The 105 Ls high-mass protostellar object IRAS 23151+5912 (original) (raw)
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The 10^ 5Lsun High-Mass Protostellar Object IRAS23151+ 5912
2007
Context. While most sources above 10 5 L ⊙ have already formed an Ultracompact Hii region (UCHii), this is not necessarily the case for sources of lower luminosity. Characterizing sources in the transition phase, i.e., very luminous objects without any detectable free-free emission, is important for a general understanding of massive star formation. Aims. Characterizing one of the most luminous High-Mass Protostellar Objects (HMPO) that has not yet formed any detectable UCHii region. Methods. The region was observed with the Submillimeter Array in three different array configurations at 875 µm in the submm continuum and spectral line emission at sub-arcsecond resolution.
The 10 5 L ⊙ high-mass protostellar object IRAS 23151+5912
Astronomy and Astrophysics, 2007
Context. While most sources above 10 5 L have already formed an Ultracompact Hii region (UCHii), this is not necessarily the case for sources of lower luminosity. Characterizing sources in the transition phase, i.e., very luminous objects without any detectable free-free emission, is important for a general understanding of massive star formation. Aims. We Characterize one of the most luminous High-Mass Protostellar Objects (HMPO) that has not yet formed any detectable UCHii region. Methods. The region was observed with the Submillimeter Array in three different array configurations at 875 µm in the submm continuum and spectral line emission at sub-arcsecond resolution.
A Rotating Molecular Disk Toward Iras 18162-2048, the Exciting Source of HH 80-81
The Astronomical Journal, 2011
We present several molecular line emission arcsec and subarcsec observations obtained with the Submillimeter Array (SMA) in the direction of the massive protostar IRAS 18162-2048, the exciting source of HH 80-81. The data clearly indicates the presence of a compact (radius≈ 425-850 AU) SO 2 structure, enveloping the more compact (radius 150 AU) 1.4 millimeter dust emission (reported in a previous paper). The emission spatially coincides with the position of the prominent thermal radio jet which terminates at the HH 80-81 and HH 80N Herbig-Haro objects. Furthermore, the molecular emission is elongated in the direction perpendicular to the axis of the thermal radio jet, suggesting a disk-like structure. We derive a total dynamic mass (disk-like structure and protostar) of 11-15 M ⊙. The SO 2 spectral line data also allow us to constrain the structure temperature between 120-160 K and the volume density 2 × 10 9 cm −3. We also find that such a rotating flattened system could be unstable due to gravitational disturbances. The data from C 17 O line emission show a dense core within this star-forming region. Additionally, the H 2 CO and the SO emissions appear clumpy and trace the disklike structure, a possible interaction between a molecular core and the outflows, and in part, the cavity walls excavated by the thermal radio jet.
IRAS 16293−2422: Evidence for Infall onto a Counterrotating Protostellar Accretion Disk
The Astrophysical Journal, 2006
We report high spatial resolution VLA observations of the low-mass starforming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH 3 CH 2 CN), methyl formate (CH 3 OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emission has a spatial scale of ∼20 ′′ and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of ∼6 ′′ and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2 ′′ that map ∼2 ′′ northeast of the A and B symmetry axis. The redshifted SiO is ∼2 ′′ northwest of blueshifted SiO along a position angle of ∼135 o which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive ∼1.4 M ⊙ interior to the SiO emission. In the same vicinity, Mundy et al. (1986) also concluded rotation of a nearly edge-on disk from OVRO observations of much stronger and ubiquitous 13 CO emission but the direction of rotation is opposite to the SiO emission findings. Taken together, SiO and 13 CO data suggest evidence for a counter-rotating disk. Moreover, archival BIMA array 12 CO data show an inverse P Cygni profile with the strongest absorption in close proximity to the SiO emission, indicating unambiguous material infall toward the counter-rotating protostellar disk at a new source location within the IRAS 16293-2422 complex. The details of these observations and our interpretations are discussed.
