Discovery of pulsar planets Wolszczan, Alex
New astronomy reviews,
1/2012, Letnik:
56, Številka:
1
Journal Article
Recenzirano
In this paper I recount the events which have led to the discovery of the first planets beyond the Solar System. The two planets circling an old neutron star, the 6.2 ms pulsar PSR B1257+12, were ...discovered in 1991 with the 1000 ft Arecibo radio telescope. The pulsar itself was detected by a large, all-sky survey conducted during the telescope maintenance period in early 1990. The subsequent timing observations have shown that the only plausible explanation of the variability of pulse arrival times of PSR B1257+12 was the existence of at least two terrestrial-mass planets around it. The third, Moon-mass planet in the system was detected in 1994, along with the measurement of perturbations resulting from a near 3: 2 mean motion resonance between the two more massive bodies, which has provided the confirmation of a planetary origin of the observed variations of pulse arrival times. Further observations and analyses have resulted in an unambiguous measurement of orbital inclinations and masses of the planets in 2003. The measured approximate coplanarity of the orbits along with the inner solar system - like dynamical properties of the pulsar planets strongly suggest their origin in a protoplanetary disk, just like in the case of planets around normal stars. The existence of such a system predicts that rocky, Earth-mass planets should be common around various kinds of stars.
After nearly three decades of discovery, many exoplanetary systems have been studied and characterized in detail with one important exception: exoplanet magnetism. Although many surveys sought to ...detect magnetospheric radio emissions from exoplanets to directly measure their magnetic field strengths, they have yet to reveal an unambiguous detection. However, the indirect detection of exoplanet magnetic fields by measuring their influence on their host stars via magnetic star-planet interactions has recently gained prominence as an alternative method of discovery. This third paper of the ROME (Radio Observations of Magnetized Exoplanets) series presents the results of a targeted radio survey of eight nearby exoplanet-hosting systems that may engage in star-planet interactions. This survey, conducted with the Arecibo radio telescope at \(\sim\)5 GHz, has the greatest frequency coverage of any to date, while providing mJy-level sensitivity over \(<\)1 s integration times. No exoplanet-induced stellar radio bursts were detected. The orbital phase coverage of candidate systems for magnetic star-planet interactions is described, and the survey results are examined within the context of the plasma flow-obstacle paradigm and searches for star-planet interactions at other wavelengths.
ABSTRACT We report upper limits to the radio and X-ray emission from the newly discovered ultracool dwarf binary WISE J104915.57-531906.1 (Luhman 16AB). As the nearest ultracool dwarf binary (2 pc), ...its proximity offers a hefty advantage to studying plasma processes in ultracool dwarfs which are more similar in gross properties (radius, mass, temperature) to the solar system giant planets than stars. The radio and X-ray emission upper limits from the Australia Telescope Compact Array and Chandra observations, each spanning multiple rotation periods, provide the deepest fractional radio and X-ray luminosities to date on an ultracool dwarf, with (5.5 GHz), (9 GHz), and . While the radio upper limits alone do not allow for a constraint on the magnetic field strength, we limit the size of any coherently emitting region in our line of sight to less than 0.2% of the radius of one of the brown dwarfs. Any source of incoherent emission must span less than about 20% of the brown dwarf radius, assuming magnetic field strengths of a few tens to a few hundred Gauss. The fast rotation and large amplitude photometric variability exhibited by the T dwarf in the Luhman 16AB system are not accompanied by enhanced nonthermal radio emission or enhanced heating to coronal temperatures, as observed on some higher mass ultracool dwarfs, confirming the expected decoupling of matter and magnetic field in cool neutral atmospheres.
ABSTRACT We report the detections of a giant planet (MARVELS-7b) and a brown dwarf (BD) candidate (MARVELS-7c) around the primary star in the close binary system, HD 87646. To the best of our ...knowledge, it is the first close binary system with more than one substellar circumprimary companion that has been discovered. The detection of this giant planet was accomplished using the first multi-object Doppler instrument (KeckET) at the Sloan Digital Sky Survey (SDSS) telescope. Subsequent radial velocity observations using the Exoplanet Tracker at the Kitt Peak National Observatory, the High Resolution Spectrograph at the Hobby Eberley telescope, the "Classic" spectrograph at the Automatic Spectroscopic Telescope at the Fairborn Observatory, and MARVELS from SDSS-III confirmed this giant planet discovery and revealed the existence of a long-period BD in this binary. HD 87646 is a close binary with a separation of ∼22 au between the two stars, estimated using the Hipparcos catalog and our newly acquired AO image from PALAO on the 200 inch Hale Telescope at Palomar. The primary star in the binary, HD 87646A, has = 5770 80 K, log g = 4.1 0.1, and Fe/H = −0.17 0.08. The derived minimum masses of the two substellar companions of HD 87646A are 12.4 0.7 and 57.0 3.7 . The periods are 13.481 0.001 days and 674 4 days and the measured eccentricities are 0.05 0.02 and 0.50 0.02 respectively. Our dynamical simulations show that the system is stable if the binary orbit has a large semimajor axis and a low eccentricity, which can be verified with future astrometry observations.
