310 research outputs found
New ATCA, ALMA and VISIR observations of the candidate LBV SK-67266 (S61): the nebular mass from modelling 3D density distributions
We present new observations of the nebula around the Magellanic candidate
Luminous Blue Variable S61. These comprise high-resolution data acquired with
the Australia Telescope Compact Array (ATCA), the Atacama Large
Millimetre/Submillimetre Array (ALMA), and VISIR at the Very Large Telescope
(VLT). The nebula was detected only in the radio, up to 17 GHz. The 17 GHz ATCA
map, with 0.8 arcsec resolution, allowed a morphological comparison with the
H Hubble Space Telescope image. The radio nebula resembles a spherical
shell, as in the optical. The spectral index map indicates that the radio
emission is due to free-free transitions in the ionised, optically thin gas,
but there are hints of inhomogeneities. We present our new public code RHOCUBE
to model 3D density distributions, and determine via Bayesian inference the
nebula's geometric parameters. We applied the code to model the electron
density distribution in the S61 nebula. We found that different distributions
fit the data, but all of them converge to the same ionised mass, ~0.1 , which is an order of magnitude smaller than previous estimates. We
show how the nebula models can be used to derive the mass-loss history with
high-temporal resolution. The nebula was probably formed through stellar winds,
rather than eruptions. From the ALMA and VISIR non-detections, plus the derived
extinction map, we deduce that the infrared emission observed by space
telescopes must arise from extended, diffuse dust within the ionised region.Comment: 17 pages, 9 figures. Authors list corrected. In press in MNRAS.
RHOCUBE code available online ( https://github.com/rnikutta/rhocube
Automated detection of extended sources in radio maps: progress from the SCORPIO survey
Automated source extraction and parameterization represents a crucial
challenge for the next-generation radio interferometer surveys, such as those
performed with the Square Kilometre Array (SKA) and its precursors. In this
paper we present a new algorithm, dubbed CAESAR (Compact And Extended Source
Automated Recognition), to detect and parametrize extended sources in radio
interferometric maps. It is based on a pre-filtering stage, allowing image
denoising, compact source suppression and enhancement of diffuse emission,
followed by an adaptive superpixel clustering stage for final source
segmentation. A parameterization stage provides source flux information and a
wide range of morphology estimators for post-processing analysis. We developed
CAESAR in a modular software library, including also different methods for
local background estimation and image filtering, along with alternative
algorithms for both compact and diffuse source extraction. The method was
applied to real radio continuum data collected at the Australian Telescope
Compact Array (ATCA) within the SCORPIO project, a pathfinder of the ASKAP-EMU
survey. The source reconstruction capabilities were studied over different test
fields in the presence of compact sources, imaging artefacts and diffuse
emission from the Galactic plane and compared with existing algorithms. When
compared to a human-driven analysis, the designed algorithm was found capable
of detecting known target sources and regions of diffuse emission,
outperforming alternative approaches over the considered fields.Comment: 15 pages, 9 figure
Exploring the multifaceted circumstellar environment of the luminous blue variable HR Carinae
Indexación: Web of Science; Scopus.We present a multiwavelength study of the Galactic luminous blue variable HR Carinae, based on new high-resolution mid-infrared (IR) and radio images obtained with the Very Large Telescope (VLT) and the Australia Telescope Compact Array (ATCA), which have been complemented by far-infrared Herschel-Photodetector Array Camera and Spectrometer (PACS) observations and ATCA archive data. The Herschel images reveal the large-scale distribution of the dusty emitting nebula, which extends mainly to the north-east direction, up to 70 arcsec from the central star, and is oriented along the direction of the space motion of the star. In the mid-infrared images, the brightness distribution is characterized by two arcshaped structures, tracing an inner envelope surrounding the central star more closely. At radio wavelengths, the ionized gas emission lies on the opposite side of the cold dust with respect to the position of the star, as if the ionized front were confined by the surrounding medium in the north-south direction. Comparison with previous data indicates significant changes in the radio nebula morphology and in the mass-loss rate from the central star, which has increased from 6.1 × 10-6M⊙ yr-1 in 1994-1995 to 1.17 × 10-5M⊙ yr-1 in 2014. We investigate possible scenarios that could have generated the complex circumstellar environment revealed by our multiwavelength data.https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stw307
