 6 Physical Parameters Adopted for Model Calculation of W3(OH )

Fig. 12.—Overlaid images of HCN and HNC in W3(OH). The solid and dashed lines are for HCN and HNC, respectively. It shows an identical peak for HCN and HNC and a more dense distribution of HNC than HCN.

Fig. 8.—LVG model calculations of CS (2–1) for G34.3+0.15 and W3(OH) with a kinematic temperature of 20 K, which was obtained from CO (1–0). The horizontal lines represent observed T R ; solid lines represent excitation temperature; dotted lines represent the model variation of T R ; and dashed lines represent the variation of optical depth.

Fig. 15.—Time evolution of fractional abundances of molecules obtained from 35 K model calculations. Pure gas-phase chemical reactions only were included, but with different input parameters as shown in the plot.

Fig. 7.—Spectral lines of HCO+, H13CO+, HCN, and HNC observed toward G34.3+0.15, IRAS 18335 0711, IRAS 18450 0200, W3(OH), and W3 IRS 5.

Fig. 4.—Spectra of lines in the ultracompact H ii region G34.3+0.15 observed with 250 kHz resolution.

Fig. 5.—Map of CS (2–1) map (upper left panel ), HCO+ (1–0) (upper right panel ), HCN (1–0) (middle left panel ), and HNC (1–0) (middle right panel ) taken toward the strong OH-emitting region W3(OH), and CS (2–1) map taken towardW3 IRS 5 (lower left panel ). Observations were carried out between 2001 November and 2002 February. Contours are drawn for the signals stronger than 0.4 K, with 5 . While the CS (2–1) map (lower right) of G34.3+0.15 drawn with the data taken from the independent project is an integrated intensity map, other map figures are contoured using the peak of signal taken from this project.

Fig. 13.—Time evolution of fractional abundances of molecules resulting from 100Kmodel calculations, which include grain-surface reactions and effects of mantle evaporation.

TABLE 1 Reported Molecular Line Surveys

Fig. 9.—Rotation diagrams for CH3CN, CH3CCH, H2CS, and CH3OH for W3(OH) and G34.3+0.15. We have used 3 mm transitions exclusively to make direct comparisons of the excitation conditions of the molecules between G34.3+0.15 and W3(OH).

Fig. 14.—Time evolution of fractional abundances of molecules resulting from 60 K model calculations in which pure gas-phase reactions were included, but the effects of mantle evaporation were not included.

Fig. 10.—Histogram showing the variations of integrated intensities of G34.3+0.15 andW3 IRS 5 relative to W3(OH). In this plot, we considered both the 3 mm survey of this work and a previous survey (Kim et al. 2000).

TABLE 3 High-Resolution (250 kHz) Observations of Missing Lines (Kim et al. 2000) and New Observations of Interesting Molecules and Isotopic Variants of G34.3+0.15

Fig. 6.—Line profiles of a point source, Cygni, in the SiO (v ¼ 1, J ¼ 2 1) line obtained with a 250 kHz and a 1 MHz spectrometer.

