W3 IRS Research Articles

Observations of Solid Carbon Dioxide in Molecular Clouds with theInfrared Space Observatory

Spectra of interstellar CO2 ice absorption features at a resolving power of lambda/Delta lambda approximate to 1500-2000 are presented for 14 lines of sight. The observations were made with the Short-Wavelength Spectrometer (SWS) of the Infrared Space Observatory (ISO). Spectral coverage includes the primary stretching mode of CO2 near 4.27 mu m in all sources; the bending mode near 15.2 mu m is also detected in 12 of them. The selected sources include massive protostars (Elias 29 [in rho Oph], GL 490, GL 2136, GL 2591, GL 4176, NGC 7538 IRS 1, NCC 7538 IRS 9, S140, W3 IRS 5, and W33 A), sources associated with the Galactic Center (Sgr A*, GCS 3 I, and GCS 4), and a background star behind a quiescent dark cloud in Taurus (Elias 16); they thus probe a diverse range of environments. Column densities of interstellar CO2 ice relative to H2O ice fall in the range 10%-23%: this ratio displays remarkably little variation for such a physically diverse sample. Comparison of the observed profiles with laboratory data for CO2-bearing ice mixtures indicates that CO2 generally exists in at least two phases, one polar (H2O dominant) and one nonpolar (CO2 dominant). The observed CO2 profiles may also be reproduced when the nonpolar components are replaced with thermally annealed ices. Formation and evolutionary scenarios for CO2 and implications for grain mantle chemistry are discussed. Our results support the conclusion that thermal annealing, rather than energetic processing due to UV photons or cosmic rays, dominates the evolution of CO2-bearing ices.

GAS-PHASE CHEMISTRY OF THE STAR FORMING REGION W3 IRS4

We have followed the chemistry of W3 IRS4, as one of the most famous regions with a chemistry similar to that found in quiescent molecular clouds. Here the time scale, since star formation, has probably been long enough for the gas-phase ion-molecule chemistry to become dominant again. We have constructed a reaction system containing the chemical families of H, C, O, N, S and metals (Me:Fe, Mg, Na and Si). A total of 282 species have been included and a network of 1270 reactions has been used. The chemical kinetic equations were integrated as a function of pseudo-time-dependent approach. The evolution of the different chemical species are followed in models of density n equal to 106 cm-3 and temperature T equal to 55 K. Different initial abundances have been assumed. Our results are in reasonable agreement with the observation, especially in Model 6. The resulting molecular abundances are compared with those obtained in the intermediate mass star NGC 2264 IRS1, as well as the low mass IRAS 16293-2422.

New Wavelength Determinations of Mid‐Infrared Fine‐structure Lines byInfrared Space ObservatoryShort Wavelength Spectrometer

We report accurate new wavelengths for 29 mid-infrared ionic fine-structure lines, based on observations with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO). Our results originate from observations of NGC 7027, NGC 6543, NGC 6302, the Circinus galaxy, Sgr A West, and W51 IRS 2. The obtained accuracies (λ/Δλ) range from 3 × 104 to 1 × 105, depending on instrumental mode and uncertainty in radial velocities.

A Comparison of Near Infrared Spectra of the Galactic Center He I Emission Line Sources and Early Type Mass Losing Stars

We have obtained R ≈ 570 resolution K band spectra of eight sources in the Galactic Center, including four sources within the IRS 16 cluster, IRS 13, IRS 1W, and the compact He I emission line sources AF (also known as AHH) and AHH NW. We have also obtained R ≈ 570 H and K band spectra of nine galactic and LMC early–type mass–losing stars, including Ofpe/WN9 and WN stars. The spectra of both the Galactic Center sources and the comparison stars show a wide range of behavior in the He I (1.70 μm, 2.06 μm, 2.11 μm) and H I (Brackett series) lines. We find significantly larger He I equivalent widths in the AF source and two galactic early type mass losing stars than in any of the LMC stars. Several of the Galactic Center He I sources are found to have higher He I velocity widths than any of the galactic or LMC early type mass losing stars. At least one source, IRS 13, shows a strong red wing to the He I 2.06 μm emission.

