Rho Oph Research Articles

2 centimeter H2CO emission in the Rho Ophiuchi cloud

Strong emission in the 2 cm J-1K/sub 1/ =2/sub 12/--2/sub 11/ line of H/sub 2/CO has been found in the rho Oph dark cloud (rho Oph B). Previously this 2 cm H/sub 2/CO line has been detected in emission only in the warm (T/sub K/>50 K) clouds OMC-1 and OMC-2. Densities in excess of 10/sup 6/ cm/sup -3/ are required to drive this 2 cm line into emission. The 2 mm J-1K/sub 1/ =2/sub 12/--1/sub 11/ ortho-H/sub 2/CO emission line at rho Oph B appears to be self-reversed when compared to optically thin lines (e.g., H/sub 2//sup 13/CO). The dense rho Oph B core has a mass of approx.100 M/sub sun/ and an extinction of A/sub v/>200 mag similar to OMC-1 or OMC-2, but differs from them in temperature, being a cold region emitting strong lines of DCO/sup +/. While near- and far-infrared and radio continuum searches cover the rho Oph B region, no known sources are coincident with the region of 2 cm H/sub 2/CO emission. More sensitive searches are needed. The lack of observed signposts of star formation in an unusually dense cold region indicates rho Oph B may represent an earlier stage of cloud evolution than eithermore » the OMC-1 or OMC-2 regions.« less

Local gamma rays and cosmic-ray acceleration by supersonic stellar winds

Supersonic stellar winds are quite common among the brightest and/or the youngest stars, i.e., O stars and B supergiants, T Tauri stars, Herbig-Haro objects etc. We propose that the shocked region at the boundary between the stellar wind and the surrounding medium is, under certain conditions, the site of acceleration of charged particles with a power-law energy spectrum, extending a suggestion proposed by Jokipii for the solar wind. This mechanism should operate up to approx.10/sup 15/ eV. On the basis of the Copernicus UV observations, we suggest that the luminous OB stars pertaining to the Gould Belt are the major sources of local cosmic rays. We present observational support to cosmic-ray acceleration by stellar wind in the rho Oph cloud, based on high-energy ..gamma..-ray observations performed by the COS B satellite. A major consequence of these views is the peculiar character of our local galactic environment as far as cosmic rays are concerned.

Observations of late-type young stars in the Rho OPH dark cloud

We present photoelectric BVRI photometry for 16 T Tau and related stars in the Rho Oph dark cloud, as well as vidicon spectroscopic observations for nine stars. The color excesses of these stars favor circumstellar dust shells as the source of the observed infrared excesses.

Origin of large interstellar grains toward Rho Ophiuchi

The paper considers why the interstellar grains toward Rho Oph are unusually large. Because the visual opacity per gram is lower than average toward Rho Oph, it is concluded that the simplest interpretation of the observations is that grain coagulation has occurred. This result may be important for understanding the evolution of interstellar clouds and may provide insight into the initial stages of the formation of large solid bodies such as planets.

Observations of interstellar H2O emission at 183 gigahertz

view Abstract Citations (78) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of interstellar H2O emission at 183 gigahertz Waters, J. W. ; Kakar, R. K. ; Kuiper, T. B. H. ; Roscoe, H. K. ; Swanson, P. N. ; Rodriguez Kuiper, E. N. ; Kerr, A. R. ; Thaddeus, P. ; Gustincic, J. J. Abstract Observations of the 183-GHz rotational transition of water vapor in interstellar molecular clouds are reported. The observations were made with a portable double-sideband superheterodyne radiometer used with the 91-cm Cassegrain telescope on board the Kuiper Airborne Observatory. An emission feature was detected in the direction of the Kleinmann-Low nebula in Orion with a peak antenna temperature of 15 K, a local standard of rest velocity of 8 km/sec, and a width of 15 km/sec. A plateau component of the emission profile is attributed to the 1-arcmin region characteristic of plateau emission from other observed molecules, with emission enhanced over that expected for thermal excitation, while the spike component observed is consistent with an optically thick source of the size of the molecular ridge in Orion at a temperature of 50 K and a column density greater than or equal to 3 x 10 to the 17th/sq cm, implying that H2O is one of the more abundant species in the Orion Molecular Cloud. Emission at 183 GHz was not detected in Sgr A, Sgr B2, W3, W43, W49, W51, DR 21, NGC 1333, NGC 7027, GL 2591 or the Rho Oph cloud; it may have been detected in M 17. Publication: The Astrophysical Journal Pub Date: January 1980 DOI: 10.1086/157609 Bibcode: 1980ApJ...235...57W Keywords: Infrared Astronomy; Interstellar Space; Microwave Emission; Nebulae; Radio Sources (Astronomy); Water Masers; Airborne Equipment; Brightness Temperature; Line Spectra; Molecules; Spectroscopic Telescopes; Astrophysics full text sources ADS |

