| 1. |
- Elia, Davide, et al.
(författare)
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The Hi-GAL compact source catalogue - II. The 360° catalogue of clump physical properties
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 504:2, s. 2742-2766
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Tidskriftsartikel (refereegranskat)abstract
- We present the 360° catalogue of physical properties of Hi-GAL compact sources, detected between 70 and 500 $\mu$m. This release not only completes the analogous catalogue previously produced by the Hi-GAL collaboration for -71° 2 á 2 67°, but also meaningfully improves it because of a new set of heliocentric distances, 120 808 in total. About a third of the 150 223 entries are located in the newly added portion of the Galactic plane. A first classification based on detection at 70 $\mu$m as a signature of ongoing star-forming activity distinguishes between protostellar sources (23 per cent of the total) and starless sources, with the latter further classified as gravitationally bound (pre-stellar) or unbound. The integral of the spectral energy distribution, including ancillary photometry from λ = 21 to 1100 $\mu$m, gives the source luminosity and other bolometric quantities, while a modified blackbody fitted to data for $\lambda \ge 160∼\mu$m yields mass and temperature. All tabulated clump properties are then derived using photometry and heliocentric distance, where possible. Statistics of these quantities are discussed with respect to both source Galactic location and evolutionary stage. No strong differences in the distributions of evolutionary indicators are found between the inner and outer Galaxy. However, masses and densities in the inner Galaxy are on average significantly larger, resulting in a higher number of clumps that are candidates to host massive star formation. Median behaviour of distance-independent parameters tracing source evolutionary status is examined as a function of the Galactocentric radius, showing no clear evidence of correlation with spiral arm positions.
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| 2. |
- Caswell, J. L., et al.
(författare)
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The 6-GHz methanol multibeam maser catalogue - I. Galactic Centre region, longitudes 345° to 6°
- 2010
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Ingår i: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - 0035-8711. ; 404:2, s. 1029-1060
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Tidskriftsartikel (refereegranskat)abstract
- We have conducted a Galactic plane survey of methanol masers at 6668 MHz using a seven-beam receiver on the Parkes telescope. Here we present results from the first part, which provides sensitive unbiased coverage of a large region around the Galactic Centre. Details are given for 183 methanol maser sites in the longitude range 345° through the Galactic Centre to 6°. Within 6° of the Galactic Centre, we found 88 maser sites, of which more than half (48) are new discoveries. The masers are confined to a narrow Galactic latitude range, indicative of many sources at the Galactic Centre distance and beyond, and confined to a thin disc population; there is no high-latitude population that might be ascribed to the Galactic bulge. Within 2° of the Galactic Centre the maser velocities all lie between −60 and +77 km s−1, a range much smaller than the 540 km s−1 range observed in CO. Elsewhere, the maser with highest positive velocity (+107 km s−1) occurs, surprisingly, near longitude 355° and is probably attributable to the Galactic bar. The maser with the most negative velocity (−127 km s−1) is near longitude 346°, within the longitude–velocity locus of the near side of the ‘3-kpc arm’. It has the most extreme velocity of a clear population of masers associated with the near and far sides of the 3-kpc arm. Closer to the Galactic Centre the maser space density is generally low, except within 0.25 kpc of the Galactic Centre itself, the ‘Galactic Centre zone’, where it is 50 times higher, which is hinted at by the longitude distribution, and confirmed by the unusual velocities.
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| 3. |
- Green, J. A., et al.
(författare)
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The 6-GHz multibeam maser survey-I. Techniques
- 2009
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 392:2, s. 783-794
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Tidskriftsartikel (refereegranskat)
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| 4. |
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| 5. |
- Pestalozzi, Michele, 1973, et al.
(författare)
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10 years of 12.2 GHz methanol maser VLBI observations towards NGC 7538 IRS1 N: proper motions and maser saturation
- 2012
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 8:5287, s. 186-187
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Konferensbidrag (refereegranskat)abstract
- We present the outcomes of the consistent analysis of 6 epochs of VLBA 12.2 GHz data obtained between 1995 and 2005 towards the known high-mass star formation reigon NGC7538 IRS1 N. Our analysis concentrates on the study of the main spectral/spatial feature, which is 20 VLBA synthesized beams in size with a distinct velocity gradient. We looked for proper motion signals relative to the central peak which, in an edge-on disc framework, is expected to be stationary. We also study the peak flux and the spatial brightness profile of the main maser feature searching for maser variability. Our results are twofold: we detect a clear proper motion signal of three spatial features (0.21, 0.1, 0.65 mas yr−1) and conclude that these can be made consistent with previous modelling of a Keplerian disc seen edge-on around a high-mass protostar. We further detect a consistent decrease of the peak flux over the time-span 1995-2005 (~ 5.4 Jy yr−1), confirmed when taking into account earlier data (1986, 1987) as well as by the 6.7 GHz maser emission. Also, the width of the spatial brightness profile of the main feature seems to decrease between 1995 and 2005 by some 50%. We consider these observables as clear signs of partial maser saturation.
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| 6. |
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| 7. |
- Pestalozzi, Michele, 1973, et al.
(författare)
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A circumstellar disk in a high-mass star-forming region
- 2004
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 603:2, s. L113-L116
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Tidskriftsartikel (refereegranskat)abstract
- We present an edge-on Keplerian disk model to explain the main component of the 12.2 and 6.7 GHz methanol maser emission detected toward NGC 7538 IRS 1N. The brightness distribution and spectrum of the line of bright masers are successfully modeled with high amplification of background radio continuum emission along velocity-coherent paths through a maser disk. The bend seen in the position-velocity diagram is a characteristic signature of differentially rotating disks. For a central mass of 30 M-., suggested by other observations, our model fixes the masing disk to have inner and outer radii of similar to 350 and similar to 1000 AU.
