W3 IRS Research Articles

SiO Masers in the Star Forming Regions W51 IRS2 and Sgr B2 MD5

The maser emission of the J = 1-0 lines of SiO in vibrationally excited states has been detected in two regions of massive star formation, W51 IRS2 and Sgr B2 MD5. The SiO masers apparently coincide with strong H2O masers in each source within the uncertainties of < 5″. Their velocity ranges fall within those of the nearest H2O masers (Figure 1). In W51 IRS2 the maser emission is observed only in the v = 2 state, and the upper limit of the v = 1 line (3σ) is 1/15th of the v = 2 line intensity. The v = 1 emission found in Sgr B2 MD5 is five times stronger than the marginally detected v = 2 emission (Figure 2). Their luminosities are comparable to those from the corresponding maser in Orion.

Aperture synthesis observations of CO emission from the W3 molecular cloud core

view Abstract Citations (37) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Aperture synthesis observations of CO emission from the W3 molecular cloud core. Claussen, M. J. ; Berge, G. L. ; Heiligman, G. M. ; Leighton, R. B. ; Lo, K. Y. ; Masson, C. R. ; Moffet, A. T. ; Phillips, T. G. ; Sargent, A. I. ; Scott, S. L. ; Wannier, P. G. ; Woody, D. P. Abstract The first aperture synthesis maps of (C-12)(O) (J = 1-0) emission from a galactic star-forming region are presented. The line and continuum emission from a 1 arcmin field centered on W3 IRS5 have been mapped with the Owens Valley millimeter-wave interferometer. Although no radio continuum emission from IRS5 was detected to a five sigma limit of 130 mJy, compact sources of high velocity red- and blue-shifted CO emission with T(B) of about 20 K were found associated with IRS5. The estimated mass in each wing is one solar mass, with density of about 100,000/cu cm. The outflow is similar to other known sources with high-velocity emission and has a short dynamic lifetime such as found in Orion. It is suggested that the two infrared sources which comprise IRS5 are in differing stages of evolution. Publication: The Astrophysical Journal Pub Date: October 1984 DOI: 10.1086/184370 Bibcode: 1984ApJ...285L..79C Keywords: Emission Spectra; Infrared Stars; Interferometry; Molecular Clouds; Radio Sources (Astronomy); Stellar Evolution; Astronomical Maps; Carbon Monoxide; Millimeter Waves; Radial Velocity; Synthetic Apertures; Astrophysics full text sources ADS | data products SIMBAD (1)

Infrared polarimetric maps of protostellar infrared sources

The authors present high-resolution polarization maps at 2.2 μm of the suspected protostellar objects S158 IRS 4, NGC 2071 IR, NGC 2264, and W3 IRS 1 and 2 and also of the cluster of infrared sources in W3. The authors evaluate the spatial structure of the maps in terms of scattering and/or grain alignment polarization mechanisms and the physical environments in these star-forming regions.

Observations of the infrared fine-structure lines of S III at 18.71 and 33.47 microns in four H II regions

Infrared fine-structure lines provide a particularly useful probe of ionized nebulae. The present investigation is concerned with measurements of the forbidden S III lines at 18.71 and 33.47 micrometers for four H II regions, S158A, S158G, G75.84+0.4, and W3 IRS 1. These lines are used to estimate densities, and comparisons are made with rms densities determined from radio observations to evaluate the importance of clumping. For the case of the optical H II region S158A, comparisons are made with both optical and forbidden O III line determinations of the density. The reported observations were made using a dual-grating, liquid-helium-cooled spectrometer containing a three-element Si:Sb detector array and a three-element Ge:Ga detector array. It is found that clumping is important in the cases of G75.84+0.4, W3 IRS 1, and M42. These three H II regions have filling factors of 0.024, 0.09, and 0.03, respectively.

