130 research outputs found
The Multiwavelength Picture of Star Formation in the Very Young Open Cluster NGC6383
We review the properties of the very young (2 Myr) open cluster NGC6383. The
cluster is dominated by the massive binary HD159176 (O7V + O7V). The distance
to NGC6383 is consistently found to be 1.3 +- 0.1 kpc and the average reddening
is determined to be E(B-V) = 0.32 +- 0.02. Several pre-main sequence candidates
have been identified using different criteria relying on the detection of
emission lines, infrared excesses, photometric variability and X-ray emission.Comment: 12 pages, 5 figures, to appear in the Handbook of Star Forming
Regions, Vol. II (The Southern Sky), ed. Bo Reipurt
Particle-Accelerating Colliding-Wind Binaries : a relevant science case for radio observations
editorial reviewedSynchrotron radiation identified in the radio domain for several tens of binary systems made of massive stars provides compelling evidence that a particle acceleration process is at work in these objects, hence their Particle-Accelerating Colliding-Wind Binary (PACWB) status. The processes at work for both particle acceleration and non-thermal emission are basically the same as for supernova remnants, but with different geometries and different physical parameters. Measurements of the synchrotron radio emission of PACWBs allow to investigate the non-thermal physics of these systems and to derive some of their properties. In this context, it is worth describing their emission properties at centimetric wavelengths, along with some expectations at longer wavelengths such as those measured by the Giant Metrewave Radio Telescope. This poster briefly reviews this science topic and outlines expectations about radio observations of these objects in their appropriate context
Observations of massive stars with the ILMT: what can we learn from (variability) studies using the ILMT?
Although massive stars constitute only a small fraction of the galactic stellar population, their influence on the galactic environment as a whole is huge. Among other features, they are the main providers of UV radiation in the interstellar medium, their strong stellar winds provide a wealth of mechanical energy in their surroundings, they enrich the medium in chemical elements, and at various evolutionary stages they are at the origin of most of galactic cosmic-rays. Massive stars display a complex, and still poorly understood behaviour, in particular regarding their time variability. In this talk, I will briefly overview some aspects of massive star studies that may benefit of photometric surveys. The census of topics presented in this contribution is intended to open questions about the potential outcome of the International Liquid Mirror Telescope for massive star studies
Prospects for radio observations of Particle-Accelerating Colliding-Wind Binaries with the Giant Metrewave Radio Telescope
Synchrotron radiation identified in the radio domain for several tens of binary systems made of massive stars provides compelling evidence that a particle acceleration process is at work in these objects, hence their Particle-Accelerating Colliding-Wind Binaries (PACWB) status. Measurements of the synchrotron radio emission allow to investigate the non-thermal physics and to derive some of their properties. Non-thermal spectra are known to increase at lower frequencies, while thermal ones increase toward higher frequencies. In this context, it is worth investigating the expectations from longer wavelengths such as those measured by the Giant Metrewave Radio Telescope in India, in complementarity with the most abundant measurements at centimetric wavelengths obtained with other radio observatories such as the VLA or ATCA.Fil: De Becker, Michaël. Université de Liège; BélgicaFil: Ishwara Chandra, C. H.. National Centre For Radio Astrophysics; IndiaFil: Benaglia, Paula. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina2nd Belgo-Indian Network for Astronomy & Astrophysics workshopBruselasBélgicaUniversité de Lièg
Synchrotron radio emission as a proxy to identify long period massive binaries
peer reviewedThe multiplicity of massive stars is known to be significantly high. Even though the majority of massive stars are located in binary systems, the census of binaries is biased toward shorter periods as longer period systems are more difficult to identify. Alternatively, the search for binary systems with longer periods may proceed differently. As massive binary systems are typically colliding-wind systems, hints for processes occurring in the colliding-wind region could be used as a valuable proxy to identify likely binary systems, and then organize dedicated spectroscopic or interferometric campaigns on a short list of pre-selected targets. In this context, any hint for synchrotron radio emission is seen as a promising indicator of long period binaries, as short period systems undergo severe free-free absorption of the synchrotron emission by the stellar wind material. Usual techniques to identify synchrotron radio emitters constitute thus valid tools to explore that poorly investigated part of the massive binary parameter space. In addition, the identification of a synchrotron emission component in a short period binary can be used as an indicator of the presence of a third companion on a still unrevealed wider orbit in a triple system
A preliminary timing analysis of two intermediate polars: UU Col and Swift J0939.7-3224
We present the preliminary timing analysis of confirmed intermediate polar UU
Col and possible intermediate polar Swift J0939.7-3224 in the optical band with
the help of long-term, high-cadence continuous photometry from Transiting
Exoplanet Survey Satellite (TESS). For UU Col, we revise previously reported
orbital and spin periods as 3.464 0.005 h and 863.74 0.08 s,
respectively. Using the second harmonic of the beat frequency, the beat period