Dynamical Structure of the Inner 100 Au of the Deeply Embedded Protostar Iras 16293–2422
The Astrophysical Journal, 2014
A fundamental question about the early evolution of low-mass protostars is when circumstellar disks may form. High angular resolution observations of molecular transitions in the (sub)millimeter wavelength windows make it possible to investigate the kinematics of the gas around newly-formed stars, for example to identify the presence of rotation and infall. IRAS16293-2422 was observed with the extended Submillimeter Array (eSMA) resulting in subarcsecond resolution (0.46 ′′ × 0.29 ′′ , i.e. ∼ 55 × 35 AU) images of compact emission from the C 17 O (3-2) and C 34 S (7-6) transitions at 337 GHz (0.89 mm). To recover the more extended emission we have combined the eSMA data with SMA observations of the same molecules. The emission of C 17 O (3-2) and C 34 S (7-6) both show a velocity gradient oriented along a northeastsouthwest direction with respect to the continuum marking the location of one of the components of the binary, IRAS16293A. Our combined eSMA and SMA observations show that the velocity field on the 50-400 AU scales is consistent with a rotating structure. It cannot be explained by simple Keplerian rotation around a single point mass but rather needs to take into account the enclosed envelope mass at the radii where the observed lines are excited. We suggest that IRAS 16293-2422 could be among the best candidates to observe a pseudo-disk with future high angular resolution observations.
A jet-like outflow toward the high-mass (proto) stellar object IRAS 18566+0408
Astronomy and Astrophysics, 2007
Context. Studies of high-mass protostellar objects reveal important information regarding the formation process of massive stars. Aims. We study the physical conditions in the dense core and molecular outflow associated with the high-mass protostellar candidate IRAS 18566+0408 at high angular resolution. Methods. We performed interferometric observations in the NH 3 (J, K) = (1, 1), (2, 2) and (3,3) inversion transitions, the SiO J = 2-1 and HCN J = 1-0 lines, and the 43 and 87 GHz continuum emission using the VLA and OVRO. Results. The 87 GHz continuum emission reveals two continuum peaks MM-1 and MM-2 along a molecular ridge. The dominant peak MM-1 coincides with a compact emission feature at 43 GHz, and arises mostly from the dust emission. For dust emissivity index β of 1.3, the masses in the dust peaks amount to 70 M for MM-1, and 27 M for MM-2. Assuming internal heating, the central luminosities of MM-1 and MM-2 are 6 × 10 4 and 8 × 10 3 L , respectively. The SiO emission reveals a well collimated outflow emanating from MM-1. The jet-like outflow is also detected in NH 3 at velocities similar to the SiO emission. The outflow, with a mass of 27 M , causes significant heating in the gas to temperatures of 70 K, much higher than the temperature of < ∼ 15 K in the extended core. Compact (<3 ) and narrow line (<1.5 km s −1 ) NH 3 (3,3) emission features are found associated with the outflow. They likely arise from weak population inversion in NH 3 similar to the maser emission. Toward MM-1, there is a compact NH 3 structure with a linewidth that increases from 5.5 km s −1 FWHM measured at 3 resolution to 8.7 km s −1 measured at 1 resolution. This linewidth is much larger than the FWHM of <2 km s −1 in the entire core, and does not appear to originate from the outflow. This large linewidth may arise from rotation/infall, or relative motions of unresolved protostellar cores.
