Dense Cores In Dark Clouds Research Articles

Dense cores in dark clouds. 9: Observations of (13)CO and C(18)O in Vela, Chamaeleon, Musca, and the Coalsack

view Abstract Citations (52) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense Cores in Dark Clouds. IX. Observations of 13CO and C 18O in Vela, Chamaeleon, Musca, and the Coalsack Vilas-Boas, J. W. S. ; Myers, P. C. ; Fuller, G. A. Abstract One hundred one condensations with average optical size less than 7 min and visual extinction greater than 2.5 mag have been selected from European Southern Observatory (ESO) J plates, extinction maps, and catalogs of southern hemisphere dark clouds for observation in the (13)CO and C(18)O J = 1 goes to 0 transitions. These regions are condensations in the dark molecular clouds Musca, Coalsack, Chamaeleon II, Chamaeleon III, and cometary globules in Vela and Gum nebula. A search for IRAS point sorces having colors of young stellar objects shows that these condensations have at most seven associated young stellar objects-far fewer than in Taurus and Ophiuchus. These 101 condensations generally have lower (13)CO and C(18)O line intensity, C(18)O optical depth, and (13)CO line width than do 90 condensations in Taurus, Ophiuchus, and Cepheus. Similarly, 47 of these southern condensations having star-count estimates of visual extinction generally have less extinction than do the 19 condensations in Taurus having extinction estimated by the same method. The C(18)O to (13)CO line-width ratio for the cometary globules in the Vela ragion is greater than for the other clouds, indicating that the (13)CO line width observed toward dark cloud condensations is related to the more extended and less dense intercondensation gas. Radial velocities suggest that the system of Vela globules has velocity dispersion 4.7 km/s, which is at least 2 times greater than the dispersion determined from formalhyde observations. The Musca filament has velocities which are slightly higher-by approximately 0.5 km/s-in the center than at the ends of the filament. Chamaeleon III has a 0.2 km/s velocity gradient and Chamaeleon II has no indication of velocity gradients. The Chamaeleon clouds and the Musca filament appear close to virial equilibrium. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174628 Bibcode: 1994ApJ...433...96V Keywords: Carbon Dioxide; Gas Dynamics; Interstellar Gas; Kinematics; Molecular Clouds; Molecular Spectra; Radio Astronomy; Astronomical Spectroscopy; Carbon 13; Ophiuchi Clouds; Radio Telescopes; Astronomy; ISM: CLOUDS; ISM: KINEMATICS AND DYNAMICS; ISM: MOLECULES full text sources ADS | data products SIMBAD (113) Related Materials (12) Part 1: 1983ApJ...264..517M Part 2: 1983ApJ...266..309M Part 3: 1983RMxAA...7..238M Part 4: 1983ApJ...270..105M Part 5: 1983ApJ...270..589B Part 6: 1988ApJ...324..907M Part 7: 1991ApJ...376..561M Part 8: 1992ApJ...384..523F Part 9: 1993ApJ...406..528G Part 11: 1994ApJ...433..117L Part 12: 1998ApJ...506..743B Part 13: 2000ApJ...532.1038V

Dense cores in dark clouds. 10: Ammonia emission in the Perseus molecular cloud complex

