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Title: Dynamical Timescale of Pre-collapse Evolution Inferred from Chemical Distribution in the Taurus Molecular Cloud-1 (TMC-1) Filament

Abstract

We present observations and analyses of the low-mass star-forming region, Taurus Molecular Cloud-1 (TMC-1). CS ( J = 2–1)/N{sub 2}H{sup +} ( J = 1–0) and C{sup 17}O ( J = 2–1)/C{sup 18}O ( J = 2–1) were observed with the Five College Radio Astronomy Observatory and the Seoul Radio Astronomy Observatory, respectively. In addition, Spitzer infrared data and 1.2 mm continuum data observed with Max-Planck Millimetre Bolometer are used. We also perform chemical modeling to investigate the relative molecular distributions of the TMC-1 filament. Based on Spitzer observations, there is no young stellar object along the TMC-1 filament, while five Class II and one Class I young stellar objects are identified outside the filament. The comparison between column densities calculated from dust continuum and C{sup 17}O 2–1 line emission shows that CO is depleted much more significantly in the ammonia peak than in the cyanopolyyne peak, while the column densities calculated from the dust continuum are similar at the two peaks. N{sub 2}H{sup +} is not depleted much in either peak. According to our chemical calculation, the differential chemical distribution in the two peaks can be explained by different timescales required to reach the same density, i.e., by different dynamical processes.

Authors:
;  [1];  [2];  [3]
  1. School of Space Research, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104 (Korea, Republic of)
  2. Square Kilometre Array Organisation, Jodrell Bank Observatory, Lower Withington, Cheshire SK11 9DL (United Kingdom)
  3. Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205 (United States)
Publication Date:
OSTI Identifier:
22661141
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, Supplement Series; Journal Volume: 229; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMMONIA; BOLOMETERS; CARBON; CARBON 17; CARBON MONOXIDE; CLOUDS; COMPARATIVE EVALUATIONS; DENSITY; FILAMENTS; MASS; MOLECULES; RADIOASTRONOMY; STAR EVOLUTION; STARS

