اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOn the possibility of radio emission of planets around pulsars
193
0
0.0
(
0
)
تأليف
Fabrice Mottez
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
A planet orbiting around a pulsar would be immersed in an ultra-relativistic under-dense plasma flow. It would behave as a unipolar inductor, with a significant potential drop along the planet. As for Io in Jupiters magnetosphere, there would be two stationary Alfven waves, the Alfven wings (AW), attached to the planet. The AW would be supported by strong electric currents, in some circumstances comparable to those of a pulsar. It would be a cause of powerful radio waves emitted all along the AW, and highly collimated through relativistic aberration. There would be a chance to detect these radio-emissions from Earth. The emission would be pulses as for ordinary pulsars; their occurrence would depend on the planet-star-observer angle. These results are still preliminary, further work needs to be done.
قيم البحث
اقرأ أيضاً
In the canonical picture of pulsars, radio emission arises from a narrow cone centered on the stars magnetic axis but many basic details remain unclear. We use high-quality polarization data taken with the Parkes radio telescope to constrain the geom
etry and emission heights of pulsars showing interpulse emission, and include the possibility that emission heights in the main and interpulse may be different. We show that emission heights are low in the centre of the beam, typically less than 3% of the light cylinder radius. The emission beams are under-filled in longitude, with an average profile width only 60% of the maximal beam width and there is a strong preference for the visible emission to be located on the trailing part of the beam. We show substantial evidence that the emission heights are larger at the beam edges than in the beam centre. There is some indication that a fan-like emission beam explains the data better than conal structures. Finally, there is a strong correlation between handedness of circular polarization in the main and interpulse profiles which implies that the hand of circular polarization is determined by the hemisphere of the visible emission.
We use the optical and near-infrared photometry from the Kepler Input Catalog to provide improved estimates of the stellar characteristics of the smallest stars in the Kepler target list. We find 3897 dwarfs with temperatures below 4000K, including 6
4 planet candidate host stars orbited by 95 transiting planet candidates. We refit the transit events in the Kepler light curves for these planet candidates and combine the revised planet/star radius ratios with our improved stellar radii to revise the radii of the planet candidates orbiting the cool target stars. We then compare the number of observed planet candidates to the number of stars around which such planets could have been detected in order to estimate the planet occurrence rate around cool stars. We find that the occurrence rate of 0.5-4 Earth radius planets with orbital periods shorter than 50 days is 0.90 (+0.04/-0.03) planets per star. The occurrence rate of Earth-size (0.5-1.4 Earth radius) planets is constant across the temperature range of our sample at 0.51 (+0.06/-0.05) Earth-size planets per star, but the occurrence of 1.4-4 Earth radius planets decreases significantly at cooler temperatures. Our sample includes 2 Earth-size planet candidates in the habitable zone, allowing us to estimate that the mean number of Earth-size planets in the habitable zone is 0.15 (+0.13/-0.06) planets per cool star. Our 95% confidence lower limit on the occurrence rate of Earth-size planets in the habitable zones of cool stars is 0.04 planets per star. With 95% confidence, the nearest transiting Earth-size planet in the habitable zone of a cool star is within 21 pc. Moreover, the nearest non-transiting planet in the habitable zone is within 5 pc with 95% confidence.
Advances in high-resolution imaging have revealed H$alpha$ emission separated from the host star. It is generally believed that the emission is associated with forming planets in protoplanetary disks. However, the nature of this emission is still not
fully understood. Here we report a modeling effort of H$alpha$ emission from the planets around the young star PDS 70. Using standard magnetospheric accretion models previously applied to accreting young stars, we find that the observed line fluxes can be reproduced using a range of parameters relevant to PDS 70b and c, with the mean mass accretion rate of log(${rm dot{M}}$) = $-8.0pm0.6$ M$_{rm Jup}$ yr$^{-1}$ and $-8.1pm0.6$ M$_{rm Jup}$ yr$^{-1}$ for PDS 70b and PDS 70c, respectively. Our results suggest that H$alpha$ emission from young planets can originate in the magnetospheric accretion of mass from the circumplanetary disk. We find that empirical relationships between mass accretion rate and H$alpha$ line properties frequently used in T Tauri stars are not applicable in the planetary mass regime. In particular, the correlations between line flux and mass accretion rate underpredict the accretion rate by about an order of magnitude, and the width at the 10% height of the line is insensitive to the accretion rate at ${rm dot{M}}$ $< 10^{-8}$ M$_{rm Jup}$ yr$^{-1}$.
Kepler-78b is a transiting Earth-mass planet in an 8.5 hr orbit discovered by the Kepler Space Mission. We performed an analysis of the published radial velocity measurements for Kepler-78 in order to derive a refined measurement for the planet mass.
Kepler-78 is an active star and radial velocity variations due to activity were removed using a Floating Chunk Offset (FCO) method where an orbital solution was made to the data by allowing the velocity offsets of individual nights to vary. We show that if we had no a priori knowledge of the transit period the FCO method used as a periodogram would still have detected Kepler-78b in the radial velocity data. It can thus be effective at finding unknown short-period signals in the presence of significant activity noise. Using the FCO method while keeping the ephemeris and orbital phase fixed to the photometric values and using only data from nights where 6-10 measurements were taken results in a K-amplitude of 1.34 +/- 0.25 m/s. a planet mass of 1.31 +/- 0.24 M_Earth, and a planet density of rho = 4.5 (-2.0/+2.2) g/cm^3. Allowing the orbital phase to be a free parameter reproduces the transit phase to within the uncertainty. The corresponding density implies that Kepler-78b may have a structure that is deficient in iron and is thus more like the Moon. Although the various approaches that were used to filter out the activity of Kepler 78 produce consistent radial velocity amplitudes to within the errors, these are still too large to constrain the structure of this planet. The uncertainty in the mass for Kepler-78b is large enough to encompass models with structures ranging from Mercury-like (iron enriched) to Moon-like (iron deficient). A more accurate K-amplitude as well as a better determination of the planet radius are needed to distinguish between these models.
The analysis of distributions of some parameters of radio pulsars emitting X-ray radiation was carried out. The majority of such pulsars has short spin periods with the average value $< P >$ = 133 msec. The distribution of period derivatives reveals
a bimodality, dividing millisecond ($< log dfrac{dP}{dt}>$ = -19.69) and normal ($< log dfrac{dP}{dt}> $ = -13.29) pulsars. Magnetic fields at the surface of the neutron star are characterized by the bimodal distribution as well. The mean values of $<log B_s>$ are $8.48$ and $12.41$ for millisecond pulsars and normal ones, respectively. The distribution of magnetic fields near the light cylinder, it does not show the noticeable bimodality. The median value of $log B_{lc}$ = 4.43 is almost three orders higher comparing with this quantity ($<log B_{lc}>$ = 1.75) for radio pulsars without registered X-ray emission. Losses of rotational energy ($<log dfrac{dE}{dt}>$ = 35.24) are also three orders higher than corresponding values for normal pulsars. There is the strong correlation between X-ray luminosities and losses of rotational energies. The dependence of the X-ray luminosity on the magnetic field at the light cylinder has been detected. It shows that the generation of the non-thermal X-ray emission takes place at the periphery of the magnetosphere and is caused by the synchrotron mechanism. We detected the positive correlations between luminosities in radio, X-ray and gamma -ray ranges. Such correlations give the possibility to carry out a purposeful search for pulsars in one of these ranges if they radiate in other one.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