view Abstract Citations (61) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense Cores in Dark Clouds. X. Ammonia Emission in the Perseus Molecular Cloud Complex Ladd, E. F. ; Myers, P. C. ; Goodman, A. A. Abstract We present a survey for dense material around young IRAS sources in the Perseus molecular cloud complex in the NH3 (J, K)=(1,1) line at 1.3 cm. NH3 emission was detected in eight, and mapped in seven, out of 10 positions chosen for study. The dense cores found typically have lower masses and narrower line widths than cores previously studied in Perseus and are located near sources of lower luminosity. NH3 cores are found throughout the Perseus complex; however, much of the detected dense gas is concentrated into two filamentary 'ridges' located in the western part. As a group, NH3 cores in Perseus have a mean line width of 0.6 km/s, mean radius of 0.12 pc, mean kinetic temperature of 13 K, and mean mass of 9 solar mass. These mean values are larger than the mean values for NH3 cores with associated stars in Taurus, but smaller than the mean values for cores associated with stars in Orion A. Some of the cores in Perseus are 'thermally dominated', with thermal and nonthermal line widths similar to most Taurus cores, while others are 'nonthermally dominated' and are more similar to the cores in Orion A. We conclude that the Perseus complex is intermediate in its star-forming potential between the predominantly low-mass star-producing regions like Taurus and the regions capable of the producing high-mass stars such as Orion A. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174629 Bibcode: 1994ApJ...433..117L Keywords: Ammonia; Interstellar Gas; Molecular Clouds; Molecular Spectra; Radio Astronomy; Radio Spectra; Sky Surveys (Astronomy); Star Formation; Astronomical Spectroscopy; Emission Spectra; Line Spectra; Stellar Mass; Astronomy; ISM: MOLECULES; ISM: INDIVIDUAL NAME: PERSEUS MOLECULAR CLOUD; RADIO LINES: ISM full text sources ADS | data products SIMBAD (31) Related Materials (12) Part 1: 1983ApJ...264..517M Part 2: 1983ApJ...266..309M Part 3: 1983RMxAA...7..238M Part 4: 1983ApJ...270..105M Part 5: 1983ApJ...270..589B Part 6: 1988ApJ...324..907M Part 7: 1991ApJ...376..561M Part 8: 1992ApJ...384..523F Part 9: 1993ApJ...406..528G Part 10: 1994ApJ...433...96V Part 12: 1998ApJ...506..743B Part 13: 2000ApJ...532.1038V

Dense cores in dark clouds. VII - Line width-size relations

Observations of 14 dense cores in lines of CS, C 18 O and NH, are combined to examine the relations between the Doppler width of a line and the spatial extent of the map of line intensity. The line width increases with map size R as R p . The deduced width of the velocity distribution of the molecule of mean mass has p = 0.20 ± 0.04, and the deduced width of the nonthermal velocity distribution has p = 0.7 ± 0.1. The values of p for eight cores with embedded stars and for six cores without embedded stars are statistically indistinguishable, but p is better determined for cores without stars

Dense cores in dark clouds. VI - Shapes

A comparison is presently conducted between 48 line-intensity maps of 16 dense cores in dark clouds, based on observations in the 13-mm line of NH3 and the 3-mm lines of CS and C(O-18). Core elongation in this sample does not differ significantly between cores with and without embedded stars; elongation appears to be a condition prior to star formation, rather than the consequence of formation. The characteristic elongation of dense cores implies that models of equilibrium between self-gravity and isotropic random motions are incomplete. The observed elongation of dense cores in projection is modeled as arising from a group of either prolate or oblate spheroids. 50 refs.

A survey for dense cores in dark clouds

view Abstract Citations (623) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Survey for Dense Cores in Dark Clouds Benson, P. J. ; Myers, P. C. Abstract A total of 149 dark cloud positions were surveyed for evidence of 'dense cores' in the (J,K) = (1,1) rotating inversion line of NH3. Clouds with strong emission were mapped to determine the position of the core, and maps of 41 cores are presented. The spectrum of the peak emission is fitted by least-squares analysis to determine the optical depth, velocity, intrinsic line width, and excitation temperature. Statistical equilibrium analysis is used to determine the density of the core and the kinetic temperature when possible. Most of the dense cores have temperatures of 10-15 K, densities of 2000-20,000/cu cm, and intrinsic linewidths of 0.2-0.9 km/s. The core masses range from about 0.5 solar in L1517B to 760 solar in L1031B, and their sizes range from 0.06 to 0.9 pc. The cores are not generally spherically shaped, wtih aspect ratios ranging from 1.1 to 4 4. Cores with stars have broader lines than cores without stars. Publication: The Astrophysical Journal Supplement Series Pub Date: September 1989 DOI: 10.1086/191365 Bibcode: 1989ApJS...71...89B Keywords: Dark Matter; Molecular Clouds; Nebulae; Pre-Main Sequence Stars; Star Formation; Ammonia; Infrared Sources (Astronomy); Astrophysics; INTERSTELLAR: MOLECULES; NEBULAE: GENERAL; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (289)