The Far Infrared Line Spectrum of the Protostar Iras 16293-2422
Astronomy and Astrophysics, 1998
We report mid-IR wavelength observations toward the low mass star forming region IRAS 16293-2422 between 45μm - 197μm with the Long Wavelength Spectrometer (LWS) on board ISO, and of the CI(609μm) line observed with the JCMT. A map of the CII(157μm) line shows that the region is relatively uncontaminated by Photo-Dissociation Region-like emission; there is only weak diffuse CII emission, which results from the illumination of the cloud by a faint UV field (G o ~ 6). The observed CI(609μm) line intensity and narrow profile is consistent with this interpretation. On-source, the LWS detected the OI(63μm) and several molecular lines. In this work we report and discuss in detail the lines which dominate the 43μm - 197μm spectrum, namely CO, H 2 O and OH rotational lines and the OI(63μm) fine-structure line. Combining the CO J up =14 to 25 observations with previous J up =6 measurements, we derive stringent limits on the density (~ 3 * 10 4 cm -3 ), temperature (~ 1500 K), and column dens...
The Formation of High-Mass Stars: from High-Mass Clumps to Accretion Discs and Molecular Outflows
High-mass stars play a significant role in the evolution of the Universe and the process that leads to the formation of such objects is still an open question in Astrophysics. The details of the structures connected to the central sources, such as the circumstellar discs and the morphology of the jets at their launching points, still lack of observational evidence. In this thesis, the high-mass star forming process is investigated in terms of the evolution of high-mass clumps selected from the ATLASGAL survey based on their 12 CO emission in the sub-millimetre. While single-dish sub-millimetre observations provide a large-scale view of the high-mass star formation process, higher angular resolution observations are required to disentangle the details of the protostars within the clumps. For this, threedimensional infrared spectroscopy was obtained for a group of RMS sources to characterise the circumstellar environment of high-mass YSOs in linear scales of ∼100-1000 AU. The ATLASGAL TOP100 sample offers a unique opportunity to analyse a statistically complete sample of high-mass clumps at different evolutionary stages. APEX data of three rotational J transitions of the CO (the CO (4-3), CO (6-5) and CO (7-6)) were used to characterise the properties of their warm gas (155 K) content and to derive the relations between the CO and the clump properties. The CO line luminosities were derived and the analysis indicated that the CO emission increases as a function of the evolutionary stage of the clumps (from infrared-weak to H ii regions) and as a function of the bolometric luminosity (L bol) and mass of the sources (M clump). The comparison of the TOP100 with low-mass objects observed in the CO (6-5) and CO (7-6), together with CO (10-9) data observed for a complementary sample of objects indicated that the dependency of the CO luminosity (L CO) with the bolometric luminosity of the sources gets steeper towards higher-J transitions. Although the CO luminosity of more luminous clumps are systematically larger than the values obtained for the less luminous sources, the individual analysis of each subsample suggests a similar dependency of L CO versus L bol for each luminosity regime. Finally, the presence of high-velocity CO emission observed for the TOP100 suggests that ∼85% of the sources are driving molecular outflows. The selection of isolated high-mass objects undergoing mass accretion is fundamental to investigate if these objects are formed through an accretion disc or if they are formed by merging of low-mass YSOs. The near-infrared window provides one of the best opportunities to investigate the interior of the sub-mm clumps and study in details their individual members. Thanks to the relatively high-resolution obtained in the K-band and the moderate reddening effectsin the K-band, a sample of eight (8) HMYSOs exhibiting large-scale H 2 outflows were selected to follow-up K-band spectroscopic observations using the NIFS spectrometer (Gemini North). All sources exhibit extended continuum emission and exhibit atomic and molecular transitions typical of embedded objects, such as Brγ, H 2 and the CO lines. The H 2 lines are tracing the launching point of the large-scale jets in scales of ∼ 100 AU in five of eight sources (63%). The identification of jets at such small scales indicates that these objects are still undergoing mass accretion. The Brγ emission probes the ionised gas around the HMYSOs. The analysis of the Brγ spectro-astrometry at sub-pixel scales suggests that the line arises from the cavity of the outflows or from rotating structures perpendicular to the H 2 jets (i.e., disc). Five sources also exhibit CO emission features (63%), and three HMYSOs display CO absorption features (38%), indicating that they are likely associated with circumstellar discs. By further investigating the kinematics of the spatially resolved CO absorption features, the Keplerian mass of three sources was estimated in 5±3, 8±5 and 30±10 M ⊙. These results support that high-mass stars are formed through discs, similarly as observed towards low-mass stars. The comparison between the collimation degree of the molecular jets or outflows detected in the NIFS data with their large-scale counterparts indicate that these structures present a relatively wide range of collimation degrees.
