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Register a new userRotation-Resolved Spectroscopy of a Very Young Asteroid, (1270) Datura
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Naruhisa Takato
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(1270) Datura is the largest member of a very young asteroid cluster that was thought to be broken-up 0.45 Myr ago. The light-curve and the rotation-resolved reflectance spectra (0.6 um - 1.0 um) were observed in order to find fresh surface. Our data show no significant spectral variation along the rotation phase. The depth of the 0.95 um absorption band, which indicates the degree of space weathering, was similar to that of an old S-type asteroid. This suggests that the reflectance spectrum in this wavelength range changes rapidly and saturates the depth of the 0.95 um absorption in less than 0.45 Myr in the main belt environment.
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The massive star origins for Type IIP supernovae (SNe) have been established through direct detection of their red supergiants progenitors in pre-explosion observations; however, there has been limited success in the detection of the progenitors of H-deficient SNe. The final fate of more massive stars, capable of undergoing a Wolf-Rayet phase, and the origins of Type Ibc SNe remains debated, including the relative importance of single massive star progenitors or lower mass stars stripped in binaries. We present an analysis of the ages and spatial distributions of massive stars around the sites of 23 stripped-envelope SNe, as observed with the Hubble Space Telescope, to probe the possible origins of the progenitors of these events. Using a Bayesian stellar populations analysis scheme, we find characteristic ages for the populations observed within $150,mathrm{pc}$ of the target Type IIb, Ib and Ic SNe to be $log (t) = 7.20$, $7.05$ and $6.57$, respectively. The Type Ic SNe in the sample are nearly all observed within $100,mathrm{pc}$ of young, dense stellar populations. The environment around SN 2002ap is an important exception both in terms of age and spatial properties. These findings may support the hypothesis that stars with $M_{init} > 30M_{odot}$ produce a relatively large proportion of Type Ibc SNe, and that these SN subtypes arise from progressively more massive progenitors. Significantly higher extinctions are derived towards the populations hosting these SNe than previously used in analysis of constraints from pre-explosion observations. The large initial masses inferred for the progenitors are in stark contrast with the low ejecta masses estimated from SN light curves.
We present a spectroscopic/photometric analysis of the rapid rotator KIC8429280, discovered by ourselves as a very young star and observed by the Kepler mission. We use spectroscopic/photometric ground-based data to derive stellar parameters, and we adopt a spectral subtraction technique to highlight the chromospheric emission in the cores of Halpha, CaII H&K and IRT lines. We fit a robust spot model to the high-precision Kepler photometry spanning 138 days. Model selection and parameter estimation is performed in a Bayesian manner using a Markov chain Monte Carlo method. We find that KIC8429280 is a cool (K2V) star with an age of ~50 Myr, based on its Li content, that has passed its T Tau phase and is spinning up approaching the ZAMS. Its high level of chromospheric activity is indicated by the radiative losses in CaII H&K and IRT, Halpha, and Hbeta lines. Furthermore, its Balmer decrement and the flux ratio of CaII IRT lines imply that these lines are mainly formed in optically-thick sources analogue to solar plages. The analysis of the Kepler data uncovers evidence of at least 7 enduring spots. Since the stars inclination is rather high, ~70{deg}, the assignment of the spots to the northern/southern hemisphere is not unambiguous. We find at least 3 solutions with nearly the same level of residuals. The distribution of the active regions is such that the spots are located around 3 latitude belts, i.e. the equator and +-(50{deg}-60{deg}), with the high-latitude spots rotating slower than the low-latitude ones. The equator-to-pole differential rotation ~0.27 rad/d is at variance with some recent mean-field models of differential rotation in rapidly rotating MS stars, which predict a much smaller latitudinal shear. Our results are consistent with the scenario of a higher differential rotation, which changes along the magnetic cycle.
Asteroid families are groups of minor planets which have a common origin in catastrophic disruptions. Young asteroid families are very interesting because they represent the product of their parent bodys fragmentation before orbital and physical evolutionary processes could have changed them. A group of minor asteroids associated with the largest body Datura(1270) is of particular interest because it has enough known members and resides in the inner part of the main asteroid belt and is easy to observe. Up to now, 7 members of this family are known. Here we discuss three new members of the Datura Family: 338309(2002 VR17), 2002 RH291 and 2014 OE206. To prove that these recently-discovered members belong to the Datura family, we conducted numeric integration with all gravitational perturbation over the last 800 kyrs. In the results, we have found that 338309(2002 VR17) and 2002 RH291 are very close to the mean orbit of this family throughout the calculation. In the case of 2014 OE206, it has a strongly chaotic orbit. The possible explanation of this is in the resonance character of its orbit.
9C J1503+4528 is a very young CSS radio galaxy, with an age of order 10^4 years. This source is therefore an ideal laboratory for the study ofthe intrinsic host galaxy/IGM properties, interactions between the radio source and surrounding ISM, links between star formation and AGN activity and the radio source triggering mechanism. Here we present the results of a spectroscopic analysis of this source, considering each of these aspects of radio source physics. We find that shock ionization by the young radio source is important in the central regions of the galaxy on scales similar to that of the radio source itself, whilst evidence for an AGN ionization cone is observed at greater distances. Line and continuum features require the presence of a young stellar population, the best-fit model for which implies an age of 5x10^6 years, significantly older than the radio source. Most interestingly, the relative sizes of radio source and extended emission line region suggest that both AGN and radio source are triggered at approximately the same time. If both the triggering of the radio source activity and the formation of the young stellar population had the same underlying cause, this source provides a sequence for the events surrounding the triggering process. We propose that the AGN activity in 9C J1503+4528 was causedby a relatively minor interaction, and that a super-massive black hole powering the radio jets must have been in place before the AGN was triggered.
The magnetar Swift ,J1818.0-1607 was discovered in March 2020 when Swift detected a 9 ms hard X-ray burst and a long-lived outburst. Prompt X-ray observations revealed a spin period of 1.36 s, soon confirmed by the discovery of radio pulsations. We report here on the analysis of the Swift burst and follow-up X-ray and radio observations. The burst average luminosity was $L_{rm burst} sim2times 10^{39}$ erg/s (at 4.8 kpc). Simultaneous observations with XMM-Newton and NuSTAR three days after the burst provided a source spectrum well fit by an absorbed blackbody ($N_{rm H} = (1.13pm0.03) times 10^{23}$ cm$^{-2}$ and $kT = 1.16pm0.03$ keV) plus a power-law ($Gamma=0.0pm1.3$) in the 1-20 keV band, with a luminosity of $sim$$8times10^{34}$ erg/s, dominated by the blackbody emission. From our timing analysis, we derive a dipolar magnetic field $B sim 7times10^{14}$ G, spin-down luminosity $dot{E}_{rm rot} sim 1.4times10^{36}$ erg/s and characteristic age of 240 yr, the shortest currently known. Archival observations led to an upper limit on the quiescent luminosity $<$$5.5times10^{33}$ erg/s, lower than the value expected from magnetar cooling models at the source characteristic age. A 1 hr radio observation with the Sardinia Radio Telescope taken about 1 week after the X-ray burst detected a number of strong and short radio pulses at 1.5 GHz, in addition to regular pulsed emission; they were emitted at an average rate 0.9 min$^{-1}$ and accounted for $sim$50% of the total pulsed radio fluence. We conclude that Swift ,J1818.0-1607 is a peculiar magnetar belonging to the small, diverse group of young neutron stars with properties straddling those of rotationally and magnetically powered pulsars. Future observations will make a better estimation of the age possible by measuring the spin-down rate in quiescence.
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