Different Stages Of Star Formation Research Articles

Molecular complexity on disc scales uncovered by ALMA

Context. The chemical composition of high-mass protostars reflects the physical evolution associated with different stages of star formation. In addition, the spatial distribution and velocity structure of different molecular species provide valuable information on the physical structure of these embedded objects. Despite an increasing number of interferometric studies, there is still a high demand for high angular resolution data to study chemical compositions and velocity structures for these objects. Aims. The molecular inventory of the forming high-mass star AFGL 4176, located at a distance of ~3.7 kpc, is studied in detail at a high angular resolution of ~0.35′′, equivalent to ~1285 au at the distance of AFGL 4176. This high resolution makes it possible to separate the emission associated with the inner hot envelope and disc around the forming star from that of its cool outer envelope. The composition of AFGL 4176 is compared with other high- and low-mass sources, and placed in the broader context of star formation. Methods. Using the Atacama Large Millimeter/submillimeter Array (ALMA) the chemical inventory of AFGL 4176 has been characterised. The high sensitivity of ALMA made it possible to identify weak and optically thin lines and allowed for many isotopologues to be detected, providing a more complete and accurate inventory of the source. For the detected species, excitation temperatures in the range 120–320 K were determined and column densities were derived assuming local thermodynamic equilibrium and using optically thin lines. The spatial distribution of a number of species was studied. Results. A total of 23 different molecular species and their isotopologues are detected in the spectrum towards AFGL 4176. The most abundant species is methanol (CH3OH) with a column density of 5.5 × 1018 cm−2 in a beam of ~0.3′′, derived from its 13C-isotopologue. The remaining species are present at levels between 0.003 and 15% with respect to methanol. Hints that N-bearing species peak slightly closer to the location of the peak continuum emission than the O-bearing species are seen. A single species, propyne (CH3C2H), displays a double-peaked distribution. Conclusions. AFGL 4176 comprises a rich chemical inventory including many complex species present on disc scales. On average, the derived column density ratios, with respect to methanol, of O-bearing species are higher than those derived for N-bearing species by a factor of three. This may indicate that AFGL 4176 is a relatively young source since nitrogen chemistry generally takes longer to evolve in the gas phase. Taking methanol as a reference, the composition of AFGL 4176 more closely resembles that of the low-mass protostar IRAS 16293–2422B than that of high-mass, star-forming regions located near the Galactic centre. This similarity hints that the chemical composition of complex species is already set in the cold cloud stage and implies that AFGL 4176 is a young source whose chemical composition has not yet been strongly processed by the central protostar.

Radiative transfer with POLARIS

Aims: We present POLARIS (POLArized RadIation Simulator), a newly developed three-dimensional Monte-Carlo radiative transfer code. POLARIS was designed to calculate dust temperature, polarization maps, and spectral energy distributions. It is optimized to handle data that results from sophisticated magneto-hydrodynamic simulations. The main purpose of the code is to prepare and analyze multi-wavelength continuum polarization measurements in the context of magnetic field studies in the interstellar medium. An exemplary application is the investigation of the role of magnetic fields in star formation processes. Methods: We combine currently discussed state-of-the-art grain alignment theories with existing dust heating and polarization algorithms. We test the POLARIS code on multiple scales in complex astrophysical systems that are associated with different stages of star formation. POLARIS uses the full spectrum of dust polarization mechanisms to trace the underlying magnetic field morphology. Results: Resulting temperature distributions are consistent with the density and position of radiation sources resulting from magneto-hydrodynamic (MHD) - collapse simulations. The calculated layers of aligned dust grains in the considered cirumstellar disk models are in excellent agreement with theoretical predictions. Finally, we compute unique patterns in synthetic multi-wavelength polarization maps that are dependent on applied dust-model and grain-alignment theory in analytical cloud models.