High-Resolution Far-Infrared Observations and Radiative-Transfer Models of W3 IRS 4 and IRS 5

High-Resolution Far-Infrared Observations and Radiative-Transfer Models of W3 IRS 4 and IRS 5

Near-infrared spectra of compact stellar wind sources at the Galactic center

We present high- and low-resolution, H- and K-band spectra on nine compact 2.2 micrometers Galactic center sources in which we clearly detect He I 2.058 micrometers emission, including the AF source, IRS 13, IRS 1W, IRS 16NE, IRS 16NW, IRS 16C, IRS 16SW, IRS 34, and IRS 6E. We have also obtained comparison spectra of both a luminous blue variable (LBV) and a WR star (P Cygni and HD 192163, respectively). Our H- and K-band spectrum of the LBV P Cygni strongly resembles the near-infrared spectra of known WN9/Ofpe stars. Our spectra of the Galactic center sources share many characteristics in common with our spectrum of P Cygni. The spectra all show emission lines of H I and He I with large He I/H line flux ratios. Some have permitted and forbidden lines of Fe II. Brackett line widths and ratios indicate the presence of strong stellar winds. In contrast to the spectrum of the WR star, none of the Galactic center sources show evidence of He II emission lines in their spectra, suggesting that none of the Galactic center sources are WR stars. Our high-resolution H-band spectrum of the AF source differs from previously published low-resolution H-band spectra in that it is rich in emission lines. Furthermore, we find two distinct spectral components to the AF source separated in space by a few arcseconds. We identify both the emission-line component of the AF source and an exciting source of IRS 13 as an LBV or WN9/Ofpe star. Our results, when combined with the results of others, also suggest that IRS 16NE, IRS 16C, IRS 16NW, IRS 34, and a component of IRS 6E are early-type, emission-line stars. The argument for IRS 16SW, however, is less compelling. We find no evidence for a compact He I emission-line source at IRS 1W. This result contradicts previous findings, suggesting that the He I source at IRS 1W may be variable. If the He I lines in IRS 1W are truly variable, a stellar component of IRS 1W may be an LBV, because LBVs are known to have variable line emission on short timescales. The nine Galactic center wind sources appear to contribute a significant fraction of the total luminosity of the central few parsecs of the Galaxy.

The W3 IRS 5 cluster: Radio continuum and water maser observations

view Abstract Citations (54) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The W3 IRS 5 Cluster: Radio Continuum and Water Maser Observations Claussen, M. J. ; Gaume, R. A. ; Johnston, K. J. ; Wilson, T. L. Abstract High sensitivity and angular resolution observations of the radio continuum toward W3 IRS 5, along with observations of strong water masers, have been made with the Very Large Array (VLA). At least seven distinct radio continuum sources have been discovered, which are most likely a cluster of B0.5-B0 stars with ionized stellar winds. This is in contrast to previous interpretations of observational data, which suggested that IRS 5 is a single massive protostar with bolometric luminosity of 2 x 105 solar luminosity. The spatial distribution of the water masers roughly follows that of the radio sources; and these masers show a gradient in radial velocity similar to that found in a larger scale molecular outflow. We suggest that previously observed, multicomponent absorption in CO infrared transitions traces outflows from the several stellar wind sources, rather than episodic outbursts from a single source. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/187270 Bibcode: 1994ApJ...424L..41C Keywords: Angular Resolution; Masers; Protostars; Radio Sources (Astronomy); Radio Spectra; Sensitivity; Spatial Distribution; Spectroscopy; Star Formation; Bolometers; Radial Velocity; Signal To Noise Ratios; Stellar Luminosity; Stellar Winds; Very Large Array (Vla); Astronomy; ISM: H II REGIONS; MASERS; RADIO CONTINUUM: ISM; STARS: FORMATION full text sources ADS | data products SIMBAD (15)

Extremely High Velocity Outflows

Extremely high velocity (EHV) wings, with full widths of 72 to 140 km s −1 , are seen on the CO J=3→2 lines toward W3 IRS 5, GL 490, NGC 2071, W28 A2 (G05.89-0.39), GL 2591, S140, and Cepheus A. Observations of 12 CO and 13 CO J=3→2 and J=2→1 lines indicate that optical depth generally decreases with increasing velocity separation from the ambient cloud velocity. Maps of the extremely high velocity (|V−V 0 |≥20 km s −1 ) and the high-velocity (5≤|V−V 0 |≤20 km s −1 ) CO emission components show that the morphology of the two components is similar in W3 IRS 5 and W28 A2 but may be different in GL 2591, S 140, and Cepheus A

Infrared spectroscopy of dense clouds in the C-H stretch region: methanol and "diamonds."