Dense cores in dark clouds. V - CO outflow

view Abstract Citations (170) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense Cores in Dark Clouds. V. CO Outflow Myers, P. C. ; Heyer, M. ; Snell, Ronald L. ; Goldsmith, P. F. Abstract Sixteen dense cores in nearby dark clouds having associated low-mass stars were surveyed in the J = 1-0 line of 12CO at 2.6 mm, and seven were found to have CO outflow. These outflows are among the weakest known, with mass loss rates of less than 10-8M_sun;yr-1, similar to those of winds from T Tauri stars. The results presented here indicate that outflows in star-core systems are sufficiently frequent; last long enough; have sufficient available momentum and kinetic energy; and have enough evidence of outflow-core interaction, in order to be the main agent of core dispersal. If so, outflows play an important role in determining the main-sequence mass of low-mass stars. Publication: The Astrophysical Journal Pub Date: January 1988 DOI: 10.1086/165948 Bibcode: 1988ApJ...324..907M Keywords: Carbon Monoxide; Molecular Clouds; Stellar Cores; Stellar Winds; T Tauri Stars; Dark Matter; Interstellar Chemistry; Star Formation; Stellar Luminosity; Stellar Mass; Stellar Spectra; Astrophysics; INTERSTELLAR: MOLECULES; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (24) Related Materials (12) Part 1: 1983ApJ...264..517M Part 2: 1983ApJ...266..309M Part 3: 1983RMxAA...7..238M Part 4: 1983ApJ...270..105M Part 5: 1983ApJ...270..589B Part 7: 1991ApJ...376..561M Part 8: 1992ApJ...384..523F Part 9: 1993ApJ...406..528G Part 10: 1994ApJ...433...96V Part 11: 1994ApJ...433..117L Part 12: 1998ApJ...506..743B Part 13: 2000ApJ...532.1038V

Near-infrared and optical observations of IRAS sources in and near dense cores

The authors report photometry from 0.4 to 20 μm of 34 IRAS point sources associated with dense cores in dark clouds. The main results of this study are: (1) Stars near cores tend to be visible T Tauri stars, while stars in cores tend to have circumstellar extinction A<SUB>V</SUB> ≡ 30 - 90 mag and luminosity ≡1 L_sun;, similar to that of T Tauri stars. (2) The typical highly obscured star is probably accompanied by a luminous structure of substellar temperature, such as a circumstellar disk. (3) In Taurus-Aurigae, stars in cores probably become visible T Tauri stars less than 1×10<SUP>5</SUP>yr after they attain luminosity greater than ≡0.1 L_sun;. This implies that they are extremely young and may still be accreting.

Dense cores in dark clouds - Young embedded stars at 2 micrometers

view Abstract Citations (56) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense cores in dark clouds : young embedded stars at 2 micrometers. Benson, P. J. ; Myers, P. C. ; Wright, E. L. Abstract Twenty-five visually opaque regions which contain strong sources of NH3 (1,1) line emission (dense cores) have been surveyed for evidence of associated stars at two microns. Five such stars have been found, of which three - in B5, L1489, and L1582 - are optically invisible and probably embedded in their associated cores. The stars in B5 and L1489 have 2-100 micron spectra and luminosity similar to those of HL Tau, a very young T Tauri star. These stars probably formed in the cores where they are now seen. These results tend to confirm earlier suggestions that low-mass stars form in dense cores. Publication: The Astrophysical Journal Pub Date: April 1984 DOI: 10.1086/184248 Bibcode: 1984ApJ...279L..27B Keywords: Early Stars; Pre-Main Sequence Stars; Stellar Cores; Stellar Evolution; Stellar Spectra; Density Distribution; Infrared Astronomy; Micrometers; Molecular Clouds; Astrophysics full text sources ADS | data products SIMBAD (8)