Full text

University of Wollongong University of Wollongong
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January 2006
A Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz: A Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz:
Observational Data and Analyses Observational Data and Analyses
S. J. Kim
KyungHee University, Korea
H. D. Kim
University of Wollongong
Y. Lee
Taeduk Radio Astronomy Observatory, Korea
Y. C. Minh
Taeduk Radio Astronomy Observatory, Korea
R. Balasubramanyam
Raman Research Institute, Bangalore, India
See next page for additional authors
Follow this and additional works at: https://ro.uow.edu.au/infopapers
Part of the Physical Sciences and Mathematics Commons
Recommended Citation Recommended Citation
Kim, S. J.; Kim, H. D.; Lee, Y.; Minh, Y. C.; Balasubramanyam, R.; Burton, M. G.; Millar, T. J.; and Lee, D. W.: A
Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz: Observational Data and Analyses
2006.
https://ro.uow.edu.au/infopapers/409
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A Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz: A Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz:
Observational Data and Analyses Observational Data and Analyses
Abstract Abstract
We have carried out observations toward the W3 complex and G34.3+0.15 using the TRAO 14 m radio
telescope to examine in detail the chemical variations occurring while molecular clouds evolve from the
prestellar to the H II region phase. Observations include spectral surveys of these objects between 84.7
and 115.6 GHz; mapping observations toward W3(OH) with the emissions of CS (2–1), HCN (1–0), HNC
(1–0), and HCO+ (1–0); and mapping of CS (2–1) emission toward W3 IRS 5. Chemical model
calculations are used to estimate the age of W3(OH) by comparing with the fractional abundances of
detected molecules. We found that G34.3+0.15 and W3(OH) are at a similar evolutionary stage, although
large differences in the fractional abundances are found in CH3CN and HC3N. Overall, the properties of
the detected species and abundances in three regions support the view that chemistry varies as
molecular clouds evolve from a cold, collapsing phase to a high-temperature phase, such as the hot core
and H II phase. Chemical model calculations for W3(OH) indicate that the evolutionary age of the cloud is
104–105 yr with temperature in the range 10–60 K.
Disciplines Disciplines
Physical Sciences and Mathematics
Publication Details Publication Details
This article was originally published as: Kim, SJ, Kim, HD, Minh, YC, et al, A Molecular Line Survey of
W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz: Observational Data and Analyses, The Astrophysical
Journal Supplement Series, 2006, 162, 161-206. Copyright 2006 University of Chicago Press. The journal
can be found here.
Authors Authors
S. J. Kim, H. D. Kim, Y. Lee, Y. C. Minh, R. Balasubramanyam, M. G. Burton, T. J. Millar, and D. W. Lee
This journal article is available at Research Online: https://ro.uow.edu.au/infopapers/409