Citation Formats

Choi, Yunhee, Lee, Jeong-Eun, Bourke, Tyler L., and II, Neal J. Evans, E-mail: yunhee.choi@khu.ac.kr, E-mail: jeongeun.lee@khu.ac.kr. Dynamical Timescale of Pre-collapse Evolution Inferred from Chemical Distribution in the Taurus Molecular Cloud-1 (TMC-1) Filament. United States: N. p., 2017. Web. doi:10.3847/1538-4365/AA69BA.
Choi, Yunhee, Lee, Jeong-Eun, Bourke, Tyler L., & II, Neal J. Evans, E-mail: yunhee.choi@khu.ac.kr, E-mail: jeongeun.lee@khu.ac.kr. Dynamical Timescale of Pre-collapse Evolution Inferred from Chemical Distribution in the Taurus Molecular Cloud-1 (TMC-1) Filament. United States. doi:10.3847/1538-4365/AA69BA.
Choi, Yunhee, Lee, Jeong-Eun, Bourke, Tyler L., and II, Neal J. Evans, E-mail: yunhee.choi@khu.ac.kr, E-mail: jeongeun.lee@khu.ac.kr. Sat . "Dynamical Timescale of Pre-collapse Evolution Inferred from Chemical Distribution in the Taurus Molecular Cloud-1 (TMC-1) Filament". United States. doi:10.3847/1538-4365/AA69BA.
@article{osti_22661141,
title = {Dynamical Timescale of Pre-collapse Evolution Inferred from Chemical Distribution in the Taurus Molecular Cloud-1 (TMC-1) Filament},
author = {Choi, Yunhee and Lee, Jeong-Eun and Bourke, Tyler L. and II, Neal J. Evans, E-mail: yunhee.choi@khu.ac.kr, E-mail: jeongeun.lee@khu.ac.kr},
abstractNote = {We present observations and analyses of the low-mass star-forming region, Taurus Molecular Cloud-1 (TMC-1). CS ( J = 2–1)/N{sub 2}H{sup +} ( J = 1–0) and C{sup 17}O ( J = 2–1)/C{sup 18}O ( J = 2–1) were observed with the Five College Radio Astronomy Observatory and the Seoul Radio Astronomy Observatory, respectively. In addition, Spitzer infrared data and 1.2 mm continuum data observed with Max-Planck Millimetre Bolometer are used. We also perform chemical modeling to investigate the relative molecular distributions of the TMC-1 filament. Based on Spitzer observations, there is no young stellar object along the TMC-1 filament, while five Class II and one Class I young stellar objects are identified outside the filament. The comparison between column densities calculated from dust continuum and C{sup 17}O 2–1 line emission shows that CO is depleted much more significantly in the ammonia peak than in the cyanopolyyne peak, while the column densities calculated from the dust continuum are similar at the two peaks. N{sub 2}H{sup +} is not depleted much in either peak. According to our chemical calculation, the differential chemical distribution in the two peaks can be explained by different timescales required to reach the same density, i.e., by different dynamical processes.},
doi = {10.3847/1538-4365/AA69BA},
journal = {Astrophysical Journal, Supplement Series},
number = 2,
volume = 229,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}
  • Seventy-five fields from the Einstein X-Ray Observatory IPC detector between 3h and 5h right ascension and 15 deg and 35 deg declination are examined to search for X-ray-emitting low-mass pre-main-sequence (PMS) stars. Six such stars were previously found; they appear to be similar to T Tauri stars but without dense circumstellar envelopes or winds. Finding charts are presented for 59 X-ray sources that may be PMS stars. While some are likely to be spurious X-ray sources, chance coincidences with unrelated stars, or non-PMS stellar sources such as RS CVn type binaries, approximately half are probably X-ray-selected PMS stars. 46 references.
  • We report Spitzer Space Telescope observations of the four lowest rotational transitions of H{sub 2} in three portions of the boundary of the Taurus molecular cloud. Emission in the two lowest transitions, S(0) and S(1), was detected in almost all pointing directions, while the S(2) and S(3) lines were marginally detected only after further averaging of data. The widespread detection of lines coming from levels 510 K and 1016 K above the molecular ground state is indicative of gas at a temperature of at least 200 K containing column densities (1-5) x 10{sup 18} cm{sup -2} of H{sub 2}. Formore » the region with the simplest geometry, we have used the Meudon PDR code to model the chemistry, radiative transfer, and excitation of molecular hydrogen. We conclude that models with acceptable values of the UV interstellar radiation field can reproduce the amount of H{sub 2} in the lowest excited state, but cannot account for the degree of excitation of the H{sub 2}. The unexpectedly high degree of excitation of the H{sub 2} in the boundary layer of a molecular cloud, which cannot be explained by the presence of stellar sources, points to an enhanced heating rate which may be the result of, e.g., dissipation of turbulence. We have in one boundary region been able to obtain the ortho-to-para ratio (OPR) for H{sub 2}, which by modeling and possible detection of the S(2) and S(3) lines has a range 1.0 {>=} OPR {>=} 0.15, although this result must be treated with caution. The fact that the ortho-to-para ratio is lower than that expected for equilibrium at the gas kinetic temperature may be indicative of circulation of material from cold, purely molecular regions into the boundary layer, possibly due to turbulent diffusion. The explanation of these data may thus be suggestive of processes that are having a significant effect on the structure and evolution of molecular clouds and the star formation that takes place within them.« less
  • Observations of giant stars in the oldest Large Magellanic Cloud (LMC) globular clusters were used to deduce metal abundances and radial velocities for the clusters. From the distribution of metallicities, radial velocities, position in the sky, position in the two-color diagram, color-magnitude diagram morphology, and distribution of ellipticities, we argue that these clusters make up a different dynamical component from the young disk (i.e., halo). Based on this conclusion, we present a tentative scenario for the early chemical and dynamical evolution of the LMC. Subject headings: clusters: globular: galaxies: Magellanic Clouds: galaxies: stellar content: stars; abundances: stars: evolution
  • We have observed five rotational transitions of cyanoacetylene in the ark cloud TMC 1 and, using a Monte Carlo radiative transfer code, have produced a model of this source which is consistent with these observations. The interaction between radiative trapping and population equilibrium was solved for the 15 lowest rotational levels of HC/sub 3/N, assuming a cylindrical geometry for the source. The model, which we envisage as representing a compact condensation embedded well within Heiles' Cloud 2, is characterized by a relatively high excitation core and a lower excitation halo. Although we cannot rule out the possibility that the highermore » excitation of the core can be attributed solely to enhanced density there, we were unable to fit the observations well without involving a temperature enhancement as well. Transitions higher in frequency than the J = 8..-->..7 line originate predominantly in the core which is characterized by a kinetic temperature of 17 K and H/sub 2/ density of 6 x 10/sup 4/ cm/sup -3/. Corresponding values for the halo are 7 K and 8 x 10/sup 3/. The column density of HC/sub 3/N in TMC 1 is estimated to be 1.1 x 10/sup 14/ cm/sup -2/.« less
  • Deuterated cyanodiacetylene (DC/sub 5/N) has been observed for the first time in an interstellar cloud. The J = 10..-->..9 and J = 9..-->..8 transitions have been detected in emission in TMC 1. The abundance ratio DC/sub 5/N/HC/sub 5/N is found to lie in the range 0.006--0.016 overlapping the range 0.013--0.017 observed for DCO/sup +//HCO/sup +/, but somewhat less than the range 0.02--0.08 determined for DC/sub 3/N/HC/sub 3/N. From these observations, it is not possible to rule out the formation of HC/sub 5/N on grain surfaces or by dissociation of larger molecules.