We present definitive detection statistics for 12.2 GHz methanol masers toward a complete sample of 6.7 GHz methanol masers detected in the Methanol Multibeam survey south of declination --20?. In ...total, we detect 250 12.2 GHz methanol masers toward 580 6.7 GHz methanol masers. This equates to a detection rate of 43.1%, which is lower than that of previous significant searches of comparable sensitivity. Both the velocity ranges and the flux densities of the target 6.7 GHz sources surpass that of their 12.2 GHz companion in almost all cases. Eighty percent of the detected 12.2 GHz methanol maser peaks are coincident in velocity with the 6.7 GHz maser peak. Our data support an evolutionary scenario whereby the 12.2 GHz sources are associated with a somewhat later evolutionary stage than the 6.7 GHz sources devoid of this transition. Furthermore, we find that the 6.7 GHz and 12.2 GHz methanol sources increase in luminosity as they evolve. In addition to this, evidence for an increase in velocity range with evolution is presented. This implies that it is not only the luminosity but also the volume of gas conducive to the different maser transitions that increases as the sources evolve. Comparison with GLIMPSE mid-infrared sources has revealed a coincidence rate between the locations of the 6.7 GHz methanol masers and GLIMPSE point sources similar to that achieved in previous studies. Overall, the properties of the GLIMPSE sources with and without 12.2 GHz counterparts are similar. There is a higher 12.2 GHz detection rate toward those 6.7 GHz methanol masers that are coincident with extended green objects.
We present a study of the mid-infrared environments and association with star formation tracers of 6.7 GHz methanol masers taken from the Methanol Multi-Beam (MMB) survey. Our ultimate goal is to ...establish the mass of the host star and its evolutionary stage for each maser site. As a first step, the GLIMPSE survey of the Galactic plane is utilized to investigate the environment of 776 methanol masers and we find that while the majority of the masers are associated with mid-infrared counterparts, a significant fraction (17 per cent) are not associated with any detectable mid-infrared emission. A number of the maser counterparts are clearly extended with respect to the GLIMPSE point spread function and we implement an adaptive non-circular aperture photometry (ANCAP) technique to determine the fluxes of the maser counterparts. The ANCAP technique doubles the number of masers with flux information at all four wavelengths compared to the number of the corresponding counterparts obtained from the GLIMPSE Point Source Catalog. The colours of the maser counterparts are found to be very similar to the smaller study carried out by Ellingsen. The MMB masers are weakly associated with extended green objects and Red MSX Survey embedded sources (YSO and H ii region classifications) with 18 and 12 per cent of masers associated with these objects, respectively. The majority of MMB masers (60 per cent) have detectable GLIMPSE infrared counterparts but have not been identified with previously recognized tracers of massive star formation; this confirms that the MMB survey has the potential to identify massive star-forming regions independent of infrared selection.
We present a graphical interface designed to demonstrate the techniques of radio interferometry used by telescopes like ALMA, e-Merlin, the JVLA and SKA, in a manner accessible to the general public. ...Interferometry is an observational technique used by astronomers to combine the signal from a few to tens to hundreds of individual small antennas to achieve high resolution images at radio and millimetre wavelengths. This graphical interface demonstrates how the number of antenna, their position relative to one another and the rotation of the Earth allow astronomers to create highly detailed images at long wavelengths.
The very fast evolution of Sakurai's object Van de Steene, G. C.; van Hoof, P. A. M.; Kimeswenger, S. ...
Proceedings of the International Astronomical Union,
10/2016, Letnik:
12, Številka:
S323
Journal Article
Recenzirano
Odprti dostop
V4334 Sgr (a.k.a. Sakurai's object) is the central star of an old planetary nebula that underwent a very late thermal pulse a few years before its discovery in 1996. We have been monitoring the ...evolution of the optical emission line spectrum since 2001. The goal is to improve the evolutionary models by constraining them with the temporal evolution of the central star temperature. In addition the high resolution spectral observations obtained by X-shooter and ALMA show the temporal evolution of the different morphological components.