We report the results of 19 years of Arecibo timing for two pulsars in the globular cluster NGC 5904 (M5), PSR B1516+02A (M5A) and PSR B1516+02B (M5B). This has resulted in the measurement of the ...proper motions of these pulsars and, by extension, that of the cluster itself. M5B is a 7.95 ms pulsar in a binary system with a >0.13 M sub(image) companion and an orbital period of 6.86 days. In deep HST images, no optical counterpart is detected within image2.5 capital sigma of the position of the pulsar, implying that the companion is either a white dwarf or a low-mass main-sequence star. The eccentricity of the orbit has allowed a measurement of the rate of advance of periastron: image. We argue that it is very likely that this periastron advance is due to the effects of general relativity, the total mass of the binary system then being image. The small measured mass function implies, in a statistical sense, that a very large fraction of this total mass is contained in the pulsar: image (1 capital sigma ); there is a 5% probability that the mass of this object is <1.72 M sub(image) and a 0.77% probability that image. Confirmation of the median mass for this neutron star would exclude most 'soft' equations of state for dense neutron matter. Millisecond pulsars (MSPs) appear to have a much wider mass distribution than is found in double neutron star systems; about half of these objects are significantly more massive than 1.44 M sub(image). A possible cause is the much longer episode of mass accretion necessary to recycle a MSP, which in some cases corresponds to a much larger mass transfer.
We present new results of timing and single-pulse measurements for 18 radio pulsars discovered in 1993-1997 by the Penn State/Naval Research Laboratory declination-strip survey conducted with the 305 ...m Arecibo Telescope at 430 MHz. Long-term timing measurements have led to significant improvements of the rotational and the astrometric parameters of these sources, including the millisecond pulsar, PSR J1709+2313, and the pulsar located within the supernova remnant S147, PSR J0538+2817. Single-pulse studies of the brightest objects in the sample have revealed an unusual "bursting" pulsar, PSR J1752+2359, two new drifting subpulse pulsars, PSR J1649+2533 and PSR J2155+2813, and another example of a pulsar with profile mode changes, PSR J1746+2540. PSR J1752+2359 is characterized by bursts of emission, which appear once every 3-5 minutes and decay exponentially on a approx45 s timescale. PSR J1649+2533 spends approx30% of the time in a null state with no detectable radio emission.
We study the long-term dynamics of the PSR 1257+12 planetary system. Using the recently determined accurate initial condition by Konacki & Wolszczan, who derived the orbital inclinations and the ...absolute masses of planets B and C, we investigate the system stability by long-term, 1 Gyr direct integrations. No secular changes of the semimajor axes, eccentricities, and inclinations appear during such an interval. This stable behavior is confirmed with the fast indicator MEGNO. The analysis of the orbital stability in the neighborhood of the nominal initial condition reveals that the PSR 1257+12 system is localized in a wide stable region of the phase space but close to a few weak two- and three-body mean motion resonances. The long-term stability is additionally confirmed by a negligible exchange of the angular momentum deficit between the innermost planet A and the pair of outer planets B and C. An important feature of the system that helps sustain the stability is the secular apsidal resonance between planets B and C with the center of libration about 180 degree . We also find useful limits on the elements of the innermost planet A that are otherwise unconstrained by the observations. Specifically, we find that the line of nodes of planet A cannot be separated by more than about plus or minus 60 degree from the nodes of the bigger companions B and C. This limits the relative inclination of the orbit of planet A to the mean orbital plane of planets B and C to moderate values. We also perform a preliminary study of the short-term dynamics of massless particles in the system. We find that a relatively extended stable zone exists between planets A and B. Beyond planet C, the stable zone appears already at distances 0.5 AU from the parent star. For moderately low eccentricities beyond 1 AU, the motion of massless particles does not suffer from strong instabilities and this zone is basically stable, independent of the inclinations of the orbits of the test particles to the mean orbital plane of the system. This is an encouraging result supporting the search for a putative dust disk or a Kuiper Belt, especially with the Spitzer Space Telescope.
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