CO observations of IC 5146

We find that the dark cloud associated with IC 5146 contains three relatively intense CO bright spots, which probably indicate the presence of embedded, newly formed stars. Signposts of massive (i.e., O) star formation such as H/sub 2/O maser, compact continuum, and bright infrared sources seem to be absent, suggesting that IC 5146 is a region where the formation of stars of later spectral type (i.e., B and later) is occurring. Comparison of our observations with other data suggests that the formation of these stars has been most intense in a small (approx.5 pc), dense, possibly compressed, molecular core located at one end of the more extended (approx.20 pc) cloud complex. The possible origin of this star-forming core is briefly discussed. We also find the IC 5146 cloud complex to be remarkably similar to the rho Oph complex in mass, size, structure, stellar content, and internal molecular velocity dispersion.

Infrared polarimetry in the Rho Ophiuchus dark cloud

Infrared polarimetry has been obtained of 16 objects in the proposed region of star formation in the rho Oph dark cloud. This study is used along with visual polarimetry, infrared photometry, and molecular line studies to deduce the cloud morphology around the very young stellar cluster.

Upper photospheric temperature models of K giants - A comparison of super-metal-rich giants with normal giants

view Abstract Citations (21) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Upper photospheric temperature models of K giants: a comparison of super-metal-rich giants with normal giants. Desikachary, K. ; Gray, D. F. Abstract The LTE version of K-line synthesis that takes partial coherency effects into account is applied to the Ca II K-line wings in the spectra of four normal K giants (Beta Gem, Nu Cyg, Rho Oph, Alpha Ari) and two super-metal-rich (SMR) K giants (Alpha Ser, Beta Oph) in order to derive upper-photospheric temperature models. A model-atmosphere flux-calibration procedure that precludes the necessity of a measured angular diameter is used in the analysis of the K-line wing profiles, on the basis of which the SMR and normal K giants are compared quantitatively. The results show that temperature enhancements of 200 to 300 K in excess of radiative-equilibrium models are required in the upper photospheres of all six stars and that the upper photospheres of the SMR star models are up to 180 K cooler than those of the normal models. The temperature enhancements are interpreted as departures from radiative equilibrium, and the differential cooling in the SMR stars is tentatively attributed to enhanced CN and CO line absorption. Publication: The Astrophysical Journal Pub Date: December 1978 DOI: 10.1086/156672 Bibcode: 1978ApJ...226..907D Keywords: Giant Stars; K Lines; K Stars; Metallic Stars; Photosphere; Stellar Models; Stellar Temperature; Calcium; Stellar Spectrophotometry; Thermodynamic Equilibrium; Astrophysics; Atmospheres:K Giants; K Giants:Line Profiles; K Giants:Metal-Rich Stars; Stellar Atmospheres: Models full text sources ADS | data products SIMBAD (7) Related Materials (1) Erratum: 1980ApJ...236.1056D