SCORPIO-II: Spectral indices of weak Galactic radio sources
In the next few years the classification of radio sources observed by the
large surveys will be a challenging problem, and spectral index is a powerful
tool for addressing it. Here we present an algorithm to estimate the spectral
index of sources from multiwavelength radio images. We have applied our
algorithm to SCORPIO (Umana et al. 2015), a Galactic Plane survey centred
around 2.1 GHz carried out with ATCA, and found we can measure reliable
spectral indices only for sources stronger than 40 times the rms noise. Above a
threshold of 1 mJy, the source density in SCORPIO is 20 percent greater than in
a typical extra-galactic field, like ATLAS (Norris et al. 2006), because of the
presence of Galactic sources. Among this excess population, 16 sources per
square degree have a spectral index of about zero, suggesting optically thin
thermal emission such as Hii regions and planetary nebulae, while 12 per square
degree present a rising spectrum, suggesting optically thick thermal emission
such as stars and UCHii regions.Comment: 12 pages, 11 figures, accepted by MNRA
The polarization mode of the auroral radio emission from the early-type star HD142301
We report the detection of the auroral radio emission from the early-type
magnetic star HD142301. New VLA observations of HD142301 detected highly
polarized amplified emission occurring at fixed stellar orientations. The
coherent emission mechanism responsible for the stellar auroral radio emission
amplifies the radiation within a narrow beam, making the star where this
phenomenon occurs similar to a radio lighthouse. The elementary emission
process responsible for the auroral radiation mainly amplifies one of the two
magneto-ionic modes of the electromagnetic wave. This explains why the auroral
pulses are highly circularly polarized. The auroral radio emission of HD142301
is characterized by a reversal of the sense of polarization as the star
rotates. The effective magnetic field curve of HD142301 is also available
making it possible to correlate the transition from the left to the right-hand
circular polarization sense (and vice-versa) of the auroral pulses with the
known orientation of the stellar magnetic field. The results presented in this
letter have implications for the estimation of the dominant magneto-ionic mode
amplified within the HD142301 magnetosphere.Comment: 5 pages, 4 figures; accepted to MNRAS Letter
THE HIGH CADENCE TRANSIENT SURVEY (HITS). I. SURVEY DESIGN AND SUPERNOVA SHOCK BREAKOUT CONSTRAINTS
Indexación: Web of Science; Scopus.We present the first results of the High Cadence Transient Survey (HiTS), a survey for which the objective is to detect and follow-up optical transients with characteristic timescales from hours to days, especially the earliest hours of supernova (SN) explosions. HiTS uses the Dark Energy Camera and a custom pipeline for image subtraction, candidate filtering and candidate visualization, which runs in real-time to be able to react rapidly to the new transients. We discuss the survey design, the technical challenges associated with the real-time analysis of these large volumes of data and our first results. In our 2013, 2014, and 2015 campaigns, we detected more than 120 young SN candidates, but we did not find a clear signature from the short-lived SN shock breakouts (SBOs) originating after the core collapse of red supergiant stars, which was the initial science aim of this survey. Using the empirical distribution of limiting magnitudes from our observational campaigns, we measured the expected recovery fraction of randomly injected SN light curves, which included SBO optical peaks produced with models from Tominaga et al. (2011) and Nakar & Sari (2010). From this analysis, we cannot rule out the models from Tominaga et al. (2011) under any reasonable distributions of progenitor masses, but we can marginally rule out the brighter and longer-lived SBO models from Nakar & Sari (2010) under our best-guess distribution of progenitor masses. Finally, we highlight the implications of this work for future massive data sets produced by astronomical observatories, such as LSST.http://iopscience.iop.org/article/10.3847/0004-637X/832/2/155/meta;jsessionid=76BDFFFE378003616F6DBA56A9225673.c4.iopscience.cld.iop.or