Multiwavelength study of the high-latitude cloud L1642: chain of star formation

L1642 is one of the two high galactic latitude (|b| > 30deg) clouds confirmed to have active star formation. We examine the properties of this cloud, especially the large-scale structure, dust properties, and compact sources in different stages of star formation. We present high-resolution far-infrared and submm observations with the Herschel and AKARI satellites and mm observations with the AzTEC/ASTE telescope, which we combined with archive data from near- and mid-infrared (2MASS, WISE) to mm observations (Planck). The Herschel observations, combined with other data, show a sequence of objects from a cold clump to young stellar objects at different evolutionary stages. Source B-3 (2MASS J04351455-1414468) appears to be a YSO forming inside the L1642 cloud, instead of a foreground brown dwarf, as previously classified. Herschel data reveal striation in the diffuse dust emission around L1642. The western region shows striation towards NE and has a steeper column density gradient on its southern side. The densest central region has a bow-shock like structure showing compression from the west and a filamentary tail extending towards east. The differences suggest that these may be spatially distinct structures, aligned only in projection. We derive values of the dust emission cross-section per H nucleon for different regions of the cloud. Modified black-body fits to the spectral energy distribution of Herschel and Planck data give emissivity spectral index beta values 1.8-2.0 for the different regions. The compact sources have lower beta values and show an anticorrelation between T and beta. Markov chain Monte Carlo calculations demonstrate the strong anticorrelation between beta and T errors and the importance of mm Planck data in constraining the estimates. L1642 reveals a more complex structure and sequence of star formation than previously known.

Magnetic flux transport by turbulent reconnection in astrophysical flows

The role of magnetohydrodynamics (MHD) turbulence in astrophysical environments is still highly debated. An important question that permeates this debate is the transport of magnetic flux. This is particularly important, for instance, in the context of star formation. When clouds collapse gravitationally to form stars, there must be some magnetic flux transport. Otherwise, the newborn stars would have magnetic fields several orders of magnitude larger than the observed ones. Also, the magnetic flux that is dragged in the late stages of the formation of a star can remove all the rotational support from the accretion disc that grows around the protostar. The efficiency of the mechanism that is often invoked to allow transport of magnetic fields at different stages of star formation, namely ambipolar diffusion, has recently been put in check. We discuss here an alternative mechanism for magnetic flux transport which is based on turbulent fast magnetic reconnection. We review recent results from three-dimensional MHD numerical simulations that indicate that this mechanism is very efficient in decoupling and transporting magnetic flux from the inner denser regions to the outskirts of collapsing clouds at different stages of star formation. We discuss this mechanism also in the context of dynamo processes and speculate that it can play a role both in solar dynamo and in accretion disc dynamo processes.

New detection of near-infrared H2line emission in AFGL 5157

Narrow-band H(2) v = 1-0 S (1) and broad-band K' imaging observations towards AFGL 5157 revealed a number of new H(2) knots associated with the NH(3) core in the region, implying that the multiple H(2) outflows are driven by a cluster of embedded point sources in the core. The shell around the infrared cluster is more clearly seen than before, showing a few of newly detected ridge-like features. A string of H(2) knots newly revealed along one lobe of the known CO outflow suggests a parsec-scaled jet emanating from a young source in the core. These H(2) outflows and jet, together with the known compact H II region, radio continuum source, and H(2)O masers further imply an extremely embedded cluster containing massive stars within it. The evidence shows that the massive young stars within the cluster are in a strong outflow stage of evolution, and together with the nearby infrared cluster in NGC1985, further confirms that star forming process propagates from the west to the east in AFGL 5157. The two types of H(2) line emission, knots and shell, may be indicators of two different stages of star formation in clusters: the shocked H(2) knots are driven by the young stellar sources embraced in the younger cluster, while the diffuse shell-like structure comes from UV photons of relatively evolved cluster. The near-infrared nebula in AFGL 5157 is found to be only associated with the evolved cluster but not observed in the embedded cluster.

Physical conditions in the NGC 6334 molecular cloud derived from non-LTE NH3(J,K)=(1,1) transitions

The high signal-to-noise ratio of the NH3(J,K) = (1,1) spectra from NGC 6334 have allowed at a first time a detailed study of departures from LTE conditions in this molecular cloud. Differences in the line shapes have shown that the surveyed region is composed of at least three overlapped sources in different stages of star formation. Comparison between physical parameters of NGC 6334 derived from LTE and non-LTE conditions are presented and discussed here.

