ABSTRACT
We study molecular emission in a massive condensation at the border of the H ii region RCW 120, paying particular attention to the Core 1 and 2 objects, the most massive fragments of the ...condensation found previously by ALMA. The latter fragment was previously suggested to host a high-mass analogue of Class 0 young stellar object. We present spectra of molecular emission in the 1 mm range made with the APEX telescope. We detect CH3OH and C34S lines in Cores 1 and 2. The CH3CN series and the SO2 lines are only found in Core 2. We estimate gas physical parameters using methanol lines and obtain gas temperature less than 100 K in both regions. Molecular hydrogen number density in Core 2 is in the range of 105−107 cm−3 and is more uncertain in Core 1. However, the detection of the CH3CN lines corresponding to highly excited transitions (Eu > 400 K) in Core 2 indicates that the region contains hot gas, while the abundances of CH3OH, CS, SO2, and CH3CN are quite low for a hot core stage. We propose that Core 2 is in the warm-up phase prior to the establishing of the hot gas chemistry. We suggest that Core 2 is in the beginning of the hot core stage. There are no detected CH3CN lines in Core 1; therefore, it might be on an even less evolved evolutionary stage.
ABSTRACT
We present a survey of molecular line emission towards the molecular cloud surrounding Herbig Be star V645 Cyg. The survey was performed with the 20-m Onsala space telescope at 3 and 4 mm. ...We detected emission lines of 33 molecules and their isotopologues from diatomic molecules to four COMs up to seven atoms. Using detected lines, we estimated molecular column densities and abundances relative to molecular hydrogen in local thermodynamic equilibrium (LTE) approximation for all molecules except for methanol, for which we obtained physical parameters using a non-LTE model. Moreover, in the basement of the non-LTE model of methanol line emission, we consider that there is a weak maser effect in the additional spectral component of 51–40 E methanol line at 84.521 GHz. We compared the molecular abundances with values found in several astrochemical templates: molecular clouds, hot cores, and photodissociation regions, and found that signatures of these different types can be found towards V645 Cyg. We also obtained maps of the cloud in several molecular emission lines. The peaks of CO and CH3OH emission are shifted from the direction of the star, but the CS, HCO+, HNC, HCN, and N2H+ emission peaks are observed directly towards the star. Exploring the gas kinematics around V645 Cyg, we found that velocity structure in the ambient molecular cloud on the scale ≈1.6–2.0 pc is not the same as within ≈0.5 pc found previously by other authors.
Molecular envelope around the HII region RCW 120 Kirsanova, M S; Pavlyuchenkov, Ya N; Wiebe, D S ...
Monthly notices of the Royal Astronomical Society,
10/2019, Volume:
488, Issue:
4
Journal Article
Peer reviewed
Open access
ABSTRACT
The H ii region RCW 120 is a well-known object, which is often considered as a target to verify theoretical models of gas and dust dynamics in the interstellar medium. However, the exact ...geometry of RCW 120 is still a matter of debate. In this work, we analyse observational data on molecular emission in RCW 120 and show that 13CO(2–1) and C18O(2–1) lines are fitted by a 2D model representing a ring-like face-on structure. The changing of the C18O(3–2) line profile from double-peaked to single-peaked from the dense molecular Condensation 1 might be a signature of stalled expansion in this direction. In order to explain a self-absorption dip of the 13CO(2–1) and 13CO(3–2) lines, we suggest that RCW 120 is surrounded by a diffuse molecular cloud, and find confirmation of this cloud on a map of interstellar extinction. Optically thick 13CO(2–1) emission and the infrared 8 $\mu$m PAH band form a neutral envelope of the H ii region resembling a ring, while the envelope breaks into separate clumps on images made with optically thin C18O(2–1) line and far-infrared dust emission.