A survey of interstellar H I from L-alpha absorption measurements. II

The Copernicus satellite surveyed the spectral region near L alpha to obtain column densities of interstellar HI toward 100 stars. The distance to 10 stars exceeds 2 kpc and 34 stars lie beyond 1 kpc. Stars with color excess E(B-V) up to 0.5 mag are observed. The value of the mean ratio of total neutral hydrogen to color excess was found to equal 5.8 x 10 to the 21st power atoms per (sq cm x mag). For stars with accurate E(B-V), the deviations from this mean are generally less than a factor of 1.5. A notable exception is the dark cloud star, rho Oph. A reduction in visual reddening efficiency for the grains that are larger than normal in the rho Oph dark cloud probably explains this result. The conversion of atomic hydrogen into molecular form in dense clouds was observed in the gas to E(B-V) correlation plots. The best estimate for the mean total gas density for clouds and the intercloud medium, as a whole, in the solar neighborhood and in the plane of the galaxy is 1.15 atoms per cu. cm; those for the atomic gas and molecular gas alone are 0.86 atoms per cu cm and 0.143 molecules per cu cm respectively. For the intercloud medium, where molecular hydrogen is a negligible fraction of the total gas, atomic gas density was found to equal 0.16 atoms per cu cm with a Gaussian scale height perpendicular to the plane of about 350 pc, as derived from high latitude stars.

A search for emission from vibrationally excited H2

view Abstract Citations (4) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A search for emission from vibrationally excited H2. Traub, W. A. ; Carleton, N. P. ; Black, J. H. Abstract A search has been conducted for the 8150-A emission line of interstellar H2 in Orion, in NGC 7027, and in the Rho Oph region, with negative results. In order that the results be consistent with the recently reported observations of H2 emission lines near 2 microns in Orion, the visual extinction must be greater than 10 mag for a 2500-K thermal-excitation model, or greater than 6-11 mag for a shock-excitation model. Finally, an ultraviolet-excitation model is introduced. Publication: The Astrophysical Journal Pub Date: July 1978 DOI: 10.1086/156244 Bibcode: 1978ApJ...223..140T Keywords: Astronomical Spectroscopy; Emission Spectra; Hydrogen Clouds; Nebulae; Astronomical Models; Interstellar Extinction; Molecular Excitation; Molecular Oscillations; Molecular Spectra; Astrophysics; Interstellar Matter:Molecular Hydrogen; Molecular Hydrogen:Orion Nebula full text sources ADS | data products SIMBAD (1)

Atomic and molecular observations of the Rho Ophiuchi dark cloud

view Abstract Citations (118) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Atomic and molecular observations of the rho Ophiuchi dark cloud. Myers, P. C. ; Ho, P. T. P. ; Schneps, M. H. ; Chin, G. ; Pankonin, V. ; Winnberg, A. Abstract The density and temperature structure, kinematics, and chemistry of the dark cloud complex near Rho Oph are studied using maps of microwave spectral-line parameters for lines of H, OH, H2CO, and CO. The spatial extent of each cloud fragment as observed in a particular line is analyzed along with the variation of line width with spatial extent and the correlations among the densities of the observed species. The results obtained indicate that: (1) the observed species have spatial extents ranging from about 0.1 to 6 pc; (2) on a scale of less than about 1 pc, the cloud is organized into two main fragments; (3) the gas density varies within the fragments as the -1.3 power of radial distance; (4) the line width of a given species increases with its spatial extent, suggesting radial contraction of the fragments with a velocity of about half that expected in free fall; and (5) the abundances of H2CO, OH, and CO are similar to those in other large dark clouds and are strongly correlated with extinction. Publication: The Astrophysical Journal Pub Date: March 1978 DOI: 10.1086/155976 Bibcode: 1978ApJ...220..864M Keywords: Absorption Spectra; Abundance; Atomic Spectra; Interstellar Gas; Microwave Spectra; Molecular Spectra; Ammonia; Carbon Monoxide; Formaldehyde; Hydrogen; Hydroxyl Emission; Infrared Spectra; Astronomy; Dark Clouds:Microwave Spectra; Dark Clouds:Molecules full text sources ADS | data products SIMBAD (3)