Measurements of forbidden line radiation of AR II /6.99 microns/ in W3 IRS 1

view Abstract Citations (7) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measurements of forbidden line radiation of AR II /6.99 microns/ in W3 IRS 1 Herter, T. ; Pipher, J. L. ; Helfer, H. L. ; Willner, S. P. ; Puetter, R. C. ; Rudy, R. J. ; Soifer, B. T. Abstract Observations of the [Ar II] (6.99 μm) line flux in W3 IRS 1 are combined with previously obtained measurements of the [Ar III] (8.99 μm) line flux. The observed ratio of [Ar II]/[Ar III] is inconsistent with the calculated ratio for an H II region with the densities required by radio observations and with a central 40,000-45,000 K star with atmosphere as described by a Mihalas model. A softer effective UV radiation field is required; a dusty model we had previously invoked fits the observations. In addition we determine that the argon abundance is n(Ar)/n(H) ≈ 8 × 10-6, a value about twice that usually adopted for normal solar abundance; however, there are uncertainties in the extinction and the model which do not allow us to preclude solar abundance. Publication: The Astrophysical Journal Pub Date: March 1981 DOI: 10.1086/158728 Bibcode: 1981ApJ...244..511H Keywords: Argon; Forbidden Bands; Hydrogen Clouds; Infrared Spectra; Nebulae; Abundance; Astronomical Models; Stellar Atmospheres; Astronomy full text sources ADS |

Angular dimensions of accreting young stars

Only a handful of astronomical objects are considered to date as likely candidates for the protostellar stage [1]. They are weak sources emitting the bulk of their energy in the near infrared. The predicted dimension of these objects is less than one arc second, so that removing the loss in resolution due to atmospheric turbulence is necessary in order to study their spatial intensity distribution. For this purpose a set of Speckle Interferometry experiments have been made in the near infrared at the Coude focus (f/181) of the Mayall 3.81 m telescope (Kitt Peak National Observatory). The detector was an InSb detector with a noise equivalent power of 10-15 W.Hz-1/2 at 3.5 μm. The signal was analysed with a scanning slit, sampled and registered. In order to avoid any problem due to possible non stationarity of the noise during long observing periods, alternate scans were made on the object and on adjacent sky to measure in similar conditions the object power and the system-and sky-noise power. We obtain by this method the modulus of the spatial spectrum between 0 and fc in the direction perpendicular to the slit with a resolution Δf = 1/L where L is the length of the scan [2]. Several sources have been studied: W3 IRS5, BN, RMon2 IRS3, CRL 2591, S 140. We present here results dealing with W3 IRS5 and BN [3]. The spectrum of these two objects shows a low frequency peak which would correspond to an extended component. W3 IRS5: This source is clearly resolved at 4.8 μm. If we fit the spectrum with a function corresponding to a source of uniform brightness with a diameter α0, we find α0 = 0.28 ± 0.08 arc sec. To determine the exact shape of the object it is necessary to scan the image in several directions. All the models proposed to date give for this source at 5 μm dimensions included in the range 0.2 to 0.33 arc sec. [4, 5, 6] in agreement with our measurement. BN: The 4.8 μm spectrum is significantly different from the W3 IRS5 spectrum. The source is not resolved at this wavelength but the upper limit of its diameter is 0.1 arc sec. The 3.45 μm spectrum is easier to interpret. If we fit the spectrum with a function corresponding to a source of uniform brightness and of diameter α0, we find α0 = 0.1 arc sec. Becklin et al. [7] fit the energy spectrum with a 530 °K blackbody curve corresponding to a 0.1 arc sec. diameter at 4.8 μm which agrees with our measurement. Bedijn et al. [8] have built a series of models for BN and give 4 possibilities and consequently 4 diameters. Our measurement is in agreement with the smallest diameter. These measurements confirm that two likely candidates for premain sequence objects in the solar neighbourhood are indeed high luminosity sources embedded in a very compact heated shell. More elaborate models are now needed which should try to reproduce not only the observed energy spectrum but also the bidimensional spatial spectrum given by Speckle interferometry.