| 1. |
- Alp, Dennis, et al.
(författare)
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The 30 Year Search for the Compact Object in SN 1987A
- 2018
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 864:2
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Tidskriftsartikel (refereegranskat)abstract
- Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.
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| 2. |
- Azulay, Rebecca, et al.
(författare)
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Binary stars in loose associations
- 2013
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Ingår i: Proceedings of the X Scientific Meeting of the Spanish Astronomical Society.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Precise determinations of dynamical masses of pre-main-sequence (PMS) stars are necessary to calibrate PMS stellar evolutionary models, whose predictions are in disagreement with measurements for masses below 1.2 solar masses. Binary stars in young, nearby loose associations (moving groups) are particularly good candidates, primarily because all members share a common age. Belonging to the AB Doradus moving group, we have observed the binary AB Dor Ba/Bb, 0.06" separation, with the Australian Long Baseline Array at 8.4 GHz. We have detected the two components Ba/Bb, which facilitates (i) a measurement of the relative orbital motion through subsequent radio maps, and (ii) an estimate of the orbital parameters, once combined the radio information with infrared relative astrometry. Our preliminary analysis shows that best-fit orbit corresponds to that with a period of 1.1 yr and semi major axis of 0.068". The sum of the masses AB Dor Ba/Bb is 0.3 +/- 0.1 solar masses. The study of this binary, along with other stars of the same association, will constitute a benchmark for testing PMS models of low-mass stars.
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| 3. |
- Guirado, J. C., et al.
(författare)
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VLTI/AMBER detection of a K=9.5 very low mass star
- 2013
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Ingår i: Memorie della Societa Astronomica Italiana. ; 84:4, s. 1044-
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Konferensbidrag (refereegranskat)abstract
- The precise determination of both the dynamical mass and infrared photometry of the close companion to AB Dor A, AB Dor C (0.090 solar masses), has provided an important benchmark for calibration of theoretical evolutionary models of low-mass young stars. However, comparison of the observed magnitudes of AB Dor C with these models suggests that they could overpredict the flux of this object, a trend also found in other young systems. One of the ambiguities remaining in AB Dor C is the possible binary nature of this star; in fact, should AB Dor C be close binary (about 10 mas separation), it could reconcile observations and models. We will report on VLTI/AMBER observations of AB Dor C addressed to discriminate between both scenarios: AB Dor C as a single object or a binary brown dwarf. We used a non-standard "off-axis" fringe tracking that allowed the detection of AB Dor C. This is, to our knowledge, one of the weakest objects detected by an infrared interferometer (Ks=9.5).
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| 4. |
- Marcaide, Jon, et al.
(författare)
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Highlights of the expansion of SN1993J
- 2012
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Ingår i: Proceedings of Science. - Trieste, Italy : Sissa Medialab. - 1824-8039. ; 163
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Konferensbidrag (refereegranskat)abstract
- SN 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’smodel. An extension of Chevalier’s model simultaneously accounts for all the light-curve andVLBI 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 dueto a combination of effects ranging from varying free-free opacity in the supernova ejecta at theshort 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 outerboundary 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.
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| 5. |
- Marti-Vidal, Ivan, 1980, et al.
(författare)
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Jet precession in the active nucleus of M81. Ongoing VLBI monitoring
- 2012
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Ingår i: Proceedings of Science. - 1824-8039. ; 2012-October
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Konferensbidrag (refereegranskat)abstract
- In a recent publication, we reported results of a multi-frequency VLBI campaign of observations of the Active Galactic Nucleus (AGN) in galaxy M\,81, phase-referenced to the supernova SN\,1993J. We were able to extract precise information on the relative astrometry of the AGN radio emission at different epochs and frequencies. We found strong evidence of precession in the AGN jet (i.e., a systematic evolution in the jet inclination at each frequency) coupled to changes in the overall flux density at the different frequencies. In these proceedings, we summarise the main contents of our previous publication and we report on (preliminary) new results from our follow-up VLBI observations, now phase-referenced to the young supernova SN2008iz. We also briefly discuss how these results match the picture of our previously-reported precession model.
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| 6. |
- Zanardo, Giovanna, et al.
(författare)
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SPECTRAL AND MORPHOLOGICAL ANALYSIS OF THE REMNANT OF SUPERNOVA 1987A WITH ALMA AND ATCA
- 2014
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 796:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive spectral and morphological analysis of the remnant of supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and thermal components of the radio emission are investigated in images from 94 to 672 GHz (lambda 3.2 mm to 450 mu m), with the assistance of a high-resolution 44 GHz synchrotron template from the ATCA, and a dust template from ALMA observations at 672 GHz. An analysis of the emission distribution over the equatorial ring in images from 44 to 345 GHz highlights a gradual decrease of the east-to-west asymmetry ratio with frequency. We attribute this to the shorter synchrotron lifetime at high frequencies. Across the transition from radio to far infrared, both the synchrotron/dust-subtracted images and the spectral energy distribution (SED) suggest additional emission beside the main synchrotron component (S-nu proportional to nu(-0.73)) and the thermal component originating from dust grains at T similar to 22 K. This excess could be due to free-free flux or emission from grains of colder dust. However, a second flat-spectrum synchrotron component appears to better fit the SED, implying that the emission could be attributed to a pulsar wind nebula (PWN). The residual emission is mainly localized west of the SN site, as the spectral analysis yields -0.4 less than or similar to alpha less than or similar to -0.1 across the western regions, with alpha similar to 0 around the central region. If there is a PWN in the remnant interior, these data suggest that the pulsar may be offset westward from the SN position.
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