Nearby Dark Clouds Research Articles

Thermal Material in Dense Cores: A New Narrow-Line Probe and Technique of Temperature Determination

A survey of dense cores in nearby dark clouds indicates that the J=4→3 transition of HC 3 N is a good tracer of very quiescent, dense gas. High spectral resolution observations at 12 positions show the line to have a median intrinsic velocity dispersion of 0.088 km s −1 as compared to 0.100 km s −1 for new high spectral resolution measurements of the NH 3 (1, 1) transition at the same positions. The narrowest HC 3 N line has an observed FWMH of only 0.14 km s −1 , corresponding to an intrinsic velocity dispersion of only 0.058±0.002 km s −1

Pre-Main Sequence Binaries: The ESO Imaging Survey

AbstractWe have observed a complete sample of southern Hα emission line pre-main sequence (PMS) stars associated with the nearby dark clouds Chamaeleon and Ophiuchus in an effort to detect binary companions. We have used the high resolution CCD camera SUSI (0.13″ /pixel) at the ESO 3.5m New Technology Telescope (NTT). The observations were carried out in the Gunn z filter (0.95μ). As a result, we have discovered 28 companions out of 160 objects surveyed in the range of angular separation 0″.5 – 10″. We present histograms of semi-major axes and of brightness ratios of these PMS binaries. Taking small incompleteness corrections into account, the frequency of PMS binaries with semi-major axes in the range 100-1500 AU is 20%, while it is only 15% in same range for solar-type Main Sequence (MS) stars. Extrapolation yields a total PMS binary frequency of 70%. Evolutionary and environmental implications are briefly discussed.

Infrared properties of IRAS sources associated with nearby dark molecular clouds

We present an analysis of the infrared properties of a sample of IRAS sources associated with nearby dark molecular clouds. Examination of the luminosities and distribution of sources in colour−colour space suggests that they are T-Tauri stars and younger embedded cores, with mass typically ∼ 1 M ○. . The broad range of colour temperatures as a function of wavelength implies the presence of extended circumstellar dust components with considerable temperature variations. We combine the IRAS data with existing broad-band photometry between ∼ 1 μm and 20 μm to construct the spectral energy distributions for a small number of sources

Near Infrared Polarimetry of Dark Clouds and Star Forming Regions - Two Micron Polarization Survey of T Tauri Stars

Infrared polarimetry is one of the most useful methods to delineate the magnetic field structure in dark clouds and star-forming regions, where the intracloud extinction is so large that optical polarimetry is inaccessible. We have been conducting a near-infrared polarization survey of background field stars and embedded sources toward nearby dark clouds and star-forming regions (Tamura 1988). Particularly, the magnetic field structure in the denser regions of the clouds are well revealed in Heiles Cloud 2 in Taurus, ρ Oph core, and NGC1333 region in Perseus (Tamura et al. 1987; Sato et al. 1988; Tamura et al. 1988). This survey also suggests an interesting geometrical relationship between magnetic field and star-formation: the IR polarization of young stellar sources associated with mass outflow phenomena is perpendicular to the magnetic fields. This relationship suggests a presence of circumstellar matter (probably dust disk) with its plane perpendicular to the ambient magnetic field. Combining with another geometrical relationship that the elongation of the denser regions of the cloud is perpendicular to the magnetic field, the geometry suggests that the cloud contraction and subsequent star-formation have been strongly affected by the magnetic fields. Thus, it is important to study the universality of such geometrical relationship between IR polarization of young stellar sources and magnetic fields. In this paper, we report the results on a 2 micron polarization survey of 39 T Tauri stars, 8 young stellar objects and 11 background field stars in Taurus dark cloud complex.

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

Polarization measurements in B5, L1 34 and Heiles Cloud 2 and evidence of newly born stars

Polarization measurement of the background stars in the region of dark globules is important to study the magnetic field geometry and grants characteristics in the globule. These parameters are important for the formation and evolution of dark globules. We made Polarimetric observations of stars in three nearby dark clouds - B5, L134 and Heiles Cloud 2. Polarization measurements of stars in the region of B5 were made with ‘MINIPOL’ (Frecker and Serkowski, 1976) on 61″ telescope of University of Arizona. Observations for the stars in the region of L134 and Heiles Cloud 2 were made using PRL Polarimeter (Deshpande et al. 1985) on 1 meter telescope of Indian Institute of Astrophysics, Bangalore. Results are presented and discussed here. Figure 1 shows the polarization vectors projected on the sky plane for the above globules.

Structure and kinematics of molecular jets

Observational studies of the structure and kinematics of the supersonic molecular gas in star-forming regions are reviewed. These studies have suggested that the bulk of the high-velocity gas may be ambient-cloud material swept up by a collimated stellar wind. The actual structures of these outflows, however, are poorly understood. One source that may provide a better understanding of molecular outflows is that in the nearby dark cloud L1551. New observations of this outflow are presented and discussed in context of the models proposed by Snell and Schloerb.