High spectral resolution (nu/delta nu = 900) studies in the 3100-2600 cm-1 (3.2-3.9 microns) range are presented of the protostars NGC 7538 IRS 9, W33A, W3 IRS 5, and S140 IRS 1. This is the spectral region in which the fundamental C-H stretching vibrations of aliphatic hydrocarbons fall. Well-resolved absorption bands at about 2825 cm-1 (3.54 microns) and 2880 cm-1 (3.47 microns) were found superposed on the low-frequency wing of the strong O-H stretch feature. The 2880 cm-1 (3.47 microns) band, a new interstellar feature, is moderately strong in the spectra of all four objects studied. The 2825 cm-1 (3.54 microns) band, previously detected toward W33A, is also in the spectrum of NGC 7538 IRS 9. The relative strength of these two bands varies, showing that they are associated with two different carriers. On the basis of comparisons with laboratory spectra, the 2825 cm-1 (3.54 microns) band is assigned to methanol (CH3OH), in agreement with the earlier work of Grim et al. (1991). This assignment is further supported by a pair of weak absorptions centered at 2600 and 2540 cm-1 (3.85 and 3.94 microns) in the spectrum of W33A recently reported by Geballe (1991). These features compare very well with laboratory spectra of CH3OH/H2O ice mixtures. The CH3OH/H2O ratio derived from the 2825 cm-1 methanol band and the 3250 cm-1 (3.08 microns) H2O feature are 0.13 and 0.40 for NGC 7538 IRS 9 and W33A, respectively. These values are smaller than the ratios of 0.61 and 0.54 derived using the 1460 cm-1 (6.85 microns) band assigned to CH3OH and the 1665 cm-1 (6.00 microns) H2O band. These apparent discrepancies may be due to a combination of scattering effects within the molecular cloud, uncertainties associated with the baselines for the 2825 cm-1 feature, and the presence of other interstellar grain materials that absorb at 1460 cm-1 (6.85 microns). Nonetheless, after H2O, CH3OH is the most abundant known interstellar ice constituent. The new band at about 2880 cm-1 (3.47 microns) falls near the position for C-H stretching vibrations in tertiary carbon atoms. The strength of this feature, in combination with the lack of strong features associated with primary (-CH3) and secondary (-CH2-) carbon atoms, suggests that the carrier of the new feature has a diamond-like structure. We therefore tentatively attribute this new feature to interstellar "diamonds." The detection of this band in the spectra of all four dense molecular clouds suggests that the carrier is ubiquitous in dense clouds. Band-strength analysis indicates that a minimum of a few percent of the available cosmic carbon is tied up in this material.

A CO J = 2 - 1 study of the outflow sources GL 490, GL 2591, M8E-IR, and W3 IRS 5

view Abstract Citations (56) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A CO J = 21 Study of the Outflow Sources GL 490, GS 2591, M8E-IR, and W3 IRS 5 Mitchell, George F. ; Hasegawa, Tatsuhiko I. ; Schella, Jason Abstract Results are presented of the mapping, at 21-arcsec resolution, of the CO J = 2 - 1 emission from four high-velocity sources. Observations of (C-13) J = 2 - 1 are combined with the (C-12)O data to determine the mass, dynamical times scales, and mass-loss rates of the outflowing gas. A comparison is made between the momentum and mass-loss rates of CO outflows previously found from GL 2591, M8E-IR, and W3 IRS 5 using the fundamental vibrational band of CO in the IR, and the momentum and mass-loss rates obtained in this paper from CO emission line data. It is concluded from the comparison that a suggested direct causal link between the IR outflows and the extended bipolar flows remains feasible, but is, as yet, unproven. Publication: The Astrophysical Journal Pub Date: February 1992 DOI: 10.1086/171042 Bibcode: 1992ApJ...386..604M Keywords: Carbon Monoxide; Infrared Sources (Astronomy); Interstellar Gas; Molecular Clouds; Molecular Flow; Bipolarity; Emission Spectra; Gas Flow; Line Spectra; Spectrum Analysis; Astrophysics; ISM: JETS AND OUTFLOWS; ISM: KINEMATICS AND DYNAMICS; RADIO LINES: MOLECULAR: INTERSTELLAR full text sources ADS | data products SIMBAD (4)

10 micron spectra of protostars and the solid methanol abundance.