A MOLECULAR LINE SURVEY OF W3(OH) AND W3 IRS 5 FROM 84.7 TO 115.6 GHz:
OBSERVATIONAL DATA AND ANALYSES
Sang-Joon Kim,
1
Hun-Dae Kim,
2
Youngung Lee,
3
Young Chol Minh,
3
Ramesh Balasubramanyam,
4
Michael G. Burton,
5
Tom J. Millar,
6
and Dong-Wook Lee
1
Received 2004 August 29; accepted 2005 May 31
ABSTRACT
We have carried out observations toward the W3 complex and G34.3+0.15 using the TRAO 14 m radio telescope to
examine in detail the chemical variations occurring while molecular clouds evolve from the prestellar to the H ii
region phase. Observations include spectral surveys of these objects between 84.7 and 115.6 GHz; mapping obser-
vations toward W3(OH) with the emissions of CS (2–1), HCN (1–0), HNC (1–0), and HCO
+
(1–0); and mapping of
CS (2–1) emission toward W3 IRS 5. Chemical model calculations are used to estimate the age of W3(OH) by
comparing with the fractional abundances of detected molecules. We found that G34.3+0.15 and W3(OH ) are at a
similar evolutionary stage, although large differences in the fractional abundances are found in CH
3
CN and HC
3
N.
Overall, the properties of the detected species and abundances in three regions support the view that chemistry varies
as molecular clouds evolve from a cold, collapsing phase to a high-temperature phase, such as the hot core and H ii
phase. Chemical model calculations for W3(OH) indicate that the evolutionary age of the cloud is 10
4
–10
5
yr with
temperature in the range 10–60 K.
Subject head inggs: H ii regions — ISM: abundances — ISM: individual (W3(OH) , W3 IRS 5, G34.3+0.15)
1. INTRODUCTION
It is known that chemical properties of molecular clouds vary
during their evolution. The onset of central protostars, compared
with the cold dark collapsing phase, plays a critical role in driv-
ing the chemistry in the surrounding dense region by providing
a high temperature and density. Molecular line surveys, among
many observational techniques, are one of the most powerful
methods for the investigation of the chemistry. The identified
molecules, which are sensitive to various chemical reactions in
the molecular clouds, can be used to investigate the formation and
evolution of molecular clouds. Representative line surveys per-
formed over the last few decades are listed in Table 1. Valuable
information on interstellar chemistry and the evolution of mo-
lecular clouds has been obtained from the surveys. However, as
shown in Table 1, they have been limited to a few objects, such as
Sgr B2 (Cummins et al.1986; Turner1989; Sutton et al.1991) and
the nearby Orion-KL region (Johansson et al. 1984; Jewell et al.
1989; Turner 1989; Blake et al. 1986, 1996; Ziurys & McGonagle
1993; Schilke et al. 1997).
Recently, other sources have been chosen for molecular line
surveys: the ultracompact H ii region G34.3+0.15 (MacDonald
et al. 1996; Kim et al. 2000); the low-mass star-forming region
IRAS 162932422 (van Dishoeck et al. 1995); the protostellar
region IRAS 174702853 (Kim et al. 2002); and the late-type
star IRC +10216 (Kawaguchi et al.1995; Cernicharo et al. 2000).
It is important to study the sources for which significant chemical
variations are expected, as predicted by models. Detailed ex-
amination has been undertaken for individual species present in
Orion-KL and Sgr B2 (Turner 1991) in order to test the models.
Although the results toward these two sources have provided us
with interesting information on the nature of dense cores, the com-
plex physical structure of Orion-KL and Sgr B 2 has limited our
understanding of the chemical processes. The molecular abun-
dances derived from these objects contain large uncertainties due
to the blending of adjacent transitions compared to low-mass and
isolated objects. Therefore, Orion-KL and Sgr B2 do not provide
a favorable environment for the study of relative chemical varia-
tions and ultimately for the determination of the evolutionary
stage, although observ ations toward the objects have enabled us
to understand the close relationship between the chemistry and the
evolution of molecular clouds.
Observations toward the hot core (MacDonald et al.1996) and
the cold halo (Thompson & MacDonald. 1999) of the source
G34.3+0.15 have revealed significant chemical variations be-
tween these two distinct physical components within this object.
A distinct chemistry was also noticed from observations of SO
2
,
CH
3
OH, and H
2
CS (Helmich et al. 1994) and submillimeter mo-
lecular line surveys (Helmich & van Dishoeck 1997) of the W3
region.
Models of gas-phase, ion-molecule chemistry can reasonably
reproduce the observed abundance of carbon-chain species in the
cold dark clouds (Herbst et al. 1984; Millar & Freeman 1984).
However, such ion-molecule chemical models alone cannot sat-
isfactorily account for the observed high abundance of mole-
cules containing H or S atoms in star-forming molecular clouds.
Coupling of gas-phase and grain-surface reactions (e.g., van
Dishoeck & Blake 1998) has been emphasized in recent chem-
ical models in order to cope with the discrepancy. Representative
models have been developed for hot cores by Millar et al. (1991)
and by Charnley et al. (1995). According to these models, hydro-
gen, sulfur, ionized, and neutral molecules are readily deposited
onto dust surfaces as the density increases during the collapsing
phase of interstellar clouds. The formation of complex, heavy spe-
cies containing hydrogen becomes inhibited, leading to slow re-
actions of those species in the earlier collapsing phase (t < 10
4
yr).
1
Department of Astronomy and Space Science, KyungHee University,
Youngin, Kyunggi 449-701, Korea; sjkim1@khu.ac.kr.
2
School of Information Technology and Computer Science, University of
Wollongong, NSW 2500, Australia.
3
T aeduk Radio Astronomy Observatory , San 36-1, Whaam-Dong, Youseong-Gu,
Taejeon 305-348, Korea.
4
Department of Astronomy and Astrophysics, Raman Research Institute,
Sadashivanagar, Bangalore 560080, India.
5
School of Physics, University of New South Wales, Sydney, NSW 2052,
Australia.
6
Department of Physics, UMIST, P.O. Box 88, Manchester M60 1QD, UK.
161
The Astrophysical Journal Supplement Series, 162:161–206, 2006 January
# 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A.