Dense cores in dark clouds. IV - HC5N observations

view Abstract Citations (112) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense cores in dark clouds. IV. HC5N observations. Benson, P. J. ; Myers, P. C. Abstract Detections or possible detections of the J = 9-8 rotational transition of HC5N in 10 new dark cloud sources are reported. All of the strong sources and most of the known sources are in Taurus. In contrast to maps of TMC-1, maps of NH3 and HC5N emission in L1544 and in TMC-1C show no relative shift of peak positions. Column densities of HC5N and (C-18)O are roughly corelated, but N(HC5N) increases faster than N(C-18)O, suggesting that the abundance of HC5N ranges from about 10 to the -10th in the weakest sources to about 10 to the -9th in the strongest sources. Comparison with predictions of chemical models indicates that this abundance variation is unlikely to be due to variations in cloud density, but it may be due to diferences in the degree of chemical evolution from cloud to cloud. If so, TMC-1 is more evolved than L183. Publication: The Astrophysical Journal Pub Date: July 1983 DOI: 10.1086/161151 Bibcode: 1983ApJ...270..589B Keywords: Astronomical Spectroscopy; Cyano Compounds; Line Spectra; Molecular Clouds; Abundance; Acetylene; Chemical Evolution; Emission Spectra; Interstellar Matter; Nebulae; Astrophysics full text sources ADS | data products SIMBAD (71) Related Materials (12) Part 1: 1983ApJ...264..517M Part 2: 1983ApJ...266..309M Part 3: 1983RMxAA...7..238M Part 4: 1983ApJ...270..105M Part 6: 1988ApJ...324..907M Part 7: 1991ApJ...376..561M Part 8: 1992ApJ...384..523F Part 9: 1993ApJ...406..528G Part 10: 1994ApJ...433...96V Part 11: 1994ApJ...433..117L Part 12: 1998ApJ...506..743B Part 13: 2000ApJ...532.1038V

Dense cores in dark clouds. III - Subsonic turbulence

In 43 dark clouds with narrow molecular lines, significant correlations exist between line width and map size of the form ..delta..vproportionalR/sup 0.5/, and between mean density and map size of the form nproportionalR/sup -1/; and the law of virial equilibrium is closely satisfied. These relations tend to confirm those found earlier for larger clouds, and extend them into the regime of subsonic turbulence. If these relations for large and small clouds reflect the same process, it is still unclear whether this process is a turbulent energy cascade, as in Kolmogorov turbulence, or simply the tendency of clouds with nproportionalR/sup -1/ to be in virial equilibrium. For the smallest clouds (''dense cores'') there is weak support for the turbulent cascade picture. In this picture viscous dissipation of turbulence is likely to play an important role in heating and star formation. The time scale for the free decay of turbulence in dense cores is < or approx. =5 x 10/sup 5/ yr, comparable to the free-fall time. Dense cores can thus form low-mass stars on free-fall time scales if their input of fresh turbulence is sufficiently reduced. This reduction may occur as a result of their small size, or their high densitymore » contrast with surrounding gas. Observed distributions of dense core properties in Taurus, Ophiuchus, and other dark cloud regions appear consistent with dense core evolution toward star formation via dissipation of turbulence. In complexes which are vigorously forming low-mass stars, dense cores are more prevalent, smaller, denser, and have narrower lines than in regions with less star formation.« less