Far-infrared observations of young clusters embedded in the R Coronae Australis and Rho Ophiuchi dark clouds

view Abstract Citations (34) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-infrared observations of young clusters embedded in the R CoronaeAustralis and rho Ophiuchi dark clouds. Wilking, B. A. ; Harvey, P. M. ; Joy, M. ; Hyland, A. R. ; Jones, T. J. Abstract Multicolor far-infrared maps in two nearby dark clouds, R Coronae Australis and Rho Ophiuchi, have been made in order to investigate the individual contribution of low-mass stars to the energetics and dynamics of the surrounding gas and dust. Emission from cool dust associated with five low-mass stars has been detected in CrA and four in Rho Oph; their far-infrared luminosities range from 2 solar luminosities to 40 solar luminosities. When an estimate of the bolometric luminosity was possible, it was found that typically more than 50 percent of the star's energy was radiated longward of 20 microns. Meaningful limits to the far-infrared luminosities of an additional 11 association members in CrA and two in Rho Oph were also obtained. The dust optical depth surrounding the star R CrA appears to be asymmetric and may control the dynamics of the surrounding molecular gas. The implications of these results for the cloud energetics and star formation efficiency in these two clouds are discussed. Publication: The Astrophysical Journal Pub Date: June 1985 DOI: 10.1086/163223 Bibcode: 1985ApJ...293..165W Keywords: Far Infrared Radiation; Infrared Stars; Molecular Clouds; Nebulae; Ophiuchi Clouds; Star Clusters; Astronomical Maps; Dust; Luminosity; Photographic Plates; Stellar Evolution; Astrophysics full text sources ADS | data products SIMBAD (18)

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

CO emission in directions of some millimeter wavelength continuum sources

view Abstract Citations (7) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CO emission in directions of some millimeter wavelength continuum sources. Kislyakov, A. G. ; Gordon, M. A. Abstract Observations of emission at 22.6 mm from 12CO, 13CO, and C18O from the nearby dark clouds L255, L673, L1471, and L1613 permit calculations of their molecular column densities for both CO and H2. Two of these clouds, L1613 and L673, are known to emit continuum radiation at millimeter wavelengths - presumably from embedded heated dust grains. The continuum emission correlates with the spatial distribution of the molecular column densities. Publication: The Astrophysical Journal Pub Date: February 1983 DOI: 10.1086/160722 Bibcode: 1983ApJ...265..766K Keywords: Carbon Monoxide; Interstellar Matter; Millimeter Waves; Molecular Clouds; Continuous Radiation; Emission Spectra; Line Spectra; Spectrum Analysis; Velocity Distribution; Astrophysics full text sources ADS | data products SIMBAD (9)

Hyperfine anomalies of HCN in cold dark clouds

We report observations of the J = 1..-->..0 line of HCN measured toward six positions in nearby low-temperature dark clouds. The measured relative intensities of the hyperfine components of the J = 1..-->..0 line are anomalous in that the F = 0..-->..1 transition is stronger than would be expected if all three components (F = 2..-->..1, F = 1..-->..1, F = 0..-->..1) had equal excitation temperatures. Differences of approximately 20% in the populations per sublevel of J = 1 could account for the observations. The results are in contrast to the situation observed in warmer molecular clouds associated with H II regions where the F = 1..-->..1 line is anomalously weak. The apparent overpopulation of J = 1, F = 0 in dark clouds may be related to the phenomenon observed in the J = 1..-->..0 transitions of HCO/sup +/ and HNC in the same objects where /sup 13/C substituted version of these species is found to be stronger than the /sup 12/C species.

On ultracold molecular gas toward the galactic center

view Abstract Citations (5) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On ultracold molecular gas toward the galactic center Zuckerman, B. ; Kuiper, T. B. H. Abstract Several positions near the galactic center (Sgr A) in the J=1-0 rotational transitions of (C-12)O, (C-13)O, and C(O-18) were observed in order to better understand the nature of the 'very cold' molecular gas whose existence was first stressed by Liszt and his colleagues (1975, 1977). It is established that several dips in the (C-12)O spectra are due to optically thick clouds of foreground CO with relatively low excitation temperatures (Tex). Tex is found to be greater than about 5.3 K for all such (C-12)O clouds in all five observed directions. Such clouds fall at the extreme low end of the measured range of Tex for nearby dark clouds, but would, nonetheless, generally be detected in sensitive emission surveys of galactic CO. Publication: The Astrophysical Journal Pub Date: February 1980 DOI: 10.1086/157686 Bibcode: 1980ApJ...235..840Z Keywords: Carbon Monoxide; Emission Spectra; Galactic Nuclei; Infrared Astronomy; Interstellar Gas; Molecular Gases; Absorption Spectra; Milky Way Galaxy; Optical Thickness; Spectral Resolution; Temperature Effects; Astrophysics full text sources ADS |

Radio observations of fragmentation and localized multiple velocity components in a group of dust clouds in Taurus

view Abstract Citations (35) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio observations of fragmentation and localized multiple velocity components in a group of dust clouds in Taurus. Clark, F. O. ; Giguere, P. T. ; Crutcher, R. M. Abstract A nearby (about 100 pc) dark cloud complex in Taurus with embedded newly formed stars has been observed in CO J = 1-0 spectral lines in order to study the kinematics of the early phases of cloud collapse. Three of eight observed regions have localized multiple velocity components in CO, which are interpreted as indicating fragmentation and resultant orbital motion of parts of the clouds. Deviations from the conservation of angular momentum expected from simple spherical collapse are apparently observed. The observed fragmentation process is widespread in the complex and is probably a common phenomenon in cloud collapse. Publication: The Astrophysical Journal Pub Date: July 1977 DOI: 10.1086/155382 Bibcode: 1977ApJ...215..511C Keywords: Carbon Monoxide; Cosmic Dust; Fragmentation; Interstellar Matter; Nebulae; Radio Observation; Angular Momentum; Gravitational Collapse; Interstellar Gas; Astrophysics full text sources ADS | data products SIMBAD (3)