Radiation from the protostar then heats up the surrounding gas and
grains, releasing volatile species from the dust surface back to gas
phase. This stage is called the hot core phase and lasts 10
4
–10
5
yr
after the onset of star formation (van Dishoeck & Blake 1998).
We surveyed W3 region to investigate the chemical evolution as
predicted by recent chemical models. We also observed G34.3+
0.15 in order to identify several missing lines from a previous sur-
vey (Kim et al. 2000). In addition, high-spectral-resolution ob-
servations for molecules of interest (CS, HCO
+
,HCN,HNC,
CH
3
CN, and CH
3
CCH) were carried out in G34.3+0.15. The W3
region contains several objects at different evolutionary stages,
and G34.3+0.15 is a well-known hot core associated with an ultra-
compact H ii region. Our TRAO observations toward W3 and
G34.3+0.15 provide us with valuable information on interstellar
chemistry, because the chemical properties of these sources, dif-
fering in mass, core size, and evolutionary stage, are useful for in-
vestigating the relationships between the chemical variations and
these parameters.
The contents of this paper are as follows: x 1 presents back-
ground information on line surveys, evolutionary scenarios, and
models presented in the literature. In x 2, general aspects of the
W3 complex, focusing on W3(OH ) and W3 IRS 5, are given. In
xx 3 and 4, we present the observational procedures, line iden-
tifications, and spectral displays. In x 5, we discuss individual
species of interest detected in the survey. In x 6, we discuss the
chemical variations as well as the isotopic ratios of C and S
atoms found from G34.3+0.15, W3(OH), and W3 IRS 5. In x 7,
the cloud morphology found from CS, HCO
+
, HCN, and HNC
mappings is presented. In x 8, chemical results from model cal-
culations are given. We summarize the results in x 9.
2. W3 COMPLEX
The W3 complex consists of several infrared sources (Wynn-
Williams & Becklin 1974; Jaffe et al. 1983; Colley 1980) at dif-
ferent evolutionary stages and core masses. The various objects
include well-developed shell structure in the H ii regions (W3B,
W3C, and near IRS 3 and IRS 4), and several ultracompact H ii
regions (W3F, W3M; and near IRS 7 and IRS 5). Strong OH and
H
2
O masers, viz. W3(OH) and W3(H
2
O), separated by 6
00
from
each other, are also observed.
At least two hot cores have been revealed in W3 from obser-
vations of NH
3
lines (Mauersberger et al. 1988). Its distance is
estimated to be 1.83 kpc, residing in the Perseus arm of the gal-
axy (Imai et al. 2000). Helmich & van Dishoeck (1997) per-
formed spectral line surveys through the 345 GHz window toward
W3 IRS 4, W3 IRS 5, and W3(OH). Significant differences in the
physical and chemical conditions were found in IRS 4, IRS 5, and
W3(H
2
O), and the gas temperature seems highest (T  220 K)
toward W3(H
2
O) compared with those in IRS 4 and IRS 5
(Helmich et al. 1994). High-velocity (V ¼ 52 km s
1
)flows
near W3 IRS 5 and an intermediate-velocity (V ¼ 26 km s
1
)
wing near W3(OH) are found in
12
CO emission (Bally & Lada
1983).
2.1. W3(OH)
The ultracompact H ii region, W3(OH), is an extensively stud-
ied site for the investigation of star formation and its influence on
the surrounding regions (Wyrowski et al. 1999). Three peaks are
distinguished with subarcsecond resolution observations in the
thermal dust continuum emission originating from the hot core
region of W3(H
2
O; Wyrowski et al. 1999). Continuum obser-
vations reveal that W3(OH) has a shell structure in the H ii region
(Dreher & Welch 1981). H66, H76, and H110 radio recom-
bination lines having full width at half-maximum (FWHM ) of
36, 41, and 69 km s
1
, respectively, are observed (Sams et al.
1996). H41,CH
3
CN [5(2)–4(2)], HCN (1–0), HCO
+
(1–0),
and
13
CO (1–0) are detected with amplitudes of 0.4, 0.1, 5.9, 5.5,
and 7.6 K, respectively, from observations with the Nobeyama
45 m telescope (Forster et al. 1990). Keto et al. (1992) made mid-
infrared and molecular line observations of W3(OH ) and com-
pared them with G34.3+0.15.
2.2. W3 IRS 5
W3 IRS 5 is a bright infrared source with a total luminosity of
3 ; 10
5
L