Dense cores in dark clouds. II - NH3 observations and star formation

view Abstract Citations (528) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense cores in dark clouds. II. NH3 observations and star formation. Myers, P. C. ; Benson, P. J. Abstract All strong, 'dense core' sources and (2, 2)-line observations are mapped in the present results of a survey of about 100 visually opaque regions in nearby dark clouds in the 1.3-cm (J, K) = (1, 1) line of NH3. Line shapes are compared with cloud motion models, and source density, size, and temperature are compared with equilibrium and stability requirements. These are found to indicate that most dense cores are in the early stages of collapse, or in near-critical equilibrium. If the latter possibility is the case, support is probably furnished by a combination of thermal and subsonic turbulent motions. Positions of the 10 known dense cores in Taurus-Auriga are correlated with emission-line star group positions. The results obtained cumulatively suggest that most of the dense cores described will form low mass stars in the next one million years. Publication: The Astrophysical Journal Pub Date: March 1983 DOI: 10.1086/160780 Bibcode: 1983ApJ...266..309M Keywords: Ammonia; Interstellar Matter; Molecular Spectra; Nebulae; Star Formation; Auriga Constellation; Emission Spectra; Line Spectra; Stellar Mass; Taurus Constellation; Astrophysics full text sources ADS | data products SIMBAD (30) Related Materials (12) Part 1: 1983ApJ...264..517M Part 3: 1983RMxAA...7..238M Part 4: 1983ApJ...270..105M Part 5: 1983ApJ...270..589B Part 6: 1988ApJ...324..907M Part 7: 1991ApJ...376..561M Part 8: 1992ApJ...384..523F Part 9: 1993ApJ...406..528G Part 10: 1994ApJ...433...96V Part 11: 1994ApJ...433..117L Part 12: 1998ApJ...506..743B Part 13: 2000ApJ...532.1038V

Dense cores in dark clouds. I - CO observations and column densities of high-extinction regions

view Abstract Citations (337) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense cores in dark clouds. I. CO observations and column densities of high-extinction regions. Myers, P. C. ; Linke, R. A. ; Benson, P. J. Abstract Ninety small (approximately 5 arcmin) visually opaque regions selected for Palomar Sky Atlas prints are surveyed in the 2.7 mm J = 1 - 0 lines of C(O-18) and (C-13)O. The regions are for the most part in complexes of obscuration, including those in Taurus and Ophiuchus. The typical C(O-18) emission region has a C(O-18) line width of 0.6 km/s, an optical depth of 0.4, an excitation temperature of 10 K, and a column density of 2 x 10 to the 15th per sq cm. It has a size of 0.3 pc, a visual extinction of approximately 11 mag, and a mass of approximately 30 solar masses. A comparison with equilibrium and collapse models suggests that purely thermal supporting motions are consistent with the present data, although this is considered unlikely. It is pointed out that if the full C(O-18) line width reflects turbulent supporting motions, nearly all of the observed clouds are consistent with stable equilibrium. If only part of the C(O-18) line width reflects supporting motions, a number of clouds are also consistent with turbulent contraction. Publication: The Astrophysical Journal Pub Date: January 1983 DOI: 10.1086/160619 Bibcode: 1983ApJ...264..517M Keywords: Carbon Monoxide; Interstellar Extinction; Interstellar Matter; Molecular Clouds; Nebulae; Spectral Line Width; Astronomical Catalogs; Astronomical Spectroscopy; Emission Spectra; Gauss Equation; Histograms; Line Spectra; Astrophysics full text sources ADS | data products SIMBAD (105) Related Materials (12) Part 2: 1983ApJ...266..309M Part 3: 1983RMxAA...7..238M Part 4: 1983ApJ...270..105M Part 5: 1983ApJ...270..589B Part 6: 1988ApJ...324..907M Part 7: 1991ApJ...376..561M Part 8: 1992ApJ...384..523F Part 9: 1993ApJ...406..528G Part 10: 1994ApJ...433...96V Part 11: 1994ApJ...433..117L Part 12: 1998ApJ...506..743B Part 13: 2000ApJ...532.1038V