Modeling the remnants of core-collapse supernovae from luminous blue variable stars
Context. Luminous blue variable stars (LBVs) are massive evolved stars that suffer sporadic and violent mass-loss events. They have been proposed as the progenitors of some core-collapse supernovae (SNe), but this idea is still debated because of a lack of strong evidence. As supernova remnants (SNRs) can carry in their morphology the fingerprints of the progenitor stars as well as of the inhomogeneous circumstellar medium (CSM) sculpted by the progenitors, the study of SNRs from LBVs could help to place core-collapse SNe in context with the evolution of massive stars. Aims. We investigate the physical, chemical, and morphological properties of the remnants of SNe originating from LBVs in order to search for signatures in the ejecta distribution and morphology of the remnants that could reveal the nature of the progenitors. Methods. As a template of LBVs, we considered the LBV candidate Gal 026.47+0.02. We selected a grid of models that describe the evolution of a massive star with properties consistent with those of Gal 026.47+0.02 and its final fate as a core-collapse SN. We developed a three-dimensional hydrodynamic model that follows the post-explosion evolution of the ejecta from the breakout of the shock wave at the stellar surface to the interaction of the SNR with a CSM characterized by two dense nested toroidal shells, parametrized in agreement with multi-wavelength observations of Gal 026.47+0.02. Results. Our models show a strong interaction of the blast wave with the CSM which determines an important slowdown of the expansion of the ejecta in the equatorial plane where the two shells lay, determining a high degree of asymmetry in the remnant. After ≈10 000 yr of evolution, the ejecta show an elongated shape forming a broad jet-like structure caused by the interaction with the shells and oriented along the axis of the toroidal shells. Models with high explosion energy show Fe-rich internal ejecta distributions surrounded by an elongated Si-rich structure with a more diffuse O-rich ejecta all around. Models with low explosion energy instead show a more homogeneous distribution of chemical elements with a very low presence of Fe-group elements. Conclusions. The geometry and density distribution of the CSM where a LBV star goes SN are fundamental in determining the properties of the resulting SNR. For all the LBV-like progenitors explored here, we found that the remnants show a common morphology, namely elongated ejecta with an internal jet-like structure, which reflects the inhomogeneous and dense pre-SN CSM surrounding the star
The rich molecular environment of the luminous blue variable star AFGL 2298
We investigated the molecular environment of AFGL 2298, an obscured Galactic
Luminous blue variable (LBV) star which hosts a highly structured circumstellar
environment with hints of multiple mass-loss events in the last few a.
We present spectral line observations of AFGL 2298 at 1 and 3 mm performed with
the IRAM 30m radio telescope. Furthermore, we report the detection of several
carbon- and nitrogen- bearing species (CO, CO, CO, CO,
HCO, HCN, HNC, HCO, CN, NH, and CH) in the
surroundings of AFGL 2298. In addition, we identified three velocity components
that clearly stand out from the Galactic background. The morphology,
kinematics, masses and isotopic ratios, together with a comparative study of
the fractional abundances, lead us to suggest that two of these components (36
and 70 km/s) have a stellar origin. The other component (46 km/s) most likely
traces swept-up interstellar material, probably harbouring also a
photon-dominated region. The first inventory of the circumstellar molecular gas
around AFGL 2298 is provided. The results are compatible with the hypothesis of
former mass-loss events, produced before the one that created the infrared
nebula. There are chemical hints of the presence of ejected stellar material,
and also swept up gas. These findings will help to better understand the
mass-loss history of this class of evolved massive stars, which heavily
influence the overall chemical evolution of the Galaxy.Comment: Accepted to Astronomy and Astrophysics. 15 pages, 4 tables, 11
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