We have searched for the strong C-O stretching absorption of solid methanol near 9.8 micrometers toward the heavily obscured protostars AFGL 961, AFGL 2591, the BN object and Mon R2 IRS 3. There is no clear evidence for this feature in the spectra, resulting in very conservative upper limits to the methanol abundance of 6% to 17% relative to solid H2O toward these objects. This is well below previous estimates of 50%-80% obtained toward W33 A, NGC 7538 IRS 9, AFGL 2136, and W3 IRS 5, which were based on the assignment of the interstellar 6.85 micrometers absorption feature to the methanol C-H bending mode. This study shows that such high methanol abundances are not a characteristic of all interstellar ices.

Episodic outflows from high-mass protostars

This paper examines the kinematics and physical properties of the outflowing gas from seven luminous deeply embedded young stellar objects or protostars: M8E-IR, GL 490, GL 2591, W3 IRS 5, NGC 7538 IRS 1, NGC 7538 IRS 9, and S140 IRS 1. The outflows are seen as blueshifted absorption features in lines of the fundamental band of CO. The CO lines seen in absorption are compared with CO lines seen in emission at mm wavelengths. New CO J = 2-1 emission-line data are presented for the first five of the sources.

Dynamical collapse of the W51 star-forming region

High-resolution molecular line and 3.4 mm continuum observations of a 2.3 arcmin field centered on W51 IRS 1 in the W51 molecular core are presented. The HCO(+) spectra show deep, wide absorptions redshifted in the cases of W51e2 and W51 IRS 2, both redshifted and blueshifted in the case of W51 IRA 1. The latter two absorptions can be explained by postulating that the W51 cloud is undergoing a large-scale dynamic collapse toward materials centered near W51e2. The HCO(+) maps reveal the presence of many clumps of emission with lower mass limits ranging from 20-50 solar and upper limits of 90 solar, suggesting that many of these clumps are gravitationally bound. H(C-13)N and SO maps reveal three molecular peaks which coincide with the NH3(3,3) peaks seen by Ho et al. (1983) and are therefore warm. A previously undetected molecular peak, H(C-13)N-4, coincides with a 3.4 mm continuum peak due to thermal dust. 48 refs.

Subarcsecond resolution observations of the central parsec of the Galaxy at 2.2 microns

Four separate lunar occultations of the Galactic center in the infrared K-band have been observed, and the results are used to estimate the size of the sources and to derive photometry. It is found that IRS 16NE, 16NW, and IRS 29 are smaller than about 510 AU and IRS 16SW-W and C are smaller than 85 AU. All sources brighter than K = 10 mag in the central pc are smaller than 510 AU and therefore seem to be stars. IRS 7 is smaller than about 100 AU. IRS 1W and 13, resolved into pairs of stars, are probably the exciting stars for these H II regions. The shape of the differential luminosity function of the stars in the central sq pc is similar to that of stars in the central 150 sq pc. There is a steady increase in star density toward the central few arcsec of the Galaxy.

Submillimeter water masers

view Abstract Citations (84) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Submillimeter Water Masers Menten, Karl M. ; Melnick, Gary J. ; Phillips, Thomas G. Abstract The first astronomical detection of the 10(29) - 9(36) transition of water vapor (H2O) at a frequency near 321 GHz is reported. The line was detected toward the star-forming regions W3(OH), W49N, W51 IRS 2, and W51 Main, and the supergiant star VY CMa. In all cases, probably, maser action is observed. Since the 10(29) level of H2O is at an energy of 1861 K above the ground state, the 10(29) - 9(36) line probes very hot molecular material. The 10(29) - 9(36) emission is found at velocities that are near the systemic velocities of the regions studied. The strongest features in spectra of the well-studied 22 GHz 6(16) - 5(23) transition are generally found at similar velocities. The 10(29) - 9(36) spectra do not show counterparts to the high-velocity features observed in the 22 GHz line, but this may be due to the limited sensitivity of the observations. Publication: The Astrophysical Journal Pub Date: February 1990 DOI: 10.1086/185663 Bibcode: 1990ApJ...350L..41M Keywords: Interstellar Masers; Late Stars; Molecular Clouds; Star Formation; Stellar Envelopes; Water Masers; Submillimeter Waves; Supergiant Stars; Water Vapor; Astrophysics; INTERSTELLAR: MOLECULES; MASERS; STARS: CIRCUMSTELLAR SHELLS; STARS: FORMATION; STARS: LATE-TYPE full text sources ADS | data products SIMBAD (4)