(Campbell et al. 1995) and is separated by 75
00
from
W3 IRS 4, which is brighter than W3 IRS 5 in the submillimeter
wavelength range (Jaffe et al. 1983). W3 IRS 5 is younger than
W3(OH) and appears to be at an earlier stage, evolving toward a
hot corelike object (Helmich et al. 1994). Very long baseline in-
terferometry measurement (Imai et al. 2000) of radial velocities
and proper motions of water masers in the W3 IRS 5 region reveals
two groups of maser components, which are associated with at
least two different outflows.
TABLE 1
Reported Molecular Line Surveys
Sources Telescope FWHM
Frequency
(GHz)
Resolution
(MHz)
Line Density
(Transition/GHz) Observations
Orion A ...................... OSO 20 m 47
00
72–91 1 8.5 Johansson et al. (1984)
IRC +10216 ............... 2.3
Orion A ...................... OVRO 10.4 m 0A5 247–263 1.03 15.2 Blake et al. (1986)
Sgr B2 ........................ BTL 7 m 2A9 70–150 1 9.14 Cummins et al. (1986)
Orion A ...................... NRAO 12 m 24
00
330–360 2 5.4 Jewell et al. (1989)
Orion A ...................... OVRO 10.4 m 0A5 215–247 16.2 17.0 Sutton et al. (1985)
Sgr B2(M) ................. CSO 10.4 m 20
00
330–355 1 6.7 Sutton et al. (1991)
Sgr B2/Orion-KL ....... NRAO 11 m 83
00
70–115 1 14.3/17.1 Turner (1989)
G34.3+0.15 ................ JCMT 15 m 13
00
330–360 0.756 0.6 Thompson & MacDonald (1999)
G34.3+0.15 ................ TRAO 14 m 58
00
86–165.3 1 2.0 Kim et al. (2000, 2001)
G34.3+0.15 ................ JCMT 15 m 14
00
330–360 0.33 11.4 MacDonald et al. (1996)
G5.890.39................ JCMT 15 m 13
00
330–360 0.756 4.7 Thompson & MacDonald (1999)
IRC +10216 ............... IRAM 30 m 19
00
129–173 1 8.6 Cernicharo et al. (2000)
IRC +10216 ............... Nobeyama 45 m 35
00
28–50 0.25 8.6 Kawaguchi et al. (1995)
Orion-KL.................... FCRAO 14 m 40
00
150–160 1 18.0 Ziurys & MacGonagle (1993)
IRAS 174702853 .... Mopra 22 m 30
00
90–96 0.5 3.5 Kim et al. (2002)
KIM ET AL.162 Vol. 162

Strong
12
CO self-absorption and
13
CO and HCN emission peaks
are seen toward IRS 5; the maximum
12
CO emission is observed
toward the compact H ii region; and a CS peak is found 8
00
west of
the OH 1720 MHz maser (Dickel et al. 1980). The possible pres-
ence of disklike structure around a cluster of embedded stars in the
mid-infrared images of IRS 5 is inferred (Persi et al. 1996). The
total H
2
mass of the molecular cores associated with IRS 5 is esti-
matedtobe1100M

derived from
13
CO (1–0) and C
18
O (1–0)
observations (Roberts et al. 1997). A luminosity of 6:0 ; 10
5
L

and a cloud mass of 1600 M

have been derived using 230 GHz
continuum observations (Gordon 1987) for the entire complex of
W3.
3. OBSERVATIONS
We carried out molecular line surveys toward W3(OH)
and W3 IRS 5 using the Taeduk Radio Astronomy Observa-
tory (TRAO) 14 m telescope between 2001 November and 2002
February. The receiver system was a low-noise SIS receiver oper-
ating in single-sideband mode. For the observations of W3(OH),
the back ends were two filter banks in serial mode, each of which
has a 1 MHz resolution and 256 MHz bandwidth, providing a total
bandwidth of 512 MHz at each local oscillator (LO) tuning. Sen-
sitive 250 kHz measurements toward W3(OH) and W3 IRS 5
were also performed using two 256 channel filter banks in parallel
mode after completing the 1 MHz observations of W3(OH), IRAS
184500200, and IRAS 183350711.
During the observations the typical system temperature was
300 K between 85 and 110 GHz and was 600 K at 115 GHz.
Position switching mode observations were carried out, taking a
reference position to be 30
0
away in right ascension, which was
confirmed to be free of emission. Calibration was performed
using the standard chopper-wheel method, which corrects for at-
mospheric attenuation and scattering of forward spillover, and
the intensity was derived in terms of T