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| 8. |
- Pestalozzi, Michele, 1973
(författare)
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A differentially rotating disc in a high-mass protostellar system
- 2009
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Ingår i: Astronomy and Astrophysics. ; 501:3
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Tidskriftsartikel (refereegranskat)abstract
- Context: A strong signature of a circumstellar disc around a high-mass protostar has been inferred from high resolution methanol maser observations in NGC 7538-IRS1 N. This interpretation has however been challenged, with a bipolar outflow proposed as an alternative explanation. Aims: We compare the two proposed scenarios for best consistency with the observations. Methods: Using a newly developed formalism, we model the optical depth of the maser emission at each observed point in the map and LOS velocity for the two scenarios. Results: We find that if the emission is symmetric around a central peak in both space and LOS velocity, then it has to arise from an edge-on disc with sufficiently fast differential rotation. Disc models successfully fit ˜100 independent measurement points in position-velocity space with 4 free parameters to an overall accuracy of 3-4%. Solutions for Keplerian rotation require a central mass of at least 4 Mȯ. Close to best-fitting models are obtained if Keplerian motion is assumed around a central mass equaling ~30 Mȯ, as inferred from other observations. In contrast, we find that classical bipolar outflow models cannot fit the data, although it could be applicable in other sources. Conclusions: Our results strongly favour the differentially rotating disc hypothesis to describe the main feature of the 12.2 (and 6.7) GHz methanol maser emission in NGC 7538 IRS1 N. Furthermore, for Keplerian rotation around a ~30 Mȯ protostar, we predict the position and velocity at which tangentially amplified masers should be detected in high dynamic range observations. Also, our model predicts the amplitude of the proper motion of some of the maser features in our data. Confirmation of a large central mass would strongly support the idea that even the highest mass stars (>20 Mȯ) form via accretion discs, similarly to low-mass stars. Finally we note that our new formalism can readily be used to distinguish between discs and outflows for thermal emitting line sources as well as masers.
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| 11. |
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| 14. |
- Pestalozzi, Michele, 1973
(författare)
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Methanol Masers as Signposts of Star Formation and VLBI Observations of Coronal Emission from Young Stars
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Using a consistent survey of the galactic plane at 6.7 GHz as a starting point, this thesis reports on the observational as well as theoretical results achieved by extensively studying of the phenomenon of class II methanol masers. The general catalogue of 6.7 GHz methanol masers in the Milky Way, gathers all known sources discovered since 1991, including the 4 new sources detected during the Onsala Blind Survey of the galactic plane. Their spatial distribution in the Galaxy follows the distribution of OB-associations hosting massive star formation, suggesting that methanol masers arise where massive stars form. Statistical considerations are presented with the aim of estimating the luminosity function of the masers. Dust continuum observations of methanol maser sites not uniquely associated to known infrared sources, were used to trace the Spectral Energy Distribution (SED) of these sites, yielding dust temperatures and enclosed masses. This study confirmed that many of 6.7 GHz methanol maser sources host large amounts of cold dust, making further evidence for classifying them as sites of (massive) star formation in an early stage. VLBI observations of strong 6.7 GHz methanol masers conducted for the first time including short baseline spacings showed that there is a considerably large, low brightness emission that was systematically resolved out at the usual spatial resolution. Various scenarios for the nature of this emission are presented as the basis for the investigation toward an explanation to this phenomenon. Theoretical work on modelling a circumstellar disc traced by methanol masers gave estimates for the mass of the central object and the extent of the masing disc in NGC7538-IRS1 N. The model fits both the spectrum and the integrated brightness profile using two parameters, the line of sight velocity gradient and the ratio between inner and outer radius. As a side project, results of 3.6 cm-continuum global VLBI observations of the young active stars YZ CMi, AD Leo and T Tauri Sb (first detection at this frequency and resolution) are presented, where size and polarisation of the coronal emission as well as accurate positions of all targets were measured. The emission mechanism for the corona could be non-thermal,and particularly for T Tauri Sb, an electron cyclotron maser is proposed to explain the flaring activity.
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| 15. |
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| 16. |
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| 17. |
- Pestalozzi, Michele, 1973, et al.
(författare)
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Radio emission from the high-mass X-ray binary BP Crucis. First detection
- 2009
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Ingår i: Astronomy & Astrophysics. - 0004-6361. ; 506
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Tidskriftsartikel (refereegranskat)abstract
- Context: BP Cru is a well known high-mass X-ray binary consisting of a late B hypergiant (Wray 977) and a neutron star, also observed as the X-ray pulsar GX 301-2. No information about emission from BP Cru in bands other than X-rays and optical has been reported. A massive X-ray binaries containing black holes can produce radio emission from a jet. Aims: To assess the presence of a radio jet, we searched for radio emission from BP Cru using the Australia Compact Array Telescope as part of a survey for radio emission from Be/X-ray transients. Methods: We probed the 41.5 d orbit of BP Cru with the Australia Telescope Compact Array, close to both periastron and apastron. Results: BP Cru was clearly detected in our data on 4, possibly 6, of 12 occasions at 4.8 and 8.6 GHz. Our data suggest that the spectral index of the radio emission is modulated either by the X-ray flux or the orbital phase of the system. Conclusions: We propose that the radio emission of BP Cru probably originates in two components: a persistent component, related to the mass donor Wray 977, and a periodic component, connected to accretion onto the neutron star, possibly originating from a (weak and short lived) jet.
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