Abstract
High-mass stars shape the interstellar medium in galaxies, and yet, largely because the initial conditions are poorly constrained, we do not know how they form. One possibility is that ...high-mass stars and star clusters form at the junction of filamentary networks, referred to as ‘hubs’. In this Letter we present the complex anatomy of a protocluster hub within an Infrared Dark Cloud (IRDC), G035.39−00.33, believed to be in an early phase of its evolution. We use high-angular resolution ({θmaj, θmin} = {1.4 arcsec, 0.8 arcsec} ∼ {0.02 pc, 0.01 pc}) and high-sensitivity (0.2 mJy beam−1; ∼0.2 Mȯ) 1.07 mm dust continuum observations from the Atacama Large Millimeter Array (ALMA) to identify a network of narrow, 0.028 ± 0.005 pc wide, filamentary structures. These are a factor of ≳3 narrower than the proposed ‘quasi-universal’ ∼0.1 pc width of interstellar filaments. Additionally, 28 compact objects are reported, spanning a mass range 0.3 Mȯ < Mc < 10.4 Mȯ. This indicates that at least some low-mass objects are forming coevally with more massive counterparts. Comparing to the popular ‘bead-on-a-string’ analogy, the protocluster hub is poorly represented by a monolithic clump embedded within a single filament. Instead, it comprises multiple intra-hub filaments, each of which retains its integrity as an independent structure and possesses its own embedded core population.
Multi-epoch radio imaging of γ-ray Nova V959 Mon Healy, F.; O'Brien, T. J.; Beswick, R. ...
Monthly notices of the Royal Astronomical Society,
08/2017, Letnik:
469, Številka:
4
Journal Article
Recenzirano
Abstract
V959 Mon (Nova Mon 2012) was first detected by the Fermi
Large Area Telescope in June 2012, as a transient gamma-ray source. Subsequent optical observations showed that this gamma-ray ...emission was due to a classical nova explosion. Multifrequency observations of V959 Mon with the Very Large Array (VLA)
between 2012 June and September revealed dramatic brightening, and a spectrum that steepened with increasing frequency. High-resolution radio images of V959 Mon using e-MERLIN are presented here, at six epochs between 2012 September and 2014 February that show morphological evolution of the source. While early e-MERLIN observations of V959 Mon show an east–west elongation in the ejecta morphology, subsequent observations suggest that the ejecta become elongated in the north–south direction. Our high-resolution observations of this surprising evolution in the structure of V959 Mon can assist us in further understanding the behaviour and morphology of nova ejecta.
Abstract
The Methanol Multibeam survey has produced the largest and most complete census of methanol and excited-state hydroxyl masers in the Galaxy to date. Observing the entire Galactic plane ...visible from the Southern hemisphere for 6668-MHz methanol and 6030/6035-MHz hydroxyl masers, to an rms sensitivity of 0.015 Jy km s−1, the survey has detected a total of 972 methanol maser sources, implying a total Galactic population of ∼1290 sources with flux densities above the survey 3σ peak flux density limit of 0.51 Jy. We present here the statistical properties of the methanol detections of the survey, including distributions in flux density, variability and range of source velocities. The data suggest that the weaker masers exhibit greater variability. We also present an analysis of the Galactic distribution of 6668-MHz methanol masers. For the Galactic distribution, we present kinematic distance resolutions to an additional 202 sources to those published previously, and collate these with previous allocations, as well as exploring a recent Bayesian distance approach based on maser parallaxes to separately determine distances. We examine Galactic structure and determine the luminosity function of the Galactic population of methanol masers. We find that more luminous masers have an evenly distributed wide range of velocity widths compared with less luminous masers being dominated by narrow velocity ranges, with the implication that this may be tied to the evolution of the host protostar(s). We also see an indication that brighter sources are seen towards the arm origins.
PDF