A
scale (Ulich & Hass
1976). The beam sizes of the TRAO 14 m telescope are 64
00
and
55
00
at 85 and 115 GHz, respectively.
The total on-source integration time of each LO tuning for the
1 MHz observation was 300 s, achieving channel-to-channel rms
noise of 0.03–0.05 K, which is consistent with that in G34.3+
0.15 (Kim et al. 2000). Therefore, these observations provided
an opportunity to compare the chemical properties of the W3 and
G34.3+0.15 regions, with data taken with the same telescope sys-
tem and sensitivity. Pointing and focusing were checked using
 Cygni.
Almost all of the molecular transitions previously detected
from the 1 MHz surveys toward G34.3+0.15 (Kim et al. 2000),
W3(OH), IRAS183350711, and IRAS 184500200 (this work)
were also considered for the 250 kHz surveys toward W3(OH) and
W3 IRS 5. We also observed selected molecules (HCO
+
,CS,
HCN, HNC, and their isotopic variants) with 250 kHz resolution
toward the ultracompact H ii region G34.3+0.15 to examine iso-
topic ratios and the HCN hyperfine ratio in detail. We measured
line emissions from SO
2
, HNCO, CH
3
OH [0(0)–1(1) E ], and
CH
3
OH [2(1)–1(1) A] transitions toward G34.3+0.15.
The detected molecules and their transitions show close agree-
ment between G34.3+0.15 and IRAS 184500200, and between
W3(OH) and IRAS 183350711, suggesting that physical/
chemical condition and evolutionary stage are similar. To estimate
physical conditions, as well as to determine the initial parameters
for chemical model calculations, mapping observations were car-
ried out toward W3(OH) for the transitions of CS (2–1) and HCN
(1–0) over 10
0
; 10
0
,HNC(1–0)over8
0
; 8
0
,andHCO
+
(1–0)
over 6
0
; 7
0
. We carried out only CS (2–1) mapping toward W3
IRS 5, because the line strengths of other species are too weak to
map with the relatively large-beam size of TRAO. Mapping ob-
servations of CS (2–1) and HCO
+
in IRAS 184500200 and
IRAS183350711were performed covering almost the same area
as W3(OH). CS (2–1) mapping of IRAS 184500200 shows ir-
regular and elongated distribution in the N-S direction, whereas for
IRAS 183350711 spherical distribution is shown. The CS (2–1)
distribution is consistent with that of 8.6 GHz radio continuum
(Walsh et al. 1998). There is no report on continuum map for IRAS
183350711. We will present images and detailed analyses of mo-
lecular lines detected in IRAS 184500200 and IRAS 18335
0711 in future work.
The source positions of W3(OH) and W3 IRS 5, and the
central position of G34.3+0.15, are as follows:
W3(OH ). — ¼ 02
h
23
m
16:
s
9,  ¼ 61