Self-reversed CO profiles in collapsing molecular clouds

view Abstract Citations (102) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Self-reversed CO profiles in collapsing molecular clouds. Snell, R. L. ; Loren, R. B. Abstract Observations of self-reversed CO line profiles in four dense molecular clouds (Mon R2, NGC 1333, W3, and Rho Oph) are discussed, and it is shown that these cases are readily explained by self-absorption in the outer layers of a nonhomologously collapsing cloud. Common features of the four clouds are reviewed, evidence is presented which indicates that the clouds are in a state of collapse rather than expansion, and it is demonstrated that the collapse is most likely nonhomologous with the collapse velocity varying as the inverse square root of cloud radius. CO line profiles are calculated with and without small amounts of turbulent broadening for a spherically symmetric nonhomologous collapsing cloud; these are compared with observed line-of-sight CO and (C-13)O line profiles. The general agreement between the line profiles given by the model with a small amount of turbulence and the observed line profiles is found to be quite good, with all the common features of the observed profiles present in the calculated profiles. An observational test of the model is proposed. Publication: The Astrophysical Journal Pub Date: January 1977 DOI: 10.1086/154909 Bibcode: 1977ApJ...211..122S Keywords: Carbon Monoxide; Gravitational Collapse; Interstellar Matter; Line Spectra; Molecular Spectra; Nebulae; Astronomical Models; Astronomical Spectroscopy; Cosmic Dust; Emission Spectra; Spectral Line Width; Astrophysics full text sources ADS |

Depletion of heavy elements toward the rho OPH dust cloud.

Measurements of extinction toward the p Oph dust cloud have suggested that the grains are abnormally large, perhaps due to enhanced depletion of heavy atoms onto grain surfaces. In an attempt to measure directly the enhanced depletion, we have compared the depletions of interstellar Na, K, and Ca toward a Sco with the apparently more normal depletions of these elements toward Oph. Data for this comparison include published column densities from optical measurements and new 21 cm H I profiles. It is shown that the cold, dense cloud toward both stars produces self-absorption in the H I emission profiles. The temperature of the cold gas and the separate column densities for the cold and hot gas have been derived. The H I spin temperatures toward the stars agree with the kinetic temperatures found from H2 data. A model of the interstellar medium toward the two stars is developed and used in the analysis of depletions of heavy elements. The Na depletion toward a Sco is enhanced by about a factor of 4 over that toward Oph, but no enhanced depletion is found for K or Ca. Enhanced depletion onto positively charged grains in the high-density p Oph dust cloud could explain this result. Subject headings: nebulae: abundances - nebulae: general

Observations of heavy-element recombination lines in the Rho Ophiuchi dark cloud at 13 centimeters wavelength

High-sensitivity observations at the carbon 140-alpha and 141-alpha recombination-line frequencies in the direction of the Rho Oph dust cloud show the presence of recombination lines of carbon and sulfur, but not of other heavy elements. These results require that the elements Si, Fe, and Mg are depleted by factors greater than 15, 10, and 2, respectively, most likely into interstellar grains, whereas sulfur is undepleted. They also require that only approximately one-sixth of the carbon is present in the gas phase in the cloud. From the observed size of the C II region together with the observed carbon depletion, it is inferred that the density in the carbon-line-emitting region is 25,000 per cu cm and that the size of the S II region is significantly larger than that of the C II region. The agreement between the widths of the recombination lines (which arise in a small region of the cloud) and those of the more widely distributed molecular species suggests that the lines in this cloud are broadened by microturbulence on a scale of much less than 0.1 pc.