is estimated as 928 s. These findings indicate that UU Col is a disc-fed
dominated disc-overflow accretor. For J0939, we establish the spin period as
2671.8 0.8 s and refine the provisionally suggested orbital period as
8.49 0.03 h. The absence of beat frequency in J0939 signifies that it
might be a pure disc-fed accretor; however, an X-ray study of this source will
help to understand its true nature.Comment: 9 pages, 3 figures, 2 tables. Proceeding paper of the 3
Belgo-Indian Network for Astronomy and Astrophysics (BINA) workshop, Accepted
for publication in the Bulletin of Li\`{e}ge Royal Society of Science
Three-dimensional orbits of the triple-O stellar system HD 150136
peer reviewedContext. HD 150136 is a triple hierarchical system and a non-thermal radio emitter. It is formed by an O3-3.5 V + O5.5-6 V close binary and a more distant O6.5-7 V tertiary. So far, only the inner orbital properties have been reliably constrained. Aims. To quantitatively understand the non-thermal emission process, accurate knowledge of the physical and orbital properties of the object is crucial. Here, we aim to investigate the orbital properties of the wide system and to constrain the inclinations of the inner and outer binaries, and with these the absolute masses of the system components. Methods. We used the PIONIER combiner at the Very Large Telescope Interferometer to obtain the very first interferometric measurements of HD 150136. We combined the interferometric observations with new and existing high resolution spectroscopic data to derive the orbital solution of the outer companion in the three-dimensional space. Results. The wide system is clearly resolved by PIONIER, with a projected separation on the plane of the sky of about 9 milli-arcsec. The best-fit orbital period, eccentricity, and inclination are 8.2 yr, 0.73 and 108 degr. We constrain the masses of the three stars of the system to 63 +/- 10, 40 +/- 6, and 33 +/- 12 Msun for the O3-3.5 V, O5.5-6 V and O6.5-7 V components. Conclusions. The dynamical masses agree within errors with the evolutionary masses of the components. Future interferometric and spectroscopic monitoring of HD 150136 should allow one to reduce the uncertainties to a few per cent only and to accurately constrain the distance to the system. This makes HD 150136 an ideal system to quantitatively test evolutionary models of high-mass stars as well as the physics of non-thermal processes occurring in O-type systems
An XMM-Newton observation of the multiple system HD 167971 (O5-8V+O5-8V+(O81)) and the young open cluster NGC6604
We discuss the results of two XMM-Newton observations of the open cluster NGC 6604 obtained in April and September 2002. We concentrate mainly on the multiple system HD 167971 (O5- 8V + O5- 8V + (O8I)). The soft part of the EPIC spectrum of this system is thermal with typical temperatures of about 2 x 106 to 9 x 106 K. The nature ( thermal vs. non-thermal) of the hard part of the spectrum is not unambiguously revealed by our data. If the emission is thermal, the high temperature of the plasma (similar to 2.3 x 10(7) to 4.6 x 10(7) K) would be typical of what should be expected from a wind-wind interaction zone within a long period binary system. This emission could arise from an interaction between the combined winds of the O5- 8V + O5- 8V close binary system and that of the more distant O8I companion. Assuming instead that the hard part of the spectrum is non-thermal, the photon index would be rather steep (similar to 3). Moreover, a marginal variability between our two XMM-Newton pointings could be attributed to an eclipse of the O5 - 8V + O5 - 8V system. The overall X-ray luminosity points to a significant X-ray luminosity excess of about a factor 4 possibly due to colliding winds. Considering HD 167971 along with several recent X-ray and radio observations, we propose that the simultaneous observation of non-thermal radiation in the X-ray (below 10.0 keV) and radio domains appears rather unlikely. Our investigation of our XMM-Newton data of NGC 6604 reveals a rather sparse distribution of X-ray emitters. Including the two bright non-thermal radio emitters HD 168112 and HD 167971, we present a list of 31 X-ray sources along with the results of the cross-correlation with optical and infrared catalogues. A more complete spectral analysis is presented for the brightest X-ray sources. Some of the members of NGC 6604 present some characteristics suggesting they may be pre-main sequence star candidates
Search for particle acceleration in two massive Wolf-Rayet stars using uGMRT observations
Large wind kinetic power of Wolf-Rayet (WR) stars make them ideal targets in
low radio frequencies to search for non-thermal emission due to relativistic
particle acceleration. In this paper, we present observations of two WR stars,
WR 114 and WR 142, in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz) using the
upgraded Giant Meterwave Radio Telescope (uGMRT). Neither star is detected in
the observed frequency bands, nor extended emission associated with them. The
upper limit to the free-free radio emission from the stellar wind enables us to
constrain the mass-loss rate of WR 114 to ; this is a factor three smaller than previously estimated
using spectroscopic modelling. If we further assume that the WR stars are
binaries, the non-detection of synchrotron emission from the putative wind
collision region implies that the stars are either in very wide binary systems
away from periastron, or that the stars are in close binary systems with an
orbital separation AU for WR 114 and AU for WR 142. The
non-detection of low-frequency radio emission from these two systems thus
provides evidence that narrows their nature, though it does not rule them out
as bonafide particle-accelerating colliding-wind binaries.Comment: 8 pages, 3 figures, accepted for publication in MNRA
- …