170 research outputs found
Radio supernovae
No full text
Only a handful of supernovae can be studied with milliarcsecond
resolution using the VLBI technique. However, such rare studies
have permitted in various cases to estimate expansion
decelerations and to obtain information on supernova ejecta and
circumstellar media, as well as on the structure of the emitting
region. We review results on high resolution observations of the
nearby radio supernovae: SN 1979C, SN 1986J, SN 1987A, and
SN 1993J. For completeness, we also review the results on the
supernova remnants in M 82.
Limit to the radio emission from a putative central compact source in SN1993J â†
No full textThe supernova SN 1993J in M 81 is the most extensively studied young radio-luminous supernova in the northern hemisphere. We recently reported results from the analysis of a complete set of very-long-baseline-interferometry (VLBI) observations of this supernova at 1.7, 2.3, 5.0, and 8.4 GHz, covering a time baseline of more than one decade. These results focused on the kinematics of the expanding shock, the particulars of its evolving non-thermal emission, the density profile of the circumstellar medium, and the evolving free-free opacity by the supernova ejecta. In the present paper, we complete our analysis by performing a search for any possible signal from a compact source (i.e., a stellar-mass black hole or a young pulsar nebula) at the center of the expanding shell. We have performed a stacking of all our VLBI images at each frequency, after subtraction of our best-fit shell model at each epoch, and measured the peak intensity in the stacked residual image. Given the large amount of available global VLBI observations, the stacking of all the residual images allows us to put upper limits to the eventual emission of a putative compact central source at the level of ~102 μJy at 5 GHz (or, more conservatively, ~192 μJy, if we make a further correction for the ejecta opacity) and somewhat larger at other wavelengths
Highlights of the expansion of SN1993J
No full textSN 1993J in M 81, a powerful radio supernova high in the northern sky, has been carefully monitored with VLBI throughout its lifetime. Its extremely circular shell-like radio structure has expanded over 15 years in a rather self-similar way in reasonable agreement with Chevalier’s
model. An extension of Chevalier’s model simultaneously accounts for all the light-curve and
VLBI results. Beyond the first year a single deceleration parameter, mtrue = 0.87± 0.02, characterizes the shock expansion. However, at short wavelengths and beyond 5 years, an enhanced deceleration, mshortwavelengths = 0.79±0.01, is measured. This enhancement is interpreted as due
to a combination of effects ranging from varying free-free opacity in the supernova ejecta at the
short wavelengths to the radial shape of the intensity of the magnetic fields in the emitting region. The final radio-loud stage is characterized by an abrupt decrease of radio emission. This large flux-density decay rate can be explained as due to the supernova shock surpassing the outer
boundary of the circumstellar medium generated by the supernova progenitor. Presently, the supernova expansion beyond the circumstellar/interstellar boundary is rather radio silent, although there are indications that the supernova remnant could be studied by LOFAR and eMERLIN
Radio Emission from Binary Stars in the AB Doradus Moving Group
No full textPrecise determination of dynamical masses of pre-main-sequence stars is essential for calibrating stellar evolution models, that are widely used to derive theoretical masses of young low-mass objects. We have determined the individual masses of the pair AB Dor Ba/Bb using Australian Long Baseline Array observations and archive infrared data, as part of a larger program directed to monitor binary systems in the AB Doradus moving group. We have detected, for the first time, compact radio emission from both stars. This has allowed us to determine the orbital parameters of both the relative and absolute orbits and, consequently, their individual dynamical masses: 0.28±0.05 M⊙ and 0.25±0.05 M⊙. Comparisons of the dynamical masses with the prediction of pre-main-sequence (PMS) evolutionary models show that the models underpredict the dynamical masses of the binary components Ba and Bb by 10-30% and 10-40%, respectively
Carbon monoxide in the cold debris of supernova 1987A
No full textWe report spectroscopic and imaging observations of rotational transitions of cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a supernova remnant. In addition to line luminosities for the CO J = 1-0, 2-1, 6-5, and 7-6 transitions, we present upper limits for all other transitions up to J = 13-12, collectively measured from the Atacama Large Millimeter Array, the Atacama Pathfinder EXperiment, and the Herschel Spectral and Photometric Imaging REceiver. Simple models show the lines are emitted from at least 0.01 M-circle dot of CO at a temperature >14 K, confined within at most 35% of a spherical volume expanding at similar to 2000 km s(-1). Moreover, we locate the emission within 1 '' of the central debris. These observations, along with a partial observation of SiO, confirm the presence of cold molecular gas within supernova remnants and provide insight into the physical conditions and chemical processes in the ejecta. Furthermore, we demonstrate the powerful new window into supernova ejecta offered by submillimeter observations
VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A),
No full textAims. We add four warmer late-type supergiants to our previous spectro-interferometric studies of red giants and supergiants.
Methods. We measure the near-continuum angular diameter, derive fundamental parameters, discuss the evolutionary stage, and study extended atmospheric atomic and molecular layers.
Results. V766 Cen (=HR 5171 A) is found to be a high-luminosity (log L/L⊙ = 5.8 ± 0.4) source of effective temperature 4290 ± 760 K and radius 1490 ± 540 R⊙, located in the Hertzsprung-Russell (HR) diagram close to both the Hayashi limit and Eddington limit; this source is consistent with a 40 M⊙ evolutionary track without rotation and current mass 27–36 M⊙. V766 Cen exhibits Na
High Precision Differential Astrometry in Large Angular Separation Pairs of Radiosources
No full textEvidence of a Substellar Companion to AB Dor C
No full textInternational audienceStudies of fundamental parameters of very low-mass objects are indispensable to provide tests of stellar evolution models that are used to derive theoretical masses of brown dwarfs and planets. However, only objects with dynamically determined masses and precise photometry can effectively evaluate the predictions of stellar models. AB Dor C (0.090 M ⊙) has become a prime benchmark for calibration of theoretical evolutionary models of low-mass young stars. One of the ambiguities remaining in AB Dor C is the possible binary nature of this star. We observed AB Dor C with the VLTI/AMBER instrument in low-resolution mode at the J, H, and K bands. The interferometric observables at the K band are compatible with a binary brown dwarf system with tentative components AB Dor Ca/Cb with a K-band flux ratio of 5% ± 1% and a separation of 38 ± 1 mas. This implies theoretical masses of 0.072 ± 0.013 M ⊙ and 0.013 ± 0.001 M ⊙ for each component, near the hydrogen-burning limit for AB Dor Ca, and near the deuterium-burning limit, straddling the boundary between brown dwarfs and giant planets, for AB Dor Cb. The possible binarity of AB Dor C alleviates the disagreement between observed magnitudes and theoretical mass-luminosity relationships
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