The Astrophysical Journal, 2013
We present 50-210 μm spectral scans of 30 Class 0/I protostellar sources, obtained with Herschel-PACS, and 0.5-1000 μm spectral energy distributions, as part of the Dust, Ice, and Gas in Time Key Program. Some sources exhibit up to 75 H2O lines ranging in excitation energy from 100 to 2000 K, 12 transitions of OH, and CO rotational lines ranging from J = 14 → 13 up to J = 40 → 39. [O I] is detected in all but one source in the entire sample; among the sources with detectable [O I] are two very low luminosity objects. The mean 63/145 μm [O I] flux ratio is 17.2 ± 9.2. The [O I] 63 μm line correlates with L bol, but not with the time-averaged outflow rate derived from low-J CO maps. [C II] emission is in general not local to the source. The sample L bol increased by 1.25 (1.06) and T bol decreased to 0.96 (0.96) of mean (median) values with the inclusion of the Herschel data. Most CO rotational diagrams are characterized by two optically thin components ({\langle { {N}}\rangle} = (0.70 +/- 1.12){{} \times 10^{49}} total particles). { {N}}_CO correlates strongly with L bol, but neither T rot nor { {N}}_CO(warm)/{ {N}}_CO(hot) correlates with L bol, suggesting that the total excited gas is related to the current source luminosity, but that the excitation is primarily determined by the physics of the interaction (e.g., UV-heating/shocks). Rotational temperatures for H2O ({\langle {T_rot}\rangle } = 194 +/- 85 K) and OH ({\langle {T_rot}\rangle } =183 +/- 117 K) are generally lower than for CO, and much of the scatter in the observations about the best fit is attributed to differences in excitation conditions and optical depths among the detected lines.
Who Is Eating the Outflow?: High-Angular Resolution Study of an Intermediate-Mass Protostar in L1206
Astronomy & Astrophysics, 2006
Up to now only a few intermediate-mass molecular outflows have been studied with enough high-angular resolution. The aim of this work is to study in detail the intermediate-mass YSO IRAS 22272+6358A, which is embedded in L1206, and its molecular outflow, in order to investigate the interaction of the outflow with the dense protostellar material, and to compare their properties with those of lower mas counterparts. We carried out OVRO observations of the 2.7 mm continuum emission, CO(1-0), C18O(1-0), and HC3N(12-11) in order to map with high-angular resolution the core of L1206, and to derive the properties of the dust emission, the molecular outflow and the dense protostellar envelope. The 2.7 mm continuum emission has been resolved into four sources, labeled OVRO~1, 2, 3, and 4. The intermediate-mass Class~0/I object OVRO 2, with a mass traced by the dust emission of 14.2 Msun, is the source associated with IRAS 22272+6358A. The CO(1-0) observations have revealed a very collimated outflow driven by OVRO 2, at a PA ~140 degr, that has a very weak southeastern red lobe and a much stronger northwestern blue lobe. Photodissociation toward the red lobe produced by the ionization front coming from the bright-rimmed diffuse HII region could be responsible of the morphology of the outflow. The spatial correlation between the outflow and the elongated dense protostellar material traced by HC3N(12-11) suggests an interaction between the molecular outflow and the protostellar envelope. Shocks produced by the molecular outflow, and possibly by the shock front preceding the ionization front could account for the southern enhancement of HC3N. The properties of the intermediate-mass protostar OVRO 2 and the molecular outflow are consistent with those of lower mass counterparts.