Formaldehyde in the rho Ophiuchi dark cloud

The 6-cm transition of H$sub 2$CO was mapped in absorption over a region approx.1degreetimesapprox.1degree with 6' resolution toward the rho Oph dark cloud. The distribution of H$sub 2$CO column density agrees well with the extinction due to dust. At least three regions of high H$sub 2$CO concentration can be identifed. Two regions of reduced H$sub 2$CO column density coincide with regions of carbon recombination-line emission, reflection nebulosity, and concentration of infrared sources. The most likely mechanisms of line intensity reduction are increased excitation temperature, due to electron collisions, and reduced column density, due to destructive C$sup +$ collisions. Both effects are associated with the observed C ii regions (s). A north-south velocity gradient of approx.0.5 km s$sup -1$ pc$sup -1$ is observed, which is probably not sufficient to stabilize the cloud against large-scale gravitational collapse. (AIP)

Interstellar K I and NA I absorption lines near rho Ophiuchi

view Abstract Citations (15) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar K I and Na I absorption lines near Rho Ophiuchi. Hobbs, L. M. Abstract Results are reported for photoelectric interferometric scans of the interstellar K I (7699 A) and Na I D1 absorption lines toward rho Oph AB and omicron Sco in the complex of dark clouds near rho Oph. The scans are found to reveal a well-marked line multiplicity toward both stars. It is shown that the resolved components of the line profiles can provide a natural explanation for the difference between the radial velocity of the strongest atomic lines of Na I and Ca II and that of the much weaker molecular lines of CH(+), CH, and CN that was previously observed toward rho Oph. The less saturated 7699-A lines toward both stars yield K I column densities roughly consistent with the calculated interstellar reddening. Publication: The Astrophysical Journal Pub Date: September 1975 DOI: 10.1086/153829 Bibcode: 1975ApJ...200..621H Keywords: Absorption Spectra; Interstellar Extinction; Interstellar Matter; Line Shape; Nebulae; Atomic Spectra; Line Spectra; Potassium; Red Shift; Sodium; Stellar Spectra; Water; Astrophysics full text sources ADS | data products SIMBAD (5)

On the velocity structure of the interstellar clouds near rho Oph.

view Abstract Citations (8) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the velocity structure of the interstellar clouds near Rho Ophiuchi. Cohen, J. G. ; Wallerstein, G. Abstract Accurate radial velocities of the optical interstellar features for some of the B stars embedded in the p Oph complex are obtained by averaging results of several photographic high-dispersion spectra. In at least one case, there is a real difference between the radial velocity of the atomic features (Na 1 and Ca ii) and the molecular ones (CH and CN). We show that it is probable that the CH and CN are concentrated either in a separate cloud (i.e., region of space) from the Ca ii and Na 1 or in a cloud whose outer parts are expanding rather than in a single cloud which is contracting or rotating. Subject headings: interstellar matter - nebulae Publication: The Astrophysical Journal Pub Date: April 1974 DOI: 10.1086/152797 Bibcode: 1974ApJ...189..259C full text sources ADS | data products SIMBAD (7)

Detection of radio recombination-line emission from the rho OPH dark cloud.

view Abstract Citations (31) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of radio recombination-line emission from the Rho Ophiuchi dark cloud. Brown, R. L. ; Knapp, G. R. Abstract Recombination-line observations in the direction of the p Oph dark cloud at 21 cm are described in which we have detected the carbon 166a and 167a lines. The excellent agreement between the velocity of these lines and the velocity of molecular lines from the p Oph cloud lead to an unequivocal identification of the regions of recombination-line emission with the dark cloud itself. The velocity width of the recombination lines Av = 2.4 km 1 is comparable with the widths of the CO and OH lines, indicating that the line must arise in cold gas. The emission measure of the line, 0.2 cm -6 pc, is sufficiently large as to require that the line originate in regions with densities n > 630 cm 2 From these observations, together with an analysis of the H I selfabsorption feature seen in the same direction, we infer that the relative electron density in the line-emitting regions of the cloud is ne/n <: 1.6 x 10- . Subject headings: molecules, interstellar - nebulae - radio lines - 21-cm radiation Publication: The Astrophysical Journal Pub Date: April 1974 DOI: 10.1086/152796 Bibcode: 1974ApJ...189..253B full text sources ADS | data products SIMBAD (3)