Infrared imaging of the compact H II region W3A

view Abstract Citations (8) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Imaging of the Compact H II Region W3A Hayward, Thomas L. ; Grasdalen, Gary L. ; Woodward, Charles E. ; Hackwell, John A. ; Gehrz, Robert D. ; Pipher, Judith L. Abstract The H II region W3A was imaged and mapped at five broad-band wavelengths from 1.65 to 20 microns and at CVF resolution in the Br-gamma line at 2.17 microns and in the nearby continuum. A newly discovered source called IRS 2c appears to be a highly reddened star similar to IRS 2. IRS 11 is another previously undetected source that lies between W3A and W3 IRS 5. The 1-20 micron spectrum of IRS 11 is due to warm dust and has a moderate silicate absorption at 9.7 microns. The most interesting source first shown on the maps, called IRS 2b, appears to be a reddened star surrounded by a centrally condensed cloud of hot dust. It is suggested that IRS 2b is a young star in a dust-clearing phase. The maps also reveal that the dust-to-gas emission ratio appears to be variable within W3A. Publication: The Astrophysical Journal Pub Date: October 1989 DOI: 10.1086/167959 Bibcode: 1989ApJ...345..894H Keywords: H Ii Regions; Infrared Sources (Astronomy); Nebulae; Astronomical Maps; Broadband; Interstellar Extinction; Molecular Clouds; Point Sources; Astrophysics; INFRARED: SOURCES; NEBULAE: H II REGIONS; NEBULAE: INDIVIDUAL ALPHANUMERIC: W3A full text sources ADS | data products SIMBAD (14)

Discovery of interstellar acetylene

Absorption by interstellar acetylene (C2H2) has been detected in the spectra of three IR sources embedded in molecular clouds. One or more lines in the 13.7 micron nu5 vibration-rotation band were detected toward GL 2591, W3 IRS 5, and OMC-1 IRc2. The observations require C2H2 abundances of about 0.0003 to 0.003 of CO. Such abundances can be explained by models in which the molecular clouds are chemically unevolved or in which gas phase abundances have been enhanced by recent evaporation of grain mantles.

High-resolution IRCCD images of the Galactic center at 2.2 and 3.5 microns

An IRCCD camera was used to obtain high-resolution images at 2.2 and 3.5 microns of the Galactic center at subarcsecond resolution. These images show that the compact nonthermal radio source Sgr A-asterisk is not coincident with any part of IRS 16; Sgr A-asterisk is found to be 1.1 + or - 0.3 arcsec west of IRS 16C. At 3.5 microns, IRS 16 is a complex object. IRS 16SW is resolved into two sources, and IRS 16C may be double or extended. From the colors and sizes of the various components, it is difficult to explain these objects as stellar clusters; the required stellar density would be too high. Finally, there is evidence that there is a blue and a red source, separated by about 1 arcsec, for each of the northern arm sources, IRS 1W, IRS 5, and IRS 10.

High-resolution H and K mapping of W51

The H-II region W51 has been mapped in the near-infrared H and K wavebands with a resolution of about 6 arcsec over an area of about 14 sq arcsec. The W51 IRS 1 source has been resolved into six components, and an arc-like extension of small H-II regions is found that seems to parallel the edge of the molecular cloud. Measurements of the fluxes and extinctions of these sources are presented. A close correspondence is noted between the present K maps and the radio maps of Scott (1978).

Warm dense gas in luminous protostellar regions - A submillimeter and far-infrared CO line study

Spectroscopic measurements of the CO J = 7-6 and J = 16-15 sub-mm/far-IR rotational lines are combined for a study of the molecular gas in four massive star formation regions: W51 IRS 2, W51 Main, G34.3+0.1, and W49. CO emission over a wide velocity range is found in three of the four regions. Mass outflows from newly formed stars in the two W51 sources carry an order-of-magnitude-greater mass and momentum than in the Orion/KL flow; it is concluded that mass outflow rates scale with source luminosity up to the most luminous galactic star formation regions.