13CO (J= 1–0) Observations of the Lupus Molecular Clouds

Large-scale 13CO (J = 1–0) observations were carried out toward the Lupus region using the new 4-m millimeter-wave telescope at Nagoya University (HPBW = 2′.7). Four molecular clouds (Lupus 1, 2, and 3 and a newly found cloud) were mapped using an 8′ grid spacing. The masses of the four clouds were estimated to be 1200, 100, 300, and 1000 M⊙, respectively. Around an infrared point source, IRAS 15398–3359, associated with Lupus 1, we discovered a CO molecular outflow with a relatively short dynamical time scale of ∼ 2000 yr, which indicates ongoing star formation in the Lupus region. Including the outflow source, about 50 candidates for young stellar objects can be found in the literature, which are apparently associated with 13CO clouds. Comparing these objects with our 13CO data, we find that the star-formation efficiency of the four clouds varies over a wide range from 0.4 to ≥ 3.8%, which might represent their different stages of star formation, or might be due to a difference in the interaction with the nearby Scorpius HI shell.

Sub-mm and far-infrared continuum observations of herbig-haro exciting stars and other yso's

We show initial results from a survey of the mm to far-IR continuum spectra of ∼ 30 YSO’s known to be exciting Herbig-Haro objects. The data are also compared with line intensities of C18O and H2CO. We include in this analysis results from other sub-mm continuum surveys of compact HII regions, T-Tauri stars and class 0 YSO’s. The results provide a statistical sample of the long-wavelength dust spectra of ∼ 60 Young Stellar Objects. Data are displayed on mm to FIR colour-colour diagrams, with the aim of trying to discriminate between different stages of star formation through general spectral characteristics, rather than detailed model fits to individual sources.

Molecular clouds and star formation. II - Star formation in the Cepheus OB3 and Perseus OB2 molecular clouds

view Abstract Citations (168) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular clouds and star formation. II. Star formation in the Cepheus OB3 and Perseus OB2 molecular clouds. Sargent, A. I. Abstract Molecular clouds of mass 10 M0 and linear extent 60 pc have been detected in the vicinity of the young OB associations Cepheus OB3 and Perseus OB2. These clouds have been mapped in the j = 1 0 transition of 12CO, and observations of 13CO and 2 mm H2CO have been made in selected regions. Three regions which illustrate different stages of star formation have been identified in the Cepheus OB3 cloud. An embedded star may be present in one region. A new subgroup of the association is being created in another. The third is probably the precursor of a star-forming region. All are situated at one edge of the molecular cloud, close to the association stars and the H ii region S1 55. The site of the currently active star-forming region adjacent to the birth sites of the older and younger subgroups of the Cepheus OB3 association suggests that each burst of star formation is produced as a result of the birth of a previous group and thus continues sequentially. Although the way in which star formation is initiated in this association is not established, it is clearly very different from the manner in which it proceeds and may well have resulted from the passage of the galactic density wave. The Perseus OB2 association and molecular cloud are found to deviate considerably from the pattern frequently observed in OB associations and typified by Cepheus 0B3. The two known stellar birth sites, IC 348 and NOC 1333, are spatially very far apart, and no other star-forming regions have been discovered. There is no evidence that the birth of stars in one region triggers star formation in an adjacent area. This may be due to the orientation of the cloud with respect to the local magnetic field. It is clear, however, that no unique mechanism produces OB associations. Subject headings: clusters: associations - interstellar: molecules nebulae: general - stars: formation Publication: The Astrophysical Journal Pub Date: October 1979 DOI: 10.1086/157378 Bibcode: 1979ApJ...233..163S Keywords: Interstellar Gas; Molecular Gases; Nebulae; Protostars; Star Formation; Astronomical Maps; Carbon Monoxide; Clouds; Early Stars; Formaldehyde; Astrophysics; Molecular Clouds:Star Formation; Star Formation:Stellar Associations full text sources ADS | data products SIMBAD (6) Related Materials (1) Part 1: 1977ApJ...218..736S