Abstract
We report the first interstellar detection of DC7N and six 13C-bearing isotopologues of HC7N towards the dark cloud TMC-1 through observations with the Green Bank Telescope, and confirm the ...recent detection of HC515N. For the average of the 13C isotopomers, DC7N, and HC515N, we derive column densities of 1.9(2) × 1011, 2.5(9) × 1011, and 1.5(4) × 1011 cm−2, respectively. The resulting isotopic ratios are consistent with previous values derived from similar species in the source, and we discuss the implications for the formation chemistry of the observed cyanopolyynes. Within our uncertainties, no significant 13C isotopomer variation is found for HC7N, limiting the significance CN could have in its production. The results further show that, for all observed isotopes, HC5N may be isotopically depleted relative to HC3N and HC7N, suggesting that reactions starting from smaller cyanopolyynes may not be efficient to form HCnN. This leads to the conclusion that the dominant production route may be the reaction between hydrocarbon ions and nitrogen atoms.
We present a survey of 56 massive star-forming regions in the 44 GHz methanol maser transition made with the Karl G. Jansky Very Large Array (VLA); 24 of the 56 fields showed maser emission. The data ...allow us to demonstrate associations, at arcsecond precision, of the Class I maser emission with outflows, H ii regions, and shocks traced by 4.5 m emission. We find a total of 83 maser components with line widths ranging from 0.17 to 3.3 km s−1, with a nearly flat distribution and a median value of 1.1 km s−1. The relative velocities of the masers with respect to the systemic velocity of the host clouds range from −2.5 to 3.1 km s−1, with a distribution peaking near zero. We also study the correlation between the masers and the so-called extended green objects (EGOs) from the GLIMPSE survey. Multiple sources in each field are revealed from IR images as well as from centimeter continuum emission from VLA archival data; in the majority of cases the 44 GHz masers are positionally correlated with EGOs, which seem to trace the younger sources in the fields. We report a possible instance of a 44 GHz maser associated with a low-mass protostar. If confirmed, this region will be the fifth known star-forming region that hosts Class I masers associated with low-mass protostars. We discuss three plausible cases of maser variability.
The results of a spectral survey of the region of massive star formation DR21OH in the 4-mm wavelength range are presented. Sixty-nine molecules and their isotopologues have been detected, ranging ...from simple diatomic or triatomic species such as SO, SiO and CCH, to complex organic molecules such as CH
3
OCHO or CH
3
OCH
3
. The obtained results qualitatively repeat the results of the survey of the same source at 3 mm. The inventories of molecules found at 3 and 4 mm overlap to a great extent. However, at 4 mm we found a number of species that have no allowed transitions in the 3-mm wavelength range, e.g., DCN, DNC, or SO
+
. The bulk of the molecules detected at 4 mm are those that are common for dense cores, e.g., HC
3
N or CH
3
CCH, but some of the detected species are typical for hot cores. The latter include complex organic molecules CH
3
OCHO, CH
3
CH
2
OH, CH
3
OCH
3
, etc. However, the detected emission of these molecules probably arises in a gas heated to 30 K only. Nine molecules, including complex species CH
3
C
3
N, CH
3
CH
2
CN, CH
3
COCH
3
, were found by spectral line stacking. This demonstrates the prospects of the method in the study of molecular clouds.