38
0
56B4 (1950.0;
Helmich et al. 1994).
W3 IRS 5.— ¼ 02
h
21
m
53:
s
1,  ¼ 61

52
0
20B0 (1950.0;
Helmich et al. 1994).
G34.3+0.15.— ¼ 18
h
50
m
46:
s
3,  ¼ 01

11
0
13B0 (1950.0;
Kim et al. 2000).
4. DATA REDUCTION AND DISPLAY
4.1. Spectra and Ima
ges
Spectra taken with the 1 MHz resolution of the 512 channels
spectrometer in serial mode have been averaged and then base-
line subtracted using the SPA data reduction package developed
at the FCRAO observatory. Some bad channels especially at the
edge of the spectra were significant at the upper frequency region
when LSB mode observations were performed. The number of
bad channels in the worst spectra is about 15–20, equivalent
to 15–20 MHz. The total bandwidth for every observation is
512 MHz, but observations were carried out by stepping the cen-
tral frequency by 500 MHz, resulting in an overlap of approxi-
mately 6 MHz between spectra.
For the 250 kHz resolution observations, the spectrometers
were configured in a parallel mode, and an average of signals
was taken. The typical noise in an averaged spectrum is 0.03–
0.05 K for 1 MHz data and 0.06–0.09 K for 250 kHz data. The
reduced spectra presented in Figures 1 and 2 were taken toward
W3(OH) with the 1 MHz and 250 kHz bandwidths, respectively.
The spectra in Figure 1 were obtained by combining two neigh-
boring spectra, giving a bandwidth of 1 GHz. In Figures 3 and
4, 250 kHz spectra taken from W3 IRS 5 and G34.3+0.15, re-
spectively, are presented.
Data taken with mapping observations were made into images
using the Contour and Trigrid functions in IDL, and then the
images were compared with those processed using CLASS. The
two images, which were drawn in terms of antenna temperature,
showed a good agreement with each other. The contour maps in
Figure 5 were made by taking signals stronger than 5 , which
corresponds to 0.4 K.
4.2. Line Identification
Line identifications were made exclusively using the catalog
of Lovas (1992). The catalog lists molecular transitions detected
from Orion-KL, Sgr B2, and from various interstellar molecular
clouds. The number of detected lines in the catalog is sufficient
for the use in the line identifications of our 3 mm observations.
The identified line frequencies were determined by Gaussian fit-
ting after correcting by the corresponding Doppler shifts of 46
and  39 km s
1
for W3(OH ) and W3 IRS 5, respectively, and
then compared with the rest frequencies from the Lovas catalog.
MOLECULAR LINE SURVEY OF W3(OH) AND W3 IRS 5 163No. 1, 2006

Frequently asked questions

Q1. What are the contributions mentioned in the paper "A molecular line survey of w3(oh) and w3 irs 5 from 84.7 to 115.6 ghz: observational data and analyses" ?

3+0. 15 using the TRAO 14 m radio telescope to examine in detail the chemical variations occurring while molecular clouds evolve from the prestellar to the H II region phase. This article was originally published as: Kim, SJ, Kim, HD, Minh, YC, et al, A Molecular Line Survey of W3 ( OH ) and W3 IRS 5 from 84. 7 to 115. 6 GHz: Observational Data and Analyses, The Astrophysical Journal Supplement Series, 2006, 162, 161-206. This journal article is available at Research Online: https: //ro. uow. edu. au/infopapers/409 A MOLECULAR LINE SURVEY OF W3 ( OH ) AND W3 IRS 5 FROM 84. 

Q2. What was used to derive temperature and column density of the species?

In particular, the rotation diagram method for HC3N, CH3CN, and CH3OH, where several transitions were observed was used to derive temperature and column density of the species. 

Q3. How did the authors obtain a column density of 1:1 for W3(OH)?

With nuclear spin degeneracy gI ¼1/4 for para and gI ¼ 3/4 for ortho (Turner 1991), the authors obtained a rotation temperature of 12.5 K, and a column density of 1:1 ; 1014 cm 2 for W3(OH) using the rotation diagram analysis. 

Q4. How do the authors estimate the age of W3(OH)?

By examining fractional abundances derived from the theoretical modelings and the observations, the authors may be able to estimate the age ofW3(OH). 

Q5. What is the effect of simultaneous observations of several K-ladder transitions of a?

simultaneous observations of several K-ladder transitions of a molecule can reduce observational errors arising from uncertainties in telescope pointing, beam efficiency, and calibrations. 

Q6. What is the column density of N2H +?

The excitation temperature ( 5 K) adopted in their calculation is a reasonable value for heavy molecules, and therefore the derived N2H + column density would not differ from the realistic density. 

Q7. What is the ratio of HCN and HNC in the LTE and optically thin conditions?

HCN has three hyperfine transitions (F ¼ 0 1, F ¼ 1 1, and F ¼ 2 1), and their intensity ratio (i.e., statistical weight) of those components in the LTE and optically thin conditions is 1:3:5. 

Q8. What is the frequency distribution of bad channels in a spectrometer?

Some bad channels especially at the edge of the spectra were significant at the upper frequency region when LSB mode observations were performed.