The excitation of methanol in the absence of external radiation is analyzed, and LTE methods for probing interstellar gas considered. It is shown that rotation diagrams correctly estimate the gas ...kinetic temperature only if they are constructed using lines whose upper levels are located in the same
K
-ladders, such as the
J
0
−
J
−1
E
lines at 157 GHz, the
J
1
−
J
0
E
lines at 165 GHz, and the
J
2
−
J
1
E
lines at 25 GHz. The gas density must be no less than 10
7
cm
−3
. Rotation diagrams constructed from lines with different
K
values for their upper levels (e.g., 2
K
−1
K
at 96 GHz, 3
K
−2
K
at 145 GHz, 5
K
−4
K
at 241 GHz) significantly underestimate the temperature, but enable estimation of the density. In addition, diagrams based on the 2
K
−1
K
lines can be used to estimate the methanol column density within a factor of about two to five. It is suggested that rotation diagrams should be used in the following manner. First, two rotation diagrams should be constructed, one from the lines at 96, 145, or 241 GHz, and another from the lines at 157, 165, or 25 GHz. The former diagram is used to estimate the gas density. If the density is about 10
7
cm
−3
or higher, the latter diagram reproduces the temperature fairly well. If the density is around 10
6
cm
−3
, the temperature obtained from the latter diagram should be multiplied by a factor of 1.5–2. If the density is about 10
5
cm
−3
or lower, then the latter diagram yields a temperature that is lower than the kinetic temperature by a factor of three or more, and should be used only as a lower limit for the kinetic temperature. The errors in the methanol column density determined from the integrated intensity of a single line can be more than an order of magnitude, even when the gas temperature is well known. However, if the
J
0
−(
J
− 1)
0
E
lines, as well as the
J
1
−(
J
− 1)
1
A
+
or
A
−
lines are used, the relative error in the column density is no more than a factor of a few.
A survey of young bipolar outflows in regions of low-to-intermediate-mass star formation has been carried out in two Class I methanol maser transitions: 70− 61A+ at 44 GHz and 4−1− 30E at 36 GHz. We ...detected narrow features towards NGC 1333I2A, NGC 1333I4A, HH25MMS and L1157 at 44 GHz, and towards NGC 2023 at 36 GHz. Flux densities of the lines detected at 44 GHz are no higher than 11 Jy and the relevant source luminosities are about 1022 erg s−1, which is much lower than those of strong masers in high-mass star formation regions. No emission was found towards 39 outflows. All masers detected at 44 GHz are located in clouds with methanol column densities of the order of or larger than a few ×1014 cm−2. The upper limits for the non-detections are typically of the order of 3–5 Jy. Observations in 2004, 2006 and 2008 did not reveal any significant variability of the 44 GHz masers in NGC 1333I4A, HH25MMS and L1157.
The hybrid gas-turbine engines for a medium-haul airliner are considered. The parametrical analysis data of two schemes using various fuels are presented. The areas of rational design parameters of ...such engines are defined. Questions of matching the work of the gas-dynamic and electrochemical components for these engines are considered.
The results of spectral observations of the region of massive star formation L379IRS1 (IRAS18265–1517) are presented. The observations were carried out with the 30-m Pico Veleta radio telescope ...(Spain) at seven frequencies in the 1-mm, 2-mm, and 3-mm wavelength bands. Lines of 24 molecules were detected, from simple diatomic or triatomic species to complex eight- or nine-atom compounds such as CH
3
OCHO or CH
3
OCH
3
. Rotation diagrams constructed from methanol andmethyl cyanide lines were used to determine the temperature of the quiescent gas in this region, which is about 40–50 K. In addition to this warm gas, there is a hot component that is revealed through high-energy lines of methanol and methyl cyanide, molecular lines arising in hot regions, and the presence of H
2
O masers and Class II methanol masers at 6.7 GHz, which are also related to hot gas. One of the hot regions is probably a compact hot core, which is located near the southern submillimeter peak and is related to a group of methanol masers at 6.7 GHz. High-excitation lines at other positions may be associated with other hot cores or hot post-shock gas in the lobes of bipolar outflows. The rotation diagrams can be use to determine the column densities and abundances of methanol (10
−9
) and methyl cyanide (about 10
−11
) in the quiescent gas. The column densities of
A
- and
E
-methanol in L379IRS1 are essentually the same. The column densities of other observedmolecules were calculated assuming that the ratios of the molecular level abundances correspond to a temperature of 40 K. The molecular composition of the quiescent gas is close to that in another region of massive star formation, DR21(OH). The only appreciable difference is that the column density of SO
2
in L379IRS1 is at least a factor of 20 lower than the value in DR21(OH). The SO
2
/CS and SO
2
/OCS abundance ratios, which can be used as chemical clocks, are lower in L379IRS1 than in DR21(OH), suggesting that L379IRS1 is probably younger than DR21(OH).
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